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Postnatal exposure to PCB 153 and PCB 180, but not to PCB 52, produces changes in activity level and stimulus control in outbred male Wistar Kyoto rats

Postnatal exposure to PCB 153 and PCB 180, but not to PCB 52, produces changes in activity level... Background: Polychlorinated biphenyls (PCBs) are a class of organic compounds that bioaccumulate due to their chemical stability and lipophilic properties. Humans are prenatally exposed via trans-placental transfer, through breast milk as infants, and through fish, seafood and fatty foods as adolescents and adults. Exposure has several reported effects ranging from developmental abnormalities to cognitive and motor deficiencies. In the present study, three experimental groups of rats were orally exposed to PCBs typically found in human breast milk and then behaviorally tested for changes in measures of stimulus control (percentage lever-presses on the reinforcer- producing lever), activity level (responses with IRTs > 0.67 s), and responses with short IRTs (< 0.67 s). Methods: Male offspring from Wistar Kyoto (WKY/NTac) dams purchased pregnant from Taconic Farms (Germantown, NY) were orally given PCB at around postnatal day 8, 14, and 20 at a dose of 10 mg/kg body weight at each exposure. Three experimental groups were exposed either to PCB 52, PCB 153, or PCB 180. A fourth group fed corn oil only served as controls. From postnatal day 25, for 33 days, the animals were tested for behavioral changes using an operant procedure. Results: PCB exposure did not produce behavioral changes during training when responding was frequently reinforced using a variable interval 3 s schedule. When correct responses were reinforced on a variable interval 180 s schedule, animals exposed to PCB 153 or PCB 180 were less active than controls and animals exposed to PCB 52. Stimulus control was better in animals exposed to PCB 180 than in controls and in the PCB 52 group. Also, the PCB 153 and PCB 180 groups had fewer responses with short IRTs than the PCB 52 group. No effects of exposure to PCB 52 were found when compared to controls. Conclusions: Exposure to PCBs 153 and 180 produced hypoactivity that continued at least five weeks after the last exposure. No effects of exposure to PCB 52 were observed. Background paints [1]. Although the manufacturing of PCBs was for- Polychlorinated biphenyls (PCBs) are a class of organic bidden in the United States and Western Europe from around 1980, PCBs are still present in the environment compounds that due to their chemical stability and resistance to degradation were used in a variety of pro- due to their chemical stability and resistance to degrada- ducts, including coolants and fluid oils for electric tion, and accumulate in the food chain due to the lipo- equipment (transformers, capacitors), plastics, and philic properties. Hence, humans are prenatally exposed via trans-placental transfer, through breast milk during infancy, and during adolescence and adulthood through * Correspondence: EspenBorga.Johansen@hiak.no consumption of contaminated food of which fish and Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway Full list of author information is available at the end of the article © 2011 Johansen et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 2 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 seafood constitute the most important sources of PCB simultaneous visual discrimination procedure developed [1-3]. for testing behavioral changes in an animal model of PCBs consist of two phenyl rings where chlorine can Attention-Deficit/Hyperactivity Disorder (ADHD) be substituted for hydrogen atoms, theoretically giving a [39-41]. total of 209 different PCB structures (congeners). The site and number of chlorine substitution(s) determine Method the molecule’s chemical and toxic properties [4,5]. The Subjects congeners most commonly found in humans are the Male offspring from Wistar Kyoto (WKY/NTac) dams ortho-substituted non-planar PCBs 118, 138, 153, and purchased pregnant from Taconic Farms (Germantown, 180, but also the less chlorinated di-ortho-substituted NY) were used. During the first three weeks, the rats non-planar congener PCB 52 has been found [6-8]. Evi- were under the care of a veterinarian at the Norwegian dence suggests that even low-level exposure to PCBs Defense Research Establishment, Kjeller, who also admi- during development can seriously impact neurobiologi- nistered the PCBs. The mother animals were caged sin- cal, cognitive, and behavioral functioning in humans and gly under standard laboratory animal conditions animals [2,9,10]. Prenatal exposure can produce abnor- (temperature ~22°C, humidity ~55%, 12 hr light/dark mal pigmentation and several developmental abnormal- cycle) in type IV macrolon cages and aspen bedding, ities at birth including gum enlargement, presence of where they also gave birth. Female offspring were culled teeth, abnormal calcification of the scull, and low birth at birth. The rats had free access to food (RM3 (E) from weight [11-13]. Neuroendocrine changes have been Special Diet Services, Witham, Essex CM8 3AD, UK) in observed following prenatal exposure which can also the home cages at all times, and free access to water at interfere with neurotransmitter systems and signal trans- all times. duction pathways [14] (for reviews, see [1,2]). PCB expo- At postnatal day (PND) 24, the rats were transported sure affects neurological as well as cognitive and motor to the University of Oslo for behavioral testing. The rats functions in humans [15-19]. Exposed humans show were experimentally naïve on arrival. A total of 29 rats increased impulsivity, reduced attention and concentra- were behaviorally tested and included in the statistical tion, poorer working memory and lower IQ scores analyses: The PCB 52 and PCB 180 groups each con- [8,18,20-24]. sisted of 9 animals, the PCB 153 group consisted of 6 Controlled studies in animals indicate that several fac- animals, and the control group consisted of 5 animals. tors influence the measured effects of PCB exposure. During habituation and response acquisition, the rats These factors include dose, age when exposed and route were housed together in twos or threes in 41 × 25 × 25 of exposure, age when effects are tested and measures (height) cm transparent cages. Following acquisition of used, and sex and species tested [25-38]. Generally, lever-pressing and throughout the rest of the study, the however, findings from animal studies are consistent rats were housed individually in the same type of cages. with research on humans, and show that PCB exposure The rats had free access to food (RM3 (E) from Special affects learning and memory, activity level, and cognitive Diet Services, Witham, Essex CM8 3AD, UK) in the functions (for reviews, see [2,3]). The behavioral changes home cage at all times, and free access to water at all following exposure have been linked to alterations in times prior to the dipper training sessions. Starting with monoamine function (dopamine and serotonin), vesicu- the dipper training session and throughout the rest of the lar transport and storage of monoamines, disruption of study, the rats were deprived of water for 21 hours a day. 2+ Ca signal transduction, and reduced long-term poten- The temperature in the housing area was ~22°C, and tiation (LTP) (for reviews, see [1,2]). the light was on from 0600 to 1800 hours. The beha- The purpose of the present study was to examine vioral training took place between 0900 and 1400 hours behavioral changes in stimulus control (i.e. the percen- seven days a week, and lasted for 33 days. tage of responses on the reinforcer-producing lever), The study was approved by the Norwegian Animal lever-directed activity level (responses with inter- Research Authority (NARA), and was conducted in response times, IRTs, > 0.67 s), and responses with accordance with the laws and regulations controlling short IRTs (< 0.67 s) in animals postnatally exposed to experiments/procedures in live animals in Norway. one of the three PCBs found in breast milk in humans (PCB 52, PCB 153, and PCB 180) compared to non- Apparatus exposed controls. Outbred male Wistar Kyoto rats were In the initial part of the study, sixteen Campden Instru- orally given a mixture of corn oil and PCB at around ments operant chambers were used. The chambers were postnatal day 8, 14, and 20 at a dose of 10 mg/kg body located in two separate rooms each containing eight weight (bw) at each exposure. Thereafter, the animals chambers and a separate computer. The number of were tested in standard operant test chambers using a operant chambers used was later reduced to eight due Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 3 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 to a computer malfunction in one of the rooms (below). was turned on during each water delivery, and the rein- Each chamber was enclosed in a sound-resistant outer forcer was available for 3 seconds. housing, was ventilated, and equipped with a grid floor. In the following two sessions, the animals were trained The animal’s working space in eight of the chambers to open the flap to gain access to the drop of water. The was25×25 ×30(height)cm(room 1),and 25 ×25 × tape was removed from the flap, no levers were present, 20 (height) cm in the other eight chambers (room 2). A and the cue lights located above the levers were off. fan producing a low masking noise and a 2.8-W house Each flap-opening turned on the cue light in the water light were on during the entire experimental session. cubicle and produced the presentation of a single drop of water. The water-dipper was lowered after 5 s irre- Each chamber was equipped with two retractable levers requiring a dead weight of at least 3 g to activate a spective of the animal’s behavior. micro-switch, and with a 2.8-W cue light located above During the subsequent two sessions, lever-pressing each lever. was shaped according to the method of successive The reinforcers (0.05 ml tap water) were delivered by approximations [43]. During the first of these sessions, a liquid dipper located in a small recessed cubicle where the animals learned to press the left lever in order to a 2.8-W cue light lit up when a reinforcer was pre- receive a reinforcer immediately following every press. sented. A 7 × 5 cm transparent plastic top-hinged flap The cue light above the left lever was lit for the entire separated the cubicle from the animal’s working space. session except during presentation of the reinforcer A computer program LabVIEW 7.1 recorded the when the light in the water cubicle was turned on. The behavior and scheduled reinforcers and lights [42]. right lever was retracted into the wall and the light above the lever was off. On the second session, the right Procedure lever was inserted and the left lever was retracted. Dur- PCB exposure. The animals were randomly assigned to ing this session, the light above the right lever was lit one of the three experimental groups or to the control the entire session except during presentation of the group and then orally given one of the three PCBs dis- reinforcer when the light in the water cubicle was solved in corn oil or corn oil: Group 1 was fed corn oil turned on. Immediately following response shaping on only and served as controls; group 2 was fed PCB 52 each lever, the animal was monitored to make sure the (2,2’,5,5’-Tetrachlorobiphenyl); group 3 was given PCB response was learned, and then left in the chamber for 153 (2,2’,4,4’,5,5’-Hexachlorobiphenyl); and group 4 was an additional 15 min to further strengthen the newly fed PCB 180 (2,2’,3,4,4’,5,5’-Heptachlorobiphenyl). The learned behavior. During this time, every press on the animals were exposed to PCB at around PND 8, PND lever produced a reinforcer. 14, and PND 20 at a dose of 10 mg/kg body weight at The variable interval 3 s schedule each exposure. The total volume given at each exposure Response acquisition was followed by five 30-min long was 0.01ml/g body weight. Exposure was performed by training sessions (sessions 8-12) using a variable interval the veterinarian during working hours, and was adminis- (VI) 3 s reinforcement schedule. tered by gavage with stomach tube. During the VI 3 s sessions and throughout the rest of The PCBs, specially purified and free from dioxin-like the study, both levers were present. At the start of the PCBs, were purchased from Patrick Anderson, Depart- session and following each reinforcer delivery, the com- ment of Chemistry, University of Umeå, Sweden. puter program semi-randomly selected which lever pro- Habituation, dipper training, and response acquisition duced the reinforcer. Lever selection was limited to a Prior to behavioral testing, the rats were assigned an maximum of 4 consecutive reinforcers on the same operant chamber and a time of testing in a semi-rando- lever to avoid the development of a lever-preference. mized and balanced way. Habituation to the operant The lever producing the reinforcer was signaled (discri- chambers started at the day following arrival (PND 25) minative stimulus) by the lit cue light located above the and lasted 30 min. During the habituation session, the lever. The light stayed lit for as long as the lever was flap between the working space and the reinforcement associated with reinforcement, but was turned off during cubicle was taped open. No levers were present, the cue reinforcer presentation. The timer for the next interval lights above the levers were off, and no reinforcers were started when the dipper was presented. Scheduled rein- delivered. forcers and reinforcers produced, but not collected, were The habituation session was followed by two 30-min accumulated and scheduled for the next correct response. dipper training sessions. The flap was taped open, no Except for during the habituation and dipper training levers were present, and the cue lights above the levers sessions, reinforcers were accessible for 3 s after the flap were off. The computer delivered water every 10 s inde- into the water cubicle was opened. Then, the dipper was pendent of the animal’s behavior using a fixed-time lowered and the cubicle light was turned off. If the flap schedule. The cue light in the small recessed cubicle was not opened within 5 s after a reinforcer presentation, Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 4 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 the water dipper was lowered and the cubicle light was reinforcers was used as a measure of sustained attention turned off. (the animal has to pay attention to and press the lever A concurrent extinction schedule was in effect on the signaled by the lit cue light located above the lever) alternative lever. The light above the alternative lever [46-48]. Percentage correct would be at chance level was always off. Thus, the present task can be described (~50%) in animals pressing the reinforcement lever and as a simultaneous visual discrimination task. the alternative lever equally often. Total number of The VI 180 s schedule lever-presses on the two levers combined was used as a A variable interval 180 s schedule (VI 180 s) was in measure of hyperactivity, and number of responses with short IRTs (< 0.67 s) was used as a measure of impulsiv- effect for 90 min on one of the two levers from session 13 to session 19 when all sixteen operant chambers ity ("premature responding” or “inability to wait”). Here, were used (Table 1). Due to a computer failure, all ani- a neutral description of the measures will be used. The mals were tested in room 1 using 8 operant chambers measures will be referred to as stimulus control, activity from session 20 and throughout the remaining sessions. (level), and responses with short IRTs, respectively. Also, session length was halved to 45 min to make it Also, the number of responses with IRTs shorter than possible to test all animals during the day-time (see 0.67 s was subtracted from the measure of activity to Table 1 for a summary of the experimental procedure). ensure independency of the two measures. The malfunctioning computer scheduled reinforcers and lights correctly, but stopped on occasion without saving Data Analysis the data. The error did not differentially affect the All statistical analyses were done in Statistica 6.0 [49]. groups as the groups were balanced across both test Data were evaluated by multivariate analyses using chambers and rooms. Wilks lambda (MANOVAs) when the degrees of free- A computer program was used to generate a Catania- dom relative to the number of levels of the repeated fac- Reynolds distribution of intervals for the VI 180 s sche- tor permitted this approach, or by univariate analyses of dule [44,45]. Inter-reinforcer intervals during the VI 180 variance (ANOVAs) adjusting the degrees of freedom sschedulerangedfrom6sto719 sand were distribu- with the Huynh-Feldt epsilon [50]. Sessions were used ted in a semi-randomized fashion across the session. as the within-subject factor and treatment as the There was neither any external stimulus signaling that a between-subjects factor. Post-hoc tests on main effects reinforcer was programmed nor any external stimulus were performed using the Tukey HSD test. signaling the time since the last response. The five training sessions (sessions 8-12) under the VI Behavioral measures 3 s schedule were analyzed separately. In a second ana- The computer recorded number of presses on the lever lysis, the last 14 sessions (sessions 20-33) under the VI producing reinforcers and on the alternative lever, num- 180 s schedule were selected because these sessions ber of flap openings to the cubicle, number of reinfor- represented relatively stable behavior. The cumulated cers produced and collected, and the time of the events. numbers of responses at the end of each session were The following measures were calculated from the used in all analyses. In the figures showing responding recorded behavior: Percentage of responses on the lever across the sessions, data from the first 45 min were producing reinforcers, responses with IRTs longer than used in sessions 13 to 19 to match the 45-min session 0.67 s, and responses with IRTs shorter than 0.67 s. length in sessions 20 to 33 (Figures 1, 2 and 3). In previous studies using the same operant procedure, One animal was able to collect reinforcers without the percentage of responses on the lever producing activating the microswitch registering flap openings causing the computer to schedule too many reinforcers. As the reinforcement contingencies were unique for this Table 1 Summary of the experimental procedure animal, it was excluded from the statistical analyses. Session number Schedule Notes Missing data were substituted by calculating the 1 Habituation means of the preceding and following sessions. The 2 - 3 FT 10 s Magazine training Grubbs’ test was used to identify and remove outliers 4 - 5 CRF Flap training [51]. A z-score exceeding the critical value represents a 6 - 7 Shaping of lever-pressing less than 5% probability of finding this value by chance alone. The critical value depends on number of subjects 8-12 VI 3 s 30 min session (N) and must be adjusted accordingly. Here, z-scores 13 - 19 VI 180 s 90 min session, 16 chambers 1 were calculated for each group of N = 5, N = 6, and 20 - 33 VI 180 s 45 min session, 8 chambers N = 9 (two groups), and the critical values used for FT: fixed time schedule of reinforcement. CRF: continuous reinforcement removing outliers in each group were, 1.71, 1.89, and schedule. VI: variable interval schedule of reinforcement. 2.21, respectively. Examination of outliers identified by Note. - Used in the analyses. Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 5 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 Figure 1 Stimulus control (percentage of responses on the reinforcer-producing lever) in the four groups. The vertical dotted line indicates when the contingencies changed from VI 3 s (sessions 8-12) to VI 180 s (sessions 13-33). the Grubb’s test for stimulus control, activity level (IRTs VI 3 s schedule of reinforcement (Figures 1, 2 and 3). The > 0.67 s), and number of responses with short IRTs analyses of activity level, however, showed a non-signifi- (< 0.67 s) under the VI 180 s schedule showed that a cant trend for a main effect of exposure, F(3,22) = 2.85; totalof15datapointswith an averagez-scoreof2.46 p = 0.061, with the PCB 52 group tending to be more were removed for one animal. The remaining outliers active than the control, PCB 153 and PCB 180 groups identified and removed by the Grubb’s test represented (Figure 2; sessions 8-12). 0.9% of the total data in the VI 180 s condition. The VI 180 s schedule (sessions 20-33) Results Stimulus control Generally, stimulus control dropped from 80% during the The ANOVA showed a statistically significant main effect VI 3 s schedule to between 60% and 70% during the VI of exposure, F(3,20) = 4.770; p = 0.011 (Figure 1). Percen- 180 s schedule (Figure 1). Fewer lever-presses were tage of responses on the lever producing reinforcers observed under the VI 3 s schedule than under VI 180s increased across sessions, reflected in a statistically signif- due to the shorter session length and the larger propor- icant main effect of session, F(13,260) = 2.161; p = 0.012. tion of time spent consuming the water (Figures 2 and 3). No other effects were found. Tukey HSD post-hoc ana- lyses of the significant maineffectof exposureshowed The VI 3 s schedule (sessions 8-12) that this effect was produced by statistically significantly There were no statistically significant group differences in better stimulus control in the PCB 180 group compared stimulus control, activity level (IRTs > 0.67 s), number of to the control group and the PCB 52 group (ps = 0.044). responses with short IRTs (< 0.67 s), number of flap open- 0.67 s)",1,0,2,0,0pc,0pc,0pc,0pc>Activity (IRTs > 0.67 s) ings, reinforcers produced, or reinforcers collected during The analysis showed a statistically significant main effect training when responding was reinforced according to a of exposure, F(3,23) = 9.11; p < 0.001. A statistically Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 6 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 Figure 2 The total number of lever-presses with IRTs > 0.67 s in the four groups. The vertical dotted line indicates when the contingencies changed from VI 3 s (sessions 8-12) to VI 180 s (sessions 13-33). significant main effect of session showed that activity collected showed a trend for a main effect of exposure, level decreased across sessions, F(13,299) = 19.84; p < F(3,25) = 3.0; p = 0.051. The average number of reinfor- 0.001. No interaction effect was found. Post-hoc ana- cers collected was 14.06 in the control group and 13.82 lyses of the main effect of exposure using Tukey HSD in the PCB 153 group, with intermediate values in the tests showed that the PCB 153 and the PCB 180 groups two other groups. were less active than the control group (p = 0.010 and To test that differences in number of reinforcers col- p = 0.004, respectively) and the PCB 52 group (p= lected between experimental and control groups did not 0.013 and p = 0.004, respectively) (Figure 2). affect the statistical results, activity level (IRTs > 0.67 s) Responses with short IRTs (< 0.67 s) and number of responses with short IRTs (< 0.67 s) The ANOVA showed a statistically significant main were divided by the number of reinforcers collected per effect of exposure, F(3,20) = 5.06; p = 0.009.Noother session for each individual animal, and the data reana- effects were found. Tukey HSD post-hoc analyses of the lyzed. The results showed the same statistically signifi- main effect of exposure showed that the PCB 52 group cant effects as when not correcting for reinforcers had more responses with short IRTs than the PCB 153 collected, with minimal changes in p-values. and the PCB 180 groups (p = 0.035 and p = 0.022, respectively) (Figure 3). Discussion Flap openings The present study examined behavioral effects of expo- There were no group differences in the number of visits sure to PCB 52, PCB 153, and PCB 180 in outbred male to the water cubicle. Wistar Kyoto (WKY/NTac) rats. The PCBs were admi- Reinforcers produced and reinforcers collected nistered orally three times between postnatal day 8 and There were no group differences in number of reinfor- 20 at a dose of 10 mg/kg body weight at each exposure. cers produced. The analyses of number of reinforcers Effects of exposure to the three ortho-substituted PCBs Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 7 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 Figure 3 The total number of lever-presses with short IRTs (< 0.67 s) in the four groups. The vertical dotted line indicates when the contingencies changed from VI 3 s (sessions 8-12) to VI 180 s (sessions 13-33). found in human breast milk were evaluated using a pro- controls (Figure 2; sessions 20-33), and stimulus control cedure developed to study behavioral changes in a rat was significantly better in the PCB 180 group compared model of Attention-Deficit/Hyperactivity Disorder to controls (Figure 1; sessions 20-33). Also, there was a [40,46]. The procedure uses an operant visual discrimi- tendency for the controls to collect more reinforcers nation task in which the reinforced (signaled) lever than the PCB 153 group. However, this difference was switched randomly following every reinforcer-delivery to small, not statistically significant, and the same signifi- assess stimulus control (the discriminative control of a cant effects were found when reanalyzing the data con- cue light on lever-presses, measured as percentage of trolling for reinforcers collected. responding on the lever producing reinforcers), activity Comparisons of the PCB groups showed that there level (total number of lever-presses with IRTs > 0.67 s), were no significant differences between the PCB 153 and responses with IRTs shorter than 0.67 s. and PCB 180 groups. However, both the PCB 180 and Data from two conditions were analyzed: During the PCB 153 groups were less active and had fewer training when a VI 3 s schedule was in effect, and dur- responses with short IRTs (< 0.67 s) than the PCB 52 ing a VI 180 s schedule when responses on the signaled group (Figures 2, 3; sessions 20-33), and stimulus con- lever produced a reinforcer (on average) every three trol was significantly better in the PCB 180 group com- minutes. The results showed no statistically significant pared to the PCB 52 group (Figure 1; sessions 20-33). differences between the groups under the VI 3 s sche- Effects of exposure to PCB 52. No behavioral changes dule (Figures 1, 2 and 3; sessions 8-12). were observed following exposure to PCB 52 in the pre- The statistical analyses of the VI 180 s condition sent study. Boix et al. exposed female Wistar rats to found no significant differences between the PCB 52 PCBs at a dose of 1 mg/kg bw from GD 7 to PND 21 and controls. In contrast, animals exposed to PCB 153 and tested the offspring when they were 3-4 months old and PCB 180 were significantly less active than the [33]. Exposure to PCB 52 impaired motor coordination Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 8 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 but did not affect Y maze performance. In two studies, from PND 3 to 13 at a dose of 5 mg/kg [34,35]. The Eriksson et al. reported learning deficits and behavioral resultsshowedthatmale, butnotfemale,offspring changes in adult mice following exposure to a single became hyperactive, had more responses with short dose of PCB 52 on PND 10 at a maximum dose of 4.1 IRTs, and showed decreased stimulus control relative to mg/kg bw [27,52]. Kodavanti et al. exposed adult male controls in an operant test similar to the one used in Long-Evans rats to the PCB mixture Aroclor 1254 con- the present study. Berger et al. found similar results in adult male Sprague-Dawley rats exposed during puberty taining PCB 153, PCB 180 as well as PCB 52 [5]. On to PCB contaminated fish or to contaminated diet con- dissection, PCB 153 and PCB 180 were found in the taining low doses of the PCB mixture Aroclor 1248 (30 brain, while PCB 52 could not be detected despite also having been present in the mixture. The PCB 52 conge- g daily portions of rodent diet supplemented with 1 ml ner is less chlorinated, and therefore, more soluble and corn oil containing 0.5 μg/g Aroclor 1248) [56]. These less stable than PCB 153 and PCB 180, and may affect findings are opposite to the findings in the present the brain differently than the two other congeners study, and may be due to the different doses and dosing [4,32,33,53,54]. regimen used in the studies. Effects of exposure to PCB 153 and PCB 180.When A range of conflicting results have been obtained in responding on the VI 180 s schedule, a marked signifi- studies of PCB mixtures like Aroclor 1254 (containing cant decrease in lever-directed activity was observed in both PCB 153 and PCB 180). Studies have reported animals exposed to PCB 153 or PCB 180 compared to changes in motor functions in young offspring of female controls. However, although lever-directed activity Sprague-Dawley rats exposed to A1254 at a dose of 10 (related to motivation and effects of reinforcers) was mg/kg/dayfrom GD11toPND 21, and long-lasting reduced in the exposed animals, it is unclear how gen- hypoactivity in adult Long-Evans rats exposed to acute eral locomotor activity was affected in the exposed ani- high doses (300 mg/kg and higher) or transitory hypoac- mals as this was not measured during the operant task. tivity after repeated exposure to doses of 30 mg/kg or While visual inspection of Figure 3 reveals a reduced higher [57,58]. Changes have also been observed in tendency for PCB 153 and PCB 180 rats to emit short radial maze performance in adult male offspring of IRTs, no significant differences between these groups Long-Evans dams exposed to Aroclor 1254 at a dose of and the control group were found. Only when the PCB 6 mg/kg/day from gestational day 6 to PND 21, and spa- 153 and PCB 180 groups were compared to the PCB 52 tial alternation deficits have been found in adult male and female offspring of Long-Evans dams exposed to 6 group did these comparisons reach statistical signifi- mg/kg from 28 days before mating to PND 16 [53,59]. cance. For the stimulus control measure, only the PCB 180 group was significantly different from the control Still, other studies have found no changes in activity or (and PCB 52) group. attention in adult offspring of Long-Evans dams exposed In our experiment, stimulus control was inversely throughout gestation and nursing to Aroclor 1254 at related to lever-directed activity. Theoretically, stimulus doses of 1.0 or 6.0 mg/kg/day, or in spatial learning in control is independent of rate of lever-pressing, and pre- young and adult offspring of Long-Evans dams exposed vious studies using an identical procedure have shown to 6 or 8 mg/kg/day from gestation to weaning that these measures can be independently affected by [9,60-62]. experimental manipulations like exposure to drugs [46]. PCB dose is probably one of several important factors Still, it is possible that activity level is linked to explora- determining the degree of cognitive and behavioral tion of other response alternatives, especially when rein- changes following exposure. Nishida et al., Eriksson et forcement rate is low, and that the better stimulus al., and Kodavanti et al. found a dose-dependent reduc- control was secondary to hypoactivity produced by the tion in activity, whereas Holene et al. and Berger et al. PCB exposure. Further, the reduced number of found an increased activity level after exposure to differ- responses with short IRTs found in the present study ent doses of PCB [5,27,34,56,58]. The combined findings could be secondary to motor problems and hypoactivity suggest a curvilinear dose-response relationship or that produced by PCB exposure. the dose-response relationships are different for different Studies of PCB 153 or PCB 180 have found impaired brain regions, functions, and behaviors [25,27,63,64]. A maze-learning in both male and female offspring of range of other critical factors are likely to contribute to Wistar dams treated orally with PCB 153 from GD 7 to the varying results in studies examining effects of PCB exposure. The organism’s age when exposed importantly PND 21 at a dose of 1 mg/kg body weight per day, and influences the degree of neurological, cognitive, and in female offspring of Wistar dams treated with PCB behavioral changes. The nervous system seems to be 180 using the same dosing regimen [31,33,55]. Holene et al. mated female DA/OLA/HSD rats with Lewis rats more sensitive to toxins during development when there and gavage-fed the dams PCB 153 every second day is a rapid growth and maturation of the brain [28]. Also, Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 9 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 the age of the organism when tested and the measures of Attention Deficit/Hyperactivity Disorder and Parkin- used to assess the effects of exposure are important vari- son’s disease where dopamine disturbance is a likely ables [31]. Findings show that the cognitive and beha- cause [2,67-70]. Studies investigating a possible vulner- vioral changes following PCB exposure vary depending ability to PCB exposure in these disorders using animal on the organism’s age at the time of testing and on the models should therefore be conducted. measures used [27,31,33]. Additionally, effects of expo- sure to PCBs may be both sex- and species-specific Conclusion [30,33-36,53]. In the present study, behavioral differ- The present study found reduced activity in rats postna- ences between groups were found only when reinforcers tally exposed to PCB 153 and PCB 180, while less robust were delivered on the average every three minutes, and result were obtained for stimulus control and responses not during frequent reinforcement, consistent with pre- with short IRTs. No effects of exposure to PCB 52 were vious results using the same procedure [39,56,65,66]. found. The behavioral changes in the animals exposed Thus, PCB exposure does not necessarily produce gen- to PCB 153 or PCB 180 were observed five weeks fol- eral behavioral problems. Exposed animals may perform lowing the last exposure suggesting that exposure has normally under some test conditions (e.g. frequent rein- long-lasting effects. Dose-response relations need to be forcement), but abnormally under others (infrequent established to determine whether this conclusion is valid reinforcement), adding to the argument that neurobeha- also for other doses. vioral effects of PCB exposure depend on a number of factors like procedures and measures used, age at expo- Acknowledgements sure and at testing, and dose and type or combination The present study was supported by grants from the Research Council of of PCBs used. Norway (NFR 175096 and 173046), and by the European Commission (Food- CT-2006-022923-ATHON). Limitations and future challenges. The number of ani- mals in the control group was smaller than originally Author details planned. To assess the original control group, a second Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway. Department of Biochemistry, Institute of Basic Medical control group consisting of seven animals was tested. Sciences, University of Oslo, Oslo, Norway. Akershus University College, These animals were littermates of the animals in the ori- Kjeller, Norway. Institute of Psychology, University of Oslo, Oslo, Norway. ginal control group, one week older at the start of beha- The Norwegian Defense Research Establishment, Kjeller, Norway. vioral testing, and had not been given corn oil. These Authors’ contributions animals were not included in the main analyses because EBJ participated in designing the study, and had the main responsibility for differences in age and corn-oil administration may have analyzing the data and drafting the manuscript. MK participated in data collection, and had with EBJ the main responsibility for the data analyses affected the behavioral measures. Therefore, the follow- and drafting the manuscript. FF participated in designing the study, made ing analyses must be interpreted with caution. Statistical the PCB-solutions used in the study, and helped drafting the manuscript. comparisons of the original and the second control PLL participated in designing the study, had the main responsibility for animal breeding and welfare, administered the PCBs, and helped drafting groups showed no significant differences in measures of the manuscript. SIV participated in designing the study and helped drafting stimulus control, activity, or responses with short IRTs the manuscript. GW was the main organizer of animal testing and data during VI 180 s. The extra controls were added to the collection, performed preliminary data analyses, and helped drafting the manuscript. TS was the coordinator of the study, participated in the design original control group and all data were reanalyzed. The and in drafting the manuscript. All authors read and approved the final results for activity level and responses with short IRTs manuscript. were in accordance with the main analyses, indicating Competing interests that the findings were not produced by a small and The authors declare that they have no competing interests. non-representative control group. The analyses of sti- mulus control, however, did not reach the conventional Received: 2 July 2010 Accepted: 26 May 2011 Published: 26 May 2011 level of significance (p = 0.09) suggesting that PCB References exposure had little effect on stimulus control or that age 1. Fonnum F, Mariussen E: Mechanisms involved in the neurotoxic effects of differences in the added controls have affected the environmental toxicants such as polychlorinated biphenyls and results. brominated flame retardants. J Neurochem 2009, 111:1327-1347. 2. Mariussen E, Fonnum F: Neurochemical targets and behavioral effects of Together with contradicting results from other studies, organohalogen compounds: an update. Crit Rev Toxicol 2006, 36:253-289. the present findings raise a call for systematic studies of 3. Safe S: Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dose-effects relations in PCB research. Studies need to dibenzofurans (PCDFs), and related compounds: environmental and mechanistic considerations which support the development of toxic include neurochemical as well as behavioral measures to equivalency factors (TEFs). Crit Rev Toxicol 1990, 21:51-88. uncover the underlying neurochemical changes. One 4. McKinney JD, Waller CL: Polychlorinated biphenyls as hormonally active contributing factor to the behavioral changes following structural analogues. Environ Health Perspect 1994, 102:290-297. 5. Kodavanti PR, Ward TR, Derr-Yellin EC, Mundy WR, Casey AC, Bush B, PCB exposure may be alterations in dopamine function Tilson HA: Congener-specific distribution of polychlorinated biphenyls in [2]. Hence, PCB exposure may play a role in the etiology Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 10 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 brain regions, blood, liver, and fat of adult rats following repeated 26. Kobayashi K, Miyagawa M, Wang RS, Suda M, Sekiguchi S, Honma T: Effects exposure to Aroclor 1254. Toxicol Appl Pharmacol 1998, 153:199-210. of in utero exposure to 2,2’,4,4’,5,5’-hexachlorobiphenyl (PCB 153) on 6. Longnecker MP, Wolff MS, Gladen BC, Brock JW, Grandjean P, Jacobson JL, somatic growth and endocrine status in rat offspring. Congenit Anom Korrick SA, Rogan WJ, Weisglas-Kuperus N, Hertz-Picciotto I, Ayotte P, (Kyoto) 2008, 48:151-157. Stewart P, Winneke G, Charles MJ, Jacobson SW, Dewailly E, Boersma ER, 27. Eriksson P, Fischer C, Fredriksson A: Polybrominated diphenyl ethers, a Altshul LM, Heinzow B, Pagano JJ, Jensen AA: Comparison of group of brominated flame retardants, can interact with polychlorinated polychlorinated biphenyl levels across studies of human biphenyls in enhancing developmental neurobehavioral defects. Toxicol neurodevelopment. Environ Health Perspect 2003, 111:65-70. Sci 2006, 94:302-309. 7. Korrick SA, Sagiv SK: Polychlorinated biphenyls, organochlorine pesticides 28. Kuchenhoff A, Eckard R, Buff K, Fischer B: Stage-specific effects of defined and neurodevelopment. Curr Opin Pediatr 2008, 20:198-204. mixtures of polychlorinated biphenyls on in vitro development of rabbit 8. Sagiv SK, Thurston SW, Bellinger DC, Tolbert PE, Altshul LM, Korrick SA: preimplantation embryos. Mol Reprod Dev 1999, 54:126-134. Prenatal organochlorine exposure and behaviors associated with 29. Sweeney AM, Symanski E: The influence of age at exposure to PBBs on attention deficit hyperactivity disorder in school-aged children. Am J birth outcomes. Environ Res 2007, 105:370-379. Epidemiol 2010, 171:593-601. 30. Castoldi AF, Blandini F, Randine G, Samuele A, Manzo L, Coccini T: Brain 9. Bushnell PJ, Moser VC, MacPhail RC, Oshiro WM, Derr-Yellin EC, Phillips PM, monoaminergic neurotransmission parameters in weanling rats after Kodavanti PR: Neurobehavioral assessments of rats perinatally exposed perinatal exposure to methylmercury and 2,2’,4,4’,5,5’- to a commercial mixture of polychlorinated biphenyls. Toxicol Sci 2002, hexachlorobiphenyl (PCB153). Brain Res 2006, 1112:91-98. 68:109-120. 31. Piedrafita B, Erceg S, Cauli O, Monfort P, Felipo V: Developmental exposure 10. Schantz SL: Developmental neurotoxicity of PCBs in humans: what do to polychlorinated biphenyls PCB153 or PCB126 impairs learning ability we know and where do we go from here? Neurotoxicol Teratol 1996, in young but not in adult rats. Eur J Neurosci 2008, 27:177-182. 18:217-227. 32. Llansola M, Montoliu C, Boix J, Felipo V: Polychlorinated biphenyls PCB 52, 11. Yamashita F, Hayashi M: Fetal PCB syndrome: clinical features, PCB 180, and PCB 138 impair the glutamate-nitric oxide-cGMP pathway intrauterine growth retardation and possible alteration in calcium in cerebellar neurons in culture by different mechanisms. Chem Res metabolism. Environ Health Perspect 1985, 59:41-45. Toxicol 2010, 23:813-820. 12. Gladen BC, Rogan WJ, Hardy P, Thullen J, Tingelstad J, Tully M: 33. Boix J, Cauli O, Felipo V: Developmental exposure to polychlorinated Development After Exposure to Polychlorinated-Biphenyls and biphenyls 52, 138 or 180 affects differentially learning or motor Dichlorodiphenyl Dichloroethene Transplacentally and Through Human- coordination in adult rats. Mechanisms involved. Neuroscience 2010, Milk. J Pediatr 1988, 113:991-995. 167:994-1003. 13. Faroon OM, Keith S, Jones D, de RC: Effects of polychlorinated biphenyls 34. Holene E, Nafstad I, Skaare JU, Sagvolden T: Behavioural hyperactivity in on development and reproduction. Toxicol Ind Health 2001, 17:63-93. rats following postnatal exposure to sub- toxic doses of polychlorinated 14. Schell LM, Gallo MV: Relationships of putative endocrine disruptors to biphenyl congeners 153 and 126. Behav Brain Res 1998, 94:213-224. human sexual maturation and thyroid activity in youth. Physiol Behav 35. Holene E, Nafstad I, Skaare JU, Krogh H, Sagvolden T: Behavioural effects in 2010, 99:246-253. female rats of postnatal exposure to sub-toxic doses of polychlorinated 15. Boucher O, Muckle G, Bastien CH: Prenatal exposure to polychlorinated biphenyl congener 153. Acta Paediatr Suppl 1999, 88:55-63. biphenyls: a neuropsychologic analysis. Environ Health Perspect 2009, 36. Schantz SL: Spatial learning deficits in adult rats exposed to ortho- 117:7-16. substituted PCB congeners during gestation and lactation. Fundam Appl 16. Roegge CS, Schantz SL: Motor function following developmental Toxicol 1995, 26:117-126. exposure to PCBS and/or MEHG. Neurotoxicol Teratol 2006, 28:260-277. 37. Gralewicz S, Wiaderna D, Lutz P, Sitarek K: Neurobehavioural functions in 17. Schantz SL, Widholm JJ, Rice DC: Effects of PCB exposure on adult progeny of rat mothers exposed to methylmercury or 2,2’, 4,4’, neuropsychological function in children. Environ Health Perspect 2003, 5,5’-hexachlorobiphenyl (PCB 153) alone or their combination during 111:357-376. gestation and lactation. Int J Occup Med Environ Health 2009, 22:277-291. 18. Vreugdenhil HJ, Mulder PG, Emmen HH, Weisglas-Kuperus N: Effects of 38. Khan MA, Lichtensteiger CA, Faroon O, Mumtaz M, Schaeffer DJ, Hansen LG: perinatal exposure to PCBs on neuropsychological functions in the The hypothalamo-pituitary-thyroid (HPT) axis: a target of nonpersistent Rotterdam cohort at 9 years of age. Neuropsychology 2004, 18:185-193. ortho-substituted PCB congeners. Toxicol Sci 2002, 65:52-61. 19. Walkowiak J, Wiener JA, Fastabend A, Heinzow B, Kramer U, Schmidt E, 39. Sagvolden T: Behavioral validation of the spontaneously hypertensive rat Steingruber HJ, Wundram S, Winneke G: Environmental exposure to (SHR) as an animal model of attention-deficit/hyperactivity disorder (AD/ polychlorinated biphenyls and quality of the home environment: effects HD). Neurosci Biobehav Rev 2000, 24:31-39. on psychodevelopment in early childhood. Lancet 2001, 358:1602-1607. 40. Sagvolden T, Russell VA, Aase H, Johansen EB, Farshbaf M: Rodent models 20. Stewart P, Reihman J, Gump B, Lonky E, Darvill T, Pagano J: Response of attention-deficit/hyperactivity disorder. Biol Psychiatry 2005, inhibition at 8 and 9 1/2 years of age in children prenatally exposed to 57:1239-1247. PCBs. Neurotoxicol Teratol 2005, 27:771-780. 41. Russell VA, Sagvolden T, Johansen EB: Animal models of attention-deficit 21. Stewart P, Fitzgerald S, Reihman J, Gump B, Lonky E, Darvill T, Pagano J, hyperactivity disorder. Behav Brain Funct 2005, 1:9. Hauser P: Prenatal PCB exposure, the corpus callosum, and response 42. National Instruments: LabVIEW (Version 7.1). Austin, Texas, USA; 2004. inhibition. Environ Health Perspect 2003, 111:1670-1677. 43. Catania AC: Learning. 4 edition. Prentice Hall N.J., Englewoods Cliffs; 1998. 22. Grandjean P, Weihe P, Burse VW, Needham LL, Storr-Hansen E, Heinzow B, 44. Reilly MP: Variable Interval Generator 1.2 2001.. Debes F, Murata K, Simonsen H, Ellefsen P, Budtz-Jorgensen E, Keiding N, 45. Catania AC, Reynolds GS: A quantitative analysis of the responding White RF: Neurobehavioral deficits associated with PCB in 7-year-old maintained by interval schedules of reinforcement. J Exp Anal Behav children prenatally exposed to seafood neurotoxicants. Neurotoxicol 1968, 11(Suppl-83). Teratol 2001, 23:305-317. 46. Sagvolden T, Xu T: l-Amphetamine improves poor sustained attention 23. Jacobson JL, Jacobson SW: Intellectual impairment in children exposed to while d-amphetamine reduces overactivity and impulsiveness as well as polychlorinated biphenyls in utero. N Engl J Med 1996, 335:783-789. improves sustained attention in an animal model of Attention-Deficit/ 24. Patandin S, Lanting CI, Mulder PG, Boersma ER, Sauer PJ, Weisglas- Hyperactivity Disorder (ADHD). Behav Brain Funct 2008, 4:3. Kuperus N: Effects of environmental exposure to polychlorinated 47. Sagvolden T, Dasbanerjee T, Zhang-James Y, Middleton F, Faraone S: biphenyls and dioxins on cognitive abilities in Dutch children at 42 Behavioral and genetic evidence for a novel animal model of Attention- months of age. J Pediatr 1999, 134:33-41. Deficit/Hyperactivity Disorder Predominantly Inattentive Subtype. Behav 25. Yang D, Kim KH, Phimister A, Bachstetter AD, Ward TR, Stackman RW, Brain Funct 2008, 4:56. Mervis RF, Wisniewski AB, Klein SL, Kodavanti PR, Anderson KA, Wayman G, 48. Sagvolden T: The alpha-2A adrenoceptor agonist guanfacine improves Pessah IN, Lein PJ: Developmental exposure to polychlorinated biphenyls sustained attention and reduces overactivity and impulsiveness in an interferes with experience-dependent dendritic plasticity and ryanodine animal model of Attention-Deficit/Hyperactivity Disorder (ADHD). Behav receptor expression in weanling rats. Environ Health Perspect 2009, Brain Funct 2006, 2:41. 117:426-435. 49. StatSoft: Statistica for Windows. Tulsa, OK: StatSoft, Inc; 2005. Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 11 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 50. Myers JL, Well AD: Research design and statistical analysis. 2 edition. and environmental factors and the dopamine hypothesis. Neuropsychol Mahwah: Lawrence Erlbaum Associates; 2003. Rev 2007, 17:39-59. 51. Grubbs FE: Procedures for detecting outlying observations in samples. doi:10.1186/1744-9081-7-18 Technometrics 1969, 11:1-21. Cite this article as: Johansen et al.: Postnatal exposure to PCB 153 and 52. Eriksson P, Fredriksson A: Developmental neurotoxicity of four ortho- PCB 180, but not to PCB 52, produces changes in activity level and substituted polychlorinated biphenyls in the neonatal mouse. Environ stimulus control in outbred male Wistar Kyoto rats. Behavioral and Brain Toxicol Pharmacol 1996, 1:155-165. Functions 2011 7:18. 53. Roegge CS, Seo BW, Crofton KM, Schantz SL: Gestational-lactational exposure to Aroclor 1254 impairs radial-arm maze performance in male rats. Toxicol Sci 2000, 57:121-130. 54. Giesy JP, Kannan K: Dioxin-like and non-dioxin-like toxic effects of polychlorinated biphenyls (PCBs): Implications for risk assessment. Crit Rev Toxicol 1998, 28:511-569. 55. Piedrafita B, Erceg S, Cauli O, Felipo V: Developmental exposure to polychlorinated biphenyls or methylmercury, but not to its combination, impairs the glutamate-nitric oxide-cyclic GMP pathway and learning in 3-month-old rats. Neuroscience 2008, 154:1408-1416. 56. Berger DF, Lombardo JP, Jeffers PM, Hunt AE, Bush B, Casey A, Quimby F: Hyperactivity and impulsiveness in rats fed diets supplemented with either Aroclor 1248 or PCB-contaminated St. Lawrence river fish. Behav Brain Res 2001, 126:1-11. 57. Nguon K, Baxter MG, Sajdel-Sulkowska EM: Perinatal exposure to polychlorinated biphenyls differentially affects cerebellar development and motor functions in male and female rat neonates. Cerebellum 2005, 4:112-122. 58. Nishida N, Farmer JD, Kodavanti PR, Tilson HA, MacPhail RC: Effects of acute and repeated exposures to Aroclor 1254 in adult rats: motor activity and flavor aversion conditioning. Fundam Appl Toxicol 1997, 40:68-74. 59. Widholm JJ, Villareal S, Seegal RF, Schantz SL: Spatial alternation deficits following developmental exposure to Aroclor 1254 and/or methylmercury in rats. Toxicol Sci 2004, 82:577-589. 60. Freeman GB, Lordo RA, Singer AW, Peters AC, Neal BH, McConnell EE, Mayes BA: An assessment of neurotoxicity of aroclors 1016, 1242, 1254, and 1260 administered in diet to Sprague-Dawley rats for one year. Toxicol Sci 2000, 53:377-391. 61. Gilbert ME, Mundy WR, Crofton KM: Spatial learning and long-term potentiation in the dentate gyrus of the hippocampus in animals developmentally exposed to Aroclor 1254. Toxicol Sci 2000, 57:102-111. 62. Zahalka EA, Ellis DH, Goldey ES, Stanton ME, Lau C: Perinatal exposure to polychlorinated biphenyls Aroclor 1016 or 1254 did not alter brain catecholamines nor delayed alternation performance in Long-Evans rats. Brain Res Bull 2001, 55:487-500. 63. Andersen ME, Yang RS, French CT, Chubb LS, Dennison JE: Molecular circuits, biological switches, and nonlinear dose-response relationships. Environ Health Perspect 2002, 110(Suppl 6):971-978. 64. Phillips KP, Foster WG, Leiss W, Sahni V, Karyakina N, Turner MC, Kacew S, Krewski D: Assessing and managing risks arising from exposure to endocrine-active chemicals. J Toxicol Environ Health B Crit Rev 2008, 11:351-372. 65. Sagvolden T, Metzger MA, Sagvolden G: Frequent reward eliminates differences in activity between hyperkinetic rats and controls. Behav Neural Biol 1993, 59:225-229. 66. Sagvolden T, Russell VA, Aase H, Johansen EB, Farshbaf M: Rodent models of attention-deficit/hyperactivity disorder. Biol Psychiatry 2005, 57:1239-1247. 67. Caudle WM, Richardson JR, Delea KC, Guillot TS, Wang M, Pennell KD, Miller GW: Polychlorinated biphenyl-induced reduction of dopamine transporter expression as a precursor to Parkinson’s disease-associated Submit your next manuscript to BioMed Central dopamine toxicity. Toxicol Sci 2006, 92:490-499. and take full advantage of: 68. Lyng GD, Snyder-Keller A, Seegal RF: Polychlorinated biphenyl-induced neurotoxicity in organotypic cocultures of developing rat ventral • Convenient online submission mesencephalon and striatum. Toxicol Sci 2007, 97:128-139. 69. 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Postnatal exposure to PCB 153 and PCB 180, but not to PCB 52, produces changes in activity level and stimulus control in outbred male Wistar Kyoto rats

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Springer Journals
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Copyright © 2011 by Johansen et al; licensee BioMed Central Ltd.
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Biomedicine; Neurosciences; Neurology; Behavioral Therapy; Psychiatry
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Abstract

Background: Polychlorinated biphenyls (PCBs) are a class of organic compounds that bioaccumulate due to their chemical stability and lipophilic properties. Humans are prenatally exposed via trans-placental transfer, through breast milk as infants, and through fish, seafood and fatty foods as adolescents and adults. Exposure has several reported effects ranging from developmental abnormalities to cognitive and motor deficiencies. In the present study, three experimental groups of rats were orally exposed to PCBs typically found in human breast milk and then behaviorally tested for changes in measures of stimulus control (percentage lever-presses on the reinforcer- producing lever), activity level (responses with IRTs > 0.67 s), and responses with short IRTs (< 0.67 s). Methods: Male offspring from Wistar Kyoto (WKY/NTac) dams purchased pregnant from Taconic Farms (Germantown, NY) were orally given PCB at around postnatal day 8, 14, and 20 at a dose of 10 mg/kg body weight at each exposure. Three experimental groups were exposed either to PCB 52, PCB 153, or PCB 180. A fourth group fed corn oil only served as controls. From postnatal day 25, for 33 days, the animals were tested for behavioral changes using an operant procedure. Results: PCB exposure did not produce behavioral changes during training when responding was frequently reinforced using a variable interval 3 s schedule. When correct responses were reinforced on a variable interval 180 s schedule, animals exposed to PCB 153 or PCB 180 were less active than controls and animals exposed to PCB 52. Stimulus control was better in animals exposed to PCB 180 than in controls and in the PCB 52 group. Also, the PCB 153 and PCB 180 groups had fewer responses with short IRTs than the PCB 52 group. No effects of exposure to PCB 52 were found when compared to controls. Conclusions: Exposure to PCBs 153 and 180 produced hypoactivity that continued at least five weeks after the last exposure. No effects of exposure to PCB 52 were observed. Background paints [1]. Although the manufacturing of PCBs was for- Polychlorinated biphenyls (PCBs) are a class of organic bidden in the United States and Western Europe from around 1980, PCBs are still present in the environment compounds that due to their chemical stability and resistance to degradation were used in a variety of pro- due to their chemical stability and resistance to degrada- ducts, including coolants and fluid oils for electric tion, and accumulate in the food chain due to the lipo- equipment (transformers, capacitors), plastics, and philic properties. Hence, humans are prenatally exposed via trans-placental transfer, through breast milk during infancy, and during adolescence and adulthood through * Correspondence: EspenBorga.Johansen@hiak.no consumption of contaminated food of which fish and Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway Full list of author information is available at the end of the article © 2011 Johansen et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 2 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 seafood constitute the most important sources of PCB simultaneous visual discrimination procedure developed [1-3]. for testing behavioral changes in an animal model of PCBs consist of two phenyl rings where chlorine can Attention-Deficit/Hyperactivity Disorder (ADHD) be substituted for hydrogen atoms, theoretically giving a [39-41]. total of 209 different PCB structures (congeners). The site and number of chlorine substitution(s) determine Method the molecule’s chemical and toxic properties [4,5]. The Subjects congeners most commonly found in humans are the Male offspring from Wistar Kyoto (WKY/NTac) dams ortho-substituted non-planar PCBs 118, 138, 153, and purchased pregnant from Taconic Farms (Germantown, 180, but also the less chlorinated di-ortho-substituted NY) were used. During the first three weeks, the rats non-planar congener PCB 52 has been found [6-8]. Evi- were under the care of a veterinarian at the Norwegian dence suggests that even low-level exposure to PCBs Defense Research Establishment, Kjeller, who also admi- during development can seriously impact neurobiologi- nistered the PCBs. The mother animals were caged sin- cal, cognitive, and behavioral functioning in humans and gly under standard laboratory animal conditions animals [2,9,10]. Prenatal exposure can produce abnor- (temperature ~22°C, humidity ~55%, 12 hr light/dark mal pigmentation and several developmental abnormal- cycle) in type IV macrolon cages and aspen bedding, ities at birth including gum enlargement, presence of where they also gave birth. Female offspring were culled teeth, abnormal calcification of the scull, and low birth at birth. The rats had free access to food (RM3 (E) from weight [11-13]. Neuroendocrine changes have been Special Diet Services, Witham, Essex CM8 3AD, UK) in observed following prenatal exposure which can also the home cages at all times, and free access to water at interfere with neurotransmitter systems and signal trans- all times. duction pathways [14] (for reviews, see [1,2]). PCB expo- At postnatal day (PND) 24, the rats were transported sure affects neurological as well as cognitive and motor to the University of Oslo for behavioral testing. The rats functions in humans [15-19]. Exposed humans show were experimentally naïve on arrival. A total of 29 rats increased impulsivity, reduced attention and concentra- were behaviorally tested and included in the statistical tion, poorer working memory and lower IQ scores analyses: The PCB 52 and PCB 180 groups each con- [8,18,20-24]. sisted of 9 animals, the PCB 153 group consisted of 6 Controlled studies in animals indicate that several fac- animals, and the control group consisted of 5 animals. tors influence the measured effects of PCB exposure. During habituation and response acquisition, the rats These factors include dose, age when exposed and route were housed together in twos or threes in 41 × 25 × 25 of exposure, age when effects are tested and measures (height) cm transparent cages. Following acquisition of used, and sex and species tested [25-38]. Generally, lever-pressing and throughout the rest of the study, the however, findings from animal studies are consistent rats were housed individually in the same type of cages. with research on humans, and show that PCB exposure The rats had free access to food (RM3 (E) from Special affects learning and memory, activity level, and cognitive Diet Services, Witham, Essex CM8 3AD, UK) in the functions (for reviews, see [2,3]). The behavioral changes home cage at all times, and free access to water at all following exposure have been linked to alterations in times prior to the dipper training sessions. Starting with monoamine function (dopamine and serotonin), vesicu- the dipper training session and throughout the rest of the lar transport and storage of monoamines, disruption of study, the rats were deprived of water for 21 hours a day. 2+ Ca signal transduction, and reduced long-term poten- The temperature in the housing area was ~22°C, and tiation (LTP) (for reviews, see [1,2]). the light was on from 0600 to 1800 hours. The beha- The purpose of the present study was to examine vioral training took place between 0900 and 1400 hours behavioral changes in stimulus control (i.e. the percen- seven days a week, and lasted for 33 days. tage of responses on the reinforcer-producing lever), The study was approved by the Norwegian Animal lever-directed activity level (responses with inter- Research Authority (NARA), and was conducted in response times, IRTs, > 0.67 s), and responses with accordance with the laws and regulations controlling short IRTs (< 0.67 s) in animals postnatally exposed to experiments/procedures in live animals in Norway. one of the three PCBs found in breast milk in humans (PCB 52, PCB 153, and PCB 180) compared to non- Apparatus exposed controls. Outbred male Wistar Kyoto rats were In the initial part of the study, sixteen Campden Instru- orally given a mixture of corn oil and PCB at around ments operant chambers were used. The chambers were postnatal day 8, 14, and 20 at a dose of 10 mg/kg body located in two separate rooms each containing eight weight (bw) at each exposure. Thereafter, the animals chambers and a separate computer. The number of were tested in standard operant test chambers using a operant chambers used was later reduced to eight due Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 3 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 to a computer malfunction in one of the rooms (below). was turned on during each water delivery, and the rein- Each chamber was enclosed in a sound-resistant outer forcer was available for 3 seconds. housing, was ventilated, and equipped with a grid floor. In the following two sessions, the animals were trained The animal’s working space in eight of the chambers to open the flap to gain access to the drop of water. The was25×25 ×30(height)cm(room 1),and 25 ×25 × tape was removed from the flap, no levers were present, 20 (height) cm in the other eight chambers (room 2). A and the cue lights located above the levers were off. fan producing a low masking noise and a 2.8-W house Each flap-opening turned on the cue light in the water light were on during the entire experimental session. cubicle and produced the presentation of a single drop of water. The water-dipper was lowered after 5 s irre- Each chamber was equipped with two retractable levers requiring a dead weight of at least 3 g to activate a spective of the animal’s behavior. micro-switch, and with a 2.8-W cue light located above During the subsequent two sessions, lever-pressing each lever. was shaped according to the method of successive The reinforcers (0.05 ml tap water) were delivered by approximations [43]. During the first of these sessions, a liquid dipper located in a small recessed cubicle where the animals learned to press the left lever in order to a 2.8-W cue light lit up when a reinforcer was pre- receive a reinforcer immediately following every press. sented. A 7 × 5 cm transparent plastic top-hinged flap The cue light above the left lever was lit for the entire separated the cubicle from the animal’s working space. session except during presentation of the reinforcer A computer program LabVIEW 7.1 recorded the when the light in the water cubicle was turned on. The behavior and scheduled reinforcers and lights [42]. right lever was retracted into the wall and the light above the lever was off. On the second session, the right Procedure lever was inserted and the left lever was retracted. Dur- PCB exposure. The animals were randomly assigned to ing this session, the light above the right lever was lit one of the three experimental groups or to the control the entire session except during presentation of the group and then orally given one of the three PCBs dis- reinforcer when the light in the water cubicle was solved in corn oil or corn oil: Group 1 was fed corn oil turned on. Immediately following response shaping on only and served as controls; group 2 was fed PCB 52 each lever, the animal was monitored to make sure the (2,2’,5,5’-Tetrachlorobiphenyl); group 3 was given PCB response was learned, and then left in the chamber for 153 (2,2’,4,4’,5,5’-Hexachlorobiphenyl); and group 4 was an additional 15 min to further strengthen the newly fed PCB 180 (2,2’,3,4,4’,5,5’-Heptachlorobiphenyl). The learned behavior. During this time, every press on the animals were exposed to PCB at around PND 8, PND lever produced a reinforcer. 14, and PND 20 at a dose of 10 mg/kg body weight at The variable interval 3 s schedule each exposure. The total volume given at each exposure Response acquisition was followed by five 30-min long was 0.01ml/g body weight. Exposure was performed by training sessions (sessions 8-12) using a variable interval the veterinarian during working hours, and was adminis- (VI) 3 s reinforcement schedule. tered by gavage with stomach tube. During the VI 3 s sessions and throughout the rest of The PCBs, specially purified and free from dioxin-like the study, both levers were present. At the start of the PCBs, were purchased from Patrick Anderson, Depart- session and following each reinforcer delivery, the com- ment of Chemistry, University of Umeå, Sweden. puter program semi-randomly selected which lever pro- Habituation, dipper training, and response acquisition duced the reinforcer. Lever selection was limited to a Prior to behavioral testing, the rats were assigned an maximum of 4 consecutive reinforcers on the same operant chamber and a time of testing in a semi-rando- lever to avoid the development of a lever-preference. mized and balanced way. Habituation to the operant The lever producing the reinforcer was signaled (discri- chambers started at the day following arrival (PND 25) minative stimulus) by the lit cue light located above the and lasted 30 min. During the habituation session, the lever. The light stayed lit for as long as the lever was flap between the working space and the reinforcement associated with reinforcement, but was turned off during cubicle was taped open. No levers were present, the cue reinforcer presentation. The timer for the next interval lights above the levers were off, and no reinforcers were started when the dipper was presented. Scheduled rein- delivered. forcers and reinforcers produced, but not collected, were The habituation session was followed by two 30-min accumulated and scheduled for the next correct response. dipper training sessions. The flap was taped open, no Except for during the habituation and dipper training levers were present, and the cue lights above the levers sessions, reinforcers were accessible for 3 s after the flap were off. The computer delivered water every 10 s inde- into the water cubicle was opened. Then, the dipper was pendent of the animal’s behavior using a fixed-time lowered and the cubicle light was turned off. If the flap schedule. The cue light in the small recessed cubicle was not opened within 5 s after a reinforcer presentation, Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 4 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 the water dipper was lowered and the cubicle light was reinforcers was used as a measure of sustained attention turned off. (the animal has to pay attention to and press the lever A concurrent extinction schedule was in effect on the signaled by the lit cue light located above the lever) alternative lever. The light above the alternative lever [46-48]. Percentage correct would be at chance level was always off. Thus, the present task can be described (~50%) in animals pressing the reinforcement lever and as a simultaneous visual discrimination task. the alternative lever equally often. Total number of The VI 180 s schedule lever-presses on the two levers combined was used as a A variable interval 180 s schedule (VI 180 s) was in measure of hyperactivity, and number of responses with short IRTs (< 0.67 s) was used as a measure of impulsiv- effect for 90 min on one of the two levers from session 13 to session 19 when all sixteen operant chambers ity ("premature responding” or “inability to wait”). Here, were used (Table 1). Due to a computer failure, all ani- a neutral description of the measures will be used. The mals were tested in room 1 using 8 operant chambers measures will be referred to as stimulus control, activity from session 20 and throughout the remaining sessions. (level), and responses with short IRTs, respectively. Also, session length was halved to 45 min to make it Also, the number of responses with IRTs shorter than possible to test all animals during the day-time (see 0.67 s was subtracted from the measure of activity to Table 1 for a summary of the experimental procedure). ensure independency of the two measures. The malfunctioning computer scheduled reinforcers and lights correctly, but stopped on occasion without saving Data Analysis the data. The error did not differentially affect the All statistical analyses were done in Statistica 6.0 [49]. groups as the groups were balanced across both test Data were evaluated by multivariate analyses using chambers and rooms. Wilks lambda (MANOVAs) when the degrees of free- A computer program was used to generate a Catania- dom relative to the number of levels of the repeated fac- Reynolds distribution of intervals for the VI 180 s sche- tor permitted this approach, or by univariate analyses of dule [44,45]. Inter-reinforcer intervals during the VI 180 variance (ANOVAs) adjusting the degrees of freedom sschedulerangedfrom6sto719 sand were distribu- with the Huynh-Feldt epsilon [50]. Sessions were used ted in a semi-randomized fashion across the session. as the within-subject factor and treatment as the There was neither any external stimulus signaling that a between-subjects factor. Post-hoc tests on main effects reinforcer was programmed nor any external stimulus were performed using the Tukey HSD test. signaling the time since the last response. The five training sessions (sessions 8-12) under the VI Behavioral measures 3 s schedule were analyzed separately. In a second ana- The computer recorded number of presses on the lever lysis, the last 14 sessions (sessions 20-33) under the VI producing reinforcers and on the alternative lever, num- 180 s schedule were selected because these sessions ber of flap openings to the cubicle, number of reinfor- represented relatively stable behavior. The cumulated cers produced and collected, and the time of the events. numbers of responses at the end of each session were The following measures were calculated from the used in all analyses. In the figures showing responding recorded behavior: Percentage of responses on the lever across the sessions, data from the first 45 min were producing reinforcers, responses with IRTs longer than used in sessions 13 to 19 to match the 45-min session 0.67 s, and responses with IRTs shorter than 0.67 s. length in sessions 20 to 33 (Figures 1, 2 and 3). In previous studies using the same operant procedure, One animal was able to collect reinforcers without the percentage of responses on the lever producing activating the microswitch registering flap openings causing the computer to schedule too many reinforcers. As the reinforcement contingencies were unique for this Table 1 Summary of the experimental procedure animal, it was excluded from the statistical analyses. Session number Schedule Notes Missing data were substituted by calculating the 1 Habituation means of the preceding and following sessions. The 2 - 3 FT 10 s Magazine training Grubbs’ test was used to identify and remove outliers 4 - 5 CRF Flap training [51]. A z-score exceeding the critical value represents a 6 - 7 Shaping of lever-pressing less than 5% probability of finding this value by chance alone. The critical value depends on number of subjects 8-12 VI 3 s 30 min session (N) and must be adjusted accordingly. Here, z-scores 13 - 19 VI 180 s 90 min session, 16 chambers 1 were calculated for each group of N = 5, N = 6, and 20 - 33 VI 180 s 45 min session, 8 chambers N = 9 (two groups), and the critical values used for FT: fixed time schedule of reinforcement. CRF: continuous reinforcement removing outliers in each group were, 1.71, 1.89, and schedule. VI: variable interval schedule of reinforcement. 2.21, respectively. Examination of outliers identified by Note. - Used in the analyses. Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 5 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 Figure 1 Stimulus control (percentage of responses on the reinforcer-producing lever) in the four groups. The vertical dotted line indicates when the contingencies changed from VI 3 s (sessions 8-12) to VI 180 s (sessions 13-33). the Grubb’s test for stimulus control, activity level (IRTs VI 3 s schedule of reinforcement (Figures 1, 2 and 3). The > 0.67 s), and number of responses with short IRTs analyses of activity level, however, showed a non-signifi- (< 0.67 s) under the VI 180 s schedule showed that a cant trend for a main effect of exposure, F(3,22) = 2.85; totalof15datapointswith an averagez-scoreof2.46 p = 0.061, with the PCB 52 group tending to be more were removed for one animal. The remaining outliers active than the control, PCB 153 and PCB 180 groups identified and removed by the Grubb’s test represented (Figure 2; sessions 8-12). 0.9% of the total data in the VI 180 s condition. The VI 180 s schedule (sessions 20-33) Results Stimulus control Generally, stimulus control dropped from 80% during the The ANOVA showed a statistically significant main effect VI 3 s schedule to between 60% and 70% during the VI of exposure, F(3,20) = 4.770; p = 0.011 (Figure 1). Percen- 180 s schedule (Figure 1). Fewer lever-presses were tage of responses on the lever producing reinforcers observed under the VI 3 s schedule than under VI 180s increased across sessions, reflected in a statistically signif- due to the shorter session length and the larger propor- icant main effect of session, F(13,260) = 2.161; p = 0.012. tion of time spent consuming the water (Figures 2 and 3). No other effects were found. Tukey HSD post-hoc ana- lyses of the significant maineffectof exposureshowed The VI 3 s schedule (sessions 8-12) that this effect was produced by statistically significantly There were no statistically significant group differences in better stimulus control in the PCB 180 group compared stimulus control, activity level (IRTs > 0.67 s), number of to the control group and the PCB 52 group (ps = 0.044). responses with short IRTs (< 0.67 s), number of flap open- 0.67 s)",1,0,2,0,0pc,0pc,0pc,0pc>Activity (IRTs > 0.67 s) ings, reinforcers produced, or reinforcers collected during The analysis showed a statistically significant main effect training when responding was reinforced according to a of exposure, F(3,23) = 9.11; p < 0.001. A statistically Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 6 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 Figure 2 The total number of lever-presses with IRTs > 0.67 s in the four groups. The vertical dotted line indicates when the contingencies changed from VI 3 s (sessions 8-12) to VI 180 s (sessions 13-33). significant main effect of session showed that activity collected showed a trend for a main effect of exposure, level decreased across sessions, F(13,299) = 19.84; p < F(3,25) = 3.0; p = 0.051. The average number of reinfor- 0.001. No interaction effect was found. Post-hoc ana- cers collected was 14.06 in the control group and 13.82 lyses of the main effect of exposure using Tukey HSD in the PCB 153 group, with intermediate values in the tests showed that the PCB 153 and the PCB 180 groups two other groups. were less active than the control group (p = 0.010 and To test that differences in number of reinforcers col- p = 0.004, respectively) and the PCB 52 group (p= lected between experimental and control groups did not 0.013 and p = 0.004, respectively) (Figure 2). affect the statistical results, activity level (IRTs > 0.67 s) Responses with short IRTs (< 0.67 s) and number of responses with short IRTs (< 0.67 s) The ANOVA showed a statistically significant main were divided by the number of reinforcers collected per effect of exposure, F(3,20) = 5.06; p = 0.009.Noother session for each individual animal, and the data reana- effects were found. Tukey HSD post-hoc analyses of the lyzed. The results showed the same statistically signifi- main effect of exposure showed that the PCB 52 group cant effects as when not correcting for reinforcers had more responses with short IRTs than the PCB 153 collected, with minimal changes in p-values. and the PCB 180 groups (p = 0.035 and p = 0.022, respectively) (Figure 3). Discussion Flap openings The present study examined behavioral effects of expo- There were no group differences in the number of visits sure to PCB 52, PCB 153, and PCB 180 in outbred male to the water cubicle. Wistar Kyoto (WKY/NTac) rats. The PCBs were admi- Reinforcers produced and reinforcers collected nistered orally three times between postnatal day 8 and There were no group differences in number of reinfor- 20 at a dose of 10 mg/kg body weight at each exposure. cers produced. The analyses of number of reinforcers Effects of exposure to the three ortho-substituted PCBs Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 7 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 Figure 3 The total number of lever-presses with short IRTs (< 0.67 s) in the four groups. The vertical dotted line indicates when the contingencies changed from VI 3 s (sessions 8-12) to VI 180 s (sessions 13-33). found in human breast milk were evaluated using a pro- controls (Figure 2; sessions 20-33), and stimulus control cedure developed to study behavioral changes in a rat was significantly better in the PCB 180 group compared model of Attention-Deficit/Hyperactivity Disorder to controls (Figure 1; sessions 20-33). Also, there was a [40,46]. The procedure uses an operant visual discrimi- tendency for the controls to collect more reinforcers nation task in which the reinforced (signaled) lever than the PCB 153 group. However, this difference was switched randomly following every reinforcer-delivery to small, not statistically significant, and the same signifi- assess stimulus control (the discriminative control of a cant effects were found when reanalyzing the data con- cue light on lever-presses, measured as percentage of trolling for reinforcers collected. responding on the lever producing reinforcers), activity Comparisons of the PCB groups showed that there level (total number of lever-presses with IRTs > 0.67 s), were no significant differences between the PCB 153 and responses with IRTs shorter than 0.67 s. and PCB 180 groups. However, both the PCB 180 and Data from two conditions were analyzed: During the PCB 153 groups were less active and had fewer training when a VI 3 s schedule was in effect, and dur- responses with short IRTs (< 0.67 s) than the PCB 52 ing a VI 180 s schedule when responses on the signaled group (Figures 2, 3; sessions 20-33), and stimulus con- lever produced a reinforcer (on average) every three trol was significantly better in the PCB 180 group com- minutes. The results showed no statistically significant pared to the PCB 52 group (Figure 1; sessions 20-33). differences between the groups under the VI 3 s sche- Effects of exposure to PCB 52. No behavioral changes dule (Figures 1, 2 and 3; sessions 8-12). were observed following exposure to PCB 52 in the pre- The statistical analyses of the VI 180 s condition sent study. Boix et al. exposed female Wistar rats to found no significant differences between the PCB 52 PCBs at a dose of 1 mg/kg bw from GD 7 to PND 21 and controls. In contrast, animals exposed to PCB 153 and tested the offspring when they were 3-4 months old and PCB 180 were significantly less active than the [33]. Exposure to PCB 52 impaired motor coordination Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 8 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 but did not affect Y maze performance. In two studies, from PND 3 to 13 at a dose of 5 mg/kg [34,35]. The Eriksson et al. reported learning deficits and behavioral resultsshowedthatmale, butnotfemale,offspring changes in adult mice following exposure to a single became hyperactive, had more responses with short dose of PCB 52 on PND 10 at a maximum dose of 4.1 IRTs, and showed decreased stimulus control relative to mg/kg bw [27,52]. Kodavanti et al. exposed adult male controls in an operant test similar to the one used in Long-Evans rats to the PCB mixture Aroclor 1254 con- the present study. Berger et al. found similar results in adult male Sprague-Dawley rats exposed during puberty taining PCB 153, PCB 180 as well as PCB 52 [5]. On to PCB contaminated fish or to contaminated diet con- dissection, PCB 153 and PCB 180 were found in the taining low doses of the PCB mixture Aroclor 1248 (30 brain, while PCB 52 could not be detected despite also having been present in the mixture. The PCB 52 conge- g daily portions of rodent diet supplemented with 1 ml ner is less chlorinated, and therefore, more soluble and corn oil containing 0.5 μg/g Aroclor 1248) [56]. These less stable than PCB 153 and PCB 180, and may affect findings are opposite to the findings in the present the brain differently than the two other congeners study, and may be due to the different doses and dosing [4,32,33,53,54]. regimen used in the studies. Effects of exposure to PCB 153 and PCB 180.When A range of conflicting results have been obtained in responding on the VI 180 s schedule, a marked signifi- studies of PCB mixtures like Aroclor 1254 (containing cant decrease in lever-directed activity was observed in both PCB 153 and PCB 180). Studies have reported animals exposed to PCB 153 or PCB 180 compared to changes in motor functions in young offspring of female controls. However, although lever-directed activity Sprague-Dawley rats exposed to A1254 at a dose of 10 (related to motivation and effects of reinforcers) was mg/kg/dayfrom GD11toPND 21, and long-lasting reduced in the exposed animals, it is unclear how gen- hypoactivity in adult Long-Evans rats exposed to acute eral locomotor activity was affected in the exposed ani- high doses (300 mg/kg and higher) or transitory hypoac- mals as this was not measured during the operant task. tivity after repeated exposure to doses of 30 mg/kg or While visual inspection of Figure 3 reveals a reduced higher [57,58]. Changes have also been observed in tendency for PCB 153 and PCB 180 rats to emit short radial maze performance in adult male offspring of IRTs, no significant differences between these groups Long-Evans dams exposed to Aroclor 1254 at a dose of and the control group were found. Only when the PCB 6 mg/kg/day from gestational day 6 to PND 21, and spa- 153 and PCB 180 groups were compared to the PCB 52 tial alternation deficits have been found in adult male and female offspring of Long-Evans dams exposed to 6 group did these comparisons reach statistical signifi- mg/kg from 28 days before mating to PND 16 [53,59]. cance. For the stimulus control measure, only the PCB 180 group was significantly different from the control Still, other studies have found no changes in activity or (and PCB 52) group. attention in adult offspring of Long-Evans dams exposed In our experiment, stimulus control was inversely throughout gestation and nursing to Aroclor 1254 at related to lever-directed activity. Theoretically, stimulus doses of 1.0 or 6.0 mg/kg/day, or in spatial learning in control is independent of rate of lever-pressing, and pre- young and adult offspring of Long-Evans dams exposed vious studies using an identical procedure have shown to 6 or 8 mg/kg/day from gestation to weaning that these measures can be independently affected by [9,60-62]. experimental manipulations like exposure to drugs [46]. PCB dose is probably one of several important factors Still, it is possible that activity level is linked to explora- determining the degree of cognitive and behavioral tion of other response alternatives, especially when rein- changes following exposure. Nishida et al., Eriksson et forcement rate is low, and that the better stimulus al., and Kodavanti et al. found a dose-dependent reduc- control was secondary to hypoactivity produced by the tion in activity, whereas Holene et al. and Berger et al. PCB exposure. Further, the reduced number of found an increased activity level after exposure to differ- responses with short IRTs found in the present study ent doses of PCB [5,27,34,56,58]. The combined findings could be secondary to motor problems and hypoactivity suggest a curvilinear dose-response relationship or that produced by PCB exposure. the dose-response relationships are different for different Studies of PCB 153 or PCB 180 have found impaired brain regions, functions, and behaviors [25,27,63,64]. A maze-learning in both male and female offspring of range of other critical factors are likely to contribute to Wistar dams treated orally with PCB 153 from GD 7 to the varying results in studies examining effects of PCB exposure. The organism’s age when exposed importantly PND 21 at a dose of 1 mg/kg body weight per day, and influences the degree of neurological, cognitive, and in female offspring of Wistar dams treated with PCB behavioral changes. The nervous system seems to be 180 using the same dosing regimen [31,33,55]. Holene et al. mated female DA/OLA/HSD rats with Lewis rats more sensitive to toxins during development when there and gavage-fed the dams PCB 153 every second day is a rapid growth and maturation of the brain [28]. Also, Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 9 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 the age of the organism when tested and the measures of Attention Deficit/Hyperactivity Disorder and Parkin- used to assess the effects of exposure are important vari- son’s disease where dopamine disturbance is a likely ables [31]. Findings show that the cognitive and beha- cause [2,67-70]. Studies investigating a possible vulner- vioral changes following PCB exposure vary depending ability to PCB exposure in these disorders using animal on the organism’s age at the time of testing and on the models should therefore be conducted. measures used [27,31,33]. Additionally, effects of expo- sure to PCBs may be both sex- and species-specific Conclusion [30,33-36,53]. In the present study, behavioral differ- The present study found reduced activity in rats postna- ences between groups were found only when reinforcers tally exposed to PCB 153 and PCB 180, while less robust were delivered on the average every three minutes, and result were obtained for stimulus control and responses not during frequent reinforcement, consistent with pre- with short IRTs. No effects of exposure to PCB 52 were vious results using the same procedure [39,56,65,66]. found. The behavioral changes in the animals exposed Thus, PCB exposure does not necessarily produce gen- to PCB 153 or PCB 180 were observed five weeks fol- eral behavioral problems. Exposed animals may perform lowing the last exposure suggesting that exposure has normally under some test conditions (e.g. frequent rein- long-lasting effects. Dose-response relations need to be forcement), but abnormally under others (infrequent established to determine whether this conclusion is valid reinforcement), adding to the argument that neurobeha- also for other doses. vioral effects of PCB exposure depend on a number of factors like procedures and measures used, age at expo- Acknowledgements sure and at testing, and dose and type or combination The present study was supported by grants from the Research Council of of PCBs used. Norway (NFR 175096 and 173046), and by the European Commission (Food- CT-2006-022923-ATHON). Limitations and future challenges. The number of ani- mals in the control group was smaller than originally Author details planned. To assess the original control group, a second Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway. Department of Biochemistry, Institute of Basic Medical control group consisting of seven animals was tested. Sciences, University of Oslo, Oslo, Norway. Akershus University College, These animals were littermates of the animals in the ori- Kjeller, Norway. Institute of Psychology, University of Oslo, Oslo, Norway. ginal control group, one week older at the start of beha- The Norwegian Defense Research Establishment, Kjeller, Norway. vioral testing, and had not been given corn oil. These Authors’ contributions animals were not included in the main analyses because EBJ participated in designing the study, and had the main responsibility for differences in age and corn-oil administration may have analyzing the data and drafting the manuscript. MK participated in data collection, and had with EBJ the main responsibility for the data analyses affected the behavioral measures. Therefore, the follow- and drafting the manuscript. FF participated in designing the study, made ing analyses must be interpreted with caution. Statistical the PCB-solutions used in the study, and helped drafting the manuscript. comparisons of the original and the second control PLL participated in designing the study, had the main responsibility for animal breeding and welfare, administered the PCBs, and helped drafting groups showed no significant differences in measures of the manuscript. SIV participated in designing the study and helped drafting stimulus control, activity, or responses with short IRTs the manuscript. GW was the main organizer of animal testing and data during VI 180 s. The extra controls were added to the collection, performed preliminary data analyses, and helped drafting the manuscript. TS was the coordinator of the study, participated in the design original control group and all data were reanalyzed. The and in drafting the manuscript. All authors read and approved the final results for activity level and responses with short IRTs manuscript. were in accordance with the main analyses, indicating Competing interests that the findings were not produced by a small and The authors declare that they have no competing interests. non-representative control group. The analyses of sti- mulus control, however, did not reach the conventional Received: 2 July 2010 Accepted: 26 May 2011 Published: 26 May 2011 level of significance (p = 0.09) suggesting that PCB References exposure had little effect on stimulus control or that age 1. Fonnum F, Mariussen E: Mechanisms involved in the neurotoxic effects of differences in the added controls have affected the environmental toxicants such as polychlorinated biphenyls and results. brominated flame retardants. J Neurochem 2009, 111:1327-1347. 2. Mariussen E, Fonnum F: Neurochemical targets and behavioral effects of Together with contradicting results from other studies, organohalogen compounds: an update. Crit Rev Toxicol 2006, 36:253-289. the present findings raise a call for systematic studies of 3. Safe S: Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dose-effects relations in PCB research. Studies need to dibenzofurans (PCDFs), and related compounds: environmental and mechanistic considerations which support the development of toxic include neurochemical as well as behavioral measures to equivalency factors (TEFs). Crit Rev Toxicol 1990, 21:51-88. uncover the underlying neurochemical changes. One 4. McKinney JD, Waller CL: Polychlorinated biphenyls as hormonally active contributing factor to the behavioral changes following structural analogues. Environ Health Perspect 1994, 102:290-297. 5. Kodavanti PR, Ward TR, Derr-Yellin EC, Mundy WR, Casey AC, Bush B, PCB exposure may be alterations in dopamine function Tilson HA: Congener-specific distribution of polychlorinated biphenyls in [2]. Hence, PCB exposure may play a role in the etiology Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 10 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 brain regions, blood, liver, and fat of adult rats following repeated 26. Kobayashi K, Miyagawa M, Wang RS, Suda M, Sekiguchi S, Honma T: Effects exposure to Aroclor 1254. Toxicol Appl Pharmacol 1998, 153:199-210. of in utero exposure to 2,2’,4,4’,5,5’-hexachlorobiphenyl (PCB 153) on 6. Longnecker MP, Wolff MS, Gladen BC, Brock JW, Grandjean P, Jacobson JL, somatic growth and endocrine status in rat offspring. Congenit Anom Korrick SA, Rogan WJ, Weisglas-Kuperus N, Hertz-Picciotto I, Ayotte P, (Kyoto) 2008, 48:151-157. Stewart P, Winneke G, Charles MJ, Jacobson SW, Dewailly E, Boersma ER, 27. Eriksson P, Fischer C, Fredriksson A: Polybrominated diphenyl ethers, a Altshul LM, Heinzow B, Pagano JJ, Jensen AA: Comparison of group of brominated flame retardants, can interact with polychlorinated polychlorinated biphenyl levels across studies of human biphenyls in enhancing developmental neurobehavioral defects. Toxicol neurodevelopment. Environ Health Perspect 2003, 111:65-70. Sci 2006, 94:302-309. 7. Korrick SA, Sagiv SK: Polychlorinated biphenyls, organochlorine pesticides 28. Kuchenhoff A, Eckard R, Buff K, Fischer B: Stage-specific effects of defined and neurodevelopment. Curr Opin Pediatr 2008, 20:198-204. mixtures of polychlorinated biphenyls on in vitro development of rabbit 8. Sagiv SK, Thurston SW, Bellinger DC, Tolbert PE, Altshul LM, Korrick SA: preimplantation embryos. Mol Reprod Dev 1999, 54:126-134. Prenatal organochlorine exposure and behaviors associated with 29. Sweeney AM, Symanski E: The influence of age at exposure to PBBs on attention deficit hyperactivity disorder in school-aged children. Am J birth outcomes. Environ Res 2007, 105:370-379. Epidemiol 2010, 171:593-601. 30. Castoldi AF, Blandini F, Randine G, Samuele A, Manzo L, Coccini T: Brain 9. Bushnell PJ, Moser VC, MacPhail RC, Oshiro WM, Derr-Yellin EC, Phillips PM, monoaminergic neurotransmission parameters in weanling rats after Kodavanti PR: Neurobehavioral assessments of rats perinatally exposed perinatal exposure to methylmercury and 2,2’,4,4’,5,5’- to a commercial mixture of polychlorinated biphenyls. Toxicol Sci 2002, hexachlorobiphenyl (PCB153). Brain Res 2006, 1112:91-98. 68:109-120. 31. Piedrafita B, Erceg S, Cauli O, Monfort P, Felipo V: Developmental exposure 10. Schantz SL: Developmental neurotoxicity of PCBs in humans: what do to polychlorinated biphenyls PCB153 or PCB126 impairs learning ability we know and where do we go from here? Neurotoxicol Teratol 1996, in young but not in adult rats. Eur J Neurosci 2008, 27:177-182. 18:217-227. 32. Llansola M, Montoliu C, Boix J, Felipo V: Polychlorinated biphenyls PCB 52, 11. Yamashita F, Hayashi M: Fetal PCB syndrome: clinical features, PCB 180, and PCB 138 impair the glutamate-nitric oxide-cGMP pathway intrauterine growth retardation and possible alteration in calcium in cerebellar neurons in culture by different mechanisms. Chem Res metabolism. Environ Health Perspect 1985, 59:41-45. Toxicol 2010, 23:813-820. 12. Gladen BC, Rogan WJ, Hardy P, Thullen J, Tingelstad J, Tully M: 33. Boix J, Cauli O, Felipo V: Developmental exposure to polychlorinated Development After Exposure to Polychlorinated-Biphenyls and biphenyls 52, 138 or 180 affects differentially learning or motor Dichlorodiphenyl Dichloroethene Transplacentally and Through Human- coordination in adult rats. Mechanisms involved. Neuroscience 2010, Milk. J Pediatr 1988, 113:991-995. 167:994-1003. 13. Faroon OM, Keith S, Jones D, de RC: Effects of polychlorinated biphenyls 34. Holene E, Nafstad I, Skaare JU, Sagvolden T: Behavioural hyperactivity in on development and reproduction. Toxicol Ind Health 2001, 17:63-93. rats following postnatal exposure to sub- toxic doses of polychlorinated 14. Schell LM, Gallo MV: Relationships of putative endocrine disruptors to biphenyl congeners 153 and 126. Behav Brain Res 1998, 94:213-224. human sexual maturation and thyroid activity in youth. Physiol Behav 35. Holene E, Nafstad I, Skaare JU, Krogh H, Sagvolden T: Behavioural effects in 2010, 99:246-253. female rats of postnatal exposure to sub-toxic doses of polychlorinated 15. Boucher O, Muckle G, Bastien CH: Prenatal exposure to polychlorinated biphenyl congener 153. Acta Paediatr Suppl 1999, 88:55-63. biphenyls: a neuropsychologic analysis. Environ Health Perspect 2009, 36. Schantz SL: Spatial learning deficits in adult rats exposed to ortho- 117:7-16. substituted PCB congeners during gestation and lactation. Fundam Appl 16. Roegge CS, Schantz SL: Motor function following developmental Toxicol 1995, 26:117-126. exposure to PCBS and/or MEHG. Neurotoxicol Teratol 2006, 28:260-277. 37. Gralewicz S, Wiaderna D, Lutz P, Sitarek K: Neurobehavioural functions in 17. Schantz SL, Widholm JJ, Rice DC: Effects of PCB exposure on adult progeny of rat mothers exposed to methylmercury or 2,2’, 4,4’, neuropsychological function in children. Environ Health Perspect 2003, 5,5’-hexachlorobiphenyl (PCB 153) alone or their combination during 111:357-376. gestation and lactation. Int J Occup Med Environ Health 2009, 22:277-291. 18. Vreugdenhil HJ, Mulder PG, Emmen HH, Weisglas-Kuperus N: Effects of 38. Khan MA, Lichtensteiger CA, Faroon O, Mumtaz M, Schaeffer DJ, Hansen LG: perinatal exposure to PCBs on neuropsychological functions in the The hypothalamo-pituitary-thyroid (HPT) axis: a target of nonpersistent Rotterdam cohort at 9 years of age. Neuropsychology 2004, 18:185-193. ortho-substituted PCB congeners. Toxicol Sci 2002, 65:52-61. 19. Walkowiak J, Wiener JA, Fastabend A, Heinzow B, Kramer U, Schmidt E, 39. Sagvolden T: Behavioral validation of the spontaneously hypertensive rat Steingruber HJ, Wundram S, Winneke G: Environmental exposure to (SHR) as an animal model of attention-deficit/hyperactivity disorder (AD/ polychlorinated biphenyls and quality of the home environment: effects HD). Neurosci Biobehav Rev 2000, 24:31-39. on psychodevelopment in early childhood. Lancet 2001, 358:1602-1607. 40. Sagvolden T, Russell VA, Aase H, Johansen EB, Farshbaf M: Rodent models 20. Stewart P, Reihman J, Gump B, Lonky E, Darvill T, Pagano J: Response of attention-deficit/hyperactivity disorder. Biol Psychiatry 2005, inhibition at 8 and 9 1/2 years of age in children prenatally exposed to 57:1239-1247. PCBs. Neurotoxicol Teratol 2005, 27:771-780. 41. Russell VA, Sagvolden T, Johansen EB: Animal models of attention-deficit 21. Stewart P, Fitzgerald S, Reihman J, Gump B, Lonky E, Darvill T, Pagano J, hyperactivity disorder. Behav Brain Funct 2005, 1:9. Hauser P: Prenatal PCB exposure, the corpus callosum, and response 42. National Instruments: LabVIEW (Version 7.1). Austin, Texas, USA; 2004. inhibition. Environ Health Perspect 2003, 111:1670-1677. 43. Catania AC: Learning. 4 edition. Prentice Hall N.J., Englewoods Cliffs; 1998. 22. Grandjean P, Weihe P, Burse VW, Needham LL, Storr-Hansen E, Heinzow B, 44. Reilly MP: Variable Interval Generator 1.2 2001.. Debes F, Murata K, Simonsen H, Ellefsen P, Budtz-Jorgensen E, Keiding N, 45. Catania AC, Reynolds GS: A quantitative analysis of the responding White RF: Neurobehavioral deficits associated with PCB in 7-year-old maintained by interval schedules of reinforcement. J Exp Anal Behav children prenatally exposed to seafood neurotoxicants. Neurotoxicol 1968, 11(Suppl-83). Teratol 2001, 23:305-317. 46. Sagvolden T, Xu T: l-Amphetamine improves poor sustained attention 23. Jacobson JL, Jacobson SW: Intellectual impairment in children exposed to while d-amphetamine reduces overactivity and impulsiveness as well as polychlorinated biphenyls in utero. N Engl J Med 1996, 335:783-789. improves sustained attention in an animal model of Attention-Deficit/ 24. Patandin S, Lanting CI, Mulder PG, Boersma ER, Sauer PJ, Weisglas- Hyperactivity Disorder (ADHD). Behav Brain Funct 2008, 4:3. Kuperus N: Effects of environmental exposure to polychlorinated 47. Sagvolden T, Dasbanerjee T, Zhang-James Y, Middleton F, Faraone S: biphenyls and dioxins on cognitive abilities in Dutch children at 42 Behavioral and genetic evidence for a novel animal model of Attention- months of age. J Pediatr 1999, 134:33-41. Deficit/Hyperactivity Disorder Predominantly Inattentive Subtype. Behav 25. Yang D, Kim KH, Phimister A, Bachstetter AD, Ward TR, Stackman RW, Brain Funct 2008, 4:56. Mervis RF, Wisniewski AB, Klein SL, Kodavanti PR, Anderson KA, Wayman G, 48. Sagvolden T: The alpha-2A adrenoceptor agonist guanfacine improves Pessah IN, Lein PJ: Developmental exposure to polychlorinated biphenyls sustained attention and reduces overactivity and impulsiveness in an interferes with experience-dependent dendritic plasticity and ryanodine animal model of Attention-Deficit/Hyperactivity Disorder (ADHD). Behav receptor expression in weanling rats. Environ Health Perspect 2009, Brain Funct 2006, 2:41. 117:426-435. 49. StatSoft: Statistica for Windows. Tulsa, OK: StatSoft, Inc; 2005. Johansen et al. Behavioral and Brain Functions 2011, 7:18 Page 11 of 11 http://www.behavioralandbrainfunctions.com/content/7/1/18 50. Myers JL, Well AD: Research design and statistical analysis. 2 edition. and environmental factors and the dopamine hypothesis. Neuropsychol Mahwah: Lawrence Erlbaum Associates; 2003. Rev 2007, 17:39-59. 51. Grubbs FE: Procedures for detecting outlying observations in samples. doi:10.1186/1744-9081-7-18 Technometrics 1969, 11:1-21. Cite this article as: Johansen et al.: Postnatal exposure to PCB 153 and 52. Eriksson P, Fredriksson A: Developmental neurotoxicity of four ortho- PCB 180, but not to PCB 52, produces changes in activity level and substituted polychlorinated biphenyls in the neonatal mouse. Environ stimulus control in outbred male Wistar Kyoto rats. Behavioral and Brain Toxicol Pharmacol 1996, 1:155-165. Functions 2011 7:18. 53. Roegge CS, Seo BW, Crofton KM, Schantz SL: Gestational-lactational exposure to Aroclor 1254 impairs radial-arm maze performance in male rats. Toxicol Sci 2000, 57:121-130. 54. Giesy JP, Kannan K: Dioxin-like and non-dioxin-like toxic effects of polychlorinated biphenyls (PCBs): Implications for risk assessment. Crit Rev Toxicol 1998, 28:511-569. 55. Piedrafita B, Erceg S, Cauli O, Felipo V: Developmental exposure to polychlorinated biphenyls or methylmercury, but not to its combination, impairs the glutamate-nitric oxide-cyclic GMP pathway and learning in 3-month-old rats. Neuroscience 2008, 154:1408-1416. 56. Berger DF, Lombardo JP, Jeffers PM, Hunt AE, Bush B, Casey A, Quimby F: Hyperactivity and impulsiveness in rats fed diets supplemented with either Aroclor 1248 or PCB-contaminated St. Lawrence river fish. Behav Brain Res 2001, 126:1-11. 57. Nguon K, Baxter MG, Sajdel-Sulkowska EM: Perinatal exposure to polychlorinated biphenyls differentially affects cerebellar development and motor functions in male and female rat neonates. Cerebellum 2005, 4:112-122. 58. Nishida N, Farmer JD, Kodavanti PR, Tilson HA, MacPhail RC: Effects of acute and repeated exposures to Aroclor 1254 in adult rats: motor activity and flavor aversion conditioning. Fundam Appl Toxicol 1997, 40:68-74. 59. Widholm JJ, Villareal S, Seegal RF, Schantz SL: Spatial alternation deficits following developmental exposure to Aroclor 1254 and/or methylmercury in rats. Toxicol Sci 2004, 82:577-589. 60. Freeman GB, Lordo RA, Singer AW, Peters AC, Neal BH, McConnell EE, Mayes BA: An assessment of neurotoxicity of aroclors 1016, 1242, 1254, and 1260 administered in diet to Sprague-Dawley rats for one year. Toxicol Sci 2000, 53:377-391. 61. Gilbert ME, Mundy WR, Crofton KM: Spatial learning and long-term potentiation in the dentate gyrus of the hippocampus in animals developmentally exposed to Aroclor 1254. Toxicol Sci 2000, 57:102-111. 62. Zahalka EA, Ellis DH, Goldey ES, Stanton ME, Lau C: Perinatal exposure to polychlorinated biphenyls Aroclor 1016 or 1254 did not alter brain catecholamines nor delayed alternation performance in Long-Evans rats. Brain Res Bull 2001, 55:487-500. 63. Andersen ME, Yang RS, French CT, Chubb LS, Dennison JE: Molecular circuits, biological switches, and nonlinear dose-response relationships. Environ Health Perspect 2002, 110(Suppl 6):971-978. 64. Phillips KP, Foster WG, Leiss W, Sahni V, Karyakina N, Turner MC, Kacew S, Krewski D: Assessing and managing risks arising from exposure to endocrine-active chemicals. J Toxicol Environ Health B Crit Rev 2008, 11:351-372. 65. Sagvolden T, Metzger MA, Sagvolden G: Frequent reward eliminates differences in activity between hyperkinetic rats and controls. Behav Neural Biol 1993, 59:225-229. 66. Sagvolden T, Russell VA, Aase H, Johansen EB, Farshbaf M: Rodent models of attention-deficit/hyperactivity disorder. Biol Psychiatry 2005, 57:1239-1247. 67. Caudle WM, Richardson JR, Delea KC, Guillot TS, Wang M, Pennell KD, Miller GW: Polychlorinated biphenyl-induced reduction of dopamine transporter expression as a precursor to Parkinson’s disease-associated Submit your next manuscript to BioMed Central dopamine toxicity. Toxicol Sci 2006, 92:490-499. and take full advantage of: 68. Lyng GD, Snyder-Keller A, Seegal RF: Polychlorinated biphenyl-induced neurotoxicity in organotypic cocultures of developing rat ventral • Convenient online submission mesencephalon and striatum. Toxicol Sci 2007, 97:128-139. 69. Sagvolden T, Johansen EB, Aase H, Russell VA: A dynamic developmental • Thorough peer review theory of Attention-Deficit/Hyperactivity Disorder (ADHD) predominantly • No space constraints or color figure charges hyperactive/impulsive and combined subtypes. Behav Brain Sci 2005, • Immediate publication on acceptance 28:397-419. 70. Swanson JM, Kinsbourne M, Nigg J, Lanphear B, Stefanatos GA, Volkow N, • Inclusion in PubMed, CAS, Scopus and Google Scholar Taylor E, Casey BJ, Castellanos FX, Wadhwa PD: Etiologic subtypes of • Research which is freely available for redistribution attention-deficit/hyperactivity disorder: brain imaging, molecular genetic Submit your manuscript at www.biomedcentral.com/submit

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