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The effect of the mGlu8 receptor agonist, (S)-3,4-DCPG on acquisition and expression of morphine-induced conditioned place preference in male rats

The effect of the mGlu8 receptor agonist, (S)-3,4-DCPG on acquisition and expression of... Background: The nucleus accumbens (NAc) plays a principal role in drug reward. It has been reported that metabo- tropic glutamate receptors (mGlu receptors) play a key role in the rewarding pathway(s). Previous studies have shown the vast allocation of the different types of mGlu receptors, including mGlu8 receptors, in regions that are associated with opioid rewards, such as the NAc. The aim of the present study was to evaluate the role of mGlu8 receptors within the NAc in the acquisition and expression phases of morphine induced conditioned place preference (CPP). Adult male Wistar rats were bilaterally implanted by two cannulas’ in the NAc and were evaluated in a CPP paradigm. Selec- tive mGlu8 receptor allosteric agonist (S-3,4-DCPG) was administered at doses of 0.03, 0.3, and 3 μg/0.5 μL saline per side into the NAc on both sides during the 3 days of morphine (5 mg/kg) conditioning (acquisition) phase, or before place preference test, or post-conditioning (expression) phase of morphine-induced CPP. Results: The results revealed that intra-accumbal administration of S-3,4-DCPG (0.3 and 3 μg) markedly decreased the acquisition in a dose-dependent manner but had no effect on expression of morphine-induced CPP. Conclusions: The findings suggest that activation of mGlu8 receptors in the NAc dose-dependently blocks the establishment of morphine-induced CPP and reduces the rewarding properties of morphine which may be related to the glutamate activity into the NAc and in reward pathway(s). These data suggest that mGlu8 receptor may be involved in conditioned morphine reward. Keywords: Metabotropic glutamate receptor type 8, Nucleus accumbens, Conditioned place preference, Morphine, Rat been considered as the basic mechanisms of drug addic- Background tion for many years. Recently, it has become progres- Drug addiction is a complex neuro-behavioral disor- sively clear that glutamate is involved in addiction and der. The rewarding effects of drugs play a vital role in that glutamatergic neurotransmission may be responsible the acquisition and expression of substance abuse [1]. for brain plastic changes that lead to addictive behavior Dopaminergic [2] and opioidergic [3] mechanisms have and relapse [4]. It is well established that glutamatergic neurotransmission in the mesocorticolimbic pathway is *Correspondence: asarihi@yahoo.com; sarihi@umsha.ac.ir 1 involved in different mechanisms of morphine depend - Neurophysiology Research Center, School of Medicine, Hamadan University of Medical Sciences, Shahid Fahmideh Street, Hamadan, Iran ence [5–7]. Glutamate is the most abundant excita- Full list of author information is available at the end of the article tory neurotransmitter in the brain and glutamatergic © The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 2 of 10 transmission accounts for up to 70% of synaptic transmis- mGlu group III has been suggested as a new target sion in the central nervous system (CNS) [8]. Thus, there to treat substance use disorder [25]. However, the role are glutamatergic projections and/or neurons expressing of mGlu8 receptor in drug dependence is still not well glutamate receptors in reward circuitry including ventral investigated and very few studies have pointed out the tegmental area (VTA), nucleus accumbens (NAc), amyg- role of mGlu8 receptor in the effects of drugs of abuse. daloid complex and frontal cortex (FC) [9, 10]. Regarding, group III mGlu receptors, pretreatment The glutamate effects are mediated by ionotropic (iGlu) microinjection of L-2-amino-4-phosphonobutyric acid and metabotropic (mGlu). mGlu receptors are G-protein (L-AP4), a non-selective agonist of group III mGlu recep- coupled receptors which have an important role in medi- tors into the dorsal striatum reduced amphetamine or ating glutamate neurotransmission in the CNS [11–13]. cocaine-induced hyperlocomotion in rats [26]. Back- mGlu receptors are classified into three groups: Group strom and Hyytia showed that administration of mGlu8 I (mGlu1 and 5), Group II (mGlu2 and 3) and Group receptor agonist S-(3,4)-DCPG during conditioning and III (mGlu4, 6, 7, and 8) [14]. The Group III family nor - extinction procedure reduced ethanol self-administration mally inhibit glutamatergic neurotransmission and has and cue-induced reinstatement of ethanol-seeking [27]. been less studied due to the lack of appropriate selective Also It is indicated that activation of mGlu4 receptor has drugs. However, this group of receptors are emerging as an important effect on the rewarding properties of alco - important contributors to stress-related disorders such hol [28] and recently Zaniewska et al. showed that mGlu4 as depression, anxiety, addiction, and schizophrenia [15, receptor activation reduces cocaine-, but not nicotine- 16]. induced locomotor sensitization [29]. Also, it has been Recent studies have identified mGlu receptors as shown that mGlu7 receptor orthosteric agonist, LSP2- potential targets for the treatment of drug addiction. For 9166 blocked morphine CPP expression and reinstate- instance it has been suggested that both subtypes of the ment after extinction [30]. group I mGlu receptors (mGlu1 and mGlu5 receptors) Despite the above-mentioned results, further inves- take part in the expression of morphine sensitization tigation is required to fully understand the role of processes but mGlu1 is not involved in the expression group III mGlu receptors in the pathological process of morphine withdrawal jumps in mice [17]. In their of drug addiction. There is also evidence that glu- study, pretreatment with the mGlu1 receptor antagonist tamate transmission in the NAc is involved in CPP EMQMCM [3-ethyl-2-methyl-quinolin-6-yl-(4-meth- induced by morphine, cocaine, or amphetamine [31]. oxy-cyclohexyl)-methanone methanesulfonate] and the A number of alterations in glutamatergic transmission mGlu5 receptor antagonist MTEP ([(2-methyl-1,3-thia- occur within the NAc after withdrawal from chronic zol-4-yl) ethynyl] pyridine) was done. The mGlu5 recep - drug exposure [31]. NAc receives glutamatergic pro- tor antagonist has been shown to block the development jections from the prefrontal cortex, thalamus, baso- of cocaine- and morphine conditioned place preference lateral amygdala (BLA), and hippocampus [10, 32, (CPP) [18–20]. In Popik and Wro´bel work, during con- 33]. The NAc is a major input structure of the basal ditionings, mice were pretreated with placebo or MPEP ganglia and integrates information from cortical and (to investigate its effect on acquisition of morphine- limbic structures to mediate goal-directed behaviors induced CPP), 20 min before morphine or placebo injec- [31]. Chronic exposure to several classes of drugs of tion. MPEP at 30, but not 10 mg/kg significantly inhibited abuse disrupts plasticity in NAc, allowing drug-asso- the acquisition as well as expression of morphine induced ciated cues to engender a pathologic motivation for CPP, but it neither produced place preference or aver- drug seeking [31]. The NAc exhibits high expression of sion, nor affected locomotor activity of mice [18]. How - mGlu receptors, especially mGlu4, 5 and 8 receptors. ever, some studies have shown contradictory results The mGlu8 receptor mRNA expression is high in the regarding the role of mGlu5 receptor in morphine CPP. NAc compared to other areas of the brain [34]. Previ- Others have even observed a potentiation in morphine ous evidences has shown that glutamate in the NAc CPP with MPEP as a mGlu5 receptor antagonists (tim- plays an important role in opioid rewards, including ing of MPEP administration was during conditioning) its expression [7], extinction [35, 36], and reinstate- [21–23]. Similarly, Group II mGlu receptors can regu- ment [35–37] of morphine-induced CPP. However, the late both reward processing and drug seeking [24] and in precise role of mGlu8 receptor in morphine-induced our previous work we showed that activation of mGlu2/3 CPP is unclear. Taken together, it seems that there is a receptors (during acquisition and expression) in the NAc type specificity in the role of mGlu receptors in differ- dose-dependently blocked both the establishment and ent steps of drug abuse on the other hand the precise the maintenance of morphine-induced CPP [7]. role of mGlu8 receptor in morphine-induced CPP is K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 3 of 10 unclear. Therefore, the goal of the current study was to assess the involvement of intra-accumbal mGlu8 600 * *** receptor in the acquisition and expression of mor- phine-induced CPP in male rats. Results The dose–response for morphine on conditioned place in the CPP paradigm was examined and as previous stud- ies, the minimum effective dose of morphine was 5  mg/ Kg [5, 6]. -200 The effect of Intra‑accumbal S‑3,4‑DCPG administration -400 on the acquisition of morphine‑induced CPP The data normality test was performed using Shapiro– Wilk test. Q-Q plot for distribution of CS data is shown in Fig.  1. These data did not pass normality test, so the Kruskal Wallis test was used. The analysis revealed that Fig. 2 The effects of the administration of saline, as a vehicle, and there was a significant difference between the saline SC different doses of S-3,4-DCPG, as a potent and selective mGlu8 injected (Saline, n = 6) and morphine SC injected + vehi- agonist, (0.03, 0.3 and 3 μg/0.5 μL) into the nucleus accumbens cle microinjection into the NAc control group (Vehicle, (NAc), 5 min before the injection of morphine (5 mg/kg, SC) and n = 7) (P = 0.0006, Fig. 2). The concurrent administration administration of maximum dose of S-3,4-DCPG into the NAc region of intra-accumbal S-3,4-DCPG and systemic morphine alone, in the conditioning days. Saline group received SC injection of saline instead of morphine during the acquisition phase. Bars during the acquisition period attenuated the rewarding represent mean ± S.E.M (Pre-conditioning; n = 8, Saline; n = 6, Vehicle; attributes of morphine in the CPP paradigm in a dose n = 7, different doses of S-3,4-DCPG (0.03 μg/0.5 μL; n = 10, 0.3 μg/0.5 dependent manner (P < 0.05, Fig.  2). In addition, admin- μL; n = 10 and 3 μg/0.5 μL; n = 9 μg/0.5 μL). *P < 0.05, ***P < 0.001, istration of the highest dose of S-3,4-DCPG (3 μg/0.5 μL) Kruskal Wallis test followed by Dunn’s multiple comparisons test alone did not affect the CS in saline-treated rats (Fig. 2). Eec ff t of intra‑accumbal S‑3,4‑DCPG administration CPP in morphine treated animals (P > 0.05, Fig.  4). com- on the expression of morphine‑induced CPP pared with the vehicle-control group. It means that S-3,4- The data normality test was performed using Shapiro– DCPG (3  μg/0.5 μL) could not reverse or attenuate the Wilk test. Q–Q plot for distribution of CS data during morphine place preference. post-conditioning (expression) phase is shown in Fig.  3. These data did not pass normality test, so the Kruskal Wallis test was used. The analysis indicated that intra- accumbal administration of S-3,4-DCPG (3  μg/0.5 μL) had no effect on the expression of morphine-induced Pre-conditioning Saline Saline Vehicle 0.03 μg DCPG Vehicle 0.3 μg DCPG DCPG (3 μg/side) 3 μg DCPG Saline + 3μg DCPG -200 0200 400 -200 0 200 400 600 Actual Actual Fig. 3 Q–Q plot for distribution of conditioning score data during Fig. 1 Q-Q plot for distribution of conditioning score data in the post-conditioning (expression) phase. These data did not pass conditioning days. These data did not pass normality test. The data normality test. The data normality test was performed using Shapiro– normality test was performed using Shapiro–Wilk test Wilk test Pre-conditioning Saline Vehicle 0.03 μg DCPG 0.3 μg DCPG 3 μg DCPG Saline + 3μg DCPG Predicted Conditioning Score (Sec) Predicted Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 4 of 10 Saline Vehicle 0.03 μg DCPG ns 0.3 μg DCPG 3 μg DCPG 300 Saline + 3μg DCPG 200 1400 1400 1600 1800 Actual Fig. 5 Q–Q plot for distribution of traveled distance data during post-conditioning or test day. These data passed normality test. The data normality test was performed using Shapiro–Wilk test -100 in rats. To our best knowledge, this is the first study which has examined the role of mGlu8 receptor within the NAc on morphine-induced CPP. Main findings of Fig. 4 The effects of the administration of highest doses of the present study can be expressed as: (a) bilateral intra- S-3,4-DCPG, as a potent and selective mGlu8 agonist (3 μg/0.5 μL) accumbal microinjection of S-3,4-DCPG dose-depend- into the nucleus accumbens (NAc) 5 min before the test on the ently reduced the acquisition of morphine-induced post-conditioning day. Bars represent mean ± S.E.M (Saline; n = 6, CPP, (b) after conditioning, intra-accumbal activation of Vehicle; n = 7, DCPG (3 μg/side); n = 6). ns: not significant, *p < 0.05. Kruskal Wallis test followed by Dunn’s multiple comparisons test mGlu8 receptor by S-3,4-DCPG at highest dose of 3  μg / 0.5 μL, it did not affect the expression of morphine- induced CPP in the rats, (c) administering the highest The effect of intra‑accumbal S‑3,4‑DCPG administration during morphine‑induced CPP on locomotor activity While our tracking system recorded the locomotion any time during the protocol (pre-conditioning, condition- ing and post-conditioning phases of the CPP paradigm), first we checked locomotion of the rats in open field test 5  min after injection to 30  min later and find no signifi - cant differences between experimental groups. For sum - marizing the results, we only reported the locomotion of the experimental groups during the post-conditioning or test day. The data normality test was performed using Shapiro–Wilk test. Q-Q plot for distribution of trave- led distance data during post-conditioning or test day is shown in Fig.  5. These data passed normality test, so the One-way ANOVA was used. One-way ANOVA followed by Newman-Keuls multi- ple comparison test [F (5, 45) = 0.1704, P = 0.9722; Fig. 6] indicated that S-3,4-DCPG did not change the traveled distance during the 10 min test period (on the post-con- ditioning or test day) in comparison with that of the vehi- cle control groups and saline SC administered group. Fig. 6 The effect of S-3,4-DCPG injection into the nucleus Discussion accumbens during morphine-induced conditioned place preference In the present study, the effect of S-3,4-DCPG as a selec - on locomotor activity. Bars represent mean ± S.E.M (Saline; n = 6, tive mGlu8 receptor allosteric agonist within the NAc on Vehicle; n = 7, different doses of S-3,4-DCPG (0.03 μg/0.5 μL; n = 11, 0.3 μg/0.5 μL; n = 11 and 3 μg/0.5 μL; n = 10 μg/0.5 μL) development of morphine-induced CPP was investigated Saline Vehicle DCPG (3 μg/side) Saline Vehicle 0.03 μg DCPG 0.3 μg DCPG 3 μg DCPG Saline + 3μg DCPG Conditioning Score (Sec) Predicted Traveled Distance (cm) K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 5 of 10 dose of S-3,4-DCPG into the NAc alone could not induce on the stereotaxic coordination, sizes of the NAc core CPP, and (d) this drug did not affect locomotor activity. and shell, the volume of injected drug and the time after Brain regions that control locomotion, such as striatum, injection to the end of the CPP session the diameter of are enriched in group III mGlu receptors [38], indicating spatio-temporal diffusion may include both parts of the the possible role for these receptors in locomotor activity. NAc [57]. Based on the rat stereotaxic coordination the Our data showed that S-3,4-DCPG did not affect loco - maximum length of the NAc (core and shell) ranged from motor activity. This indicates that mGlu8 receptors does 16 to 22 mm with a mean value (± SD) of 19.4 ± 1.5  mm not play a chief role in locomotor activity. On the con- and no asymmetry between right and left, it means a trary, it has been shown that other group III mGlu recep- sphere with 0.8 to 1.1 mm radius. Even with a conserva- tors (such as mGlu4 and mGlu7 receptors) are involved tive estimation we can say that the spatio-temporal diffu - in the locomotion [28, 39, 40], that could be explained sion of our injected volume should include both part of receptors type specificity in the role of mGlu receptors the NAc. Therefore, we can’t consider one part effective on locomotor activity, site specificity and by the animal and completely exclude the effects of drug on another species used and/or by the dose of agonists. part. Since two decades, glutamatergic system has been Findings from other studies confirm the findings of involved in drug addiction. Among the components of the current study regarding the inhibitory role of mGlu the glutamatergic system, the presynaptic mGlu recep- receptor activation in the NAc on drug induced CPP tors have recently received much attention because of acquisition. Bahi showed that systemic injection of their role in glutamate release and regulation of gluta- mGlu8 receptor agonist decreases voluntary ethanol matergic responses. Up to present day only a few studies intake and ethanol-induced CPP in C57BL/6J mice [58]. on the role of mGlu8 receptor in morphine dependence Several studies have suggested that mGlu8 receptors have been reported. Numerous findings confirm that are involved in associative learning [59, 60]. Associa- the Group III mGlu receptors family plays an important tive learning and synaptic long-term potentiation (LTP) role in drug addiction, regulating transmitter release and depend on the same cellular mechanisms [61], which is behavioral plasticity in the limbic system [41, 42]. consistent with our results regarding the inhibitory role Previous studies have shown that mGlu receptors are of mGlu8 receptors in morphine induced CPP. It is pos- involved in the acquisition and expression of morphine- sible that DCPG impair the formation of an association induced CPP [5, 6]. The NAc plays a crucial role in devel - between the environmental cues in the morphine-paired oping physical dependence on morphine [43]. Morphine compartment and the rewarding properties of the eliminates the inhibitory effects of dopamine on gluta - drug [62] without influencing the rewarding effects of matergic inputs to the NAc neurons and enhances glu- morphine. tamatergic transmission to the NAc neurons, especially On the other hand, we found that mGlu8 receptor acti- from the BLA to the NAc [44]. Other observations have vation in the NAc has no effect on morphine reward after reported that repeated exposure to opioids enhances the acquisition. Consistent with the results of the present function of mGlu receptors and presynaptic stimulation study, findings from other studies showed that after con - of these receptors results in reduced glutamate release ditioning, mGlu8 receptor activation had no effect on the [45, 46]. It has also been shown that attenuation of glu- expression of spatial conditioning relative to ethanol [58]. tamatergic neurotransmission through presynaptic mGlu The systemic injection of cocaine decreases mGlu8 receptor agonists is effective in suppressing drug craving receptor protein levels in rat striatum. The decrease in and substance use [27]. mGlu8 receptor protein expression in the striatum may The NAc can be subdivided into core and shell subre - indicate a decrease in mGlu8 autoreceptors in corticostri- gions [47] and a number of studies suggest that these sub- atal terminals on the other hand as we know, presynaptic regions may be differentially involved in reward-related mGlu8 receptor inhibits glutamate release from corticos- learning and locomotion [48–50]. Our data did not per- triatal terminals [63]. This transient deletion of inhibitory mit a direct investigation of the relative contribution of tone by mGlu8 receptor may be necessary to stimulate the two subregions. There is some evidences indicating increased local release of glutamate and stimulate loco- the role of the NAc shell in the acquisition of CPP [31, motor activity. Lack of presynaptic mGlu8 receptor can 51]. However, there are also studies showing the involve- disrupt glutamatergic translocation in corticostriatal syn- ment of the NAc Core too [31, 52–54]. In addition, some apses, that is consistent with other mechanisms involved studies have shown the role of whole NAc in this issue in behavioral responses to acute stimulation by cocaine including our previous studies [5, 55, 56]. On the other [63]. hand, there is no difference in case of mGlu8 receptor In conclusion, the results of the current study revealed density between NAc shell and core [34]. Finally, based that intra-accumbal injection of mGlu8 receptor agonist Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 6 of 10 (S-3,4-DCPG) in a dose-dependent manner reduced atlas of rat brain (Paxinos and Watson, 2007). Two guide the acquisition while it had no effect on the expression cannulae (23-Gauge) with 12  mm length were inserted of morphine-induced CPP. Taken together, the avail- into the holes aiming at the NAc. The guiding cannulae able evidences indicate an important modulatory rather were anchored with a jeweler’s screw and the incision than necessary role for mGluR8 in NAc based morphine was closed with dental cement. After surgery, dummy reward. It can be proposed that the plasticity related to inner cannulae that extended 0.5  mm beyond the guid- mGlu8 receptor downstream proteins during CPP of ing cannulae were inserted into the guiding cannulae morphine could account for the behavioral response and left in place until injections were made. All rats were found by S-3,4-DCPG. Future studies are needed to allowed to recover for 1 week before starting the behavio- characterize the specific mechanisms of action of mGlu8 ral testing. receptor in acquisition and expression of morphine- induced place preference in rats. Intra‑accumbal injection The rats were gently restrained by hand and the dummy Methods cannulae were removed from the guiding cannulae. Animal Drugs were directly injected into the NAc through the 10-week male Wistar rats weighing between 200 and guiding cannulae using injector cannulae (30-gauge, 250  g were obtained from animal breeding colony of 1  mm below the tip of the guiding cannula). Polyethyl- Hamadan University of Medical Sciences (Hamadan, ene tubing (PE-20) was used for attaching the injector Iran). They were maintained on 12/12  h light/dark cycle cannula to the 1-μl Hamilton syringe. Doses of selective (light on at 7 AM) and had access to freely available food mGluR8 allosteric agonist, S-3,4-DCPG, (0.03, 0.3, and and water in their home cages (temperature 22 °C ± 2 °C). 3  μg/0.5 μL saline per side) were administered into the Wood shavings were used for the rats’ bedding, which NAc. The injection volume into the NAc was 0.5 μL/side was changed daily. Lighting within cages during day for all groups. Injections were made bilaterally over a 50 s hours should be held at lux ranges below thresholds of period and the injection cannulae were left in the guiding aversion for rats. We used LED lights (25 lx). In order to cannulae for an additional 60  s in order to facilitate the conduct behavioral tests, it is necessary to increase the diffusion of the drugs. level of light (approximately 210 lx). All experiments were performed in accordance with the guide for the Care and Place conditioning apparatus and protocol Use of Laboratory Animals (National Institutes of Health A three-compartment CPP apparatus was used in the Publication, No. 80–23, revised 1996) and were approved experiments. The apparatus was comprised of three by the institutional ethics committee at Hamadan Uni- plexiglass compartments. The apparatus was divided into versity of Medical Sciences. two equal-sized compartments (30 cm × 30  cm × 40  cm) with the third Sect.  (30  cm × 15  cm × 40  cm) being the Drugs null section which connected the two equal-sized sec- In the current study in order to conduct the experiments tions. Both compartments had white backgrounds with the following drugs were used as following: Morphine black stripes in different orientations (vertical vs. hori - sulfate (Temad, Iran) was dissolved in normal saline zontal). To provide a tactile difference between the com - (0.9% NaCl) (S)-3,4-Dicarboxyphenylglycine (S-3,4- partments, one of them had a smooth plastic floor, while DCPG) (Tocris, UK), a selective mGluR8 allosteric ago- the other compartment had a net-like floor (metal grid). nist, was also dissolved in normal saline (0.9% NaCl). In this apparatus, rats showed no consistent preference It is worth mentioning that control and vehicle groups for either compartment. The CPP protocol has been pre - received saline. viously described [5]. An unbiased allocation was used. Rats with a neutral preference (45–55% for either side) Stereotaxic surgery and drug administration were randomly allocated their drug-paired side (unbiased Subjects were anesthetized by Xylazine (10  mg/kg) and allocation). In the CPP paradigm, the conditioning score Ketamine (100 mg/kg) and placed in the stereotaxic appa- (CS) and distance traveled were calculated based on a ratus (Stoelting, USA) with the incisor bar set at approxi- video recorded by a CCD camera with 30 frames per sec- mately 3.3 mm below horizontal zero in order to achieve ond (30 fps) resolution. The camera was placed 2 m above a flat skull position. After an incision was made to expose the CPP boxes and the locomotion tracking was meas- the rat’s skull, two points were determined and holed ured by Maze Router homemade software, a video track- into the skull at stereotaxic coordinates of 1.4 ± 0.4  mm ing system for automation of behavioral experiments. anterior to bregma, ± 1.5 mm lateral to the sagital suture, CPP paradigm took place for 5 continuous days, which and 6.5 mm ventral from top of the skull according to the consisted of three distinct phases: pre-conditioning, K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 7 of 10 conditioning and post-conditioning [5, 6]. The schedule or odd. Odd animals received subcutaneous (SC) injec- of the CPP paradigm is shown in Fig. 7a. tion of saline and morphine (5  mg/kg) pairing in alter- native morning and afternoon design with an interval Pre‑conditioning phase of 6  h. The vice versa program for even animals was On day 1, each rat was separately placed in the apparatus done. This phase consisted of a 3-day schedule of con - for 10 min, with free access to all compartments. Animal ditioning sessions. A total of six sessions (30 min each) movements were recorded by Maze Router tracking soft- was carried out. During these 3 conditioning days, in ware and analyzed on the same day. Rats with any com- 3 sessions, animals were confined to one compartment, partment preference were omitted from the experiment. under the drug influence. During other three sessions, 3 rats were excluded from this study due to compartment they were injected with saline while confined to the preference. Then rats were randomly assigned to one of other compartment. Access to the other compartments the two groups (odd and even) for place conditioning [5]. was blocked on these days. Place preference was calcu- lated as a preference score (time spent in drug paired Conditioning phase zone-time spent in the saline paired zone) [5, 6]. During The morphine conditioning phase, also known as the this phase, saline group animals received saline in both acquisition phase, were conducted on days 2, 3 and 4. compartments during alternative morning and after- Each group of animals was randomly divided into even noon design with an interval of 6  h. Locomotor data were also collected throughout CPP testing in order to assess the development of behavioral sensitization. Conditioning phase Morphine (5 mg/kg; s.c.) Post‑conditioning phase OR Expression On the 5th day, the partition was removed and the rats Saline phase could access the entire apparatus. The mean time spent for each rat in both compartments during a 10-min period was recorded. In order to calculate the condi- Day 2 4 1 3 5 tioning score, the difference in the time spent for the Pre-test Post test drug- and saline-paired places was considered as the Acquisition phase preference criteria. In the acquisition tests, no injection was given on the post-conditioning day. Expression Acquisition phase phase Experimental design The effect of intra‑accumbal administration of mGluR8 Morphine (5 mg/kg; s.c.) OR Saline allosteric agonist (S‑3,4‑DCPG) on the acquisition Intra-NAc microinjection of S-3,4-DCPG of morphine‑induced CPP (0.03, 0.3 and 3 μg/0.5 μL) OR Saline (0.5 μL) To investigate the effects of mGlu8 agonist on the Expression acquisition of morphine-induced CPP, bilaterally intra- Acquisition phase c phase accumbal injection of S-3,4-DCPG (0.03, 0.3, and 3  μg/0.5  μL) [64] was done 5  min prior to each mor- phine injection (5  mg/kg; SC) during the 3  days of Intra-NAc microinjection of S-3,4-DCPG conditioning phase (Fig.  7a, b). During this phase, a (3 μg/0.5 μL) OR vehicle-control group received saline (0.5  μL) instead Saline (0.5 μL) of S-3,4-DCPG into the NAc, prior to SC injection Fig. 7 Graphical scheme to show behavioral protocol. a Acquisition of morphine. Moreover, to rule out the possibility and expression phases of Morphine-induced conditioned place that S-3,4-DCPG administration alone had reward- preference (CPP) by injection of morphine (5 mg/kg; sc) during 3 days. b To investigate the role of mGlu8 in the nucleus accumbens ing or aversive effects on the CPP, a separate group of (NAc) in the acquisition of morphine-induced CPP, the animals in rats received the highest doses (3  μg/0.5  μL) of S-3,4- the separate groups received S-3,4-DCPG, (0.03, 0.3, and 3 μg/0.5 μL DCPG prior to saline injection (1  mL/kg; SC) instead saline) or saline into the NAc 5 min before the rats received morphine of morphine during the conditioning days. Saline group during acquisition phase. c To find out the role of mGlu8 in the received saline SC injection instead of morphine during expression of morphine -induced CPP, the animals received highest dose of S-3,4-DCPG (3 μg/0.5 μL saline) or Saline 5 min prior to CPP the conditioning phase. test Post test Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 8 of 10 The effects of intra‑accumbal S‑3,4‑DCPG injection on the expression of morphine‑induced CPP In order to examine the effects of the highest dose of S-3,4-DCPG (3  μg/ 0.5  μL) on the expression of mor- phine-induced CPP, the rats were bilaterally given S-3,4- DCPG or saline into the NAc 5  min prior to CPP test (Fig.  7c). In addition, a control vehicle group received saline (0.5  μL) through the NAc instead of S-3,4-DCPG before CPP test on post-conditioning phase. The saline group received saline instead of morphine during the conditioning phase. Locomotor activity measurement The locomotor activity of each rat was recorded using the locomotion tracking apparatus by a video tracking sys- Fig. 8 Histology. Schematic illustration of rat brain coronal sections tem (Router maze software). In these experiments, the showing the approximate location of the NAc injection sites. The total distance traveled (in centimeters) by each rat was numbers show the anterior–posterior coordinates relative to bregma. measured in pre- and post-tests for all groups. Atlas plates were adapted from Paxinos and Watson (Paxinos and Watson, 2007). Scale is 1 mm. It should be noted that some points are completely or partially overlapped ( Vehicle; n = 31, Treatment; n = 44) Histology After behavioral testing, all the rats implanted with injection cannulae were deeply anesthetized with Acknowledgements The authors would like to express their gratitude to the staff of the Neuro - Ketamine and Xylazine. They were then transcardi- physiology Research Center for helping them carry out this project. ally perfused with 0.9% saline and then a 10% forma- lin solution. The brains were removed, blocked, and Authors’ contributions AS, SS and SAK designed the project, wrote the manuscript and performed cut coronally (by using a vibratome) in 50 μm sections the statistical analysis, revised the manuscript and supervised the project. through to the cannulae. All the rats with cannula NK, ZE, SAK, IS and AS were involved in laboratory works and experimental placement 1  mm distant from the intended injection design of the work. AS, SS and MN were involved in data collection and lab assessments, and study designing. All authors read and approved the final site were removed from the data (Fig.  8). It should manuscript. be noted that some points are completely or partially overlapped. Funding The study was funded by Vice-chancellor for Research and Technology, Hama- dan University of Medical Sciences (No. 9505052611). Availability of data and materials Statistics The data are available for any scientific use with kind permission. Data were processed by commercially available soft- ware GraphPad Prism 8.0.2. The data normality test Ethics approval and consent to participate All experimental procedures using rats were conducted in accordance with was performed using Shapiro–Wilk test. If the data the animal care and use guidelines approved by the institutional ethics com- passed normality test (Shapiro–Wilk test greater than mittee at Hamadan University of Medical Sciences (Code of Ethics Committee: 0.05), we used one-way analysis of variance (ANOVA) Grant Number: IR.UMSHA.REC.1397.362) and were performed in accordance with the National Institutes of Health Guide for Care and Use of Laboratory followed by post hoc analysis (Newman–Keuls multiple Animals. comparison test). But If the data did not pass normality test (Shapiro–Wilk test less than 0.05), Kruskal Wallis Consent for publication Not applicable. test was used followed by Dunn’s multiple compari- sons test. The Kruskal Wallis test is the non parametric Competing interests alternative to the one-way ANOVA. Multiple student’s The authors declare that they have no competing interests. t-test was used to compare pre-conditioning with saline Author details or highest dose of S-3,4-DCPG (3  μg/0.5 μL). P-values 1 Neurophysiology Research Center, School of Medicine, Hamadan University less than 0.05 (P < 0.05) were considered to be statisti- of Medical Sciences, Shahid Fahmideh Street, Hamadan, Iran. Department of Neuroscience, School of Sciences and Advanced Technology in Medicine, cally significant. K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 9 of 10 Hamadan University of Medical Sciences, Hamadan, Iran. Department 22. van der Kam EL, De Vry J, Tzschentke TM. The mGlu5 receptor antagonist of Physiology, Faculty of Medicine, Hamadan University of Medical Sciences, 2-methyl-6-(phenylethynyl) pyridine (MPEP) supports intravenous self- Hamadan, Iran. administration and induces conditioned place preference in the rat. Eur J Pharmacol. 2009;607(1–3):114–20. Received: 24 November 2020 Accepted: 5 February 2021 23. Rutten K, Van Der Kam EL, De Vry J, Bruckmann W, Tzschentke TM. The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) potenti- ates conditioned place preference induced by various addictive and non-addictive drugs in rats. Addict Biol. 2011;16(1):108–15. 24. Morishima Y, Miyakawa T, Furuyashiki T, Tanaka Y, Mizuma H, Nakanishi S. Enhanced cocaine responsiveness and impaired motor coordination in References metabotropic glutamate receptor subtype 2 knockout mice. Proc Natl 1. Koob GF. Drugs of abuse: anatomy, pharmacology and function of reward Acad Sci. 2005;102(11):4170–5. pathways. Trends Pharmacol Sci. 1992;13:177–84. 25. de Sa Nogueira D, Bourdy R, Filliol D, Quessada C, McCort-Tranchepain 2. Diana M. The dopamine hypothesis of drug addiction and its potential I, Acher F, et al. LSP2–9166, an orthosteric mGlu4 and mGlu7 receptor therapeutic value. Front Psychiatry. 2011;2:64. agonist, reduces cocaine self-administration under a progressive ratio 3. Le Merrer J, Becker JA, Befort K, Kieffer BL. Reward processing by the schedule in rats. Neurosci Lett. 2020. https ://doi.org/10.1016/j.neule opioid system in the brain. Physiol Rev. 2009;89(4):1379–412. t.2020.13560 3. 4. Tzschentke T, Schmidt W. Glutamatergic mechanisms in addiction. 26. Mao L, Wang JQ. Distinct inhibition of acute cocaine-stimulated motor Molecular psychiatry. 2003;8(4):373–82. activity following microinjection of a group III metabotropic glutamate 5. Vatankhah M, Karimi-Haghighi S, Sarihi A, Haghparast A. Intra-accumbal receptor agonist into the dorsal striatum of rats. Pharmacol Biochem administration of AMN082, a metabotropic glutamate receptor type Behav. 2000;67(1):93–101. 7 allosteric agonist, inhibits the acquisition but not the expression of 27. Bäckström P, Hyytiä P. Suppression of alcohol self-administration and morphine-induced conditioned place preference in rats. Neurosci Lett. cue-induced reinstatement of alcohol seeking by the mGlu2/3 receptor 2018;681:56–61. agonist LY379268 and the mGlu8 receptor agonist (S)-3, 4-DCPG. Eur J 6. Roohi N, Sarihi A, Shahidi S, Zarei M, Haghparast A. Microinjection of the Pharmacol. 2005;528(1–3):110–8. mGluR5 antagonist MTEP into the nucleus accumbens attenuates the 28. Blednov YA, Walker D, Osterndorf-Kahanek E, Harris RA. Mice lacking acquisition but not expression of morphine-induced conditioned place metabotropic glutamate receptor 4 do not show the motor stimulatory preference in rats. Pharmacol Biochem Behav. 2014;126:109–15. effect of ethanol. Alcohol. 2004;34(2–3):251–9. 7. Baharlouei N, Sarihi A, Komaki A, Shahidi S, Haghparast A. Blockage of 29. Zaniewska M, Przegaliński E, Filip M, Pilc A, Doller D. Inhibitory actions acquisition and expression of morphine-induced conditioned place of mGlu 4 receptor ligands on cocaine-, but not nicotine-, induced preference in rats due to activation of glutamate receptors type II/III in sensitizing and conditioning locomotor responses in rats. Pharmacol Rep. nucleus accumbens. Pharmacol Biochem Behav. 2015;135:192–8. 2014;66(2):205–11. 8. Platt SR. The role of glutamate in central nervous system health and 30. Hajasova Z, Canestrelli C, Acher F, Noble F, Marie N. Role of mGlu7 recep- disease—a review. Vet J. 2007;173(2):278–86. tor in morphine rewarding effects is uncovered by a novel orthosteric 9. Gass JT, Olive MF. Glutamatergic substrates of drug addiction and alco- agonist. Neuropharmacology. 2018;131:424–30. holism. Biochem Pharmacol. 2008;75(1):218–65. 31. Scofield M, Heinsbroek J, Gipson C, Kupchik Y, Spencer S, Smith A, et al. 10. Groenewegen HJ, Wright CI, Beijer AV, Voorn P. Convergence and The nucleus accumbens: mechanisms of addiction across drug classes segregation of ventral striatal inputs and outputs. Ann N Y Acad Sci. reflect the importance of glutamate homeostasis. Pharmacol Rev. 1999;877(1):49–63. 2016;68(3):816–71. 11. Conn PJ, Pin JP. Pharmacology and functions of metabotropic glutamate 32. Brog JS, Salyapongse A, Deutch AY, Zahm DS. The patterns of afferent receptors. Annu Rev Pharmacol Toxicol. 1997;37:205–37. innervation of the core and shell in the “accumbens” part of the rat 12. Pin JP, Duvoisin R. The metabotropic glutamate receptors: structure and ventral striatum: immunohistochemical detection of retrogradely trans- functions. Neuropharmacology. 1995;34(1):1–26. ported fluoro-gold. J Comp Neurol. 1993;338(2):255–78. 13. Karimi SA, Komaki A, Salehi I, Sarihi A, Shahidi S. Role of group II metabo- 33. Heimer L, Alheid GF, De Olmos J, Groenewegen HJ, Haber SN, Harlan RE, tropic glutamate receptors (mGluR2/3) blockade on long-term potentia- et al. The accumbens: beyond the core-shell dichotomy. J Neuropsychia- tion in the dentate gyrus region of hippocampus in rats fed with high-fat try Clin Neurosci. 1997;9(3):354–81. diet. Neurochem Res. 2015;40(4):811–7. 34. Messenger MJ, Dawson LG, Duty S. Changes in metabotropic gluta- 14. Conn PJ, Pin J-P. Pharmacology and functions of metabotropic glutamate mate receptor 1–8 gene expression in the rodent basal ganglia motor receptors. Annu Rev Pharmacol Toxicol. 1997;37(1):205–37. loop following lesion of the nigrostriatal tract. Neuropharmacology. 15. Goudet C, Chapuy E, Alloui A, Acher F, Pin J-P, Eschalier A. Group III 2002;43(2):261–71. metabotropic glutamate receptors inhibit hyperalgesia in animal models 35. Fan Y, Niu H, Rizak JD, Li L, Wang G, Xu L, et al. Combined action of of inflammation and neuropathic pain. PAIN . 2008;137(1):112–24. MK-801 and ceftriaxone impairs the acquisition and reinstatement of 16. Lavreysen H, Dautzenberg FM. Therapeutic potential of group III metabo- morphine-induced conditioned place preference, and delays morphine tropic glutamate receptors. Curr Med Chem. 2008;15(7):671–84. extinction in rats. Neurosci Bull. 2012;28(5):567–76. 17. Kotlinska J, Bochenski M. Comparison of the effects of mGluR1 and 36. Vatankhah M, Sarihi A, Komaki A, Shahidi S, Haghparast A. AMN082-a mGluR5 antagonists on the expression of behavioral sensitization to the metabotropic glutamate receptor type 7 allosteric agonist in the NAc locomotor effect of morphine and the morphine withdrawal jumping in facilitates extinction and inhibits the reinstatement of morphine-induced mice. Eur J Pharmacol. 2007;558(1–3):113–8. conditioned place preference in male rats. Brain Res Bull. 2018;140:28–33. 18. Popik P, Wrobel M. Morphine conditioned reward is inhibited by MPEP, 37. Tahsili-Fahadan P, Carr GV, Harris GC, Aston-Jones G. Modafinil blocks the mGluR5 antagonist. Neuropharmacology. 2002;43(8):1210–7. reinstatement of extinguished opiate-seeking in rats: mediation by a 19. Herzig V, Schmidt WJ. Eec ff ts of MPEP on locomotion, sensitization and glutamate mechanism. Neuropsychopharmacology. 2010;35(11):2203. conditioned reward induced by cocaine or morphine. Neuropharmacol- 38. Amalric M, Lopez S, Goudet C, Fisone G, Battaglia G, Nicoletti F, et al. ogy. 2004;47(7):973–84. Group III and subtype 4 metabotropic glutamate receptor agonists: 20. Aoki T, Narita M, Shibasaki M, Suzuki T. Metabotropic glutamate discovery and pathophysiological applications in Parkinson’s disease. receptor 5 localized in the limbic forebrain is critical for the develop- Neuropharmacology. 2013;66:53–64. ment of morphine-induced rewarding effect in mice. Eur J Neurosci. 39. Palucha A, Klak K, Branski P, Van der Putten H, Flor PJ, Pilc A. Activation of 2004;20(6):1633–8. the mGlu7 receptor elicits antidepressant-like effects in mice. Psychop - 21. van der Kam EL, De Vry J, Tzschentke TM. 2-Methyl-6 (phenylethynyl)- harmacology. 2007;194(4):555–62. pyridine (MPEP) potentiates ketamine and heroin reward as assessed by 40. Salling MC, Faccidomo S, Hodge CW. Nonselective suppression of acquisition, extinction, and reinstatement of conditioned place prefer- operant ethanol and sucrose self-administration by the mGluR7 ence in the rat. Eur J Pharmacol. 2009;606(1–3):94–101. Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 10 of 10 positive allosteric modulator AMN082. Pharmacol Biochem Behav. 54. Zhou Y, Yan E, Cheng D, Zhu H, Liu Z, Chen X, et al. The projection from 2008;91(1):14–20. ventral CA1, not prefrontal cortex, to nucleus accumbens core mediates 41. Hu G, Duffy P, Swanson C, Ghasemzadeh MB, Kalivas PW. The regula- recent memory retrieval of cocaine-conditioned place preference. Front tion of dopamine transmission by metabotropic glutamate receptors. J Behav Neurosci. 2020;14:209. Pharmacol Exp Ther. 1999;289(1):412–6. 55. Alizamini MM, Farzinpour Z, Ezzatpanah S, Haghparast A. Role of intra- 42. Mao L, Guo M, Jin D, Xue B, Wang JQ. Group III metabotropic glutamate accumbal orexin receptors in the acquisition of morphine-induced receptors and drug addiction. Front Med. 2013;7(4):445–51. conditioned place preference in the rats. Neurosci Lett. 2017;660:1–5. 43. Inoue M, Mishina M, Ueda H. Locus-specific rescue of GluRϵ1 NMDA 56. Baharlouei N, Sarihi A, Moradi M, Zarrabian S, Haghparast A. Microinjec- receptors in mutant mice identifies the brain regions important for tion of the mGluR2/3 agonist, LY379268, into the nucleus accumbens morphine tolerance and dependence. J Neurosci. 2003;23(16):6529–36. attenuates extinction latencies and the reinstatement of morphine- 44. Yuan K, Sheng H, Song J, Yang L, Cui D, Ma Q, et al. Morphine treat- induced conditioned place preference in rats. Behav Pharmacol. ment enhances glutamatergic input onto neurons of the nucleus 2018;29(5):385–92. accumbens via both disinhibitory and stimulating effect. Addict Biol. 57. Freund N, Manns M, Rose J. A method for the evaluation of intracranial 2017;22(6):1756–67. tetrodotoxin injections. J Neurosci Methods. 2010;186(1):25–8. 45. Kenny PJ, Markou A. The ups and downs of addiction: role of metabo- 58. Bahi A. Decreased anxiety, voluntary ethanol intake and ethanol-induced tropic glutamate receptors. Trends Pharmacol Sci. 2004;25(5):265–72. CPP acquisition following activation of the metabotropic glutamate 46. Manzoni OJ, Williams JT. Presynaptic regulation of glutamate release receptor 8 “mGluR8.” Pharmacol Biochem Behav. 2017;155:32–42. in the ventral tegmental area during morphine withdrawal. J Neurosci. 59. Gerlai R, Adams B, Fitch T, Chaney S, Baez M. Performance deficits of 1999;19(15):6629–36. mGluR8 knockout mice in learning tasks: the effects of null mutation and 47. Zahm DS. An integrative neuroanatomical perspective on some subcorti- the background genotype. Neuropharmacology. 2002;43(2):235–49. cal substrates of adaptive responding with emphasis on the nucleus 60. Boccella S, Marabese I, Iannotta M, Belardo C, Neugebauer V, Mazzitelli M, accumbens. Neurosci Biobehav Rev. 2000;24(1):85–105. et al. Metabotropic glutamate receptor 5 and 8 modulate the amelio- 48. Di Chiara G. Nucleus accumbens shell and core dopamine: differential rative effect of ultramicronized palmitoylethanolamide on cognitive role in behavior and addiction. Behav Brain Res. 2002;137(1–2):75–114. decline associated with neuropathic pain. Int J Mol Sci. 2019;20(7):1757. 49. Parkinson JA, Olmstead MC, Burns LH, Robbins TW, Everitt BJ. Dissociation 61. Maren S. Synaptic mechanisms of associative memory in the amygdala. in effects of lesions of the nucleus accumbens core and shell on appeti- Neuron. 2005;47(6):783–6. tive pavlovian approach behavior and the potentiation of conditioned 62. Fendt M, Schmid S. Metabotropic glutamate receptors are involved in reinforcement and locomotor activity byd-amphetamine. J Neurosci. amygdaloid plasticity. Eur J Neurosci. 2002;15(9):1535–41. 1999;19(6):2401–11. 63. Zhang G-C, Vu K, Parelkar NK, Mao L-M, Stanford IM, Fibuch EE, et al. 50. Sellings LH, Clarke PB. Segregation of amphetamine reward and locomo- Acute administration of cocaine reduces metabotropic glutamate tor stimulation between nucleus accumbens medial shell and core. J receptor 8 protein expression in the rat striatum in vivo. Neurosci Lett. Neurosci. 2003;23(15):6295–303. 2009;449(3):224–7. 51. Olive MF, Koenig HN, Nannini MA, Hodge CW. Elevated extracellular CRF 64. Dobi A, Sartori SB, Busti D, Van der Putten H, Singewald N, Shigemoto levels in the bed nucleus of the stria terminalis during ethanol with- R, et al. Neural substrates for the distinct effects of presynaptic group drawal and reduction by subsequent ethanol intake. Pharmacol Biochem III metabotropic glutamate receptors on extinction of contextual fear Behav. 2002;72(1–2):213–20. conditioning in mice. Neuropharmacology. 2013;66:274–89. 52. Alaghband Y, Kramár E, Kwapis JL, Kim ES, Hemstedt TJ, López AJ, et al. CREST in the nucleus accumbens core regulates cocaine conditioned Publisher’s Note place preference, cocaine-seeking behavior, and synaptic plasticity. J Springer Nature remains neutral with regard to jurisdictional claims in pub- Neurosci. 2018;38(44):9514–26. lished maps and institutional affiliations. 53. Miyamoto Y, Iida A, Sato K, Muramatsu S-I, Nitta A. 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The effect of the mGlu8 receptor agonist, (S)-3,4-DCPG on acquisition and expression of morphine-induced conditioned place preference in male rats

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Abstract

Background: The nucleus accumbens (NAc) plays a principal role in drug reward. It has been reported that metabo- tropic glutamate receptors (mGlu receptors) play a key role in the rewarding pathway(s). Previous studies have shown the vast allocation of the different types of mGlu receptors, including mGlu8 receptors, in regions that are associated with opioid rewards, such as the NAc. The aim of the present study was to evaluate the role of mGlu8 receptors within the NAc in the acquisition and expression phases of morphine induced conditioned place preference (CPP). Adult male Wistar rats were bilaterally implanted by two cannulas’ in the NAc and were evaluated in a CPP paradigm. Selec- tive mGlu8 receptor allosteric agonist (S-3,4-DCPG) was administered at doses of 0.03, 0.3, and 3 μg/0.5 μL saline per side into the NAc on both sides during the 3 days of morphine (5 mg/kg) conditioning (acquisition) phase, or before place preference test, or post-conditioning (expression) phase of morphine-induced CPP. Results: The results revealed that intra-accumbal administration of S-3,4-DCPG (0.3 and 3 μg) markedly decreased the acquisition in a dose-dependent manner but had no effect on expression of morphine-induced CPP. Conclusions: The findings suggest that activation of mGlu8 receptors in the NAc dose-dependently blocks the establishment of morphine-induced CPP and reduces the rewarding properties of morphine which may be related to the glutamate activity into the NAc and in reward pathway(s). These data suggest that mGlu8 receptor may be involved in conditioned morphine reward. Keywords: Metabotropic glutamate receptor type 8, Nucleus accumbens, Conditioned place preference, Morphine, Rat been considered as the basic mechanisms of drug addic- Background tion for many years. Recently, it has become progres- Drug addiction is a complex neuro-behavioral disor- sively clear that glutamate is involved in addiction and der. The rewarding effects of drugs play a vital role in that glutamatergic neurotransmission may be responsible the acquisition and expression of substance abuse [1]. for brain plastic changes that lead to addictive behavior Dopaminergic [2] and opioidergic [3] mechanisms have and relapse [4]. It is well established that glutamatergic neurotransmission in the mesocorticolimbic pathway is *Correspondence: asarihi@yahoo.com; sarihi@umsha.ac.ir 1 involved in different mechanisms of morphine depend - Neurophysiology Research Center, School of Medicine, Hamadan University of Medical Sciences, Shahid Fahmideh Street, Hamadan, Iran ence [5–7]. Glutamate is the most abundant excita- Full list of author information is available at the end of the article tory neurotransmitter in the brain and glutamatergic © The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 2 of 10 transmission accounts for up to 70% of synaptic transmis- mGlu group III has been suggested as a new target sion in the central nervous system (CNS) [8]. Thus, there to treat substance use disorder [25]. However, the role are glutamatergic projections and/or neurons expressing of mGlu8 receptor in drug dependence is still not well glutamate receptors in reward circuitry including ventral investigated and very few studies have pointed out the tegmental area (VTA), nucleus accumbens (NAc), amyg- role of mGlu8 receptor in the effects of drugs of abuse. daloid complex and frontal cortex (FC) [9, 10]. Regarding, group III mGlu receptors, pretreatment The glutamate effects are mediated by ionotropic (iGlu) microinjection of L-2-amino-4-phosphonobutyric acid and metabotropic (mGlu). mGlu receptors are G-protein (L-AP4), a non-selective agonist of group III mGlu recep- coupled receptors which have an important role in medi- tors into the dorsal striatum reduced amphetamine or ating glutamate neurotransmission in the CNS [11–13]. cocaine-induced hyperlocomotion in rats [26]. Back- mGlu receptors are classified into three groups: Group strom and Hyytia showed that administration of mGlu8 I (mGlu1 and 5), Group II (mGlu2 and 3) and Group receptor agonist S-(3,4)-DCPG during conditioning and III (mGlu4, 6, 7, and 8) [14]. The Group III family nor - extinction procedure reduced ethanol self-administration mally inhibit glutamatergic neurotransmission and has and cue-induced reinstatement of ethanol-seeking [27]. been less studied due to the lack of appropriate selective Also It is indicated that activation of mGlu4 receptor has drugs. However, this group of receptors are emerging as an important effect on the rewarding properties of alco - important contributors to stress-related disorders such hol [28] and recently Zaniewska et al. showed that mGlu4 as depression, anxiety, addiction, and schizophrenia [15, receptor activation reduces cocaine-, but not nicotine- 16]. induced locomotor sensitization [29]. Also, it has been Recent studies have identified mGlu receptors as shown that mGlu7 receptor orthosteric agonist, LSP2- potential targets for the treatment of drug addiction. For 9166 blocked morphine CPP expression and reinstate- instance it has been suggested that both subtypes of the ment after extinction [30]. group I mGlu receptors (mGlu1 and mGlu5 receptors) Despite the above-mentioned results, further inves- take part in the expression of morphine sensitization tigation is required to fully understand the role of processes but mGlu1 is not involved in the expression group III mGlu receptors in the pathological process of morphine withdrawal jumps in mice [17]. In their of drug addiction. There is also evidence that glu- study, pretreatment with the mGlu1 receptor antagonist tamate transmission in the NAc is involved in CPP EMQMCM [3-ethyl-2-methyl-quinolin-6-yl-(4-meth- induced by morphine, cocaine, or amphetamine [31]. oxy-cyclohexyl)-methanone methanesulfonate] and the A number of alterations in glutamatergic transmission mGlu5 receptor antagonist MTEP ([(2-methyl-1,3-thia- occur within the NAc after withdrawal from chronic zol-4-yl) ethynyl] pyridine) was done. The mGlu5 recep - drug exposure [31]. NAc receives glutamatergic pro- tor antagonist has been shown to block the development jections from the prefrontal cortex, thalamus, baso- of cocaine- and morphine conditioned place preference lateral amygdala (BLA), and hippocampus [10, 32, (CPP) [18–20]. In Popik and Wro´bel work, during con- 33]. The NAc is a major input structure of the basal ditionings, mice were pretreated with placebo or MPEP ganglia and integrates information from cortical and (to investigate its effect on acquisition of morphine- limbic structures to mediate goal-directed behaviors induced CPP), 20 min before morphine or placebo injec- [31]. Chronic exposure to several classes of drugs of tion. MPEP at 30, but not 10 mg/kg significantly inhibited abuse disrupts plasticity in NAc, allowing drug-asso- the acquisition as well as expression of morphine induced ciated cues to engender a pathologic motivation for CPP, but it neither produced place preference or aver- drug seeking [31]. The NAc exhibits high expression of sion, nor affected locomotor activity of mice [18]. How - mGlu receptors, especially mGlu4, 5 and 8 receptors. ever, some studies have shown contradictory results The mGlu8 receptor mRNA expression is high in the regarding the role of mGlu5 receptor in morphine CPP. NAc compared to other areas of the brain [34]. Previ- Others have even observed a potentiation in morphine ous evidences has shown that glutamate in the NAc CPP with MPEP as a mGlu5 receptor antagonists (tim- plays an important role in opioid rewards, including ing of MPEP administration was during conditioning) its expression [7], extinction [35, 36], and reinstate- [21–23]. Similarly, Group II mGlu receptors can regu- ment [35–37] of morphine-induced CPP. However, the late both reward processing and drug seeking [24] and in precise role of mGlu8 receptor in morphine-induced our previous work we showed that activation of mGlu2/3 CPP is unclear. Taken together, it seems that there is a receptors (during acquisition and expression) in the NAc type specificity in the role of mGlu receptors in differ- dose-dependently blocked both the establishment and ent steps of drug abuse on the other hand the precise the maintenance of morphine-induced CPP [7]. role of mGlu8 receptor in morphine-induced CPP is K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 3 of 10 unclear. Therefore, the goal of the current study was to assess the involvement of intra-accumbal mGlu8 600 * *** receptor in the acquisition and expression of mor- phine-induced CPP in male rats. Results The dose–response for morphine on conditioned place in the CPP paradigm was examined and as previous stud- ies, the minimum effective dose of morphine was 5  mg/ Kg [5, 6]. -200 The effect of Intra‑accumbal S‑3,4‑DCPG administration -400 on the acquisition of morphine‑induced CPP The data normality test was performed using Shapiro– Wilk test. Q-Q plot for distribution of CS data is shown in Fig.  1. These data did not pass normality test, so the Kruskal Wallis test was used. The analysis revealed that Fig. 2 The effects of the administration of saline, as a vehicle, and there was a significant difference between the saline SC different doses of S-3,4-DCPG, as a potent and selective mGlu8 injected (Saline, n = 6) and morphine SC injected + vehi- agonist, (0.03, 0.3 and 3 μg/0.5 μL) into the nucleus accumbens cle microinjection into the NAc control group (Vehicle, (NAc), 5 min before the injection of morphine (5 mg/kg, SC) and n = 7) (P = 0.0006, Fig. 2). The concurrent administration administration of maximum dose of S-3,4-DCPG into the NAc region of intra-accumbal S-3,4-DCPG and systemic morphine alone, in the conditioning days. Saline group received SC injection of saline instead of morphine during the acquisition phase. Bars during the acquisition period attenuated the rewarding represent mean ± S.E.M (Pre-conditioning; n = 8, Saline; n = 6, Vehicle; attributes of morphine in the CPP paradigm in a dose n = 7, different doses of S-3,4-DCPG (0.03 μg/0.5 μL; n = 10, 0.3 μg/0.5 dependent manner (P < 0.05, Fig.  2). In addition, admin- μL; n = 10 and 3 μg/0.5 μL; n = 9 μg/0.5 μL). *P < 0.05, ***P < 0.001, istration of the highest dose of S-3,4-DCPG (3 μg/0.5 μL) Kruskal Wallis test followed by Dunn’s multiple comparisons test alone did not affect the CS in saline-treated rats (Fig. 2). Eec ff t of intra‑accumbal S‑3,4‑DCPG administration CPP in morphine treated animals (P > 0.05, Fig.  4). com- on the expression of morphine‑induced CPP pared with the vehicle-control group. It means that S-3,4- The data normality test was performed using Shapiro– DCPG (3  μg/0.5 μL) could not reverse or attenuate the Wilk test. Q–Q plot for distribution of CS data during morphine place preference. post-conditioning (expression) phase is shown in Fig.  3. These data did not pass normality test, so the Kruskal Wallis test was used. The analysis indicated that intra- accumbal administration of S-3,4-DCPG (3  μg/0.5 μL) had no effect on the expression of morphine-induced Pre-conditioning Saline Saline Vehicle 0.03 μg DCPG Vehicle 0.3 μg DCPG DCPG (3 μg/side) 3 μg DCPG Saline + 3μg DCPG -200 0200 400 -200 0 200 400 600 Actual Actual Fig. 3 Q–Q plot for distribution of conditioning score data during Fig. 1 Q-Q plot for distribution of conditioning score data in the post-conditioning (expression) phase. These data did not pass conditioning days. These data did not pass normality test. The data normality test. The data normality test was performed using Shapiro– normality test was performed using Shapiro–Wilk test Wilk test Pre-conditioning Saline Vehicle 0.03 μg DCPG 0.3 μg DCPG 3 μg DCPG Saline + 3μg DCPG Predicted Conditioning Score (Sec) Predicted Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 4 of 10 Saline Vehicle 0.03 μg DCPG ns 0.3 μg DCPG 3 μg DCPG 300 Saline + 3μg DCPG 200 1400 1400 1600 1800 Actual Fig. 5 Q–Q plot for distribution of traveled distance data during post-conditioning or test day. These data passed normality test. The data normality test was performed using Shapiro–Wilk test -100 in rats. To our best knowledge, this is the first study which has examined the role of mGlu8 receptor within the NAc on morphine-induced CPP. Main findings of Fig. 4 The effects of the administration of highest doses of the present study can be expressed as: (a) bilateral intra- S-3,4-DCPG, as a potent and selective mGlu8 agonist (3 μg/0.5 μL) accumbal microinjection of S-3,4-DCPG dose-depend- into the nucleus accumbens (NAc) 5 min before the test on the ently reduced the acquisition of morphine-induced post-conditioning day. Bars represent mean ± S.E.M (Saline; n = 6, CPP, (b) after conditioning, intra-accumbal activation of Vehicle; n = 7, DCPG (3 μg/side); n = 6). ns: not significant, *p < 0.05. Kruskal Wallis test followed by Dunn’s multiple comparisons test mGlu8 receptor by S-3,4-DCPG at highest dose of 3  μg / 0.5 μL, it did not affect the expression of morphine- induced CPP in the rats, (c) administering the highest The effect of intra‑accumbal S‑3,4‑DCPG administration during morphine‑induced CPP on locomotor activity While our tracking system recorded the locomotion any time during the protocol (pre-conditioning, condition- ing and post-conditioning phases of the CPP paradigm), first we checked locomotion of the rats in open field test 5  min after injection to 30  min later and find no signifi - cant differences between experimental groups. For sum - marizing the results, we only reported the locomotion of the experimental groups during the post-conditioning or test day. The data normality test was performed using Shapiro–Wilk test. Q-Q plot for distribution of trave- led distance data during post-conditioning or test day is shown in Fig.  5. These data passed normality test, so the One-way ANOVA was used. One-way ANOVA followed by Newman-Keuls multi- ple comparison test [F (5, 45) = 0.1704, P = 0.9722; Fig. 6] indicated that S-3,4-DCPG did not change the traveled distance during the 10 min test period (on the post-con- ditioning or test day) in comparison with that of the vehi- cle control groups and saline SC administered group. Fig. 6 The effect of S-3,4-DCPG injection into the nucleus Discussion accumbens during morphine-induced conditioned place preference In the present study, the effect of S-3,4-DCPG as a selec - on locomotor activity. Bars represent mean ± S.E.M (Saline; n = 6, tive mGlu8 receptor allosteric agonist within the NAc on Vehicle; n = 7, different doses of S-3,4-DCPG (0.03 μg/0.5 μL; n = 11, 0.3 μg/0.5 μL; n = 11 and 3 μg/0.5 μL; n = 10 μg/0.5 μL) development of morphine-induced CPP was investigated Saline Vehicle DCPG (3 μg/side) Saline Vehicle 0.03 μg DCPG 0.3 μg DCPG 3 μg DCPG Saline + 3μg DCPG Conditioning Score (Sec) Predicted Traveled Distance (cm) K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 5 of 10 dose of S-3,4-DCPG into the NAc alone could not induce on the stereotaxic coordination, sizes of the NAc core CPP, and (d) this drug did not affect locomotor activity. and shell, the volume of injected drug and the time after Brain regions that control locomotion, such as striatum, injection to the end of the CPP session the diameter of are enriched in group III mGlu receptors [38], indicating spatio-temporal diffusion may include both parts of the the possible role for these receptors in locomotor activity. NAc [57]. Based on the rat stereotaxic coordination the Our data showed that S-3,4-DCPG did not affect loco - maximum length of the NAc (core and shell) ranged from motor activity. This indicates that mGlu8 receptors does 16 to 22 mm with a mean value (± SD) of 19.4 ± 1.5  mm not play a chief role in locomotor activity. On the con- and no asymmetry between right and left, it means a trary, it has been shown that other group III mGlu recep- sphere with 0.8 to 1.1 mm radius. Even with a conserva- tors (such as mGlu4 and mGlu7 receptors) are involved tive estimation we can say that the spatio-temporal diffu - in the locomotion [28, 39, 40], that could be explained sion of our injected volume should include both part of receptors type specificity in the role of mGlu receptors the NAc. Therefore, we can’t consider one part effective on locomotor activity, site specificity and by the animal and completely exclude the effects of drug on another species used and/or by the dose of agonists. part. Since two decades, glutamatergic system has been Findings from other studies confirm the findings of involved in drug addiction. Among the components of the current study regarding the inhibitory role of mGlu the glutamatergic system, the presynaptic mGlu recep- receptor activation in the NAc on drug induced CPP tors have recently received much attention because of acquisition. Bahi showed that systemic injection of their role in glutamate release and regulation of gluta- mGlu8 receptor agonist decreases voluntary ethanol matergic responses. Up to present day only a few studies intake and ethanol-induced CPP in C57BL/6J mice [58]. on the role of mGlu8 receptor in morphine dependence Several studies have suggested that mGlu8 receptors have been reported. Numerous findings confirm that are involved in associative learning [59, 60]. Associa- the Group III mGlu receptors family plays an important tive learning and synaptic long-term potentiation (LTP) role in drug addiction, regulating transmitter release and depend on the same cellular mechanisms [61], which is behavioral plasticity in the limbic system [41, 42]. consistent with our results regarding the inhibitory role Previous studies have shown that mGlu receptors are of mGlu8 receptors in morphine induced CPP. It is pos- involved in the acquisition and expression of morphine- sible that DCPG impair the formation of an association induced CPP [5, 6]. The NAc plays a crucial role in devel - between the environmental cues in the morphine-paired oping physical dependence on morphine [43]. Morphine compartment and the rewarding properties of the eliminates the inhibitory effects of dopamine on gluta - drug [62] without influencing the rewarding effects of matergic inputs to the NAc neurons and enhances glu- morphine. tamatergic transmission to the NAc neurons, especially On the other hand, we found that mGlu8 receptor acti- from the BLA to the NAc [44]. Other observations have vation in the NAc has no effect on morphine reward after reported that repeated exposure to opioids enhances the acquisition. Consistent with the results of the present function of mGlu receptors and presynaptic stimulation study, findings from other studies showed that after con - of these receptors results in reduced glutamate release ditioning, mGlu8 receptor activation had no effect on the [45, 46]. It has also been shown that attenuation of glu- expression of spatial conditioning relative to ethanol [58]. tamatergic neurotransmission through presynaptic mGlu The systemic injection of cocaine decreases mGlu8 receptor agonists is effective in suppressing drug craving receptor protein levels in rat striatum. The decrease in and substance use [27]. mGlu8 receptor protein expression in the striatum may The NAc can be subdivided into core and shell subre - indicate a decrease in mGlu8 autoreceptors in corticostri- gions [47] and a number of studies suggest that these sub- atal terminals on the other hand as we know, presynaptic regions may be differentially involved in reward-related mGlu8 receptor inhibits glutamate release from corticos- learning and locomotion [48–50]. Our data did not per- triatal terminals [63]. This transient deletion of inhibitory mit a direct investigation of the relative contribution of tone by mGlu8 receptor may be necessary to stimulate the two subregions. There is some evidences indicating increased local release of glutamate and stimulate loco- the role of the NAc shell in the acquisition of CPP [31, motor activity. Lack of presynaptic mGlu8 receptor can 51]. However, there are also studies showing the involve- disrupt glutamatergic translocation in corticostriatal syn- ment of the NAc Core too [31, 52–54]. In addition, some apses, that is consistent with other mechanisms involved studies have shown the role of whole NAc in this issue in behavioral responses to acute stimulation by cocaine including our previous studies [5, 55, 56]. On the other [63]. hand, there is no difference in case of mGlu8 receptor In conclusion, the results of the current study revealed density between NAc shell and core [34]. Finally, based that intra-accumbal injection of mGlu8 receptor agonist Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 6 of 10 (S-3,4-DCPG) in a dose-dependent manner reduced atlas of rat brain (Paxinos and Watson, 2007). Two guide the acquisition while it had no effect on the expression cannulae (23-Gauge) with 12  mm length were inserted of morphine-induced CPP. Taken together, the avail- into the holes aiming at the NAc. The guiding cannulae able evidences indicate an important modulatory rather were anchored with a jeweler’s screw and the incision than necessary role for mGluR8 in NAc based morphine was closed with dental cement. After surgery, dummy reward. It can be proposed that the plasticity related to inner cannulae that extended 0.5  mm beyond the guid- mGlu8 receptor downstream proteins during CPP of ing cannulae were inserted into the guiding cannulae morphine could account for the behavioral response and left in place until injections were made. All rats were found by S-3,4-DCPG. Future studies are needed to allowed to recover for 1 week before starting the behavio- characterize the specific mechanisms of action of mGlu8 ral testing. receptor in acquisition and expression of morphine- induced place preference in rats. Intra‑accumbal injection The rats were gently restrained by hand and the dummy Methods cannulae were removed from the guiding cannulae. Animal Drugs were directly injected into the NAc through the 10-week male Wistar rats weighing between 200 and guiding cannulae using injector cannulae (30-gauge, 250  g were obtained from animal breeding colony of 1  mm below the tip of the guiding cannula). Polyethyl- Hamadan University of Medical Sciences (Hamadan, ene tubing (PE-20) was used for attaching the injector Iran). They were maintained on 12/12  h light/dark cycle cannula to the 1-μl Hamilton syringe. Doses of selective (light on at 7 AM) and had access to freely available food mGluR8 allosteric agonist, S-3,4-DCPG, (0.03, 0.3, and and water in their home cages (temperature 22 °C ± 2 °C). 3  μg/0.5 μL saline per side) were administered into the Wood shavings were used for the rats’ bedding, which NAc. The injection volume into the NAc was 0.5 μL/side was changed daily. Lighting within cages during day for all groups. Injections were made bilaterally over a 50 s hours should be held at lux ranges below thresholds of period and the injection cannulae were left in the guiding aversion for rats. We used LED lights (25 lx). In order to cannulae for an additional 60  s in order to facilitate the conduct behavioral tests, it is necessary to increase the diffusion of the drugs. level of light (approximately 210 lx). All experiments were performed in accordance with the guide for the Care and Place conditioning apparatus and protocol Use of Laboratory Animals (National Institutes of Health A three-compartment CPP apparatus was used in the Publication, No. 80–23, revised 1996) and were approved experiments. The apparatus was comprised of three by the institutional ethics committee at Hamadan Uni- plexiglass compartments. The apparatus was divided into versity of Medical Sciences. two equal-sized compartments (30 cm × 30  cm × 40  cm) with the third Sect.  (30  cm × 15  cm × 40  cm) being the Drugs null section which connected the two equal-sized sec- In the current study in order to conduct the experiments tions. Both compartments had white backgrounds with the following drugs were used as following: Morphine black stripes in different orientations (vertical vs. hori - sulfate (Temad, Iran) was dissolved in normal saline zontal). To provide a tactile difference between the com - (0.9% NaCl) (S)-3,4-Dicarboxyphenylglycine (S-3,4- partments, one of them had a smooth plastic floor, while DCPG) (Tocris, UK), a selective mGluR8 allosteric ago- the other compartment had a net-like floor (metal grid). nist, was also dissolved in normal saline (0.9% NaCl). In this apparatus, rats showed no consistent preference It is worth mentioning that control and vehicle groups for either compartment. The CPP protocol has been pre - received saline. viously described [5]. An unbiased allocation was used. Rats with a neutral preference (45–55% for either side) Stereotaxic surgery and drug administration were randomly allocated their drug-paired side (unbiased Subjects were anesthetized by Xylazine (10  mg/kg) and allocation). In the CPP paradigm, the conditioning score Ketamine (100 mg/kg) and placed in the stereotaxic appa- (CS) and distance traveled were calculated based on a ratus (Stoelting, USA) with the incisor bar set at approxi- video recorded by a CCD camera with 30 frames per sec- mately 3.3 mm below horizontal zero in order to achieve ond (30 fps) resolution. The camera was placed 2 m above a flat skull position. After an incision was made to expose the CPP boxes and the locomotion tracking was meas- the rat’s skull, two points were determined and holed ured by Maze Router homemade software, a video track- into the skull at stereotaxic coordinates of 1.4 ± 0.4  mm ing system for automation of behavioral experiments. anterior to bregma, ± 1.5 mm lateral to the sagital suture, CPP paradigm took place for 5 continuous days, which and 6.5 mm ventral from top of the skull according to the consisted of three distinct phases: pre-conditioning, K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 7 of 10 conditioning and post-conditioning [5, 6]. The schedule or odd. Odd animals received subcutaneous (SC) injec- of the CPP paradigm is shown in Fig. 7a. tion of saline and morphine (5  mg/kg) pairing in alter- native morning and afternoon design with an interval Pre‑conditioning phase of 6  h. The vice versa program for even animals was On day 1, each rat was separately placed in the apparatus done. This phase consisted of a 3-day schedule of con - for 10 min, with free access to all compartments. Animal ditioning sessions. A total of six sessions (30 min each) movements were recorded by Maze Router tracking soft- was carried out. During these 3 conditioning days, in ware and analyzed on the same day. Rats with any com- 3 sessions, animals were confined to one compartment, partment preference were omitted from the experiment. under the drug influence. During other three sessions, 3 rats were excluded from this study due to compartment they were injected with saline while confined to the preference. Then rats were randomly assigned to one of other compartment. Access to the other compartments the two groups (odd and even) for place conditioning [5]. was blocked on these days. Place preference was calcu- lated as a preference score (time spent in drug paired Conditioning phase zone-time spent in the saline paired zone) [5, 6]. During The morphine conditioning phase, also known as the this phase, saline group animals received saline in both acquisition phase, were conducted on days 2, 3 and 4. compartments during alternative morning and after- Each group of animals was randomly divided into even noon design with an interval of 6  h. Locomotor data were also collected throughout CPP testing in order to assess the development of behavioral sensitization. Conditioning phase Morphine (5 mg/kg; s.c.) Post‑conditioning phase OR Expression On the 5th day, the partition was removed and the rats Saline phase could access the entire apparatus. The mean time spent for each rat in both compartments during a 10-min period was recorded. In order to calculate the condi- Day 2 4 1 3 5 tioning score, the difference in the time spent for the Pre-test Post test drug- and saline-paired places was considered as the Acquisition phase preference criteria. In the acquisition tests, no injection was given on the post-conditioning day. Expression Acquisition phase phase Experimental design The effect of intra‑accumbal administration of mGluR8 Morphine (5 mg/kg; s.c.) OR Saline allosteric agonist (S‑3,4‑DCPG) on the acquisition Intra-NAc microinjection of S-3,4-DCPG of morphine‑induced CPP (0.03, 0.3 and 3 μg/0.5 μL) OR Saline (0.5 μL) To investigate the effects of mGlu8 agonist on the Expression acquisition of morphine-induced CPP, bilaterally intra- Acquisition phase c phase accumbal injection of S-3,4-DCPG (0.03, 0.3, and 3  μg/0.5  μL) [64] was done 5  min prior to each mor- phine injection (5  mg/kg; SC) during the 3  days of Intra-NAc microinjection of S-3,4-DCPG conditioning phase (Fig.  7a, b). During this phase, a (3 μg/0.5 μL) OR vehicle-control group received saline (0.5  μL) instead Saline (0.5 μL) of S-3,4-DCPG into the NAc, prior to SC injection Fig. 7 Graphical scheme to show behavioral protocol. a Acquisition of morphine. Moreover, to rule out the possibility and expression phases of Morphine-induced conditioned place that S-3,4-DCPG administration alone had reward- preference (CPP) by injection of morphine (5 mg/kg; sc) during 3 days. b To investigate the role of mGlu8 in the nucleus accumbens ing or aversive effects on the CPP, a separate group of (NAc) in the acquisition of morphine-induced CPP, the animals in rats received the highest doses (3  μg/0.5  μL) of S-3,4- the separate groups received S-3,4-DCPG, (0.03, 0.3, and 3 μg/0.5 μL DCPG prior to saline injection (1  mL/kg; SC) instead saline) or saline into the NAc 5 min before the rats received morphine of morphine during the conditioning days. Saline group during acquisition phase. c To find out the role of mGlu8 in the received saline SC injection instead of morphine during expression of morphine -induced CPP, the animals received highest dose of S-3,4-DCPG (3 μg/0.5 μL saline) or Saline 5 min prior to CPP the conditioning phase. test Post test Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 8 of 10 The effects of intra‑accumbal S‑3,4‑DCPG injection on the expression of morphine‑induced CPP In order to examine the effects of the highest dose of S-3,4-DCPG (3  μg/ 0.5  μL) on the expression of mor- phine-induced CPP, the rats were bilaterally given S-3,4- DCPG or saline into the NAc 5  min prior to CPP test (Fig.  7c). In addition, a control vehicle group received saline (0.5  μL) through the NAc instead of S-3,4-DCPG before CPP test on post-conditioning phase. The saline group received saline instead of morphine during the conditioning phase. Locomotor activity measurement The locomotor activity of each rat was recorded using the locomotion tracking apparatus by a video tracking sys- Fig. 8 Histology. Schematic illustration of rat brain coronal sections tem (Router maze software). In these experiments, the showing the approximate location of the NAc injection sites. The total distance traveled (in centimeters) by each rat was numbers show the anterior–posterior coordinates relative to bregma. measured in pre- and post-tests for all groups. Atlas plates were adapted from Paxinos and Watson (Paxinos and Watson, 2007). Scale is 1 mm. It should be noted that some points are completely or partially overlapped ( Vehicle; n = 31, Treatment; n = 44) Histology After behavioral testing, all the rats implanted with injection cannulae were deeply anesthetized with Acknowledgements The authors would like to express their gratitude to the staff of the Neuro - Ketamine and Xylazine. They were then transcardi- physiology Research Center for helping them carry out this project. ally perfused with 0.9% saline and then a 10% forma- lin solution. The brains were removed, blocked, and Authors’ contributions AS, SS and SAK designed the project, wrote the manuscript and performed cut coronally (by using a vibratome) in 50 μm sections the statistical analysis, revised the manuscript and supervised the project. through to the cannulae. All the rats with cannula NK, ZE, SAK, IS and AS were involved in laboratory works and experimental placement 1  mm distant from the intended injection design of the work. AS, SS and MN were involved in data collection and lab assessments, and study designing. All authors read and approved the final site were removed from the data (Fig.  8). It should manuscript. be noted that some points are completely or partially overlapped. Funding The study was funded by Vice-chancellor for Research and Technology, Hama- dan University of Medical Sciences (No. 9505052611). Availability of data and materials Statistics The data are available for any scientific use with kind permission. Data were processed by commercially available soft- ware GraphPad Prism 8.0.2. The data normality test Ethics approval and consent to participate All experimental procedures using rats were conducted in accordance with was performed using Shapiro–Wilk test. If the data the animal care and use guidelines approved by the institutional ethics com- passed normality test (Shapiro–Wilk test greater than mittee at Hamadan University of Medical Sciences (Code of Ethics Committee: 0.05), we used one-way analysis of variance (ANOVA) Grant Number: IR.UMSHA.REC.1397.362) and were performed in accordance with the National Institutes of Health Guide for Care and Use of Laboratory followed by post hoc analysis (Newman–Keuls multiple Animals. comparison test). But If the data did not pass normality test (Shapiro–Wilk test less than 0.05), Kruskal Wallis Consent for publication Not applicable. test was used followed by Dunn’s multiple compari- sons test. The Kruskal Wallis test is the non parametric Competing interests alternative to the one-way ANOVA. Multiple student’s The authors declare that they have no competing interests. t-test was used to compare pre-conditioning with saline Author details or highest dose of S-3,4-DCPG (3  μg/0.5 μL). P-values 1 Neurophysiology Research Center, School of Medicine, Hamadan University less than 0.05 (P < 0.05) were considered to be statisti- of Medical Sciences, Shahid Fahmideh Street, Hamadan, Iran. Department of Neuroscience, School of Sciences and Advanced Technology in Medicine, cally significant. K ahvandi et al. Behav Brain Funct (2021) 17:1 Page 9 of 10 Hamadan University of Medical Sciences, Hamadan, Iran. Department 22. van der Kam EL, De Vry J, Tzschentke TM. The mGlu5 receptor antagonist of Physiology, Faculty of Medicine, Hamadan University of Medical Sciences, 2-methyl-6-(phenylethynyl) pyridine (MPEP) supports intravenous self- Hamadan, Iran. administration and induces conditioned place preference in the rat. Eur J Pharmacol. 2009;607(1–3):114–20. Received: 24 November 2020 Accepted: 5 February 2021 23. Rutten K, Van Der Kam EL, De Vry J, Bruckmann W, Tzschentke TM. The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) potenti- ates conditioned place preference induced by various addictive and non-addictive drugs in rats. Addict Biol. 2011;16(1):108–15. 24. Morishima Y, Miyakawa T, Furuyashiki T, Tanaka Y, Mizuma H, Nakanishi S. Enhanced cocaine responsiveness and impaired motor coordination in References metabotropic glutamate receptor subtype 2 knockout mice. Proc Natl 1. Koob GF. Drugs of abuse: anatomy, pharmacology and function of reward Acad Sci. 2005;102(11):4170–5. pathways. Trends Pharmacol Sci. 1992;13:177–84. 25. de Sa Nogueira D, Bourdy R, Filliol D, Quessada C, McCort-Tranchepain 2. Diana M. The dopamine hypothesis of drug addiction and its potential I, Acher F, et al. LSP2–9166, an orthosteric mGlu4 and mGlu7 receptor therapeutic value. Front Psychiatry. 2011;2:64. agonist, reduces cocaine self-administration under a progressive ratio 3. Le Merrer J, Becker JA, Befort K, Kieffer BL. Reward processing by the schedule in rats. Neurosci Lett. 2020. https ://doi.org/10.1016/j.neule opioid system in the brain. Physiol Rev. 2009;89(4):1379–412. t.2020.13560 3. 4. Tzschentke T, Schmidt W. Glutamatergic mechanisms in addiction. 26. Mao L, Wang JQ. Distinct inhibition of acute cocaine-stimulated motor Molecular psychiatry. 2003;8(4):373–82. activity following microinjection of a group III metabotropic glutamate 5. Vatankhah M, Karimi-Haghighi S, Sarihi A, Haghparast A. Intra-accumbal receptor agonist into the dorsal striatum of rats. Pharmacol Biochem administration of AMN082, a metabotropic glutamate receptor type Behav. 2000;67(1):93–101. 7 allosteric agonist, inhibits the acquisition but not the expression of 27. Bäckström P, Hyytiä P. Suppression of alcohol self-administration and morphine-induced conditioned place preference in rats. Neurosci Lett. cue-induced reinstatement of alcohol seeking by the mGlu2/3 receptor 2018;681:56–61. agonist LY379268 and the mGlu8 receptor agonist (S)-3, 4-DCPG. Eur J 6. Roohi N, Sarihi A, Shahidi S, Zarei M, Haghparast A. Microinjection of the Pharmacol. 2005;528(1–3):110–8. mGluR5 antagonist MTEP into the nucleus accumbens attenuates the 28. Blednov YA, Walker D, Osterndorf-Kahanek E, Harris RA. Mice lacking acquisition but not expression of morphine-induced conditioned place metabotropic glutamate receptor 4 do not show the motor stimulatory preference in rats. Pharmacol Biochem Behav. 2014;126:109–15. effect of ethanol. Alcohol. 2004;34(2–3):251–9. 7. Baharlouei N, Sarihi A, Komaki A, Shahidi S, Haghparast A. Blockage of 29. Zaniewska M, Przegaliński E, Filip M, Pilc A, Doller D. Inhibitory actions acquisition and expression of morphine-induced conditioned place of mGlu 4 receptor ligands on cocaine-, but not nicotine-, induced preference in rats due to activation of glutamate receptors type II/III in sensitizing and conditioning locomotor responses in rats. Pharmacol Rep. nucleus accumbens. Pharmacol Biochem Behav. 2015;135:192–8. 2014;66(2):205–11. 8. Platt SR. The role of glutamate in central nervous system health and 30. Hajasova Z, Canestrelli C, Acher F, Noble F, Marie N. Role of mGlu7 recep- disease—a review. Vet J. 2007;173(2):278–86. tor in morphine rewarding effects is uncovered by a novel orthosteric 9. Gass JT, Olive MF. Glutamatergic substrates of drug addiction and alco- agonist. Neuropharmacology. 2018;131:424–30. holism. Biochem Pharmacol. 2008;75(1):218–65. 31. Scofield M, Heinsbroek J, Gipson C, Kupchik Y, Spencer S, Smith A, et al. 10. Groenewegen HJ, Wright CI, Beijer AV, Voorn P. Convergence and The nucleus accumbens: mechanisms of addiction across drug classes segregation of ventral striatal inputs and outputs. Ann N Y Acad Sci. reflect the importance of glutamate homeostasis. Pharmacol Rev. 1999;877(1):49–63. 2016;68(3):816–71. 11. Conn PJ, Pin JP. Pharmacology and functions of metabotropic glutamate 32. Brog JS, Salyapongse A, Deutch AY, Zahm DS. The patterns of afferent receptors. Annu Rev Pharmacol Toxicol. 1997;37:205–37. innervation of the core and shell in the “accumbens” part of the rat 12. Pin JP, Duvoisin R. The metabotropic glutamate receptors: structure and ventral striatum: immunohistochemical detection of retrogradely trans- functions. Neuropharmacology. 1995;34(1):1–26. ported fluoro-gold. J Comp Neurol. 1993;338(2):255–78. 13. Karimi SA, Komaki A, Salehi I, Sarihi A, Shahidi S. Role of group II metabo- 33. Heimer L, Alheid GF, De Olmos J, Groenewegen HJ, Haber SN, Harlan RE, tropic glutamate receptors (mGluR2/3) blockade on long-term potentia- et al. The accumbens: beyond the core-shell dichotomy. J Neuropsychia- tion in the dentate gyrus region of hippocampus in rats fed with high-fat try Clin Neurosci. 1997;9(3):354–81. diet. Neurochem Res. 2015;40(4):811–7. 34. Messenger MJ, Dawson LG, Duty S. Changes in metabotropic gluta- 14. Conn PJ, Pin J-P. Pharmacology and functions of metabotropic glutamate mate receptor 1–8 gene expression in the rodent basal ganglia motor receptors. Annu Rev Pharmacol Toxicol. 1997;37(1):205–37. loop following lesion of the nigrostriatal tract. Neuropharmacology. 15. Goudet C, Chapuy E, Alloui A, Acher F, Pin J-P, Eschalier A. Group III 2002;43(2):261–71. metabotropic glutamate receptors inhibit hyperalgesia in animal models 35. Fan Y, Niu H, Rizak JD, Li L, Wang G, Xu L, et al. Combined action of of inflammation and neuropathic pain. PAIN . 2008;137(1):112–24. MK-801 and ceftriaxone impairs the acquisition and reinstatement of 16. Lavreysen H, Dautzenberg FM. Therapeutic potential of group III metabo- morphine-induced conditioned place preference, and delays morphine tropic glutamate receptors. Curr Med Chem. 2008;15(7):671–84. extinction in rats. Neurosci Bull. 2012;28(5):567–76. 17. Kotlinska J, Bochenski M. Comparison of the effects of mGluR1 and 36. Vatankhah M, Sarihi A, Komaki A, Shahidi S, Haghparast A. AMN082-a mGluR5 antagonists on the expression of behavioral sensitization to the metabotropic glutamate receptor type 7 allosteric agonist in the NAc locomotor effect of morphine and the morphine withdrawal jumping in facilitates extinction and inhibits the reinstatement of morphine-induced mice. Eur J Pharmacol. 2007;558(1–3):113–8. conditioned place preference in male rats. Brain Res Bull. 2018;140:28–33. 18. Popik P, Wrobel M. Morphine conditioned reward is inhibited by MPEP, 37. Tahsili-Fahadan P, Carr GV, Harris GC, Aston-Jones G. Modafinil blocks the mGluR5 antagonist. Neuropharmacology. 2002;43(8):1210–7. reinstatement of extinguished opiate-seeking in rats: mediation by a 19. Herzig V, Schmidt WJ. Eec ff ts of MPEP on locomotion, sensitization and glutamate mechanism. Neuropsychopharmacology. 2010;35(11):2203. conditioned reward induced by cocaine or morphine. Neuropharmacol- 38. Amalric M, Lopez S, Goudet C, Fisone G, Battaglia G, Nicoletti F, et al. ogy. 2004;47(7):973–84. Group III and subtype 4 metabotropic glutamate receptor agonists: 20. Aoki T, Narita M, Shibasaki M, Suzuki T. Metabotropic glutamate discovery and pathophysiological applications in Parkinson’s disease. receptor 5 localized in the limbic forebrain is critical for the develop- Neuropharmacology. 2013;66:53–64. ment of morphine-induced rewarding effect in mice. Eur J Neurosci. 39. Palucha A, Klak K, Branski P, Van der Putten H, Flor PJ, Pilc A. Activation of 2004;20(6):1633–8. the mGlu7 receptor elicits antidepressant-like effects in mice. Psychop - 21. van der Kam EL, De Vry J, Tzschentke TM. 2-Methyl-6 (phenylethynyl)- harmacology. 2007;194(4):555–62. pyridine (MPEP) potentiates ketamine and heroin reward as assessed by 40. Salling MC, Faccidomo S, Hodge CW. Nonselective suppression of acquisition, extinction, and reinstatement of conditioned place prefer- operant ethanol and sucrose self-administration by the mGluR7 ence in the rat. Eur J Pharmacol. 2009;606(1–3):94–101. Kahvandi et al. Behav Brain Funct (2021) 17:1 Page 10 of 10 positive allosteric modulator AMN082. Pharmacol Biochem Behav. 54. Zhou Y, Yan E, Cheng D, Zhu H, Liu Z, Chen X, et al. The projection from 2008;91(1):14–20. ventral CA1, not prefrontal cortex, to nucleus accumbens core mediates 41. Hu G, Duffy P, Swanson C, Ghasemzadeh MB, Kalivas PW. The regula- recent memory retrieval of cocaine-conditioned place preference. Front tion of dopamine transmission by metabotropic glutamate receptors. J Behav Neurosci. 2020;14:209. Pharmacol Exp Ther. 1999;289(1):412–6. 55. Alizamini MM, Farzinpour Z, Ezzatpanah S, Haghparast A. Role of intra- 42. Mao L, Guo M, Jin D, Xue B, Wang JQ. Group III metabotropic glutamate accumbal orexin receptors in the acquisition of morphine-induced receptors and drug addiction. Front Med. 2013;7(4):445–51. conditioned place preference in the rats. Neurosci Lett. 2017;660:1–5. 43. Inoue M, Mishina M, Ueda H. Locus-specific rescue of GluRϵ1 NMDA 56. Baharlouei N, Sarihi A, Moradi M, Zarrabian S, Haghparast A. Microinjec- receptors in mutant mice identifies the brain regions important for tion of the mGluR2/3 agonist, LY379268, into the nucleus accumbens morphine tolerance and dependence. J Neurosci. 2003;23(16):6529–36. attenuates extinction latencies and the reinstatement of morphine- 44. Yuan K, Sheng H, Song J, Yang L, Cui D, Ma Q, et al. Morphine treat- induced conditioned place preference in rats. Behav Pharmacol. ment enhances glutamatergic input onto neurons of the nucleus 2018;29(5):385–92. accumbens via both disinhibitory and stimulating effect. Addict Biol. 57. Freund N, Manns M, Rose J. A method for the evaluation of intracranial 2017;22(6):1756–67. tetrodotoxin injections. J Neurosci Methods. 2010;186(1):25–8. 45. Kenny PJ, Markou A. The ups and downs of addiction: role of metabo- 58. Bahi A. Decreased anxiety, voluntary ethanol intake and ethanol-induced tropic glutamate receptors. Trends Pharmacol Sci. 2004;25(5):265–72. CPP acquisition following activation of the metabotropic glutamate 46. Manzoni OJ, Williams JT. Presynaptic regulation of glutamate release receptor 8 “mGluR8.” Pharmacol Biochem Behav. 2017;155:32–42. in the ventral tegmental area during morphine withdrawal. J Neurosci. 59. Gerlai R, Adams B, Fitch T, Chaney S, Baez M. Performance deficits of 1999;19(15):6629–36. mGluR8 knockout mice in learning tasks: the effects of null mutation and 47. Zahm DS. An integrative neuroanatomical perspective on some subcorti- the background genotype. Neuropharmacology. 2002;43(2):235–49. cal substrates of adaptive responding with emphasis on the nucleus 60. Boccella S, Marabese I, Iannotta M, Belardo C, Neugebauer V, Mazzitelli M, accumbens. Neurosci Biobehav Rev. 2000;24(1):85–105. et al. Metabotropic glutamate receptor 5 and 8 modulate the amelio- 48. Di Chiara G. Nucleus accumbens shell and core dopamine: differential rative effect of ultramicronized palmitoylethanolamide on cognitive role in behavior and addiction. Behav Brain Res. 2002;137(1–2):75–114. decline associated with neuropathic pain. Int J Mol Sci. 2019;20(7):1757. 49. Parkinson JA, Olmstead MC, Burns LH, Robbins TW, Everitt BJ. Dissociation 61. Maren S. Synaptic mechanisms of associative memory in the amygdala. in effects of lesions of the nucleus accumbens core and shell on appeti- Neuron. 2005;47(6):783–6. tive pavlovian approach behavior and the potentiation of conditioned 62. Fendt M, Schmid S. Metabotropic glutamate receptors are involved in reinforcement and locomotor activity byd-amphetamine. J Neurosci. amygdaloid plasticity. Eur J Neurosci. 2002;15(9):1535–41. 1999;19(6):2401–11. 63. Zhang G-C, Vu K, Parelkar NK, Mao L-M, Stanford IM, Fibuch EE, et al. 50. Sellings LH, Clarke PB. Segregation of amphetamine reward and locomo- Acute administration of cocaine reduces metabotropic glutamate tor stimulation between nucleus accumbens medial shell and core. J receptor 8 protein expression in the rat striatum in vivo. Neurosci Lett. Neurosci. 2003;23(15):6295–303. 2009;449(3):224–7. 51. Olive MF, Koenig HN, Nannini MA, Hodge CW. Elevated extracellular CRF 64. Dobi A, Sartori SB, Busti D, Van der Putten H, Singewald N, Shigemoto levels in the bed nucleus of the stria terminalis during ethanol with- R, et al. Neural substrates for the distinct effects of presynaptic group drawal and reduction by subsequent ethanol intake. Pharmacol Biochem III metabotropic glutamate receptors on extinction of contextual fear Behav. 2002;72(1–2):213–20. conditioning in mice. Neuropharmacology. 2013;66:274–89. 52. Alaghband Y, Kramár E, Kwapis JL, Kim ES, Hemstedt TJ, López AJ, et al. CREST in the nucleus accumbens core regulates cocaine conditioned Publisher’s Note place preference, cocaine-seeking behavior, and synaptic plasticity. J Springer Nature remains neutral with regard to jurisdictional claims in pub- Neurosci. 2018;38(44):9514–26. lished maps and institutional affiliations. 53. Miyamoto Y, Iida A, Sato K, Muramatsu S-I, Nitta A. Knockdown of dopamine D2 receptors in the nucleus accumbens core suppresses methamphetamine-induced behaviors and signal transduction in mice. Int J Neuropsychopharmacol. 2015;18(4):pyu038. Re Read ady y to to submit y submit your our re researc search h ? Choose BMC and benefit fr ? Choose BMC and benefit from om: : fast, convenient online submission thorough peer review by experienced researchers in your field rapid publication on acceptance support for research data, including large and complex data types • gold Open Access which fosters wider collaboration and increased citations maximum visibility for your research: over 100M website views per year At BMC, research is always in progress. Learn more biomedcentral.com/submissions

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