Access the full text.
Sign up today, get DeepDyve free for 14 days.
Loading next page...
/lp/springer-journals/asymmetry-in-the-brain-influenced-the-neurological-deficits-and-qcGikuzAS5
- Publisher
- Springer Journals
- Copyright
- Copyright © 2008 by Gao and Zhang; licensee BioMed Central Ltd.
- Subject
- Biomedicine; Neurosciences; Neurology; Behavioral Therapy; Psychiatry
- eISSN
- 1744-9081
- DOI
- 10.1186/1744-9081-4-57
- pmid
- 19102754
- Publisher site
- See Article on Publisher Site
Abstract
Background: Paw preference in rats is similar to human handedness, which may result from dominant hemisphere of rat brain. However, given that lateralization is the uniqueness of the humans, many researchers neglect the differences between the left and right hemispheres when selecting the middle cerebral artery occlusion (MCAO) in rats. The aim of this study was to evaluate the effect of ischemia in the dominant hemisphere on neurobehavioral function and on the cerebral infarction volume following MCAO in rats. Methods: The right-handed male Sprague-Dawley rats asserted by the quadrupedal food-reaching test were subjected to 2 hours MCA occlusion and then reperfusion. Results: The neurological scores were significantly worse in the left MCAO group than that in the right MCAO group at 1 h, 24 h, 48 h and 72 h (p <0.05 respectively). There was a trend toward better neurobehavioral function recovery in the right MCAO group than in the left MCAO group. The total infarct volume in left MCAO was significantly larger than that in the right (p < 0.05). Conclusion: The neurobehavioral function result and the pathological result were consistent with the hypothesis that paw preference in rats is similar to human handedness, and suggested that ischemia in dominant hemisphere caused more significant neurobehavioral consequence than in another hemisphere following MCAO in adult rats. Asymmetry in rat brain should be considered other than being neglected in choice of rat MCAO model. Background about the difference between the right MCAO and the left Focal cerebral ischemia models in rats have gained MCAO in rat. increasing acceptance in recent years for their relevance to human beings [1,2]. But rat brain injury produced by It had been established that lateralization is the unique- MCAO varies considerably in its size and distribution. The ness of the humans [3-5]. However, this concept has been sides picked for MCA occlusion is also different between challenged. That paw preference in rats is similar to laboratory studies. However, little is really recognized human handedness has been known for decades, as stated Page 1 of 5 (page number not for citation purposes) Behavioral and Brain Functions 2008, 4:57 http://www.behavioralandbrainfunctions.com/content/4/1/57 by Rogers "... lateralization in humans is not unique either than 21 and ambidextrous when the RPE score was in nature or extent [6]." However, it has been less well rec- between 22 and 28. ognized that lateralization of paw in rats may result from dominant hemisphere of rat brain. Greater ischemic sever- Middle cerebral artery occlusion (MCAO) model ity in dominant hemisphere may be even more controver- The transient focal cerebral ischemia rat model has been sial. We indeed suspected that the left and the right MCAO described by Longa EZ et al previously [10]. Briefly, 24 rat models might be different, in that the two hemispheres right-handed male Sprague-Dawley rats fasted overnight in the rat are not the same entirely. Therefore, the present were randomized to two groups: the right MCAO group: study was designed to investigate whether there is a sham (n = 3), ischemia (n = 9); and the left MCAO group: greater stroke severity in the dominant hemisphere in sham (n = 3), Ischemia (n = 9). The rats were anesthetized transient focal ischemia rat model. with 8% chloral hydrate (300 mg/kg, i.p.) and were posi- tioned supine. Under an operating microscope, the right (or left in the second group) common, internal, and exter- Methods The paw preference determination nal carotid arteries were exposed through a para-median The Animal Subjects Committee of Qingdao University incision of the neck. The external carotid artery was Medical College approved this protocol. A modified ligated. A 4-0 nylon surgical thread with round tip coated quadrupedal food-reaching test developed by Tang and with poly-L-lysine was inserted about 18–20 mm through Verstynen [7] has been used previously (Figure 1) to assess external carotid artery until the distal end met mild resist- the paw preference in male Spraque-Dawley rats (Depart- ance, indicating the occlusion of the origin of the middle ment of Experimental Animals, Chinese Academy of Sci- cerebral artery (MCA). The suture was inserted into the ence, Shanghai, China) weighting 260~280 g [8]. Briefly, corresponding MCA in each group. rats adapted to the animal room for one week were deprived of food for two days and then individually After 2 h occlusion, reperfusion was instituted by with- placed in a metal housing cage with two front openings drawing intraluminal suture. The sham-operated animals separated by 1 cm in the day of paw preference test. The were treated identically but the MCA was not occluded. openings in the testing cage were small enough to allow access to food by a forepaw only, not by the snout. An Rectal temperature was continuously monitored and observer scored the numbers of right and left paw reaches. maintained at approximately 37°C with heat lamps and a Rats were classified as right-hander, left-hander, and heat pad. After restoration of blood flow, the animals were mixed-hander based on the binomial probability distribu- allowed to recover at ambient temperature (25°C, by an tion test [9]: rats were considered as right-handed if the air-conditioner). The efficiency of MCAO was determined right-paw entry (RPE) score was equal to or greater than by the neurological assessment according to the modified 29, left-handed when the score was equal to or smaller method described by Bederson at al [11]. Schematic diagram showing the mo Figure 1 dified quadrupedal food-reaching test originally developed by Tang and Verstynen (2002) Schematic diagram showing the modified quadrupedal food-reaching test originally developed by Tang and Verstynen (2002). Page 2 of 5 (page number not for citation purposes) Behavioral and Brain Functions 2008, 4:57 http://www.behavioralandbrainfunctions.com/content/4/1/57 Neurological deficits assessment forelimb placing deficits were clearly present at 50 min- Within the 72-h observation period, behavioral tests were utes following MCAO. The neurological deficits scores performed daily in all 24 rats before and during MCAO by after 2 h MCAO were significantly worse in the left MCAO an investigator who was blinded to the experimental group than that in the right MCAO at 1 h, 24 h, 48 h and groups. The tests have been used previously to evaluate 72 h (8.2 ± 0.6 versus 7.5 ± 0.7, 9.5 ± 0.4 versus 8.3 ± 0.2, various aspects of neurological function: the postural 8.8 ± 0.3 versus 7.6 ± 0.3, and 8.5 ± 0.3 versus 7.0 ± 0.3, p reflex test developed by Bederson at al [11] to examine < 0.05 respectively). There was a trend toward better neu- upper body posture while the animal is suspended by the rological function recovery in the right MCAO than in the tail. In the dysfunctional paw test, the contra lateral fore- left MCAO group (Figure 2). The result showed that paw or hind paw was pulled toward the body, and the lesions in dominant hemisphere produced a more severe time to re-extend each paw was scored as: 0 (< 1 second), and prolonged neurological deficit. 1 (< 5 seconds), or 2 (> 5 seconds). In the postural reflex test, the rat was pushed in the contra lateral direction and Assessment of brain damage scored as: 0 (resistance to lateral push), 1 (initially Examination of the areas of cerebral infarction revealed reduced but progressive resistance), 2 (reduced resist- pancellular necrosis as well as dense areas of eosinophilic, ance), or 3 (lateral down fall). In the circling test, move- shrunken neurons along the edges of the infarct. An exten- ments were scored as: 0 (straight movement), 1 sive brain infarct was found in the dorsolateral and lateral (movement to the right), 2 (circling movement), or 3 (no portions of neocortex and the entire caudoputamen in rat movement). Each score was summed and represented as a brains. Smaller areas of cortical infarct were found in rat single overall neurological score (0 to 10). with right MCAO compared with left MCAO. With 2 h MCAO, the total brain infarct volume was significantly Brain infarct assessment larger in rats with left MCAO than that in the right MCAO 3 3 Rats were allowed to survive for 72 h. After decapitation, group (Figure 3, 102.1 ± 8.8 mm versus 97.0 ± 11.2 mm ; the brains were immediately removed, post-fixed for 2 h p = 0.04 < 0.05). This result suggested that the volume of in 20% sucrose in 4% paraformaldehyde and kept in 30% cerebral infarction in the dominant hemisphere was larger sucrose in 0.01 mol/L PBS until they sunk to the bottom. than that in the non-dominant hemisphere in adult rats. Coronal sections (30 μm) were cut on a freezing micro- tome and kept in cryoprotective solution at -20°C. Brain Discussion sections were stained with hematoxylin and eosin (H&E). It has been extensively believed that handiness is one of To quantity brain infarct volume and depict infarct fre- the prominent markers of functional asymmetry of quency distribution, coronal sections were viewed using human brain. A lateralized population means that more Leica Q500 IW image processing system (Leica, Bensheim, than 50% of the individuals are lateralized in the same Germany). The volume of cerebral infarction was calcu- direction. It is true that approximately 90% of human lated as the product of cross-sectional area for all sections population shows a right hand preference in the United and distance between sections, using the formula: States [12]. However in population-level, several lines of evidences have demonstrated that lateralization in V = t(A1+A2+...+An) - t(A1+An)/2 humans is not unique either in nature or extent. There is now accumulating evidence for population-level asym- ); V: cerebral infarction volume (mm metries in animals including rats and other rodent ani- mals [13]. In rats, population-level right-handedness was t: 30μ (distance between neighbor slices); reported early in1930. The distribution of hand prefer- ence in rats is similar to human hand preference. There- A: the cerebral infarction area at each slice. fore the uniqueness of men in population-level right- handedness is rejects [7]. On the contrary, a lot of research Statistical analysis reports especially in the relatively old literature indicated Values are presented as mean ± SD. Differences between no population-level right-handedness in the rat. These groups were analyzed with Student's two-tailed t-test. In seemingly inconsistent results in the literature can be the behavior test, comparison of groups was made by explained in the terms of the differences among testing Mann-Whitney U test. α level was set to 0.05 to determine methods according to Tang and Verstynen [7]. statistical significance. The result of paw preference in rats using the modified computerized food-reaching test by Tang and Verstynen Results Neurological deficits score comparisons [7] showed that 99.5% of the right handed rats first used Neurological deficits were observed in all rats. All animals their right paw to reach the food, meanwhile only 0.5% of exhibited impairment of postural reflexes. Contralateral these using the left paw to reach the food. Similar to the Page 3 of 5 (page number not for citation purposes) HV DORJLROHXU Behavioral and Brain Functions 2008, 4:57 http://www.behavioralandbrainfunctions.com/content/4/1/57 7) * + 7 VFR V+ W 0 R Compari sutures Figure 2son of total neurological scores at various times after 2 hours of MCAo in rats with left MCA suture and right MCA Comparison of total neurological scores at various times after 2 hours of MCAo in rats with left MCA suture and right MCA sutures. Normal neurological deficit scores are 0; maximal score is 10. right handed ones, 98.6% of the left-handed rats first used responses was significantly shorter from the left brain their left paw to reach the food, meanwhile only 1.4% first than the right brain [17]. The asymmetric cognitive con- used their right paw in food reaching. In the present study trol in an animal model may have a major impact in many we selected the right-handed rats using the modified food- aspects of biology in respect to normal functioning, supe- reaching test and found that about 80% of rats were right- rior talents, and diseases. The insular cortex is involved in handed and nearly 20% of rats were left-handed. In order almost half of patients with nonlacunar ischemic MCA to get enough number of rats for the present study we territory strokes. Major insular involvement is associated chose the majority (the right-handed adult rats). Also we with large MCA territory infarcts, proximal MCA occlu- used only male adult rats to avoid the estrogenic hor- sions, and greater stroke severity [18]. The right-handed mones interferences on the paw preference and cerebral rats with their left hemisphere of the brain as the domi- infarction. nant hemisphere were selected in the present study. The total cerebral infarction volume produced by the left The asymmetry in the rat brain also influenced the chem- MCAO was larger than that in the right MCAO, and a sig- ical asymmetry including dopamine and norepinephrine nificantly more severe and prolonged neurological deficit in normal adult rats or in the rat with cerebral infarction was demonstrated in adult rats following MCAO. So our involving cortex and of frontal cortex in particular [14]. As present study was consistent with the concept of asymme- expected, hand preference in rats is controlled by the con- try of rat brain on the neurological function and patholog- tralateral primary motor cortex, since handiness was ical observation following MCAO. reversed after ablation of this region [15]. In the right- handed rats the left hemisphere could play a more impor- Therefore it might be speculated that it is urgent to pay tant role in the process of new visual-motor learning [16]. more attention to the asymmetry in the rat brain when Regarding the role of left-brain in cognitive function, it using the MCAO rat model. The limitation of the present was also shown that the latency of visual evoked study includes the number of animals used in each group, Page 4 of 5 (page number not for citation purposes) &$ HU DI RXU K K 5, /( Behavioral and Brain Functions 2008, 4:57 http://www.behavioralandbrainfunctions.com/content/4/1/57 Authors' contributions ZM and GH were responsible for design and writing of the manuscript. GH carried out the data acquisition and anal- yses. Both authors read and approved the final manu- script. Acknowledgements We thank Dr. Yunliang Guo, Institute of Cerebrovascular Diseases, and Affiliated Hospital of Qingdao University Medical College, for technical advice. We also thank Mr. Jingyang Wang, engineer of computer center, Shinan District of Qingdao for his excellent technical assistance in data processing. References 1. Ginsberg MD, Busto R: Rodent models of cerebral ischemia. Stroke 1989, 20:1627-1642. 2. Garcia JH, Yoshida Y, Chen H: Progression from ischemic injury to infarct following middle cerebral artery occlusion in the rat. Am J Pathol 1993, 142:623-635. 3. Glick SD, Ross DA: Right-sided population bias and lateraliza- tion of activity in normal rats. Brain Res 1981, 205:222-225. 4. Napieralski JA, Banks RJ, Chesselet MF: Motor and somatosensory deficits following uni- and bilateral lesions of the cortex Left Right induced by aspiration or thermocoagulation in the adult rat. Exp Neurol 1998, 154:80-88. 5. Pence S: Paw preference in rats. Basic Clinical Physiology and Phar- macology 2002, 13:41-49. 6. Rogers LJ: Evolution of hemispheric specialization: Advan- tages and disadvantages. Brain Lang 2000, 73:236-253. Comparison of total infarct vo r Figure 3 ight MCA sutures groups 72 h luafter mes in l MCAO in rats eft MCA sutures and 7. Tang AC, Verstynen T: Early life environment modulates hand- Comparison of total infarct volumes in left MCA edness in rats. Behav Brain Res 2002, 131:1-7. sutures and right MCA sutures groups 72 h after 8. Gao H, Cheng J: Dominance in the rat brain and choice of cer- MCAO in rats. ebral ischemia models. Medical Recapitulate(in chineses) 2002, 8:58-59. 9. Betaneur C, Neveu PJ, Le Moal M: Strain and sex differences in the degree of paw preference in mice. Behav Brain Res 1991, and therefore the inability to perform more extensive sta- 45:97-101. 10. Longa EZ, Weinstein PR, Carlson S, Cummins R: Reversible middle tistical analysis of all variables such as body weight in cerebral artery occlusion without craniectomy in rats. Stroke terms of their relations with cerebral infarction volumes. 1989, 20:84-91. It is hoped that further studies will be directed toward this 11. Bederson JB, Pitts LH, Tsuji M, Nishimura MC, Davis RL, Bartkowski H: Rat middle cerebral artery occlusion: Evaluation of the goal. model and development of neurologic examination. Stroke 1986, 17:472-476. 12. Gilbert A, Wysoki C: Hand preference and age in the United Conclusion States. Neuropsychologia 1992, 30:601-608. Our experiments using neurological behavioral function 13. Elalmis DD, GüNEN KTZ, Binokay S: Differential contributions of evaluation and brain pathological study showed that cer- right and left brains to paw skill in right- and left-paw female rats. Int J Neurosci 2003, 113:1023-1042. ebral infarction in dominant hemisphere produced larger 14. Robinson RG: Differential behavioral and biochemical effects brain infarct volume and a more severe and prolonged of right and left hemispheric cerebral infarction in rat. Science neurological deficit significantly in adult rats following 1979, 205:707-710. 15. Cohen JD, Castro-Alamancos MA: Skilled motor learning does MCAO. The present result was consistent with the hypoth- not enhance long-term depression in the motor cortex in esis that paw preference in rats is similar to human hand- vivo. J Neurophysiol 2005, 93:1486-1497. 16. Rousselet GA, Mace MJ, Fabre-Thorpe M: Is it an animal? Is it a edness. Asymmetry in rat brain should be considered human face? Fast processing in upright and inverted natural other than being neglected in choice of rat MCAO model. scenes. J Vis 2003, 3:440-455. 17. Simpson D, Erwin CW, Linnoila M: Ethanol and menstrual cycle interactions in the visual evoked response. Electroencephalogr List of abbreviations used Clin Neurophysiol 1981, 52:28-35. MCAO: the middle cerebral artery occlusion; MCA: the 18. Fink JN, Selim MH, Kumar S, Voetsch B, Fong WC, Caplan LR: Insu- lar cortex infarction in acute middle cerebral artery terri- middle cerebral artery; RPE: right-paw entry; H&E: hema- tory stroke: predictor of stroke severity and vascular lesion. toxylin and eosin. Arch Neurol 2005, 62:1081-1085. Competing interests The authors declare that they have no competing interests. Page 5 of 5 (page number not for citation purposes) Total infarction volume(mm3)
Journal
Behavioral and Brain Functions – Springer Journals
Published: Dec 22, 2008