Research On Cerebral Dopaminergic Mechanisms Of Cognitive Behavioral Deficits Post-MCC In Rats

Objective: To establish the model of multiple cerebral concussion(MCC) inrats, observe dopaminergic neurons and its nerve fiber post-MCC, our target is tostudy dopaminergic neurons changes in brain regions related to cognitivedeficits, so as to understand the neurobiologic mechanisms of cognitive behavioraldysfunction after MCC in rats.Methods: A rat MCC model was duplicated by using a metallic pendulum-strikerconcussivedevice. Forty-eight male Sprague—Dawley rats were randomly dividedinto six MCC groups:1d, 2d, 4d, 8d, 16d and 24d group(n=8, in each group). One controlwas used(n=8). Learning and memory ability were detected respectivelyfollowing-MCC days 1～7, 8～14 and 15～21 with MWM. The substantia nigra parscompact (SNC) and ventral tegmental area (VTA) in midbrain, prefrontal cortex,anterior cingulate cortex, caudate putamen, accumbens nucleus, olfactory tubercle,post cingulate cortex, frontoparietal cortex and entorhinal cortex were stainedwith anti-tyrosine hydroxylase(Anti-TH) and anti-dopamine-beta-hydroxylase(Anti-DBH) monoclonal antibody by the immunohistochemistry S-P method. The numberof TH-positive neurons in the SNC and VTA in midbrain were observed and countedusing optical microscope and the expression of dopaminergic nerve fiber in thedifferent brain area was also detected. Dopaminergic neurons and its fiber in thebrain area mentioned above were quantitated by image analysis system.Results: (1)In MCC8d and MCC24d groups, compared with the control group, thelatency to find the platform was much longer but there were no statistically differences (P＞0.05). However, compared with the control group, in 9th～10th and13th～14th day in MCC16d group there were significant differences (P＜0.05).Compared with the control, probe trials demonstrated that the MCC producedreductions in the percent dwell time in the target quadrant, and there werestatistically differences (P＜0.05) in the MCC8d and MCC16d groups. However, therewere no significant differences (P＞0.05) between the MCC24d group and the controlgroup. (2)The changes of TH-positive neurons in the SNC and VTA after MCC as followed:Compared with the control group, TH-positive neurons in the SNC increased in the1d group following MCC, reached a peak in the 8d group, after that decreasedgradually, there were significant differences in the 4d and 8d groups (p＜0.05). Andthe number of neurons in the VTA rised dramatically in the 2d,4d,8d, and 16d groups(p＜0.05, vs control). In addition, the number of them reached the peak in the4d and almost recovered in the 24d group. (3) The changes of TH-positive neuronsquantitated by image analysis system in the SNC and VTA post- MCC as followed:In the 4d and 8d groups in SNC and in the 2d, 4d, 8d and 16d groups in VTA, itrevealed statistical differences compared with the control group (p＜0.05). (4)The expression of dopaminergic nerve fiber counted using optical microscope inthe different brain regions as followed: The difference of the density ofdopaminergic nerve fiber in accumbens nucleus was the most obvious in the 1d, 4d,and 16d groups (p＜0.008, vs control), and the most striking change in olfactorytubercle was in the 1d and 8d groups (p≤0.008, vs control). In entorhinal cortex,there were statistical differences compared with the control group in the 8d groups(p＜0.008). In other brain regions, such as prefrontal cortex, anterior cingulatecortex, caudate putamen, frontoparietal cortex and post cingulate cortex, theexpression of TH-positive fiber obviously rose to some degree. However, all thepost-injury groups revealed no statistical differences compared with the controlgroup(p＞0.008). (5) The changes of TH-positive fiber quantitated by image analysissystem in some brain area as followed: In prefrontal cortex, all the groups wereobserved on the rise, especially in the 4d and 8d groups post-MCC (p＜0.05). Compared with control, TH-positive fiber in anterior cingulate cortex increaseddramatically in all groups following MCC (p≤0.01, vs control). There weresignificant differences in the 1d, 4d and 16d groups in caudate putamen (p＜0.05), andso did in all injuryed groups but 1d and 2d in accumbens nucleus (p＜0.01). Moreover,we found dense TH-positive fiber in the 1d and 8d groups in olfactory tubercleandin all injuryed groups in frontoparietal cortex (p＜0.05, vs control). Both postcingulate cortex and entorhinal cortex had a large amount of TH-positive fiberin the 1d and 2d groups, so did entorhinal cortex in the 8d groups (p＜0.05, vscontrol). The immunologic reactions of DBH were negative in all experimentsmentioned above.Conclusions: 1. The multiple cerebral concussion (MCC) model in rats wasestablished successfully using a metallic pendulum-striker concussive device;2. Multiple cerebral concussion has impaired effects on learning and memory inrats in intermediate term; 3. The expression of dopaminergic neurons and its fiberfollowing MCC in rats rised in cerebral cortex, as well as in caudate putamen,accumbens nucleus, olfactory tubercle, substantia nigra, compact and venttegmental area; 4. The changes between Morris water maze test and TH-positiveproduct are essentially unanimous in rats of post-MCC in different time; 5. Thecognitive behavioral deficits post-MCC in rats may be related to the changes ofdopaminergic neurons and its nerve fiber post-injury.