A Study On The Interaction Between Serotoninergic And Cholinergic Neurons Following Multiple Cerebral Concussion In Rats

Objective:To establish the model of multiple cerebral concussion(MCC)in rats,observe the histological changes of serotoninergic and cholinergic neurons in the cerebral cortex,basal forebrain and brainstem reticular formation post-MCC.Our aim is to study the interaction of serotoninergic-cholinergic nerve in brain regions related to cognitive deficits,thus to understand the neurobiologic mechanisms of cognitive behavioral dysfunction after MCC in rats.Methods:Animal model of MCC in rats was developed using a metallic pendulum-striker concussive device.36 male Sprague-Dawley rats were randomly divided into six MCC groups(the group of 1d,2d,4d,8d,16d and 24d post-injury,n=6).One control group was used(n=6).Frozen sections were stained with anti-TPH(tryptophan hydroxylase)and anti-ChAT(choline acetyltransferase)antibodies immunochemistry S-P method.The number of ChAT-positive neurons in the basal forebrain were observed and counted using optical microscope.The expression of serotoninergic and cholinergic nerve in the different brain area was also detected and quantitated by image analysis system.Results:(1)Compared with the control group,Loss of cholinergic neurons was observed in brain areas mentioned-above post-MCC.The significant loss of cholinergic neurons was examined from the first day to the 24th day post-injury in the medial septal nucleus,the 2th day post-injury in the ventral nucleus of vertical limb diagonal band,the 1th day post-injury in the ventral nucleus of horizontal limb diagonal band and the basal nucleus of Meynert(P＜0.05 vs.control).Loss of cholinergic neurons was significantly diferently in the nucleus of lateral hypothalamic area on the 1th day post-injury.(2)The positive expression of cholinergic neurons decreased significantly in the medial septal nucleus of the 16th and 24 th day post-injury.The expression of cholinergic neurons in the nucleus of vertical limb diagonal band attenuated markedly on 4th day,then increased slightly,but dropped again on 24th day post-injury(P＜0.05 vs.control).The ventral nucleus of horizontal limb diagonal band dropped obviously on 24th day post-injury(P＜0.05 vs.control).The expression of cholinergic nucleus of Meynert attenuated markedly on 2th and 4th day,then increased slightly,then dropped again on 16th day post-injury (P＜0.05 vs.control).The expression of lateral hypothalamic area on 2th and 4th day post-injury dropped obviously(P＜0.05 vs.control).The expression of cholinergic neurons decreased significantly in ventral tegmental nucleus from the 2th day to 8th day post-injury and hypoglossal nucleus from the 1th day to 16th day post-injury.The expression of cholinergic neurons in the paramedan reticular nucleus attenuated markedly on 1th and 2 th day,then increased slightly,but dropped obviously again on 16th day post-injury(P＜0.05 vs.control).The expression of cholinergic neurons decreased significantly compared with the control group in the level of pontine nucleus from the 1st day to 16th day post-injury.The expression of the level of trapezoid body attenuated markedly on 1th and 2th day,then increased slightly,but dropped again on 8th and 16th day post-injury(P＜0.05 vs.control).The expression of the level of olivary nucleus was seriously lower than the control group on the 1th,2th,4th and 16th post-injury(P＜0.05 vs.control).(3)The expression of TPH-positive fiber up-regulated conspicuously post-MCC. Compared with the control group,the expression of TPH in MS in the 1st,2nd,4th,8th and 16th day post-injury revealed statistical differences(P＜0.05)and 4d group reached a peak.In the 2nd, 4th and 8th day groups in the VDB and in the 1d and 4d groups in the HDB increased obviously(P＜0.05).Compare with the control group,the TPH-positive fiber in the mfb rised dramatically in the 2nd,4th and 8th day post-injury.The expression in the frontal cortex reached peak in the 4th and 8th day and the Cortex of parietal lobe reached peak in the 8th day.Although the expression of TPH positive in the Meynert nucleus also rised,there were no sighificant differences.The expression of fiber in the LH and CPU in the 8th day are obviously higher than the control group(P＜0.05).An ascending tendency of TPH positive expression in the brainstem, including the dorsal raphe nucleus,median raphe nucleus,raphe magnus nucleus and raphe pallidus nucleus was observed.Compared with the control group,the TPH-positive neurons rised obviously in the 2nd,4th,8th and 16th day post-injury in the dorsal raphe nucleus,from the 2nd to 24th day post-injury in median raphe nucleus,the 1st,2nd and 4th day post-injury in raphe magnus nucleus and the 1st post-injury in raphe pallidus nucleus.(4)The expression of TPH-positive was ascending tendency in different brain areas,including MS,VDB,HDB,NBM, LH and BRF post-MeG.AT the same time,expression of ChAT-positive was decreasing after injury.Conclusions:1.The multiple cerebral concussion(MEG)model in rats was established successfully using a metallic pendulum-striker concussive device;2.Cognitive function deficits could related with the decreasing tendency of the cholinergic neurons and their expression was observed in the basal forebrain,brainstem reticular formation following MCC in rats;3.The expressed variation of TPH-postive opposited to the ChAT-positive in cortex,basal forebrain and brainstem reticular formation.There could be the interaction between serotoninergic and cholinergic neurons in different encephalic regions related to cognition and memory function. We speculate that serotonin increase could facilitate the acetylcholine release,which caused cognitive dysfunction in rats.