The Study On Functional Reorganization And Structural Plasticity Of Oralfacial Area And Hegu Point Area In Motor Cortex After Deprivation Of Facial Nerves

ObjectiveTo observe the functional reorganization and structural plasticity of Hegu point area and oralfacial area in the primary motor cortex of rhesus macaques and rats without facial nerve,by intracortical electrical stimulation and neural in order to explore the biological mechanism of specific relationship between oralfacial area and Hegu point area.MethodsFirstly,we try to figure out the characteristics of high molecular weight biotinylated dextran amine(BDA)by means of the presence of BDA labeling in the thalamocortical prejected axons and corticothalamic projected cell somas.We select 17 rats,and inject BDA in ventral posteromedial nucleus.After histology experiment,we focus on morphology of neurons and fibers on cortex.In addition,in order to find out the optimal survival times of animals for obtaining the high quality on anterogradely labeled axon and retrogradely labeled dendrites of neurons.Secondly,we select 10 rats.Five rats' facial nerve trunks are transected.20-30 days later,we map the M1 representation pattern in normal rats and rats with facial nerve transected by intracortical electrical stimulation method.After stimulation,we inject BDA to face area of motor cortex,and CTB to hand area of motor cortex.10 days later,we study the morphological changes.Pyramidal cell somas,dendrites,axons,the projection between ipsilateral cortex and contralateral cortex and the projection between primary somatosensory cortex(S1)and primary motor cortex(Ml)are main observation targets.We compare the densities of varicosities between two groups.Finally,based on the above two studies,we begin to carry out the experiment in rhesus macaques.One rhesus macaque's facial nerve trunk has been transected for one year;one rhesus macaque's facial nerve trunk has been transected for one month.Two rhesus macaques are normal.We map the M1 representation pattern in normal rhesus macaques and rhesus macaques with facial nerve transected by intracortical electrical stimulation method.After stimulation,we inject BDA to face area of motor cortex,and CTB to Hegu area of motor cortex.7-10 days later,we study the morphological changes.Neuron somas,dendrites,axons in cervical spine,facial nucleus,face area of M1 are main targets.Besides,we compare the morphological changes of astrocytes and neurons between ipislateral side and contralateral side of facial nucleus from a rhesus macaques whose facial nerve trunk has been transected for one month.Results1.High molecular weight biotinylated dextran amine can be effectively used for tracing both anterogradely and retrogradely.High quality of the labeled axon arbors and dendrites of neurons with biotinylated dextran amine depends on the optimal survival times of animals after the injection.And the optimal survival time is 10 days in thalamocortical and corticothalamic pathways in rat.Streptavidin-Alexa Fluor 594 staining method presents detailed neural labeling with BDA and is especially suitable for viewing under confocal laser scanning microscopy,which is better than standard ABC staining method.2.There is no statistical difference of the number of record sites between two groups(P>0.05).There is statistical difference of hand sides'distribution in X axisof the representative maps between two groups(P<0.05).In transected rats,there is an enlargement of the hand representation in motor cortex and it invade the presumed region of the face,which indicates functional reorganization has taken place in the two areas.There is statistical difference of densties of varicosities of axons in oralfacial area between two groups(P<0.05).The density of varicosities of transected rats reduces,which means structural reorganization has taken place.There are reciprocal connections between ipsilateral cortex and contralateral cortex and the projection between S1 and M1.3.In transected macaques,there are an enlargement of the Hegu point representation in motor cortex and it invade the presumed region of the face,which indicates functional reorganization has taken place in the two areas.After transaction of facial nerve trunk one month,functional reorganization exists in M1 of macaque.The density of varicosities of transected macaque reduces,which suggests structural reorganization has taken place.The involving side of facial nucleus of transected macaque has degenerative changes.ConclusionAfter deprivation of facial nerve trunk,Hegu point area in motor cortex invase the oralfacial area,which means functional reorganization.At the same time,reduction of the density of varicosities may be the structural basis for functional reorganization,which may be one of the biological mechanisms of specific relationship between oralfacial area and Hegu point area.