SYNAPTIC STRIPPING IN THE HUMAN FACIAL NUCLEUS

An autopsy case of severe peripheral facial nerve paresis with disconn ection of synapses from facial motor neurons is reported. A 77-year-ol d man presented with left-sided otitis media and subsequent developmen t of facial nerve paresis. Three months later, the patient died of an acute gastrointestinal bleeding from a chronic duodenal ulcer. Gross i nspection of the brain revealed non-stenosing arteriosclerotic vascula r changes and a single small cystic lesion in the right putamen. Micro scopically, marked chromatolytic changes were observed in the left fac ial nucleus. Immunocytochemistry for synaptophysin revealed a marked l oss of afferent synaptic contacts from somatic and stem dendritic surf ace membranes of all chromatolytic motor neurons. Wrapping of a number of neurons by newly formed glial fibrillary acidic protein-positive a strocytic cell processes could be detected in the regenerating facial motor nucleus. In addition, expression of HLA-DR was increased on a sm all number of microglia and perivascular cells. These changes were abs ent from the contralateral, normal-appearing facial nucleus. To our kn owledge, this case provides the first evidence for disconnection of sy napses following peripheral nerve lesioning in humans. Occurrence of s ynaptic stripping is likely to explain nuclear hyperexcitability and f ailure of recovery of complex fine motor movements that are commonly o bserved following peripheral injury to the facial nerve.