EVIDENCE FOR REACTIVE ASTROCYTES IN RAT VESTIBULAR AND COCHLEAR NUCLEI FOLLOWING UNILATERAL INNER-EAR LESION

We investigated whether unilateral removal of the labyrinthine and coc hlear receptors induces a macroglial reaction in rat vestibular and co chlear nuclei using vimentin and glial fibrillary acidic protein (GFAP ) immunochemical markers. Antibody binding was visualized using the av idin-biotin method and 3,3'-diaminobenzidine as the peroxidase substra te. In addition, double-labelling experiments were performed using spe cific secondary fluorescent antibodies. Potentially degenerating axon terminals were also studied using a silver impregnation method. In nor mal adult rats, vimentin was found only in ependymal cells, tanicytes around the fourth ventricle, endothelial cells in the blood vessels an d Bergmann glia in the molecular layer of the cerebellum. In lesioned rats, all deafferented vestibular and ventral cochlear nuclei showed s trong vimentin immunoreactivity. Furthermore, double-labelling experim ents demonstrated that these vimentin-positive cells were also GFAP-po sitive. The reaction became evident on the second day after the lesion , was intense for 3-8 days and then declined until day 21. No vimentin immunoreactivity could be detected at the level of the ipsilateral do rsal cochlear nucleus. Therefore, unilateral inner ear lesion induced an astroglial reaction within the deafferented vestibular and cochlear nuclei. The decrease in the resting discharge of the primary vestibul ar afferents and/or in the deafferented central vestibular neurons may induce the glial reaction in the vestibular complex, whereas both deg eneration and silence of the cochlear nerve and central cochlear neuro ns are most probably responsible for the cochlear vimentin-immunoreact ive staining. The role of the reactive astrocytes in the vestibular co mpensation process remains to be determined.