AGE-DEPENDENT EFFECTS OF THE ONSET OF A CONDUCTIVE HEARING-LOSS ON THE VOLUME OF THE COCHLEAR NUCLEUS SUBDIVISIONS AND THE EXPRESSION OF C-FOS IN THE MONGOLIAN GERBIL (MERIONES-UNGUICULATUS)

A monaural conductive hearing loss was induced by interrupting the cha in of the middle ear ossicles on the right side in gerbils of four dif ferent age groups (P12-14, P20-21, P42 and P84). The volumes of the co chlear nucleus subdivisions and the number of cells that expressed imm unoreactivity for c-fos after noise stimulation were determined on the left and right side in the deprived animals, and in undeprived contro l animals when they reached the age of 6 months. The anteroventral coc hlear nucleus on the deprived side was reduced in volume when the depr ivation started before the age of 3 months. The other cochlear nucleus subdivisions showed no systematic age-dependent reductions. The expre ssion of c-fos in the dorsal cochlear nucleus appeared more resistant to a hearing loss, with deprivation being more effective in younger an imals. c-fos expression was also dramatically reduced in the ventral c ochlear nucleus, regardless of age at the onset of hearing loss.