Deafness induced cell size changes in rostral AVCN of the guinea pig

The right cochleae of 250-350 g guinea pigs were lesioned by topical administration of neomycin in the middle ear cavity. Eight weeks after the lesion, the cochleae and cochlear nuclei were analyzed. Cochlear hair cell loss was assessed, and cell areas of spherical bushy cells in the rostral anteroventral cochlear nucleus (AVCN) were compared between the lesioned and normal hearing sides for each animal. In five animals with both inner and outer hair cell loss in the lesioned cochlea, the average area of neuronal somata in the rostral AVCN in the lesioned side was 22% smaller than the average area of these cells in the normal hearing side. In two animals with outer hair cell loss but inner hair cells remaining, there was no difference in cell size between the lesioned and non-lesioned AVCN. These results provide evidence that there is significant shrinkage in AVCN cell size in the mature mammal after hearing loss associated with inner hair cell loss.