DISTRIBUTION OF GLIAL FIBRILLARY ACIDIC PROTEIN (GFAP) IN THE COCHLEAR NUCLEUS OF ADULT AND AGED RATS

The age-related change in glial fibrillary acidic protein (GFAP) immmu noreactivity was analyzed in young (3 months) and old (24 months) adul t rat cochlear nuclei (CN). Quantitative analyses show a significant i ncrease with age, in the number of GFAP positive astrocytes and proces ses in the old adult when compared with the young adult rat. There was also a differential distribution of GFAP immunoreactivity in the youn g adult CN where it predominates in the granular cell region, whereas in old rats, the GFAP immunoreactivity distribution was homogeneous in all parts of the nucleus. There was no change in the total number of neurons between these two stages in any part of the nucleus except for the antero-ventral CN, where a decrease in neuronal number was observ ed in the aged rats. The increase in GFAP immunoreactivity was related to an increase of both GFAP positive astrocyte number and processes. The increase of GFAP positive astrocytes may be due either to an alter ation of auditory nerve fibers, changing the trophic interactions with post-synaptic cells, or to intrinsic alterations of CN neurons and lo cal circuits reflecting aging of the CN.