LOCALIZATION OF NEUROTROPHIN-3-LIKE IMMUNOREACTIVITY IN THE RAT COCHLEAR NUCLEUS

Immunohistochemistry as well as immunohistofluorescence were used to i nvestigate the distribution of the neurotrophin-3 (NT3) in the adult r at cochlear nucleus. We found a widespread distribution of NT3 immunol abeled neurons throughout the three divisions of this nucleus. NT3-lik e immunoreactivity was clearly population-specific, with some cell gro ups heavily (various small neurons and granule cells) or moderately (l arge neurons of the ventral cochlear nucleus) stained, while others re mained negative (a major fraction of medium and large neurons of the d orsal cochlear nucleus). Double-labeling experiments were performed us ing antibody against the glial fibrillary acid protein, a classic mark er for mature astrocytes. This colocalization study revealed that NT3 immunoreactivity was also present in a subpopulation of astrocytes, pa rticularly in the glia limitans and their projections. Numerous small cells also colocalized NT3 together with the glial marker in the granu le cell domain and in the molecular cell layer of the dorsal cochlear nucleus. These results suggest that NT3 may exist in widespread popula tions of adult cochlear nucleus neurons as well as in glial cells. Thi s abundant distribution of NT3-like immunoreactivity implies that this neurotrophin may have an important role in the continued maintenance of mature cochlear nucleus and makes it an attractive candidate for pl aying a role in regulation or stabilization of neuronal circuits in th is nucleus. (C) 1998 Wiley-Liss, Inc.