DEVELOPMENTAL DISTRIBUTION OF ASTROCYTIC PROTEINS IN THE RAT COCHLEARNUCLEUS

To investigate the developmental distribution of cochlear nucleus (CN) astrocytes, we used immunocytochemical localization of glial fibrilla ry acidic protein (GFAP) and S100 beta in rats at 0, 5, 10, 15, 21, 30 postnatal days plus the adult. Differential developmental trends were observed for both proteins. The spatial distribution showed a progres sive increase of the number of GFAP-immunoreactive (GFAP-IR) astrocyte s during development. GFAP positive cells occurred first in the granul e cell domain of the ventral CN and in the molecular cell layer of the dorsal CN, then followed an outside to inside pattern of progression. The GFAP-IR reached an adult distribution 1 month after birth. By con trast with GFAP, the apparition of S100 beta-immunoreactivity (S100 be ta-IR) was abrupt (between 0 and 5 days) followed by a rapid stabiliza tion of density and distribution of IR cells (between 15 and 21 days). The developmental distribution of S100 beta-IR cells occurred from th e posterodorsal region and progressed toward a rostroventral direction . With contrast to GFAP-IR astrocytes, S100 beta-positive cells were m ainly restricted to the central part of the CN, while only few IR astr ocytes were observed in the granule cell domain of the ventral CN or i n the molecular cell layer of the dorsal CN. This differential distrib ution suggests that both antigens were expressed by two different cell populations at least, it is obvious during the first postnatal week. The gradual expression of GFAP and S100 beta is interpreted as reflect ing the time course of astrocytic maturation. These data suggest that the maturation of CN astrocytes may be linked to the final maturation of CN neurons. (C) 1998 Elsevier Science B.V.