Glial fibrillary acidic protein (GFAP)-immunoreactivity is reduced by castration in the interpeduncular nucleus of male rats

The interpeduncular nucleus of adult male rats was investigated for glial fibrillary acidic protein immunoreactivity. In intact animals the nucleus had an outstandingly intense immunostaining, particularly at its periphery, including the rostral, lateral, dorsomedial and dorsolateral subnuclei where, in addition to neuropil astrocytes, a substantial amount of perivascualr glia was found. Four weeks after castration, immunostaining decreased markedly in the core region of the nucleus corresponding to the caudal and medial subnuclei, and to a much lesser extent at the periphery. The immunoreactivity in pericapillary astrocytes proved to be insensitive to castration. Testosterone, if administered after castration prevented or restituted the loss of immunoreactivity. Beyond 4 months after castration, the effect of testosterone gradually declined. It is concluded that testosterone stimulates the expression of glial fibrillary acidic protein immunoreactivity in the interpeduncular nucleus. Our findings support the argument that gonadal steroids can influence astrocytes also in non-endocrine areas of the brain.