Astrocytes immunoreactive for glial fibrillary acidic protein (GFAP) are increased in the mediobasal hypothalamus in hypogonadal (hpg) mice.

The actions of gonadal steroids on neuronal activity in the hypothalamus are well documented, but the effects on glial cells are less clear. Here we have investigated glial cell activity in normal and hypogonadal (hpg) mice, in which gonadal development is arrested postnatally. Astrocytes immunoreactive for filial fibrillary acidic protein (GFAP) were examined throughout the hypothalamus, using immunohistochemical techniques. The number of GFAP immunoreactive (GFAP-IR) cells was 25-fold higher in the mediobasal hypothalamus of hpg compared with normal mice, but there was no evidence of a sex difference in either hpg or normal mice. Castration of normal mice on the fifth postnatal day did not result in any hypothalamic astrocytosis. Treatment of adult hpg mice with estradiol-17beta, testosterone, or 5alpha-dihydrotestosterone significantly reduced the number of GFAP-positive cells in the periventricular area, but they were still 10-20 times higher in number than in normal mice. In hpg mice treated from birth with testosterone propionate, the staining pattern was still markedly abnormal. Ependymal tanycytes, which also express GFAP-IR, were significantly shorter in male hpg compared with normal male mice. These results suggest that the GFAP-IR cells in the hypothalamus are partially affected by sex steroids, but that other factors, possibly related to the congenital defect in hpg mice, are also involved.