Influence of gonadal steroids on the glial fibrillary acidic protein-immunoreactive astrocyte population in young rat hippocampus

It is known that expression of glial fibrillary acidic protein (GFAP) as an astrocyte-specific marker can be regulated by levels of circulating gonadal steroids during postnatal development. In addition, astrocytes play an important role in the physiology of the hippocampus, a brain region considered sexually dimorphic at the neuronal level in rodents. To evaluate the contribution of glial cells to gender-related differences in the hippocampus, we estimated the number of GFAP-immunoreactive (GFAP-IR) astrocytes in the hippocampus (CA1 and CA3 areas, dorsal and ventral regions) of male and female rats aged 30 days. Groups of 30-day-old masculinized females (TP-females; injected with testosterone propionate at birth) and feminized males (FLU-males, castrated and treated with flutamide, an androgen receptor antagonist) were included to assess the effects of gonadal hormones on these hippocampal astrocytes. Using the optical fractionator method, the total number of GFAP-IR cells found in CA1 and CA3 areas was significantly higher in males compared to that in age-matched females. This numerical pattern was reversed in TP-females and FLU-males in both hippocampal areas. In addition, more GFAP-IR cells were found in dorsal hippocampus than in the ventral region in the CA1 area from all experimental groups, whereas this result was found in the CA3 area from males and TP-females. Our results suggest an essential contribution of gonadal hormones to gender differences found in the astrocyte population of the rat hippocampus during development. (C) 2004 Wiley-Liss, Inc.