GONADAL-HORMONES DOWN-REGULATE REACTIVE GLIOSIS AND ASTROCYTE PROLIFERATION AFTER A PENETRATING BRAIN INJURY

Astrocytes are a target for gonadal steroids in the normal brain. The putative modulation by gonadal hormones of the astrocytic reaction to brain injury was assessed in this study. Male and female adult Wistar albino rats were gonadectomized and, one month later, their brains wer e lesioned by a longitudinal incision crossing the parietal cerebral c ortex, the CA1 field of the dorsal hippocampus and the dentate gyrus. Males were injected either with testosterone (20 mug/rat) or vehicle i mmediately after surgery. Females were injected either with 17beta est radiol (250 mug/rat), progesterone (500 mug/rat) or vehicle. Hormonal injections were repeated 24 and 48 h after brain injury. All animals r eceived injections of 5'-bromodeoxyuridine (BrdU) to label proliferati ng cells. Histological sections from the brain of animals killed 72 h after surgery were used for the double immunohistochemical localizatio n of BrdU and glial fibrillary acidic protein (GFAP). The number of GF AP-immunoreactive astrocytes and the number of double labelled astrocy tes (GFAP + BrdU) were recorded as a function of the distance to the l esion site in the parietal cerebral cortex, the CA1 field of the hippo campus and the dentate gyrus. Testosterone, estradiol and progesterone treatments resulted in a significant decrease in the number of GFAP-i mmunolabelled reactive astrocytes in the vicinity of the wound. The nu mber of double labelled cells and the labelling index (proportion of G FAP-immunoreactive astrocytes labelled with BrdU) varied according to the cerebral area, the distance to the wound and the sex of the animal s, and were significantly decreased by gonadal steroids in all the are as examined. These results indicate that gonadal hormones may decrease gliosis and astrocyte proliferation after a penetrating brain injury.