Effects of gonadotropin releasing hormone and estradiol on c-fos expression in the rat hippocampus.
The effects of ovariectomy, estradiol, and gonadotropin releasing hormone (GnRH) on the protein synthetic activity of hippocampal neurons were studied with immunohistochemistry for the proto-oncogene c-fos. Ovariectomy caused a reduction in the number of c-fos-positive neurons to 16% in area CA(1) and to 25% in area CA(3) when compared to that in the intact control animal. The dentate gyrus was only slightly affected. The decline in the number of c-fos-immunoreactive neurons in the Ammon's horn was partially reversed by a single intravenous injection of estradiol which resulted in the expression of c-fos in 71% of the neurons in area CA(1) and 74% in CA(3) when compared to the numbers of positive cells in the control animals. Similarly, intracerebroventricular injections of 10 muM GnRH caused an increase in the number of c-fos-positive cells to 68% in area CA(1) and to 52% in area CA(3) compared to that in the control animals. The induction of c-fos synthesis after estradiol and GnRH was transient and reached a maximum after 1 to 2 h before it declined to pretreatment levels after 8 h. The results suggest that both estradiol and GnRH exert specific effects on protein synthesis in certain neurons of the hippocampus and that these effects of the hormones are, at least in part, mediated by c-fos.
Jennes
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Department of Anatomy, Wright State University Schoot of Medicine, Dayton, Ohio 45435, USA.