Influence of gonadectomy and steroid hormone replacement therapy on the gonadotropin-releasing hormone neuronal system in the anterior preoptic area of the frog (Rana esculenta) brain.

Effects of gonadectomy and sex steroid replacement therapy were studied on the anterior preoptic area-located GnRH-immunoreactive neurons in males and females of the frog, Rana esculenta. Removal of gonads caused a drastic reduction in the immunostaining as well as in the number of GnRH neurons in the anterior preoptic area of the brain in both sexes. Replacement therapy with estradiol-17 beta, testosterone, and 5 alpha-dihydrotestosterone, given alone or in combination, enhanced the somal accumulation of immunoreactive material in GnRH neurons and also their number. These effects, however, varied to some extent from steroid to steroid, a combination of testosterone and 5 alpha-dihydrotestosterone being most effective in gonadectomized males, whereas that of estradiol-17 beta and testosterone was most effective in gonadectomized females. The present data are the first to demonstrate that androgen and estrogen can influence the immunoreactive GnRH neurons in the anterior preoptic area of the amphibian brain.