Effect of Castration and Steroid Replacement on Immunoreactive Gonadotropin-Releasing Hormone in the Hypothalamus and Preoptic Area*

Abstract

The effect of castration alone or castration and subsequent administration of testosterone propionate to males or estradiol benzoate (EB) to females on the content and distribution of gonadotropin-releasing hormone (GnRH) in the median eminence and organum vasculosum of the lamina terminalis (OVLT) was studied in rats and mice. Specimens were labeled with the peroxidase-antiperoxidase method of imrnunocytochemistry using an antiserum to synthetic GnRH conjugated to bovine serum albumin. Five weeks after castration, the content of immunoreactive GnRH in the median eminence of rats and mice of both sexes was markedly depleted. The reduction in GnRH stores was most obvious in axons and nerve endings in the middle and caudal regions of the median eminence. Replacement therapy with gonadal steroids reversed the castrationinduced reduction in GnRH content. EB failed to completely restore GnRH in the median eminence of ovariectomized mice to control levels, but otherwise there were no differences in the effectiveness of replacement therapy with respect to sex or species. None of the experimental treatments had any effect on the distribution or content of GnRH associated with the OVLT.These observations suggest that: 1) after removal of the negative feedback action of gonadal steroids, there is an increased level of secretory activity by GnRH-producing neurons ending in the median eminence; 2) testosterone propionate in orchidectomized males and EB in ovariectomized females return the elevated secretory rate of such neurons to levels similar to those in intact control animals; and 3) GnRH neurons ending in the OVLT may not be directly involved in the negative feedback control of gonadotropin secretion. {Endocrinology 106: 1442, 1980)

In vivo Activity of the LHRH Pulse Generator as Determined with Push-Pull Perfusion of the Anterior Pituitary Gland of Unrestrained Intact and Castrate Male Rats

“…Therefore, one effect of castration in male rats is a decrease in the amplitude of the LHRH signal, which would suggest that there is less LHRH available for release within the LHRH neurons of castrate animals. This finding is supported by numerous studies de monstrating reduced LHRH concentration by radioimmu noassay and immunocytochemistry within the hypothala mus of castrate versus intact male rats and restoration of hypothalamic LHRH concentration following testosterone administration to castrate males [1, [9][10][11][12][13]16,17], Due to this attenuation in the strength of the LHRH signal, no determi nation of frequency could be performed from sampling MBH neurons: however, in the present experiment a signif icant increase in frequency of the LHRH signals reaching the anterior pituitary was measured in castrate compared to intact male rats. Therefore, one can argue that the LHRH from MBH neurons following castration has undergone two major op posing changes -an apparent increase in frequency of LHRH release and a decrease in the amplitude of the LHRH signal.…”

Increase of Gonadotropin-Releasing Hormone Concentration in Pituitary Portal Blood after Substance P Administration in Male Rats

“…At least part of this inhibitory action of gonadal steroids takes place throughout the hypothalamic regulation of GnRH release. Gonadectomy decreased the GnRH content in the medial basal hypothalamus (MBH) [21, 41, 42, 43], increased the GnRH concentration in pituitary portal blood [44], and raised the GnRH pulse amplitude reaching the anterior pituitary gland [45]. The inhibitory effect of gonadal steroids was observed in our experiments as well.…”

Immunocytochemical Localization of Luteinizing Hormone-Releasing Hormone in Male and Female Rat Brains

“…The smaller size of the terminals in MCG relative to the OVLT and ME illustrates the less er density of fibers in this terminal field. Since gonadectomy in creases the rate of release of LHRH from terminals in the median eminence [II,34] and decreases the amount of immunoreactive LHRH in fibers in the median eminence as determined in this and other studies [2,8,13,19], the same inverse relationship between LHRH content of terminal fields and presumed release rate has been assumed for the other two terminal fields analyzed. E2 = Es tradiol: slashed symbols for male and female indicate a gonadectomized condition.…”