Melatonin Acts in the Brain to Mediate Seasonal Steroid Inhibition of Luteinizing Hormone Secretion in the White-Footed Mouse (Peromyscus leucopus)

Abstract

A melatonin-induced supersensitivity of the gonadotropin-secretory system to the negative feedback action of sex steroids is thought to be important to the timing of seasonal reproduction. However, little is knownconcerning this action of melatonin. In the present study the antigonadal action of melatonin in the anterior hypothalamus (AH) of the white-footed mouse, Peromyscus leucopus, was used to examine the neuroendocrine mechanism whereby melatonin enhances the sensitivity to sex steroid negative feedback. Mice received a melatonin-containing pellet in the AH for 14 weeks, at which time they were castrated and treated sc with a Silastic testosterone (T) capsule for 3 weeks. At the time of castration, weight of the testes and the concentration of T in the blood of mice with a melatonin pellet were greatly reduced compared to mice with a blank (melatonin-free) implant in the AH (P < 0.01). In mice treated with melatonin the physiological dose of T significantly reduced the concentrations of LH in blood and pituitary (P < 0.05). This dose of T, however, had little effect on LH in mice with a blank pellet in the AH. Melatonin in the AH markedly increased the content of gonadotropinreleasing hormone (GnRH) in the mediobasal hypothalamus (P < 0.05) in mice treated with T; however, there was little effect of melatonin and/or T in any other region examined. Melatonin and T had little effect on the contents of immunoreactive @-endorphin (B-EP) in the hypothalamus, but T alone increased the content of B-EP in the preoptic area. These results are evidence that melatonin and T act in concert to induce the reproductively-quiescent state by suppressing secretion of GnRH from the hypothalamus.

Melatonin Receptor Sites in the Syrian Hamster Brain and Pituitary. Localization and Characterization Using [125|]lodomelatonin*

“…Studies using intracerebral melatonin implants have however indicated that the photoperiodic effects of melatonin are mediated via a site in or near the hypothalamus (10)(11)(12). The results of the present study show discretely localized high-affinity melatonin receptors restricted to the hypothalamus and epithalamus of the brain and the purs tuberalis of the pituitary.…”

“…The localization of these low-affinity receptors within the brain, pituitary and other tissues is remarkably ubiquitous and, as yet, their physiological significance is unknown (4)(5)(6)(7)(8)(9). The widespread distribution found for the low-affinity melatonin receptor contrasts with reports that the photoperiodic effects of melatonin can only be induced by very localized intracerebral administration of the compound (10)(11)(12).…”

6-MBOA affects testis size, but not delayed-type hypersensitivity, in white-footed mice (Peromyscus leucopus)

“…We assessed effects of 6-MBOA on reproductive parameters and DTH in long-day breeding whitefooted mice. This species was chosen because individuals i) exhibit seasonal changes in immune activity and reproductive capacity (Johnston et al 1980b;Pyter et al 2005b), ii) some of these changes are mediated by melatonin (Johnston et al 1980a;Glass et al 1988), and iii) individuals consume a variety of foods in the wild, including plants (King 1968). Other species known to be sensitive reproductively to 6-MBOA have not been as well characterized.…”

Accelerated puberty and late-onset hypothalamic hypogonadism in female transgenic skinny mice overexpressing leptin

“…Tissues were homogenized in 1 N acetic acid and 20 mM hydrochloride and were eluted through a SepPak C18 cartridge (Waters Associates, Milford, Massachusetts, USA) (30). Blood was sampled from the retroorbital sinus of mice under slight anesthesia with ether.…”