The Arcuate Nucleus and the Control of Gonadotropin and Prolactin Secretion in the Female Rhesus Monkey (Macaca mulatta)*

Abstract

Attempts were made to destroy selectively the arcuate nucleus with radiofrequency current in adult female rhesus monkeys as a first step in identifying the areas of the mediobasal hypothalamus (MBH) that are responsible for the neural control of gonadotropin secretion in this species. Extensive or complete destruction of the arcuate region was produced in three animals and in two of these the lesion was confined primarily to the arcuate region and the dorsal aspect of the posterior median eminence. These lesions resulted in the cessation of LH and FSH secretion and blocked the positive feedback action of estradiol on gonadotropin release but did not appear to influence grossly basal thyroid and adrenocortical function, or to abolish GH discharge in response to insulin hypoglycemia. Adenohypophysial infarcts were not observed and exogenous LHRH and TRH induced marked discharges of the appropriate anterior pituitary hormones. In two additional animals with large hypothalamic lesions, destruction of the arcuate region was incomplete. In this group only partial inhibition of gonadotropin secretion was observed. LH and FSH secretion did not appear to be influenced in one animal bearing a large MBH lesion that entirely spared the arcuate region. Although serum prolactin remained at pre-lesion control levels after placement of the two relatively discrete lesions confined to the arcuate region, unambiguous increases in the secretion of this hormone were observed when the area of destruction encompassed tissue anterior and/or dorsal to the arcuate region. These observations suggest that the arcuate region is the primary structure mediating the hypothalamic control of gonadotropin secretion in the rhesus monkey. They also suggest that, in this species, the regions of the MBH involved with the regulation of gonadotropin release and those which control prolactin secretion are anatomically distinct.

Generation and synchronization of gonadotropin-releasing hormone (GnRH) pulses: intrinsic properties of the GT1-1 GnRH neuronal cell line.

“…A synchronous and intermittent discharge of multiple GnRH neurons (6) is required for episodic increases in the concentration of GnRH in hypophyseal portal blood. This intermittent secretion is the result ofan oscillator, the so-called GnRH pulse generator, localized in the mediobasal hypothalamic-anterior hypothalamic-preoptic area (7)(8)(9). In both the rat (7) and monkey (8) surgical deafferentation of the mediobasal hypothalamus does not interfere with GnRH pulses.…”

“…In both the rat (7) and monkey (8) surgical deafferentation of the mediobasal hypothalamus does not interfere with GnRH pulses. Lesions of the arcuate nuclei in primates, which destroy many of the GnRH neurons, abolish the ultradian pattern of release, and neural activity within this region has been correlated with the pulses (6,9). Furthermore, superfused hypothalamic fragments in vitro release GnRH in a pulsatile fashion (10).…”

Sex Hormones and Infertility

“…Gonadotropin-releasing hormone (GnRH) is a decapeptide pulsatile produced by neurons with cell bodies primarily in the arcuate nucleus of the hypothalamus (1). Embryologically, these neurons originate from the olfactory area and then migrate to their adult locations (2).…”

Neuroendocrine control of ovarian function in the primate

“…Their axons are directed towards the median eminence and terminate in the vicinity of the long portal vessels, which descend along the pituitary stalk to irrigate the anterior pituitary gland. This Gn-RH pathway appears to be a major one in the monkey, in so far as the control of gonadotrophin secretion is concerned ; lesion of the arcuate nucleus results in a rapid decrease in the circulating concentrations of both LH and FSH (Plant et al, 1978a). As in the rodent, another Gn-RH pathway originates from the anterior hypothalamic-preoptic area, its fibres terminating in the organum vasculosum laminae terminalis (OVLT) or extending along the surface of the optic nerve to the median eminence.…”