Endocrinology, Vol 115, 2445-2452, Copyright © 1984 by Endocrine Society

ARTICLES

An increase in single unit activity of the medial basal hypothalamus occurs during the progesterone-induced luteinizing hormone surge in the female rhesus monkey

RR Yeoman and E Terasawa

Accumulated evidence from our laboratory indicates that a positive feedback effect of progesterone (P) occurs at the hypothalamic level. The present study in female rhesus monkeys examined the effects of P on single unit activity of neurons in the hypothalamus and on LH release. Single unit activity was recorded by inserting a flexible stainless steel electrode into the hypothalamus of the monkey, which was restrained in a chair under light ketamine sedation. The firing rate of the single unit activity of the ventral hypothalamus (1.5 +/- 0.2 spikes/sec; n = 57) in ovariectomized estrogen-primed monkeys was slow and was slower in the ventral hypothalamus than in the dorsal hypothalamus (6.2 +/- 0.8 spikes/sec; n = 80). P injection resulted in a dramatic increase in unit activity of the ventral hypothalamus (4.7 +/- 0.6 spikes/sec; n = 111), but not of the dorsal hypothalamus (5.3 +/- 0.7 spikes/sec; n = 72), and induced a concomitant release of LH. Both increases in circulating LH and unit activity of the ventral hypothalamus were significantly correlated over time (P less than 0.02). In contrast, oil injections induced neither change. Therefore, in the rhesus monkey, P seems to activate neural substrates in the ventral hypothalamus to promote the release of LHRH and, subsequently, LH.

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