Progestin receptors in substance P‐immunoreactive neurons in the hypothalamus of male guinea pigs after behaviorally effective estradiol pulse treatment

Abstract

Pulsatile administration of estradiol effectively primes orchidectomized (ORCH) male guinea pigs to display progesterone-facilitated lordosis. In contrast, a single injection of estradiol benzoate (EB) is not behaviorally effective. In ovariectomized female guinea pigs, estradiol pulses induce progestin receptors selectively in substance P neurons in the ventrolateral hypothalamus (VLH), a site at which estradiol primes females to respond behaviorally to progesterone. To test the hypothesis that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P neurons in the VLH in males, ORCH animals received a single injection of EB 40 h before, or two pulses of estradiol-17 beta, 39 and 11 h before perfusion. Colchicine was administered intracerebroventricularly prior to perfusion. The only difference found between the two estradiol treatment groups was a higher number of progestin receptor-immunoreactive (PR-IR) cells in the rostral VLH of estradiol pulse-treated males. There were no significant differences in the number of PR-IR cells in the mid- or caudal VLH, nor in the number of substance P-immunoreactive (SP-IR) neurons in the VLH/ventromedial hypothalamus (VMH) of animals receiving the two estradiol treatments. Furthermore, the percentage of PR-IR cells in the VLH also immunoreactive for SP did not differ between the estradiol pulse- (22%-25%) and the EB-injected animals (22%-32%). These data do not support the hypothesis that administration of behaviorally effective estradiol pulses, as compared to behaviorally ineffective EB injections, induce progestin receptors selectively in substance P neurons in the VLH of male guinea pigs.

Colocalization of Progesterone Receptor and Somatostatin Immunoreactivities in the Hypothalamus of the Male and Female Guinea Pig

“…The present study shows that SOM is another neuro peptide in the VL whose synthesis may be regulated by progesterone since further immunocytochemical studies have demonstrated the presence of neurotensin [19], sub stance P [21,22] and opiates [23] in the PR-IR neurons of the guinea pig VL. At present we do not know whether these neuropeptides coexist within the same neurons con taining PR or represent separate populations.…”

“…We found that only a very small fraction of the population of SOM-IR neurons in the Ar possess PR and that neither male nor female preoptic and hypothalamic periventricular SOM Progesterone Receptor in Hypothalamic Somatostatin Neurons neurons contain PR. As such, SOM can now be added to the list of neuropeptides found in PR-IR neurons in the VL of the guinea pig such as neurotensin [ 19] substance P [21,22] and enkephalin [23],…”

Projections from Ventrolateral Hypothalamic Neurons Containing Progestin Receptor‐ and Substance P‐Immunoreactivity to Specific Forebrain and Midbrain Areas in Female Guinea Pigs

“…However, many of these steroid sensitive cells in guinea pigs clearly lie outside of the cytoarchitecturally defined ventromedial nucleus. In both rats and guinea pigs, many of the estrogen and progestin receptor-containing neurons in this region, also contain substance P (2,5,6,7). This finding suggests that substance P may be used as a neurotransmitter by these neurons and that its release may be influenced by estradiol and progesterone.…”

Down‐Regulation of Estrogen Receptor Immunoreactivity by 17β‐estradiol in the Guinea Pig Forebrain

“…Female guinea pigs were exposed to a single injection of E,-17p at a dose similar to that used for injections in pulsatile paradigms which resulted in sex behavior (17)(18)(19)(20). Immunostaining for estrogen receptors in the estrogen receptor-rich areas of the midportion of ventrolateral hypothalamus ( VLH ), caudal portions of the arcuate hypothalamic nucleus (Arc), medial preoptic nucleus (MPO), and the medial amygdaloid nucleus ( M e ) was examined at various time points following the injection.…”