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Titolo:
EVIDENCE THAT THE MEDIOBASAL HYPOTHALAMUS IS THE PRIMARY SITE OF ACTION OF ESTRADIOL IN INDUCING THE PREOVULATORY GONADOTROPIN-RELEASING-HORMONE SURGE IN THE EWE
Autore:
CARATY A; FABRENYS C; DELALEU B; LOCATELLI A; BRUNEAU G; KARSCH FJ; HERBISON A;
Indirizzi:
INRA,STN PHYSIOL REPROD MAMMIFERES DOMEST F-37380 NOUZILLY FRANCE UNIV MICHIGAN,REPROD SCI PROGRAM ANN ARBOR MI 48109 BABRAHAM INST,NEUROENDOCRINOL LAB CAMBRIDGE CB2 4AT ENGLAND
Titolo Testata:
Endocrinology
fascicolo: 4, volume: 139, anno: 1998,
pagine: 1752 - 1760
SICI:
0013-7227(1998)139:4<1752:ETTMHI>2.0.ZU;2-M
Fonte:
ISI
Lingua:
ENG
Soggetto:
RECEPTOR-IMMUNOREACTIVE CELLS; LUTEINIZING-HORMONE; PREOPTIC AREA; TYROSINE-HYDROXYLASE; ESTROGEN-RECEPTORS; OVARIECTOMIZED EWE; GONADAL-STEROIDS; MEDIAN-EMINENCE; ANESTROUS EWES; SECRETION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
48
Recensione:
Indirizzi per estratti:
Citazione:
A. Caraty et al., "EVIDENCE THAT THE MEDIOBASAL HYPOTHALAMUS IS THE PRIMARY SITE OF ACTION OF ESTRADIOL IN INDUCING THE PREOVULATORY GONADOTROPIN-RELEASING-HORMONE SURGE IN THE EWE", Endocrinology, 139(4), 1998, pp. 1752-1760

Abstract

Although a neural site of action for estradiol in inducing a LH surgevia a surge of GnRH is now well established in sheep, the precise target(s) for estrogen within the brain is unknown. To address this issue, two experiments were conducted during the breeding season using an artificial model of the follicular phase. In the first experiment, bilateral 17 beta-estradiol microimplants were positioned in either the medial preoptic area (MPOA) or the mediobasal hypothalamus (MBH), and LHsecretion was monitored. An initial negative feedback inhibition of LH secretion was observed in ewes that had estradiol microimplants located in the MPOA (6 of 6 ewes) or caudal MBH in the vicinity of the arcuate nucleus (4 of 4). In contrast, a normal LH surge was only found in animals bearing estradiol microimplants in the MBH (5 of 10). Detailed analysis of estradiol microimplant location with respect to the estrogen receptor-alpha-immunoreactive cells of the hypothalamus revealedthat 4 of the 5 ewes exhibiting a LH surge had microimplants located bilaterally within or adjacent to the area of estrogen receptor-expressing cells of the ventromedial nucleus. Two of these ewes exhibited a LH surge without showing any form of estrogen negative feedback. In the second experiment, we used the technique of hypophyseal portal bloodcollection to monitor GnRH secretion directly at the time of the LH surge induced by estradiol delivered either centrally or peripherally. Central estradiol implants induced the GnRH surge. The duration and mean plasma concentration of GnRH during the surge were not different between animals given peripheral or central MBH estradiol implants. Cholesterol-filled MBH microimplants did not evoke a GnRH surge. We conclude that the ventromedial nucleus is the primary site of action for estradiol in stimulating the preovulatory GnRH surge of the ewe, whereas the MPOA and possibly the caudal MBH are sites at which estrogen can act to inhibit LH secretion. These data provide evidence for the sites within the ovine hypothalamus responsible for mediating the bimodal influence of estradiol on GnRH secretion and suggest that different, andpossibly independent, neuronal cell populations are responsible for the negative and positive feedback actions of estradiol.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 04/12/20 alle ore 16:31:13