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Titolo:
PHOTOPERIODIC SYNCHRONIZATION OF A CIRCANNUAL REPRODUCTIVE RHYTHM IN SHEEP - IDENTIFICATION OF SEASON-SPECIFIC TIME CUES
Autore:
WOODFILL CJI; WAYNE NL; MOENTER SM; KARSCH FJ;
Indirizzi:
UNIV MICHIGAN,REPROD SCI PROGRAM ANN ARBOR MI 48109 UNIV MICHIGAN,REPROD SCI PROGRAM ANN ARBOR MI 48109 UNIV MICHIGAN,DEPT PHYSIOL ANN ARBOR MI 48109
Titolo Testata:
Biology of reproduction
fascicolo: 4, volume: 50, anno: 1994,
pagine: 965 - 976
SICI:
0006-3363(1994)50:4<965:PSOACR>2.0.ZU;2-S
Fonte:
ISI
Lingua:
ENG
Soggetto:
LUTEINIZING-HORMONE SECRETION; NEGATIVE FEEDBACK ACTION; BREEDING-SEASON; ENDOGENOUS RHYTHM; MELATONIN PATTERN; GROUND-SQUIRRELS; ESTROUS-CYCLE; SUFFOLK EWE; ESTRADIOL; LONG;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
45
Recensione:
Indirizzi per estratti:
Citazione:
C.J.I. Woodfill et al., "PHOTOPERIODIC SYNCHRONIZATION OF A CIRCANNUAL REPRODUCTIVE RHYTHM IN SHEEP - IDENTIFICATION OF SEASON-SPECIFIC TIME CUES", Biology of reproduction, 50(4), 1994, pp. 965-976

Abstract

Seasonal reproduction in the ewe is generated by an endogenous circannual rhythm of reproductive neuroendocrine activity. Exposure to as few as 70 days of photoperiodic information a year is sufficient to synchronize the rhythm. The present study was conducted to identify which portions of the photoperiodic cycle are utilized for synchronization. For this purpose, we used pinealectomized ewes that could not respond reproductively to changes in day length. Selected photoperiodic information was provided via infusion of melatonin, a hormone that provides the neuroendocrine code for day length in this species. Melatonin was delivered according to circadian patterns. The infusion patterns were tailored to mimic those of melatonin secretion in pineal-intact ewes during one of the four seasons: winter, spring, summer, or autumn. The infusions were provided for 90 days a year during each of the three years following pinealectomy. The ewes were ovariectomized and treated with constant-release Silastic capsules containing estradiol; reproductive neuroendocrine activity was monitored by measurement of serum concentrations of LH. In the absence of exogenous melatonin, most (19 of 24) pinealectomized controls exhibited circannual LH cycles that were not in synchrony. indicating that the rhythm was free-running. Melatonin synchronized the rhythm (such that the period was 365 days and the stages of the rhythm were both concurrent among animals and in appropriate phase with the geophysical year), but not all melatonin patterns were equally effective in this regard. The most effective melatonin patterns mimicked those of secretion during summer. Spring and autumn melatonin patterns were less effective, and winter melatonin patterns were ineffective. These results support the concept that there is a seasonal specificity with regard to the photoperiodic cues that synchronizethe circannual rhythm of reproductive neuroendocrine activity in the ewe. The rhythm is synchronized most effectively by long-day photoperiodic cues perceived on or around the summer solstice.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 29/11/20 alle ore 18:34:14