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Clarke I.J.,Monash University | Caraty A.,CNRS Physiology of Reproduction and Behaviors
Advances in Experimental Medicine and Biology | Year: 2013

Wild and domesticated species display seasonality in reproductive function, controlled predominantly by photoperiod. Seasonal alterations in breeding status are caused by changes in the secretion of gonadotropin-releasing hormone (GnRH) that are mediated by upstream neuronal afferents that regulate the GnRH cells. In particular, kisspeptin appears to play a major role in seasonality of reproduction, transducing the feedback effect of gonadal steroids as well as having an independent (nonsteroid dependent) circannual rhythm. A substantial body of data on this issue has been obtained from studies in sheep and hamsters and this is reviewed here in detail. Kisspeptin function is upregulated during the breeding season in sheep, stimulating reproductive function, but contradictory data are found in Siberian and Syrian hamsters. The relative quiescence of kisspeptin cells in the nonbreeding season can be counteracted by administration of the peptide, leading to activation of reproductive function. Although there is a major role for melatonin in the transduction of photoperiod to the reproductive system, kisspeptin cells do not appear to express the melatonin receptor, so the means by which seasonality changes the level of kisspeptin activity remains unknown. © Springer Science+Business Media, LLC 2013. Source


Druart X.,CNRS Physiology of Reproduction and Behaviors
Reproduction in Domestic Animals | Year: 2012

Sperm transit in the female tract is a critical event for the success of fertilization. From their deposition in the vagina to final migration in the oviduct, sperm pass through the different compartments of the genital tract in which they encounter different environments. The cervix and the uterotubal junction (UTJ) are two barriers with different relative importance according to the species. The protein composition, the degree of glycosylation and the hydration of the cervical mucus change during the oestrous cycle. Several sperm surface proteins are associated with their migration through the cervical mucus and the UTJ. Data regarding the interaction of sperm with secretions of the epithelial tissue lining the different compartments of the female genital tract during the sperm transit are reviewed, with a particular emphasis on the migration of sperm through the cervix. © 2012 Blackwell Verlag GmbH. Source


Dardente H.,CNRS Physiology of Reproduction and Behaviors
Journal of Neuroendocrinology | Year: 2012

Most mammals living at temperate latitudes exhibit marked seasonal variations in reproduction. In long-lived species, it is assumed that timely physiological alternations between a breeding season and a period of sexual rest depend upon the ability of day length (photoperiod) to synchronise an endogenous timing mechanism called the circannual clock. The sheep has been extensively used to characterise the time-measurement mechanisms of seasonal reproduction. Melatonin, secreted only during the night, acts as the endocrine transducer of the photoperiodic message. The present review is concerned with the endocrine mechanisms of seasonal reproduction in sheep and the evidence that long day length and thyroid hormones are mandatory to their proper timing. Recent evidence for a circadian-based molecular mechanism within the pars tuberalis of the pituitary, which ties the short duration melatonin signal reflecting long day length to the hypothalamic increase of triiodothyronine (T3) through a thyroid-stimulating hormone/deiodinase2 paracrine mechanism is presented and evaluated in this context. A parallel is also drawn with the golden hamster, a long-day breeder, aiming to demonstrate that features of seasonality appear to be phylogenetically conserved. Finally, potential mechanisms of T3 action within the hypothalamus/median eminence in relationship to seasonal timing are examined. © 2011 The Author. Journal of Neuroendocrinology © 2011 Blackwell Publishing Ltd. Source


Hut R.A.,University of Groningen | Dardente H.,CNRS Physiology of Reproduction and Behaviors | Riede S.J.,University of Groningen
Current Biology | Year: 2014

Deep hibernators that spend winter in a hypothermic coma below ground can still emerge and reproduce in spring at the right moment. A recent study shows that specific cells of the pituitary may harbor the internal calendar responsible for this. © 2014 Elsevier Ltd. Source


Dardente H.,CNRS Physiology of Reproduction and Behaviors
Current Biology | Year: 2015

Endogenous long-term timing is a key component of seasonality. Where and how are such rhythms generated? Recent findings pointed to the pituitary pars tuberalis, already implicated in photoperiod responsiveness. Now, a new study provides mechanistic insights which support this hypothesis. © 2015 Elsevier Ltd. Source

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