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Am J Physiol Regul Integr Comp Physiol. 2005 Jan;288(1):R234-42. Epub 2004 Aug 19.

Conflicting effects of exercise on the establishment of a short-photoperiod phenotype in Syrian hamster.

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ULP-CNRS UMR 7518, Neurobiologie des Rythmes, IFR Neurosciences 37, 12 rue de l'Université, 67000 Strasbourg, France.


In the Syrian hamster, winter seasonal inhibition of reproduction occurs in response to decreasing day length. This inhibitory response is modulated by nonphotic cues. In particular, access to a running wheel has been shown to produce incomplete gonadal regression. The present study sought to determine whether this occurs as a consequence of wheel effect on adaptation of the circadian system to short days or whether downstream physiological responses are involved. Short-day adaptation of the circadian clock, which is located in the suprachiasmatic nucleus (SCN) of the hypothalamus, was tested by lengthening the photosensitive phase of the SCN (assayed by light-induced c-Fos expression in the SCN) as a parameter. We found that wheel-running activity does not inhibit the integration of the photoperiodic change by the SCN even if complete testicular regression is prevented. Moreover, this exercise was even capable of accelerating the lengthening of the photosensitive phase after the transfer to short day length. Thus, although wheel-running activity inhibits the short photoperiod-induced gonadal regression, it acts on the SCN to accelerate the integration of the photoperiodic change by the biological clock.

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