Kerbeshian M C, Bronson F H
Department of Zoology, University of Texas, Austin 78712, USA.
Physiol Behav. 1996 Jul;60(1):165-70. doi: 10.1016/0031-9384(95)02244-9.
Access to running wheels stimulates testicular recrudescence in meadow voles whose reproductive axes have been suppressed by short day lengths. The present experiments addressed the mechanism by which running stimulates the reproductive system. The results from two experiments suggest that running acts specifically to override the short day length suppression of the gonads: access to running wheels had no stimulatory effect on the testes of meadow voles housed in long day lengths, and the degree to which running stimulated the testes of meadow voles housed under short day lengths was significantly correlated with the degree to which the voles were reproductively photoresponsive. A third experiment queried whether running shifts the circadian clock in such a way as to cause an overlap between the short day length photoperiod and the period of sensitivity to light. This proved not to be the case: access to running wheels stimulated testicular recrudescence in meadow voles housed in constant darkness. Two experiments demonstrated that access to a running wheel did not alter short day length profiles of pineal melatonin content or the nocturnal rise in pineal melatonin content in the absence of light. Finally, daily patterns of circulating corticosterone levels did differ between voles with and without access to running wheels, although the difference could not be attributed to differences in the circadian system. Overall, these experiments suggest that running stimulates gonadal recrudescence by acting on the pathway by which photoperiod suppresses reproduction downstream of melatonin production.
