Photoperiodism and Reproduction in Golden Hamsters: Circadian Organization and the Termination of Photorefractoriness1

Abstract

The photorefractory period of the adult golden hamster is characterized by failure of the reproductive system to respond to short-day treatment with gonadal regression. The reproductive system of photorefractory hamsters remains functional irrespective of ambient photoperiod. Prolonged treatment with long days terminates photorefractoriness in hamsters, restoring the ability of the animals' hypothalamo-hypophysio-gonadal axis to respond to short daylengths. The basis of the photorefractory hamster's ability to discriminate long from short days in terminating the refractory period is a circadian oscillation of photosensitivity.