Photoperiodic Influences on Testicular Regression, Recrudescence and the Induction of Scotorefractoriness in Male Golden Hamsters

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Abstract
Hamster testes which have undergone short photoperiod-induced atrophy become refractory to the effects of short photoperiod after spontaneous or light-induced recrudescence. This phenomenon was termed, "scotorefractoriness." Experiment 1 established that mere testicular regression was not sufficient to induce scotorefractoriness. Testes of some animals which were regressed by 6 or 9 wk of exposure to a LD [light dark] 2:22 photoperiod (short days) and recrudesced by 9 wk of exposure to a LD 14:10 photoperiod (long days) subsequently regressed again in response to a second 9 wk exposure to LD 2:22; others appeared scotorefractory. Experiment 2 determined that animals which achieved complete testicular regression during 9 wk of LD 2:22 were less sensitive to the stimulating effects of long days than were animals which were in LD 2:22 for 12-15 wk. The transition from long to short days initiates gonadal atrophy, permits subsequent testicular recrudescence and also induces scotorefractoriness. Short day exposure initially decreases the sensitivity of the neuroendocrine-testicular axis to the effects of long days; the subsequent recovery of sensitivity to photostimulation may parallel processes involved in spontaneous testicular recrudescence.