Photoperiodic influences on testicular regression, recrudescence and the induction of scotorefractoriness in male golden hamsters. Biology of Reproduction 17

Hamstei testes which have undergone short photoperiod-induced atrophy become refractory to the effects of short photoperiod after spontaneous or light-induced recrudescence (Reiter, 1974). We have termed this phenomenon, “scotorefractoriness. ” The present experiments assessed relations between photoperiod-induced testicular regression, recrudescence and scotorefractoriness. Experiment 1 established that mere testicular regression was not sufficient to induce scotore-fractoriness. Testes of some animals which were regressed by 6 or 9 weeks of exposure to a LD 2:22 photoperiod (short days) and recrudesced by 9 weeks of exposure to a LD 14:10 photoperiod (long days) subsequently regressed again in response to a second 9 week exposure to LD 2:22; others appeared scotorefractory. Experiment 2 determined that animals which achieved complete testicular regression during 9 weeks 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 weeks. The transition from long to short days initiates g#{246}nadal 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 photostimula-ton may parallel processes involved in spontaneous testicular recrudescence