Photoperiodic Influences on Testicular Regression in the Golden Hamster: Termination of Scotorefractoriness

Abstract

Hamsters whose testes have regressed and recrudesced during the animals’ exposure to short photoperiods are insensitive to short days (scotorefractoriness). To restore sensitivity to short days, hamsters must first experience many weeks of long days (Reiter, 1972). The precise photoperiodic requirements for the termination of scotorefractoriness were investigated. Animals with spontaneously recrudesced testes were subjected to different durations and patterns of long day exposure to test the hypothesis that a restricted long day-sensitive period exists. Twenty weeks of photostimulation uniformly allowed regression to occur upon return of the animals to short days; hamsters exposed to 10 weeks of photostimulation were generally rendered sensitive to short days, but their testes did not regress as rapidly nor as consistently. This effect was obtained regardless of the pattern of photostimulation after spontaneous recrudescence. There was some indication that episodes of photostimulation can summate over intervals of 1, but not 10 weeks of short days or darkness. The results indicate that scotorefractoriness is not an all-or-none phenomenon; photostimulation during the refractory period acts principally to alter the rate of regression upon reexposure to short days. It is unlikely that a restricted long day-sensitive phase exists in the golden hamster.