Effects of age and photoperiod on reproduction and the spleen in the marshrice rat (Oryzomys palustris)

To examine the interactions between age and photoperiod on reproduction and spleen weights, we exposed adult male and female rice rats of various ages to photoperiods of 16:8-h light-dark photoperiods (16L:8D) or 12L:12D. Aft er 10 wk, animals were killed and the following data were recorded: weights of testes, seminal vesicles, uterus, ovaries, body, and spleen and, in add ition, vaginal patency. Young adult males displayed a greater degree of tes ticular and seminal vesicle regression in short photoperiods than did older males; the testes of most older males did not regress in response to short photoperiods. Spleen weight was unresponsive to short photoperiods in all males, but was affected by age. Females, however, exhibited reproductive or gan regression and decreased vaginal patency in response to short photoperi ods at all ages examined. Body weights were affected by photoperiod in youn g females, and, as in males, photoperiod had no effect on spleen weights. T hese data suggest that the reproductive response to photoperiod in adult ma le rice rats declines with age, whereas in adult females it does not.