Effect of photoperiod on gonadal maintenance and development in the marsh rice rat (Oryzomys palustris).

Reproductive responsiveness to photoperiod was examined in adult and prepubertal rice rats. In Experiment 1, adult males on 16L:8D and 14L:10D maintained testicular size, while exposure to 12L:12D and 10L:14D resulted in testicular regression, followed by spontaneous testicular recrudescence. Adult females (Experiment 2) on long photoperiods had larger uterine and ovarian weights at most times examined and maintained vaginal patency compared to females on short photoperiods. Reproductive development of male rice rats (Experiment 3) was stimulated on 16L:8D and 14L:10D with rapid testicular development occurring by 12 weeks of age, while in males reared on 12L:12D and 10L:14D reproductive development proceeded slowly and was completed at approximately 26 weeks of age. Females on 16L:8D and 14L:10D experienced rapid uterine development compared to those on 12L:12D and 10L:14D. Ovarian weights on 14L:10D were significantly greater than ovarian weights on 12L:12D. Finally, vaginal patency was attained more rapidly on 16L:8D than on 14L:10D and was markedly inhibited on 12L:12D and 10L:14D. These data show that reproduction in adult male and female rice rats is regulated, at least in part, by photoperiod and that reproductive development in juveniles is also under photoperiodic control.