TESTICULAR REGRESSION AND RECRUDESCENCE WITHOUT SUBSEQUENT PHOTOREFRACTORINESS IN SIBERIAN HAMSTERS

Adult male Siberian hamsters transferred from 16 h light/day (16L) to 14 h light/day (14L) underwent gonadal regression and recrudescence ov er the course of 24 wk; the duration of reproductive quiescence was sh orter by 10 wk than in hamsters transferred from 16L to 10L. A decreas e in day length (DL) at week 12 from 14L to 10L greatly extended the d uration of testicular involution, whereas transfer at week 12 from 10L to 8L was without effect. Hamsters that had manifested gonadal regres sion and recrudescence in 14L immediately initiated a second regressio n when challenged with 10L. Intermediate DLs induce gonadal regression and recrudescence without rendering hamsters refractory to shorter DL s. Intermediate DLs sufficient to initiate gonadal regression may be t oo long to trigger the interval timer that eventually induces refracto riness to shorter DLs and may be successively interpreted as short and long days, respectively, by Siberian hamsters.