Timing of testicular recrudescence in Siberian hamsters is unaffected by pinealectomy or long-day photoperiod after 9 weeks in short days

In this study, the authors asked whether pinealectomy or temporary exposure to a stimulatory photoperiod affects the timing of spontaneous testicular recrudescence in adult Siberian hamsters chronically exposed to short days (9:15 light:dark). In Experiment 1, hamsters were pinealectomized after 6, 9, or 12 weeks in short days. Pinealectomy after 9 or 12 weeks did not affe ct the timing of spontaneous gonadal growth (27.7 +/- 1.9 and 25.4 +/- 1.3 weeks, respectively) compared to sham-operated controls (28.6 +/- 0.9 weeks ). Enlarged testes occurred earlier in animals that were pinealectomized af ter 6 weeks in short days (21.8 +/- 2.1 weeks). In Experiment 2, adult hams ters were exposed to short days for 9 weeks, transferred to long days (16:8 Light:dark) for 4 weeks, and then returned to short days for 23 additional weeks. Although long-day interruption caused gonadal growth in 15 out of 1 9 hamsters, the temporary long-day exposure did not affect the timing of sp ontaneous gonadal growth following return to short days (28.2 +/- 0.9 weeks ) in 10 of the 15, relative to the timing observed in control hamsters cont inuously maintained in short days (28.2 +/- 1.1 weeks). Four out of 19 hams ters did not show gonadal growth following long-day exposure. Spontaneous g onadal growth in these hamsters (28.0 +/- 1.4 weeks) also occurred at the s ame time as controls. The remaining 5 hamsters exhibited enlarged testes fo llowing long-day exposure (12.0 +/- 0.0 weeks) but were refractory to the s econd short-day exposure. All hamsters exhibited entrainment of wheel-runni ng activity following the change in photoperiod. A final group of 13 animal s were pinealectomized before long-day transfer. They exhibited gonadal gro wth (at 17.2 +/- 0.8 weeks) but failed to regress a second time when return ed to short days. The timing of gonadal growth in these animals was delayed relative to the sham-operated hamsters temporarily transferred to long day s (Experiment 2) but accelerated relative to the hamsters pinealectomized a t 9 weeks, which remained continuously in short days (Experiment 1). The re sults of both experiments suggest that a pineal-independent process mediate s the timing of spontaneous gonadal growth in Siberian hamsters chronically exposed to a short-day photoperiod.