PHOTOPERIOD REGULATES TESTIS CELL APOPTOSIS IN DJUNGARIAN HAMSTERS

Reproductive activity in the Djungarian hamster is controlled by seaso nal variations in day length. Exposure to long days stimulates testis development, while exposure to short days induces testis regression. W e recently found that testis regression after gonadotropin deprivation in rats is associated with increases in apoptosis. Here we sought to determine whether or not apoptosis is associated with the testis regre ssion and/or recrudescence that occurs naturally in seasonally breedin g mammals. Newborn male hamsters were maintained on long days (16L:8D) until 3 wk of age before being transferred to short days (8L:16D). Fo llowing decreases in serum FSH within 3 days of exposure to short days , testis weight decreased by 52% at Day 10, reaching a 70% decrease af ter 21 days. Analysis of testis cell DNA fragmentation showed a 4.9-fo ld increase of low-molecular weight DNA as early as 5 days after trans fer to short days; this was followed by a time-dependent decrease. The observed increases in testis cell apoptosis were correlated with decr eases in serum testosterone, but decreases in Leydig cell LH receptor content were delayed. In a second study, 6-wk-old hamsters with regres sed testes due to a 3-wk exposure to short days were transferred back to long days. After increases in serum FSH within 3 days of photostimu lation, a 2-fold elevation in testis weight was found at Day 5. The in crease in testis weight was associated with a 65% decrease of testis a poptosis within 5 days of photostimulation. Also, increases in serum t estosterone and LH receptor content were observed after 5 and 10 days of exposure to long days, respectively. These data indicate that neuro endocrine changes (including FSH release) induced by varying photoperi od length alter testis cell apoptosis, suggesting also that the induct ion or inhibition of apoptosis plays an important role in testis regre ssion and/or recrudescence. The Djungarian hamster provides a valuable model for studying the neuroendocrine control of testis apoptosis in, photoperiodic mammals.