Short photoperiod affects reproductive function but not dehydroepiandrosterone concentrations in male deer mice (Peromyscus maniculatus).

Cessation of breeding is central among the suite of winter-coping strategies used by small rodents to survive energy-demanding winter conditions. Animals use photoperiod to predict the onset of winter and initiate, well in advance of deteriorating conditions, seasonal adaptations. Exposure to short photoperiod leads to regression of the reproductive system in long-day breeding animals. Likewise, exposure to short days leads to enhanced immune function among several rodent species studied. Because dehydroepiandrosterone (DHEA) increases immune function in virtually all studies reported to date, we sought to determine if DHEA concentrations might be influenced by photoperiod, thereby suggesting a mechanism whereby short photoperiod may enhance immune function. Male deer mice (Peromyscus maniculatus) were exposed to either short or long days for 10 weeks. Short photoperiods caused significant reduction in all reproductive organs measured relative to animals housed in long days. However, DHEA concentrations did not differ between short- and long-day mice. Taken together, these data suggest that short-day enhancement of immune function in deer mice is independent of DHEA concentrations.