Temperature and photoperiod interact to affect reproduction and GnRH synthesis in male prairie voles

Prairie voles (Microtus ochrogaster), like most rodent species, exhibit a phenotypic polymorphism in reproductive response to winter conditions or to short day lengths in the laboratory. Laboratory studies on seasonally breeding species have traditionally focused on the role of photoperiod in modulating reproduction and other seasonal adaptions, However, because animals use proximate environmental factors in addition to photoperiod to phase seasonal adaptions with the appropriate time of year, the present study investigated the interaction of photoperiod and temperature on reproductive function and the gonadotropin-releasing hormone (GnRH) neuronal system. Male prairie. voles were housed in either long (LD 16:8) or short (LD 8:16) photoperiods, Voles in each photoperiodic condition were also exposed to either mild (20 degrees C) or low (8 degrees C) temperatures, After 10 weeks, voles were killed and their brains were processed using in situ hybridization for mRNA for proGnRH. The results suggest that GnRH synthesis is not affected by exposure to a single inhibitory proximate factor (i.e. short days or low temperatures alone), even when reproduction is inhibited, whereas a combination of inhibitory proximate factors leads to a decrease in GnRH synthesis (i.e, fewer neurones staining for mRNA for proGnRH). These data suggest that the neuroendocrine mechanisms regulating seasonal alterations in reproductive function are likely to differ between harsh and mild winters.