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

Prairie voles (Microtus ochrogaster), like most rodent species, exhibit a p henotypic polymorphism in reproductive response to winter conditions or to short day lengths in the laboratory. Laboratory studies on seasonally breed ing species have traditionally focused on the role of photoperiod in modula ting reproduction and other seasonal adaptions, However, because animals us e proximate environmental factors in addition to photoperiod to phase seaso nal adaptions with the appropriate time of year, the present study investig ated the interaction of photoperiod and temperature on reproductive functio n and the gonadotropin-releasing hormone (GnRH) neuronal system. Male prair ie. voles were housed in either long (LD 16:8) or short (LD 8:16) photoperi ods, Voles in each photoperiodic condition were also exposed to either mild (20 degrees C) or low (8 degrees C) temperatures, After 10 weeks, voles we re killed and their brains were processed using in situ hybridization for m RNA 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 t emperatures alone), even when reproduction is inhibited, whereas a combinat ion 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 reproduct ive function are likely to differ between harsh and mild winters.