Meeting Abstract
All animals use environmental cues to accurately time life-history events. How the brain decodes information about the environment to produce adaptive changes in physiology and behavior, however, is poorly understood. We asked if low temperature dormancy activates seasonal reproduction by altering the synthesis and release of gonadotropin-releasing hormone (GnRH) in the brain. We used the well-studied red-sided garter snake (Thamnophis sirtalis parietalis) for this study, as 4 weeks of low temperature exposure is both necessary and sufficient to induce reproduction in northern populations of this species. Male and female snakes were collected from the field and hibernated at 4 or 10°C in complete darkness. At 0, 2, 4, 8, and 16 weeks, plasma was collected from a subset of 8 snakes for steroid hormone assay; brains were processed for immunohistochemistry. The total number of GnRH cells within the forebrain was quantified for each individual. We also measured GnRH soma size to assess changes in the relative activity of GnRH neurons during dormancy. In males, GnRH cell number (P = 0.004), GnRH cell area (P = 0.015), and plasma androgen concentrations (P = 0.024) increased significantly over time. In addition, males hibernated at 4°C for 16 weeks tended to have a higher number of GnRH cells (P = 0.064), a larger GnRH cell area (P = 0.052), and higher plasma androgens (P = 0.024) than males hibernated at 10°C. Intriguingly, female snakes showed no changes in GnRH cell number or soma size during winter dormancy at either temperature, a finding that corroborates known sex differences in the timing of reproductive activities in this species. Collectively, these data provide critical insight for understanding the environment-organism interactions that govern differences in reproductive timing.
