Meeting Abstract

P2.168  Monday, Jan. 5  Melatonin alters arginine vasotocin immunoreactivity in green treefrogs (Hyla cinerea). LUTTERSCHMIDT, D.I.*; WILCZYNSKI, W.; Georgia State University, Atlanta; Georgia State University, Atlanta lutterschmidt@gsu.edu

The arginine vasopressin/vasotocin (AVP/AVT) system plays an important role in regulating sexual behavior, including mediating responses to sociosexual stimuli. Although reproduction is regulated seasonally in many animals, few studies have investigated whether seasonal changes in reproductive behavior are concurrent with seasonal changes in AVP/AVT. Previous work in our laboratory demonstrated a seasonal increase in AVT-immunoreactive cell number in green treefrogs (Hyla cinerea). In the present study, we investigated whether melatonin mediates this seasonal change in AVT immunoreactivity. Treatment of green treefrogs with melatonin-filled silastic capsule implants for 4 weeks significantly altered AVT immunoreactivity, although these differences depended significantly upon sex. In male treefrogs melatonin treatment significantly increased AVT-immunoreactive cell number in the suprachiasmatic nucleus and caudal hypothalamus, while in female frogs melatonin did not significantly influence AVT immunoreactivity. Similar to previous studies, we also observed a significant sex difference in the number of AVT-immunoreactive cells in frogs treated with a blank implant, with female frogs having more immunoreactive cells in the suprachiasmatic nucleus and caudal hypothalamus than male frogs. These results indicate that the AVP/AVT system is an important target for melatonin in facilitating seasonal changes in reproductive physiology and behavior.