| Many non-equatorial species, including rodents such as hamsters, mice, and voles, are photoperiodic. In these species, changes in day length provide cues for the onset of their reproductive season. Alterations in photoperiod can result in profound morphological, physiological, and behavioral changes. These seasonal alterations require changes in the structure and function of the adult nervous system. It is this potential for neural plasticity in an adult animal that is of particular interest. Syrian hamsters are an excellent model species in which to examine seasonal changes in the brain, because photoperiodic mechanisms controlling their seasonal breeding have been well characterized. They also display high levels of territorial aggression and a well-studied form of scent marking known as flank marking. The medial preoptic area-anterior hypothalamic continuum (MPOA-AH) is a key neuroanatomical area in the control of aggression and flank marking. In addition, arginine-vasopressin (AVP) and its V1a receptors within the MPOA-AH are necessary for the expression of aggression and flank marking. Finally, the expression of flank marking and the transcriptional regulation of V1a receptors are gonadal steroid dependent. Therefore, changes in day length resulting in alterations in circulating gonadal steroids can be used to characterize the plasticity within the AVP system. This dissertation set out to study the effects of natural changes in gonadal steroids on the AVP circuitry and how it controls several social behaviors. Four chapters are included which examine the effects of day length on flank marking, aggression, and V1a receptors. |
