The nonapeptide oxytocin (OXY) is a pivotal hormone in the central response to mating in male and female rodents. The brain of both sexes show dramatic changes in OXY immunoreactivity and topography during and after mating. This proposal will pursue the questions of how CNS physiological dynamics such as peptide synthesis, release and content account for the changes seen in OXY immunoreactivity during sexual interaction. In vivo microdialysis and in situ hybridization techniques have recently been mastered in this laboratory and they will be utilized to detect changes in OXY release and gene expression across time after sexual interaction. This proposal will also try to determine what aspects of sexual behavior are controlled by CNS OXY. Since central OXY administration has been shown to alter both female and male sexual behaviors, this proposal will attempt to determine whether blocking OXY systems with either antisera or antagonist analogues given centrally results in decrements in any particular aspect of sexual interactions. OXY blocking agents will also be used to analyze the importance of an intact OXY system to optimal fertility rates. This proposal will begin the task of how OXY affects sexual behaviors and how OXY and the behaviors affect fertility. The long-term goal of this work is to integrate these findings with the myriad other behavioral and physiological effects of OXY in an attempt to determine how this hormone, that is at the core of reproductive physiology, manipulates behavioral and endocrine systems to accomplish reproduction.