Social behaviors are differentially regulated by varying neural activity across a social behavior network. We hypothesize that much of this signaling has anxiolytic and anxiogenic effects, which then modulate behavioral choices and the frequency and intensity of behavioral outputs. We have been assessing neural activation at nodes within this network by quantifying induction of the immediate early gene product Fos, a marker of recent neural activity, throughout the brain of a relatively small and simple vertebrate model organism, the male brown anole lizard (Anolis sagrei). Using fluorescent immunohistochemistry, we are currently examining Fos-colocalization within hypothalamic neurons producing either or both corticotropin-releasing factor (CRF) and mesotocin (the nonmammalian oxytocin homologue). Data analyzed thus far demonstrate a significant increase in both CRF and MT activity in the paraventricular hypothalamus in association with the expression of sexual behaviors. These results suggest that courtship is stressful but perhaps MT signaling allows for the expression of prosocial behaviors in such a context. We are also assessing Fos density at various basal forebrain sites thought to be involved in the regulation of behavioral decision-making. Fos-induction increases associated with courtship behavior have thus far been observed within the medial amygdala and bed nucleus of the stria terminalis. These results will be integrated with already concluded analyses demonstrating differential activation of brain-wide populations of catecholamine-producing neurons, as well as various hypothalamic populations producing vasotocin (the nonmammalian vasopressin homologue) across different social behavior interactions. Our goals are to extend the mapping of the social behavior neural network by examining interactions among anxiety-related source and target nodes, and to then use this information to investigate relevant nodes across individuals to determine individual differences in neural circuitry that underlie variation in behavioral propensities and decision-making.