Three specific aims are proposed to address the overall hypothesis that arginine vasopressin (AVP) has significant roles in the retention of maternal behavior, the expression maternal aggression, and that there are potential connections between central AVP levels and the expression of maternal behavior and aggression. In addition, the potential connection between AVP's effects on maternal behavior and its established role in social recognition will be explored. In Specific Aim 1, we postulate that AVP may play a role in the retention of maternal behavior. In contrast to the wealth of research supporting AVP's role in social recognition and parental behavior in other rodent species, there is a paucity of research focusing on AVP and maternal behavior or aggression in the rat. Specific Aim 2 will attempt to determine if AVP modulates maternal aggression. It has been shown that AVP stimulates aggression in non-lactating rodents, but its role in maternal aggression is uncertain. Specific Aim 3 will investigate AVP anatomy in lactating rodents by examining AVP and AVP mRNA levels in behaviorally relevant nuclei in lactating rats using RIA and RNase protection, and potential correlations between AVP and aggression will be explored. [unreadable] [unreadable] [unreadable]