Food competition and social experience effects on V1a receptor binding in the forebrain of male Long–Evans hooded rats

The present study investigated the effect of social status in Long–Evans hooded rats established during food competition on V1a vasopressin receptor (V1aR) binding in the lateral septum (LS), medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), anterior hypothalamus (AH), and central/basolateral amygdala (CeB). Serum concentration of testosterone (T) and corticosterone (CORT) was also measured. In Experiment 1, thirty-two lever-trained weight-matched rat pairs were placed in operant chambers where a single bar press provided access to milk reinforcement. A dominant–subordinate relationship, determined by the duration of drinking, was evident in 88% of the pairs. Sixteen rats were lever-trained but did not interact and served as no-treatment (NT) controls. In the LS, V1aR binding in the subordinate (SUB) group was significantly higher than in the dominant (DOM) group. V1aR binding was significantly higher in the LS, BNST, CeB, and AH in the NT group than in the other groups. The levels of CORT and T were not affected significantly by group membership. Experiment 2 investigated whether the binding effect in the LS was related to differences in fluid consumption. The results did not indicate a significant effect of fluid consumption. In the rat, V1aR binding in several forebrain areas seems to be affected by brief periods of social interactions, and, in the LS, it also appears to be related to dominance status.