Social motivation is reduced in vasopressin 1b receptor null mice despite normal performance in an olfactory discrimination task

In this study, we characterized more thoroughly the social behavior of vasopressin 1b receptor null (V1bR-/-) mice. We confirmed that V1bR-/- males exhibit less social aggression than their wild-type (V1bR+/+) littermates. We tested social preference by giving male subjects a choice between pairs of soiled or clean bedding. In general, V1bR+/+ mice spent significantly more time engaged in chemoinvestigation of these social stimuli than V1bR-/- mice. Male V1bR+/+ mice preferred female-soiled bedding over male-soiled bedding, male-soiled bedding over clean bedding, and female-soiled bedding over clean bedding. In contrast, V1bR-/- males failed to exhibit a preference for any bedding. This difference in behavior is not explained by an anosmic condition as there were no differences between V1bR-/- and V1bR+/+ mice in their abilities to detect a cookie buried in clean bedding, or in their ability to perform in an operant conditioning task using a fully automated liquid dilution olfactometer. In the latter task, male V1bR-/- mice were fully capable of discriminating between male and female mouse urine. The latencies to learn this task did not differ between the two genotypes. Thus, a V1bR-/- male's ability to differentiate between male and female chemosensory cues appears no different than that of a V1bR+/+ male's. We propose that the V1bR plays an important role in social motivation, perhaps by coupling the processing, integration, and/or interpretation of chemosensory cues with the appropriate behavioral response.