Vasopressin 1b receptor knock-out impairs memory for temporal order

Mice lacking a functional vasopressin 1b receptor (Avpr1b) display decreased levels of aggression and social memory. Here, we used Avpr1b-knock-out (Avpr1b(-/-)) mice to examine whether an abnormality of this receptor results in specific cognitive deficits in the domain of hippocampal function. Avpr1b(-/-) mice were deficient in sociability and in detecting social novelty, extending previous findings of impairment in social recognition in these mutants. Avpr1b(-/-) mice could recognize previously explored objects and remember where they were experienced, but they were impaired in remembering the temporal order of presentation of those objects. Consistent with this finding, Avpr1b(-/-) mice were also impaired on an object-odor paired associate task that involved a temporal discontiguity between the associated elements. Finally, Avpr1b(-/-) mice performed normally in learning a set of overlapping odor discriminations and could infer relationships among odors that were only indirectly associated (i.e., transitive inference), indicating intact relational memory. The Avpr1b is expressed at much higher levels than any other part of the brain in the pyramidal cells of hippocampal CA2 area, a subfield of the hippocampus that has physiological and genetic properties that distinguish it from subfields CA1 and CA3. The combined results suggest that the Avpr1b, perhaps in CA2, may play a highly specific role in social behavior and episodic memory. Because schizophrenia and bipolar disorder are associated with a unique pathology in CA2 and impairments in both social behavior and episodic memory, this animal model could provide insights into the etiology of these disorders.