Ann. N.Y. Acad. Sci. ISSN 0077-8923 ANNALS OF THE NEW YORK ACADEMY OF SCIENCES Issue: Trends in Neuroendocrinology Vasopressin and social odor processing in the olfactory bulb and anterior olfactory nucleus Douglas W. Wacker, 1,2 Mario Engelmann, 3 Vicky A. Tobin, 1 Simone L. Meddle, 1,4 and Mike Ludwig 1 1 Centre for Integrative Physiology, University of Edinburgh, Edinburgh, United Kingdom. 2 Department of Biology, Colgate University, Hamilton, New York. 3 Institute of Biochemistry and Cell Biology, Otto von Guericke University Magdeburg, Magdeburg, Germany. 4 The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom Address for correspondence: Mike Ludwig, Centre for Integrative Physiology, University of Edinburgh, Hugh Robson Bldg., George Square, Edinburgh EH8 9XD, United Kingdom. mike.ludwig@ed.ac.uk Central vasopressin facilitates social recognition and modulates numerous complex social behaviors in mammals, including parental behavior, aggression, affiliation, and pair-bonding. In rodents, social interactions are primarily mediated by the exchange of olfactory information, and there is evidence that vasopressin signaling is important in brain areas where olfactory information is processed. We recently discovered populations of vasopressin neurons in the main and accessory olfactory bulbs and anterior olfactory nucleus that are involved in the processing of social odor cues. In this review, we propose a model of how vasopressin release in these regions, potentially from the dendrites, may act to filter social odor information to facilitate odor-based social recognition. Finally, we discuss recent human research linked to vasopressin signaling and suggest that our model of priming-facilitated vasopressin signaling would be a rewarding target for further studies, as a failure of priming may underlie pathological changes in complex behaviors. Keywords: olfaction; social memory; social recognition Central vasopressin and social behavior Vasopressin secreted from the posterior pituitary gland into the systemic circulation regulates pe- ripheral targets, notably the kidney and the blood vessels. However, this nonapeptide also has impor- tant behavioral functions that are not linked to its classical neurohypophyseal release. For exam- ple, microinjection of vasopressin into the anterior hypothalamus–medial preoptic area of subordinate male hamsters induces flank marking, a dominance- related behavior, 1 whereas microinjection of a vaso- pressin receptor antagonist reduces flank marking and biting in dominant hamsters when exposed to subordinates. 1,2 Further insight in the relevance of cen- tral vasopressin for social behavior has come from nontraditional laboratory model organisms. Highly affiliative, monogamous male prairie voles (Microtus ochrogaster ) given a continual infusion of vasopressin into the lateral ventricle not only show increased aggression toward strangers, but also increased partner preference. 3 Interestingly, such effects on affiliative behavior are not inducible by vasopressin in the promiscuous montane vole (M. montanus). 4 This association between sociality and vasopressin signaling also extends into other vertebrate classes. Highly affiliative, colonial bird species show increased aggression when injected with vasotocin (the avian homolog of mammalian vasopressin) into the lateral septum, whereas terri- torial species show an attenuation in aggression. 5–7 Vasopressin acts centrally on vasopressin 1a and 1b receptors (V1a, V1b). Neural vasopressin binding patterns show differences that parallel differences in mating strategies in voles, with promiscuous species showing higher levels of binding in the lateral sep- tum than monogamous species. 8 Further studies re- vealed that a noncoding region upstream of the V1a receptor gene is crucial to the expression of social doi: 10.1111/j.1749-6632.2010.05885.x 106 Ann. N.Y. Acad. Sci. 1220 (2011) 106–116 c  2011 New York Academy of Sciences.