Role of the vomeronasal system in vasopressinergic modulation of social recognition in rats.

To assess the role of the vomeronasal organ (VNO) in the dependence of social recognition on vasopressinergic transmission, vomerectomized rats were compared to intact and castrated male rats. Removal of the VNO significantly decreased the duration of social investigation and temporarily impaired social recognition. In contrast to sham-operated animals and non-operated animals, lesioned rats were no longer responsive to the blocking effect of the antagonist of the vasopressor receptors of vasopressin (dPTyr(Me)AVP, 30 micrograms/kg subcutaneously) on social recognition. Consequently, VNO-lesioned rats behave like castrates, in spite of the lack of effect of removal of the VNO on plasma testosterone levels. These results suggest that androgen-dependent vasopressinergic neurons are part of the VNO pathway and that the VNO system is important for processing and storage of socially relevant information in male rat.