Rats and mice also display short-term memories of recently encountered individuals, which decay in ∼1 hr ( Gheusi et al., 1994 Popik and van Ree, 1998). In rodents, enduring social memories are a component of a variety of complex social and reproductive processes, including pair bond formation in monogamous species ( Demas et al., 1997) and selective pregnancy termination in mice ( Kaba et al., 1989 Keverne, 1998). Across species, social memories are required for kin recognition and for the establishment of dominant–subordinate relationships.
Social recognition forms the foundation on which all social relationships are built. With site-specific injections of OT and an OT antagonist, we demonstrate that OT receptor activation in the medial amygdala is both necessary and sufficient for social recognition in the mouse. OT knock-out, but not WT, mice showed dramatic increases in Fos-IR in the somatosensory cortex and the hippocampus, suggesting alternative processing of social cues in these animals. Projections sites of the medial amygdala also failed to show a Fos-IR induction in the OT knock-out mice. Wild-type, but not OT knock-out mice exhibited an induction of Fos-IR in the medial amygdala. Using c-Fos immunoreactivity (Fos-IR) as a marker of neuronal activation in this initial encounter, we found similar neuronal activation in the wild-type (WT) and OT knock-out mouse in olfactory bulbs, piriform cortex, cortical amygdala, and the lateral septum. OT given before, but not after, the initial encounter restores social recognition in OT knock-out mice. Here we demonstrate that OT acts in the medial amygdala during the initial exposure to facilitate social recognition. OT treatment fully restores social recognition. Oxytocin (OT) knock-out mice fail to recognize familiar conspecifics after repeated social exposures, despite normal olfactory and spatial learning abilities.