Oxytocin in the medial amygdala is essential for social recognition in themouse

Oxytocin (OT) knock-out mice fail to recognize familiar conspecifics after repeated social exposures, despite normal olfactory and spatial learning ab ilities. OT treatment fully restores social recognition. Here we demonstrat e that OT acts in the medial amygdala during the initial exposure to facili tate social recognition. OT given before, but not after, the initial encoun ter restores social recognition in OT knock-out mice. Using c-Fos immunorea ctivity (Fos-IR) as a marker of neuronal activation in this initial encount er, 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. Wild-type, but not OT knock-out mice exhibited an induction of Fos-IR in the medial amygdala. Projections sites of the medial amygdala also failed to show a Fos-IR induction in the OT knock-out mice. OT knock- out, but not WT, mice showed dramatic increases in Fos-IR in the somatosens ory cortex and the hippocampus, suggesting alternative processing of social cues in these animals. With site-specific injections of OT and an OT antag onist, we demonstrate that OT receptor activation in the medial amygdala is both necessary and sufficient for social recognition in the mouse.