Enhanced social interactions in rats following chronic, centrally infused oxytocin

Most studies investigating the behavioral effects of centrally administered oxytocin (OT) have been confined to single acute injections followed by brief behavioral observations lasting up to 90 min. The present study examines the behavioral effects of chronic, centrally administered OT in male rats observed continuously for prolonged periods of time. Either artificial cerebrospinal fluid or OT was centrally infused (via osmotic minipump) to gonadally intact male rats. Behavioral observations were made on males paired with either ovariectomized or estrous females during a 6-h time period. Most striking was the observation that durations of physical contact were doubled in pairs containing OT-infused males, even in the absence of sexual interactions. Also, OT-infused males showed significantly higher levels of anogenital sniffing of females and autogrooming; however, sexual interactions were unaffected by chronic OT. Chronic OT had no effect on body temperature, analgesia, or exploratory behavior in an open field. These findings suggest that chronic OT in male rats has behavioral effects that may significantly enhance adult social (nonsexual) interactions, possibly through alterations in olfactory and somatosensory information processing.