Oxytocin: who needs it?

The neuropeptide oxytocin has been implicated in the initiation of maternal behavior, based on studies in rats and sheep. Females in both of these species naturally avoid infants until parturition when they begin to show an intense interest in maternal care. Oxytocin pathways in the brain appear to be important for this transition from avoidance to approach of the young. Recent studies in mice with a null mutation of the oxytocin gene suggest a different scenario. These mice, which completely lack oxytocin, exhibit full maternal and reproductive behavior, except for a deficit in milk ejection. Apparently, oxytocin is not essential for maternal behavior in this species. Consistent with the role of oxytocin for the transition from avoidance to approach in rats and sheep, nulliparous mice show full maternal behavior and therefore do not require the peptide for the initiation of maternal care. The species differences in the behavioral effects of oxytocin are associated with profound species differences in the location of oxytocin receptors in the brain. Recent transgenic studies suggest that these species differences in the neuroanatomical distribution of oxytocin receptors may be a function of inter-species variation in the flanking region of the oxytocin receptor gene. So, who needs oxytocin? For maternal care, not mice and (possibly) other species, like primates, with promiscuous parental care. Most important, in considering the behavioral or cognitive functions of oxytocin, one cannot accurately extrapolate across species unless one knows the species have the same neuroanatomical location of oxytocin receptors.