Oxytocin but not vasopressin facilities social recognition following injection into the medial preoptic area of the rat brain

Social recognition of juvenile rats by adult male residents has been shown to be modulated by peripheral administration of neurohypophyseal hormones vasopressin and oxytocin. In the present study, the effects of these peptides on social recognition were investigated after local injection into the medial preoptic area of the hypothalamus. It was found that oxytocin given in a wide range of doses (0.3–1000 pg) facilitated social recognition. This effect was not blocked by pretreatment with oxytocin receptor antagonist desGly(NH₂)⁹-d(CH₂)₅[Tyr(Me)²Thr⁴]OVT. Oxytocin injected into the septum in doses of 0.03–3 pg was not effective. Administration of vasopressin (100 or 1000 pg), [pGlu⁴,Cyt⁶]AVP-(4-8) (200 pg) or [pGlu⁴,Cyt⁶]AVP-(4-9) (200 pg) into the medial preoptic area did not influence social recognition. It is concluded that the medial preoptic area is a sensitive brain site for the oxytocin-induced facilitation of social recognition in rats.