Is oxytocin-induced grooming mediated by uterine-like receptors?

In this study, we examined whether the mechanisms mediating the induction of grooming behavior by oxytocin (OT) is similar to mechanisms mediating the effects of OT on uterine contractility. Sprague-Dawley strain female rats were injected intracerebroventricularly (ICV) with OT or OT analogues and then were observed for grooming behaviors 25 minutes later for 30 minutes. The uterotonic analogue deamino-OT injected ICV at equimolar doses to 1 μg OT significantly elevated grooming scores although less than did OT. Other agonist analogues were not effective in inducing an increase in grooming behavior. The simultaneous ICV injection of the analogue [Pen¹, Phe², Thr⁴, Δ³, ⁴Pro⁷, Orn⁸]-OT, which blocked the effects of OT on uterine contractility, also blocked the effect of OT on grooming behavior. Injection of the same dose of this antagonist analogue did not affect the increased grooming behavior after AVP injection. Pretreatment with 5 mg/kg of the prostaglandin synthetase inhibitor indomethacin significantly inhibited OT-induced grooming. We have concluded from these data that the mechanism underlying the effect of OT on grooming is similar to its effects on uterine contractility in some respects. However, observations that the OT antagonist analogue blocked OT-but not AVP-induced grooming may suggest that more than one receptor or mechanism exists by which nonapeptides initiate excessive grooming.