THE OLFACTORY-BULB - A CRITICAL SITE OF ACTION FOR OXYTOCIN IN THE INDUCTION OF MATERNAL-BEHAVIOR IN THE RAT

Expanding on research showing that oxytocin originating in the hypotha lamic paraventricular nucleus acts to decrease olfactory processing at the level of the olfactory bulb, we explored the importance of oxytoc in acting on the olfactory bulb for the onset of maternal behaviour in Wistar rats. Experiment 1 was designed to test whether spontaneous ma ternal behaviour following natural delivery is blocked by bilateral in fusions of a low dose (5 fmol) of the oxytocin antagonist (5)[Tyr(Me)( 2),Thr(4),Tyr-NH29]ornithine-vasotocin into the olfactory bulb immedia tely after the delivery of the first pup and again just before a test for maternal behaviour. Intrabulbar infusions of the antagonist marked ly delayed the occurrence of all components (retrieval, licking, nest building, crouching) of maternal behaviour, whereas intracerebroventri cular infusions of the antagonist were without effect on any component as compared with intrabulbar infusions of saline. Experiment 2 was un dertaken to determine whether infusions of oxytocin into the bulb indu ce a rapid onset of maternal behaviour in virgin rats. Forty-eight hou rs before pup presentation virgins were ovariectomized and treated wit h oestradiol benzoate. Immediately before pup presentation a low dose (20 pmol) of oxytocin or saline was infused bilaterally into the bulb or lateral ventricle. Intrabulbar infusions of oxytocin induced full m aternal behaviour in half of the animals tested within 2 h of pup expo sure, in contrast to the ineffectiveness of intracerebroventricular in fusions of oxytocin and intrabulbar infusions of saline. These results suggest that the olfactory bulb is a critical site where oxytocin act s to induce a rapid onset of maternal behaviour.