Gz. Yu et al., THE OLFACTORY-BULB - A CRITICAL SITE OF ACTION FOR OXYTOCIN IN THE INDUCTION OF MATERNAL-BEHAVIOR IN THE RAT, Neuroscience, 72(4), 1996, pp. 1083-1088
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.