Abstract
Oxytocin (OT) within the olfactory bulb (OB) has been known to play pivotal roles in the induction of maternal behaviour, olfactory recognition of offspring and the preservation of social recognition. However, the cellular mechanisms of OT' actions in the OB remain to be elucidated. Microcircuits in the OB are relatively simple and include the prominent reciprocal dendrodendritic synapse between mitral and granule cells. Glutamate released from mitral cell dendrites activates the dendrites of granule cells, which in turn mediate GABAergic dendrodendritic inhibition back onto mitral cell dendrites. This feedback inhibition at the reciprocal synapses regulates mitral cell activity. In virgin rats, pup odours are aversive and maternal behaviour is not elicited until this aversion is overcome. We have indicated that OT released at parturition modulates olfactory inputs at the level of the OB and thereby facilitates maternal behaviour. Whether OT acts directly on mitral cells, on granule cells or on both has yet to be determined. By using primary OB cultures and whole-cell recording techniques, we have demonstrated that OT facilitates spontaneous EPSCs in granule cells by both pre- and postsynaptic mechanisms and depresses spontaneous IPSCs in mitral cells by a presynaptic mechanism. Taken together with in vivo electrophysiology and in situ hybridization histochemistry, the results suggest that OT predominantly facilitates dendrodendritic interactions between mitral and granule cells by acting on both cells, thereby depressing mitral cell firing. [Jpn J Physiol 54 Suppl:S62 (2004)]
