Neurotransmitter interaction in release of intranuclear oxytocin in magnocellular nuclei of the hypothalamus.

Oxytocin (OT) is released within the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus in response to several stimuli. However, the neurotransmitters that control this intranuclear OT release are unknown. In vivo microdialysis was used to examine the roles of norepinephrine and histamine in intranuclear OT release in conscious, lactating female rats. Administration of alpha- or beta-noradrenergic agonists, or histamine, increased OT release in the PVN. In addition, the increase in PVN OT evoked by exogenous histamine was prevented by simultaneous blockade of either H1 or H2 receptors. Furthermore, histamine-induced release of intranuclear OT was also prevented by blockade of alpha-adrenergic receptors. Finally, the increase in magnocellular OT release induced by suckling was abolished by administration of alpha-adrenergic antagonists. These data demonstrate that norepinephrine and histamine are important neurotransmitters for release of intranuclear OT, and histamine releases intranuclear OT by stimulating norepinephrine release.