Localization of kappa opioid receptors in oxytocin magnocellular neurons in the paraventricular and supraoptic nuclei

It has been demonstrated previously that K opioid receptor agonists, such a s dynorphin, inhibit oxytocin secretion in the rat. To determine whether K agonists act directly on oxytocin-containing magnocellular neurons to inhib it hormone secretion, we utilized immunofluorescence to examine the cellula r localization of K opioid receptors in the rat paraventricular and supraop tic nuclei. K Opioid receptor immunoreactivity co-localized with oxytocin-c ontaining cell bodies, their axons and axon terminals. Thus, our results su ggest that K opioid receptor agonists can exert direct inhibitory actions o n oxytocin magnocellular neurons. (C) 2001 Elsevier Science B.V. All rights reserved.