OXYTOCIN RECEPTORS ON OXYTOCIN NEURONS - HISTOAUTORADIOGRAPHIC DETECTION IN THE LACTATING RAT

1. The purpose of the present study was the detection at the cellular scale the oxytocin (OT) receptors involved in the facilitatory effect of this neuropeptide on its own release during the milk ejection refle x. 2. OT binding sites were demonstrated in brain sections by using a highly Selective I-125-labelled OT antagonist detected by film- and hi stoautoradiography.3. Film autoradiographs revealed the presence of OT binding sites in the hypothalamic magnocellular (supraoptic, paravent ricular and anterior commissural) nuclei in lactating rats, suckled or not, This detection was only possible after acute I.C.V. injection of OT antagonist which probably induced an upregulation of the OT bindin g sites to autoradiographically detectable levels, 4. Combined applica tion of histoautoradiographic and immunohistochemical techniques showe d that the OT binding sites were concentrated on OT magnocellular neur ones. Labelling concerned cell bodies and dendrites but not the axons and endings in the pituitary neural lobe. 5. The presently detected. s omatodendritic autoreceptors on OT neurones probably mediate the facil itatory effect of OT on its own release during the milk ejection refle x.