Projections from the ventromedial nucleus of the hypothalamus contain oxytocin binding sites

Experiments were conducted to determine the source of steroid-dependent oxytocin (OT) receptors that surround the ventrolateral portion of the ventromedial hypothalamic nucleus (vl-VMN). Ovariectomized rats received sham or unilateral electrolytic lesions of the vl-VMN. Three days later and for the next 4 days, animals were injected with 10 micrograms of estradiol benzoate (EB). OT receptors were labelled with 125I-d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]OVT and binding was assessed with autoradiographic methods. Lesions of the vl-VMN reduced OT receptor binding in the area surrounding the nucleus by over 80% indicating that the majority of OT receptors in the ventromedial hypothalamus are located on fibers originating within the VMN.