The influence of the paraventriculo-spinal pathway, and oxytocin and vasopressin on sympathetic preganglionic neurones.

In anaesthetized rats the effect of two procedures was studied on antidromically identified sympathetic preganglionic neurones (SPN) in the second thoracic (T) segment of the spinal cord: the application of iontophoresed oxytocin and vasopressin, and bipolar electrical stimulation of the paraventricular nucleus of the hypothalamus (PVN). In the majority of cases (16/23) oxytocin inhibited SPN firing, 1/23 being excited. Vasopressin inhibited 8/14 neurones and excited 4/14. PVN stimulation inhibited SPN apparently by an action on the membrane of SPN. The possibility that oxytocin and vasopressin act as transmitters in the paraventriculo-spinal pathway, and their possible involvement in the mediation of PVN evoked inhibition of SPN activity has been discussed.