Effects of vasopressin and other neuropeptides on rostral medullary sympathoexcitatory neurons ‘in vitro’

Abstract

Neurons with intrinsic pacemaker activity and presumed sympathoexcitatory function were recorded in rat tissue slices within the confines of the rostroventrolateral reticular nucleus (RVL). These cells were excited in dose-dependent fashion by arginine vasopressin (AVP, 10 −8–10 −6 M) but not by oxytocin (up to 10 −7 M). The effect of AVP was mimicked by the V 1-selective agonist [Phe 2, Orn 8]vasotocin (VT) (1 μM) but not by the V 2-agonist [Val 4, d-Arg 8]vasopressin (VP) (1.9 μM). The effect of AVP (10 −7 M) was completely blocked by SKF 101926 (10 −7 M), a non-selective antagonist and by d(CH 2) 5[Tyr(Me) 2]AVP, a V 1-selective antagonist but was unaffected by the V 2-selective antagonist d(CH 2) 5[ d-Ile 2,Ile 4,Ala-NH 2 9]AVP. These cells were also activated by thyrotropin-releasing hormone (TRH) (10 −7–10 −6 M), calcitonin gene-related peptide (CGRP) (4 × 10 −8M), substance P, (10 −6 M), neuropeptide Y (NPY) (10 −8 M) and inhibited by Met-enkephalin (10 −6 M) and morphine (2 mM). Corticotropin-releasing factor (CRF) (10 −7 M) and angiotensin II (10 −6 M) were ineffective. In conclusion, RVL pacemaker neurons have vasopressin receptors reminiscent of the V 1 (vascular and pressor) subtype. Their pacemaking activity is modulated by low doses of several other peptides also known to produce large vasomotor effects after introduction into the cerebroventricular space.