Vasopressin-mediated slow EPSPs in a mammalian sympathetic ganglion

Vasopressin is one of numerous neuropeptides contained in sympathetic ganglia, but whose function remains unresolved. In this report, we present electrophysiological evidence that arginine-vasopressin (AVP) is a neurotransmitter in guinea pig inferior mesenteric ganglion (IMG). AVP superfused over the IMG, in vitro, produced in a population of neurons a membrane depolarization accompanied by a resistance increase, both of which were blocked by a specific V1 receptor antagonist. Moreover, slow excitatory postsynaptic potentials (EPSPs) elicited by repetitive nerve stimulation were attenuated in 75% of cells tested in the presence of excess AVP, and occasionally in the presence of the antagonist. Thus, AVP joins substance P as a putative transmitter of slow potentials in the guinea pig IMG.