Facilitation of nicotinic response in the guinea pig prevertebral neurons by substance P.

Fast excitatory postsynaptic potentials (f-EPSPs) evoked in guinea-pig inferior mesenteric ganglion cells were augmented during the course of non-cholinergic EPSP which is thought to be mediated by a substance P (SP)-like peptide. SP applied exogenously likewise increased the f-EPSPs and nicotinic depolarizations induced by acetylcholine applied by pressure ejection. Contrary to several earlier studies where SP was reported to interfere with nicotinic receptor activation, our results show that the peptide facilitates nicotinic transmission in the inferior mesenteric ganglia.