Neurokinin A in capsaicin-sensitive neurons of the guinea-pig inferior mesenteric ganglia: an additional putative mediator for the non-cholinergic excitatory postsynaptic potential.
The presence of neurokinin-A-like immunoreactivity in guinea-pig inferior mesenteric ganglia was detected by radioimmunoassay procedures. Pretreating the animals with capsaicin 7 days prior to experimentations reduced the mean content of neurokinin-A-like immunoreactivity by 85% from its control value of 150 +/- 31.3 fmol per ganglion. High-performance liquid chromatography revealed that neurokinin-A-like immunoreactivity was heterogenous as in addition to neurokinin A, peaks corresponding to the amphibian tachykinin eledoisin and to neuropeptide K were detected, and they too were depleted by capsaicin. Electrophysiological studies showed that neurokinin A applied either by superfusion or by pressure ejection evoked a slow depolarization in the majority of inferior mesenteric ganglia neurons in vitro. Neurokinin-A-evoked depolarizations in the majority of cells tested were associated with a small increase in membrane input resistance. However, the responses were increased by membrane hyperpolarization: the extrapolated mean equilibrium potential of neurokinin-A-induced depolarization was -36 mV. Removal of extracellular sodium but not chloride ions suppressed the neurokinin-A-induced depolarization. The slow depolarization elicited either by exogenously applied substance P or by repetitive stimulation of hypogastric nerves was reversibly eliminated in the presence of neurokinin A. Collectively, our studies suggest that neurokinin-A-like immunoreactivity may coexist with substance-P-like immunoreactivity in capsaicin-sensitive fibers in the guinea-pig prevertebral ganglia and that the similarity of the actions of neurokinin A on the one hand and substance P on the other raises the possibility that non-cholinergic excitatory potentials elicited in the inferior mesenteric ganglia may be generated by not one but a number of closely related tachykinins.
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004594:Electrophysiology; D005260:Female; D005728:Ganglia, Sympathetic / Q000032:analysis / Q000502:physiology*; D006168:Guinea Pigs; D008297:Male; D015288:Neurokinin A; D009479:Neuropeptides / Q000032:analysis* / Q000494:pharmacology; D018377:Neurotransmitter Agents; D011863:Radioimmunoassay; D013373:Substance P / Q000494:pharmacology; D009435:Synaptic Transmission
D009479:Neuropeptides; D018377:Neurotransmitter Agents; D013373:Substance P; D015288:Neurokinin A; D002211:Capsaicin