Substance P as an excitatory transmitter of primary afferent neurons in guinea-pig sympathetic ganglia.
Electrophysiological and neurochemical experiments were carried out to examine a possible transmitter role substance P in the prevertebral ganglia of the guinea-pig. When potentials were recorded intracellularly from neurons of the isolated ganglia, stimulation of the pre- or postganglionic nerves elicited a non-cholinergic slow excitatory postsynaptic potential (EPSP). This synaptic potential was compared with the effects of substance P. Brief application of substance P caused a depolarization of the ganglion cells with a similar time course to that of the non-cholinergic slow EPSP. Changes in membrane resistance during the substance P-induced depolarization resembled those associated with the non-cholinergic slow EPSP. During the substance P-induced depolarization the non-cholinergic slow EPSP was markedly depressed. Attempts were made to determine the origin of the fibers eliciting the non-cholinergic slow EPSP. In the inferior mesenteric ganglia isolated together with preganglionic nerves that retained intact connections with spinal nerve roots, dorsal root stimulation evoked a non-cholinergic slow EPSP but not a cholinergic fast EPSP in the ganglion cells, whereas ventral root stimulation caused only cholinergic fast EPSPs. Following the prolonged treatment with capsaicin, the non-cholinergic slow EPSP was greatly depressed or abolished. Radioimmunoassay revealed that after ligation or section of pre- or postganglionic nerves an accumulation of substance P occurred in the proximal stumps of the interrupted nerves. Stimulation with high potassium medium evoked a release of immunoreactive substance P from the prevertebral ganglia and the release was calcium-dependent. The present findings suggests that axon collaterals of certain visceral primary efferents form synapses with principal cells in the prevertebral ganglia and release substance P as a transmitter for the non-cholinergic slow EPSP.
D000320:Adrenergic Fibers / Q000502:physiology; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001339:Autonomic Fibers, Preganglionic / Q000502:physiology; D001370:Axonal Transport / Q000187:drug effects; D002211:Capsaicin / Q000494:pharmacology; D002799:Cholinergic Fibers / Q000502:physiology; D005071:Evoked Potentials / Q000187:drug effects; D005727:Ganglia, Spinal / Q000502:physiology; D005728:Ganglia, Sympathetic / Q000502:physiology*; D006168:Guinea Pigs; D008297:Male; D009474:Neurons / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D011863:Radioimmunoassay; D013373:Substance P / Q000008:administration & dosage / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects
D013373:Substance P; D011188:Potassium; D002211:Capsaicin