Substance P actions on sensory neurons.

SP is involved in sensory transmission as a mediator of excitation at target tissues following its release from the terminals of certain primary afferent fibers. In view of the pronounced SP effects on the perikarya of sensory neurons, it seems reasonable to suggest that its actions may extend to autoreceptors and to the enhancement of the excitabilities of sensory neurons that do not synthesize the peptide. This hypothesis would be strengthened by the demonstration of nonsynaptic release of SP within sensory ganglia, which would provide another site for interaction of SP with the various component cells of the sensory system.