The peripheral substance P-ergic system.

In this review we have described the distribution, precise quantities and physico-chemical characteristics of Substance P in the central nervous system and in 7 peripheral organs. In keeping with the main reported actions of substance P as a modulator of both smooth muscle tone and blood vessel diameter, nerve fibres containing the peptide are frequently seen in close proximity to smooth muscle fibres and blood vessels. The postulated role of substance P as a sensory transmitter has been fully supported by the finding of significant concentrations of the peptide not only in primary sensory neurons but also in their central and peripheral branches. Its transport and release at afferent terminals is further validated by the significant depletion of substance P which occurred in the corresponding tissue after ligation of a sensory nerve (vagus), destruction of a ganglion (i.e., Gasserian ganglion leading to depletion from ocular structures) and treatment with capsaicin. The ultrastructural secretory granules containing Substance P are shown here by a novel immunocytochemical procedure using gold-labelled antibodies on ultrathin sections to correspond to a sub-class of the large, dense, p-type neurosecretory vesicles, with characteristic size (mean 85 +/- 15 nm), electron density and limiting membrane.