Patterns of innervation of sympathetic vascular neurons by peptide-containing primary sensory fibers

The purpose of this study was to determine whether there is a specific orga nization of the primary sensory innervation on to identified vascular neuro ns in the inferior mesenteric ganglion (IMG) in guinea-pig. Retrograde trac ers were placed intraluminally in inferior mesenteric artery (IMA) or infer ior mesenteric vein (IMV) in vitro to identify ganglionic neurons as arteri al, venous or unlabeled neurons. The distribution of primary sensory nerve fibers containing calcitonin gene-related peptide (CGRP), neuronal nitric o xide synthase (NOS) and substance P immunoreactivity (SP-IR) was compared b efore and after treatment with capsaicin. In control animals the density of immunoreactivity varied both with the transmitter and the type of neuron i nnervated. The density of immunoreactivity for all the three substances was reduced by capsaicin treatment. The degree of reduction of immunoreactivit y in the fibers varied with the transmitter and the type of neuron. The den sity of CORP and SP immunoreactive fibers was greatest around unlabeled neu rons; 78% of the CORP fibers were of primary sensory origin and sill of the SP fibers were primary sensory. Around arterial neurons 44% of the CGRP fi bers were of primary sensory origin and around venous 68% were primary sens ory. NOS positive innervation around venous neurons was denser than around arterial neurons and ail of it was completely (97%) eliminated by capsaicin , indicating that it was solely of primary sensory origin. We conclude that the primary sensory fibers innervating the IMG are differentially distribu ted to arterial and Venous neurons and that the pattern of distribution is characteristic for each sensory neurotransmitter. (C) 1999 Elsevier Science B.V. All rights reserved.