Immunohistochemical study of the sympathetic and sensory innervation to the blood vessels of the dog forepaw.

Immunohistochemical staining of arteries supplying the dog forepaw showed a dense distribution of nerve fibers which were immunoreactive to tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), substance P (SP), and calcitonin gene-related peptide (CGRP) around the vascular walls. The density of each immunoreactive fiber tended to increase in the peripheral branch of the vascular tree. Retrograde axonal tracing with Fast Blue from the artery revealed that these immunoreactive fibers originated from NPY-containing catecholaminergic as well as VIP/SP/CGRP-containing non-catecholaminergic neurons in the stellate ganglion and SP/CGRP-containing neurons in the dorsal root ganglia of segments C7 to Th1. After stellate ganglionectomy, TH-, NPY-, and, VIP-immunoreactive fibers disappeared completely from the arterial walls while approximately 40% of SP- and CGRP-immunoreactive fibers remained. The present results indicate that the artery of the dog forepaw receive triple innervation of adrenergic sympathetic, non-adrenergic sympathetic, and sensory fibers, and suggest that about 40% of SP- and CGRP-immunoreactive fibers are of sensory origin.