Distribution of calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, substance P and dopamine beta-hydroxylase immunoreactive nerve fibres in the trachea of sheep.

The distribution of nerve fibres containing calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), substance P (SP) and the catecholamine enzyme marker dopamine beta-hydroxylase (DBH) in the trachea of sheep was investigated by immunohistochemical methods. A semi-quantitative assessment of the extent of the nerve fibres immunoreactive for the various antigens was also made. Moderate to large numbers of CGRP-like immunoreactive (CGRP-Li) nerve fibres were present in all parts of the trachea including the epithelial layer, lamina propria, smooth muscle, closer to the mucous glands and blood vessels, and in the elastic fibre connective tissue layer. Although SP-Li nerve fibres had a similar distribution to CGRP, they were absent from the epithelial layer and only small numbers of fibres were present in other areas. Moderate numbers of VIP-Li fibres were present in the smooth muscle and close to mucous glands and blood vessels. Moderate numbers of NPY-Li fibres were present in the smooth muscle with smaller numbers close to mucous glands and blood vessels. Large numbers of DBH-Li nerve fibres were present in the smooth muscle and they had a similar distribution to NPY. The presence of both NPY and DBH in most DBH-Li nerve fibres was established by a double-straining technique, but not all the DBH-Li fibres contained NPY. The DBH/NPY-Li nerve fibres in the smooth muscle formed an extensive and dense interconnecting network and were the most common types of nerve fibres observed.