Peptide-containing nerve fibers in the respiratory tract of the ferret.

The ferret is widely used in functional and neuromorphological studies on the respiratory tract. We have examined the occurrence and distribution of peptide-containing and adrenergic nerve fibers (using dopamine-beta-hydroxylase as a marker). Adrenergic nerve fibers and fibers storing vasoactive intestinal peptide have a widespread distribution along the entire respiratory tract. Adrenergic nerve fibers were found in the lamina propria, as well as around blood vessels and glands and in smooth muscle. Nerve fibers storing vasoactive intestinal peptide occurred in the epithelium, the lamina propria, around blood vessels and glands, and among muscle bundles. Substance P-, neurokinin A- and calcitonin gene-related peptide-containing nerve fibers predominated beneath and within the epithelium along the entire respiratory tract. Neuropeptide Y-containing nerve fibers were prominent among smooth muscle bundles and around glands. The blood vessels in the wall of the airways were richly supplied with peptide-containing nerve fibers and adrenergic fibers. Ganglia located over the outer or dorsal surface of the tracheal wall harbored vasoactive intestinal peptide-containing nerve cell bodies. Substance P and neurokinin A invariably coexisted in the same nerve fibers. Further, coexistence of substance P/neurokinin A and calcitonin gene-related peptide was observed in the nerve fibers associated with the epithelium. Vasoactive intestinal peptide, neuropeptide Y and occasionally also substance P coexisted in the population of nerve fibers associated with blood vessels and smooth muscle. Many adrenergic nerve fibers contained neuropeptide Y.