The peptidergic innervation of the guinea pig's respiratory tract was examined immunohistochemically. We investigated 3 kinds of peptides in this study-SP, VIP, L-Enk. SP was detected extensively throughout the respiratory tract-nose, larynx, trachea and it's peripheral. But the other 2 kinds of peptides stained poorly or not at all.
In the nasal mucosa, fine varicose SP fibers were clearly seen in the subepithelial region, and some of them passed through the epithelial layer. Also we were able to find them around the blood vessels and the acini of nasal glands, but SP fibers were scarce around the ducts. Between the nasal glands, there were fine varicose SP nerve bundles, which innervated the nasal glands, blood vessels and epithelial region.
In the laryngeal mucosa, the distribution pattern of SP fibers was the same as in the nose, and some SP fibers were detected in the epithelial region. In the branches of the vagus nerve which run in the laryngeal region, we were able to see many SP fibers and occasionally even SP nerve cell bodies. Around the laryngeal glands and arteries, SP fibers stained well, but there seemed to be very few in the veins.
In the tracheal region, we were able to observe many fibers in the smooth muscle, subepithelial region, glands and tracheal blood vessels. These fibers mentioned above were most numerous in the lower region of the main trachea near the carina and then lessening the number of them in the bronchi and bronchioles. SP immunoreactive nerve cell bodies were found in the tracheobroncheal region, mostly near the carina. Some SP fibers may have originated from these cell bodies along the trachea, bronchi and bronchioles.
Such SP fibers in the respiratory tract were distributed in the same way as the cholinergic nerve fibers, suggesting that SP nerves in the respiratory tract may regulate the vasodilatation, the secreation of the glands and the contraction of the smooth muscle in coordination with cholinergic nerves.
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