The occurrence, distribution and coexistence pattern of an array of neuropeptides and tyrosine hydroxylase in the human larynx, trachea, bronchi and lungs were studied by immunocytochemistry. A rich supply of nerve fibers containing vasoactive intestinal peptide (VIP) was seen close to blood vessels, glands and nonvascular smooth muscle. Pituitary adenylate cyclase-activating peptide (PACAP)-containing fibers were numerous among bundles of smooth muscle. Moderate numbers of helospectin-containing nerve fibers were seen in the nonvascular smooth muscle. The majority of neuropeptide Y (NPY)-containing fibers were located in the nonvascular smooth muscle; some fibers also occurred around blood vessels and glands. Substance P (SP) and calcitonin gene-related peptide (CGRP) -containing fibers were generally few and distributed beneath the epithelium, among bundles of smooth muscle, around blood vessels and glands. A conspicuous finding was the lack of SP- and CGRP-containing fibers within the respiratory epithelium. Galanin-containing nerve fibers were moderate in number among bundles of smooth muscle. Tyrosine hydroxylase-containing fibers were numerous around blood vessels and glands. The majority of the VIP-containing nerve fibers present in nonvascular smooth muscle also stored PACAP and helospectin. A subpopulation of VIP-containing fibers in both vascular and nonvascular smooth muscle and around glands stored NPY. Additionally, galanin was found to occur in many VIP-containing fibers located among bundles of smooth muscle.

Three methods have been used to study the sympathetic and parasympathetic innervation of the vocal cord: paraformaldehyde-induced fluorescence, electron microscopy, and the peroxidase-antiperoxidase technique. Each method has been successful in determining adrenergic fibers, autonomic endings, and the neuropeptides VIP and NPY, respectively. The close relationship between these neuropeptides and the autonomic endings (adrenergic and cholinergic), and the presence of the neuropeptides in the chorion of the vocal cord, around glands and vessels, gives new evidence that autonomic innervation plays a role in the functioning of this part of the larynx.

An experimental model is described for recording laryngeal evoked potentials at the brainstem level through electrical stimulation of the superior laryngeal nerve. Rabbits were divided into two groups according to age: Group 1 consisted of 20 adults (over 6 months old), while group 2 was comprised of 1‐month‐old rabbits. Under general anesthesia, the superior laryngeal nerve was electrically stimulated and the corresponding evoked potentials were recorded by needle electrodes placed close to the dorsal and ventral aspects of the brain stem. Clear age‐related differences were observed for latency, amplitude, and morphology of the potentials. This fact suggests postnatal maturation of the nerve structures, both peripheral and central. Sectioning the superior laryngeal nerve abolished all responses. Adduction of both vocal cords was observed in conjunction with the use of stimulation.

The topographic distribution of Nucleus Ambiguus (NA) motor neurons innervating the intrinsic laryngeal musculature in the guinea pig has not been studied previously. We used 25 guinea pigs anaesthetized by Penthrane (Methoxyflurane) inhalation. Horseradish peroxidase type VI (40%) was used. The motor neurons traced are distributed in cellular groups elongated rostro-caudally in a tract of the brain stem situated between a rostral plane compatible with the location of the retrofacial nucleus, and a caudal plane some millimetres below the obex. The motor neurons observed do not exhibit differential morphology in relation to the different muscles studied.

The distribution of neurons in the dorsal motor nucleus of the vagus nerve (DMNV) that innervate the supraglottic and glottic areas of the larynx of the guinea pig have been studied using the horseradish peroxidase (HRP) technique. Following soaking of the superior laryngeal nerve in a solution of HRP, labeled neurons were always located ipsilaterally, at levels between the estria acustica and the caudal end of the inferior olivary nucleus. Characteristically, the neurons were small or medium in size.