Neurotransmitters and Neuromodulators Involved in Laryngeal Innervation

Abstract

The distribution and role of neurotransmitters and neuromodulators in laryngeal innervation are reviewed, and our recent findings regarding the nitrergic innervation of the larynx are demonstrated for the better understanding of the complexity of the laryngeal innervation system. Noradrenergic innervation of the larynx was studied with fluorescence histochemistry and electron microscopy after application of 5-hydroxydopamine. These studies confirmed the existence of noradrenergic innervation for the submucosal glands and blood vessels, and the origin and course of noradrenergic nerve fibers contained in the laryngeal nerves and their destinations in the larynx. Cholinergic innervation of the larynx has not been clarified in detail. Many kinds of neuropeptides have been demonstrated to be involved in laryngeal innervation. Vasoactive intestinal polypeptide originating from intralaryngeal ganglionic neurons participates in laryngeal vasodilation and reduction of laryngeal seromucous secretion. Neuropeptide Y nerve fibers are few in the larynx, and most originate from the superior cervical ganglion. They are distributed around the large or medium-sized blood vessels, especially arteries. They are also associated with excretory structures. Substance P was the first neuropeptide found to be a sensory neurotransmitter in the laryngeal afferent system. It is also involved in regulation of laryngeal blood flow and secretion. Calcitonin gene-related peptide is associated with the sensory, autonomie, and motor innervation of the larynx. The majority of enkephalin nerve fibers are located close to excretory structures, although no information on the physiological significance of enkephalin is available. In addition to the above neuropeptides, the peptides histidine isoleucine, histidine methionine, and helospectin have been shown to exist in the larynx. The nitrergic innervation of the larynx has been recently studied with NADPH-diaphorase histochemistry and immunohistochemistry using antiserum against nitric oxide synthase. Nitric oxide originates from the neurons in the intralaryngeal ganglia and is believed to modulate blood flow and secretion of the larynx. It controls the laryngeal exocrine secretion in cooperation with intrinsic vasoactive intestinal polypeptide and/or extrinsic calcitonin gene-related peptide. Nitric oxide from the nodose ganglion may modulate nociception of the larynx. The existence of nitrergic neurons located in the intrinsic laryngeal muscles has been demonstrated. Many of them are bipolar or pseudounipolar, so they might be sensory in nature. The effect of injury of the recurrent laryngeal nerve on the induction of nitric oxide synthase in the laryngeal motoneurons is also discussed.

Ability of the Vericator to Detect Smugglers at a Mock Security Checkpoint

“…This oscillation is found in voluntary muscles and is generally termed 'physiological tremor' (Lippold, 1971), but for VSA, is termed 'microtremor' (Shipp & Izdebski, 1981). The autonomic nervous system has been shown to innervate the larynx (Hisa et al, 1999). In VSA, the working hypothesis is that microtremors are suppressed, via autonomic mechanisms, when psychological stress is created (Reeves, 1980).…”

The Effects of Vagal Stimulation on Laryngeal Vascular Resistance and Intraluminal Pressure in the Dog

“…On the other hand, Laitinen et al (1987a) suggested that vasodilatation caused by parasympathetic nerve stimulation in nose and trachea after atropine administration, may be mediated by the release of neuropeptides such as VIP. Recent studies in which the role and distribution of neurotransmitters and neuromodulators are investigated, suggest that NPY, VIP, NOS-1 and CGRP take an important part in the regulation of laryngeal blood flow (Hisa et al 1999 ;Lyon 2000).…”

Intrinsic laryngeal muscle activity in response to autonomic nervous system activation

“…One pathway implicated in the development and propagation of FVDs is the autonomic nervous system (ANS). The autonomic innervation of the larynx is fairly well established, with respect to both anatomical and immunohistochemical findings . However, in the context of FVDs, the diagnosis of which is often based on observations of elevated laryngeal muscle tension, it is unclear how ANS‐driven effects would manifest in terms of muscle activity.…”

“…In summary, abundant evidence exists regarding autonomic innervations of the larynx . However, details regarding specific, autonomically driven laryngeal responses remain unclear.…”