Localization of heme oxygenase-2 in the canine larynx.

The localization of heme oxygenase-2 (HO-2) in the larynx of the dog was investigated using immunohistochemistry. HO-2-positive cells were seen among neurons in intralaryngeal ganglia. Nerve fibers positive to HO-2 immunohistochemistry were seen surrounding laryngeal glands and arterioles and also in the adventitia of arterioles. HO-2-positive fibers were also seen running parallel to the mucosa in the lamina propria but no positive fibers were seen in the epithelium. Some of the intramuscular neurons found in the intrinsic laryngeal muscles were HO-2-positive, although no positive motor fibers were seen, and the neuromuscular junctions were also HO-2-negative. The results implicate the participation of HO-2-in the parasympathetic innervation of the larynx.

Involvement of carbon monoxide in the innervation of the canine cervical esophagus and trachea.

We investigated the involvement of carbon monoxide (CO) in the innervation of the canine cervical esophagus and trachea by means of immunohistochemistry using an antiserum against heme oxygenase-2 (HO-2). We detected HO-2-immunoreactive nerve fibers around the blood vessels and submucosal glands of the esophagus and trachea. We found HO-2-immunoreactive neurons in ganglia in the trachea and in the myenteric plexus of the esophagus. These results suggest that CO is involved as a neurotransmitter in the innervation of the canine esophagus and trachea.

Induction of nitric oxide synthase activity in nucleus ambiguus motoneurons after injury to the rat recurrent laryngeal nerve.

Recent studies have implicated nitric oxide (NO) in neuronal degeneration and plasticity in the motor nervous system. In the present study, we investigated the induction of nitric oxide synthase (NOS) in the motoneurons in the nucleus ambiguus (NA) after injury to the rat recurrent laryngeal nerve (RLN) using nicotinamide-adenine-dinucleotide-phosphate-diaphorase (NADPH-d) histochemistry. NADPH-d reactivity was clearly induced in motoneurons in the ipsilateral NA after transection or avulsion of the RLN, compared with control animals. This finding suggests that NO may play an important role in the pathogenesis of RLN paralysis. Another interesting finding in the present study was the induction of NADPH-d reactivity in nerve terminals of the NA after RLN injury. This finding suggests that RLN injury has some effect on nitrergic input to the NA and a direct effect on the motoneurons.

Neurotransmitters and neuromodulators involved in laryngeal innervation.

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, autonomic, 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.