Tadatsugu Maeyama

Substance P immunoreactive nerve fibers of the canine laryngeal mucosa.

Substance P (SP) immunoreactive nerve endings in the laryngeal mucosa were studied by PAP immunohistochemistry with light and electron microscopy. SP immunoreactive sensory endings were observed in the epithelium as intra-epithelial free nerve endings and taste bud-like structures. A small number of autonomic SP immunoreactive nerve fibers were observed running parallel to arterioles which were over 30 μm in diameter and terminated in glandular cells. Contrary to findings by silver impregnation, intraepithelial free nerve endings were more frequently observed on the lower surface of the vocal cord. The taste bud-like structures were classified into two different types: (1) simple terminations and (2) reticular terminations, according to the mode of the SP immunoreactive nerve fiber. Immature or degenerated taste bud-like structures in the larynx were assumed to be mechanical receptors because these receptors lacked outer taste pores and taste hairs.

Morphologic study of the laryngeal taste buds in the cat.

The distribution of laryngeal taste buds (TBs) and their neural components in the cat were investigated by immunohistochemistry and electron microscopy. The antisera used in this study were against cytokeratin, protein gene product 9.5 (PGP9.5), neuron‐specific enolase (NSE), S‐100 protein, calbindin‐D, calcitonin gene‐related peptide (CGRP), and substance P(SP).

Sensory nerve endings in the mucosa of the epiglottis--morphologic investigations with silver impregnation, immunohistochemistry, and electron microscopy.

This study was conducted in order to investigate the structure of sensory nerve endings of the human epiglottis and substance P immunoreactive nerve fibers of the canine epiglottis in relationship to physiologic functions of the larynx. The human epiglottis was observed by light microscopy (silver impregnation) and electron microscopy, and the canine epiglottis was studied by peroxidase-anti-peroxidase (PAP) immunohistochemistry. The results are summarized as follows: (1) In the membranes of the epiglottis, we observed free endings of simple or complex tree shape, corpuscle endings with glomerular patterns, and taste-bud-like structures, and (2) electron microscopic studies revealed varicosity of the terminal axon with processes that contained small, clear and large, dense cored vesicles. Substance P was observed in these structures, and it was suggested that substance P was related to perception in the larynx.

Misdirected regeneration of injured recurrent laryngeal nerve in the cat

INTRODUCTION Misdirected regeneration (MR) frequently occurs following injury to the recurrent laryngeal nerve (RLN) resulting in neurotmesis or axonotmesis. Physiological and anatomic parameters involved in the functional recovery of the larynx following freezing injury or neurorrhaphy of the RLN were studied. A multi-facilitated approach is undertaken to clarify the functional abnormalities caused by the MR after recurrent laryngeal nerve injury. MATERIALS AND METHODS Three groups of adult cats were studied. These included controls, cats with recurrent laryngeal neurorrhaphy, and cats with recurrent laryngeal nerve freeze injuries. From 2 weeks to 9 months after the nerve injury, the animals were studied endoscopically and with electromyography (EMG). Using the same animal, the number and location of motoneurons supplying the ipsilateral posterior cricoarytenoid (PCA) muscle were examined with horseradish peroxidase (HRP). Animals were subsequently sacrificed to study the pattern of reinnervation. RESULTS Following neurorrhaphy all cats had vocal cord paralysis. After neurorrhaphy, effective motion function did not return in the affected vocal cord and it remained fixed in the paramedian position. Although EMG of the laryngeal muscles of the affected side showed interference voltage, the pattern of activities was markedly different from that of the unaffected side, and reciprocity among the laryngeal muscles was not restored. The number of PCA motoneurons recovered to the normal range, but a considerable number of neuronal bodies were dispersed outside the normal PCA area. This indicates misdirected reinnervation to the PCA muscle by motoneurons that originally served other laryngeal muscles. In the freezing injury, effective vocal cord movement finally recovered after 6 months. At this time, EMG showed a normal pattern, although a relatively small amount of misdirected neurons was observed. DISCUSSION Functional recovery of vocal cord motion does not occur following neurorrhaphy. Prominently disorganized arrangement of laryngeal motor neurons was observed in the horseradish peroxidase study. This suggests that inappropriate reinnervation develops in spite of reapproximation and suturing. Altered central organization of the motor nucleus is a significant pathogenic factor in the loss of laryngeal muscular coordination following recurrent laryngeal nerve lesions. The degree of recovery is related to the mechanism of injury.

Laryngeal Reflex Mechanism during Deglutition—Observation of Subglottal Pressure and Afferent Discharge

In this investigation, particular attention was paid to elucidate the laryngeal reflex mechanism of protective closure and the sensory function of the larynx during deglutition. For this purpose, three different experimental procedures were adopted: (1) subglottal pressure of felines was measured during deglutition using a pressure transducer; (2) subglottal pressure of human beings was measured during deglutition using a pressure transducer; and (3) afferent discharges from superior and recurrent laryngeal nerves of felines were recorded. The following conclusions appear justified. (1) Feline and human subglottal pressure during deglutition showed the following pattern. The pressure rises with onset of deglutition, temporarily drops during laryngeal elevation, rises again during the downward movement of the larynx, and drops again at the end of the glutltion. This pattern was not affected by the resection of the unilateral recurrent laryngeal nerve. (2) The superior laryngeal nerve is involved in the sensory function of the pharynx, larynx, and trachea. At least two types of afferent discharges from superficial and infernal sensory nerves are suspected. Afferent discharges from the recurrent laryngeal nerves in the larynx and trachea are not as distinct as those of the superior laryngeal nerve, and this seems to correspond with various changes in the thorax. During deglutition, afferent discharges were recorded from superior to recurrent laryngeal nerves.

Glottic Closure during Swallowing in the Recurrent Laryngeal Nerve-Paralyzed Cat

Glottic closing pressure and time were quantitatively analyzed during deglutition and in reflex glottic closure elicited by superior laryngeal nerve stimulation by means of a catheter pressure transducer in the cat. Duration and peak pressure of glottic closure during deglutition were 322.6 ± 32.2 msec (mean ± SE) and 57.5 ± 6.0 mmHg, respectively, whereas peak pressure of the reflex glottic closure was 21.7 ± 6.1 mmHg in control animals. When the recurrent laryngeal nerve was denervated unilaterally, decrease in peak glottic closing pressure on swallowing was only about 36%, whereas the peak pressure of reflex glottic closure was markedly diminished to 4.5 ± 4.6%. When bilateral recurrent laryngeal nerves denervated, decrease in peak pressure during deglutition showed no greater significance than It did after unilateral denervation. Inferior constrictors myotomy in addition to bilateral recurrent laryngeal nerve denervation reduced peak pressure to nearly zero. These results indicate that on swallowing, the inferior constrictors cooperate with the intrinsic laryngeal adductors, thus playing a very important role in reinforcing glottic closure, a function that is unlikely during reflex glottic closure.

Intracordal Injection Increases Glottic Closing Force in Recurrent Laryngeal Nerve Paralysis

Glottic closing pressure during swallowing was measured in the cat with a catheter pressure transducer to study the effectiveness of intracordal injection in increasing glottic pressure in unilateral recurrent laryngeal nerve paralysis. Swallows were elicited by pouring water into the pharynx while the animal was under light anesthesia with ketamine. Peak pressure of the glottic closure for the control group during deglutition was 68.0 ± 10.5 mm Hg (mean ± standard deviation). Peak pressure decreased to 22.0 ± 3.6 mm Hg just after sectioning of the unilateral recurrent laryngeal nerve, and rose to 39.8 ± 8.3 mm Hg by silicon injection into the paralyzed vocal fold. In a study of chronic cases 1 month or more after unilateral recurrent laryngeal nerve section, peak pressure was 49.1 ± 23.4 mm Hg, and varied widely from 21 to 92 mm Hg because of differences in the position of the paralyzed vocal fold and the degree of compensation by the unaffected vocal fold. In the group that had the paralyzed vocal fold fixed in the median position, peak pressure was almost the same as that of the control group. When the paralyzed vocal fold was fixed in either the paramedian or lateral position, peak pressure was 33.3 ± 7.0 mm Hg. This value was significantly elevated to 45.8 ± 10.4 mm Hg by injection of silicon, though it remained lower than that of the control. These results suggest that the decrease in glottic closing force during swallowing as a result of unilateral recurrent laryngeal nerve lesion is compensated for by the unaffected vocal fold to some degree and is improved by intracordal injection.

The fine structure of intraepithelial free nerve endings in the canine vocal cord mucosa.

Innervation of the epithelium on the undersurface of the canine vocal cords was investigated by transmission electron microscopy. In the subepithelial lamina propria, nerve bundles containing unmyelinated fibers were observed. The nerve bundles, encircled by basal lamina, were enclosed by a thin connective tissue layer and by flattened flbroblast-like cells. With nerve bundles approaching the epithelium, the axons divided repeatedly and entered the epithelial layer. In the epithelial cells, nerve axons formed knob-like swellings that contained a small number of large granular vesicles and a large number of small agranular vesicles. A sensory function responsive to irritant chemical stimuli and to mechanical stimuli is presumed for these vesicle-containing nerve processes.

Localization of Laryngeal Motoneurons in the Medulla Oblongata of Guinea Pigs

The distribution of motoneurons in the brain stem innervating the laryngeal muscles cricothyroid, posterior cricoarytenoid, and thyroarytenoid-lateral cricoarytenoid in the adult guinea pig was investigated. Horseradish peroxidase was injected into individual muscles or applied to the cut end of the superior laryngeal nerve and the recurrent laryngeal nerve. The laryngeal motoneuron pool of guinea pig is divided into two separate areas: the rostral retrofacial nucleus and the caudal nucleus ambiguus. Superior laryngeal and cricothyroid motoneurons were present only in the retrofacial nucleus, while recurrent laryngeal motoneurons were present in both the nucleus ambiguus and the retrofacial nucleus. Posterior cricoarytenoid motoneurons were located in the rostral and ventrolateral part of the recurrent laryngeal motoneuron pool in the nucleus ambiguus. The thyroarytenoid-lateral cricoarytenoid motoneurons partially overlapped the posterior cricoarytenoid pool and extended more dorsomedially and caudally in the nucleus. Our findings on the distribution of perikarya in the laryngeal motoneuron of the guinea pig are essentially the same as those of other mammals.

Beaded nerve terminals in feline laryngeal mucosa

To investigate the mechanism of airway defense reflex, beaded nerve terminals were studied by immunohistochemical techniques. In the supraglottic region the density of PGP 9.5–immunoreactive nerve fibers was the highest at the base of the glottic surface in the epiglottis, and in the glottic region it was the highest in the arytenoid region. In the subglottic region the number of positive nerve fibers was less than the number at the base of the glottic surface in the epiglottis, and when the laryngeal mucosa was processed with NaOH to dissolve the epithelium, it was possible to observe beaded nerve terminals more clearly. These beaded nerve terminals were found just beneath, in the epithelial basement membrane. Electron microscopic examination of beaded nerve terminals revealed a large quantity of secretory granules and mitochondria, suggesting that their structure is similar to that of nerve terminals. Thus these beaded nerve terminals may function as mechanoreceptors. (Otolaryngol Head Neck Surg 1998;119:113–6.)