Novel Adaptation of a Validated Tactile Aesthesiometer to Evaluate Laryngopharyngeal Sensation.

OBJECTIVES: To evaluate laryngopharyngeal sensation at specific subsites using a novel adaptation of a buckling force aesthesiometer for delivery of calibrated tactile stimuli. STUDY DESIGN: Cross-sectional. METHODS: Twenty-two healthy adults (12 men, 10 women) were tested for responses to tactile forces, using 30-mm 6-0, 5-0, and 4-0 nylon monofilaments to map sensation of the aryepiglottic (AE) fold, lateral pyriform sinus (PS), and medial PS bilaterally. The outcome measures were the laryngeal adductor reflex (LAR) and patient reported rating of perceptual strength. RESULTS: Rates of triggered LAR response grew monotonically with increasing tactile force at a mean (SD) stimulus duration of 663 (164) msec across all three subsites. The AE fold and medial PS had similar profiles and were the most responsive, while the lateral PS was the least responsive. Low force (6-0) response rate was ≤14% for all subsites. High force (4-0) response rate was 91% for AE fold and medial PS, and 23% for lateral PS. The perceptual strength gradient was in the lateral to medial trajectory. CONCLUSION: Normative data for LAR response rates to low, medium, and high stimulation forces will be useful to assess sensory dysfunction in a variety of laryngopharyngeal disorders, including aspiration, dysphagia, chronic cough, and spasmodic dysphonia. In turn, that information will guide the creation of innovative treatments. LAR response profiles to low and high force stimuli will inform the development of screening tools to diagnose laryngopharyngeal hypersensitivity and hyposensitivity conditions. LEVEL OF EVIDENCE: 3b Laryngoscope, 131:1324-1331, 2021.

Human laryngeal sensory receptor mapping illuminates the mechanisms of laryngeal adductor reflex control.

OBJECTIVE: The laryngeal adductor reflex (LAR) is an airway protective response triggered by sensory laryngeal receptors. It is unknown whether different glottic and supraglottic subsites vary in their reflex elicitation abilities. The recent discovery that a bilateral LAR is present in humans under general anesthesia upon laryngeal mucosal stimulation has enabled us to map the sensory receptor density for LAR elicitation at different laryngeal subsites. Our findings expose the likely mechanisms of LAR control. METHODS: Prospective series of 10 patients undergoing laryngoscopy. Laryngeal subsites (epiglottic tip, membranous vocal fold, midventricular vocal fold, posterior supraglottis, epiglottic petiole) were stimulated via direct laryngoscopy with a bipolar probe. Vocal fold responses were recorded by endotracheal tube and hook wire electrodes, and visual observation. RESULTS: Posterior supraglottic stimulation elicited bilateral LARs in all patients at all intensities. Membranous vocal folds, epiglottic petiole, and subglottis elicited no LAR. Ventricular fold and epiglottic tip responses converted from ipsi- to bilateral at high intensities. CONCLUSION: There are likely three checkpoints for control of the LAR in humans. These checkpoints protect against inappropriate LAR activation during volitional tasks without compromising airway protection: 1) topographical differences in receptor density with the highest density in subsites most likely to contact foreign substances; 2) absence of receptors in membranous vocal folds; and 3) central summation threshold for crossed interneuron activation at brainstem level where only strong intensity stimuli will elicit bilateral responses. Checkpoint dysfunction provides a novel framework to diagnose and treat disease processes, including aspiration, laryngospasm, and sudden infant death. LEVEL OF EVIDENCE: 4. Laryngoscope, E365-E370, 2018.

Afferent nerve ending density in the human laryngeal mucosa: potential implications on endoscopic evaluation of laryngeal sensitivity.

Laryngeal sensitivity is crucial for maintaining safe swallowing, thus avoiding silent aspiration. The sensitivity test, carried out by fiberoptic endoscopic examination of swallowing, plays an important role in the assessment of dysphagic patients. The ventricular folds appear to be more sensitive than the epiglottis during the sensitivity test. Therefore, this study aimed to investigate the mechanical sensitivity of the supraglottic larynx. In seven healthy adults undergoing microlaryngoscopy to remove vocal cord polyps, we excised mucosal samples from the epiglottis and ventricular folds. We measured afferent nerve fiber density by immunoelectron microscopy. All of the subjects underwent an endoscopic sensitivity test based on lightly touching the laryngeal surface of the epiglottis and ventricular folds. The discomfort level was self-rated by the subjects on the visual analog scale. Samples were fixed and stored in cryoprotectant solution at 4 °C. Sections were stained with the protein gene product 9.5, a pan-neuronal selective marker. Nerve fiber density was calculated as the number of fibers per millimeter length of section. The mean nerve fiber density was higher in ventricular samples than in epiglottis samples (2.96 ± 2.05 vs 0.83 ± 0.51; two-sided p = 0.018). The mean visual analog scale scores were significantly higher for touching the ventricular folds than for touching the epiglottis (8.28 ± 1.11 vs 4.14 ± 1.21; two-sided p = 0.017). The higher sensitivity of the ventricular region should be considered for further refining clinical endoscopic evaluation of laryngeal sensitivity.

The distribution of transient receptor potential melastatin-8 in the rat soft palate, epiglottis, and pharynx.

Immunohistochemistry for transient receptor potential melastatin-8 (TRPM8), the cold and menthol receptor, was performed on the rat soft palate, epiglottis and pharynx. TRPM8-immunoreactive (IR) nerve fibers were located beneath the mucous epithelium, and occasionally penetrated the epithelium. These nerve fibers were abundant in the posterior portion of the soft palate and at the border region of naso-oral and laryngeal parts of the pharynx. The epiglottis was free from such nerve fibers. The double immunofluorescence method demonstrated that TRPM8-IR nerve fibers in the pharynx and soft palate were mostly devoid of calcitonin gene-related peptide-immunoreactivity (CGRP-IR). The retrograde tracing method also demonstrated that 30.1 and 8.7 % of sensory neurons in the jugular and petrosal ganglia innervating the pharynx contained TRPM8-IR, respectively. Among these neurons, the co-expression of TRPM8 and CGRP-IR was very rare. In the nodose ganglion, however, pharyngeal neurons were devoid of TRPM8-IR. Taste bud-like structures in the soft palate and pharynx contained 4-9 TRPM8-IR cells. In the epiglottis, the mucous epithelium on the laryngeal side had numerous TRPM8-IR cells. The present study suggests that TRPM8 can respond to cold stimulation when food and drinks pass through oral and pharyngeal cavities.

Pituitary adenylatecyclase-activating polypeptide-immunoreactive nerve fibers in the rat epiglottis and pharynx.

The distribution of pituitary adenylatecyclase-activating polypeptide-immunoreactive (PACAP-IR) nerve fibers was studied in the rat epiglottis and pharynx. PACAP-IR nerve fibers were located beneath the mucous epithelium, and occasionally penetrated the epithelium. These nerve fibers were abundant on the laryngeal side of the epiglottis and in the dorsal and lateral border region between naso-oral and laryngeal parts of the pharynx. PACAP-IR nerve fibers were also detected in taste buds within the epiglottis and pharynx. In addition, many PACAP-IR nerve fibers were found around acinar cells and blood vessels. The double immunofluorescence method demonstrated that distribution of PACAP-IR nerve fibers was similar to that in CGRP-IR nerve fibers in the epithelium and taste bud. However, distributions of PACAP-IR and CGRP-IR nerve fibers innervating mucous glands and blood vessels were different. The retrograde tracing method also demonstrated that PACAP and CGRP were co-expressed by vagal and glossopharyngeal sensory neurons innervating the pharynx. These findings suggest that PACAP-IR nerve fibers in the epithelium and taste bud of the epiglottis and pharynx which originate from the vagal and glossopharyngeal sensory ganglia include nociceptors and chemoreceptors. The origin of PACAP-IR nerve fibers which innervate mucous glands and blood vessels may be the autonomic ganglion.

[The epiglottis, a glosso-laryngeal structure: an anatomic study of its innervation]. / L'épiglotte, structure glosso-laryngée. Etude anatomique de son innervation.

The epiglottis is known as a laryngeal structure. The authors studied the innervation of epiglottis using the Sihler method on six human epiglottises. Innervation of the epiglottis depended on the rami from the vagus, glossopharyngeal and hypoglossal nerves. By its innervation, epiglottis seems to be a glosso-laryngeal structure, as is confirmed by embryology, histology and clinical applications.

Glycoconjugate in rat taste buds.

The taste buds of the fungiform papillae, circumvallate papilla, foliate papillae, soft palate and epiglottis of the rat oral cavity were examined by lectin histochemistry to elucidate the relationships between expression of glycoconjugates and innervation. Seven out of 21 lectins showed moderate to intense staining in at least more than one taste bud. They were succinylated wheat germ agglutinin (s-WGA). Dolichos biflorus agglutinin (DBA), Bandeiraea simplicifolia lectin-I (BSL-I), Ricinus communis agglutinin-I (RCA-I), peanut agglutinin (PNA), Ulex europaeus agglutinin-I (UEA-I) and Phaseolus vulgaris agglutinin-L (PHA-L). UEA-I and BSL-I showed moderate to intense staining in all of the taste buds examined. They strongly stained the taste buds of the epiglottis, which are innervated by the cranial nerve X. UEA-I intensely stained the taste buds of the fungiform papillae and soft palate, both of which are innervated by the cranial nerve VII. The taste buds of circumvallate papilla and foliate papillae were innervated by the cranial nerve IX and strongly stained by BSL-I. Thus, UEA-I and BSL-I binding glycoconjugates, probably alpha-linked fucose and alpha-D-galactose, respectively, might be specific for taste buds. Although the expression of these glycoconjugates would be related to the innervation of the cranial nerve X, the differential expression of alpha-linked fucose and alpha-D-galactose might be related to the innervation of the cranial nerve VII and IX, respectively.

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.

Electromyographic activity of the hyoepiglotticus muscle in dogs.

We examined the respiratory-related electromyographic (EMG) activity of the hyoepiglotticus muscle using fine wire bipolar electrodes, inserted perorally in five anaesthetised (IV chloralose) tracheostomised dogs studied in the prone, mouth open position. The integrated HE EMG was measured in arbitrary units (a.u.) during resting breathing via the upper airway, and on a breath-by-breath basis during progressive increases in respiratory drive induced by infusion of CO2 into the inspired gas. The HE demonstrated inspiratory activity which increased linearly in relation to ventilation (r = 0.85 +/- 0.06, p < 0.001) due to an increase in both phasic (8.8 +/- 1.8 to 32.4 +/- 9.2 a.u.) and tonic (0.2 +/- 0.1 to 26.3 +/- 13.3 a.u.) activity (both p < 0.05). In addition, HE EMG developed substantial phasic expiratory activity (1.3 +/- 1.1 to 13.8 +/- 4.4 a.u., p < 0.05). We conclude that the canine HE exhibits inspiratory and expiratory related activity which is augmented during increased respiratory drive. These findings imply active control of epiglottic position during breathing in dogs.

Influence of hyoepiglotticus muscle contraction on canine upper airway geometry.

We examined the effect of hyoepiglotticus (HE) muscle contraction on epiglottic position in 4 anaesthetised (IV choralose, pentobarbitone sodium) tracheostomised, mechanically ventilated dogs studied in the prone mouth open position. Computerised axial tomography (coronal plane) was used to measure the vertical distance between the tip of the epiglottis (E) and (1) the soft palate (SP) (i.e. E-SP distance) and (2) the dorsal wall of the nasopharynx (N) (i.e. E-N distance). Duplicate runs of graded electrical stimulation of the HE muscle, using bilateral bipolar fine wire electrodes, were performed in each animal and resulted in a progressive increase in both the E-SP distance (baseline of 0.5 +/- 0.5 to a maximum of 13.1 +/- 2.3 mm, mean +/- SE) and the E-N distance (29.1 +/- 2.0 to a maximum of 42.2 +/- 2.7 mm, both p < 0.02). We conclude that HE contraction moves the epiglottis ventrally away from the soft palate thus opening and enlarging the oral pathway for airflow.

Morphologic study of the laryngeal taste buds in the cat.

The distribution of laryngeal taste buds (TBs) and their neutral 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). Taste bud cells were specifically immunoreactive to the antibodies of human cytokeratin subtypes 8 and 18 (CAM5.2). On observation with CAM5.2, TBs were seen distributed on the laryngeal surface of the epiglottis and spread caudally along the aryepiglottic folds, reaching peak density at the laryngeal side of the arytenoid tubercle. The PGP9.5 and NSE immunoreactivities were recognized in TB cells and nerve fibers, both within the TBs and in the subepithelial connective tissue. S-100 protein immunoreactivities were not found in any of the cells in the TBs but were found exclusively in the subepithelial neural elements. The calbindin-D, CGRP, and SP immunoreactivities were confined to a part of the neural elements that was very thin. Taste pores, taste villi, neuronal varicosity, and synapselike structures were observed by scanning and transmission electron microscopic study. From these results it is considered that the TBs act as a chemical receptor.

Nerve endings in the epithelium and submucosa of human epiglottis.

An electron-microscopic study of the sensory innervation of human epiglottis was undertaken. The nerve supply of this structure was abundant; numerous free unmyelinated nerve endings of 2.5-3 microns were observed in the stratified epithelium of the epiglottis associated with clear cells containing mitochondria, rough endoplasmic reticulum, microtubules and dense-cored granules. The nerve and cell complex resembled a corpuscular structure, probably of a quimiosensitive character. In the submucosa, unmyelinated nerves were observed which may come from deeper myelinated trunks, and some of them entered the epithelium. Encapsulated corpuscles were also found in the submucosa. Four elements could be distinguished: nerve endings, lamellar cells, interlamellar substance, and capsule. Our observations at an ultrastructural level complete previous observations by means of light microscopy indicating that the epiglottis is a zone with an important innervation in the epithelium as well as in the submucosa. This sensory innervation probably bears a relation to reflexes, such as cough and deglution, to protect the airways.

Fine structure of taste buds located on the lamb epiglottis.

BACKGROUND: Taste buds located on the aryepiglottal folds and laryngeal surface of the epiglottis are the principal receptors responsible for the initiation of the laryngeal chemoreflex. In contrast to the wealth of information available concerning the ultrastructure of oral taste buds, little comparable data exists for taste buds located at the entrance to the larynx. Therefore, the present study was designed to investigate the fine structure of taste buds located on the lamb epiglottis. MATERIALS: Stained thick and semi-serial thin sections from taste buds located on the lamb epiglottis were examined with light and electron microscopy. RESULTS: Based on morphological criteria, three types of cells could be identified in the taste bud: Type I, Type II, and basal cells. Both Type I and Type II cells extended into the apical taste pore, but there were differences between these two cell types with regard to nuclear profiles, electron density, and the relative density of ribosomes, apical mitochondria, and rough and smooth endoplasmic reticulum. Basal cells did not extend a process into the taste pore. Nerve processes were observed throughout the taste bud. Synapses were observed between both Type I and Type II cells and nerve fibers. These synapses exhibited membrane thickenings and accumulations of clear and dense-cored vesicles of varying proportions in the taste cell cytoplasm adjacent to membrane specializations. CONCLUSIONS: The taste buds located on the lamb epiglottis share several structural similarities to taste buds located in the oral cavity and other regions of the pharynx and larynx of many mammalian species. The presence of synapses on both Type I and Type II cells of the lamb epiglottal taste bud suggests that both cell types are involved in laryngeal chemoreception.

[Autonomic and peptidergic innervation of the human larynx]. / Die autonome und peptiderge Innervation des menschlichen Kehlkopfes.

Autonomic and peptidergic innervation of the human larynx (vocal cords, ventricular folds, epiglottis, subglottic region and recurrent nerves) was studied by application of single and double immunocytochemistry and radioimmunoassay. In all tissues investigated, immunoreactivities for a variety of regulatory peptides were detected and included vasoactive intestinal polypeptide (VIP), peptide histidine methionine (PHM), helospectin, neuropeptide Y (NPY), C-flanking peptide of NPY (C-PON), calcitonin gene-related peptide (CGRP), substance P and neurokinin A. In the recurrent nerves, only a few peptide-immunoreactive nerve fibers were found. The laryngeal region of the epiglottis and the subglottic region showed characteristic corpuscular nerves containing substance P and CGRP running underneath and within the epithelium.

Response characteristics of lamb pontine neurons to stimulation of the oral cavity and epiglottis with different sensory modalities.

1. To better understand sensory information processing in pontine neurons that receive afferent fiber terminations from oral cavity and upper airway receptors, we investigated the response characteristics of single neurons to stimulation of the oral cavity and epiglottis with different stimulus modalities. These response characteristics were then compared with previously recorded response properties of neurons located in other brain stem regions that receive oral cavity and upper airway sensory inputs. 2. Receptive field sizes of pontine neurons were mapped, and responses to mechanical, thermal, and chemical stimuli were determined. A total of 47 neurons were isolated and most neurons were located near the dorsomedial border of the rostral trigeminal subnucleus oralis and caudal principal trigeminal nucleus. The likelihood that a particular stimulus modality would elicit a response was somewhat dependent on a neuron's location. Neurons that responded to chemical stimuli were always located outside the trigeminal nucleus, whereas neurons that responded exclusively to mechanical or thermal stimuli were more frequently located in the trigeminal nucleus. Receptive fields were mapped for 45 of the 47 neurons. Forty-three of the neurons had a single ipsilateral receptive field and > 80% of the receptive fields were > 100 mm2. The majority of neurons responded to only one of the three stimulus modalities. The remaining neurons were multimodal and the combination of stimulus modalities most frequently observed was mechanical and chemical. 3. Mechanical stimuli were the most effective of the three stimulus modalities, eliciting responses in > 65% of the neurons. Neurons that responded to mechanical stimuli were generally rapidly adapting and a moving stimulus was more effective than a punctate stimulus. Mechanosensitive neurons that also responded to chemical stimuli exhibited larger mean response frequencies than mechanosensitive neurons that did not respond to chemical stimuli. Chemical stimuli elicited responses in about half the neurons. A greater percentage of neurons with receptive fields on the epiglottis than neurons with oral cavity receptive fields responded to chemical stimuli. The effectiveness of a chemical stimulus was dependent on a neuron's receptive field. NH4Cl was the most effective stimulus for neurons with receptive fields located in the oral cavity, whereas KCl was more effective for neurons with receptive fields on the epiglottis. Thermal stimuli were relatively ineffective whatever the location of a neuron's receptive field. The majority of neurons showed an increase in response frequency to cooling the receptive field and in all thermosensitive neurons the response was restricted to the dynamic phase of thermal stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Response characteristics of lamb trigeminal neurons to stimulation of the oral cavity and epiglottis with different sensory modalities.

A region of the trigeminal complex located at the border of the subnucleus interpolaris and subnucleus caudalis receives not only trigeminal nerve inputs from the face, tongue and palate, but also afferent terminations from other nerves which innervate the oral cavity and upper airway. To increase our understanding of the types of sensory information relayed to this region of the trigeminal nucleus, we investigated the response characteristics of single neurons to stimulation of the tongue, palate and epiglottis. Receptive field size and location of 83 trigeminal neurons were mapped, and responses to mechanical, thermal and chemical stimuli were recorded. About 90% of the neurons had one receptive field and no convergence between the oral cavity and epiglottis was observed. Furthermore, only about 15% of the trigeminal neurons responded to more than one stimulus modality. A moving mechanical stimulus elicited responses in over 90% of the cells, and 84% responded to moving and punctate mechanical stimuli. These mechanosensitive neurons generally exhibited rapidly adapting responses. Thermal and chemical stimuli were relatively ineffective. Cooling a receptor surface most often produced excitation, and warming inhibition. Responses to chemical stimuli were only observed for salts at high concentrations. These results suggest that, like oral cavity information relayed by the trigeminal nerve, afferent terminations in the trigeminal nucleus from other nerves subserving the oral cavity and upper airway function to relay mechanical sensory information.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of neurons in the lamb nucleus tractus solitarius to stimulation of the caudal oral cavity and epiglottis with different stimulus modalities.

Receptors located in the posterior oral cavity and on the epiglottis play an important role in the initiation of upper airway reflexes such as swallowing, gagging, coughing and apnea. Peripheral nerves which innervate these receptor areas terminate in the nucleus tractus solitarius (NTS). We have recorded the responses of 61 neurons in the lamb NTS to stimulation of the caudal tongue, palate and epiglottis with mechanical, chemical and thermal stimuli and mapped receptive field location. Although there was some overlap in the areas of the NTS from which neurons with oral cavity and epiglottal receptive fields could be recorded, a significant difference was observed in the mean recording sites of the two groups of neurons. Neurons with oral cavity receptive fields were located more rostral, lateral and ventral in the NTS than neurons with receptive fields on the epiglottis. Little convergence of sensory input onto single cells in the NTS was observed between the oral cavity and the epiglottis. Only one NTS neuron had a receptive field in both of these receptor areas. In contrast, a large number of neurons with oral cavity receptive fields received input from two receptor areas. These neurons had a receptive field on the tongue which was located directly beneath the receptive field on the palate. Mechanical stimuli were the most effective for neurons with either oral cavity or epiglottal receptive fields and thermal stimuli were the least effective. Neurons which responded to mechanical stimuli responded better to a moving stimulus than to a punctate one, and large increases in the strength of a punctate stimulus were required to elicit significant increases in response frequency. Most NTS neurons responded to more than one of the stimulus modalities. However, a significant difference in the mean number of stimulus modalities which elicited responses was observed between neurons with oral cavity and epiglottal receptive fields. The number of multimodal neurons with epiglottal receptive fields was higher than those with oral cavity receptive fields. The multimodal nature of neurons which responded to epiglottal or oral cavity stimulation combined with their location in reflexogenic areas of the NTS suggests that these neurons could be important in the integration of afferent input from the oral cavity and upper airway. If these NTS neurons are involved in the control of oral and upper airway reflexes it would be important for them to respond to as many of the stimulus cues as possible and the majority of these neurons do just that.

Response properties of fibers in the hamster superior laryngeal nerve.

The purpose of the present investigation was to record electrophysiological responses from single fibers in the hamster superior laryngeal nerve (SLN) that were responsive to chemical stimulation of the larynx. Twenty chemical solutions, commonly used in studies of mammalian gustatory physiology, were applied to taste buds on and around the epiglottis. These stimuli were dissolved in physiological saline. Responses were the number of impulses elicited over a 15-s period following stimulus onset, above or below the background activity elicited by a previous rinse with saline. Unlike fibers in the hamster chorda tympani or glossopharyngeal nerves, SLN units were not easily classifiable into response types. Excitatory stimuli were primarily acids and bitter-tasting stimuli, with the order of their effectiveness being urea much greater than tartaric acid greater than HCl greater than KCl greater than citric acid greater than caffeine greater than quinine hydrochloride greater than acetic acid. The sweet-tasting stimuli and most salts other than KCl were primarily inhibitory, with the order of inhibitory effectiveness being CaCl2 greater than sucrose greater than fructose greater than LiCl greater than NaNO3 greater than Li2SO4 greater than NaCl. A hierarchical cluster analysis of fibers yielded no distinct clusters, yet differing sensitivities across the fibers were suggested. SLN fibers are highly responsive to sour and bitter stimuli, although they are not sensitive to fine differences in taste quality, as are fibers in other gustatory nerves.

Responses of lamb nucleus of the solitary tract neurons to chemical stimulation of the epiglottis.

Previous research has shown that applications of chemical stimuli to the epiglottis produced distinct patterns of activity in the lamb superior laryngeal nerve. To determine the response characteristics of second-order neurons, we recorded from single cells in the lamb nucleus of the solitary tract (NST) while stimulating the epiglottis with 0.5 M KCl, NH4Cl, NaCl, LiCl, distilled water, 0.005 M citric acid and 0.01 N HCl. Most neurons responded to more than one of the chemical solutions. The order of effective stimuli was KCl = NH4Cl greater than distilled water greater than HCl greater than citric acid greater than NaCl greater than LiCl. An analysis of the variation in response frequency over time found that different chemical stimuli produced significantly different response patterns in NST neurons. A comparison of the mean neural response profiles of NST neurons and superior laryngeal nerve fibers for each of the stimuli found that only the response profiles elicited by NH4Cl were significantly different. In addition to their responses to chemical solutions, almost one-third of the NST neurons responded to the rinse following application of at least some of the stimuli and 80% of the neurons were excited by mechanical stimulation of the epiglottis with a soft brush. Also, a small number of neurons exhibited a rhythmic response coordinated with respiration. The majority of recording sites were located in areas of the NST linked to swallowing and respiration suggesting that the response patterns of NST neurons elicited by chemical stimulation of receptors on the epiglottis may play a role in upper airway reflexes.

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 micron 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: simple terminations and 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.