Morphology and chemical characteristics of subepithelial laminar nerve endings in the rat epiglottic mucosa (original) (raw)
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Identification and characterization of a specific sensory epithelium in the rat larynx
The Journal of Comparative Neurology, 2004
A specific laryngeal sensory epithelium (SLSE), which includes arrays of solitary chemoreceptor cells, is described in the supraglottic region of the rat. Two plates of SLSE were found, one on each side of the larynx. The first plate was located in the ventrolateral wall of the larynx, and the second was located in the interarytenoidal region. In SLSE, immunoblotting showed the presence of ␣-gustducin and phospholipase C 2 (PLC2), which are two markers of chemoreceptor cells. At immunocytochemistry, laryngeal immunoreactivity for ␣-gustducin was localized mainly in solitary chemosensory cells. Double-label immunocytochemistry using confocal microscopy demonstrated that ␣-gustducinexpressing cells in large part colocalize type III IP 3 receptor (IP 3 R3), another key molecule in bitter taste perception. However, some IP 3 R3-expressing cells do not colocalize ␣-gustducin. At ultrastructural immunocytochemistry, these cells showed packed apical microvilli, clear cytoplasmic vesicles, and cytoneural junctions. SLSE was characterized by high permeability to a tracer due to poorly developed junctional contacts between superficial cells. Junctions were short in length and showed little contact with the terminal web. Ultrastructural analysis showed deep pits among the superficial cells. In SLSE, high density of intraepithelial nerve fibers was found. The lamina propria of the SLSE appeared thicker than that in other supraglottic regions. It was characterized by the presence of a well-developed subepithelial nerve plexus. The immunocytochemical and ultrastructural data suggested that SLSE is a chemoreceptor located in an optimal position for detecting substances entering the larynx from the pharynx or the trachea.
Intraepithelial Nerve Fibers Project Into the Lumen of the Larynx
The Laryngoscope, 2004
Objectives/Hypothesis: Studies on the morphology and location of the sensory receptors in the laryngeal mucosa have resulted in insufficient and sometimes conflicting data. In the present study the authors analyzed the distribution and morphology of sensory nerve plexuses and terminal fibers in the laryngeal mucosa of the rat. Study Design: Two groups of Male Wistar rats were used in this laboratory study; the larynx of the first group were used to analyse the sensitive innervation of its epithelium, whereas the larynx of the second group (controls) were tested for the specificity of the antibodies used. Methods: The larynges of the animals were entirely removed after perfusion, and coronal or horizontal sections were immunoprocessed for further randomized analysis of the mucosa. Primary afferents were detected by immunoreaction to two widely recognized markers of sensory nerves, calcitonin generelated peptide and substance P, and visualized using diaminobenzidine as a chromogen. Results: The nerve plexuses were more densely distributed in the dorsal half of the vocal folds and in the laryngeal aspect of the epiglottis. Dense networks of fine fibers with many varicosities en passant, immunoreactive for both calcitonin gene-related peptide and substance P, occurred in the lamina propria and along the epithelial thickness. Calcitonin gene-related peptideimmunoreactive and substance P-immunoreactive fibers extended across the epithelium and projected to the laryngeal lumen itself, reaching the space between the cilia. Conclusion: The projection of intraepithelial nerve fibers into the lumen of the larynx indicates that in the absence of mucus, nerve endings may be exposed and thus receive direct stimulation from airborne substances. Furthermore, it suggests that the laryngeal mucosa of the rat may constitute an experimental model for studying the direct activation or manipulation of primary afferents at the periphery and neurogenic inflammation.
The central projections of the laryngeal nerves in the rat
Journal of Anatomy, 2011
The larynx serves respiratory, protective, and phonatory functions. The motor and sensory innervation to the larynx controlling these functions is provided by the superior laryngeal nerve (SLN) and the recurrent laryngeal nerve (RLN). Classical studies state that the SLN innervates the cricothyroid muscle and provides sensory innervation to the supraglottic cavity, whereas the RLN supplies motor innervation to the remaining intrinsic laryngeal muscles and sensory innervation to the infraglottic cavity, but recent data suggest a more complex anatomical and functional organisation. The current neuroanatomical tracing study was undertaken to provide a comprehensive description of the central brainstem connections of the axons within the SLN and the RLN, including those neurons that innervate the larynx. The study has been carried out in 41 adult male Sprague-Dawley rats. The central projections of the laryngeal nerves were labelled following application of biotinylated dextran amines onto the SLN, the RLN or both. The most remarkable result of the study is that in the rat the RLN does not contain any afferent axons from the larynx, in contrast to the pattern observed in many other species including man. The RLN supplied only special visceromotor innervation to the intrinsic muscles of the larynx from motoneurons in the nucleus ambiguus (Amb). All the afferent axons innervating the larynx are contained within the SLN, and reach the nucleus of the solitary tract. The SLN also contained secretomotor efferents originating from motoneurons in the dorsal motor nucleus of the vagus, and special visceral efferent fibres from the Amb. In conclusion, the present study shows that in the rat the innervation of the larynx differs in significant ways from that described in other species.
Expression of ENaC subunits in sensory nerve endings in the rat larynx
Neuroscience Letters, 2006
We investigated the expression of three subunits of epithelial sodium channel (ENaC), ␣ENaC, ENaC and ␥ENaC, in the nodose ganglion and laryngeal mucosa of rat by RT-PCR analysis and immunohistochemistry. PCR products of predicted size for ␣ENaC, ENaC and ␥ENaC subunits were amplified from extract of nodose ganglion. Immunohistochemically, nodose ganglion neurons of medium to large diameter were immunoreactive for ␣ENaC, ENaC and ␥ENaC. In the deep region of laryngeal submucosal layer, thick nerve fibers without varicosities were immunoreactive for ␣ENaC, ENaC and ␥ENaC. In the laryngeal mucosa, terminal arborizations of the nerve endings, that immunoreacted for ␣ENaC, ENaC and ␥ENaC were scattered in the lamina propria just beneath the epithelia of epiglottis and laryngeal vestibule. Double immunofluorescence with calretinin revealed that they were laminar nerve endings. Some thick nerve fibers near the laryngeal taste buds were also immunoreactive for ENaC and ␥ENaC, but negative for ␣ENaC. In the larynx, ENaC channels may play important roles in mechanotransduction in the laminar endings and in the mechano-and chemotransductions in the taste bud-associated nerve fibers.
Innervation of the larynx, pharynx, and upper esophageal sphincter of the rat
Journal of Comparative Neurology, 1994
We identified a ‘semicircular’ compartment of the rat thyropharyngeus muscle at the pharyngoesophageal junction and used the glycogen depletion method to determine how the fibers of this muscle (as well as all others of the pharynx and larynx) are innervated by different cranial nerve branches. The semicircular compartment appears anatomically homologous to the human cricopharyngeus muscle, an important component of the upper esophageal sphincter. While we found very little overlap in the muscle targets of the pharyngeal, superior laryngeal and recurrent laryngeal nerves within the pharynx and larynx, the semicircular muscle receives a dual, interdigitating innervation from two vagal branches: the pharyngeal nerve and a branch of the superior laryngeal nerve we call the dorsal accessory branch. After applying horseradish peroxidase to either of these two nerves, we compared the distribution and number of cells labeled in the brainstem. The dorsal accessory branch conveys a more heterogeneous set of efferent fibers than does the pharyngeal nerve, including the axons of pharyngeal and esophageal motor neurons and parasympathetic preganglionic neurons. The observed distribution of labeled motor neurons in nucleus ambiguus also leads us to suggest that the semicircular compartment is innervated by two subsets of motor neurons, one of which is displaced ventrolateral to the main pharyngeal motor column. This arrangement raises the possibility of functional differences among semicircular compartment motor neurons correlated with the observed differences in brainstem location of cell bodies. © 1994 Wiley-Liss, Inc.
Mucosal afferents mediate laryngeal adductor responses in the cat
Journal of applied physiology (Bethesda, Md. : 1985), 2002
Laryngeal adductor responses (LAR) close the airway in response to stimulation of peripheral afferents in the superior laryngeal nerve. Although both mucosal afferents and proprioceptive receptors are present in the larynx, their relative contribution for reflex elicitation is unknown. Our purpose was to determine which receptor types are of importance in eliciting the LAR. A servomotor with displacement feedback was used to deliver punctate displacements to the body of the arytenoid cartilage and overlying mucosa on each side of the larynx in eight anesthetized cats. The same displacements were delivered both before and after surgical excision of the overlying mucosa. With the mucosa intact, early short-latency component R1 LAR responses recorded from the thyroarytenoid muscles were frequent (ipsilateral > 92%, contralateral > 95%). After the mucosa was removed, the LAR became infrequent (<3%) and was reduced in amplitude in both the ipsilateral and contralateral thyroaryt...
Ultrastructure of the ganglion on human internal laryngeal nerve
Neuroscience Research, 1994
There is now definite evidence for the presence of a macroscopic ganglion on the human internal laryngeal nerve, with the distribution of its post-ganglionic fibres to the glands in the saccule and to the glands at the root of epiglottis in the vicinity of the opening of the saccule. This ganglion could be identified as early as 14 weeks in human foetal larynx, which contains immature neurons. Seven ganglia, dissected from human laryngectomy specimens and resected for carcinoma larynx, were studied by electron microscopy. Ultrastructurally. the neurons and the synaptic terminals had both small, round, luscent vesicles and dense core vesicles. Symmetrical, asymmetrical and electrical synaptic complexes were noted. A few neurons revealed degenerative changes suggestive of axotomy. The location of the ganglion on the internal laryngeal nerve, a branch of nervus vagus, and ultrastructural demonstration of large and small dense core vesicles and small luscent vesicles in the neurons of this ganglion, lead us to believe that the ganglion is parasympathetic in nature.
The location and axonal projections of laryngeal motoneurons (LMn) have been studied in rats and cats using horseradish peroxidase as a retrograde tracer. LMn are located in the caudal part of the ambiguus nucleus in both species. In the cat, LMn are organized in two groups with a specific orientation of their dendritic trees. LMn axonal projections are ipsilateral in cats and bilateral in rats. In the early literature there was some controversy about the uni-or bilateral origin of ambiguus nucleus (AN) fibers projecting to the laryngeal muscles in mammals [2]. Recently it has been reported that following transection and horseradish peroxidase (HRP) impregnation of left vagus nerve in both rats and monkeys, bilateral labeling of neurons appeared in the AN in rats, but only ipsilateral AN neurons showed HRP reaction products in monkeys [7]. On electrophysiological grounds, it has also been reported that the electrical stimulation of the contralateral recurrent laryngeal nerve (RLn) in cats fails to induce any antidromic field potential in the AN [l], Another not well-known aspect is the precise distribution of laryngeal motoneurons (LMn), although in previous reports it has been suggested that they are located in the posterior part of the AN [10] except a small group situated in the retrofacial nucleus [5]. The present study was undertaken to reexamine in detail the morphological organization of LMn in both cats and rats, using HRP as a retrograde tracer. Experiments were carried out on 5 cats and l0 rats anesthetized with ketamine (35 mg/kg, i.m.) and 12.5s/o urethane solution (6 mllkg), respectively. In both cats and rats a tracheotomy was made in order to freely manipulate the larynx. A total amount of 15 ¡rl (cats) and 5 ¡rl (rats) of a 5090 HRP solution (Sigma type VI) was injected bilaterally into the laryngeal muscles by means of a Hamilton microsyringe.
Projections of the internal branch of the superior laryngeal nerve in the cat.
LUCIER, G E., R. EGIZII AND J. 0. DOSTROVSKY Projections ofthe rnfernal branch ofthe superior laryngeal nerve ofrhr car. BRAIN RES BULL M(5) [713][714][715][716][717][718][719][720][721] 1986.-The internal branch of the supenor laryngeal nerve (tSLN) conveys sensory afferent mformatton from receptors located m the laryngeal mucosa. The objecttves of thts study were. to determine the specific anatomical locatton of iSLN cell bodies within the nodose ganglion, to ascertam whether the jugular ganglion mtght also contain ISLN atferent bodies; to determine whether the iSLN contains sympathetic efferents onginatmg m the cervical sympathettc ganglion; to determme whether the cell bodies of these efferents, if present, are localized wtthm a specdic region of thts ganglion and to trace the transganghonic projectton of ISLN afferents mto the bram stem. Horseradish peroxidase was applied to the iSLN m ten adult cats. Following a survival period of 72 hours, the animals were sacnficed and the tissue was processed according to the tetramethylbenztdme method. Reaction product was locahzed in the rostra1 end of the nodose ganglion extending into the exiting vagus nerve, m the caudal end of theJugular ganglion and m the postenor portion of the cervrcal sympathettc ganglion. Tr~sganglionic projections to the nucteus tractus sobtanus were localized prtmardy rn the dorsolateral subnucleus with substantial amounts of reaction product also in the intermediate and Interstitial subnuclei. Except for a small bilateral projection observed m the commissural subnucleus, no other proJecttons were seen to any other bram stem structures Internal superior laryngeal nerve Nucleus of the solitary tract
Activity of respiratory laryngeal motoneurons during fictive coughing and swallowing
Experimental Brain Research, 2000
Membrane potential changes and discharges from 28 laryngeal motoneurons were recorded intracellularly in the caudal nucleus ambiguus of decerebrate, paralyzed and ventilated cats. Electrical activities were recorded from 17 expiratory laryngeal motoneurons (ELMs) with maximal depolarizing membrane potential in early expiration, and from 11 inspiratory laryngeal motoneurons (ILMs) with maximal depolarizing membrane potential in inspiration. Activities during breathing were compared with those observed during fictive coughing and swallowing evoked by electrical stimulation of the superior laryngeal nerves. These non-respiratory behaviors were evidenced in paralyzed animals by characteristic discharge patterns of the phrenic, abdominal nerves and pharyngeal branch of the vagus nerve. We recorded the activity of 11 ELMs and 5 ILMs during coughing in which ELMs, but not ILMs, exhibited increased membrane depolarization and discharge frequencies. Membrane depolarization and discharge frequencies of all ELMs were also significantly increased during swallowing. In addition, membrane depolarization of most ELMs (15/17) was preceded by a short-lasting hyperpolarization due to chloride-dependent inhibitory mechanisms occurring at the onset of swallowing. Out of 10 ILMs tested during swallowing, 7 exhibited membrane depolarization, preceded in 5 cases by a short-lasting hyperpolarization. Discharge frequencies of ILMs were significantly reduced during swallowing. The same pattern of phasic activities of ILMs and ELMs was observed during coughing and breathing, suggesting the involvement of similar excitatory pathways in both behaviors. These results imply that the duration of activation and the discharge frequency of neurons of the central generator for breathing that drive laryngeal motoneurons are enhanced during coughing. During swallowing, in addition to central excitatory mechanisms, laryngeal motoneurons are subjected to an initial inhibition of unknown origin. This inhibition probably contributes to the temporal organization of the swallowing motor sequence.