Location of sensory nerve cells that provide calbindin-containing laminar nerve endings in myenteric ganglia of the rat esophagus

Innervation of the mammalian esophagus

Understanding the innervation of the esophagus is a prerequisite for successful treatment of a variety of disorders, e.g., dysphagia, achalasia, gastroesophageal reflux disease (GERD) and non-cardiac chest pain. Although, at first glance, functions of the esophagus are relatively simple, their neuronal control is considerably complex. Vagal motor neurons of the nucleus ambiguus and preganglionic neurons of the dorsal motor nucleus innervate striated and smooth muscle, respectively. Myenteric neurons represent the interface between the dorsal motor nucleus and smooth muscle but they are also involved in striated muscle innervation. Intraganglionic laminar endings (IGLEs) represent mechanosensory vagal afferent terminals. They also establish intricate connections with enteric neurons. Afferent information is implemented by the swallowing central pattern generator in the brainstem, which generates and coordinates deglutitive activity in both striated and smooth esophageal muscle and orchestrates esophageal sphincters as well as gastric adaptive relaxation. Disturbed excitation/inhibition balance in the lower esophageal sphincter results in motility disorders, e.g., achalasia and GERD. Loss of mechanosensory afferents disrupts adaptation of deglutitive motor programs to bolus variables, eventually leading to megaesophagus. Both spinal and vagal afferents appear to contribute to painful sensations, e.g., non-cardiac chest pain. Extrinsic and intrinsic neurons may be involved in intramural reflexes using acetylcholine, nitric oxide, substance P, CGRP and glutamate as main transmitters. In addition, other molecules, e.g., ATP, GABA and probably also inflammatory cytokines, may modulate these neuronal functions.

Tachykinins are involved in local reflex modulation of vagally mediated striated muscle contractions in the rat esophagus via tachykinin NK1 receptors

The objective of the present study was to investigate the hypothesis of the presence of a local neural reflex modulating the vagally mediated contractions of striated muscle in the rat esophagus and to determine the possible involvement of tachykinins in such a local neural reflex. Electrical stimulation of the vagus nerve evoked twitch contractile responses that were abolished by d-tubocurarine (5 microM). Capsaicin (1-100 microM) inhibited the vagally mediated twitch contractions o f the normal rat esophageal preparations concentration-dependently but not those of the neonatally capsaicin-treated ones. NG-nitro-L-arginine methyl ester (100 microM), a nitric oxide synthase inhibitor, blocked the inhibitory effect of capsaicin and exogenous application of a nitric oxide donor (1 mM) inhibited the vagally mediated twitch contractions. Capsaicin suppressed acetylcholine release from the normal rat esophageal segments evoked by vagus nerve stimulation but not that from the neonatally capsaicin-treated ones. A selective tachykinin NK1 receptor antagonist (0.1 or 1 microM) attenuated the inhibitory effect of capsaicin. However, antagonists of tachykinin NK2, tachykinin NK3 and calcitonin gene-related peptide receptors (1 microM) did not have any effect. A tachykinin NK1 receptor agonist (1 or 5 microM) inhibited the vagally mediated twitch contractions, which was prevented by NG-nitro-L-arginine methyl ester (100 microM). These data suggest that the rat esophagus might have a local neural reflex inhibiting the vagally mediated striated muscle motility, which consists of capsaicin-sensitive sensory neurons and myenteric nitrergic neurons, and that tachykinins might be involved in the neural reflex through tachykinin NK1 receptors.

Effect of mCOUP-TF1 deficiency on the glossopharyngeal and vagal sensory ganglia

Immunohistochemistry for calcitonin gene-related peptide (CGRP), tyrosine hydroxylase and calbindin D-28k was performed on the glossopharyngeal and vagal ganglia in mCOUP-TFI knockout mice to know the effect of its deficiency on different types of primary sensory neurons. In wild type and heterozygous mice, the glossopharyngeal and vagal ganglia contained abundant CGRP-, tyrosine hydroxylase- and calbindin D-28k-immunoreactive (IR) neurons. In the ganglia of mCOUP-TFI knockout mice, a 38% decrease of CGRP-IR neurons was detected. However, the number of tyrosine hydroxylase- or calbindin D-28k-neurons was not altered by the mCOUP-TFI deficiency. In the tongue of knockout mice, the number of CGRP-IR nerve fibers decreased compared to wild-type and heterozygous mice. The development of CGRP-IR petrosal neurons, which supply innervation of the tongue, may depend on mCOUP-TFI.

Local differences in vagal afferent innervation of the rat esophagus are reflected by neurochemical differences at the level of the sensory ganglia and by different brainstem projections

The objective of the present study was to characterize further the vagal afferent fibers in the rat esophagus, particularly those in its uppermost part, their cell bodies in vagal sensory ganglia, and their central projections. We applied immunohistochemistry for calretinin, calbindin, and calcitonin gene-related peptide (CGRP); retrograde tracing with FluoroGold; and transganglionic tracing with wheat germ agglutinin-horseradish peroxidase in combination with neurectomies. Vagal terminal structures in the muscularis propria of the whole esophagus consisted of calretinin-immunoreactive intraganglionic laminar endings that were linked to cervical vagal and recurrent laryngeal nerve pathways. The mucosa of the uppermost esophagus was innervated by a very dense net of longitudinally arranged, calretinin-positive fibers that were depleted by section of the superior laryngeal nerve. Distal to this area, the mucosa was virtually devoid of calretinin-immunoreactive vagal afferents. Calretinin-positive mucosal fibers in the upper cervical esophagus were classified into four types. One type, the finger-like endings, was sometimes immunoreactive also for CGRP. About one-third of cell bodies in vagal sensory ganglia retrogradely labeled from the upper cervical esophagus expressed CGRP, whereas two-thirds coexpressed calretinin and calbindin but not CGRP. In addition to the central subnucleus of the nucleus of the solitary tract, vagal afferents from the upper cervical esophagus also projected heavily to the interstitial subnucleus. This additional projection was attributed to mucosal afferents traveling through the superior laryngeal nerve. The present study provides a possible morphological basis for bronchopulmonary and aversive reflexes elicited upon stimulation of the esophagus.

Calbindin D28k-immunoreactive afferent nerve endings in the laryngeal mucosa

The distribution of the calbindin D28k in the laryngeal sensory structures was studied by immunohistochemistry, immunoelectronmicroscopy, and double immunofluorescence with calretinin-immunoreactivity. Moreover, origin of the nerve endings were observed using retrograde tracer, fast blue. Immunoreactivity for calbindin D28k was found in the various types of nerve endings in the larynx, namely, laminar nerve endings, nerve endings associated with the taste buds, intraepithelial nerve endings, and endocrine cells. The laminar endings with calbindin D28k-immunoreactivity were observed in the subepithelial connective tissue. In some endings, terminals were expanded. The laminar endings were also observed in the perichondrium of the epiglottic cartilage. In the epiglottic and arytenoid epithelia, thick nerve fibers with calbindin D28k-immunoreactivity ascending to taste buds and intragemmal nerve fibers were also observed. Within the epithelial layer, intraepithelial free nerve endings with calbindin D28k-immunoreactivity were observed. Furthermore, diffuse endocrine cells were observed within the laryngeal epithelium. By immunoelectron microscopy, immunoreaction products in the endings mentioned above were localized in the cytoplasm of the axon terminals and nerve fibers which contained with numerous mitochondria. Out of the 100 laminar endings, 18 endings were immunopositive for both calbindin D28k and calretinin, 33 were positive for calbindin D28k but negative for calretinin, and 49 were positive for only calretinin in the double immunofluorescence microscopy. The nerve fibers associated with the taste buds and the free nerve endings, which immunostained for calbindin D28k, were not stained with antibody against calretinin. After injection of the fast blue in the laryngeal mucosa, fast blue-labeled cells were mainly observed in the nodose ganglia. Of the total number of labeled cell in the nodose and dorsal root ganglia at the level C1 to Th2, 65.1% occurred in nodose ganglia (572/879, n = 6). In the nodose ganglia, 79.7% of labeled cells (456/572) were immunoreacted for calbindin D28k. The distribution of calbindin D28k-immunoreactivity may be differnt from that of calretinin. It is suggested that calbindin D28k have regulatory role on intracellular calcium concentration in the laryngeal sensory corpuscles.

Anterograde tracing and immunohistochemical characterization of potentially mechanosensitive vagal afferents in the esophagus

Vagal mechanosensitive afferents with an important functional role in esophageal peristalsis are well known from physiological studies. It is not known whether these fibers represent a separate subpopulation among all vagal afferents projecting to the esophageal wall. A morphological and immunohistochemical description of vagal afferents was undertaken to define their possible homo- or heterogeneity. The peripheral projections of vagal afferents were anterogradely labeled by injection of wheatgerm agglutinin conjugated to horseradish peroxidase into the nodose ganglion of rats. The anterogradely transported tracer was detected by tyramide amplification in conjunction with immunohistochemistry for Ca(2+)-binding proteins recently identified in different types of mechanosensory endings. It was found that vagal afferents represented a morphologically and structurally homogeneous population projecting to the myenteric ganglia of the esophagus, where they terminated as highly branched endings. Vagal afferent terminals, however, were different in their staining intensity for calretinin and calbindin, which ranged from intense to no detectable immunofluorescence. The fluorescence intensity of Ca(2+)-binding proteins within the vagal terminating branches was graded and the average staining intensity determined of all terminating branches in the upper, middle, and lower thirds of the esophagus. The average staining intensity was highest in the upper third of the esophagus and then declined in a statistically significant manner in the middle and lower thirds. This result suggests different requirements for intracellular Ca(2+)-buffering capacities in vagal afferents depending on their position along the esophageal axis and corroborates studies reporting a segmental organization of esophageal motility. Immunohistochemical evidence of substance P (SP) in a subset of vagal terminals was demonstrated. Hence, an effector role of vagal afferents on esophageal peristalsis by the release of SP, as has been proposed by physiological studies, is also supported by immunohistochemical data.

Ultrastructure of intramural ganglia in the striated muscle portions of the guinea pig oesophagus

The ultrastructure of the myenteric plexus located in the striated muscle portion of the guinea pig oesophagus was examined and compared with that of the plexus associated with the smooth muscle portion of the rest of the digestive tract. The oesophageal ganglia had essentially the same architecture as those of the smooth muscle portion, such as a compact neuropil without the intervention of connective tissue and blood vessels. Some features, however, were particular to the striated muscle part of the oesophagus. It was clearly demonstrated that myelinated fibres, probably sensory terminals of vagal origin, join the myenteric ganglia. Synapses and terminal varicosities are sparsely distributed within the ganglia and fewer morphological types of axon varicosities could be distinguished compared with other regions. Glial cells are well developed in the oesophageal myenteric ganglia. These cells outnumber the ganglion cells, having a higher ratio than in the lower digestive tract, and form numerous cytoplasmic lamellar processes. The lamellar processes, located at the surface of the ganglia, considerably reduce the area of neuronal membrane which directly contacts the basal lamina. The role of these lamellar processes in the oesophageal ganglia is discussed.

Tyramide amplification allows anterograde tracing by horseradish peroxidase-conjugated lectins in conjunction with simultaneous immunohistochemistry

Current protocols for a combined approach of anterograde tracing with carbocyanine dyes or horseradish peroxidase (HRP) conjugates and immunohistochemistry represent a compromise between sensitive detection of the tracer and the immunohistochemical procedure. Therefore, it was investigated whether the use of tyramide amplification allows sensitive anterograde tracing with wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in conjunction with simultaneous immunohistochemistry. Vagal afferents were anterogradely labeled by injection of WGA-HRP into the nodose ganglion of rats. By use of tyramide-biotin amplification, a dense fiber plexus of vagal afferents was visualized centrally in the nucleus of the solitary tract and in retrogradely labeled neurons in the dorsal vagal nucleus. In the esophagus and duodenum, large- and small-caliber vagal fibers and terminals could be demonstrated comparably to conventional tracing technique using carbocyanine dyes or WGA-HRP and TMB histochemistry. Combination with immunohistochemistry could easily be done, requiring only one more incubation step, and did not result in loss of sensitivity of the tracing. With this method and confocal microscopy, the presence of Ca binding proteins in vagal afferent terminals could be demonstrated. Tyramide amplification allows sensitive anterograde tracing with low background staining in conjunction with immunohistochemistry of a-axonal markers.

Neurocalcin-immunopositive neurons in the rat sensory ganglia

Distribution of neurocalcin, a calcium-binding protein having three EF hand motifs, in the rat sensory ganglia was demonstrated immunochemically and immunohistochemically. Immunoblot analysis of trigeminal, nodose and dorsal root ganglia homogenates revealed an immunoreactive band at approximately 24 kDa. Neurons labeled by the neurocalcin-antiserum represent 54%, 41% and 46% cells in the trigeminal, nodose and dorsal root ganglia, respectively. Size distribution of immunopositive cells showed a varying range. Most large cells (more than 80%) showed immunoreactivity in the trigeminal and dorsal root ganglia. A double immunofluorescent study was performed to determine the colocalization with calbindin D28k or parvalbumin, which are both calcium-binding proteins. In the trigeminal and dorsal root ganglia, almost all calbindin- or parvalbumin-immunoreactive neurons showed neurocalcin-immunoreactivity, whereas approximately 30-40% neurocalcin-immunopositive cells had calbindin- or parvalbumin-immunoreactivity. In the nodose ganglia, parvalbumin showed localization similar to other ganglia, but about half the calbindin-immunoreactive neurons had neurocalcin-immunoreactivity. These studies show that neurocalcin-immunopositive neurons are widely distributed in the sensory ganglia and most calbindin- or parvalbumin-immunoreactive neurons also contain neurocalcin. In the sensory neurons, neurocalcin may have a significant role in calcium signaling.