Sensory innervation of the canine esophagus, stomach, and duodenum

Mucosal neuroimmune mechanisms in gastro-oesophageal reflux disease (GORD) pathogenesis

Gastro-oesophageal reflux disease (GORD) is a chronic condition characterised by visceral pain in the distal oesophagus. The current first-line treatment for GORD is proton pump inhibitors (PPIs), however, PPIs are ineffective in a large cohort of patients and long-term use may have adverse effects. Emerging evidence suggests that nerve fibre number and location are likely to play interrelated roles in nociception in the oesophagus of GORD patients. Simultaneously, alterations in cells of the oesophageal mucosa, namely epithelial cells, mast cells, dendritic cells, and T lymphocytes, have been a focus of GORD research for several years. The oesophagus of GORD patients exhibits both macro- and micro-inflammation as a response to chronic acidic reflux at the epithelium. In other conditions of the GI tract, such as IBS and IBD, well-characterised bidirectional processes between immune cells and mucosal nerve fibres contribute to pathogenesis and symptom generation. Sensory alterations in these conditions such as nerve fibre outgrowth and hypersensitivity can be driven by inflammatory processes, which promote visceral pain signalling. This review will examine what is currently known of the molecular pathways linking inflammation and sensory perception leading to the development of GORD symptoms and explore potentially relevant mechanisms in other GI regions which may indicate new areas in GORD research.

Oxaliplatin-Induced Damage to the Gastric Innervation: Role in Nausea and Vomiting

Nausea and vomiting are common gastrointestinal side effects of oxaliplatin chemotherapy used for the treatment of colorectal cancer. However, the mechanism underlying oxaliplatin-induced nausea and vomiting is unknown. The stomach is involved in the emetic reflex but no study investigated the effects of oxaliplatin treatment on the stomach. In this study, the in vivo effects of oxaliplatin treatment on eating behaviour, stomach content, intrinsic gastric neuronal population, extrinsic innervation to the stomach, levels of mucosal serotonin (5-hydroxytryptamine, 5-HT), and parasympathetic vagal efferent nerve activity were analysed. Chronic systemic oxaliplatin treatment in mice resulted in pica, indicated by increased kaolin consumption and a reduction in body weight. Oxaliplatin treatment significantly increased the stomach weight and content. The total number of myenteric and nitric oxide synthase-immunoreactive neurons as well as the density of sympathetic, parasympathetic, and sensory fibres in the stomach were decreased significantly with oxaliplatin treatment. Oxaliplatin treatment significantly increased the levels in mucosal 5-HT and the number of enterochromaffin-like cells. Chronic oxaliplatin treatment also caused a significant increase in the vagal efferent nerve activity. The findings of this study indicate that oxaliplatin exposure has adverse effects on multiple components of gastric innervation, which could be responsible for pica and gastric dysmotility.

Thoracoscopic resection of a large lower esophageal schwannoma: A case report and review of the literature

BACKGROUND

Esophageal schwannomas originating from Schwann cells are extremely rare esophageal tumors. They commonly occur in the upper and middle esophagus but less frequently in the lower esophagus. Herein, we report a rare case of a large lower esophageal schwannoma misdiagnosed as a leiomyoma. We also present a brief literature review on lower esophageal schwannomas.

CASE SUMMARY

A 62-year-old man presented with severe dysphagia lasting 6 mo. A barium esophagogram showed that the lower esophagus was compressed within approximately 5.5 cm. Endoscopy revealed the presence of a large submucosal protuberant lesion in the esophagus at a distance of 32-38 cm from the incisors. Endoscopic ultrasound findings demonstrated a 4.5 cm × 5.0 cm hypoechoic lesion. Chest computed tomography revealed a mass of size approximately 53 mm × 39 mm × 50 mm. Initial tests revealed features indicative of leiomyoma. After multidisciplinary discussions, the patient underwent a video-assisted thoracoscopic partial esophagectomy. Further investigation involving immunohistochemical examination confirming palisading spindle cells as positive for S100 and Sox10 led to the final diagnosis of a lower esophageal schwannoma. There was no tumor recurrence or metastasis during follow-up.

CONCLUSION

The final diagnosis of esophageal schwannoma requires histopathological and immunohistochemical examination. The early appropriate surgery favors a remarkable prognosis.

Effects of alcohol on brain oxygenation and brain hypoxia induced by intravenous heroin

Alcohol is the most commonly used psychoactive drug, often taken in conjunction with opioid drugs. Since both alcohol and opioids can induce CNS depression, it is often assumed that alcohol potentiates the known hypoxic effects of opioid drugs. To address this supposition, we used oxygen sensors to examine the effects of alcohol on brain oxygenation and hypoxic responses induced by intravenous heroin in awake, freely moving rats. To eliminate robust sensory effects of alcohol following its oral or intraperitoneal delivery, alcohol was administered directly into the stomach via chronically implanted intragastric catheters at human relevant doses. Alcohol delivered at a 0.5 g/kg dose did not affect brain oxygen levels, except for a weak transient increase during drug delivery. This phasic oxygen increase was stronger at a 2.0 g/kg alcohol dose and followed by a weaker tonic increase. Since alcohol absorption from intragastric delivery is much slower and more prolonged than with intraperitoneal or intravenous injections, the rapid rise of brain oxygen levels suggests that alcohol has a direct action on sensory afferents in the stomach well before the drug physically reaches brain tissue via circulation. Despite slow tonic increases in brain oxygen, alcohol at the 2.0 g/kg dose strongly potentiates heroin-induced oxygen responses, increasing both the magnitude and duration of oxygen decrease. Therefore, under the influence of alcohol, the use of opioid drugs becomes much more dangerous, increasing brain hypoxia and enhancing the probability of serious health complications, including coma and death.

Esophageal afferent innervation and its role in gastro-esophageal reflux disease symptoms

PURPOSE OF REVIEW

Despite the wide prevalence of gastro-esophageal reflux disease (GERD), the neurophysiological mechanisms underlying heartburn perception in the esophagus of patients with GERD remains incompletely understood. Recent studies have highlighted the potential influence sensory afferent nerves innervating the oesophageal epithelium may have on heartburn pathogenesis. The purpose of this review is to consider the current understanding of esophageal afferent neuronal innervation, including the nociceptive role of acid-sensing receptors expressed on these sensory nerves, in relation to pain perception in the esophagus of GERD patients.

RECENT FINDINGS

Central and peripheral pathways of sensitization following noxious stimulation of nociceptive receptors expressed on afferent nerves can regulate the strength of sensory nerve activation in the esophagus, which can result in the amplification or suppression of afferent signal transmission. The localization and characterization of mucosal sensory afferent nerves vary between GERD phenotypes and may explain the heterogeneity of symptom perception in patients with apparently similar levels of reflux.

SUMMARY

In this review, we discuss the relevance of afferent esophageal innervation in heartburn perception, with a particular focus on the pathways of reflux-induced activation of nociceptive nerves.

Vagus Nerves Provide a Robust Afferent Innervation of the Mucosa Throughout the Body of the Esophagus in the Mouse

The vagal afferent nerves regulate swallowing and esophageal motor reflexes. However, there are still gaps in the understanding of vagal afferent innervation of the esophageal mucosa. Anatomical studies found that the vagal afferent mucosal innervation is dense in the upper esophageal sphincter area but rare in more distal segments of the esophagus. In contrast, electrophysiological studies concluded that the vagal afferent nerve fibers also densely innervate mucosa in more distal esophagus. We hypothesized that the transfection of vagal afferent neurons with adeno-associated virus vector encoding green fluorescent protein (AAV-GFP) allows to visualize vagal afferent nerve fibers in the esophageal mucosa in the mouse. AAV-GFP was injected into the vagal jugular/nodose ganglia in vivo to sparsely label vagal afferent nerve fibers. The esophageal tissue was harvested 4-6 weeks later, the GFP signal was amplified by immunostaining, and confocal optical sections of the entire esophagi were obtained. We found numerous GFP-labeled fibers in the mucosa throughout the whole body of the esophagus. The GFP-labeled mucosal fibers were located just beneath the epithelium, branched repeatedly, had mostly longitudinal orientation, and terminated abruptly without forming terminal structures. The GFP-labeled mucosal fibers were concentrated in random areas of various sizes in which many fibers could be traced to a single parental axon. We conclude that the vagus nerves provide a robust afferent innervation of the mucosa throughout the whole body of the esophagus in the mouse. Vagal mucosal fibers may contribute to the sensing of intraluminal content and regulation of swallowing and other reflexes.

Influence of Acrylamide Administration on the Neurochemical Characteristics of Enteric Nervous System (ENS) Neurons in the Porcine Duodenum

The digestive tract, especially the small intestine, is one of the main routes of acrylamide absorption and is therefore highly exposed to the toxic effect of acrylamide contained in food. The aim of this experiment was to elucidate the effect of low (tolerable daily intake—TDI) and high (ten times higher than TDI) doses of acrylamide on the neurochemical phenotype of duodenal enteric nervous system (ENS) neurons using the pig as an animal model. The experiment was performed on 15 immature gilts of the Danish Landrace assigned to three experimental groups: control (C) group—pigs administered empty gelatine capsules, low dose (LD) group—pigs administered capsules with acrylamide at the TDI dose (0.5 μg/kg body weight (b.w.)/day), and the high dose (HD) group—pigs administered capsules with acrylamide at a ten times higher dose than the TDI (5 μg/kg b.w./day) with a morning feeding for 4 weeks. Administration of acrylamide, even in a low (TDI) dose, led to an increase in the percentage of enteric neurons immunoreactive to substance P (SP), calcitonin gene-related peptide (CGRP), galanin (GAL), neuronal nitric oxide synthase (nNOS), and vesicular acetylcholine transporter (VACHT) in the porcine duodenum. The severity of the changes clearly depended on the dose of acrylamide and the examined plexus. The obtained results suggest the participation of these neuroactive substances in acrylamide-inducted plasticity and the protection of ENS neurons, which may be an important line of defence from the harmful action of acrylamide.

Phenotypic distinctions between the nodose and jugular TRPV1-positive vagal sensory neurons in the cynomolgus monkey

Vagal capsaicin-sensitive afferent C-fibers play an important role in the maintenance of visceral homeostasis and contribute to symptoms in visceral diseases. Based on their developmental origin two functionally distinct types of vagal C-fibers are recognized: those with neurons in the vagal nodose ganglia (derived from epibranchial placodes) and in the vagal jugular ganglia (from neural crest). Studies in nonprimate species demonstrated that the vagal nodose and jugular C-fibers differ in activation profile, neurotrophic regulation, and expression of neurotransmitters. We hypothesized that the expression of selected markers related to key phenotypic properties of vagal C-fibers in the cynomolgus monkey is similar to that reported in nonprimate species. We performed single-cell RT-PCR on nodose and jugular putative C-fiber (TRPV1-positive) neurons isolated from the cynomolgus monkey. We found that the expression of purinergic P2X receptors that underlie selective responsiveness of nodose C-fiber terminals to ATP was conserved in that P2X2 and P2X3 subunits were expressed in nodose, but only P2X3 subunit was expressed in jugular TRPV1-positive neurons. Also conserved was the preferential expression of neurotrophic receptor TrkB in the nodose and preprotachykinin-A in the jugular TRPV1-positive neurons. Several key distinctions in gene expression between nodose and jugular TRPV1-positive (C-fiber) neurons that have been noted in mice, rats, and guinea pigs, are conserved in the cynomolgus monkey. Our results support the translatability of distinct vagal C-fiber phenotypes to primates.

Distinct Expression of Phenotypic Markers in Placodes- and Neural Crest-Derived Afferent Neurons Innervating the Rat Stomach

BACKGROUND

Visceral pain is initiated by activation of primary afferent neurons among which the capsaicin-sensitive (TRPV1-positive) neurons play an important role. The stomach is a common source of visceral pain. Similar to other organs, the stomach receives dual spinal and vagal afferent innervation. Developmentally, spinal dorsal root ganglia (DRG) and vagal jugular neurons originate from embryonic neural crest and vagal nodose neurons originate from placodes. In thoracic organs the neural crest- and placodes-derived TRPV1-positive neurons have distinct phenotypes differing in activation profile, neurotrophic regulation and reflex responses. It is unknown to whether such distinction exists in the stomach.

AIMS

We hypothesized that gastric neural crest- and placodes-derived TRPV1-positive neurons express phenotypic markers indicative of placodes and neural crest phenotypes.

METHODS

Gastric DRG and vagal neurons were retrogradely traced by DiI injected into the rat stomach wall. Single-cell RT-PCR was performed on traced gastric neurons.

RESULTS

Retrograde tracing demonstrated that vagal gastric neurons locate exclusively into the nodose portion of the rat jugular/petrosal/nodose complex. Gastric DRG TRPV1-positive neurons preferentially expressed markers PPT-A, TrkA and GFRα₃ typical for neural crest-derived TRPV1-positive visceral neurons. In contrast, gastric nodose TRPV1-positive neurons preferentially expressed markers P2X₂ and TrkB typical for placodes-derived TRPV1-positive visceral neurons. Differential expression of neural crest and placodes markers was less pronounced in TRPV1-negative DRG and nodose populations.

CONCLUSIONS

There are phenotypic distinctions between the neural crest-derived DRG and placodes-derived vagal nodose TRPV1-positive neurons innervating the rat stomach that are similar to those described in thoracic organs.

Distinct and common expression of receptors for inflammatory mediators in vagal nodose versus jugular capsaicin-sensitive/TRPV1-positive neurons detected by low input RNA sequencing

Capsaicin-sensitive sensory C-fibers derived from vagal ganglia innervate the visceral organs, and respond to inflammatory mediators and noxious stimuli. These neurons play an important role in maintenance of visceral homeostasis, and contribute to the symptoms of visceral inflammatory diseases. Vagal sensory neurons are located in two ganglia, the jugular ganglia (derived from the neural crest), and the nodose ganglia (from the epibranchial placodes). The functional difference, especially in response to immune mediators, between jugular and nodose neurons is not fully understood. In this study, we microscopically isolated murine nodose and jugular capsaicin-sensitive / Trpv1-expressing C-fiber neurons and performed transcriptome profiling using ultra-low input RNA sequencing. RNAseq detected genes with significantly differential expression in jugular and nodose neurons, which were mostly involved in neural functions. Transcriptional regulators, including Cited1, Hoxb5 and Prdm12 showed distinct expression patterns in the two C-fiber neuronal populations. Common and specific expression of immune receptor proteins was characterized in each neuronal type. The expression of immune receptors that have received little or no attention from vagal sensory biologists is highlighted including receptors for certain chemokines (CXCLs), interleukins (IL-4) and interferons (IFNα, IFNγ). Stimulation of immune receptors with their cognate ligands led to activation of the C-fibers in isolated functional assays.

The expression profile of acid-sensing ion channel (ASIC) subunits ASIC1a, ASIC1b, ASIC2a, ASIC2b, and ASIC3 in the esophageal vagal afferent nerve subtypes

Acid-sensing ion channels (ASICs) have been implicated in esophageal acid sensing and mechanotransduction. However, insufficient knowledge of ASIC subunit expression profile in esophageal afferent nerves hampers the understanding of their role. This knowledge is essential because ASIC subunits form heteromultimeric channels with distinct functional properties. We hypothesized that the esophageal putative nociceptive C-fiber nerves (transient receptor potential vanilloid 1, TRPV1-positive) express multiple ASIC subunits and that the ASIC expression profile differs between the nodose TRPV1-positive subtype developmentally derived from placodes and the jugular TRPV1-positive subtype derived from neural crest. We performed single cell RT-PCR on the vagal afferent neurons retrogradely labeled from the esophagus. In the guinea pig, nearly all (90%-95%) nodose and jugular esophageal TRPV1-positive neurons expressed ASICs, most often in a combination (65-75%). ASIC1, ASIC2, and ASIC3 were expressed in 65-75%, 55-70%, and 70%, respectively, of both nodose and jugular TRPV1-positive neurons. The ASIC1 splice variants ASIC1a and ASIC1b and the ASIC2 splice variant ASIC2b were similarly expressed in both nodose and jugular TRPV1-positive neurons. However, ASIC2a was found exclusively in the nodose neurons. In contrast to guinea pig, ASIC3 was almost absent from the mouse vagal esophageal TRPV1-positive neurons. However, ASIC3 was similarly expressed in the nonnociceptive TRPV1-negative (tension mechanoreceptors) neurons in both species. We conclude that the majority of esophageal vagal nociceptive neurons express multiple ASIC subunits. The placode-derived nodose neurons selectively express ASIC2a, known to substantially reduce acid sensitivity of ASIC heteromultimers. ASIC3 is expressed in the guinea pig but not in the mouse vagal esophageal TRPV1-positive neurons, indicating species differences in ASIC expression.

Co-expression patterns of cocaine- and amphetamine-regulated transcript (CART) with neuropeptides in dorsal root ganglia of the pig

In the present study the neuronal distribution of CART was evaluated immunohistochemically in porcine dorsal root ganglia (DRGs). In co-localization studies the co-expression patterns of CART with SP, CGRP, galanin, CALB and LENK were investigated by means of triple immunohistochemical stainings. In porcine DRGs, the expression of CART was found in approximately 5% of primary sensory neurons. The vast majority (ca. 95%) of CART-immunoreactive (IR) neurons were small and middle sized, and only 5% were categorized as large. CART-IR neurons additionally exhibiting the presence of SP/CGRP (ca. 12%), SP/CALB (ca. 12%), SP/LENK (ca. 5%) were found. The vast majority of CART-IR/CGRP-IR neurons did not display immunoreaction to SP (ca. 60%). Subclasses of CART-IR/LENK-IR/SP-negative (ca. 5%), as well as CART-IR/CALB-IR/SP-negative neurons (ca. 10%), were also visualized. In addition, CART-IR neurons with no immunoreactivities to any of the neuropeptides studied were also shown. In porcine DRGs none of the CART-IR neurons exhibited the presence of galanin. The results obtained in the study suggest that CART may functionally modulate the activity of the porcine primary sensory neurons. It is concluded that co-expression of CART with CGRP, SP, LENK and CALB in subsets of the pig L1-L6 DRGs neurons provide anatomical evidence for a CART role in pain processing.

Identifying spinal sensory pathways activated by noxious esophageal acid

BACKGROUND

The transient receptor potential vanilloid 1 (TRPV1) channel is critical for spinal afferent signaling of burning pain throughout the body. Such pain frequently originates from the esophagus, following acid reflux. The contribution of TRPV1 to spinal nociceptor signaling from the esophagus remains unclear. We aimed to identify the spinal afferent pathways that convey nociceptive signaling from the esophagus, specifically those sensitive to acid, and the extent to which TRPV1 contributes.

METHODS

Acid/pepsin (150 mM HCl/1 mg mL(-1) pepsin) or saline/pepsin was perfused into the esophageal lumen of anesthetized wild-type and TRPV1 null mice over 20 min, followed by atraumatic perfuse fixation and removal of the cervical and thoracic spinal cord and dorsal root ganglia (DRG). To identify neurons responsive to esophageal perfusate, immunolabeling for neuronal activation marker phosphorylated extracellular receptor-regulated kinase (pERK) was used. Labeling for calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4) was then used to characterize responsive neurons.

KEY RESULTS

Esophageal acid/pepsin perfusion significantly increased the number of pERK-immunoreactive (IR) neurons in the DRG and the cervical and thoracic spinal cord dorsal horn (DH) relative to saline/pepsin (DRG P < 0.01; cervical DH P < 0.05 and thoracic DH P < 0.005). The number of pERK-IR neurons following acid perfusion was significantly attenuated in TRPV1 -/- mice (DH P < 0.05 and DRG P < 0.05).

CONCLUSIONS & INFERENCES

This study has identified populations of spinal afferent DRG neurons and DH neurons involved in signaling of noxious acid from the esophagus. There is a major contribution of TRPV1 to signaling within these pathways.

The neural crest- and placodes-derived afferent innervation of the mouse esophagus

BACKGROUND

The mouse is an invaluable model for mechanistic studies of esophageal nerves, but the afferent innervation of the mouse esophagus is incompletely understood. Vagal afferent neurons are derived from two embryonic sources: neural crest and epibranchial placodes. We hypothesized that both neural crest and placodes contribute to the TRPV1-positive (potentially nociceptive) vagal innervation of the mouse esophagus.

METHODS

Vagal jugular/nodose ganglion (JNG) and spinal dorsal root ganglia (DRG) neurons were retrogradely labeled from the cervical esophagus. Single cell RT-PCR was performed on the labeled neurons.

KEY RESULTS

In the Wnt1Cre/R26R mice expressing a reporter in the neural crest-derived cells we found that both the neural crest- and the placodes-derived vagal JNG neurons innervate the mouse esophagus. In the wild-type mouse the esophageal vagal JNG TRPV1-positive neurons segregated into two subsets: putative neural crest-derived purinergic receptor P2X(2) -negative/preprotachykinin-A (PPT-A)-positive subset and putative placodes-derived P2X(2) -positive/PPTA-negative subset. These subsets also segregated by the expression of TrkA and GFRα(3) in the putative neural crest-derived subset, and TrkB in the putative placodes-derived subset. The TRPV1-positive esophageal DRG neurons had the phenotype similar to the vagal putative neural crest-derived subset.

CONCLUSIONS & INFERENCES

The TRPV1-positive (potentially nociceptive) vagal afferent neurons innervating the mouse esophagus originate from both neural crest and placodes. The expression profile of the receptors for neurotrophic factors is similar between the neural crest-derived vagal and spinal nociceptors, but distinct from the vagal placodes-derived nociceptors.

In gastroesophageal reflux disease, differential gene expression in the duodenum points towards enhanced chylomicron production and secretion

BACKGROUND

Duodenal signaling affects esophageal motility and perception, both pathophysiological factors in gastroesophageal reflux disease (GERD). Duodenal gene expression abnormalities, contributing to altered esophageal sensorimotor function, have not been reported to date.

AIM

To identify differentially expressed genes in GERD patients' duodenum.

METHODS

Twenty GERD patients (total 24-h acid exposure 6-12%, SAP ≥95%) and ten healthy controls (HC) were included. Two weeks prior to duodenal biopsy collection, ten patients discontinued proton pump inhibitor (PPI) treatment and ten took maximum dose PPI. RNA was profiled on an Affymetrix Human Genome U133 Plus 2.0 array (Affymetrix, Santa Clara, CA, USA). Genes exhibiting a fold change ≥ 1.4 (t test p value <1E-4) were considered differentially expressed. A subset of 21 differentially expressed genes was selected for confirmatory TaqMan low-density array RT-PCR. Mucosal apolipoprotein A-IV (apoA-IV) and cholecystokinin (CCK) concentrations were determined by ELISA and RIA, respectively.

RESULTS

In GERD patients off PPI, 23 up- and 23 down-regulated genes relative to HC were found. In GERD patients on PPI, 33 and five genes were higher, respectively, lower expressed. The majority of up-regulated genes were associated with lipid absorption, particularly triglyceride resynthesis and intracellular vesicular transport, rate-limiting processes for chylomicron production and secretion. Differential expression of 11 genes was confirmed by RT-PCR. Mucosal apoA-IV and CCK concentrations (signaling proteins released upon chylomicron secretion) were similar in GERD patients and HC.

CONCLUSIONS

The identified mRNA expression differences suggest that in GERD patients' duodenum, the chylomicron production and secretion potential is elevated, and may underlie a mechanism by which postprandial duodenal signaling contributes to GERD symptom generation.

Roles of gastro-oesophageal afferents in the mechanisms and symptoms of reflux disease

Oesophageal pain is one of the most common reasons for physician consultation and/or seeking medication. It is most often caused by acid reflux from the stomach, but can also result from contractions of the oesophageal muscle. Different forms of pain are evoked by oesophageal acid, including heartburn and non-cardiac chest pain, but the basic mechanisms and pathways by which these are generated remain to be elucidated. Both vagal and spinal afferent pathways are implicated by basic research. The sensitivity of afferent fibres within these pathways may become altered after acid-induced inflammation and damage, but the severity of symptoms in humans does not necessarily correlate with the degree of inflammation. Gastro-oesophageal reflux disease (GORD) is caused by transient relaxations of the lower oesophageal sphincter, which are triggered by activation of gastric vagal mechanoreceptors. Vagal afferents are therefore an emerging therapeutic target for GORD. Pain in the absence of excess acid reflux remains a major challenge for treatment.

New technologies to investigate the brain-gut axis

Functional gastrointestinal disorders are commonly encountered in clinical practice, and pain is their commonest presenting symptom. In addition, patients with these disorders often demonstrate a heightened sensitivity to experimental visceral stimulation, termed visceral pain hypersensitivity that is likely to be important in their pathophysiology. Knowledge of how the brain processes sensory information from visceral structures is still in its infancy. However, our understanding has been propelled by technological imaging advances such as functional Magnetic Resonance Imaging, Positron Emission Tomography, Magnetoencephalography, and Electroencephalography (EEG). Numerous human studies have non-invasively demonstrated the complexity involved in functional pain processing, and highlighted a number of subcortical and cortical regions involved. This review will focus on the neurophysiological pathways (primary afferents, spinal and supraspinal transmission), brain-imaging techniques and the influence of endogenous and psychological processes in healthy controls and patients suffering from functional gastrointestinal disorders. Special attention will be paid to the newer EEG source analysis techniques. Understanding the phenotypic differences that determine an individual’s response to injurious stimuli could be the key to understanding why some patients develop pain and hyperalgesia in response to inflammation/injury while others do not. For future studies, an integrated approach is required incorporating an individual’s psychological, autonomic, neuroendocrine, neurophysiological, and genetic profile to define phenotypic traits that may be at greater risk of developing sensitised states in response to gut inflammation or injury.

Characterization of T9-T10 spinal neurons with duodenal input and modulation by gastric electrical stimulation in rats

Gastric electrical stimulation (GES) has been suggested as a therapy for patients with gastric motility disorders or morbid obesity. However, it is unclear whether GES also affects intestinal sensory and motor functions. Furthermore, little is known about intraspinal visceroreceptive transmission and processing for duodenal afferent information. The aims of this study were to characterize responses of thoracic spinal neurons to duodenal distension, to determine the afferent pathway and to examine the effects of GES on activity of these neurons. Extracellular potentials of single T9-T10 spinal neurons were recorded in pentobarbital anesthetized, paralyzed, ventilated male rats (n=19). Graded duodenal distension (DD, 0.2-0.6 ml, 20 s) was produced by water inflation of a latex balloon surgically placed into the duodenum. One pair of platinum electrodes (1.0-1.5 cm apart) was sutured onto the serosal surface of the lesser curvature of the stomach. GES with four sets of parameters was applied for one minute: GES-A (6 mA, 0.3 ms, 40 Hz, 2 s on, 3 s off), GES-B (6 mA, 0.3 ms, 14 Hz, 0.1 s on, 5 s off), GES-C (6 mA, 3 ms, 40 Hz, 2 s on, 3 s off) and GES-D (6 mA, 200 ms, 12 pulses/min). Results showed that 33/117 (28%) spinal neurons responded to noxious DD (0.4 ml, 20 s). Of these, 7 (6%) neurons had low-threshold responses to DD (<or=0.2 ml) and 26 (22%) had high-threshold responses to DD (>or=0.4 ml). DD-responsive spinal neurons were encountered more frequently in deeper (depth: 0.3-1.2 mm) than in superficial laminae (depth: <0.3 mm) of the dorsal horn (24/67 vs. 9/50, P<0.05). DD excited all 9 superficial neurons. In contrast, 20 deeper neurons were excited and 4 neurons were inhibited by DD. Activity of DD-responsive neurons was affected more frequently with GES-C (13/15, 87%) than GES-A (6/16, 38%), -B (3/15, 20%) and -D (5/14, 36%) (P<0.01). Bilateral cervical vagotomy did not significantly alter the effects of DD and GES on 5/5 neurons. Resiniferatoxin (2.0 microg/kg, i.v.), an ultrapotent agonist of transient receptor potential vanilloid receptor-1 (TRPV1), abolished DD responses and GES effects on all neurons examined in vagotomized rats. Additionally, 29/33 (88%) DD-responsive neurons received inputs from somatic receptive fields on the back, flank and medial/lateral abdominal areas. It was concluded that GES mainly exerted an excitatory effect on T9-T10 spinal neurons with duodenal input transmitted by sympathetic afferent fibers expressing TRPV1; spinal neuronal responses to GES were strengthened with an increased pulse width and/or frequency of stimulation; T9-T10 spinal neurons processed input from the duodenum and might mediate effects of GES on duodenal sensation and motility.

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.

Brain processing of esophageal sensation in health and disease

This case study demonstrates that patients with NCCP can be subclassified on the basis of sensory responsiveness and neurophysiologic profiles. This approach identifies specific abnormalities within the CNS processing of esophageal sensation in individual patients, allowing us to objectively differentiate those with sensitized esophageal afferents from those that are hypervigilant to esophageal sensations. The importance of this approach is to underline that NCCP comprises a heterogeneous group of patients. and only when we have defined the phenotype of this condition and identified groups of patients with specific CNS abnormalities will it be possible to perform clinical studies aimed at answering specific hypotheses. The development of a comprehensive pathophysiologic model that identifies the specific causes of symptoms in patients with esophageal hypersensitivity will allow the future management strategies of these patients to be targeted more specifically and efficiently. This will have great benefits to patients'well-being and health care use.

Responses and afferent pathways of C1-C2 spinal neurons to cervical and thoracic esophageal stimulation in rats

Because vagal and sympathetic inputs activate upper cervical spinal neurons, we hypothesized that stimulation of the esophagus would activate C(1)-C(2) neurons. This study examined responses of C(1)-C(2) spinal neurons to cervical and thoracic esophageal distension (CED, TED) and afferent pathways for CED and TED inputs to C(1)-C(2) spinal neurons. Extracellular potentials of single C(1)-C(2) spinal neurons were recorded in pentobarbital-anesthetized male rats. Graded CED or TED was produced by water inflation (0.1-0.5 ml) of a latex balloon. CED changed activity of 48/219 (22%) neurons; 34 were excited (E), 12 were inhibited (I), and 2 were E-I. CED elicited responses for 18/18 neurons tested after ipsilateral cervical vagotomy, for 12/14 neurons tested after bilateral vagotomy and for 9/11 neurons tested after bilateral vagotomy and C(6)-C(7) spinal cord transection. TED changed activity of 31/190 (16%) neurons (28E, 3 I). Ipsilateral cervical vagotomy abolished TED-evoked responses of 5/12 neurons. Bilateral vagotomy eliminated responses of 2/4 neurons tested, and C(6)-C(7) spinal transection plus bilateral vagotomy eliminated responses of 2/2 neurons. Thus inputs from CED to C(1)-C(2) neurons most likely entered upper cervical dorsal roots, whereas inputs from TED were dependent on vagal pathways and/or sympathetic afferent pathways that entered the thoracic dorsal roots. These results supported a concept that C(1)-C(2) spinal neurons play a role in integrating visceral information from cervical and thoracic esophagus.

Afferent pathways and responses of T3–T4 spinal neurons to cervical and thoracic esophageal distensions in rats

The purposes of this study were to (1) compare responses of T(3)-T(4) spinal neurons to thoracic and cervical esophageal distension (TED, CED) and (2) determine afferent pathways for esophageal input to these neurons. Extracellular potentials of single superficial and deeper T(3)-T(4) neurons were recorded in pentobarbital anesthetized male rats. Graded TED or CED was produced by water inflation (0.1-0.5 ml) of a latex balloon. TED changed activity of 121/432 (28%) neurons (114 were excited); CED activated 69/269 (26%) neurons (56 were excited). Of 151 neurons that were tested for responses to both TED and CED, 40 (26%) neurons responded to both TED and CED. Mean duration of excitatory responses in convergent neurons to TED was significantly longer than the duration of responses to CED (31.4+/-2.8 vs. 25.4+/-1.0 s, n=34, P<0.05). A total of 105 out of 121 (87%) and 66 out of 69 (96%) neurons responsive to TED and CED had somatic fields. Spinal transection at rostral C(1) and at C(7)-C(8) indicated that excitatory responses to TED resulted from activation of afferent input that entered thoracic spinal segments; whereas, excitatory responses to CED resulted from afferent inputs entering cervical or thoracic spinal segments. These data showed that the upper thoracic spinal cord received sensory information from the esophagus through cervical and/or thoracic spinal visceral afferent pathways.

Responses and afferent pathways of C(1)-C(2) spinal neurons to gastric distension in rats

Some evidence shows that the upper cervical spinal cord might play an important role in propriospinal processing as a sensory filter and modulator for visceral afferents. The aims of this study were to determine (1). the responses of C(1)-C(2) spinal neurons to gastric distension and (2). the relative contribution of vagal and spinal visceral afferent pathways for transmission of gastric input to the upper cervical spinal cord. Extracellular potentials of single C(1)-C(2) spinal neurons were recorded in pentobarbital anesthetized male rats. Graded gastric distension (20-80 mm Hg) was produced by air inflation of a latex balloon surgically placed in the stomach. Sixteen percent of the neurons (32/198) responded to gastric distension; 17 neurons were excited and 15 neurons were inhibited by gastric distension. Spontaneous activity of neurons with inhibitory responses was higher than those neurons with excitatory responses (18.1+/-2.7 vs. 3.8+/-1.7 impulses s(-1), p<0.001). Twenty-eight of thirty-two (87.5%) neurons responded to mechanical stimulation of somatic fields on head, neck, ears or shoulder. Most lesion sites of neurons with excitatory responses were found in laminae V, VII; however, neurons with inhibitory responses were in laminae III, IV. Bilateral cervical vagotomy abolished responses of 4/8 neurons tested. Spinal transection at C(6)-C(7) abolished responses of the other four neurons that still responded to gastric distension after bilateral vagotomy. Results of these data supported the concept that a group of C(1)-C(2) spinal neurons might play a role in processing sensory information from the stomach that travels in vagal and spinal visceral afferent fibers.

Upper thoracic respiratory interneurons integrate noxious somatic and visceral information in rats

The aim of this study was to determine if thoracic respiratory interneurons (TRINs) might receive peripheral noxious somatic and visceral inputs. Extracellular potentials of 78 respiration-related T(3) neurons, whose activity was driven by central respiratory output, were recorded from the intermediate zone in pentobarbital anesthetized, paralyzed, and ventilated male rats. These neurons were identified as interneurons by their locations and by the absence of antidromic activation from the cervical sympathetic trunk and cerebellum. Thoracic esophageal distension (ED) was produced by water inflation of a latex balloon (0.1-0.5 ml, 20 s). A catheter was placed in the pericardial sac to administer 0.2 ml bradykinin (10(-5) M) for noxious cardiac stimulation. Of 78 TRINs examined for ED, activity of 24 TRINs increased and activity of 8 TRINs decreased. Intrapericardial bradykinin increased activity in 26/65 TRINs tested and decreased activity in 5 TRINs. Seventy-four TRINs were tested for effects of brush, pressure, and pinch of the chest and upper back areas. No TRINs responded to brushing hair. Low-threshold responses to pressure were observed in 27 TRINs. Fourteen TRINs were wide dynamic range and 4 TRINs had high-threshold responses. Peripheral stimuli affected all types of TRINs, including inspiratory, expiratory, and biphasic neurons. Simultaneous phrenic recordings showed that effects of various somatic and visceral stimuli on TRINs were independent of central respiratory drive. Various somatovisceral and viscerovisceral patterns of input were observed in TRINs. The results suggested that TRINs participate in intraspinal processing and integration of nociceptive information from somatic fields and visceral organs.

Selective vagal afferent dysfunction in dogs with congenital idiopathic megaoesophagus

Congenital idiopathic megaoesophagus (CIM) is a rare, naturally occurring disorder of the dog that is characterised by deficient motility and dilatation of the oesophagus. Recent studies indicate that the vagal sensory system mediating reflexes induced by oesophageal distension is defective in, and may underlie the pathomechanism of this disorder. We sought to establish whether other distension sensitive vagal afferent systems were impaired in CIM, or whether the vagal afferent dysfunction was selective. Thus, we examined the Hering-Breuer lung inflation reflex (HBR), which is subserved by a contiguous and physiologically similar vagal afferent system, in five dogs with CIM in which oesophageal vagal afferent dysfunction had been demonstrated. At varying levels of lung inflation, we found the HBR to be normally graded and of normal strength in affected dogs and that this result was unlikely to be influenced by other factors known to alter the strength of the reflex. These observations provide evidence for an organ specific, selective vagal afferent dysfunction in dogs with CIM. It is possible that similar processes may be active in disorders of visceral organ systems subserved by vagal afferents in other species, including man.

An overview of esophageal sensory receptors

The neurophysiological basis of esophageal pain and discomfort is not well known. Functional disorder, such as noncardiac chest pain, is thought to be associated with hypersensitivity of primary afferents innervating the esophagus and/or sensitization of spinal dorsal horn cells receiving input from the organ. Although we have accumulated a large body of information about the morphologic structure and neuropeptide contents of the extrinsic primary afferents, we lack a full understanding of its integrative function in esophageal pain. The esophagus is innervated dually by vagus and spinal nerves. The majority of sensory afferents in the vagal and spinal pathway are pseudounipolar cells, with their cell bodies (soma) located in the nodose and dorsal root ganglia, respectively. These afferent fibers innervate serosa (adventitia), longitudinal and circular muscles, and mucosa of the esophagus. Afferents innervating the muscle are sensitive to intraluminal distension. In the vagus, these afferents exhibit low threshold for response, whereas the spinal afferents, including the splanchnic nerve afferents, have either low or high thresholds for response. In addition, these afferents are chemosensitive. Both vagal and spinal afferents also innervate the mucosa of the esophagus. These fibers are exquisitely sensitive to light touch of the mucosa and are sensitive to pH and chemicals. The spinal afferents, including splanchnic nerve afferents, project to the spinal cord, spanning from upper cervical (C1) to upper lumbar (L2) segments. A majority of the spinal dorsal horn neurons receiving input from the esophageal spinal afferents also receives somatic converging input. The somatic receptive fields are distributed mainly ipsilaterally over the chest and forearm area. These spinal dorsal horn neurons exhibit either excitatory, inhibitory, or biphasic (i.e., excitation followed by inhibition) responses to esophageal distension.

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.

Vagal efferent and afferent innervation of the rat esophagus as demonstrated by anterograde DiI and DiA tracing: focus on myenteric ganglia

Anterograde tracing with the carbocyanine tracer DiI and the aminostyrol derivative DiA was used to selectively label fibers from the nucleus ambiguus, dorsal motor nucleus and nodose ganglion, respectively, terminating in the rat esophagus, and to compare them with the innervation of the gastric fundus in the same animals. Ambiguus neurons terminated on motor endplates distributed mainly to the ipsilateral half of the esophagus. There was no evidence of preganglionic innervation of myenteric ganglia from ambiguus neurons. Neurons of the dorsal motor nucleus supplied sparse fibers to only about 10% of enteric ganglia in the esophagus while they innervated up to 100% of myenteric ganglia in the stomach. Neurons of the nodose ganglion terminated profusely on more than 90% of myenteric ganglia of the esophagus and on about 50% of ganglia in the stomach. Afferent vagal fibers were also frequently found in smooth muscle layers starting at the esophago-gastric junction. In contrast, they were extremely rare in the striated muscle part of the esophagus. These morphological data suggest a minor influence of neurons of the dorsal motor nucleus and a prominent influence of vagal afferent terminals onto myenteric neurons in the rat esophagus.

Source modeling of esophageal evoked potentials

Evoked potentials can be recorded from the scalp after stimulation of the esophagus by balloon distension. The purpose of this study was to estimate the number and localization of sources contributing to the esophageal evoked potential (EEP). The EEP was recorded from 32 scalp electrodes in 5 healthy subjects. Spatio-temporal dipole modeling was performed in the time interval from 185 msec to 525 msec after stimulation (mean values). The EEP was best explained by the combined activity of 1 dipole located relatively high in the midline and 2 lateral dipoles. Given the anatomical projection of esophageal sensory fibers and the location of these dipoles the sources were probably located in the cingulate gyri and insular cortex. There was no evidence that sources in the lower brain-stem contributed to the scalp recorded EEP.

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

To determine the origin of the calbindin-containing laminar nerve endings in the myenteric ganglia of the rat esophagus, retrograde tracing experiments combined with immunohistochemistry using an antibody for calbindin were carried out. After Fast blue was injected into the cervical portion of the esophagus, labeled neurons were found bilaterally in the nodose ganglion and dorsal root ganglia of C1 to T3. 80% of the total neurons in the nodose ganglion and 20% of those in the dorsal root ganglia showed calbindin immunoreactivity. Moreover, 79% of Fast-blue-labeled neurons found in the nodose ganglion and 18% of those in the dorsal root ganglia were immunoreactive for calbindin. These results suggest that the calbindin antibody we used is useful as a marker for identifying esophageal vagal afferents derived from the nodose ganglion. The calbindin-immunoreactive nerve fibers forming the laminar endings in the myenteric ganglia of the rat cervical esophagus are mainly derived from sensory neurons in the nodose ganglion and partly derived from those in the cervical and upper thoracic dorsal root ganglia. Calbindin-containing laminar nerve endings may be related to mechanoreceptors in the esophagus.

Swallowing performance in patients with vocal fold motion impairment

Twenty-seven patients with vocal fold motion impairment underwent detailed pharyngoesophagel manometry with a strain gauge assembly linked to a computer recorder. Nine were known to have lesions of the central vagal trunk or nucleus, 9 had recurrent laryngeal nerve (RLN) palsy, and the remainder were idiopathic. The site of the lesion was a more important determinant of subjective swallowing performance than the position of the involved cord at laryngoscopy. Patients with central lesions had lower tonic and contraction upper esophageal sphincter (UES) pressures than 25 age-matched controls, suggesting that high cervical branches of the lower cranial nerves are important in UES excitatory innervation. RLN palsy patients showed significantly increased pharyngeal contraction amplitude and reduced pharyngoesophageal wave durations. The results suggest that the dysphagia associated with vocal fold motion impairment is not simply due to the disruption of laryngeal deglutitive kinetics, but to independent effects on pharyngeal function.

Distribution and origin of the peripheral innervation of rat cervical esophagus

Several neurotransmitters, neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), galanin, enkephalin, calcitonin-gene related peptide (GGRP), substance P, as well as nitric oxide synthase (NOS), and the noradrenergic marker tyrosine-hydroxylase (TH) were localized by immunocytochemistry in the cervical esophagus of rat. Nerve fibers containing the neuropeptides, NOS, and TH were distributed in the myenteric plexus, around muscle bundles and small blood vessels. Injection of the retrograde tracer True Blue (TB) into the cervical esophagus resulted in the appearance of labeled nerve cell bodies in the superior cervical, the stellate, the nodose, the sphenopalatine, the dorsal root ganglia at levels C2-C7, and in local ganglia close to the thyroid. Most of the TB-labeled nerve cell bodies in the superior cervical ganglia contained NPY. In the stellate ganglion, a few labeled nerve cell bodies contained VIP whereas an additional few cell bodies stored VIP. In local ganglia, the majority of labeled cell bodies contained VIP. In the nodose ganglion and cervical dorsal root ganglia, the majority of the labeled nerve cell bodies stored CGRP. The results indicate that the cervical esophagus has a dense innervation with multiple neurotransmitters emanating from several ganglia. As judged by the pattern of nerve fiber distribution, they may regulate esophageal peristalsis and blood flow, some of them possibly in a cooperative manner.

Vagal afferent dysfunction in naturally occurring canine esophageal motility disorder

Few studies have examined the vagal afferent innervation of the esophagus in naturally occurring esophageal motility disorders. The present study assessed the integrity of distension-sensitive vagal afferents innervating the esophagus in naturally occurring canine megaesophagus. In the dog, esophageal distension induces reflex inhibition of crural diaphragm electromyographic activity that is mediated by vagal afferents innervating esophageal mechanoreceptors. This reflex was measured during stepwise esophageal distension in six dogs with congenital idiopathic megaesophagus, two dogs with megaesophagus secondary to esophageal striated muscle disease, and eight matched controls. In contrast to control dogs, inhibition of crural electromyographic activity was not observed in megaesophagus dogs with esophageal distension within the control volume range. With esophageal distensions far in excess of the control volume range, inhibition of crural electromyographic activity was not observed in five of six dogs with congenital idiopathic megaesophagus, while crural inhibition was observed in the two dogs with secondary megaesophagus. These findings indicate that a defect is present in the vagal afferent innervation to the esophagus in a majority of dogs with congenital idiopathic megaesophagus.

Multichannel recording of cerebral potentials evoked by esophageal balloon distension in humans

In order to obtain insight in the generator localization of esophageal evoked potentials, cerebral responses were recorded from 32 scalp electrodes in five healthy volunteers (two male; three female; age 20-30 years), using series of 50 balloon inflations with 15 ml of air. Sequential topographical mapping of waveforms was performed in each subject. Biphasic waveforms were recorded. At Fpz, a positive deflection at 300 and a negative deflection at 465 msec (P300 and N465) were recorded and at Pz, N300 and P465. At Cz the first peak (N270) was slightly earlier than 300 msec. Waveforms were left to right symmetrical. At distal electrodes, biphasic waveforms were recorded (P300 and N465). In four subjects, a gradual phase shift occurred in between the waveforms at midline electrode Cz and the left and right mastoids. Brain mapping showed phase reversals between central negativity and surrounding positivity at about 300 msec, and between central positivity and surrounding negativity at 400-500 msec. Our data suggest the presence of more than one generator in the anterior and dorsal part of the insula and/or dorsal periinsular cortex.

Immunohistochemical demonstration of calbindin-containing nerve endings in the rat esophagus

Immunoreactivity for calbindin was found in nerve endings with irregular laminar shapes in the rat esophagus. In the myenteric ganglia, laminar endings of a range of sizes formed a complex network and appeared to lie at the surface of the ganglion. The myenteric ganglia that contained nerve endings were most abundant in the upper portion of the esophagus, their number decreasing orally to anally. Calbindin-immunoreactive nerve cell bodies were scattered throughout the esophagus. Laminar terminals were found in the connective tissue of the lamina propria immediately beneath the epithelium and in the muscularis mucosae. Occasional nerve branches formed a network of aborizing endings that surrounded part of the submucosal arterioles. Immunoreactive nerve endings in the mucosa and submucosa were present only in the upper part of the cervical esophagus. Unilateral vagotomy caused a remarkable decrease in the number of the myenteric ganglia containing the calbindin-immunoreactive laminar endings after 15 days or survival; in some of ganglia, the laminar structures disappeared and nerve endings showing weak immunoreactivity had an indistinct appearance, so that the outline of the ganglia became obscure. In operated rats at 24 days, the number of innervated ganglia was about half that in normal rats. However, there was no change in the morphology and the occurrence of the immunoreactive laminar structures in the mucosa and submucosa after denervation. The results show that many of the laminar endings that are immunoreactive for calbindin in the myenteric ganglia are derived from the vagus nerve. Thus, the calbindin-immunoreactive nerve endings with laminar expansions that are found in the rat esophageal wall could be sensory receptors.

Morphological relationships of choleragenoid horseradish peroxidase-labeled spinal primary afferents with myenteric ganglia and mucosal associated lymphoid tissue in the cat esophagogastric junction

The goal of the present study was to gain insight into the environmental factors influencing the activity of primary spinal afferent fibers in the different layers of the esophagogastric junction of the cat and, thus, to analyze the relationships of these afferents with various cellular components. Spinal primary afferent fibers were selectively labeled by anterogradely transported choleragenoid horseradish peroxidase conjugate (B-HRP). B-HRP was injected into the thoracic dorsal root ganglion at the T8-T13 levels. 6-Hydroxydopamine-induced sympathectomy was performed prior to B-HRP injection in order to prevent otherwise unavoidable labeling of sympathetic fibers in the gut wall. Numerous labeled fibers ran between, around, and within the myenteric ganglia. Others crossed the muscle layers directly and entered the mucosa, where some ran near granulocytes and around or through solitary lymphoid follicles. Labeled fibers were observed in the squamous esophageal epithelium but not in the fundic glandular epithelium. The fibers in the myenteric area are probably connected to the muscular tension receptors that have been detected by electrophysiologic techniques. This assumption is based on the observation that only a few fibers appear to terminate in muscle layers and on the fact that the myenteric area is very narrow and subject to powerful forces. Fibers in the myenteric ganglia could be involved in local efferent functions. Fibers in the mucosa could act as nociceptors and might be involved in local immunological responses.