Distribution of immunoreactive substance P in opossum esophagus

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.

Localization of substance P (SP)-immunoreactivity in the myenteric plexus of the rat esophagus

The present immunohistochemical study was performed to examine the number, distribution, and chemical coding of intrinsic substance P (SP) neurons and nerve fibers within the esophagus and discuss their functional roles. Many SP neurons and nerve fibers were found in the myenteric plexus, and the SP neurons gradually decreased from the oral side toward the aboral side of the esophagus. Double-immunolabeling showed that most SP neurons were cholinergic (positive for choline acetyltransferase), and few were nitrergic (positive for nitric oxide synthase). Some cholinergic SP nerve terminals surrounded cell bodies of several myenteric neurons. In the muscularis mucosa and lower esophageal sphincter, and around blood vessels, numerous SP nerve endings were present, and many of them were cholinergic. Also, SP nerve endings were found on only a few motor endplates of the striated muscles, and most of them were calcitonin gene-related peptide (CGRP)-positive. Retrograde tracing using Fast Blue (FB) showed that numerous sensory neurons in the dorsal root ganglia (DRGs) and nodose ganglion (NG) projected to the esophagus, and most FB-labeled SP neurons were CGRP-positive. These results suggest that the intrinsic SP neurons in the rat esophagus may play roles as, at least, motor neurons, interneurons, and vasomotor neurons, which are involved in local regulation of smooth muscle motility, neuronal transmission, and blood circulation, respectively. Moreover, SP nerve endings on only a minority of motor endplates may be extrinsic, derived from DRGs or NG, and possibly detect chemical circumstances within motor endplates to modulate esophageal motility.

Advances in acupuncture at Zusanli point on esophageal motor function

Acupuncture at Zusanli point can affect esophageal motor function, but its mechanism is still not clear. Most researchers consider that its action is associated with neurohumoral factors. This article reviews recent advancement of acupuncture at Zusanli (ST 36) point on esophageal motor function, including acupoints hierarchical structure and dissection characteristics, neural conduction mechanism, neurotransmitters regulation, etc. Acupuncture at ST 36 point might lead to wholesome regulation on esophagus, which was of notably significant for dynamic esophageal disease therapy.

Gender differences in pain and biomechanical responses after acid sensitization of the human esophagus

Our aims were to investigate gender differences to multimodal stimulations of the esophagus after experimentally induced sensitization. Thirty healthy age-matched subjects, 13 males and 17 females, were included. Pain evoked by mechanical and thermal stimuli was assessed before and after perfusion of the lower esophagus with 0.1 N hydrochloric acid. Males were more sensitive to the baseline mechanical stimuli (P < 0.01) and tolerated a lower volume of acid (P = 0.04). After acid perfusion, males were more sensitive than females to distensions (cross-sectional area P = 0.001 and volume P = 0.001). Acid perfusion sensitized both males (P = 0.03) and females (P = 0.04) to heat stimulation but not to cold stimulation (males, P = 0.09; females, P = 0.8). The referral areas for pain evoked by mechanical and thermal stimuli were larger in females compared with males both before and after acid perfusion (P = 0.002). In females only the referred pain area increased to heat stimulations (P = 0.02). Acid infusion resulted in a more hyperreactive esophagus (P = 0.03) but the hyperreactivity was not gender-dependent. In conclusion, males were more sensitive to mechanical and chemical esophageal stimuli and showed acid-evoked mechanical hyperalgesia. Females had significantly larger referred pain areas to the stimulations. The differentiated response to peripheral and central pain mechanisms may explain the gender-related differences seen in several gastrointestinal disorders.

Tachykinins contribute to nerve-mediated contractions in the human esophagus

BACKGROUND & AIMS

Tachykinins mediate nonadrenergic, noncholinergic excitation in the gastrointestinal tract, but their role in esophageal peristalsis remains unclear.

METHODS

We used muscle strips from the distal third of human esophagus, obtained from patients undergoing esophagectomy for cancer, to investigate the contribution of tachykinins to nerve-mediated contractions. Isometric tension responses to agonists or electrical field stimulation were recorded in circular and longitudinal muscle strips.

RESULTS

Tachykinins produced concentration-dependent increases in tension in circular and longitudinal muscle strips, with the following order of potency: beta-Ala(8)-neurokinin (NK) A (4-10) > NKB > substance P, suggesting NK(2) receptor involvement. The NK(2) receptor antagonist, SR48968 (1 micromol/L), inhibited responses to tachykinins in both muscles. Nerve activation produced on- and off-contractions in circular muscle and a duration-contraction in longitudinal muscle. Atropine (10 micromol/L)-insensitive nerve-evoked contractions were identified for the 3 types of responses. SR48968 produced concentration-dependent inhibition of atropine-insensitive on- and off-contractions but had no effect on the duration-contraction. At low stimulus frequency (1 Hz), on-contractions showed greater sensitivity to SR48968 than off-contractions.

CONCLUSIONS

Nerve-mediated contractions in the human esophagus have a significant atropine-insensitive component. Tachykinins acting on NK(2) receptors can account for some, but not all, of this response, suggesting that other excitatory mechanisms also contribute.

Neuromuscular control of esophageal peristalsis

The esophagus is a muscular conduit connecting the pharynx and the stomach. Its function is controlled by an intrinsic nervous system and by input from the central nervous system through the vagus nerve. Peristalsis in its striated muscle is directed by sequential vagal excitation arising in the brain stem, whereas peristalsis in its smooth muscle involves complex interactions among the central and peripheral neural systems and the smooth muscle elements of the esophagus. The peripheral neuronal elements responsible for producing esophageal off-response, relaxation of the lower esophageal sphincter, and hyperpolarization of the circular esophageal muscle cells reside in the myenteric plexus of the esophagus. For many years these nerves were considered nonadrenergic and noncholinergic because the inhibitory neurotransmitter released on their activation was unknown. We now know that nitric oxide or a related compound is that inhibitory neurotransmitter. The primary excitatory neurotransmitter controlling esophageal motor function is acetylcholine. Some disorders of esophageal motor function, including diffuse esophageal spasm and achalasia, may result from defects in or an imbalance between these excitatory and inhibitory neuromuscular systems.

Tachykinins in the gut. Part I. Expression, release and motor function

The preprotachykinin-A gene-derived peptides substance P and neurokinin (NK) A are expressed in distinct neural pathways of the mammalian gut. When released from intrinsic enteric or extrinsic primary afferent neurons, tachykinins have the potential to influence both nerve and muscle by way of interaction with three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Most prominent among the effects of tachykinins is their excitatory action on gastrointestinal motor activity, which is seen in virtually all regions and layers of the mammalian gut. This action depends not only on a direct activation of the muscle through NK1 and/or NK2 receptors, but also on stimulation of excitatory enteric motor pathways through NK3 and/or NK1 receptors. In addition, tachykinins can inhibit motor activity by stimulating either inhibitory neuronal pathways or interrupting excitatory relays. A synopsis of the available data indicates that endogenous substance P and NKA interact with other enteric transmitters in the physiological control of gastrointestinal motor activity. Derangement of the regulatory roles of tachykinins may be a factor in the gastrointestinal dysmotility associated with infection, inflammation, stress and pain. In a therapeutic perspective, it would seem conceivable, therefore, that tachykinin agonists and antagonists are adjuncts to the treatment of motor disorders that involve pathological disturbances of the gastrointestinal tachykinin system.

Review article: factors protecting the oesophagus against acid-mediated injury

Reflux of gastric acid and pepsins into the lower oesophagus causes symptoms such as heartburn and nausea, and tissue injury leading to erosive oesophagitis and stricture formation. This article reviews the mechanisms involved in protecting the oesophagus against acid-mediated injury, including the role of the lower oesophageal sphincter, secondary oesophageal peristalsis and swallowed saliva. The oesophageal mucosa has inherent abilities to resist acid damage, and recent data from three laboratories suggest a secretory function with local production of bicarbonate and mucus responsive to local acidification. The evidence for these putative oesophageal defence mechanisms is discussed.

NADPH-diaphorase-positive nerve fibers in smooth muscle layers of opossum esophagus: gradients in density

Nitric-oxide-releasing nerves regulate esophageal smooth muscle function. The density of such nerve fibers may differ in the different functional parts of the esophagus. We used both inspection and gray-scale analysis of digitized images to seek differences in density of such nerve fibers, stained for reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase), between esophageal body and esophago-gastric sphincter and between smooth muscle layers in the opossum esophagus. Sections of Swiss roll preparations of the entire organ were stained for NADPH-diaphorase and for immunoreactivity to vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), galanin (GAL), substance P (SP) and constitutive nitric oxide synthase (cNOS). In the circular muscle layer, NADPH-diaphorase-positive fibers were most abundant at the cephalic end of the esophageal body with a significant decline toward and through the esophago-gastric sphincter. In the longitudinal muscle layer and the longitudinally-oriented muscularis mucosae, NADPH-diaphorase-positive nerve fibers were most abundant at the esophago-gastric sphincter with a significant decline toward and through the striated-smooth muscle junction. cNOS immunoreactivity co-localized with NADPH-diaphorase activity. Fibers stained for CGRP immunoreactivity were distributed like the NADPH-diaphorase-positive fibers. Fibers stained for immunoreactivity to the other peptides (VIP, GAL, SP) showed no clear differences in distribution along the esophagus in any of the muscle layers.

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.

Colocalization of NADPH-diaphorase activity and certain neuropeptides in the esophagus of opossum (Didelphis virginiana)

Nitric oxide and various neuropeptides in the myenteric plexus regulate esophageal motility. We sought colocalization of nitric oxide synthase and neuropeptides in frozen sections of mid-portion of smooth-muscled opossum esophagus using NADPH-diaphorase activity to mark the synthase and immunoreactivity to detect peptides. The peptides, all with demonstrated physiological activity in this organ, were calcitonin gene-related peptide, galanin, neuropeptide Y, substance P, and vasoactive intestinal polypeptide. The ExtrAvidin Peroxidase immunostain for each peptide was carried up to the final peroxidase reaction with 3-amino-9-ethyl-carbazole. The NADPH-diaphorase reaction was applied with short incubation to provide light staining just before the peroxidase reaction was performed. We examined sections for the proportions of singly and dually labeled nerve cells in the myenteric plexus. NADPH-diaphorase activity was highly colocalized with calcitonin gene-related peptide (59%), galanin (54%), and vasoactive intestinal polypeptide (53%). It showed little colocalization with neuropeptide Y (10%) and substance P (8%). The proportions of all nerve cells containing each of the substances were: NADPH-diaphorase--33%, calcitonin gene-related peptide--30%, galanin--55%, neuropeptide Y--16%, substance P--35%, and vasoactive intestinal polypeptide--58%. We conclude that the nerves responsible for peristalsis in the esophagus may act by releasing nitric oxide along with other inhibitory substances, calcitonin gene-related peptide, galanin, and vasoactive intestinal polypeptide, but not excitatory substances, neuropeptide Y and substance P.

Vasoactive intestinal contractor: localization in the opossum esophagus and effects on motor functions

BACKGROUND/AIMS

Vasoactive intestinal contractor (VIC), an endothelinlike peptide and a putative gastrointestinal hormone, contracts gastrointestinal smooth muscle. The aim was to study VIC in relation to esophageal function.

METHODS

Intramural nerves in opossum esophageal smooth muscle strips were stimulated in the presence of various concentrations of VIC and were stained for VIC immunoreactivity.

RESULTS

VIC caused an atropine-resistant increase in the amplitude of nerve-induced contractions of the circular muscle. VIC alone contracted longitudinal muscle, and this effect was nearly eliminated by 1 mmol/L atropine. VIC caused an atropine-resistant increase in the resting tone of the lower esophageal sphincter muscle, but it did not affect nerve-induced relaxation of that muscle. VIC-immunoreactive nerve fibers occurred in the longitudinal muscle layer, in the muscularis mucosae, and around the ducts of esophageal glands. A few such fibers were found in the circular muscle layer. Nerve fibers and cell bodies of the myenteric plexus showed VIC immunoreactivity. In the stomach, immunoreactive nerve fibers occurred in muscularis mucosae and circular muscle but not in longitudinal muscle.

CONCLUSIONS

VIC is localized in neuronal elements of the opossum esophagus and excites contractions in esophageal smooth muscle.

Effect of various neurotransmitters and electrical field stimulation on smooth muscle preparations from the esophagus of horses

The effects of various neurotransmitters and electrical field stimulation on muscle strips from the distal equine esophagus were studied. Acetylcholine (ACH) caused concentration dependent (1.1-55 x 10(-6) mol/l) contractions of the longitudinal and circular muscle strips from the distal esophagus as well as from the lower esophageal sphincter (LES). Atropine (10(-5) mol/l) blocked these contractions. Noradrenaline (NA) induced concentration related (1.1-55 x 10(-6) mol/l) contractions of the muscle strips from the LES. This excitatory effect of noradrenaline was antagonized by the alpha 1-receptor antagonist prazosin. Tetrodotoxin (5 x 10(-6) mol/l) did not affect the contractile response of the muscle strips to noradrenaline (55 x 10(-6) mol/l). Noradrenaline (1.1-55 x 10(-6) mol/l) had no excitatory effect on the circular and the longitudinal muscle strips from the esophagus. Furthermore, noradrenaline induced a concentration dependent (1.1-55 x 10(-6) mol/l) relaxation of the longitudinal muscle strips from the esophagus. The relaxing effect of NA was antagonized by the beta-receptor antagonist propranolol (10(-5) mol/l). Histamine (10(-7)-10(-6) mol/l) elicited a contraction in 4 out of 18 muscle preparations from the LES. The histamine induced contractions were partly antagonized by the H1-receptor antagonist clemastine (10(-4) mol/l) and fully abolished by the H2-receptor antagonist clemastine (10(-4) mol/l). Electrical field stimulation (EFS, 5 Hz, 2 ms; 500 mA; 10 Hz, 2 ms; 500 mA) produced tetrodotoxin sensitive contractions in all three types of muscle strips. Atropine (10(-5) mol/l) fully suppressed these contractions in most preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of esophageal pain

Esophageal pain is transmitted via the sympathetic nervous system to the spinal cord, in which pain from visceral and somatic sources ascends to higher centers in the brain. Primary afferent neurons are bipolar, with the peripheral end specialized to be a sensory receptor. Nociceptors of somatosensory afferents are free nerve endings that can be activated by mechanical, thermal, or chemical stimuli. Esophageal nociceptive neurons have not been specifically identified but probably are also free nerve endings. Most esophageal spinal mechanoreceptors have been shown to be nociceptive. Some esophageal mechanonociceptors have a wide dynamic range and respond to physiologic and painful stimuli, while others have a high threshold of stimulation and are solely nociceptive. Esophageal spinal afferents have their cell bodies in the dorsal root ganglia and contain substance P and calcitonin gene-related peptide. These putative neurotransmitters are transported in both the peripheral and central directions of bipolar afferent neurons. Primary afferent neurons are likely to also contain an excitatory amino acid neurotransmitter such as glutamate. Centrally, nociceptive primary afferents terminate on neurons in specific layers of the dorsal horn of the spinal cord. Convergence of multiple visceral afferents with somatic afferents onto the same dorsal horn neurons may explain referred pain. A patient's inability to distinguish esophageal from cardiac pain may be due to convergence of pain pathways. Second-order neurons in the dorsal horn project in the anterolateral system to the brain. Within the anterolateral system, nociception ascends in the spinothalamic, spinoreticular, and spinomesencephalic tracts. The thalamus relays fast pain to the postcentral areas of the parietal lobe of the cortex. Pathways to the reticular formation are slow and may mediate the increased arousal that occurs in response to pain. The spinomesencephalic tract projects to midbrain sites including the periaqueductal gray. Organ-specific pathways in the brain have yet to be defined, but neuroanatomic tracing techniques employing neurotropic viruses are being developed. The perception of pain can be influenced at multiple levels, such as the receptor in the esophagus, the synapses in the dorsal horn of the spinal cord or thalamus, or the cortex. A fundamental mechanism of modulating nociception is descending inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Peptidergic innervation of the human esophageal smooth muscle

Studies were performed to define the peptidergic nature of intramural nerves in the human esophagus. Cryosections of uninvolved surgically resected tissues from 14 individuals were studied by immunofluorescence for the localization of 10 neuropeptides. Myenteric neurons showed bombesin-, calcitonin gene-related peptide-, galanin-, substance P-, vasoactive intestinal polypeptide-, leucine-enkephalin-, methionine-enkephalin-, neuropeptide Y-, and somatostatin-like immunoreactivity. Submucous neurons had all the above except neuropeptide Y, methionine-enkephalin, leucine-enkephalin, and bombesin. Both groups of neurons received nerve terminations positive for calcitonin gene-related peptide, galanin, neuropeptide Y, substance P, and vasoactive intestinal polypeptide. Myenteric neurons additionally received terminations positive for neuropeptide Y, methionine-enkephalin, and somatostatin. All muscle layers had varicose fibers that reacted for calcitonin gene-related peptide, galanin, neuropeptide Y, and substance P. Longitudinal and circular muscle received few nerves reactive for leucine-enkephalin, whereas methionine-enkephalin was localized in a few nerve endings in the circular muscle. Somatostatin- and bombesin-reactive nerves occurred in longitudinal muscle. No cholecystokinin-reactive nerves were found. This study extends the results of previous studies and shows the previously undescribed presence of calcitonin gene-related peptide- and galanin-reactive nerves in the human esophagus and identifies neuropeptides that may serve as motor, sensory, and modulatory neurotransmitters of esophageal nerves.

Mucosal peptidergic innervation of the opossum esophagus and anal canal: a comparison with snout skin

Nerves within and under the esophageal epithelium of the opossum esophagus were investigated morphologically with osmication and immunohistochemically for ten neuropeptides. The structurally similar but functionally diverse epithelia of the anal canal and snout skin, on which no immunohistochemical information exists, were similarly investigated for comparison. Total innervation was estimated from osmication, which revealed intraepithelial nerves in all three tissues in the following order of density: snout skin greater than anal canal greater than esophagus. Calcitonin gene-related peptide and substance P occurred in all three organs. The snout skin had intraepithelial galanin nerves but not vasoactive intestinal polypeptide, while conversely the esophagus and anal canal had vasoactive intestinal polypeptide but not galanin. All peptides found intraepithelially also occurred subepithelially. Calcitonin gene-related peptide, galanin, neuropeptide Y, substance P and vasoactive intestinal polypeptide subepithelial nerves occurred in all the tissues, while gastrin releasing peptide nerves occurred infrequently in the subepithelial regions of the esophagus and anal canal, but not the snout skin. As these epithelia neither secrete nor absorb, their nerves are presumably sensory. The peptides investigated could not account for all intraepithelial nerves demonstrated by osmium. Differences in the innervation of these epithelia may result from their differing sensory requirements.

Central neural control of esophageal motility: a review

We review recent studies on the central neural control of esophageal motility, emphasizing the anatomy and chemical coding of esophageal pathways in the spinal cord and medulla. Sympathetic innervation of the proximal esophagus is derived primarily from cervical and upper thoracic paravertebral ganglia, whereas that of the lower esophageal sphincter and proximal stomach is derived from the celiac ganglion. In addition to noradrenaline, many sympathetic fibers in the esophagus contain neuropeptide Y (NPY), and both noradrenaline and NPY appear to decrease blood flow and motility. Preganglionic neurons innervating the cervical and upper thoracic ganglia are located at lower cervical and upper thoracic spinal levels. The preganglionic innervation of the celiac ganglion arises from lower thoracic spinal levels. Both acetylcholine (ACh) and enkephalin (ENK) have been localized in sympathetic preganglionic neurons, and it has been suggested that ENK acts to pre-synaptically inhibit ganglionic transmission. Spinal afferents from the esophagus are few, but have been described in lower cervical and thoracic dorsal root ganglia. A significant percentage contain calcitonin gene-related peptide (CGRP) and substance P (SP). The central distribution of spinal afferents, as well as their subsequent processing within the spinal cord, have not been addressed. Medullary afferents arise from the nodose ganglion and terminate peripherally both in myenteric ganglia, where they have been postulated to act as tension receptors, and, to a lesser extent, in more superficial layers. Centrally, these afferents appear to end in a discrete part of the nucleus of the solitary tract (NTS) termed the central subnucleus. The transmitter specificity of the majority of these afferents remains unknown. The central subnucleus, in turn, sends a dense and topographically discrete projection to esophageal motor neurons in the rostral portion of the nucleus ambiguous (NA). Both somatostatin-(SS) and ENK-related peptides have been localized in this pathway. Finally, motor neurons from the rostral NA innervate striated portions of the esophagus. In addition to ACh, these esophageal motor neurons contain CGRP, galanin (GAL), N-acetylaspartylglutamate (NAAG), and brain natriuretic peptide (BNP). The physiological effect of these peptides on esophageal motility remains unclear. Medullary control of smooth muscle portions of the esophagus have not been thoroughly investigated.