We recently reported the involvement of AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid) receptor subunit upregulation and phosphorylation in the rostral cingulate cortex (rCC) as the underlying mechanism of acute esophageal acid‐induced cortical sensitization. Based on these findings, we proposed to investigate whether prolonged esophageal acid exposures in rats exhibit homeostatic synaptic scaling through downregulation of AMPA receptor expression in rCC neurons. We intended to study further whether this compensatory mechanism is impaired when rats are pre‐exposed to repeated esophageal acid exposures neonatally during neuronal development.

Background We recently reported an increase in N-methyl-D-aspartate (NMDA) receptor subunit expression and CaMKII-dependent phosphorylation of NR2B in the rostral cingulate cortical (rCC) neurons following esophageal acid exposure in rats. As alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors mediate the fast excitatory transmission and play a critical role in synaptic plasticity, in this study, we investigated the effect of esophageal acid exposure in rats on the expression of AMPA receptor subunits and the involvement of these molecular alterations in acid-induced sensitization of neurons in the anterior cingulate (ACC) and midcingulate (MCC) cortices. Methods In molecular study, we examined GluA1 and GluA2 expression and phosphorylation in membrane preparations and in the isolated postsynaptic densities (PSDs) from rats receiving acute esophageal exposure of either saline (control group) or 0.1 NHCl(experimental group). In electrophysiological study, the effect of selective AMPA receptor (Ca2+ permeable) antagonist IEM-1460 and CaMKII inhibitor KN-93 was tested on responses of cortical neurons during acid infusion to address the underlying molecular mechanism of acid-induced sensitization. Key Results The acid exposure significantly increased expression of GluA1, pGluA1Ser(831), and phosphorylated CaMKIIThr(286), in the cortical membrane preparations. In isolated PSDs, a significant increase in pGluA1Ser(831) was observed in acid-treated rats compared with controls. Microinjection of IEM-1460 or KN-93 near the recording site significantly attenuated acid-induced sensitization of cortical neurons. Conclusions & Inferences The underlying mechanism of acid-induced cortical sensitization involves upregulation and CaMKII-mediated phosphorylation of GluA1. These molecular changes of AMPA receptors subunit GluA1 in the cortical neurons might play an important role in acid-induced esophageal hypersensitivity.

The aim of this study was to determine the role of the superior laryngeal nerve (SLN) in the following esophageal reflexes: esophago-upper esophageal sphincter (UES) contractile reflex (EUCR), esophago-lower esophageal sphincter (LES) relaxation reflex (ELIR), secondary peristalsis, pharyngeal swallowing, and belch. Cats ( N = 43) were decerebrated and instrumented to record EMG of the cricopharyngeus, thyrohyoideus, geniohyoideus, and cricothyroideus; esophageal pressure; and motility of LES. Reflexes were activated by stimulation of the esophagus via slow balloon or rapid air distension at 1 to 16 cm distal to the UES. Slow balloon distension consistently activated EUCR and ELIR from all areas of the esophagus, but the distal esophagus was more sensitive than the proximal esophagus. Transection of SLN or proximal recurrent laryngeal nerves (RLN) blocked EUCR and ELIR generated from the cervical esophagus. Distal RLN transection blocked EUCR from the distal cervical esophagus. Slow distension of all areas of the esophagus except the most proximal few centimeters activated secondary peristalsis, and SLN transection had no effect on secondary peristalsis. Slow distension of all areas of the esophagus inconsistently activated pharyngeal swallows, and SLN transection blocked generation of pharyngeal swallows from all levels of the esophagus. Slow distension of the esophagus inconsistently activated belching, but rapid air distension consistently activated belching from all areas of the esophagus. SLN transection did not block initiation of belch but blocked one aspect of belch, i.e., inhibition of cricopharyngeus EMG. Vagotomy blocked all aspects of belch generated from all areas of esophagus and blocked all responses of all reflexes not blocked by SLN or RLN transection. In conclusion, the SLN mediates all aspects of the pharyngeal swallow, no portion of the secondary peristalsis, and the EUCR and ELIR generated from the proximal esophagus. Considering that SLN is not a motor nerve for any of these reflexes, the role of the SLN in control of these reflexes is sensory in nature only.

Background and alms: Several types of gastric surgeries have been associated with early satiety, dyspepsia and food intolerances. We aimed to examine alterations in gastric vagal afferents following gastric surgery-fundus ligation.Methods: Six week old, male Sprague-Dawley rats underwent chronic ligation (CL) of the fundus. Sham rats underwent abdominal surgery, but without ligation. Another group of rats underwent acute ligation (AL) of the fundus immediately prior to experiments. CL and sham rats were allowed to grow to age 3-4 months. Food intake and weights were recorded post-operatively. Gastric compliance and gastric wall thickness was measured at baseline and during gastric distension (GD). Extracellular recordings were made to examine response characteristics of vagal afferent fibers to GD and to map the stomach receptive field (RF). The morphological structures of afferent terminals in the stomach were examined with retrograde tracings from the nodose ganglion.Results: The CL group consumed significantly less food and weighed less than sham control. The mean compliance of the CL group was significantly less than control, but higher than the AL group. The spontaneous firing and responses to GD of afferent fibers from the CL rats were significantly higher than AL rats. There was a marked expansion of the gastric RF in the CL rats with significant reorganization and regeneration of intramuscular array (IMA) terminals. There was no difference in total wall or muscle thickness among the groups.Conclusion: CL results in aberrant remodeling of IMAs with expansion of the gastric RF and alters the mechano-transduction properties of vagal afferent fibers. These changes could contribute to altered sensitivity following gastric surgery. (C) 2009 IBRO. Published by Elsevier Ltd. All rights reserved.

Gastro-esophageal acid reflux can stimulate esophageal vagal sensory afferents by activating proton-sensitive ion channel transient receptor vanilloid one (TRPV1). The objective of this study was to investigate the response characteristics of vagal afferent fibers of rats to acid (0.1 N HCl) and capsaicin (CAP) following esophagitis and differential effects of two classes of TRPV1 antagonists on responses of vagal afferent fibers. The chronic reflux was induced by ligating the fundus of the stomach and partial constriction of pylorus. Extracellular single fiber recordings were made from the cervical vagal afferent fibers from naive control and fundus-ligated (FL) esophagitis rats. Innervations of fibers were identified to esophageal distension (ED) and subsequently tested to CAP and acid before and after injection of TRPV1 antagonist JYL1421 or AMG9810 (10 μmol/kg i.v.). Seventy-five vagal afferent fibers from 70 rats were identified to ED. Intra-esophageal CAP (0.1 ml of 1 mg/ml) excited 39.5% (17/43, 5/22 from naive and 12/21 from FL rats) fibers. In contrast, i.v. injection of CAP (0.03–0.3 μmol/kg) dose-dependently excited 72% (42/58) fibers. Responses to CAP were significantly greater for fibers from FL rats (n=32) than naive rats (n=25). TRPV1 antagonists JYL1421 and AMG9810 (10 μmol/kg) significantly blocked response to CAP. Intra-esophageal acid infusion stimulated 5/17 (29.4%) fibers from naive rats and 12/28 (42%) from FL rats. Effect of acid was significantly blocked by AMG9810, but not by JYL1421. Results indicate that following esophagitis the number of fibers responsive to CAP and acid is greater than noninflamed esophagus, which may contribute to esophageal hypersensitivity. Acid-induced excitation of vagal sensory afferents can be differentially attenuated by different classes of TRPV1 antagonists. Therefore, TRPV1 antagonists play a key role in attenuation of hypersensitivity following reflux-induced esophagitis. The use of TRPV1 antagonists could be an alternative to the traditional symptoms-based treatment of chronic acid reflux and esophageal hypersensitivity.

A possible mechanism of oesophageal hypersensitivity is the acid-induced activation of transient receptor potential vanilloid receptor 1 (TRPV1) in the primary sensory neurons. We investigated TRPV1 expression and its colocalization with substance P (SP) and isolectin B4 (IB4)-positive cells in the thoracic dorsal root ganglia (DRGs) and nodose ganglia (NGs) of rats with reflux-induced oesophagitis (RO). RO was developed by fundus ligation and partial obstruction of the pylorus of Sprague-Dawley rats. Four groups of rats were used; fundus ligated acute (RO 48 h), chronic 7 days (RO 7D), RO 7D + omeprazole (7D + Omz, 40 mg kg(-1), i.p.) and sham-operated controls. Immunohistochemical analysis of TRPV1, SP and IB4 expression were carried out in spinal cord (SC), DRGs and NGs. RO rats exhibited significant inflammation and increase in TRPV1-ir and SP-ir expressions in the SC, DRGs and NGs. The maximum colocalization of TRPV1 and SP was observed in RO 7D rats, but Omz prevented inflammation and over expression of TRPV1 and SP. TRPV1-ir significantly increased in IB4-positive cells in DRGs and SC, but not in the NGs. Results document that acid-induced oesophagitis increases TRPV1 expression in both SP- and IB4-positive sensory neurons. The over expression of TRPV1 may contribute to oesophageal hypersensitivity observed in gastro-oesophageal reflux disease (GORD).

AR Stent generated negative pressures secondary to siphon effect

Studies in humans have documented that acute acid infusion into the esophagus leads to decrease in threshold for sensations to mechanical distension of the esophagus. It is not known whether acid infusion leads to sensitization of brainstem neurons receiving synaptic input from vagal afferent fibers innervating the esophagus. The aim of this study was to investigate the correlation of responses of vagal afferents and brainstem neurons after acute infusion of acid (0.1 N HCl)+pepsin (1 mg/ml) into the esophagus of cats. The vagal afferent fibers (n=20) exhibited pressure-dependent increase in firing to graded esophageal distension (5–80 mm Hg). Infusion of acid+pepsin into the esophagus produced a significant increase in ongoing resting firing of five of 16 fibers (31%) tested. However, their responses to graded esophageal distension did not change when tested 30 min after infusion. Pepsin infusion did not change the resting firing and response to esophageal distension (n=4). Twenty-one brainstem neurons were recorded that responded in an intensity-dependent manner to graded esophageal distension. Responses of 12 excited neurons were tested after intra-esophageal acid+pepsin infusion. Neurons exhibited a decrease in threshold for response to esophageal distension and increase in firing after acid+pepsin infusion. The sensitization of response after intra-esophageal acid remained unaffected after cervical (C1–C2) spinal transection (n=3). Results indicate that the esophageal distension-sensitive neurons in the brainstem exhibit sensitization of response to esophageal distension after acute acid+pepsin exposure. The sensitization of brainstem neurons is possibly initiated by increased spontaneous firing of the vagal afferent fibers to acid+pepsin, but not to sensitized response of vagal distension-sensitive afferent fibers to esophageal distension. Results also indicate that spinal pathway does not contribute to sensitization of brainstem neurons.

The aim of this study was to identify the medullary vagal nuclei involved in the different phases of swallowing activated physiologically in a species with an esophagus similar to human. In decerebrate cats, the pharyngeal (0.5–1.0 ml water in pharynx (N=6)) or esophageal (1–3 ml air in esophagus (N=5)) phases of swallowing were stimulated separately once per minute for 3 h, and we compared the resulting c-fos immunoreactivity within neuronal cell nuclei of the dorsal motor nucleus (DMN), nucleus tractus solitarius (NTS) and nucleus ambiguus (NA) with a sham control group (N=5). We found that the pharyngeal phase was associated with an elevated number of c-fos positive neurons in the intermediate (NTSim), interstitial (NTSis), ventromedial (NTSvm) subnuclei of the NTS, caudal DMN, and dorsal NA; and the esophageal phase was associated with an elevated number of c-fos positive neurons in the central (NTSce), ventral, dorsolateral, ventrolateral subnuclei of the NTS, rostral DMN, and ventral NA. We concluded that the pharyngeal and esophageal phases of swallowing are associated with different sets of NTS subnculei; and the DMN and NA may contain functionally different populations of motor neurons situated rostrocaudally and dorsoventrally associated with the different phases of swallowing. The central pattern generator (CPG) for swallowing probably receives significant peripheral feedback, and the NTSvm may participate in the transition of the pharyngeal to the esophageal phase of swallowing.

Deglutitive airway protective mechanisms include glottal closure, epiglottal descent, and anterosuperior displacement of the larynx. Aspiration of swallowed material may occur during the pre-, intra-, or postpharyngeal phase of swallowing. Our objectives were to determine the relative contribution of the airway protective mechanisms during each phase of swallow in 14 decerebrated cats before and after suprahyoid myotomy, epiglottectomy, and unilateral cordectomy. After myotomy, superior excursions of the hyoid, thyroid, and cricoid cartilages and anteroposterior diameter of maximum upper esophageal spincter (UES) opening were significantly diminished, but the incidence of pharyngeal residue significantly increased ( P < 0.05). No aspiration was observed in the predeglutitive period. After myotomy, the incidence of aspiration significantly increased in both intra- and postdeglutitive periods. Epiglottectomy did not alter aspiration incidence, but unilateral cordectomy resulted in a 100% incidence of intra- and postdeglutitive aspiration. In conclusion, glottal closure constitutes the primary mechanism for prevention of intra- and postdeglutitive aspiration, but laryngeal elevation may assist this function. Bolus pulsion without laryngeal distraction can open the UES, but at risk of aspiration due to decreased pharyngeal clearance. The epiglottis provides no apparent airway protection during any phase of swallowing.