Effects of vasopressin and long pulse-low frequency gastric electrical stimulation on gastric emptying, gastric and intestinal myoelectrical activity and symptoms in dogs

Identification of Arginine-Vasopressin Receptor 1a (Avpr1a/Avpr1a) as a Novel Candidate Gene for Chronic Visceral Pain Sheds Light on the Potential Role of Enteric Neurons in the Development of Visceral Hypersensitivity

Chronic abdominal pain in the absence of ongoing disease is the hallmark of disorders of gut-brain interaction (DGBIs), including irritable bowel syndrome (IBS). While the etiology of DGBIs remains poorly understood, there is evidence that both genetic and environmental factors play a role. In this study, we report the identification and validation of arginine-vasopressin receptor 1A (Avpr1a) as a novel candidate gene for visceral hypersensitivity (VH), a primary peripheral mechanism underlying abdominal pain in DGBI/IBS. Comparing 2 C57BL/6 (BL/6) substrains (C57BL/6NTac and C57BL/6J) revealed differential susceptibility to the development of chronic VH following intrarectal zymosan instillation, a validated preclinical model for postinflammatory IBS. Using whole-genome sequencing, we identified a single-nucleotide polymorphism differentiating the 2 strains in the 5' intergenic region upstream of Avpr1a, encoding the protein Avpr1a. We used behavioral, histological, and molecular approaches to identify distal colon-specific gene expression and neuronal hyperresponsiveness covarying with Avpr1a genotype and VH susceptibility. While the 2 BL/6 substrains did not differ across other gastrointestinal phenotypes (eg, fecal water retention), VH-susceptible BL/6NTac mice had higher colonic Avpr1a mRNA and protein expression. These results parallel findings that patients' colonic Avpr1a mRNA expression corresponded to higher pain ratings. Moreover, neurons of the enteric nervous system were hyperresponsive to the Avpr1a agonist arginine-vasopressin, suggesting a role for enteric neurons in the pathology underlying VH. Taken together, these findings implicate differential regulation of Avpr1a as a novel mechanism of VH susceptibility as well as a potential therapeutic target specific to VH. PERSPECTIVE: This article presents evidence of Avpr1a as a novel candidate gene for VH in a mouse model of IBS. Avpr1a genotype and/or tissue-specific expression represents a potential biomarker for chronic abdominal pain susceptibility.

Identification of arginine-vasopressin receptor 1a (Avpr1a/AVPR1A) as a novel candidate gene for chronic visceral pain

Chronic abdominal pain in the absence of ongoing disease is the hallmark of disorders of gut-brain interaction (DGBIs), including irritable bowel syndrome (IBS). While the etiology of DGBIs remains poorly understood, there is evidence that both genetic and environmental factors play a role. In this study, we report the identification and validation of Avpr1a as a novel candidate gene for visceral hypersensitivity (VH), a primary peripheral mechanism underlying abdominal pain in DGBI/IBS. Comparing two C57BL/6 (BL/6) substrains (C57BL/6NTac and C57BL/6J) revealed differential susceptibility to the development of chronic VH following intrarectal zymosan (ZYM) instillation, a validated preclinical model for post-inflammatory IBS. Using whole genome sequencing, we identified a SNP differentiating the two strains in the 5' intergenic region upstream of Avpr1a, encoding the protein arginine-vasopressin receptor 1A (AVPR1A). We used behavioral, histological, and molecular approaches to identify distal colon-specific gene expression differences and neuronal hyperresponsiveness covarying with Avpr1a genotype and VH susceptibility. While the two BL/6 substrains did not differ across other gastrointestinal (GI) phenotypes (e.g., GI motility), VH-susceptible BL/6NTac mice had higher colonic Avpr1a mRNA and protein expression. Moreover, neurons of the enteric nervous system were hyperresponsive to the AVPR1A agonist AVP, suggesting a role for enteric neurons in the pathology underlying VH. These results parallel our findings that patients' colonic Avpr1a mRNA expression was higher in patients with higher pain ratings. Taken together, these findings implicate differential regulation of Avpr1a as a novel mechanism of VH-susceptibility as well as a potential therapeutic target specific to VH.

Oxytocin and Vasopressin Systems in Obesity and Metabolic Health: Mechanisms and Perspectives

PURPOSE OF REVIEW

The neurohypophysial endocrine system is identified here as a potential target for therapeutic interventions toward improving obesity-related metabolic dysfunction, given its coinciding pleiotropic effects on psychological, neurological and metabolic systems that are disrupted in obesity.

RECENT FINDINGS

Copeptin, the C-terminal portion of the precursor of arginine-vasopressin, is positively associated with body mass index and risk of type 2 diabetes. Plasma oxytocin is decreased in obesity and several other conditions of abnormal glucose homeostasis. Recent data also show non-classical tissues, such as myocytes, hepatocytes and β-cells, exhibit responses to oxytocin and vasopressin receptor binding that may contribute to alterations in metabolic function. The modulation of anorexigenic and orexigenic pathways appears to be the dominant mechanism underlying the effects of oxytocin and vasopressin on body weight regulation; however, there are apparent limitations associated with their use in direct pharmacological applications. A clearer picture of their wider physiological effects is needed before either system can be considered for therapeutic use.

The Effect of Gastric Electrical Stimulation on Small Bowel Motility in Patients With Gastroparesis and Concomitant Pancreatic and Small Bowel Dysfunction: From Animal Model to Human Application

BACKGROUND/AIMS

Patients with gastroparesis often have biliary/pancreatic and small bowel symptoms but the effects of gastric electrical stimulation on small bowel electrical activity of the mid-gut have not been studied. Animal model aim: Establish gastric and upper small bowel/biliary slow wave activity relationships with electrical stimulation. Human study aim: Demonstrate improvement in symptoms associated with proximal small bowel dysmotility in gastric stimulated patients.

MATERIALS AND METHODS

Animal model: In vivo evoked responses of duodenal and Sphincter of Oddi measures recorded during gastric electrical stimulation in a nonsurvival swine model (N = 3). High-resolution electrical slow wave mapping of frequency, amplitude, and their ratio, for duodenal and Sphincter of Oddi electrical activity were recorded. Human study: Patients (N = 8) underwent temporary gastric stimulation with small bowel electrodes. Subjective and objective data was collected before and after temporary gastric stimulation. Symptom scores, gastric emptying times, and mucosal electrograms via low-resolution mapping were recorded.

RESULTS

Animal gastric stimulation resulted in some changes in electrical activity parameters, especially with the highest energies delivered but the changes were not statistically significant. Human study revealed improvement in symptom and illness severity scores, and changes in small bowel mucosal slow wave activity.

CONCLUSIONS

Gastric electrical stimulation in an animal model seems to show nonsignificant effects small bowel slow wave activity and myoelectric signaling, suggesting the existence of intrinsic neural connections. Human data shows more significance, with possible potential for therapeutic use of electrical stimulation in patients with gastroparesis and pancreato-biliary and small bowel symptoms of the mid-gut. This study was limited by the nonsurvival pig model, small sample size, and open label human study.

Long-Pulse Gastric Electrical Stimulation Repairs Interstitial Cells of Cajal and Smooth Muscle Cells in the Gastric Antrum of Diabetic Rats

Background/Aims

The damage of interstitial cells of Cajal and smooth muscle cells has far-reaching implications in the pathogenesis of gastroparesis in diabetic patients. Gastric electrical stimulation (GES) is an efficient therapy for gastric motility disorders, but the mechanisms of GES require clarification.

Methods

Male rats were randomly divided into the control group, diabetic rat group (DM), diabetic rats with sham GES group (DM + SGES), and diabetic rats with different frequency GES group (DM + GES) (GES1: 5.5 cpm, 100 ms, 4 mA; GES2: 5.5 cpm, 300 ms, 4 mA; and GES3: 5.5 cpm, 550 ms, 2 mA). Gastric contractions were explored using the organ bath technique. The alterations of interstitial cells of Cajal, the SCF/c-kit pathway, and smooth muscle cells were also investigated.

Results

(1) Gastric contractions were significantly improved in the DM + GES group compared with those in the DM group. (2) The damage of interstitial cells of Cajal was prevented in the DM + GES group in contrast to the DM group. Moreover, long-pulse GES increased the expression of the SCF/c-kit pathway. More proliferated interstitial cells of Cajal in muscle layers were observed obviously in the DM + GES group. (3) The number of smooth muscle cells in the DM group was not significantly decreased compared with that in the control group. However, ultrastructural changes were distinctly damaged in the DM group. The application of GES protected against the alteration of the ultrastructures of smooth muscle cells.

Conclusions

Long-pulse GES improves gastric contraction possibly by enhancing the proliferation of interstitial cells of Cajal and restoring the injury of smooth muscle cells.

Gastric myoelectric activity during cisplatin-induced acute and delayed emesis reveals a temporal impairment of slow waves in ferrets: effects not reversed by the GLP-1 receptor antagonist, exendin (9-39)

Preclinical studies show that the glucagon-like peptide-1 (GLP-1) receptor antagonist, exendin (9-39), can reduce acute emesis induced by cisplatin. In the present study, we investigate the effect of exendin (9-39) (100 nmol/24 h, i.c.v), on cisplatin (5 mg/kg, i.p.)-induced acute and delayed emesis and changes indicative of ‘nausea’ in ferrets. Cisplatin induced 37.2 ± 2.3 and 59.0 ± 7.7 retches + vomits during the 0-24 (acute) and 24-72 h (delayed) periods, respectively. Cisplatin also increased (P<0.05) the dominant frequency of gastric myoelectric activity from 9.4 ± 0.1 to 10.4 ± 0.41 cpm and decreased the dominant power (DP) during acute emesis; there was a reduction in the % power of normogastria and an increase in the % power of tachygastria; food and water intake was reduced. DP decreased further during delayed emesis, where normogastria predominated. Advanced multifractal detrended fluctuation analysis revealed that the slow wave signal shape became more simplistic during delayed emesis. Cisplatin did not affect blood pressure (BP), but transiently increased heart rate, and decreased heart rate variability (HRV) during acute emesis; HRV spectral analysis indicated a shift to ‘sympathetic dominance’. A hyperthermic response was seen during acute emesis, but hypothermia occurred during delayed emesis and there was also a decrease in HR. Exendin (9-39) did not improve feeding and drinking but reduced cisplatin-induced acute emesis by ~59 % (P<0.05) and antagonised the hypothermic response (P<0.05); systolic, diastolic and mean arterial BP increased during the delayed phase. In conclusion, blocking GLP-1 receptors in the brain reduces cisplatin-induced acute but not delayed emesis. Restoring power and structure to slow waves may represent a novel approach to treat the side effects of chemotherapy.

High-resolution mapping of gastric slow-wave recovery profiles: biophysical model, methodology, and demonstration of applications

Slow waves play a central role in coordinating gastric motor activity. High-resolution mapping of extracellular potentials from the stomach provides spatiotemporal detail on normal and dysrhythmic slow-wave patterns. All mapping studies to date have focused exclusively on tissue activation; however, the recovery phase contains vital information on repolarization heterogeneity, the excitable gap, and refractory tail interactions but has not been investigated. Here, we report a method to identify the recovery phase in slow-wave mapping data. We first developed a mathematical model of unipolar extracellular potentials that result from slow-wave propagation. These simulations showed that tissue repolarization in such a signal is defined by the steepest upstroke beyond the activation phase (activation was defined by accepted convention as the steepest downstroke). Next, we mapped slow-wave propagation in anesthetized pigs by recording unipolar extracellular potentials from a high-resolution array of electrodes on the serosal surface. Following the simulation result, a wavelet transform technique was applied to detect repolarization in each signal by finding the maximum positive slope beyond activation. Activation-recovery (ARi) and recovery-activation (RAi) intervals were then computed. We hypothesized that these measurements of recovery profile would differ for slow waves recorded during normal and spatially dysrhythmic propagation. We found that the ARi of normal activity was greater than dysrhythmic activity (5.1 ± 0.8 vs. 3.8 ± 0.7 s; P < 0.05), whereas RAi was lower (9.7 ± 1.3 vs. 12.2 ± 2.5 s; P < 0.05). During normal propagation, RAi and ARi were linearly related with negative unit slope indicating entrainment of the entire mapped region. This relationship was weakened during dysrhythmia (slope: -0.96 ± 0.2 vs -0.71 ± 0.3; P < 0.05).NEW & NOTEWORTHY The theoretical basis of the extracellular gastric slow-wave recovery phase was defined using mathematical modeling. A novel technique utilizing the wavelet transform was developed and validated to detect the extracellular slow-wave recovery phase. In dysrhythmic wavefronts, the activation-to-recovery interval (ARi) was shorter and recovery-to-activation interval (RAi) was longer compared with normal wavefronts. During normal activation, RAi vs. ARi had a slope of -1, whereas the weakening of the slope indicated a dysrhythmic propagation.

Simultaneous anterior and posterior serosal mapping of gastric slow-wave dysrhythmias induced by vasopressin

NEW FINDINGS

What is the central question of this study? This study aimed to provide the first comparison of simultaneous high-resolution mapping of anterior and posterior gastric serosa over sustained periods. What is the main finding and its importance? Episodes of spontaneous gastric slow-wave dysrhythmias increased significantly following intravenous infusion of vasopressin compared with the baseline state. A number of persistent dysrhythmias were defined, including ectopic activation, conduction block, rotor, retrograde and collision/merger of wavefronts. Slow-wave dysrhythmias could occur either simultaneously or independently on the anterior and posterior gastric serosa, and interacted depending on activation-repolarization and frequency dynamics. High-resolution mapping enables mechanistic insights into gastric slow-wave dysrhythmias and is now achieving clinical translation. However, previous studies have focused mainly on dysrhythmias occurring on the anterior gastric wall. The present study simultaneously mapped the anterior and posterior gastric serosa during episodes of dysrhythmias induced by vasopressin to aid understanding of dysrhythmia initiation, maintenance and termination. High-resolution mapping (8 × 16 electrodes on each serosa; 20-74 cm2 ) was performed in anaesthetized dogs. Baseline recordings (21 ± 8 min) were followed by intravenous infusion of vasopressin (0.1-0.5 IU ml-1 at 60-190 ml h-1 ) and further recordings (22 ± 13 min). Slow-wave activation maps, amplitudes, velocity, interval and frequency were calculated, and differences compared between baseline and postinfusion. All dogs demonstrated an increased prevalence of dysrhythmic events following infusion of vasopressin (17 versus 51%). Both amplitude and velocity demonstrated significant differences (baseline versus postinfusion: 3.6 versus 2.2 mV; 7.7 versus 6.5 mm s-1 ; P < 0.05 for both). Dysrhythmias occurred simultaneously or independently on the anterior and posterior serosa, and then interacted according to frequency dynamics. A number of persistent dysrhythmias were compared, including the following: ectopic activation (n = 2 animals), conduction block (n = 1), rotor (n = 2), retrograde (n = 3) and collision/merger of wavefronts (n = 2). We conclude that infusion of vasopressin induces gastric dysrhythmias, which occur across a heterogeneous range of frequencies and patterns. The results demonstrate that different classes of gastric dysrhythmias may arise simultaneously or independently in one or both surfaces of the serosa, then interact according to their relative frequencies. These results will help to inform interpretation of clinical dysrhythmia.

Impact of electrical stimulation of the stomach on gastric distension-induced emesis in the musk shrew

BACKGROUND

Gastric electrical stimulation (GES) is implicated as a potential therapy for difficult-to-treat nausea and vomiting; however, there is a lack of insight into the mechanisms responsible for these effects. This study tested the relationship between acute GES and emesis in musk shrews, an established emetic model system.

METHODS

Urethane-anesthetized shrews were used to record emetic responses (monitoring intra-tracheal pressure and esophageal contractions), respiration rate, heart rate variability, blood pressure, and gastrointestinal electromyograms. We investigated the effects of acute GES pulse duration (0.3, 1, 5, and 10 ms), current amplitude (0.5, 1, and 2 mA), pulse frequency (8, 15, 30, and 60 Hz), and electrode placement (antrum, body, and fundus) on emesis induced by gastric stretch, using a balloon.

KEY RESULTS

There were four outcomes: (i) GES did not modify the effects of gastric stretch-induced emesis; (ii) GES produced emesis, depending on the stimulation parameters, but was less effective than gastric stretch; (iii) other physiological changes were closely associated with emesis and could be related to a sub-threshold activation of the emetic system, including suppression of breathing and rise in blood pressure; and (iv) a control experiment showed that 8-OH-DPAT, a reported 5-HT1A receptor agonist that acts centrally as an antiemetic, blocked gastric stretch-induced emesis.

CONCLUSIONS AND INFERENCES

These results do not support an antiemetic effect of acute GES on gastric distension-induced emesis within the range of conditions tested, but further evaluation should focus on a broader range of emetic stimuli and GES stimulation parameters.

Long-pulse gastric electrical stimulation protects interstitial cells of Cajal in diabetic rats via IGF-1 signaling pathway

AIM: To investigate the effects of different parameters of gastric electrical stimulation (GES) on interstitial cells of Cajal (ICCs) and changes in the insulin-like growth factor 1 (IGF-1) signal pathway in streptozotocin-induced diabetic rats.

METHODS: Male rats were randomized into control, diabetic (DM), diabetic with sham GES (DM + SGES), diabetic with GES1 (5.5 cpm, 100 ms, 4 mA) (DM + GES1), diabetic with GES2 (5.5 cpm, 300 ms, 4 mA) (DM + GES2) and diabetic with GES3 (5.5 cpm, 550 ms, 2 mA) (DM + GES3) groups. The expression levels of c-kit, M-SCF and IGF-1 receptors were evaluated in the gastric antrum using Western blot analysis. The distribution of ICCs was observed using immunolabeling for c-kit, while smooth muscle cells and IGF-1 receptors were identified using α-SMA and IGF-1R antibodies. Serum level of IGF-1 was tested using enzyme-linked immunosorbent assay.

RESULTS: Gastric emptying was delayed in the DM group but improved in all GES groups, especially in the GES2 group. The expression levels of c-kit, M-SCF and IGF-1R were decreased in the DM group but increased in all GES groups. More ICCs (c-kit⁺) and smooth muscle cells (α-SMA⁺/IGF-1R⁺) were observed in all GES groups than in the DM group. The average level of IGF-1 in the DM group was markedly decreased, but it was up-regulated in all GES groups, especially in the GES2 group.

CONCLUSION: The results suggest that long-pulse GES promotes the regeneration of ICCs. The IGF-1 signaling pathway might be involved in the mechanism underlying this process, which results in improved gastric emptying.

Acupuncture-based modalities: novel alternative approaches in the treatment of gastrointestinal dysmotility in patients with systemic sclerosis

BACKGROUND

The gastrointestinal (GI) dysmotility of systemic sclerosis (SSc, scleroderma) patients requires careful evaluation and intervention. The lack of effective prokinetic drugs motivate researchers to search for alternative treatments.

OBJECTIVES

We present an overview of the pathophysiology of SSc GI dysmotility and the advances in its management, with particular focus on acupuncture-related modalities and innovative therapies.

DATA SOURCES

Original research articles were identified based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline methodology. We have searched the MEDLINE database using Medical Subject Heading (MeSH) for all English and non-English articles with an English abstract from 2005 to October 2012.

RESULTS

Only four original articles of various study designs were found studying Complementary and Alternative Medicine (CAM) therapies for SSc patients. Despite the small patient study numbers, CAM treatments, acupressure, and transcutaneous electroacupuncture, showed self-reported and physiologic evidence of improvement of GI functioning and/or symptoms in SSc patients.

CONCLUSIONS

CAM therapies include experimental modalities with the potential to offer relief of symptoms from GI dysmotility. Larger studies are needed to investigate their optimal use in patient subsets to tailor therapies to patient needs.

Pacing the gut in motility disorders

Similar to cardiac pacing, gastrointestinal (GI) pacing is an attractive idea and may become a promising therapy, as the GI organs, like the heart, have their own natural pacemakers. Over the past 10 years, electrical stimulation of the gut has received increasing attention among researchers and clinicians. Several clinical studies have shown that gastric electrical stimulation (GES) with short pulses is able to reduce nausea and vomiting in patients with gastroparesis and that GES with long pulses is able to pace the intrinsic gastric slow waves and thus normalize gastric dysrhythmia. However, possible placebo effects cannot be ruled out, although recent animal studies have revealed various peripheral and central mechanisms involved with GES. Electrical stimulation of the small intestine, colon, or anal sphincter also has been reported for the treatment of dumping syndrome, constipation, and fecal incontinency. Similarly, there is a lack of placebo-controlled studies. In our opinion, pacing of the gut has great potential for the treatment of various GI motor disorders. However, none of the commercially available devices is designed for pacing the gut. The lack of well-suited devices and the invasive nature of gut pacing slow down the progress and clinical applications of gut pacing.

Short pulse gastric electrical stimulation for cisplatin-induced emesis in dogs

BACKGROUND

In a previous study, we investigated the ameliorating effect of gastric electrical stimulation (GES) with a single set of parameters on emesis and behaviors suggestive of nausea induced by cisplatin in dogs. The aim of this study was to investigate the effects of GES with different parameters on cisplatin-induced emesis in dogs.

METHODS

Seven dogs implanted with gastric serosal electrodes were studied in six randomized sessions: one control session with cisplatin (2 mg kg(-1)) and five sessions with cisplatin plus GES of different parameters: GES-A: 14 Hz, 5 mA, 0.3 ms, 0.1 s on and 5 s off; GES-B: increased frequency and on-time; GES-C: increased frequency; GES-D: increased frequency and pulse width; and GES-E: increased frequency and amplitude. Gastric slow waves and emetic responses were recorded in each session.

KEY RESULTS

(i) Cisplatin induced emetic responses and gastric dysrhythmia. The peak time of the emetic response was during the fourth hour after cisplatin. (ii) GES with appropriate parameters reduced cisplatin-induced emesis. The number of vomiting times during the 6 h after cisplatin was 7.0 ± 1.4 in the control, 4.7 ± 1.2 with GES-A (P = 0.179), 4.2 ± 1.2 with GES-B (P = 0.109), 7.0 ± 0.8 with GES-C (P = 0.928), 2.1 ± 0.3 with GES-D (P = 0.005) and 4.7 ± 1.5 with GES-E (P = 0.129). However, none of the GES parameters could improve gastric dysrhythmia.

CONCLUSIONS & INFERENCES

Gastric electrical stimulation with appropriate parameters reduces cisplatin-induced emetic responses and behaviors suggestive of nausea in dogs. Among the tested parameters, GES with increased pulse width seems to produce better relief of cisplatin-induced emesis.

Nitric oxide in enteric nervous system mediated the inhibitory effect of vasopressin on the contraction of circular muscle strips from colon in male rats

BACKGROUND

Arginine vasopressin (AVP) is widely used in the treatment of critical diseases with hypotension, but the reports about its effect on gastrointestinal motility are controversial. The purpose of this study was to characterize the role of AVP in the regulation of colonic motility and the underlying mechanism.

METHODS

The contraction of the circular muscle strips (CM) of colon in male rats was monitored by a polygraph. The expressions of cytoplasmic inducible nitric oxide synthase (iNOS), I-κB, and the nuclear P65 in proximal colon were measured by Western blot. The V(1) receptors (V(1) Rs) and iNOS were localized by immunohistochemistry. The content of nitric oxide (NO) in the colon was measured by Griess reagent at the absorbance of 560 nm.

KEY RESULTS

Arginine vasopressin (10(-10) -10(-6) mol L(-1)) caused a concentration-dependent inhibition on CM contraction. Pretreatment with one of the following chemicals, including V-1880 (10(-7) mol L(-1)), TTX (10(-5) mol L(-1)), L-NAME (10(-4) mol L(-1)), NPLA (10(-7) mol L(-1)), SMT (10(-3) mol L(-1)), and PDTC (10(-3) mol L(-1)), attenuated the inhibitory effect of AVP on CM contraction. Arginine vasopressin increased the expression of iNOS and the content of NO in proximal colon. These effects were attenuated by pretreatment with PDTC (10(-3) mol L(-1)). Following AVP administration, the amount of cytoplasmic I-κB decreased, but that of nuclear P65 increased. Double immunofluorescence labeling revealed that V(1) Rs and iNOS were co-localized on the cells of myenteric plexus in proximal colon.

CONCLUSIONS & INFERENCES

Arginine vasopressin inhibited the contraction of CM in proximal colon. This effect was mediated by NO produced from NF-κB-iNOS pathway and neuronal NOS activation in myenteric plexus.

Gastric electrical stimulation reduces visceral sensitivity to gastric distention in healthy canines

The aim of this study was to investigate the effects and mechanisms of gastric electrical stimulation (GES) on proximal stomach distention-induced visceral sensitivity. Isobaric gastric distention was performed using a barostat system in 8 normal and 6 vagotomized dogs and animal behaviors were noted and graded. The normal dogs were studied in 4 sessions: control (no GES), short pulse GES, long pulse GES, and dual-pulse GES, and the vagotomized dogs were studied in three sessions: control (no GES), long pulse GES and guanethidine. It was found that: 1) proximal stomach distention-induced behavioral changes were mediated by vagal and sympathetic pathways. The total behavior score (TBS) was 40.6 ± 7.4 in the controls, 15.3 ± 8.9 in vagotomized dogs (P=0.006 vs. control) and 8.8 ± 0.9 in the vagotomized dogs with guanethidine (P=0.04 vs. vagotomy). The behavioral changes were mediated via the vagal pathway at distention pressures below 20 mmHg, but mediated via both the vagal and sympathetic pathways at distention pressures equal to and above 20 mmHg. 2) GES with long pulses or dual pulses but not short pulses reduced the distention-induced behavioral score (P=0.003, P=0.006 and P=0.7, respectively) and the effects of GES of long pulses might be mediated via the vagal and sympathetic pathways. In conclusion, gastric distention-induced visceral sensitivity is mediated via the vagal pathway at low distention pressures but via both vagal and sympathetic pathways at high distention pressures. GES with long but not short pulses reduces distention-induced visceral sensitivity.

Effects and mechanisms of electrical stimulation of the stomach, duodenum, ileum, and colon on gastric tone in dogs

Previous studies have shown that gastric tone is inhibited by the electrical stimulation of some parts of the gut. The aims of this study were to investigate the effects of gastric electrical stimulation (GES), duodenal electrical stimulation (DES), ileal electrical stimulation (IES), and colonic electrical stimulation (CES) on gastric tone and the possible mechanism of electrical stimulation on gastric tone. Experiments were performed to study: (1) the effects of the four stimulations (GES, DES, IES, CES) on gastric tone; (2) the role of the nitrergic pathway's involvement in the effect of IES on gastric tone. Each dog was implanted with one pair of gastric, duodenal, ileal, and colonic electrodes and a gastric cannula. A computerized barostat was used to assess gastric tone by measuring the gastric intra-balloon volume. We found that: (1) all methods of stimulation significantly inhibited gastric tone; (2) the percentage of increase in gastric volume was highest with CES and lowest with DES; however, there was no significant difference in the percentage of inhibition among the four stimulations; (3) the inhibitory effect of IES on gastric tone was abolished by intravenous nitric oxide synthase inhibitor. It was concluded that electrical stimulation of the stomach, intestine, or colon with long pulses has an inhibitory effect on gastric tone, and the most effective stimulation is CES. The inhibitory effect is not organ-specific and is unrelated to the distance between the stimulation site and the affected organ. The inhibitory effect of IES on gastric tone is mediated by the nitrergic pathway.

Long pulse gastric electrical stimulation induces regeneration of myenteric plexus synaptic vesicles in diabetic rats

BACKGROUND

Gastric electrical stimulation (GES) may improve delayed gastric emptying in diabetic gastroparesis, but whether enteric nervous system (ENS) is directly involved in its mechanism of improvement in gastric motility is unclear. The aims were to investigate the correlation between the changes in ENS and effects of long pulse GES on them in diabetic rats induced by streptozotocin (STZ).

METHODS

Electron microscopy, immunohistochemistry, RT-PCR and western blot were used to evaluate changes of myenteric plexus neurons and synaptic vesicles in different stages of the diabetic rats. The effects of GES were detected by same methods after pacing wires were implanted and then diabetes was induced and followed by long pulse GES.

KEY RESULTS

Since 6 weeks after STZ injection, the nerve fibres were incompact and synaptic vesicles in myenteric neurons reduced. Furthermore, the myenteric neurons showed severe damage such as partial depletion of the axon, swelling of mitochondria and seriously decreased synaptic vesicles in 12 weeks after STZ injection. The synaptophysin and PGP9.5-positive area and expressions of synaptophysin mRNA and protein decreased with the duration of diabetes. Long pulse GES could induce increase of myenteric neuronal synaptic vesicles, synaptophysin and PGP9.5-positive area and in myenteric plexus. The synaptophysin mRNA and protein expression rose after GES, whatever GES beginning early or late, short-term or long-term.

CONCLUSIONS & INFERENCES

The longer duration of diabetes, the more significant damages to myenteric neurons and synaptic vesicles of diabetic rats; long pulse GES could induce regeneration of myenteric plexus synaptic vesicles, thereby reform gastric motility.

Reduced normogastric electrical activity associated with emesis: A telemetric study in ferrets

AIM: To characterize the gastric myoelectric activity (GMA) and intra-abdominal pressure changes induced by emetic stimuli (apomorphine and cisplatin) in the ferret.

METHODS: GMA and intra-abdominal pressure were recorded in conscious, unrestrained ferrets surgically implanted with radiotelemetry transmitters. Animals were challenged with apomorphine (0.25 mg/kg sc) and cisplatin (10 mg/kg ip), and the emetic response was quantified via direct observation and intra-abdominal pressure recording for 1 and 4 h, respectively. The GMA was analyzed by spectral analysis; the parameters used to characterize the GMA were the dominant frequency (DF) and the repartition of spectral power in the bradygastric, normogastric and tachygastric frequency ranges.

RESULTS: Retches were identified on the intra-abdominal pressure trace as peaks 0.30 ± 1.01 s in duration and 59.57 ± 2.74 mmHg in amplitude, vomit peaks were longer (0.82 ± 0.06 s, P < 0.01) and reached a higher pressure (87.73 ± 8.12 mmHg, P < 0.001). The number of retches and vomits quantified via direct observation [apomorphine: 65.5 ± 11.8 retches + vomits (R+V), cisplatin: 202.6 ± 64.1 R+V] and intra-abdominal pressure (apomorphine: 68.3 ± 13.7 R+V, n = 8; cisplatin: 219.0 ± 69.2 R+V, n = 8) were correlated (r = 0.97, P < 0.0001) and the timing of emesis was consistent between the 2 methods. Apomorphine induced a decrease in normogastria from 45.48% ± 4.35% to 36.70 ± 4.34% (n = 8, P < 0.05) but the DF of the slow waves was not changed [8.95 ± 0.25 counts/min (cpm) vs 8.68 ± 0.35 cpm, n = 8, P > 0.05]. Cisplatin induced a decrease in normogastria from 55.83% ± 4.30% to 29.22% ± 5.16% and an increase in bradygastria from 14.28% ± 2.32% to 31.19% ± 8.33% (n = 8, P < 0.001) but the DF (9.14 ± 0.13 cpm) remained unchanged (P > 0.05). The GMA changes induced by cisplatin preceded the emetic response as normogastria was reduced for 1 h before the onset of emesis (57.61% ± 5.66% to 39.91% ± 5.74%, n = 6, P < 0.05). Peri-emesis analysis revealed that the GMA was significantly disturbed during and immediately after, but not immediately before, the emetic episodes.

CONCLUSION: The induction of emesis is reliably associated with a disrupted GMA, but changes may also occur prior to and following the emetic response.

Effects of dual pulse gastric electrical stimulation on gastric tone and compliance in dogs

BACKGROUND

Gastric electrical stimulation (GES) with short pulses improves nausea and vomiting in patients with gastroparesis, whereas GES with long pulses improves gastric motility.

AIMS

To assess the effects of a novel method of GES using dual pulse (both short and long pulses) on gastric tone, compliance and sympathovagal activity in dogs.

MATERIALS AND METHODS

The study was performed in 7 dogs implanted with a gastric cannula and a pair of gastric serosal electrodes for dual pulse GES. The study was composed of a number of sessions on different days with different stimulation parameters, including variations in the number of short pulses and stimulation amplitude.

RESULTS

(1) Dual pulse GES of one short pulse and one long pulse with various amplitudes inhibited gastric tone (p<0.05) but did not alter sympathetic or vagal activity. (2) Dual pulse GES with five short pulses and one long pulse not only inhibited gastric tone, but also reduced sympathetic activity and increased vagal activity (p<0.05). (3) Dual pulse GES with five short pulses and one long pulse significantly increased gastric compliance.

CONCLUSIONS

Dual pulse GES reduces gastric tone and increases gastric compliance. The variation in the number of short pulse affects the sympathetic and vagal activities, whereas, the increase in stimulation strength enhances its effects on gastric tone.

Feasibility of gastric electrical stimulation by percutaneous endoscopic transgastric electrodes

BACKGROUND

Gastric electrical stimulation has been used for the treatment of drug refractory GI motility disorders and for the treatment of obesity. Both these indications have involved surgical placement of gastric electrodes, which adds to the complexity and cost of the procedure. Endoscopic placement is therefore an attractive alternative approach for this therapy.

OBJECTIVE

Our purpose was to investigate the feasibility, safety, and efficacy of percutaneous endoscopic electrodes for gastric electrical stimulation.

DESIGN AND SETTING

Experimental animal study in hound dogs.

INTERVENTIONS

Percutaneous endoscopic transgastric electrode (PETE) placement was carried out by using a pair of gastric pacing wires attached to a percutaneous endoscopic gastrostomy tube. In addition, 4 pairs of gastric serosal electrodes were implanted surgically for comparison. The efficacy of the percutaneous endoscopic electrodes was defined by their ability to entrain gastric slow waves and the induction of dysrhythmia.

RESULTS

(1) The PETE recorded gastric slow waves comparable to the serosal electrodes. (2) Gastric electrical stimulation with long pulses delivered by the PETE, at a frequency of 10% higher than the intrinsic gastric slow wave frequency, entrained gastric slow waves. (3) Gastric electrical stimulation delivered by the PETE, at a tachygastric frequency, induced gastric dysrhythmia.

LIMITATIONS

This was an animal study; however, its results are expected to be reproducible in humans, with PETE kept in place for even a longer duration than 6 to 8 weeks.

CONCLUSION

PETE placement is both feasible and safe. PETEs are effective, having a potential for use in treatment of both gastroparesis and obesity.

Inhibitory effects of gastrointestinal electrical stimulation on rectal tone are both organ-specific and distance-related in dogs

PURPOSE

A phenomenon of cross-talk has been noted that electrical stimulation of one part of the gut affects another part of the gut. This study was designed to investigate whether the effect of electrical stimulation of one part of the gut on another part of the gut was related to the organ or the distance between the stimulation site and the affected organ, and the mechanism of ileum electrical stimulation on rectal tone.

METHODS

This study was performed in 13 healthy dogs (16-28 kg) in the fasting state. Experiments were performed to study 1) effects of gastric electrical stimulation, duodenal electrical stimulation, ileum electrical stimulation, and colonic electrical stimulation on rectal tone, and 2) the sympathetic and nitrergic pathways involved in the effects of ileum electrical stimulation on rectal tone. A computerized barostat was used to assess rectal tone.

RESULTS

All methods of stimulations significantly inhibited rectal tone. Duodenal electrical stimulation was least effective in reducing rectal tone. The percentage of increase in rectal volume was distance-related with duodenal electrical stimulation, ileum electrical stimulation, and colonic electrical stimulation but organ-specific with gastric electrical stimulation. The inhibitory effect of ileum electrical stimulation on rectal tone was abolished by N omega-nitro-L-arginine but not guanethidine.

CONCLUSIONS

Electrical stimulation of the stomach, intestine, or colon with long pulses has an inhibitory effect on rectal tone. This inhibitory effect is organ-specific as well as associated with the distance between stimulation site and affected organs. The inhibitory effect of ileum electrical stimulation on rectal tone is mediated by the nitrergic but not sympathetic pathway.

Effects of gastric electrical stimulation with short pulses and long pulses on gastric dysrhythmia and signs induced by vasopressin in dogs

AIMS

This study was to investigate the effect of gastric electrical stimulation (GES) with short pulses, long pulses, short-pulse trains or long-pulse trains on gastric dysrhythmia and motion-sickness signs induced by vasopressin.

METHODS

Seven male beagle dogs implanted with four pairs of electrodes on gastric serosa were studied. The study was performed in six sessions in a randomized order. In session 1 or 2, either saline or vasopressin was infused without GES. In session 3, 4, 5 and 6, GES with short pulses, long pulses, trains of short pulses or trains of long pulses was performed before and during vasopressin infusion. Gastric slow waves and motion-sickness signs were recorded in each session.

RESULTS

(1) Vasopressin induced gastric dysrhythmia and motion sickness-like signs (ANOVA, P < 0.001). (2) GES with short pulses or trains of short pulses was capable of preventing vasopressin-induced emetic response (P < 0.001), but did not normalize gastric dysrhythmia. (3) GES with long pulses or trains of long pulses was able to normalize gastric dysrhythmia induced by vasopressin (P < 0.001), but showed no effects on vasopressin-induced motion-sickness signs.

CONCLUSION

GES with short pulses or trains of short pulses prevents vasopressin-induced emetic response with no improvement in gastric dysrhythmia. GES with long pulses or trains of long pulses normalizes gastric dysrhythmia induced by vasopressin with no effects on signs.

Two-channel gastric pacing with a novel implantable gastric pacemaker accelerates glucagon-induced delayed gastric emptying in dogs

BACKGROUND

The aim of the current study was to investigate the efficacy of 2-channel gastric electrical stimulation (GES) with a custom-made implantable pacemaker on delayed gastric emptying and gastric dysrhythmia induced by glucagon in dogs.

METHODS

Six dogs were studied in 4 randomized session (saline, glucagon, glucagon with single-channel or 2-channel GES). GES was applied via the first pair of electrodes for single-channel GES or the first and third pairs of electrodes for 2-channel GES. Gastric emptying was assessed for 90 minutes and gastric slow waves were recorded at the same time.

RESULTS

Both single-channel and 2-channel GES improved gastric dysrhythmia (P < .05 vs glucagon session). Two-channel GES but not single-channel GES improved glucagon-induced delayed gastric emptying at 30 minutes, 45 minutes, 60 minutes, 75 minutes, and 90 minutes.

CONCLUSION

Two-channel GES with a novel implantable pacemaker is more efficient and effective than single-channel GES in improving delayed gastric emptying induced by glucagon. This implantable multipoint pacemaker may provide a new option for treatment of gastric motility disorders.

A novel method of 2-channel dual-pulse gastric electrical stimulation improves solid gastric emptying in dogs

BACKGROUND

Gastric electrical stimulation (GES) is known to improve vomiting with short pulses, normalize dysrhythmia with long pulses, and accelerate gastric emptying with 2 channels. The aim of this study was to assess the effects of a new method GES, namely, 2-channel GES with dual pulses on gastric emptying of solids as well as gastric dysrhythmia and emetic responses.

METHODS

Seven beagle dogs implanted with 4 pairs of electrodes were studied. A novel method of GES was proposed: 2-channel dual-pulse GES in which each stimulus was composed of a short pulse followed with a long pulse, and stimulation was delivered at 2 different locations. The study was performed to test the effects of this new method of GES on vasopressin-induced delayed gastric emptying of solids, gastric dysrhythmia, and emetic responses.

RESULTS

(1) Vasopressin-induced gastric dysrhythmia and emetic responses, as well as delayed gastric emptying of solids (P < .01). (2) Two-channel, but not 1-channel, dual-pulse GES was able to accelerate vasopressin-induced delayed gastric emptying of solids. (3) Both 1- and 2-channel dual-pulse GES was capable of improving dysrhythmia and emetic responses (P < .01).

CONCLUSIONS

The novel method of 2-channel dual-pulse GES is capable of accelerating gastric emptying of solids and improving dysrhythmia and emetic responses induced by vasopressin. This new method of GES may have a potential for gastroparesis.

Feasibility of gastric electrical stimulation by use of endoscopically placed electrodes

BACKGROUND

Gastric electrical stimulation (GES), which has been reported to have therapeutic potentials for gastroparesis and obesity, involves the surgical placement of electrodes with the patient under general anesthesia. New methods are needed for implanting GES electrodes in a safer and more feasible way.

OBJECTIVE

Our purpose was to investigate the safety and feasibility of placing electrodes endoscopically for GES.

DESIGN AND SETTING

A pilot study.

SUBJECTS

Six female hound dogs that weighed 13 to 22 kg.

INTERVENTIONS

Endoscopically placed electrodes passed through the abdomen and the stomach wall.

MAIN OUTCOME MEASUREMENTS

The study was performed in dogs surgically implanted with gastric serosal electrodes and endoscopically implanted electrodes. The experiment consisted of a 30-minute baseline, a 30-minute GES, and a 30-minute recovery. GES was performed through endoscopically placed electrodes. Gastric slow waves were simultaneously recorded with the serosal electrodes and the endoscopically placed electrodes.

RESULTS

(1) The slow wave frequency recorded from the endoscopically placed electrodes was significantly correlated with that from the serosal electrodes (r = 0.97, P < .002). (2) GES through the endoscopically placed electrodes was able to entrain gastric slow waves. (3) No gastric leakage into the abdominal cavity was noted and the dogs were healthy and comfortable. (4) The endoscopically placed electrodes remained for 2 to 3 weeks.

LIMITATIONS

The fixation of the electrodes needs to be improved for longer-term uses.

CONCLUSIONS

GES may be accomplished without surgery by inserting the electrode wire through the abdomen under endoscopy. The study results indicate that the endoscopically placed electrodes are effective for GES and do not result in any adverse events.

Effects of gastric electrical stimulation on hippocampus gastric distension responsive neurons and the expression of motilin and neuronal nitric oxide synthase in rats

AIM: To explore the effects of gastric electrical stimulation (GES) on gastric distension (GD) responsive neurons in rat hippocampus, and study the expression of neuronal nitric oxide synthase (nNOS) and motilin (MTL) in rat brain for exploring the central mechanism of GES.

METHODS: Fifty adult Wistar rats were used in this experiment. The effects of GES on GD responsive neurons in hippocampus CA1 area were observed by recording extracellular potentials of single neuron. GD responsive neurons were classified as GD-excitatory (GD-E) and GD-inhibitory (GD-I) neurons according to their responses to GD. GES with 3 sets of parameters were applied for 1 minute respectively: GES-A (6 mA, 0.3 ms, 40 Hz, 2 s-on, 3 s-off) with standard pulse trains; GES-B with increased wave width to 3 ms and GES-C with decreased frequency to 20 Hz. Two hours after GES-A was applied, we observed the expression of nNOS immunoreactive positive neurons in hippocampus by fluorescent immunohistochemistry and the content of motilin in rat brain by radioimmunoassay.

RESULTS: Eighty-seven neurons in hippocampus CA1 area were recorded and 79 responded to gastric distension (GD, 3-5 mL, 10-30 s). Of the 79 GD responsive neurons, 40 (50.6%) were GD-E neurons and 39 (49.4%) were GD-I ones. 62.5%, 100% and 62.3% of GD-E neurons were excited by GES-A, -B, and -C respectively. GES-B excited more GD-E neurons than GES-C (P = 0.016). Among the GD-I neurons, 63.6%, 85.7% and 50.0% neurons were excited by GES-A, -B and -C respectively. GES-C was noted to be less effective comparing with GES-A (P = 0.041) or GES-B (P = 0.021). Two hours after GES-A was used, the expressions of nNOS positive neurons significantly decreased in the CA1 and CA2-3 area of hippocampus (16.75 ± 0.91 cells/mm²vs 20.46 ± 1.30 cells/mm², P < 0.05; 14.91 ± 1.17 cells/mm²vs 18.73 ± 1.10 cells/mm², P < 0.05) and the content of motilin peptide decreased obviously in the hypothalamus (48.93 ± 6.98 fmol/mg vs 96.23 ± 12.93 fmol/mg, P < 0.01), mesencephalon (53.17 ± 8.96 fmol/mg vs 30.96 ± 4.86 fmol/mg, P < 0.05), medulla oblongata (46.27 ± 7.83 fmol/mg vs 73.86 ± 9.37 fmol/mg, P < 0.05) and hippocampus (32.23 ± 6.51 fmol/mg vs 62.72 ± 10.07 fmol/mg, P < 0.05) by radioimmunoassay.

CONCLUSION: GES may activate the gastric distension responsive neurons in hippocampus CA1 area and the excitatory effect of GES is related to the frequency and wave width of stimulation. Decreased expression of nNOS and motilin in the brain may also take part in the central mechanism of GES.

Dual pulse intestinal electrical stimulation normalizes intestinal dysrhythmia and improves symptoms induced by vasopressin in fed state in dogs

To assess effects of dual pulse intestinal electrical stimulation (DPIES) on intestinal dysrhythmia and motility, and symptoms induced by vasopressin in conscious dogs. The study was performed in three postprandial sessions (control; vasopressin; DPIES) in six dogs with two pairs of electrodes chronically implanted on the serosal surface of the proximal jejunum and with a chronic duodenal fistula. A manometric catheter was advanced into the small intestine via the intestinal cannula. Motility and intestinal slow waves were recorded. Symptoms were assessed. During vasopressin infusion, the percentage of normal intestinal slow wave frequency was decreased (P < 0.01), reflected as a significant increase in the percentage of both bradygastria and tachygastria; the motility index decreased (P < 0.01) and the symptom score increased (P < 0.01). In the session of DPIES, the percentage of normal slow wave frequency was recovered (P < 0.05 vs vasopressin), attributed to a reduction in both bradyarrhythmia and tachyarrhythmia; the symptom score was reduced (P < 0.05 vs vasopressin); the motility index was not significantly increased. These results suggest that vasopressin induces intestinal dysrhythmia and emetic symptoms and inhibits intestinal motility. Dual pulse intestinal electrical stimulation is capable of improving intestinal dysrhythmia and emetic symptoms but not impaired intestinal motility induced by vasopressin.

Systematic review: applications and future of gastric electrical stimulation

BACKGROUND

Over the past 20 years, gastric electrical stimulation has received increasing attention among researchers and clinicians.

AIM

To give a systematic review on the effects, mechanisms and applications of gastric electrical stimulation.

METHODS

Medline was used to identify the articles to be included in this review. Key words used for the search included gastric electrical stimulation, gastric pacing, electrical stimulation, stomach, gastrointestinal motility, central nervous system, gastroparesis, nausea and vomiting; obesity and weight loss. Combinational uses of these keywords were made to identify relevant articles. Most of the articles included in this review ranged from 1985 to 2006.

RESULTS

Based on the general search, the review was structured as follows: (i) peripheral and central effects and mechanisms of gastric electrical stimulation; (ii) clinical applications of gastric electrical stimulation for gastroparesis and obesity and (iii) future development of gastric electrical stimulation.

CONCLUSIONS

Great progress has been made during the past decades. Gastric electrical stimulation has been shown to be effective in normalizing gastric dysrhythmia, accelerating gastric emptying and improving nausea and vomiting. Implantable device has been made available for treating gastroparesis as well as obesity. However, development of a new device and controlled clinical studies are required to further prove clinical efficacy of gastric electrical stimulation.

Signals for nausea and emesis: Implications for models of upper gastrointestinal diseases

Nausea and vomiting are amongst the most common symptoms encountered in medicine as either symptoms of diseases or side effects of treatments. In a more biological setting they are also important components of an organism's defences against ingested toxins. Identification of treatments for nausea and vomiting and reduction of emetic liability of new therapies has largely relied on the use of animal models, and although such models have proven invaluable in identification of the anti-emetic effects of both 5-hydroxytryptamine(3) and neurokinin(1) receptor antagonists selection of appropriate models is still a matter of debate. The present paper focuses on a number of controversial issues and gaps in our knowledge in the study of the physiology of nausea and vomiting including: The choice of species for the study of emesis and the underlying behavioural (e.g. neophobia), anatomical (e.g. elongated, narrow abdominal oesophagus with reduced ability to shorten) and physiological (e.g. brainstem circuitry) mechanisms that explain the lack of a vomiting reflex in certain species (e.g. rats); The choice of response to measure (emesis[retching and vomiting], conditioned flavour avoidance or aversion, ingestion of clay[pica], plasma hormone levels[e.g. vasopressin], gastric dysrhythmias) and the relationship of these responses to those observed in humans and especially to the sensation of nausea; The stimulus coding of nausea and emesis by abdominal visceral afferents and especially the vagus-how do the afferents encode information for normal postprandial sensations, nausea and finally vomiting?; Understanding the central processing of signals for nausea and vomiting is particularly problematic in the light of observations that vomiting is more readily amenable to pharmacological treatment than is nausea, despite the assumption that nausea represents "low" intensity activation of pathways that can evoke vomiting when stimulated more intensely.

Therapeutic potentials of a novel method of dual-pulse gastric electrical stimulation for gastric dysrhythmia and symptoms of nausea and vomiting

BACKGROUND

The aims of this study were to investigate the effects and mechanisms of a novel method of gastric electrical stimulation on the prevention of vasopressin-induced emetic response and gastric dysrhythmias.

METHODS

Fifteen dogs (10 normal, 5 vagotomized) chronically implanted with gastric serosal electrodes were used in a 3-session study (vasopressin, vasopressin plus 2-channel stimulation [DCS], and vasopressin plus dual-pulse stimulation [DPS]).

RESULTS

Vasopressin induced gastric dysrhythmias and motion sickness-like symptoms (P < .05) and these effects were blocked partially with vagotomy. Both methods of DCS and DPS were capable of preventing vasopressin-induced gastric dysrhythmias (P < .05) and motion sickness-like symptoms (P < .05). The antiemetic effects of the proposed methods of DCS and DPS were abolished by vagotomy but their antidysrhythmic effects were not blocked by vagotomy.

CONCLUSIONS

DCS and DPS are able to reduce vasopressin-induced gastric dysrhythmia and symptoms of nausea and vomiting. The vagal pathway is involved in the antiemetic effect but not the antidysrhythmic effect of the proposed methods of stimulation.

Effects of gastric electrical stimulation on responsive neurons to gastric distension and expression of orexin in rats

AIM: To investigate the effects of gastric electri-cal stimulation (GES) on responsive neurons to gastric distension (GD) in ventromedia hypotha-lamus (VMH) and the expression of orexin in rat brain.

METHODS: Fifty-two adult Wistar rats were used in this experiment. The effects of GES on GD responsive neurons in VMH were observed by recording extracellular potentials of single neuron. GD responsive neurons were classified as GD-excitatory (GD-E) and GD-inhibitory (GD-I) ones according to their responses to GD. GES with three sets of parameters were applied for one minute respectively: GES1 (6 mA, 0.3 ms, 40 Hz, 2 s-on, 3 s-off) with standard pulse trains; GES2 with reduced on-time to 0.1 s and GES3 with decreased frequency to 20 Hz. After GES1 was using for 2 h, we observed the expression of orexin-A immunoreactive (orexin-A-IR) positive neurons in lateral hypothalamus area (LHA) by fluorescent immunohistochemistry and the content of orexin in rat brain by radioimmunoassay.

RESULTS: Ninety neurons in VMH were recorded, of which 82 (85.41%) responded to GD (3-5 mL, 10-30 s). Of the 82 GD responsive neurons, 31 (37.8%) were GD-E neurons and 51 (62.2%) were GD-I neurons. 55.0%, 17.6%, and 14.3% of GD-E neurons were excited by GES1, GES2, and GES3 respectively. More GD-E neurons were excited by GES1 than by GES2 and GES3 (P = 0.002 and 0.016, respectively). Of the GD-I neurons, 63.6%, 37.9%, and 51.9% neurons were excited by GES1, GES2, and GES3, respectively. GES2 was noted to be less effective in comparison with GES1 (P = 0.043). After GES1 was in application for 2 h, the levels of orexin-A-IR positive neurons were significantly decreased in LHA as comopared with those in control group (6.97 ± 1.51/0.1 mm2 vs 26.62 ± 8.30/0.1 mm2, P < 0.01), and the content of orexin peptide was decreased obviously in the hypothalamus (112.54 ± 11.58 fmol/mg vs 185.23 ± 15.22 fmol/mg, P < 0.01), mesencephalon (71.95 ± 8.45 fmol/mg vs 98.48 ± 12.02 fmol/mg, P < 0.05), medulla oblongata (72.36 ± 6.58 fmol/mg vs 101.29 ± 15.22 fmol/mg, P < 0.05), solitary tract nucleus (69.12 ± 4.99 fmol/mg vs 89.21 ± 9.23 fmol/mg, P < 0.05) by radioimmunoassay. However, the content of orexin peptide had no significant change in pons.

CONCLUSION: GES may activate the GD responsive neurons in VMH and the excitatory effect of GES is related to the frequency and time of stimulation. Decreased expression of orexin in the brain may also take part in the central mechanism of GES.

Efficiency and efficacy of multi-channel gastric electrical stimulation

Gastric electrical stimulation (GES) using single channel has been under investigation for its therapeutic potential for gastroparesis. The aim of this study was to study the efficacy and efficiency of multi-channel GES in accelerating gastric emptying in dogs. The study was performed in eight dogs, and gastric emptying of liquid was assessed in three randomized sessions of control, one-channel GES and four-channel GES. It was found that (i) GES of both one-channel and four-channel was able to completely entrain the slow waves in the entire stomach. However, the stimulation energy required by four-channel GES was only 1% of that required by one-channel GES. (ii) Four-channel, but not one-channel, GES significantly and substantially accelerated gastric emptying. An increase of 121.0 and 93.9% was noted with four-channel GES at 30 and 60 min after the meal, respectively. It was concluded that four-channel GES is substantially more efficient and effective than conventional single-channel GES in improving gastric emptying. It is worthy to explore its therapeutic potential for gastroparesis in clinical settings.

Two-channel gastric electrical stimulation accelerates delayed gastric emptying induced by vasopressin

The aim of this study was to investigate the effects of two-channel gastric electrical stimulation (GES) on delayed gastric emptying, gastric dysrhythmias, and motion sickness-like symptoms induced by vasopressin. Seven dogs implanted with four pairs of gastric electrodes and a duodenal cannula were studied in four randomized sessions (saline, vasopressin, single-channel GES, and two-channel GES). The experiment in each session was conducted sequentially as follows: 30-min baseline, ingestion of a liquid meal, 30-min iv infusion of vasopressin or saline, and two 30-min postprandial recordings. In the GES sessions, GES was applied via the first pair of electrodes for single-channel GES or the first and third pairs of electrodes for two-channel GES. Gastric emptying was collected every 15 min via the cannula for a period of 90 min. Results were as follows. (1) Vasopressin induced gastric dysrhythmias, motion sickness-like symptoms, and delayed gastric emptying (P < 0.01, ANOVA). (2) GES normalized gastric dysrhythmias (P < 0.01) but showed no effects on vasopressin-induced emetic response. (3) Two-channel GES improved delayed gastric emptying induced by vasopressin. In comparison with the vasopressin session, two-channel GES, but not single-channel GES, significantly increased gastric emptying at 30 min (43.9+/-12.6 vs. 27.5+/-7.7%; P < 0.03), 60 min (75.3+/-15.1 vs. 54.0+/-17.8%; P < 0.05), and 90 min (91.6+/-9.8 vs. 80.3+/-9.0%; P < 0.05). GES with long pulses is able to normalize gastric dysrhythmias. Two-channel GES improves delayed gastric emptying induced by vasopressin.