Modulatory effects and afferent pathways of gastric electrical stimulation on rat thoracic spinal neurons receiving input from the stomach

Gastric Electrical Stimulation for the Treatment of Gastroparesis or Gastroparesis-Like Symptoms: A Systemic Review and Meta-Analysis

BACKGROUND

The effects of gastric electrical stimulation are not fully understood. We aimed to assess the efficacy of gastric electrical stimulation (GES) for patients with gastroparesis and gastroparesis-like symptoms.

MATERIALS AND METHODS

We searched PubMed, Scopus, Cochrane, Web of Science, Embase, and Science Direct to identify controlled trials and cohort studies. We used random effects models to estimate pooled effects. A total of nine studies met the criteria and were included for the final qualitative synthesis and the quantitative analysis. We examined the mean absolute differences (MD) and 95% CIs.

RESULTS

Nine studies (n = 730) met the criteria and were included for the final qualitative synthesis and the quantitative analysis. There was significant improvement in gastrointestinal (GI) total symptom score (TSS) with the GES group compared with controls during the randomized blind trials. This effect was sustained at 12 months after treatment compared with before treatment (MD = -6.07; 95% CI, -4.5 to -7.65; p < 0.00001). The pooled effect estimate showed a significant improvement in frequency of weekly vomiting episodes at 12 months compared with before treatment (MD = -15.59; 95% CI, -10.29 to -20.9; p < 0.00001).

CONCLUSION

GES appears beneficial, with significant improvement in GI TSS, weekly vomiting frequency, gastric emptying study, and quality of life.

Somatotopic organization of autonomic reflexes by acupuncture

Acupuncture has been practiced for more than 2000 years in China and now all over the world. One core idea behind this medical practice is that stimulation at specific body regions (acupoints) can distantly modulate organ physiology, but the underlying scientific basis has been long debated. Here, I summarize evidence supporting that long-distant acupuncture effects operate partly through somato-autonomic reflexes, leading to activation of sympathetic and/or parasympathetic pathways. I then discuss how the patterning of the somatosensory system along the rostro-caudal axis and the cutaneous-deep tissue axis might explain acupoint specificity and selectivity in driving specific autonomic pathways, particularly those modulating gastrointestinal motility and systemic inflammation.

Gastric Electrical Stimulation: Role and Clinical Impact on Chronic Nausea and Vomiting

Gastric electrical stimulation (GES) is currently used as an alternative treatment for medically refractory gastroparesis. GES has been initially developed to accelerate gastric motility, in order to relieve the symptoms of the patients. Subsequent studies, unfortunately, failed to demonstrate the acceleration of gastric emptying using high-frequency stimulation – low energy stimulation although the technique has shown a clinical impact with a reduction of nausea and vomiting for patients with gastroparesis. The present review details the clinical efficacy of GES in gastroparesis as well as its putative mechanisms of action.

Yokukansan Suppresses Gastric Hypersensitivity and Eosinophil-associated Microinflammation in Rats With Functional Dyspepsia

Background/Aims

Herbal medicine is an important complementary therapy for functional dyspepsia (FD). However, its effect against gastric hypersensitivity in patients with FD has rarely been evaluated. Yokukansan (YKS), a traditional Japanese herbal medicine, is effective against neuropathic and inflammatory pain. This study aims to use a maternal separation (MS) stress-induced FD model to investigate the effects of YKS against gastric hypersensitivity, gastric motility, and duodenal micro-inflammation.

Methods

The MS stress model was established by separating newborn Sprague-Dawley rats from their mothers for 2 hours a day from postnatal days 1 to 10. At the age of 7-8 weeks, the rats were treated with YKS at a dose of 5 mL/kg (1 g/kg) for 7 consecutive days. After YKS treatment, electromyographic activity in the acromiotrapezius muscle by gastric distention and the gastric-emptying rate were assessed. Immunohistochemical analysis of eosinophils in the duodenum and phosphorylated extracellular signal-regulated kinase (p-ERK) 1/2 in the spinal cord was performed.

Results

YKS treatment suppressed MS stress-induced gastric hypersensitivity and decreased the elevated levels of p-ERK1/2 in the spinal cord. In the gastroduodenal tract, YKS inhibited eosinophil-associated micro-inflammation but did not improve gastric dysmotility.

Conclusions

YKS treatment improved gastric hypersensitivity by alleviating eosinophil-associated micro-inflammation in the gastroduodenal tract. This treatment may be considered an effective therapeutic option for epigastric pain and micro-inflammation in patients with FD.

Neural signalling of gut mechanosensation in ingestive and digestive processes

Eating and drinking generate sequential mechanosensory signals along the digestive tract. These signals are communicated to the brain for the timely initiation and regulation of diverse ingestive and digestive processes - ranging from appetite control and tactile perception to gut motility, digestive fluid secretion and defecation - that are vital for the proper intake, breakdown and absorption of nutrients and water. Gut mechanosensation has been investigated for over a century as a common pillar of energy, fluid and gastrointestinal homeostasis, and recent discoveries of specific mechanoreceptors, contributing ion channels and the well-defined circuits underlying gut mechanosensation signalling and function have further expanded our understanding of ingestive and digestive processes at the molecular and cellular levels. In this Review, we discuss our current understanding of the generation of mechanosensory signals from the digestive periphery, the neural afferent pathways that relay these signals to the brain and the neural circuit mechanisms that control ingestive and digestive processes, focusing on the four major digestive tract parts: the oral and pharyngeal cavities, oesophagus, stomach and intestines. We also discuss the clinical implications of gut mechanosensation in ingestive and digestive disorders.

Impact of adaptive gastric electrical stimulation on weight, food intake, and food intake rate in dogs

BACKGROUND

Gastric electrical stimulation (GES) has been studied for decades as a promising treatment for obesity. Stimulation pulses with fixed amplitude and pulse width are usually applied, but these have limitations with regard to overcoming habituation to GES and inter-subject variation. This study aims to analyze the efficacy of an adaptive GES protocol for reducing food intake and maintaining lean weight in dogs.

METHODS

Six beagle dogs were implanted with a remotely programmable gastric stimulator. An adaptive protocol was designed to increase the stimulation energy proportionally to the excess of food consumption, with respect to the dogs' maintenance energy requirements. After surgery and habituation to experimental conditions, the dogs went through both a control and a stimulation period of 4 weeks each, in a randomized order. The stimulation parameters were adapted daily. Body weight, food intake, food intake rate, and postprandial cutaneous electrogastrograms (EGG) were recorded to assess the effect of adaptive GES.

RESULTS

Adaptive GES decreased food intake and food intake rate (p < 0.05) resulting in weight maintenance. In the absence of GES, the dogs gained weight (p < 0.05). Postprandial EGG dominant frequency was accelerated by GES (p < 0.05). The strategy of adapting the stimulation energy was effective in causing significant mid-term changes.

CONCLUSION

Adaptive GES is effective for reducing food intake and maintaining lean weight. The proposed adaptive strategy may offer benefits to counter habituation and adapt to inter-subject variation in clinical use of GES for obesity.

Strategies to Refine Gastric Stimulation and Pacing Protocols: Experimental and Modeling Approaches

Gastric pacing and stimulation strategies were first proposed in the 1960s to treat motility disorders. However, there has been relatively limited clinical translation of these techniques. Experimental investigations have been critical in advancing our understanding of the control mechanisms that innervate gut function. In this review, we will discuss the use of pacing to modulate the rhythmic slow wave conduction patterns generated by interstitial cells of Cajal in the gastric musculature. In addition, the use of gastric high-frequency stimulation methods that target nerves in the stomach to either inhibit or enhance stomach function will be discussed. Pacing and stimulation protocols to modulate gastric activity, effective parameters and limitations in the existing studies are summarized. Mathematical models are useful to understand complex and dynamic systems. A review of existing mathematical models and techniques that aim to help refine pacing and stimulation protocols are provided. Finally, some future directions and challenges that should be investigated are discussed.

Surgical Treatment for Refractory Gastroparesis: Stimulator, Pyloric Surgery, or Both?

BACKGROUND

Several surgical options exist for refractory gastroparesis (Gp) including gastric electric stimulation (GES) and pyloric surgery (PS) such as pyloromyotomy or pyloroplasty. Few studies exist comparing the outcomes of these surgeries.

AIM

Compare the clinical outcomes of GES, PS, and simultaneous GES+PS for refractory Gp.

METHODS

Patients undergoing surgical intervention at our medical center from January 2016 to April 2019 were given pre- and post-surgery questionnaires to assess their response to intervention: Patient Assessment of Upper Gastrointestinal Symptoms (PAGI-SYM) grading symptoms and Clinical Patient Grading Assessment Scale (CPGAS) grading response to treatment. Results are expressed as mean ± SE.

RESULTS

One hundred thirty-two patients underwent surgical intervention; 12 were excluded. Mean CPGAS improvement overall was 2.8 ± 0.2 (p < 0.01): GES+PS had CPGAS score at 3.6 ± 0.5, pyloric interventions 3.1 ± 0.5, and GES 2.5 ± 0.4 (p > 0.05). Mean improvement in Gastroparesis Cardinal Symptom Index (GCSI) total score was 1.0 ± 0.1 (p < 0.01), with improvement of 1.1 ± 0.2 for GES + PS, 0.9 ± 0.2 for GES, and 0.9 ± 0.2 for PS (p > 0.05). GES and GES + PS, but not PS only, significantly improved symptoms of nausea and vomiting (p < 0.01). Among gastroparesis subtypes, patients with diabetic gastroparesis had more improvement on nausea/vomiting subscale compared with idiopathic gastroparesis (p = 0.028).

CONCLUSIONS

Patients with refractory symptoms of Gp undergoing GES, PS, or combined GES+PS each had significant improvement of their GCSI total score. GES and combined GES+PS significantly improved nausea/vomiting. These results suggest GES or combined GES+PS appears better for nausea/vomiting predominant refractory Gp.

Gastric Electric Stimulation for Refractory Gastroparesis

OBJECTIVE

To outline the use and utility of gastric electric stimulation (GES) as a therapeutic intervention for gastroparesis.

METHODS

Review of the literature.

RESULTS

Gastroparesis is characterized by delayed gastric emptying, with symptoms of nausea, vomiting, early satiety, postprandial fullness, and abdominal pain. Some patients with gastroparesis do not respond to medical intervention, and for these patients surgical intervention may be warranted. GES utilizes high-frequency gastric neurostimulation to facilitate gastric emptying and reduce symptoms of gastroparesis. It is indicated for patients with idiopathic and diabetic gastroparesis who have nausea and vomiting as their primary symptoms and who have not responded to medical therapy. GES has also been used in postsurgical and pediatric gastroparesis patients. Optimizing the outcome of this surgical treatment through proper patient selection and meticulous surgical technique is essential as there are inherent risks to the procedure. Nonblinded studies of GES for medically refractory gastroparesis have demonstrated therapeutic symptomatic benefit, whereas randomized controlled trials have not. New interventions such as pyloromyotomy and pyloroplasty are reasonable alternatives or addendums to GES.

CONCLUSION

GES may be considered among the therapies available for treating patients with refractory symptoms of gastroparesis. More studies, specifically those comparing GES, pyloromyotomy, GES combined with pyloromyotomy, and placebo, are needed to help guide therapy selection for refractory gastroparesis.

Outcomes of surgical intervention for refractory gastroparesis: a systematic review

BACKGROUND

Gastroparesis (GP) is characterized by delayed gastric emptying with symptoms of nausea, vomiting, early satiety, postprandial fullness, and abdominal pain. Various surgical options exist to treat GP not responding to medical treatments (refractory GP), including gastric electric stimulation (GES), gastrectomy (GTx), and pyloric interventions (PI), whereas the outcomes of these procedures have been published; few comparison studies exist.

METHODS

PubMed literature review for articles from September 1988 to October 2017 was performed for prospective and retrospective analyses reporting >5 patients. Unweighted (per study) and weighted (per patient) overall improvement and improvement in symptoms of nausea, vomiting, and abdominal pain were calculated and compared for the different procedures.

RESULTS

Of 325 studies satisfying search criteria, 38 met the study criteria and were included for analysis. Total response to intervention, both weighted and unweighted, was greater with PIs compared to GES (P < 0.05). For unweighted symptom improvements, nausea improved more with PI than with GES (P < 0.05). GES improved vomiting more than epigastric pain (P < 0.05). For weighted symptom improvements, pyloric surgery and GTx improved vomiting compared to GES (P < 0.05).

CONCLUSIONS

Published outcomes of GES, pyloric surgery, and GTx for refractory GP are compared. Pyloromyotomy/pyloroplasty improves patient response greater than with GES. Weighing by number of studies, pyloric surgery improves nausea and abdominal pain greater than GES. For GES, vomiting is more likely to improve than abdominal pain. Weighing by number of patients, pyloric surgery and GTx improved vomiting compared to GES.

Gastrointestinal Peptides During Chronic Gastric Electrical Stimulation in Patients With Intractable Vomiting

OBJECTIVES

Gastric electrical stimulation (GES) is an alternative therapy to treat patients with intractable vomiting. A preclinical study has demonstrated the modulation of the gastrointestinal (GI) peptide ghrelin by GES but such mechanism has never been investigated in patients. The aim of this work was to assess the effect of GES on GI peptide levels in patients with intractable vomiting.

MATERIALS AND METHODS

Twenty-one patients were randomized to receive either ON or OFF GES, 14 completed the study (10 ON, 4 OFF stimulation). Vomiting episodes, gastric emptying, and gastrointestinal quality of life index (GIQLI) were assessed. Gastric and blood samples were collected before and four months after the ON period of gastric stimulation. mRNA and/or peptide levels were assessed in gastric biopsies for ghrelin, leptin, and NUCB2/nesfatin-1 and in duodenal biopsies for glucagon-like peptide 1 (GLP-1) and peptide YY (PYY) using RT-qPCR and multiplex technology. Ghrelin, leptin, GLP-1, PYY, gastric inhibitory peptide (GIP), and NUCB2/nesfatin-1 levels also were quantified in blood samples.

RESULTS

Among clinical parameters, vomiting episodes were slightly reduced by GES (p = 0.09). In tissue, mRNA or protein levels were not modified following chronic GES. In blood, a significant reduction of postprandial PYY levels (p < 0.05) was observed at M4 and a reduction of NUCB2/nesfatin-1 levels in fasted patients (p < 0.05). Increased plasma leptin levels after GES were correlated with reduction of vomiting and improvement of GIQLI.

CONCLUSIONS

GES reduces NUCB2/nesfatin-1 levels under fasting conditions and postprandial PYY levels in patients suffering from nausea and/or vomiting refractory to pharmacological therapies.

Surgical approaches to treatment of gastroparesis: gastric electrical stimulation, pyloroplasty, total gastrectomy and enteral feeding tubes

Gastric electrical stimulation (GES) is neurostimulation; its mechanism of action is affecting central control of nausea and vomiting and enhancing vagal function. GES is a powerful antiemetic available for patients with refractory symptoms of nausea and vomiting from gastroparesis of idiopathic and diabetic causes. GES is not indicated as a way of reducing abdominal pain in gastroparetic patients. The need for introducing a jejunal feeding tube means intensive medical therapies are failing, and is an indication for the implantation of the GES system, which should always be accompanied by a pyloroplasty to guarantee accelerated gastric emptying.

The acute effects of a new type of implantable gastric electrical stimulators featuring varied pulse widths on beagle dogs' food intake and gastric accommodation

BACKGROUND

To improve the therapeutic effects of gastric electrical stimulation (GES) for obesity, an animal experiment was conducted using a new type of stimulators. Proper parameters of GES were selected, and the impacts of GES on the food intake and gastric accommodation of canines were observed.

METHODS

Eight beagle dogs were operated on, and GES was performed on them. Firstly, GES was performed to determine the right parameters according to symptoms. Secondly, the so selected parameters were used in a 3-day GES procedure, during which process food intake, body weight, and symptoms were recorded. Thirdly, the gastric capacities before and after GES with different pulse widths were measured by means of a barostat.

RESULTS

The selected parameters varied for each dog, with the pulse widths ranging from 0.3 to 6 ms. The food consumption after GES dropped significantly as compared with the amount observed in the sham stimulation. Tolerance to stimulation could be observed during GES. The post-GES gastric fundus capacity increased evidently in comparison with the capacity before GES, suggesting significant distention as compared with sham stimulation. Given an increment of 2 ms in the pulse width twice, the gastric capacity continued to distend each time.

CONCLUSIONS

GES featuring pulse trains with wider and individualized pulse widths could inhibit food consumption of dogs. The stimulation parameters should be selected individually and adjusted periodically. GES of this mode could also increase the fasting gastric capacity with certain dose-related effects. The new type of stimulators may be more suitable for the treatment of human obesity than traditional stimulators.

Changes of neuronal activities after gut electrical stimulation with different parameters and locations in lateral hypothalamus area of obese rats

This study tested the effects of the gastrointestinal pulse train electrical stimulation with different parameters and at different locations on the neuronal activities of the lateral hypothalamus area (LHA) in obese rats in order to find the optimal stimulation parameter and location. Eight gastric electrical stimulations (GES) with different parameters were performed and the neuronal activities of gastric-distension responsive (GD-R) neurons in LHA were observed. The effects of stimulations with 8 parameters were compared to find the optimal parameter. Then the optimal parameter was used to perform electrical stimulation at duodenum and ileum, and the effects of the duodenal and ileac stimulation on the GD-R neurons in LHA were compared with the gastric stimulation of optimal parameter. The results showed that GES with the lowest energy parameter (0.3 ms, 3 mA, 20 Hz, 2 s on, 3 s off) activated the least neurons. The effects of GES with other parameters whose pulse width was 0.3 ms were not significantly different from those of the lowest energy parameter. Most gastric stimulations whose pulse width was 3 ms activated more LHA neurons than the smallest energy parameter stimulation, and the effects of those 3 ms gastric stimulations were similar. Accordingly, the lowest energy parameter was recognized as the optimal parameter. The effects of stimulations with the optimal parameter at stomach, duodenum and ileum on the LHA neuronal activities were not different. Collectively, gastrointestinal electrical stimulation (GIES) with relatively large pulse width might have stronger effects to the neuronal activities of GD-R neurons in LHA of obese rats. The effects of the GIES at different locations (stomach, duodenum and ileum) on those neurons are similar, and GES is preferential because of its easy clinical performance and safety.

Parameter selection and stimulating effects of an adjustable gastric electrical stimulator in dogs

Background

Gastric electrical stimulation (GES) has been proposed as a promising therapeutic option in treating obesity for 20 years. Currently, the available device of GES cannot meet the clinical needs. The purpose of this study is to verify the effect of a new type of adjustable gastric electrical stimulator in reducing food intake and body weight.

Methods

Eight beagle dogs randomly followed GES and sham GES for 3 months in a crossover design. Parameters were adjusted and individualized during the experiment. Symptoms of GES were recorded, and the effective parameters were selected. Resistance to GES was assessed. Food intake and body weight were measured to evaluate the effect of GES.

Results

The effective parameters were varied among the dogs. Resistance to GES was observed in different periods in dogs. Parameters needed to be adjusted every 10.2 ± 2.1 days during the period of GES. Food intake during GES for 3 months was significantly reduced than that during sham GES of 3 months (P < 0.05). With the decreased food intake, body weight was significantly reduced by the end of GES of 3 months compared with that of sham GES of 3 months (P < 0.05).

Conclusions

Food intake and body weight of dogs are significantly reduced by adjustable GES. Individual parameters and resistance during GES are required to be considered. The new adjustable device may have good prospects of clinical application for obesity.

Retrograde gastric electrical stimulation suppresses calorie intake in obese subjects

OBJECTIVE

The effect of acute retrograde gastric electrical stimulation (RGES) on food intake, gastric accommodation, and gastric emptying in obese patients was investigated.

METHODS

Simple obesity patients underwent RGES or sham stimulation. The maximum food intake volume was determined and the total calorie of consumed food was calculated. Gastric emptying was determined by (99m) -diethylenetriaminepentaacetic acid scintigraphy.

RESULTS

Sixteen obese patients were studied, with a median BMI of 32.1 (IQR, 31.2, 33.8) kg/m(2) . The median gastric emptying time was 106.1 (IQR, 81.8, 122.4) min with sham stimulation and 113.0 (IQR, 83.7, 124.8) min with RGES (P = 0.352). The mean maximum satiety food intake was 580 (IQR, 510, 725) mL with sham stimulation and 490 (IQR, 385, 590) mL with RGES (P = 0.003). No statistically significant difference was noted between sham stimulation and RGES in the 1 and 2-h food retention rate. The total calories of maximum satiety food intake with sham stimulation were 985.2 (IQR, 842.5, 1063.1) kcal and 759.9 (IQR, 547.9, 784.9) kcal with RGES (P = 0.007).

CONCLUSIONS

Acute RGES reduces calorie intake by decreasing gastric accommodation in obese subjects.

Effects and mechanisms of gastric electrical stimulation on visceral pain in a rodent model of gastric hyperalgesia secondary to chemically induced mucosal ulceration

BACKGROUND

Gastric electrical stimulation (GES) has been suggested as a potential treatment for patients with gastric motility disorders. The aim of this study was to examine the effects and mechanisms of GES on visceral pain in awaken rats.

METHODS

Under anesthesia, acetic acid was injected into the submucosal layer of the stomach wall in Sprague-Dawley (SD) male rats. Each rat was chronically placed with an intragastric balloon and two pairs of electrodes on gastric serosa for GES and at the neck muscles for electromyography (EMG) recordings respectively. The study was composed of four experiments. Exp 1 was designed to determine optimal GES parameters in reducing EMG response to gastric distention (GD). Exp 2 was performed to investigate the effect of GES on gastric tone/accommodation. Exp 3 was to investigate if the opioid pathway was involved in the analgesic effects of GES. Exp 4 was to assess the effectiveness of GES on the spinal cord neurons (T9-T10) responding to GD.

KEY RESULTS

(i) Gastric electrical stimulation with a train on of 0.1 s and off of 0.4 s, 0.25 ms, 100 Hz, and 6 mA significantly reduced GD-induced EMG responses at GD 40, 60, and 80 mmHg. (ii) The inhibitory effects of GES on the GD-induced EMG responses were blocked by Naloxone. (iii) GES inhibited 90% of high-threshold (HT) spinal neurons in response to GD. However, GES with the same parameters only suppressed 36.3% low-threshold (LT) neuronal response to GD.

CONCLUSIONS & INFERENCES

Gastric electrical stimulation with optimal parameters inhibits visceral pain; the analgesic effect of GES on visceral pain is mediated via the endogenous opioid system and the suppression of spinal afferent neuronal activities.

Blunted Peripheral and Central Responses to Gastric Mechanical and Electrical Stimulations in Diet-induced Obese Rats

Background/Aims

The increase in the prevalence of obesity is attributed to increased food intake and decreased physical activity in addition to genetic factors. Altered gut functions have been reported in obese subjects, whereas, little is known on the possible alterations in brain-gut interactions in obesity. The aim of the study was to explore possible alterations in gastric myoelectrical activity, gastric emptying, autonomic functions and central neuronal responses to gastric stimulations in diet-induced obese rats.

Methods

Gastric myoelectrical activity, gastric emptying and heart rate variability were recorded in lean and obese rats; extracellular neuronal activity in the ventromedial hypothalamus and its responses to gastric stimulations were also assessed.

Results

(1) Gastric emptying was significantly accelerated but gastric myoelectrical activity was not altered in obese rats; (2) the normal autonomic responses to feeding were absent in obese rats, suggesting an impairment of postprandial modulation of autonomic functions; and (3) central neuronal responses to gastric stimulations (both balloon distention and electrical stimulation) were blunted in obese rats, suggesting impairment in the brain-gut interaction.

Conclusions

In diet-induced obese rats, gastric emptying is accelerated, postprandial modulations of autonomic functions is altered and central neuronal responses to gastric stimulations are attenuated. These alterations in peripheral, autonomic and brain-gut interactions may help better understand pathogenesis of obesity and develop novel therapeutic approaches for obesity.

Technical note: Evaluation of tined endoscopically placed mucosal leads for temporary gastric neurostimulation

OBJECTIVE

To compare larger diameter corkscrew-tined leads with previously described intracardiac pacing leads for temporary gastric neurostimulation in a canine model.

MATERIALS AND METHODS

Two mongrel dogs underwent gastroscopy under general anesthesia, with endoscopic placement of two cardiac leads (1 mm tine diameter, 4 mm depth) placed sequentially in 1) transverse configuration in the distal antrum mucosa; 2) longitudinal (1 cm apart) configuration in gastric corpus. Stomach was then stimulated with maximal parameters to induce neutrally mediated contraction. Procedures were then repeated with larger leads (5 mm tine diameter, 8 mm length). Gastric contractions were measured with serosal strain transducers.

RESULTS

Leads were placed endoscopically without difficulty. Neither lead type punctured through to the serosa of the stomach. Neither cardiac nor larger leads were capable of eliciting any gastric contractile activity with endoscopic placement either in the transverse or longitudinal orientations.

DISCUSSION

While successful on the serosal side, both the cardiac leads and the larger alternative leads failed to produce stomach contraction when implanted mucosally. This may be due to the elastic nature of the mucosa, which was observed to twist around both types of leads significantly, hindering proper penetration into the muscularis.

CONCLUSION

These results suggest that the current concept of temporary gastric electrical neurostimulation via a mucosal approach must be reevaluated, as the procedure most likely does not accurately mimic electrical stimulation in the muscularis.

Gastric electrical stimulation parameter dependently alters ventral medial hypothalamic activity and feeding in obese rats

Gastric electrical stimulation (GES) has been used to treat obesity with unclear mechanisms and limited parameter ranges. This study explores effects of GES parameters on ventral medial hypothalamic (VMH) activity, feeding, and body weight in diet-induced obese (DIO) rats. For experiment 1, discharge rates were recorded in 39 gastric distension-responsive (GD-R) neurons in 12 DIO rats. Basal rates were compared with rates under GES using varied pulse amplitudes, widths, frequencies, and train-on times. For experiment 2, a crossover experiment in 16 DIO rats measured food intake and weight effects of GES pulse width, the parameter with the steepest neuronal response gradient in experiment 1. Treatments were sham and 0.5-, 2.0-, and 5.0-ms pulse GES. In experiment 1, 11 of 13 GES parameter sets tested produced significantly (P < 0.05) altered discharge rates of GD-R neurons. Increases in pulse amplitude (P < 0.05) and width (P < 0.0001) produced significant upward linear trends in response over the range tested, with the trend being strongest for pulse width. In experiment 2, over 4 days of 0.5-, 2.0-, and 5.0-ms GES treatment, food intake was 9.6% (P < 0.05), 21.0% (P < 0.0001), and 47.3% (P < 0.0001) lower than under sham-GES, whereas body weight changes were 0.7 (P = 0.48), 2.2 (P < 0.05), and 3.5 (P < 0.002) percentage points lower, respectively. We concluded that GES pulse width increases had the largest effect on VMH neuronal activity, and these effects were paralleled by pulse width-dependent reductions in food intake and body weight. Lengthening pulse width beyond the range used in prior clinical studies may be critical to making GES a viable obesity treatment.

Bloating in gastroparesis: severity, impact, and associated factors

OBJECTIVES

Bloating is commonly reported in gastroparesis, but its prevalence, impact, and associated factors are uninvestigated. We aimed to quantify the prevalence of bloating in gastroparesis and relate its severity to clinical factors and quality of life.

METHODS

Survey, examination, and scintigraphy data were compared in 335 gastroparesis patients from 6 centers of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) Gastroparesis Clinical Research Consortium. Bloating severity was stratified using Gastroparesis Cardinal Symptom Index (GCSI) bloating subscale scores.

RESULTS

Bloating severity of at least mild (GCSI ≥2) and severe (GCSI ≥4) grades were reported by 76 and 41% of patients, respectively. Bloating severity related to female gender (P<0.0001) and overweight status (P=0.04) on regression analysis and correlated with intensity of nausea, postprandial fullness, visible distention, abdominal pain, and altered bowel function (P<0.05). Disease etiology, smoking status, and gastric emptying did not relate to bloating subset (P>0.05). Disease-specific quality of life and general measures of well-being were progressively impaired with increasing bloating severity (P=0.01). Probiotic use (P=0.03) and use of antidepressants with significant norepinephrine reuptake inhibitor activity (P=0.045) use related to bloating severity; antiemetic use trended higher with worsening bloating (P=0.06).

CONCLUSIONS

Bloating is prevalent in gastroparesis and is severe in many individuals. Bloating severity relates to female gender, body weight, and intensity of other symptoms. The symptom impairs quality of life but is not influenced by gastric emptying rates. Antiemetics, probiotics, and antidepressants with significant norepinephrine reuptake inhibitor activity may affect reports of bloating. These findings provide insight into this underappreciated symptom of gastroparesis.

Gastric electrical stimulation for gastroparesis: a goal greatly pursued, but not yet attained

The lack of an effective medical treatment for gastroparesis has pushed the research of new techniques of gastric electrical stimulation (GES) for nearly half a century of experimentation with a large variety of electrical stimuli delivered to the gastric wall of animals and patients with gastroparesis. Three principal methods are currently available: gastric low-frequency/high-energy GES with long pulse stimulation, high-frequency/low-energy GES with short pulse stimulation and neural sequential GES. The first method aims to reset a regular slow wave rhythm, but has variable effects on contractions and requires devices with large and heavy batteries unsuitable for implantation. High-frequency/low-energy GES, although inadequate to restore a normal gastric electro-mechanical activity, improves dyspeptic symptoms, such as nausea and vomiting, giving patients a better quality of life together with a more satisfactory nutritional status and is suitable for implantation. Unfortunately, the numerous clinical studies using this type of GES, with the exception of two, were not controlled and there is a need for definitive verification of the effectiveness of this technique to justify the cost and the risks of this procedure. The last method, which is neural sequential GES, consists of a microprocessor-controlled sequential activation of a series of annular electrodes along the distal two thirds of the stomach and is able to induce propagated contractions causing forceful emptying of the gastric content. The latter method is the most promising, but has been used only in animals and needs to be tested in patients with gastroparesis before it is regarded as a solution for this disease.

Cellular effects of gastric electrical stimulation on antral smooth muscle cells in rats

The cellular effects of gastric electrical stimulation (GES), which has recently been introduced as a potential therapy for the treatment of gastroparesis and obesity, were investigated in rat antrum smooth muscle cells (SMCs). Effects on cell membrane potentials of single electrical current pulses (pulse width from 0.1 ms to 200 ms) and 2-s pulse train stimuli with different pulse widths (0.1–4 ms), different frequencies (20–200 Hz), and different intensities were studied: 1) the stimulus amplitude had an exponential relationship to the pulse width from 2 ms to 200 ms, along with a rapidly rising strength-duration curve at pulse widths less than 5 ms, and a relatively flat curve at pulse widths greater than 50 ms; 2) when the pulse frequency was at 80 Hz or above, pulse train electrical stimulation, with a pulse width of 2 ms or above but not ≤1 ms, was able to depolarize cell membrane potentials to above −30 mV and/or generate action potentials. Electrical stimulation with a single long pulse and a width of 50 ms or greater is effective in depolarizing cell membrane potentials of SMCs with low amplitude. Pulse train electrical stimulation with a pulse width of ≤1 ms fails to generate action potentials in SMCs, whereas pulse train electrical stimulation with a pulse width of 2–4 ms and a sufficiently high pulse frequency is able to generate action potentials. These cellular findings may be useful in optimizing stimulation parameters of GES.

Methods of gastric electrical stimulation and pacing: a review of their benefits and mechanisms of action in gastroparesis and obesity

Development of gastric electrical stimulation techniques for treatment of gastric dysmotility syndromes and obesity has been a long-standing goal of investigators and clinicians. Depending on stimulus parameters and sites of stimulation, such methods have a range of theoretical benefits including entrainment of intrinsic gastric electrical activity, eliciting propagating contractions and reducing symptomatology in patients with gastroparesis and reducing appetite and food intake in individuals with morbid obesity. Additionally, gastric stimulation parameters have extragastrointestinal effects including alteration of systemic hormonal and autonomic neural activity and modulation of afferent nerve pathways projecting to the central nervous system that may represent important mechanisms of action. Numerous case series and smaller numbers of controlled trials suggest clinical benefits in these two conditions, however better controlled trials are mandated to confirm their efficacy. Current research is focusing on novel stimulation methods to better control symptoms in gastroparesis and promote weight reduction in morbid obesity.

Central neuronal mechanisms of gastric electrical stimulation in diabetic gastroparesis

OBJECTIVE

The mechanisms underlying symptom improvement in gastric electrical stimulation (GES) are not fully understood. Modulation of the central nervous system excitability may be involved. The objective of the study was to investigate the central effects of GES, including the possible modulation of the visceral sensory nervous system.

MATERIAL AND METHODS

A gastric electrical stimulator was implanted in seven diabetic patients with medically refractory gastroparesis. A double-blinded protocol was used to investigate the patients at baseline and one month after recovery with the stimulator turned on and off (1-month periods). The following assessments were carried out: mechanical, thermal and electrical stimulations with sensory recordings in the esophagus and duodenum, and standardized, self-administered, daily symptom questionnaires.

RESULTS

No difference was found between baseline and the on- and off periods in overall gut pain thresholds across all stimulus modalities in the esophagus (p=0.63), duodenum (p=0.19) or esophagus and duodenum combined (p=0.76). No difference in the sensory response to mechanical stimulation was found in the esophagus before (all p>0.31) and after (all p>0.43) smooth muscle relaxation with butylscopolamine. Similar findings were observed in the duodenum. No differences were found in thermal sensitivity (esophagus (p=0.67) and duodenum (p=0.17)), sensory response to electrical stimulation (esophagus (p=0.57) and duodenum (p=0.52)) or induced somatic referred pain areas (esophagus (p=0.75) and duodenum (p=0.51)). No difference was seen in the induced somatic referred pain areas or self-reported symptoms.

CONCLUSIONS

No evidence was found for GES-induced modulation of the visceral sensory system and central excitability. However, GES has been proven to modulate the central nervous system in animal studies, necessitating further human experiments in order unambiguously to establish the possible central effects of GES.

Analysis of Electromyographic Signals from Rats' Stomaches for Detection and Classification of Motility

This paper presents the analysis of the electromyographic signals from rat stomaches to identify and classify contractions. The results were validated with both visual identification and an ultrasonic system to guarantee the reference. Some parameters were defined and associated to the energy of the signal in frequency domain and grouped in a P vector. The parameters were statistically analyzed and according to the results, an artificial neuronal network was designed to use the P vectors as inputs to classify the electrical signals related to the contraction conditions. A first approach classification was performed with and without contraction classes (CR and NCR), then the same database were subdivided in four classes: with induced contraction (ICR), spontaneous contraction (SCR), without contraction due a post mortem condition (PMR) or under physiological conditions (PNCR). In a two-class classifier, performance was 86%, 93% and 91% of detections for each electrogastromyografic (EGMG) signal from each of three pairs of electrodes considered. Because in the four-class classifier, enough data was not collected for the first pair, then a three-class classifier with 82% of performance was used. For the other two EGMG signals electrode pairs, performance was of 76% and 86% respectively. Based in the results, the analysis of P vectors could be used as a contraction detector in motility studies due to different stimuli in a rat model.

Intraesophageal chemicals enhance responsiveness of upper thoracic spinal neurons to mechanical stimulation of esophagus in rats

Esophageal hypersensitivity is one of the most common causes of noncardiac chest pain in patients. In this study, we investigated whether exposure of the esophagus to acid and other chemical irritants affected activity of thoracic spinal neurons responding to esophageal distension (ED) in rats. Extracellular potentials of single thoracic (T3) spinal neurons were recorded in pentobarbital sodium-anesthetized, -paralyzed, and -ventilated male rats. ED (0.2 or 0.4 ml, 20 s) was produced by water inflation of a latex balloon placed orally into the middle thoracic region of the esophagus. The chemicals were administered via a tube that was passed through the stomach and placed in the thoracic esophagus. To irritate the esophagus, 0.2 ml of HCl (0.01 N), bradykinin (10 microg/ml), or capsaicin (10 microg/ml) were injected for 1-2 min. Only neurons excited by ED were included in this study. Results showed that intraesophageal instillation of HCl, bradykinin, and capsaicin increased activity in 3/20 (15%), 7/25 (28%), and 9/20 (45%) neurons but enhanced excitatory responses to ED in 9/17 (53%), 8/15 (53%), and 7/11 (64%) of the remaining spinal neurons, respectively. Furthermore, intraesophageal chemicals were more likely to enhance the responsiveness of low-threshold neurons than high-threshold neurons to the esophageal mechanical stimulus. Normal saline (pH 7.4, 0.2 ml) or vehicle instilled in the esophagus did not significantly affect activity or ED responses of neurons. We conclude that enhanced responses of thoracic spinal neurons to ED by the chemically challenged esophagus may provide a possible pathophysiological basis for visceral hypersensitivity in patients with gastroesophageal reflux and/or esophagitis.

Duodenal afferent input converges onto T9-T10 spinal neurons responding to gastric distension in rats

Clinically, the overlap of gastroduodenal symptoms, such as visceral pain or hypersensitivity, is often observed in functional gastrointestinal disorders. The underlying mechanism may be related to intraspinal neuronal processing of noxious convergent inputs from the stomach and the intestine. The purpose of this study was to examine whether single low thoracic (T9-T10) spinal neurons responded to both gastric and duodenal mechanical stimulation. Extracellular potentials of single T9-T10 spinal neurons were recorded in pentobarbital anesthetized, paralyzed, and ventilated male rats. Graded gastric distensions (GD, 20, 40, 60 mm Hg, 20 s) were induced by air inflation of a latex balloon surgically placed in the stomach. Graded duodenal distensions (DD, 0.2, 0.4, 0.6 ml, 20 s) were produced by water inflation of a latex balloon placed into the duodenum. Of 70 deeper (depth from dorsal surface of spinal cord: 0.3-1.2 mm) spinal neurons responsive to noxious GD (> or =40 mm Hg), 44(63%) also responded to noxious DD (> or =0.4 ml). Similarly, 13/17 (76%) superficial neurons (depth <0.3 mm) responded to both GD and DD. Of 57 gastroduodenal convergent neurons, 41 (72%) had excitatory and 6 had inhibitory responses to both GD and DD; the remaining neurons exhibited multiple patterns of excitation and inhibition. 43/57 (75%) gastroduodenal convergent neurons had low-threshold (< or =20 mm Hg) responses to GD, whereas 42/57 (74%) of these neurons had high-threshold (> or =0.4 ml) responses to DD. In addition, 34/40 (85%) gastroduodenal convergent neurons had somatic receptive fields on the back, flank, and medial/lateral abdominal areas. These results suggested that superficial and deeper T9-T10 spinal neurons received innocuous and/or noxious convergent inputs from mechanical stimulation of the stomach and duodenum. Gastroduodenal convergent spinal neurons might contribute to intraspinal sensory transmission for cross-organ afferent-afferent communication between the stomach and duodenum and play a role in visceral nociception and reflexes.

Synchronized gastric electrical stimulation improves delayed gastric emptying in nonobese mice with diabetic gastroparesis

The aim of this study was to investigate the effect and mechanism of synchronized gastric electrical stimulation (SGES) on gastric emptying in nonobese mice with diabetic gastroparesis (DB-GP). Eight control mice and 48 nonobese diabetic (NOD) mice with two pairs of gastric electrodes were used in this study. The study included seven groups in a randomized order [control, diabetes (DB), DB-GP, DB + SGES, DB-GP + SGES, DB-GP + Atropine, and DB-GP + SGES + Atropine groups]. In the control, DB, DB-GP, and DB-GP + Atropine groups, gastric emptying was measured in BLAB/cJ mice (control group) or NOD mice with a duration of diabetes of 0-7 days (DB group) or 28-35 days (DB-GP or DB-GP + Atropine group). In the DB + SGES, DB-GP + SGES, and DB-GP + SGES + Atropine groups, the experiment was the same as the corresponding DB, DB-GP, and DB-GP + Atropine groups except that SGES was applied during the experiment. SGES was applied via the proximal pair of electrodes and synchronized with the intrinsic gastric slow waves. The following results were obtained: 1) gastric emptying was delayed in NOD mice with a duration of diabetes of 28-35 days; 2) SGES was able to significantly increase gastric emptying in both diabetic mice and diabetic gastroparetic mice; and 3) the excitatory effect of SGES was completely blocked by atropine. SGES accelerates gastric emptying in NOD mice with diabetic gastroparesis. The effect of SGES on gastric emptying is mediated via the cholinergic pathway. These findings suggest that SGES may have a therapeutic potential for treating patients with diabetic gastroparesis.

Gastrocardiac afferent convergence in upper thoracic spinal neurons: a central mechanism of postprandial angina pectoris

The aim of this study was to examine whether gastric afferent information converged onto upper thoracic spinal neurons that received noxious cardiac input. Extracellular potentials of single upper thoracic (T3) spinal neurons were recorded in pentobarbital-anesthetized, paralyzed, ventilated male rats. Gastric distension (GD) (20, 40, 60 mm Hg, 20 seconds) was produced by air inflation of a latex balloon surgically placed in the stomach. A catheter was placed in the pericardial sac to administer bradykinin solution (10 microg/mL, 0.2 mL, 1 minute) as a noxious cardiac stimulus. Noxious GD (> or =40 mm Hg) altered activity of 26 of 31 (84%) spinal neurons receiving cardiac input. Twenty-two (85%) gastrocardiac convergent neurons were excited, and 1 neuron was inhibited by both intrapericardial bradykinin and GD; the remainder exhibited biphasic response patterns. Twenty-three of 26 (88%) gastrocardiac neurons also received convergent somatic input from the chest, triceps, and upper back areas. Bilateral cervical vagotomy did not significantly affect excitatory responses to GD in 5 of 5 neurons tested. Spinal transection at the C1 segment after vagotomy did not affect excitatory responses to GD in 3 of 4 neurons but abolished the GD response in 1 neuron. These data showed that a gastric stimulus excited T3 spinal neurons with noxious cardiac input primarily by way of intraspinal ascending pathways.

PERSPECTIVE

Convergence of gastric afferent input onto upper thoracic spinal neurons receiving noxious cardiac input that was observed in the present study may provide a spinal mechanism that explains stomach-heart cross-organ communication, such as postprandial triggering and worsening of angina pectoris in patients with coronary artery disease.

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

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

Modulatory effects and afferent pathways of gastric electrical stimulation on rat thoracic spinal neurons receiving input from the stomach

Gastric electrical stimulation (GES) has been suggested as a potential therapy for patients with obesity or gastric motility disorders. The aim of this study was to investigate the spinal mechanism of GES effects on gastric functions. Extracellular potentials of single spinal (T9-T10) neurons were recorded in pentobarbital anesthetized, paralyzed, ventilated male rats (n=19). Gastric distension (GD) was produced by air inflation of a balloon. One pair of platinum electrodes (1.0-1.5cm apart) was sutured onto the serosal surface of the lesser curvature of the stomach. GES with four sets of parameters was applied for 1min: GES-A (6mA, 0.3ms, 40Hz, 2s on, 3s off), GES-B (6mA, 0.3ms, 14Hz, 0.1s on, 5s off), GES-C (6mA, 3ms, 40Hz, 2s on, 3s off), GES-D (6mA, 200ms, 12pulses/min). 62/158 (39%) spinal neurons responded to GD (20, 40, 60mmHg, 20s. Most GD-responsive neurons (n=43) had excitatory responses; the remainder had inhibitory (n=12) or biphasic responses (n=7). GES-A, -B, -C and -D affected activity of 12/33 (36%), 4/31 (13%), 22/29 (76%) and 13/30 (43%) GD-responsive neurons, respectively. Bilateral cervical vagotomy did not significantly alter mean excitatory neuronal responses to GD (n=5) or GES (n=6). Resiniferatoxin (2.0microg/kg, i.v.), an ultrapotent agonist of vanilloid receptor-1, abolished excitatory responses to GD and GES in 4/4 neurons recorded in vagotomized rats. The results suggested that GES mainly had an excitatory effect on T9-T10 spinal neurons with gastric inputs; neuronal responses to GES were strengthened with stimulation at an increased pulse width and/or number of pulses. The modulatory effect of GES involved thoracic spinal (sympathetic) afferent fibers containing vanilloid receptor-1.