Effects of gastric electrical field stimulation with long pulses on gastric emptying in dogs

Study on effects of electrical stimulation on rabbit esophageal body motility in vivo

Electric stimulation (ES) could induce contraction of intestinal smooth muscle. The aim of this study was to analyze the effects of ES on esophageal motility and the underlying mechanism in vivo. Twenty-eight rabbits were equipped with a pair of subserosa electrodes (connected to an electrical stimulator) in the lower segment of the esophagus. The ES signal consisted of bipolar rectangular pulse trains, lasting for 3 s, with different amplitudes (1 mA, 3 mA, 5 mA and 10 mA), and frequencies (10 Hz, 20 Hz and 50 Hz). The amplitude of the contraction was recognized by high-resolution manometry. The effect of ES was tested under anesthesia and following administration of atropine, phentolamine or L-NAME. ES induced esophageal contraction at the stimulated site. A statistically significant increase in esophageal pressure was observed when the stimulation amplitude was above 3 mA. The increase in esophageal pressure was associated with the amplitude of stimulus as well as the frequency. During stimulation, atropine, phentolamine and L-NAME had no effect on the increase of esophageal pressure induced by ES. These findings implied that ES induced esophageal contraction were not mediated via the NANC, adrenergic or cholinergic pathway. The amplitude of esophageal contraction was current and frequency dependent.

Colon electrical stimulation: potential use for treatment of obesity

Obesity is one of the most prevalent health problems in the United States. Current therapeutic strategies for the treatment of obesity are unsatisfactory. We hypothesized the use of colon electrical stimulation (CES) to treat obesity by inhibiting upper gastrointestinal motility. In this preliminary study, we aimed at studying the effects of CES on gastric emptying of solid, intestinal motility, and food intake in dogs. Six dogs, equipped with serosal colon electrodes and a jejunal cannula, were randomly assigned to receive sham-CES or CES during the assessment of: (i) gastric emptying of solids, (ii) postprandial intestinal motility, (iii) autonomic functions, and (iv) food intake. We found that (i) CES delayed gastric emptying of solids by 77%. Guanethidine partially blocked the inhibitory effect of CES on solid gastric emptying; (ii) CES significantly reduced intestinal contractility and the effect lasted throughout the recovery period; (iii) CES decreased vagal activity in both fasting and fed states, increased the sympathovagal balance and marginally increased sympathetic activity in the fasting state; (iv) CES resulted in a reduction of 61% in food intake. CES reduces food intake in healthy dogs and the anorexigenic effect may be attributed to its inhibitory effects on gastric emptying and intestinal motility, mediated via the autonomic mechanisms. Further studies are warranted to investigate the therapeutic potential of CES for obesity.

The effect on gastric tone of gastric electrical stimulation with trains of short pulses varies with sites and stimulation conditions

BACKGROUND

Gastric electrical stimulation (GES) can improve symptoms in patients with gastroparesis and induce weight loss in obese subjects.

AIMS

To evaluate the effect on gastric tone of GES under different conditions at different sites of the stomach.

METHODS

Eleven dogs were implanted with a gastric cannula and two pairs of stimulation electrodes (in the middle of the lesser curvature and of the greater curvature, 10 cm from the pylorus). Gastric tone was assessed with a barostat. GES was applied using: (1) Enterra conditions (14 Hz, 5 mA, 0.3 ms, 0.1 s on, 5 s off); (2) modified Enterra conditions (40 Hz, 5 mA, 0.3 ms, 0.1 s on, 5 s off); and (3) implantable gastric stimulation (IGS) conditions (40 Hz, 5 mA, 0.3 ms, 2 s on, 3 s off). Six sessions were performed randomly with each animal on six separate days.

RESULTS

(1) At the lesser curvature, GES with modified Enterra conditions significantly elevated gastric volume from 96.9 +/- 8.3 ml at baseline to 133.9 +/- 11.7 ml (P = 0.015) and a similar effect was observed with IGS (91.3 +/- 7.1 ml vs. 186.3 +/- 27.1 ml, P = 0.013). GES with Enterra conditions had no such an effect. (2) At the greater curvature, GES with Enterra conditions significantly increased gastric volume from basal 94.1 +/- 4.4 ml to 122.1 +/- 11.3 ml (P = 0.032); modified Enterra conditions had the opposite effect (96.5 +/- 9.0 ml vs. 77.4 +/- 11.7 ml, P = 0.025) and no significant effect was observed with IGS conditions.

CONCLUSION

The effects of GES on gastric tone vary with the conditions and sites of stimulation. These findings may help to explain the distinct effects of GES therapy in patients with gastroparesis and obesity.

The effect of sham feeding on neurocardiac regulation in healthy human volunteers

BACKGROUND

Distension and electrical stimuli in the esophagus alter heart rate variability (HRV) consistent with activation of vagal afferent and efferent pathways. Sham feeding stimulates gastric acid secretion by means of vagal efferent pathways. It is not known, however, whether activation of vagal efferent pathways is organ- or stimulus-specific.

OBJECTIVE

To test the hypothesis that sham feeding increases the high frequency (HF) component of HRV, indicating increased neurocardiac vagal activity in association with the known, vagally mediated, increase in gastric acid secretion.

METHODS

Continuous electrocardiography recordings were obtained in 12 healthy, semirecumbent subjects during consecutive 45 min baseline, 20 min sham feeding (standard hamburger meal) and 45 min recovery periods. The R-R intervals and beat-to-beat heart rate signal were determined from digitized electrocardiography recordings; power spectra were computed from the heart rate signal to determine sympathetic (low frequency [LF]) and vagal (HF) components of HRV.

RESULTS

Heart rate increased during sham feeding (median 70.8 beats/min, 95% CI 66.0 to 77.6; P<0.001), compared with baseline (63.6, 95% CI 60.8 to 70.0) and returned to baseline levels within 45 min. Sham feeding increased the LF to HF area ratio (median: 1.55, 95% C.I 1.28 to 1.77; P<0.021, compared with baseline (1.29, 95% CI 1.05 to 1.46); this increase in LF to HF area ratio was associated with a decrease in the HF component of HRV.

CONCLUSIONS

Sham feeding produces a reversible increase in heart rate that is attributable to a decrease in neurocardiac parasympathetic activity despite its known ability to increase vagally mediated gastric acid secretion. These findings suggest that concurrent changes in cardiac and gastric function are modulated independently by vagal efferent fibres and that vagally mediated changes in organ function are stimulus- and organ-specific.

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.

Therapeutic potential of synchronized gastric electrical stimulation for gastroparesis: enhanced gastric motility in dogs

The aim of this study was to determine the effects and mechanism of synchronized gastric electrical stimulation (SGES) on gastric contractions and gastric emptying. The first experiment was designed to study the effects of SGES on antral contractions in four randomized sessions. Sessions 1 (control) and 2 (atropine) were performed in the fasting state, composed of three 30-min periods (baseline, stimulation, and recovery). Sessions 3 (control) and 4 (SGES performed during 2nd 20-min period) were performed in the fed state, consisting of two 20-min periods; glucagon was injected after the first 20-min recording. The second experiment was designed to study the effect of SGES on gastric emptying and consisted of two sessions (control and SGES). SGES was delivered with train duration of 0.5-0.8s, pulse frequency of 40 Hz, width of 2 ms, and amplitude of 4 mA. We found that 1) SGES induced gastric antral contractions in the fasting state. The motility index was 1.3 +/- 0.5 at baseline and 6.1 +/- 0.7 (P = 0.001) during SGES. This excitatory effect was completely blocked by atropine. 2) SGES enhanced postprandial antral contractions impaired by glucagon. 3) SGES significantly accelerated glucagon-induced delayed gastric emptying. Gastric emptying was 25.5 +/- 11.3% without SGES and 38.3 +/- 10.7% with SGES (P = 0.006 vs. control). This novel method of SGES induces gastric antral contractions in the fasting state, enhances glucagon-induced antral hypomotility in the fed state, and accelerates glucagon-induced delayed gastric emptying. The effect of SGES on antral contractions is mediated via the cholinergic pathway.

Long-pulse gastric electrical stimulation at tachygastrial frequency reduces food intake by inhibiting proximal gastric tone

OBJECTIVE

To investigate the effects of long pulse gastric electrical stimulation (GES) at a tachygastrial frequency on food intake, gastric tone and gastric myoelectrical activity (GMA).

MATERIAL AND METHODS

Of twelve dogs implanted with electrodes and a gastric cannula, 6 underwent truncal vagotomy. Stimulus consisted of long pulses with a frequency of 9 cycles/min. Experiment one was performed in all dogs to test for food intake with or without GES. Experiment two on six normal dogs consisted of baseline, GES and recovery periods. Gastric volume and GMA were recorded.

RESULTS

1) GES reduced food intake in both normal (398.5+/-111.7 g versus 573.0+/-97.9 g; p<0.02) and vagotomized dogs (170.6+/-100.4 g versus 401.0+/-97.3 g; p<0.05). 2) Gastric volume was increased with stimulation from 168.4+/-17.7 ml to 301.1+/-34.1 ml (p<0.02 ANOVA) and maintained at 271.8+/-27.6 ml. 3) The percentages of normal slow waves before, during and after GES were 83.3+/-4.6%, 38.0+/-3.5% and 61.0+/-12.5%, respectively (p=0.02 ANOVA).

CONCLUSION

Long-pulse GES at tachygastrial frequency substantially reduces food intake, and is not mediated by the vagal pathway but attributed to relaxation of the stomach and impairment of intrinsic GMA.

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.

Inhibitory effects of sildenafil on gastric motility and gastric slow waves in dogs

The aim of this study was to investigate the effects of sildenafil on gastric motility and gastric slow waves in dogs. The study was performed in healthy dogs and composed of three experiments. The first experiment was designed to study the effects of sildenafil on gastric emptying and gastric slow waves. The second experiment was used to investigate the effects of sildenafil on gastric tone. The third experiment was used to study the effects of sildenafil on postprandial antral contractions. (i) Sildenafil did not alter gastric emptying of liquid. (ii) Sildenafil had no effects on dominant frequency and percentage of normal gastric slow waves. The dominant power of gastric slow waves was, however, significantly reduced with sildenafil (P < 0.02). (iii) Fasting gastric volume with sildenafil was significantly higher than that at baseline (P < 0.0005) or in the control session (P < 0.002). However, the postprandial gastric volume was not altered with sildenafil. (iv) Sildenafil inhibited gastric antral motility. The contraction index was 338.5 +/- 39.99 at baseline and 122.5 +/- 20.3 after the injection of sildenafil (P = 0.003). Sildenafil inhibits fundic tone and antral motility but does not seem to delay gastric emptying of liquid in dogs. The amplitude but not the frequency or regularity of the gastric slow wave is inhibited by sildenafil.

Electroacupuncture accelerates solid gastric emptying and improves dyspeptic symptoms in patients with functional dyspepsia

The aims of this study were to investigate the effects of electroacupuncture (EA) at ST36 and PC6 points on solid gastric emptying and dyspeptic symptoms in patients with functional dyspepsia. Nineteen patients with functional dyspepsia (FD) were involved in the study, consisting of two parts: (1) acute effects of EA on solid gastric emptying in FD patients with delayed gastric emptying and (2) short-term (2-week) effects of EA on symptoms in FD patients with normal gastric emptying. Results were as follows. (1) Ten of the19 patients showed delayed gastric emptying of solids, and acute EA significantly improved delayed gastric emptying; the halftime for gastric emptying was reduced from 150.3+/-48.4 to 118.9+/-29.6 min (P=0.007). (2) In the nine patients with normal gastric emptying, 2-week EA significantly decreased the symptom score, from 8.2+/-3.3 at baseline to 1.6+/-1.1 (P < 0.001) at the end of treatment. We conclude that EA at the ST36 and PC6 points accelerates solid gastric emptying in FD patients with delayed gastric emptying and relieves dyspeptic symptoms in FD patients with normal gastric emptying.

Gastric or intestinal electrical stimulation-induced increase in gastric volume is correlated with reduced food intake

OBJECTIVE

Satiation has recently been shown to be associated with gastric volume or gastric tone. Electrical stimulation has been shown to reduce food intake and increase gastric volume, or reduce gastric tone. The aim of this study was to investigate the correlation between gastric or intestinal electrical stimulation (GES/IES)-induced increase in gastric volume and food intake.

MATERIAL AND METHODS

GES/IES was performed on 14 dogs implanted with electrodes and a gastric cannula. Food intake was measured and gastric volume was assessed using barostat with or without GES/IES.

RESULTS

Food intake was correlated to weight (r = 0.62, p = 0.02) as well as the fasting gastric volume (r = 0.59, p = 0.02). GES/IES reduced food intake (240.8 versus 445.0 g, p < 0.005) and increased gastric volume in the fasting state (263.4 versus 74.4 ml, p < 0.0001). Reduced food intake was correlated to the preprandial gastric volume (r = - 0.58, p = 0.02) and postprandial increase in gastric volume with GES/IES (r = 0.56, p = 0.03). CONCLUSIONS. GES/IES reduces food intake and increases gastric volume measured by barostat. The GES/IES-induced increase in gastric volume (or reduced gastric tone) is correlated with reduced food intake during GES/IES.

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.

Looking to the future: electrical stimulation for obesity

Among all classes of therapies for morbid obesity-behavioral, drugs, devices, and surgery-devices for electrical stimulation are a relatively new approach. This article reviews the history of electrical therapies for the gastrointestinal tract with an emphasis on the development of stimulation for obesity. Based on similar animal work, electrical stimulation of the gastrointestinal tract has been applied to treat morbid obesity much in the way it has been used to treat nausea and vomiting. The current status of gastrointestinal electrical stimulation for the treatment of morbid obesity is reviewed, with an emphasis on human studies. The physics of electrical stimulation and the possible mechanism of stimulation in the gastrointestinal tract, including for the treatment of morbid obesity, are also discussed. Future work on stimulation for obesity offers the opportunity for better understanding of possible mechanisms of action.

Anal electrical stimulation with long pulses increases anal sphincter pressure in conscious dogs

PURPOSE

This study was designed to investigate the effects and mechanisms of anal electric stimulation with long pulses on anal sphincter pressure in conscious dogs.

METHODS

The study was performed after enema in nine healthy female hound dogs and composed of four randomized sessions ("dose"-response, anal electric stimulation only, or with atropine or phentolamine). The anal sphincter pressure was measured by using manometry and quantified by using the area under the contractile curve (mmHg/sec). Anal electric stimulation was performed via a pair of ring electrodes attached to a manometric catheter. The stimulation parameters in all but dose-response sessions included a frequency of 20 ppm, pulse width of 200 ms, and amplitude of 3 mA.

RESULTS

The anal sphincter pressure was 55.7 +/- 6 at baseline and increased by 37 percent to 76.4 +/- 6.5 during electric stimulation (P = 0.009). The increase of anal pressure during stimulation was positively correlated with the stimulation energy (r = 0.395; P < 0.01). The excitatory effect of electric stimulation was sustained for at least 20 minutes. Atropine did not alter anal pressure and did not abolish the excitatory effect of anal electric stimulation on the sphincter. Phentolamine reduced anal pressure from the baseline value of 50.5 +/- 4.7 to 33.1 +/- 5.4 (P = 0.019). The electric stimulation induced increase in anal pressure was dropped from 19 +/- 2.6 to 9.9 +/- 2.8 (P = 0.029) at the presence of phentolamine.

CONCLUSIONS

Anal electric stimulation with long pulses increases anal sphincter pressure in an energy-dependent manner. The alpha-adrenergic but not the cholinergic pathway at least partially mediates the excitatory effect of anal electric stimulation.

Effects and mechanisms of long-pulse gastric electrical stimulation on canine gastric tone and accommodation

Gastric electrical stimulation (GES) has been applied to treat gastroparesis and morbid obesity. The aims of this study were to evaluate the sites of stimulation and the mechanisms of GES on gastric tone and accommodation. Gastric tone and accommodation were evaluated with a barostat in surgically prepared dogs. GES was applied at seven different locations, and gastric tone was assessed at each site. The effect of truncal vagotomy on gastric tone and accommodation and the role of the nitrergic pathway were also evaluated. We have found: 1) GES induced varying degrees of gastric relaxation at all tested locations in normal dogs; 2) Gastric volume was also significantly increased with GES in vagotomized dogs and the change tended to be lower than that of normal animals; 3) Gastric accommodation was reduced during GES in both the normal and vagotomized dogs and the reduction tended to be more in the vagotomized animals; 4) The GES-induced increase in gastric volume was partially abolished by intravenous nitric oxide synthase inhibitor. GES at various sites of the stomach exerts inhibitory effect on gastric tone; the most effective sites are in the antrum along the lesser or greater curvature; the inhibitory effect of GES on gastric tone is partially mediated by the vagal and nitrergic pathway.

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.

Tachygastria induced by gastric electrical stimulation is mediated via alpha- and beta-adrenergic pathway and inhibits antral motility in dogs

BACKGROUND

It is known that tachygastria is associated with gastric hypomotility and retrograde gastric electrical stimulation (RGES) delays gastric emptying and is proposed for treating obesity. The aim was to investigate the effects and mechanisms of RGES on postprandial antral contraction in dogs.

METHODS

Seven dogs were implanted with a gastric cannula and three pairs of gastric serosal electrodes. Antral contractions and gastric myoelectrical activity were recorded immediately after a solid meal, with or without RGES, or with GES on the corpus, or with RGES under administration of propranolol. The stimulus was composed of long pulses with a tachygastrial frequency.

RESULTS

(i) GES at the tachygastrial frequency impaired gastric myoelectrical activity and induced tachygastria (anovaP<0.05). (ii) GES at the tachygastrial frequency suppressed antral contractions (anovaP<0.01) and the effect was stronger with retrograde stimulation than forward stimulation (P<0.05). (iii) GES-induced tachygastria was correlated with antral hypomotility (r=-0.60, P=0.01). (iv) Propranolol and phentolamine abolished GES-induced tachygastria and antral hypomotility.

CONCLUSIONS

Long-pulse RGES at a tachygastrial frequency suppresses postprandial antral contractions, which is attributed to an induction of tachygastria via the alpha- and beta-adrenergic pathway.

Gastric electrical stimulation modulates neuronal activity in nucleus tractus solitarii in rats

Implantable gastric electric stimulation (GES) has been under investigation for the treatment of gastric motor disorders and obesity. However, possible central mechanisms involving the effects of GES on gastric function are unclear. The purpose of this study was to examine the effects of GES with different parameters on neuronal activity in the nucleus tractus solitarii (NTS) of the medulla. Extracellular potentials of single neurons in NTS were recorded in pentobarbital anesthetized, paralyzed, ventilated male rats. GES with four sets of parameters was applied for one minute: GES-A (6 mA, 0.3 ms, 40 Hz, 2 s-on and 3 s-off), GES-B (20 mA, 0.3 ms, 40 Hz, 2 s-on and 3 s-off), GES-C (6 mA, 6 ms, 40 Hz, 2 s-on and 3 s-off), and GES-D (6 mA, 200 ms, 12 imps/min). 35/118 (30%) neurons in NTS were responsive to gastric distension (GD, 20 mmHg, 20 s). Forty-one percent, 67%, 76% and 42% of all the responsive NTS neurons were affected by GES-A, -B, -C and -D, respectively. More NTS neurons with gastric inputs were affected with GES-C (19/25) than with GES-A (11/27, P<0.05) and GES-D (10/24, P<0.05). Maximal excitatory responses (17.9+/-2.6 imp/s) of NTS neurons to GES-C were significantly greater than GES-D (9.7+/-4.8 imp/s, P<0.05), whereas average duration of excitatory response (74.8+/-4.3 s) of NTS neurons to GES-B was significant longer than GES-A (60.3+/-3.3 s). Gastric electrical stimulation primarily has an excitatory effect on NTS neurons receiving input from the stomach; the central neuronal response to GES is enhanced with stimulation using an increased pulse width and/or amplitude. This modulatory effect of GES on the central neurons receiving vagal inputs may contribute to the neural mechanisms of GES therapy for the treatment of patients with obesity and gastric motility disorders.

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.

Inhibitory effects of stress on postprandial gastric myoelectrical activity and vagal tone in healthy subjects

The aim was to investigate gastric myoelectrical activity (GMA) and vagal activity in response to stress. The study was performed in 10 healthy subjects in three sessions (control, relaxation and stress). The control session was composed of 30-min recordings before and 30-min recordings after a test meal. The protocol of two other sessions was similar except that the fasting recording was extended to 60 min and the subjects were continuously watching a horror movie (stress) or guided meditation tape (relaxation) after the 30-min baseline. GMA was recorded using electrogastrography and heart rate variability (HRV) was derived from the electrocardiogram. Meal resulted in a postprandial increase in the dominant frequency (2.91 cpm vs 3.17 cpm, P < 0.007), dominant power (30.0 dB vs 32.5 dB, P < 0.05), and percentage of normal slow waves (79.8%vs 87.4%, P = 0.09). Similar responses were found in the relaxation session. Stress inhibited all these normal postprandial response and reduced the regularity of gastric slow waves (82.0%vs 66.0%, P < 0.01). In addition, spectral analysis of the HRV demonstrated an inhibition of postprandial vagal activity and an increase of postprandial sympathetic activity with stress. Stress has an inhibitory effect on postprandial GMA and this may involve both vagal and sympathetic pathway.