Central neuronal mechanisms of intestinal electrical stimulation: effects on duodenum distention-responsive (DD-R) neurons in the VMH of rats

Intestinal Electrical Stimulation Enhances Release of Postprandial Incretin Hormones Via Cholinergic Mechanisms

INTRODUCTION

Intestinal electrical stimulation (IES) has been reported to reduce body weight and improve glucose tolerance in obese and diabetic rats. Our study aimed to investigate possible IES mechanisms involving incretin hormones using intraduodenal glucose infusion in rats. We hypothesized that the enhanced release of postprandial glucagon-like peptide-1 (GLP-1) at early phase by IES was mediated through neuro/paracrine mechanisms involving the vagal nerve and glucose-dependent insulinotropic peptide (GIP).

METHODS

Fifteen normal male Sprague-Dawley rats chronically implanted with duodenal electrodes for IES, and an intra-duodenum catheter for the infusion of glucose were studied in a series of sessions with IES of different parameters with and without atropine and M3 receptor antagonist. Blood samples were collected via the tail vein for the measurement of blood glucose, and plasma GLP-1, and GIP.

RESULTS

(1) Compared to sham-IES, IES of 0.3 ms reduced blood glucose by 16.5-28.4% between 30 and 120 min (all time points p < 0.05), and IES of 3-ms reduced blood glucose at 60 (12.6%) and 90 min (11.8%). IES of 0.3 ms showed a greater hypoglycemic effect than 3 ms (p = 0.024) at 30 min. (2) IES elevated plasma GLP-1 with 0.3 ms (p = 0.001) and with 3 ms p = 0.03). (3) IES substantially elevated plasma GIP with 0.3 ms (p = 0.002) and with 3 ms (p < 0.001). (4) Pretreatment of atropine and the M3 receptor antagonist 4-DAMP blocked the effects of IES on GLP-1, GIP, and blood glucose.

CONCLUSIONS

IES reduces postprandial blood glucose by enhancing the release of GLP-1 and GIP mediated via the cholinergic mechanism.

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.

Gastric stimulation for weight loss

The prevalence of obesity is growing to epidemic proportions, and there is clearly a need for minimally invasive therapies with few adverse effects that allow for sustained weight loss. Behavior and lifestyle therapy are safe treatments for obesity in the short term, but the durability of the weight loss is limited. Although promising obesity drugs are in development, the currently available drugs lack efficacy or have unacceptable side effects. Surgery leads to long-term weight loss, but it is associated with morbidity and mortality. Gastric electrical stimulation (GES) has received increasing attention as a potential tool for treating obesity and gastrointestinal dysmotility disorders. GES is a promising, minimally invasive, safe, and effective method for treating obesity. External gastric pacing is aimed at alteration of the motility of the gastrointestinal tract in a way that will alter absorption due to alteration of transit time. In addition, data from animal models and preliminary data from human trials suggest a role for the gut-brain axis in the mechanism of GES. This may involve alteration of secretion of hormones associated with hunger or satiety. Patient selection for gastric stimulation therapy seems to be an important determinant of the treatment’s outcome. Here, we review the current status, potential mechanisms of action, and possible future applications of gastric stimulation for obesity.

A potential and novel therapy for obesity: "appendix" electrical stimulation in dogs

BACKGROUND

Intestinal electrical stimulation (IES) has been introduced as a potential therapy for obesity. However, it is unknown whether the effects of IES on gastrointestinal motility and food intake are location-specific. The aim of this study was to assess the effects of "appendix" (cecum in dog) electrical stimulation (AES) on gastric tone, gastric emptying, and food intake in dogs.

METHODS

Twelve healthy dogs were used in three experiments. In experiments 1 and 2, gastric tone and food intake were studied in six dogs implanted with a gastric cannula and one pair of stimulation electrodes in the "appendix." Experiment 3 was performed to study gastric emptying in six dogs with a duodenal cannula and one pair of stimulation electrodes in the "appendix."

RESULTS

(1) AES resulted in proximal gastric distention, with gastric volume increased from 114.9 ± 10.7 mL at baseline to 301.7 ± 37.1 mL during AES (p = 0.001), and the effect was completely blocked by a nitric oxide synthase inhibitor. (2) Gastric emptying was delayed at 90 min from 69.8 ± 9.5% in the control session to 15.2 ± 3.6% in the AES session (p = 0.002). 3) AES reduced food intake (average daily intake over a 1-week period) by 55.4% (550.4 ± 17.6 g at control vs. 245.7 ± 17.1 g with AES, p < 0.001).

CONCLUSIONS

AES reduces gastric tone via the nitrergic pathway, delays gastric emptying, and inhibits food intake in healthy dogs. These data suggest the therapeutic potential of AES for obesity. Additionally, AES is technically more feasible than electrical stimulation of the stomach or duodenum because a stimulator with electrodes may be placed into the appendix via colonoscopy.