Effects and Mechanisms of Vagal Nerve Stimulation on Body Weight in Diet-Induced Obese Rats

Background: Vagal nerve stimulation (VNS) has recently been indicated as a novel method for treating obesity. However, the optimal stimulation parameters were unknown and mechanisms were poorly understood. The aim of this study was to investigate the effects of VNS on food intake and body weight in diet-induced obesity (DIO) rats and its possible mechanism involving autonomic functions and gut hormones. Methods: Ten control rats and 16 DIO rats were chronically implanted with one pair of electrodes in the subdiaphragmatic vagal nerve. VNS with different stimulation parameters and sham-VNS were performed in control rats. In a chronic study, 8 DIO rats were applied with VNS and another 8 DIO rats were treated with sham-VNS for 4 weeks. Food intake, body weight, gastric emptying, heart rate variability (HRV), and gut hormones were evaluated. Results: In DIO rats, the food intake (p < 0.001) and body weight (p < 0.001) were significantly decreased in the VNS group, compared with the sham-VNS group. VNS decreased the sympathovagal ratio (p = 0.003) and increased vagal activity (p = 0.032) assessed from the spectral analysis of HRV. It also increased plasma levels of glucagon-like peptide-1 (p = 0.012), polypeptide YY (p = 0.008), and pancreatic polypeptide (p = 0.008) in DIO rats. Physiologically, VNS delayed solid gastric emptying (p < 0.001) and increased gastric volume (p = 0.004). Conclusion: VNS with appropriate parameters reduced food intake and body weight by delaying gastric emptying mediated via the enhancement of vagal activity and release of anorexigenic hormones.