Effects and Mechanisms of Vagal Nerve Stimulation on Food Intake and Body Weight in Rats Fei Dai 1, Yong Lei 1 and J D Z Chen 1, 2 1 Veterans Research and Education Foundation, VA Medical Center, Oklahoma city, OK 2 Division of Gastroenterology, University of Texas Medical Branch, Galveston, TX

Obesity 1/3 obese 2/3 obese or overweight 400,000 deaths 147 billion cost Prevalence is still increasing

Electrical Stimulation for Obesity We Eat We Exercise What can this do for us? ?

Vagal nerve stimulation for obesity VNS of 5000Hz to block vagal activity Significant weight loss in open label studies Controlled clinical trial did not reach endpoint

Aims To study the feasibility of VNS at low frequency for treating obesity and possible mechanisms of action in a rodent model of obesity

Searching for effective VNS Normal rats (N-10) Food intake test with VNS during eating Different parameters test VNS1 (40Hz, 2s-on and 3s-off, 0.2ms, 6mA), VNS2 (40Hz, 2s-on and 3s-off, 0.6ms, 6mA), VNS3 (40Hz, continuous, 0.2ms, 6mA), VNS4 (40Hz, continuous, 0.6ms, 6mA 10 days/each parameter set

** * * * Sham-VNS vs. VNS p<0.001 VNS reduced food intake VNS3 (40Hz, continuous, 0.2ms, 6mA),

Experimental Procedure 4 wk VNS/sham VNS Autonomic function measure (HRV) Gastric emptying/volume tests GLP-1, PYY and ghrelin Pancreatic polypeptide

VNS reduced food intake in DIO rats (4 weeks ) * * ** * Sham-VNS vs. VNS p<0.001 p<0.001

25% reduction in weight with VNS of 4 wks * Sham-VNS vs. VNS p<0.001 * * * * Total 4 weeks Sham-VNS vs. VNS p<0.001 VNS decreased weight in DIO rats

VNS delayed gastric emptying 40% decrease P<0.001

VNS increased gastric volume Substantial decrease p=0.004 VNS Sham-VNS

VNS increased plasma PP

VNS “normalized” autonomic function VNS inhibited sympathetic activity and increased vagal activity P=0.246 P=0.005 P=0.003 P=0.425 P<0.001 P=0.462 P=0.024 P=0.003 P=0.032

Ghrelin: reduced in obesity but not altered by VNS

GLP-1: increased with VNS

PYY: increased with VNS

Conclusions  VNS at a low frequency of 40Hz reduces food intake and body weight in DIO rats  Possible mechanisms of action  Aterations in autonomic functions  Inhibited motility  Increase in GLP-1 and PYY

VNS in obese rats 16 rats randomly divided into two groups: ♦ 8 rats with VNS3 (40Hz, continuous, 0.2ms, 6mA) ♦ 8 rats with sham-VNS for 4 week Experiment 2: Effects of optimal VNS parameter on food intake and body weight in DIO rats

Experimental protocols Experiment 3: Effects of VNS on heart rate variability (HRV) in DIO rats  A special amplifier was used to record the electrocardiogram (ECG) via three cutaneous electrodes.  The ECG was recorded for 30 min at baseline and 30 min after VNS3/sham-VNS in the fasting state and postprandial state.  The sympathovagal activity was assessed using spectral analysis of the HRV signal.

Experimental protocols ♦ The rats were fasted for a period of 24 hours and given 1.5g high fat food. ♦ During the 90-min postprandial period, 8 DIO rats were applied with VNS3, 8 rats applied with sham- VNS. ♦ Ninety minutes after the feeding, the gastric volumes were measured and the content of the stomach were removed for the assessment of gastric emptying. Experiment 4: Effects of VNS on solid gastric emptying and gastric volumes in DIO rats

Experimental protocols ♦ After being fasted for 12 h, 8 SD rats were received sham-VNS, 8 DIO rats were applied with VNS3, 8 DIO rats applied with sham-VNS for 2 hours; during 2 h without food in the restrainers. ♦ After stimulation, blood sample was collected from the tail vein. Plasma Ghrelin, GLP-1, PYY and PP were measured on duplicate samples using commercially available kits. Experiment 5: Effects of VNS on gut hormones in DIO rats