Vagal afferent is involved in short-pulse gastric electrical stimulation in rats

This study investigated the effect of gastric electrical stimulation (GES) on vagal activity and its possible vagal afferent-mediated mechanisms. Sixty rats implanted with gastric serosal electrodes were divided into six groups (control, vehicle, local capsaicin, perivagal capsaicin, systemic capsaicin, and vagotomy). GES with six sets of parameters was performed in the control group; and GES with one set of effective parameters was performed in the other five groups. Spectral analysis of heart rate variability was used to assess vagal activity. Regular gastric slow waves were recorded in the control rats with a frequency of 4.8 cycles/min. Vagotomy significantly reduced the frequency of the gastric slow wave but did not induce dysrhythmia. Capsaicin did not alter the gastric slow wave. Short-pulse (300-microsec) GES significantly increased vagal activity at a frequency four times the intrinsic slow-wave frequency. Stimulation at a lower frequency or with a long pulse (300 msec) had no effect on vagal activity. Vagotomy or capsaicin administered perivagally, systemically, or locally abolished the effect of GES on the vagal activity. GES with short but not long pulses is capable of altering vagal activity. This effect is mediated by capsaicin-sensitive vagal afferent fibers.