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 (1.0–1.5 cm apart) was sutured onto the serosal surface of the lesser curvature of the stomach. GES with four sets of parameters was applied for 1 min: 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), GES-D (6 mA, 200 ms, 12 pulses/min). 62/158 (39%) spinal neurons responded to GD (20, 40, 60 mmHg, 20 s. 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 (2.0 μg/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.