Gastric electrical stimulation modulates neuronal activity in nucleus tractus solitarii in rats

Implantable gastric electric stimulation (GES) has been under investigation for the treatment of gastric motor disorders and obesity. However, possible central mechanisms involving the effects of GES on gastric function are unclear. The purpose of this study was to examine the effects of GES with different parameters on neuronal activity in the nucleus tractus solitarii (NTS) of the medulla. Extracellular potentials of single neurons in NTS were recorded in pentobarbital anesthetized, paralyzed, ventilated male rats. GES with four sets of parameters was applied for one minute: GES-A (6 mA, 0.3 ms, 40 Hz, 2 s-on and 3 s-off), GES-B (20 mA, 0.3 ms, 40 Hz, 2 s-on and 3 s-off), GES-C (6 mA, 6 ms, 40 Hz, 2 s-on and 3 s-off), and GES-D (6 mA, 200 ms, 12 imps/min). 35/118 (30%) neurons in NTS were responsive to gastric distension (GD, 20 mmHg, 20 s). Forty-one percent, 67%, 76% and 42% of all the responsive NTS neurons were affected by GES-A, -B, -C and -D, respectively. More NTS neurons with gastric inputs were affected with GES-C (19/25) than with GES-A (11/27, P<0.05) and GES-D (10/24, P<0.05). Maximal excitatory responses (17.9+/-2.6 imp/s) of NTS neurons to GES-C were significantly greater than GES-D (9.7+/-4.8 imp/s, P<0.05), whereas average duration of excitatory response (74.8+/-4.3 s) of NTS neurons to GES-B was significant longer than GES-A (60.3+/-3.3 s). Gastric electrical stimulation primarily has an excitatory effect on NTS neurons receiving input from the stomach; the central neuronal response to GES is enhanced with stimulation using an increased pulse width and/or amplitude. This modulatory effect of GES on the central neurons receiving vagal inputs may contribute to the neural mechanisms of GES therapy for the treatment of patients with obesity and gastric motility disorders.