Neural mechanism of acupuncture-induced gastric relaxations in rats.

Acupuncture has been used to treat gastrointestinal symptoms in China for more than 3000 years. However, the mechanism of the beneficial effects of acupuncture remains unknown. Strain gauge transducers were implanted on the serosal surface of the stomach to record circular muscle contractions in thiobutabarbital-anesthetized rats. Acupuncture on the right lower abdomen caused a transient relaxation of the stomach. Acupuncture-induced gastric relaxations were abolished by guanethidine, propranolol, splanchnic ganglionectomy, spinal cord transection, and spinomedullary transection. In contrast, N(G)-nitro-L-arginine, phentolamine, truncal vagotomy, and pontomedullary transection had no effect. Acupuncture increased the number of c-Fos immunopositive cells at the ventrolateral medulla (VLM). It is concluded that acupuncture-induced gastric relaxations are mediated via the somatosympathetic reflex. Its afferent limb is composed of abdominal cutaneous and muscle afferent nerves. Its efferent limb is the gastric sympathetic nerve and the reflex center is within the medulla. VLM neurons may play an important role in mediating this reflex.