Neural mechanisms of the reflex inhibition and excitation of gastric motility elicited by acupuncture-like stimulation in anesthetized rats

The effects of acupuncture-like stimulation of the various segmental areas on gastric motility were examined in anesthetized rats. An acupuncture needle (diameter 340 μm) was inserted into the skin and underlying muscles at a depth of 4–5 mm and was twisted right and left once every second for 60 s. Gastric motility in the pyloric region was measured with the balloon method. Gastric motility was inhibited by acupuncture-like stimulation applied to the abdomen and lower chest region, and was often excited when the limbs were stimulated, in all cases in which stimuli were delivered to the skin and muscles, the skin alone, and the underlying muscles alone. The inhibitory gastric response to abdominal stimulation was accompanied by an increase in the activity of the gastric sympathetic efferent nerve and was abolished by severance of either the sympathetic nerve branches to the stomach or the lower thoracic spinal nerves. The abdominal stimulation enhanced the activity of the lower thoracic spinal afferent nerves. The excitatory gastric response to hindpaw stimulation was accompanied by an increase in the activity of the gastric vagal efferent nerve and was abolished by severance of either the bilateral vagi or the femoral and sciatic nerves. The hindpaw stimulation enhanced the activity of the femoral and sciatic afferent nerves. In the spinalized animals, the inhibitory gastric response elicited by abdominal stimulation was present, and the hindpaw stimulation did not produce any gastric response. We conclude that the inhibitory gastric response elicited by acupuncture-like stimulation of the abdomen is a reflex response. Its afferent nerve pathway is composed of abdominal cutaneous and muscle afferent nerves, the efferent nerve pathway is the gastric sympathetic nerve, and its reflex center is within the spinal cord. The excitatory gastric response elicited by acupuncture-like stimulation of a hindpaw is also a reflex response. Its afferent nerve pathway is composed of hindpaw cutaneous and muscle afferent nerves, the efferent nerve pathway is the gastric vagal efferent nerve, and its reflex center requires the presence of the brain. Furthermore, the excitatory and the inhibitory gastric reflex responses were not influenced by i.v. administration of naloxone (0.4–4 mg/kg), suggesting that endogenous opioids are not involved in the present reflexes.