Neural mechanisms of reflex facilitation and inhibition of gastric motility to stimulation of various skin areas in rats.

1. Experiments were performed on chloralose-urethane anaesthetized rats to determine the involvement of extrinsic gastric autonomic nerves in reflex facilitation and inhibition of gastric motility when mechanical nociceptive stimulation was delivered to either hind paw or abdominal skin, respectively. 2. After bilaterally sectioning the splanchnic nerves in vagal intact animals, the reflex facilitation of gastric motility produced by hind paw stimulation persisted, but the reflex inhibition previously produced by abdominal skin stimulation disappeared. 3. Hind paw stimulation increased efferent activity of the gastric branch of the vagus nerve, but stimulation of abdominal skin had little influence. 4. Bilateral vagotomy in splanchnic nerve intact animals did not influence the gastric reflex inhibition by abdominal skin stimulation, but either abolished gastric reflex facilitation produced by hind paw stimulation or reversed the reflex facilitation response to slight reflex inhibition. 5. Efferent activity of the gastric sympathetic nerve was greatly increased by abdominal skin stimulation, and was either slightly increased or not influenced by hind paw stimulation. 6. It was concluded that reflex increase of efferent activity of the gastric vagi was responsible for the gastric motility facilitation produced by hind paw stimulation, and also that reflexly increased efferent activity of the gastric sympathetic nerves resulted in gastric motility inhibition produced by abdominal skin stimulation. It is suggested efferents are inhibitory. 7. After spinal transection at the cervical level, the reflex facilitation of gastric motility previously produced by stimulation of a hind paw was completely abolished, or reversed to slight reflex inhibition, while reflex inhibition of gastric motility produced by stimulation of abdominal skin remained. It was concluded that the gastric reflex inhibition was a spinal reflex. 8. Interaction between reflex facilitation and inhibition of gastric motility during simultaneous stimulation of both hind paws and abdominal skin was observed as partial cancellation of each effect by the other. However, sympathetic reflex inhibition of gastric motility seemed to be much stronger than the vagal reflex facilitatory effect.