Activation of visceral thin-fiber afferents increases respiratory output in cats.

Respiratory responses to chemical activation of thin-fiber afferents from the stomach and the gallbladder were measured in anesthetized cats. Capsaicin or bradykinin applied to the serosal surface of either the stomach or the gallbladder elicited increases in breathing and phrenic nerve activity. Transection of the cervical vagi or the carotid sinus nerves had no effect on these responses. However, the respiratory responses to visceral stimulation were abolished by bilateral transection of the splanchnic nerves. We conclude that activation of thin-fiber afferents from the stomach and gallbladder causes a reflex increase in respiratory output. The initial afferent limb of this reflex is via the splanchnic nerves.