Involvement of gastrointestinal mechano- and intestinal chemoreceptors in vagal reflexes: an electrophysiological study.

The role of gastrointestinal mechanoreceptors and intestinal chemoreceptors in the genesis of vago-vagal reflexes was assessed by recording single vagal efferent fibre discharge in the urethane-anaesthetized ferret during procedures known to activate discrete populations of gastrointestinal afferent fibres. Distension of the stomach, duodenum and jejunum was used to activate mechanoreceptors while perfusion of the intestinal loops with various chemical solutions was used to activate mucosal chemoreceptors. Mechanical stimulation of the stomach and/or intestine was effective in modulating vagal efferent discharge in 90% of units tested. The response (either excitation or inhibition of efferent firing) was characterized by its short-latency (less than 1 s), slow-adaptation, and rapid return on removal of the stimulus. In contrast, chemical stimulation was much less potent evoking clear-cut responses in only 26 of the 109 efferent units. Luminal HCl was the most effective stimulus accounting for 81% of the efferent responses although these were of long-latency (greater than 1 min), gradual in onset and poorly maintained. Other efferent responses to HCl and hypertonic saline were characterized by a long-latency, sudden increase in discharge associated with the prodrome of vomiting. We conclude that while the mechanosensitive afferent input is well represented in terms of the genesis of vagal reflexes, the chemosensitive afferent input may be more important in behavioural aspects of visceral stimuli like vomiting.