Modulation of vagal efferent fibre discharge by mechanoreceptors in the stomach, duodenum and colon of the ferret.

1. A single-fibre-dissection technique was used to investigate the reflex modulation of vagal efferent fibre discharge by afferent fibres from various parts of the gastrointestinal tract of the urethane-anaesthetized ferret. 2. All but four of the 168 efferent fibres isolated in this study were spontaneously active. The majority of these had discharge frequencies of less than 6 spikes/sec. 3. All the efferent units received an afferent input from mechanoreceptors in the stomach. Two main types of response to gastric distension were seen: (i) an increase in efferent discharge and (ii) a decrease or complete suppression of efferent discharge. 4. The vagal efferent discharge was also modulated by duodenal and colonic distension, with the major effect being one of inhibition. 5. Bilateral vagotomy completely abolished the response to gastric distension in 68% of the units tested. The response to colonic and duodenal distension, however, was relatively unaffected by vagotomy. Thus the vagus provides the major afferent pathway from the stomach to these vagal efferent fibres, whilst the major input from the duodenum and colon is via a non-vagal pathway. Both vagal and splanchnic afferents therefore converge on to the vagal nucleus. 6. The destinations of these vagal efferent fibres and their possible functions are discussed.