Effects of atropine on the central mechanism of deglutition in anesthetized sheep.

The role of acetylcholine in the central mechanism of swallowing remains a matter of debate. The aim of this work, conducted in sheep, was to assess the effects of anti-muscarinic drugs (mainly atropine) on the activity of peripheral muscles involved in the oropharyngeal and esophageal phases of swallowing, and on that of dorsal medulla interneurons which program swallow-induced esophageal contractions and therefore belong to the so-called central pattern generator. Our results were obtained in anesthetized animals by means of electromyographic and manometric recordings of peripheral muscle contractions associated with microelectrode recordings of medullary interneuron discharge. They show that both interneuron discharge and primary esophageal contractions that follow the oropharyngeal component of swallowing were suppressed under atropine (0.1--0.5 mg/kg). In contrast, atropine did not impede the swallowing oropharyngeal component, the secondary peristalsis and the "deglutitive inhibition," which affects the esophageal motility during the oropharyngeal phase of swallowing. In conclusion, muscarinic receptors (probably not those of M(1)type) appear to control the primary peristalsis, but neither the secondary peristalsis nor the deglutitive inhibition.