Studies on opossum esophageal longitudinal muscle function

To characterize the neuromuscular mechanisms responsible for control of esophageal longitudinal muscle function, in vivo and in vitro preparations of the intact opossum esophagus were studied using both miniature strain gauge transducers and a specially designed transducer that measured longitudinal axis movement of the entire esophagus. Esophageal shortening in response to swallowing was abolished by atropine in virtually all animals, whereas in 4 of 11 animals there was a significant noncholinergic component to shortening evoked by vagal efferent nerve stimulation. Balloon distention evoked atropine-sensitive esophageal shortening due to contractions occurring at and below the site of distention, which was then followed, upon balloon deflation, by noncholinergic longitudinal muscle contractions aboral to the balloon. A similar two-component response was recorded in response to electrical stimulation or balloon distention in vitro. Although the shortening occurring during stimulation was atropine sensitive, both components could be activated in the presence of tetrodotoxin. These studies indicate that the primary functional innervation to the opossum longitudinal muscle esophagus is cholinergic; noncholinergic and myogenic mechanisms are also demonstrable, but it is unclear whether they have a significant functional role.