STUDIES ON OPOSSUM ESOPHAGEAL LONGITUDINAL MUSCLE FUNCTION

To characterize the neuromuscular mechanisms responsible for control o f esophageal longitudinal muscle function, in vivo and in vitro prepar ations of the intact opossum esophagus were studied using both miniatu re strain gauge transducers and a specially designed transducer that m easured longitudinal axis movement of the entire esophagus. Esophageal shortening in response to swallowing was abolished by atropine in vir tually 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 dist ention, which was then followed, upon balloon deflation, by noncholine rgic longitudinal muscle contractions aboral to the balloon. A similar two-component response was recorded in response to electrical stimula tion or balloon distention in vitro. Although the shortening occurring during stimulation was atropine sensitive, both components could be a ctivated 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 a lso demonstrable, but it is unclear whether they have a significant fu nctional role.