Effects of drugs and electrical field stimulation on isolated muscle strips from rabbit pharyngoesophageal segment

Muscle activity of isolated muscle strips from the middle pharyngeal constrictor, the inferior pharyngeal constrictor, the cricopharyngeal muscle, and the cervical esophagus of the rabbit was studied in organ baths in response to drugs and electrical field stimulation. These muscles of the pharyngoesophageal segment seem to lack an autonomic adrenergic and cholinergic innervation, as determined by responses to specific drugs. The nerve-evoked contractile responses of the two lower muscles of the segment were almost completely abolished by the curarelike drug gallamine, suggesting a somatic cholinergic nerve supply. However, in the two upper muscles, the major part of the response was resistant to gallamine, which suggests involvement of non-adrenergic, nonmuscarinic, nonnicotinic receptors in the transmission of nerve impulses in these muscles. These results suggest a differential innervation of the upper and lower pharyngeal muscles.