Some pharmacological properties of neuromuscular transmission in the oviduct of the locust, Locusta migratoria

The effects of various pharmacological agents on neurally evoked contractions of the visceral muscles of the oviduct of Locusta migratoria have been examined. The pentapeptide, proctolin, at low concentrations (10−11 M−10−10 M), induced an increase in the amplitude of neurally evoked contractions and basal tonus, and induced the appearance and increased the frequency of myogenic contractions. Glutamate, at 10−4 M, produced a small transient contraction which in some preparations was accompanied by a reduction in amplitude of neurally evoked contractions. Octopamine, at 10−6 M, reduced the amplitude of neurally evoked contractions and also resulted in a relaxation of the muscles. The octopaminergic effects were inhibited by the α‐aminergic antagonist phentolamine. Neurally evoked contractions were unaffected by dopamine, 5‐HT or the acetylcholine receptor antagonists atropine and hexamethonium. Acetylcholine increased the amplitude of neurally evoked contractions, but only at the high concentration of 10−3 M. The possible role of proctolin and glutamate as excitatory neuro‐transmitters and the inhibitory action of octopamine is discussed.