Classification of neuromuscular blocking agents in a new neuromuscular preparation of the chick in vitro

Abstract

A neuromuscular preparation of the chick is described: 1. 1. The sciatic nerve-tibilis anterior muscle preparation of the 2–10 days old chick fulfils all criteria of an assay preparation and differentiates between curare-like and decamethonium-like agents. 2. 2. The preparation responds to supramaximal nerve stimuli with twitches, which are of constant height during 6–8 hr. The twitch amplitude is decreased by curare-like drugs in concentrations of 0.5 μg/ml and more. This effect is dose-dependent. 3. 3. The preparation responds to the administration of decamethonium-like drugs with a slow contracture, the force and velocity of which is dose-dependent, and a decrease in the height of the twitch. The time curve of these two effects of decamethonium-like drugs is not the same. Threshold dose for contractures is about 0.1 μg/ml. 4. 4. Curare-like compounds in doses of times threshold and more antagonize or prevent the slow contractures caused by decamethonium-like drugs, dose-dependently. 5. 5. The effects are easily reversible and also reproducible in the same preparation during a day. 6. 6. A resemblance is suggested between the chick slow fibre response and the responses of the cat extra-ocular muscle and the mammalian intrafusal muscle to decamethonium-like compounds; the possibility of a presynaptic site of action apart from a post-synaptic one of the decamethonium-like drugs in the chick muscle is postulated.