Abstract

The effects of succinylcholine, d- tubocurarine, edrophonium and neostigmine on the superior rectus and tibialis anterior muscles were simultaneously determined in the cat. Succinylcholine increased the superior rectus muscle tension but decreased the twitch response of both muscles. A smaller dose of succinylcholine was required to depress the tibialis anterior twitch response. The injection of d-tubocurarine also depressed the twitch response of the superior rectus and tibialis anterior muscles, and the latter was more sensitive to the action of d-tubocurarine. In 50% of the animals, d-tubocurarine increased the superior rectus muscle tension. Edrophonium increased the twitch response of both muscles and the tension of the superior rectus muscle. Neostigmine often increased the superior rectus muscle tension and always increased the twitch response of this muscle. The effect on the tibialis anterior muscle twitch response was either a decrease, an increase or a decrease followed by an increase. Following depression of the twitch response of the superior rectus and tibialis anterior muscles by d-tubocurarine, the injection of edrophonium or neostigmine restored the twitch response to the control level. However, the superior rectus muscle tension was elevated. Both edrophonium and neostigmine increased the magnitude of response to succinylcholine.