A CHARACTERIZATION OF THE STIMULATION OF MAMMALIAN MUSCLE SPINDLES BY SUCCINYLCHOLINE

¹ Department of Pharmacology, University of Illinois College of Medicine, Chicago 12, Illinois

The stimulation of the stretch receptors in muscle spindles of the lateral or medial gastrocnemius muscle of cats by succinylcholine (SCh) was characterized in functionally single sensory nerve fiber preparations.

There was no tachyphylaxis with the repeated intravenous administrations of a constant dose of SCh.

The log dose-peak frequency response curve obtained for SCh had a skewed sigmoid shape.

The infusion of SCh at rates of 200 or 400 µg/kg/minute produced a gradual rise in the discharge frequency to a plateau level which was a constant for the particular infusion employed. With greater infusion rates (800 or 1600 µg/kg/minute) an initial high frequency discharge occurred which produced a peak in the infusion response curve; the discharge frequency then dropped to a constant plateau level.

Pretreatment with physostigmine potentiated the response of both a single rapid injection and an infusion of SCh; this was manifested by a decrease in the onset time of the response, an increased peak frequency, and a prolonged decay time for the response.