Central effects of succinylcholine and decamethonium on monosynaptic reflexes

¹ Department of Anatomy, School of Medicine, University of California at Los Angeles; and Long Beach Veterans Administration Hospital, Long Beach, California

Observations have been made in cats upon central mechanisms responsible for reduction in monosynaptic responses of triceps surae motoneurons following intravenous injection of decamethonium or succinylcholine. Two-thirds of extensor motoneurons show an increase in random firing under the influence of these drugs. Interference by this enhanced discharge with potentials induced in the ventral root and horn by stimulation of the ventral root was demonstrated. Monosynaptic responses are reduced in some motoneurons which are not caused to fire randomly with SCh injection. Depression of the monosynaptic reflex by SCh is attenuated in animals treated with dihydro-beta-erythroidine or strychnine, suggesting the presence of inhibition in the SCh effect. Monosynaptic reflexes of flexor muscles are reduced by SCh. This indicates that inhibition by the enhanced discharge of flower-spray afferents is not requisite. Supraspinal levels are not essential for appearance of the SCh effect.