A Comparison of Generalized Reflex Myoclonic Reactions Elicitable in Cats Under Chloralose Anesthesia and Under Strychnine

Abstract

Some neurophysiological correlates of the generalized motor reactions (reflex myoclonus) which can be evoked in cats under chloralose anesthesia were detd. The stimulus (light, sound, touch, etc.) must be suddenly applied; single electrical shocks to peripheral nerves must excite Lloyd''s group II fibers to be effective; group III fibers may also be effective. In non-curarized animals the reaction occurs almost simultaneously in widely separated muscles after a relatively long latency. Although the movement is characteristically one of flexion, both flexors and extensors contract together. The late generalized reaction occurs independently of early segmental reflexes. In curarized prepns. nerve excitation arises in the forelegs before it arises in the hindlegs. In general, the latency is longer for more caudally applied stimuli; if 2 stimuli are presented through the same neural segments, max. facilitation occurs simultaneously, but if they enter the central nervous system through widely separated segments, the caudal must precede the rostral. The reaction is enhanced by parenteral-ly admn. strychnine and is abolished caudal to an acute transec-tion of the spinal cord. In contrast, during the generalized convulsive reactions which can be evoked in spinal strychninized cats, the stimulated segments respond 1st, and spread to distant segments occurs only thereafter. Excitation of group II peripheral nerve fibers is necessary for these effects. Results are interpreted to indicate that, whereas strychnine enchances rostral and caudal spread of intersegmental reflexes throughout the spinal cord, the reflex myoclonic reaction evoked under chloralose is due to a long reflex circuit involving supraspinal structures.