Mechanisms of Stepping Rhythm Formation in Decerebrated and Chronic Spinal Cats under Epidural Stimulation

摘要

A study was made of the stepping pattern formation in decerebrated and in chronic spinal cats dur-ing epidural stimulation (ES). The hindlimb stepping performance depended on the parameters of ES and affer-ent input. At non-optimal ES parameters, no stepping was induced, only muscle reflexes followed the stimula-tion rhythm. Optimized ES (3-5 Hz, 50-100 UA for decerebrated and 20-30 Hz, 150-250 A for spinal cats)evoked coordinated stepping movements at a natural rate (0.8-1 Hz) accompanied by electromyographic burstactivity of the corresponding muscles. In decerebrated cats, the bursts are formed owing to modulation of earlyresponses and the late polysynaptic activity. In chronic spinal cats, this process is mainly due to amplitude mod-ulation of the early responses. Formation of the stepping pattern in decerebrated cats involves spinal interneu-rons responsible for the polysynaptic activity, which allows its correction based on processing the afferent sig-nals. Activation of this system in chronic spinal cats can be realized by afferent stimulation alone, without ES.