Weight-bearing hindlimb stepping in treadmill-exercised adult spinal cats.

Hindlimb locomotion on a motor-driven treadmill was studied in 5 cats spinalized at a low thoracic level adults. Six months after surgery, the cats were anesthetized and implanted for electromyographic (EMG) and force recordings in hindlimb muscles. For the last 5 months of the spinalization period, the hindlimbs of each cat were exercised daily for 30 minutes on a treadmill. Data were collected during hindlimb locomotion on a treadmill across the entire range of speeds each cat could accommodate. All trials were filmed (100 frames/s) for kinematic analysis. EMG data were recorded from the soleus (Sol), medial gastrocnemius (MG), tibialis anterior (TA) and extensor digitorum longus (EDL). Forces were recorded in vivo from the Sol and MG tendons. All cats could sustain full weight-bearing stepping without the need for mechanical stimulation of the tail. Although the general stepping pattern of the spinal cats was remarkably similar to that of normal cats, several key differences were identified. Compared to normal cats, the adult spinal cats walked at a lower range of speeds and exhibited a longer swing phase duration. The Sol produced forces and displayed activation periods comparable to those observed in normal cats. The MG of adult spinal cats, however, produced lower forces and had a later onset of activation in comparison to normal cats. Each of the muscles in all spinal cats exhibited tremor during stepping. These results suggest that there were limitations in the activation levels of some hindlimb flexor and extensor muscles during treadmill locomotion. These data further suggest that, in normal cats, accommodation to treadmill speed is accomplished by modulating supraspinal input to the lumbar spinal cord while leaving many of the timing details to be regulated by lumbar spinal networks.

Reflex conditioning in a spinal man.

A man with a completely transected spinal cord and a spastic neurogenic bladder was conditioned to void upon the presentation of an external stimulus. A classical conditioning paradigm was employed in which strong abdominal shock (unconditioned stimulus) was paired with an initially neutral mild electrical stimulation of the thigh (conditioned stimulus; CS). After the pairing trials, a reliable conditioned response of urination was elicited by the CS alone. The conditioned response did not extinguish over time, and the procedure left the bladder with clinically safe residual amounts of urine. Practical implications of the conditioning technique for the treatment of spastic neurogenic bladder conditions in spinally injured patients are discussed, as is the theoretical significance of conditioning at the reflex level in the absence of cortical involvement.