Functional Maps of the Intact and Transected Lumbosacral Spinal Cord  in the Decerebrate Cat Using Subdural Electrical Stimulation

Patterson, Jacqueline

doi:https://doi.org/10.21985/n2-s85y-g089

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Functional Maps of the Intact and Transected Lumbosacral Spinal Cord in the Decerebrate Cat Using Subdural Electrical Stimulation

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Electrical spinal cord stimulation is an emerging treatment for spinal cord injury that can improve walking and bladder control, among many other functions. While the anatomical location of the motor pools for muscles involved in locomotion in the lumbosacral cord has been identified, the map of the functional output of subdural electrical stimulation of the lumbosacral cord in both the intact and transected states is still relatively unknown. This represents a significant gap in knowledge in spinal cord injury rehabilitation. Our first goal was to determine what hindlimb muscles are activated by subdural electrical stimulation of the intact lumbar spinal cord of the cat. Our second goal was to determine how those patterns of activation are affected by transection. In eight decerebrate cats with intact spinal cords, eight locations were stimulated starting from the caudal portion of lumbar segment L3 to the border of sacral segments S1 and S2. Stimulation was repeated 15 times at each location at 1 Hz with stimulation amplitudes high enough to evoke muscle responses without causing tissue injury. Electromyography (EMG) was measured in nine hindlimb muscles: tibialis anterior, soleus, lateral gastrocnemius, medial gastrocnemius, sartorius, vastus lateralis, biceps femoris posterior, gluteus medius, and pectineus. EMG peak to peak amplitude of the short-latency response (presumably monosynaptic), and rectified integrated EMG of the long latency response were used to assess muscle response. The spinal cord was then transected above L3, and this protocol was then repeated. In the intact cord, for most muscles, the most effective stimulus was at or near the motor pool. However, some muscles, including the sartorius, were also strongly activated outside of their motor pools. After transection, there was an overall significant change in the responses at both short and long latencies. On an individual muscle basis, the intact and transected responses largely overlapped at earlier latencies, but during the longest latency window, a few muscles had significant differences between the intact and transected responses at multiple stimulation locations. These results suggest that subdural electrical stimulation in the intact cord results in muscle activity that largely aligns with but is broader than the motor pools, and that changes in the acute transected cord. Further research is needed to understand how the maps are affected by chronic spinal cord injury.

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