Striking functional characteristics of the lumbar and sacral neuronal circuitries for stepping in the in vivo adult spinal rat

Society for Neuroscience Chicago Nanosymposium Advances in SCI Research and Plasticity

Authors: *P. SHAH1, C. PRESTON1, H. ZHONG2, R. R. ROY2, V. R. EDGERTON2, Y. P. GERASIMENKO3; 1Stony Brook Univ., Stony Brook, NY; 2Univ. of California Los Angeles, Los Angeles, CA; 3Pavlov Inst. of Physiol., St Petersburg, Russian Federation

We recently demonstrated that electrically enabling motor control (eEmc) simultaneously at lumbar (L2) and sacral (S1) segments of the spinal cord influence the excitability of the spinal networks to evoke a much stronger stepping response in spinal rats than when stimulating at either segment alone. An L2 pulse applied at specific times after an S1 pulse evokes a variable stepping pattern, i.e., poor to coordinated stepping depending on the time of onset of the L2 pulse relative to the S1 pulse. In contrast, an L2 pulse prior to an S1 pulse consistently generates robust stepping. In all scenarios, the S1 pulse consistently amplifies the EMG bursting activity in the hindlimb muscles. These results suggest that in spinal rats L2 serves to generate a locomotor rhythm, whereas S1 functions as a potent ‘modulator’ of sensory input to modulate the amplitude of the response. To test this idea, we hypothesized that a re-transection at L2 would dramatically impede stepping, whereas re-transection at S1 would retain the pattern generation and formation features of the more rostral cord, but attenuate the EMG bursting and kinematics features of stepping. Adult rats (n=8) underwent a mid-thoracic spinal cord transection (ST) at T10. The rats then were divided into two groups: one group had a re-transection at L2 and the other group had a re-transection at S1. The rats were tested for stepping ability (kinematics motion analysis and EMG) before and after the re-transection with eEmc at L2 or S1. Stimulation at L2 in the absence of S1 (transections at T10 and S1) facilitated bilateral and rhythmic, albeit irregular, stepping, whereas stimulation at S1 in the absence of L2 (transections at T10 and L2) elicited a very weak stepping pattern.

Nanosymposium 197. Advances in Spinal Cord Injury Research Location: S403
Support: RFBR grant № 13-04- 01091 Russian Scientific Fund project № 14-45-00024 Start-up funds allocated to PS by the Stony Brook University
Disclosures: P. Shah: None. C. Preston: None. H. Zhong: None. R.R. Roy: None. V.R. Edgerton: None. Y.P. Gerasimenko: None.

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