The primary goal of this subproject is to assess the extent of both spontaneous and transplant-mediated recovery of the specific motor behavior, interlimb coordination, in adult cats with static loading (compression) spinal cord injury. The proposed experiments will determine (1) if spontaneous recovery of forelimb-hindlimb coordination requires long propriospinal connections; (2) if fetal spinal cord transplants can promote recovery of forelimb-hindlimb coordination in adult cats that do not spontaneously recover this function; and (3) if there are spared pathways (i.e., long propriospinal and/or alternative pathways) that can be associated with recovery of coordination. Interlimb coordination will be quantitatively evaluated during goal- oriented overground and quadrupedal treadmill locomotion in both injured cats and in cats that have received early (1-2 weeks post-injury) or late (after spontaneous recovery of function has plateaued) suspensions of fetal spinal cord. The integrity of the long propriospinal system will be assessed anatomically with tract tracing (WGA-HRP) and electrophysiologically with conditioned test paradigms. With these techniques, the presence or absence of the long propriospinal system, as well as other systems, can be correlated with recovery of forelimb- hindlimb coordination during locomotion. Restoration of interlimb coordination in the absence of anatomical and physiological evidence for intact long propriospinal connections would suggest that this recovery is due to """"""""functional reconnectivity."""""""" In this context, """"""""functional reconnectivity"""""""" could occur as the result of the unmasking or activation of latent functions in alternate pathways since some systems have the capacity to mediate functions other than those they normally subserve, and/or by establishing novel polysynaptic relays through the grafts. The results of these experiments should enhance our understanding of the mechanisms underlying the normal plasticity that is associated with recovery of a specific sensorimotor function as well as the transplant mediated mechanisms associated with recovery of the same function. In addition, these findings will also indicate if the time interval between injury and transplantation is critical to the recovery of function.
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