Stepping by chronic spinal cats.

We investigated the consequences of spinal cord transection in adult cat. All became capable of stepping upon a treadmill. Two of six animals stepped in the first postoperative testing session, 1 week after surgery. It took up to 6 weeks for the others to start stepping. None of the cats became capable of hindquarter support within 2 months after surgery. There was permanent loss of fore-hindlimb coordination and increased variability in the duration of each step cycle and its components. Coordination between the hindlimbs was also impaired, as signaled by increased variability in the time between foot contacts with the belt. These changes may be due to the loss of timing signals coming down from supraspinal levels to the segmental step generators or - alternatively - to decreased excitability of segmental motoneurons leading to less precise execution of stepping commands from the hypothetical pattern generators.