Disuse muscle atrophy exacerbates motor neuronal degeneration caudal to the site of spinal cord injury.

Spinal cord injury is often followed by disuse muscle atrophy. The effect of disuse muscle atrophy on motor neurons below the level of spinal cord lesions is not fully understood. We produced spinal contusions in the mid-thoracic segment (Th7/8) of rats. To promote disuse muscle atrophy, their hind limbs were immobilized. Alpha-motor neurons in L4/5 at 3 weeks postinjury showed signs of degeneration associated with disuse muscle atrophy. Muscle atrophy alone did not produce a significant α-motor neuronal degeneration. Our results demonstrate that disuse muscle atrophy within the context of spinal cord injury exacerbates motor neuronal degeneration in caudal regions remote from the injury.