Neurophysiological assessment of afferent and efferent conduction in the injured spinal cord of monkeys

Abstract

✓ Controlled compression of the spinal cord at a given pressure using the circumferential cuff technique has yielded consistent, reproducible cord injury in primates. To test the constancy of the mechanical factors involved, functional tests were performed to study spinal cord conduction before, immediately after, and up to 3 hours after the injury. Two long fiber tracts were tested, the dorsal funiculus and the pyramidal tract. Afferent conduction testing was carried out extradurally recording the afferent volley in the posterior column following sciatic nerve stimulation. The normal triphasic volley before injury changed after injury into a large monophasic positive “killed end potential” at the site of the lesion; an iso-electric line rostral to the lesion site indicated a complete afferent conduction block up to the end of the experiment (3 hours after injury). Efferent conduction was tested by stimulating the pyramidal tract in the cord above the injury site with a special extradural electrode and observing the most distal hind limb movements (flexion of the hallux). The neurophysiology of this type of spinal cord recording and stimulation is discussed as well as its possible importance in establishing the severity of a spinal cord injury, the response to treatment, and the prognosis in patients with spinal cord injuries.