Locomotor deficits induced by experimental spinal cord demyelination are abolished by spontaneous remyelination

Demyelinating lesions induced by intraspinal injection of gliotoxin have been studied for many years in order to gain insights into reasons for failure of remyelination and to improve understanding of the axonal conduction disorders in multiple sclerosis. Although the electrophysiological correlates of experimental demyelination and remyelination are well established, the behavioural effects have not been investigated. In this study we aimed to determine whether behavioural deficits could be detected during spinal cord demyelination, and furthermore, whether remyelination was associated with return of lost function. We used injections of the gliotoxin ethidium bromide into the dorsal funiculus of the cervical spinal cord of the rat to induce zones of demyelination and compared the effects on locomotion with those resulting from saline injections. The resulting locomotor deficits were quantified by analysis of foot placement during traverse of a horizontal 18 mm diameter wooden beam. Following ethidium bromide injection there was a decrease in security of foot placement, that recovered by approximately 5 weeks post-injection. In a second experiment, remyelination was prevented by exposure of the spinal cord to 40 Gy of X-irradiation. Behavioural deficits were induced as before, but the animals failed to recover throughout the duration of the experiment. Saline-injected animals in both experiments exhibited minimal deficits and quickly recovered. We conclude that demyelination produces detectable behavioural deficits which disappear following spontaneous remyelination.