Differential changes in axonal conduction following CNS demyelination in two mouse models

Transgenic and disease model mice have been used to investigate the molecular mechanisms of demyelinating diseases. However, less attention has been given to elucidating changes in nerve conduction in these mice. We established an experimental system to measure the response latency of cortical neurons and examined changes in nerve conduction in cuprizone-induced demyelinating mice and in myelin basic protein-deficient shiverer mice. Stimulating and recording electrodes were placed in the right and left sensori-motor cortices, respectively. Electrical stimulation of the right cortex evoked antidromic responses in left cortical neurons with a latency of 9.38 +/- 0.31 ms (n = 107; mean +/- SEM). While response latency was longer in mice at 7 days and 4 weeks of cuprizone treatment (12.35 +/- 0.35 ms, n = 102; 11.72 +/- 0.29 ms, n = 103, respectively), response latency at 7 days and 4 weeks after removal of cuprizone was partially restored (10.72 +/- 0.45 ms, n = 106; 10.27 +/- 0.34 ms, n = 107, respectively). Likewise, electron microscopy showed cuprizone-induced demyelination in the corpus callosum and nearly complete remyelination after cuprizone removal. We also examined whether the myelin abnormalities in shiverer mice affected their response latencies. But there were no significant differences in response latencies in shiverer (9.83 +/- 0.24 ms, n = 103) and wild-type (9.33 +/- 0.22 ms, n = 112) mice. The results of these electrophysiological assessments imply that different demyelinating mechanisms, differentially affecting axon conduction, are present in the cuprizone-treated and shiverer mice, and may provide new insights to understanding the pathophysiology of demyelination in animal models in the CNS.