|dc.description.abstracteng||Axonal damage, often followed by axonal degeneration, is the main cause of persisting disabilities in multiple sclerosis (MS) patients and already occurs in early stages of the disease. Disease progression is in addition characterized by degenerative processes such as oligodendroglial death, demyelination and axonal damage/ degeneration, which seem at least in part uncoupled from inflammation. It has been demonstrated that axonal damage is most pronounced in early actively demyelinating MS lesions. Furthermore, demyelinated axons show a higher vulnerability than properly myelinated axons. Thus, remyelination and the formation of new nodes of Ranvier seem to be neuroprotective. Hence, in the present study I investigated the temporal and functional relation between myelin protein expression and acute axonal damage during remyelination in remyelinating/ remyelinated MS lesions and in the cuprizone mouse model. Furthermore, I used this model to assess the therapeutic potential of the ion channel blockers 4-aminopyridine (4-AP) and amiloride with regard to protection from axonal damage.
C57Bl/6 mice were treated for six weeks with the copper chelator cuprizone (0.25% in normal chow) which leads to demyelination of the brain, especially of the corpus callosum. After discontinuation of the cuprizone diet, remyelination occurs within a few days and is completed after several weeks during which the brains were harvested and analyzed. The pathology in the corpus callosum was analyzed by histopathology, quantitative PCR and electron microscopy. The corpus callosum of mice was rapidly remyelinated during the first week of cuprizone free diet. Furthermore, a reconstitution of the density of oligodendrocytes, which was comparable to untreated mice, was accomplished one week after cuprizone withdrawal. Microgliosis was significantly diminished already after two days of remyelination and declines even further thereafter, while astrogliosis persisted during remyelination. Furthermore, mice exhibited a continuous decrease of acutely damaged axons during remyelination. Remarkably, acute axonal damage that was directly associated with complete or partial myelination was observed by confocal microscopy. Over time the quantity of myelinated axonal spheroids increased significantly, which, given the strong regenerative processes observed, suggests that remyelination may occur randomly and independent of axonal functionality. Furthermore, myelinated acutely damaged axons were also seen in early remyelinating MS lesions. These results suggest that remyelination may occur independent of axonal transport disturbances in MS, however, this hypothesis has still to be substantiated in future studies.||de