Methotrexate neurotoxicity: in vitro studies using cerebellar explants from rats.

The mechanism of methotrexate (MTX)-induced neurotoxicity was investigated using cerebellar explant cultures from fetal rats. After 3 weeks of growth, myelinated cultures were treated with MTX at 1 microM, lysolecithin at 1 mg/dl, or unaltered nutrient medium. Myelin sheaths devoid of axons were observed by histological and electron microscopic preparations after 2 weeks of MTX exposure. After 5 weeks, cultures were almost entirely devoid of myelin sheaths. Myelin basic protein in the media removed from the cultures showed an increase in concentration after 3 weeks of MTX exposure and was significantly greater than control after 5 weeks of exposure. 2',3'-Cyclic nucleotide 3'-phosphohydrolase activity, a measure of oligodendroglial function, was not significantly different in the MTX group compared to controls. Lysolecithin-treated cultures showed widespread destruction and an early increase in myelin basic protein release into the medium. These data indicate that, in the cerebellar explant cultures, MTX is primarily a neuronal toxin, and the demyelination is a consequence of axonal loss and is not related to a change in oligodendroglial cell function. These findings provide new insight into the pathogenesis of MTX-induced neurotoxicity.