Neuronal Injury Secondary to Intrathecal Methotrexate in a Rat Model

Abstract

The purpose of this study was to determine if intrathecally administered methotrexate causes neuronal injury in the cortex of the brain in a rat model. This study was designed to mimic methotrexate treatment in children with acute lymphoblastic leukemia (ALL). Current treatment includes intrathecal chemotherapy, which is administered directly into the central nervous system. While this has significantly improved survival rates, late neurocognitive deficits have been observed. Six Fischer 344 rats were treated with either 4mg/kg methotrexate or artificial cerebral spinal fluid as controls. After five days the rats were sacrificed, brains were sliced into 5μm sections and stained for H and E. Images were taken of the superior, medial, and inferior areas of both sides of the cortex at 40x magnification. Neurons were counted using the ImageJ program (National Institutes of Health). Statistical significance (p<0.05) was found in the medial areas as hypothesized, with the percentage of healthy neurons greater in the control (mean ± SD = 71.7 ± 21.8) versus treatment (55.6 ± 32.9) rats. Although statistical significance (p<0.05) was obtained, contrary to the hypothesis the percentage of healthy neurons was greater in the treatment (66.1 ± 25.0) versus control (51.7 ± 34.1) rats in the inferior areas.