Apparent diffusion coefficient on rat brain and nerves intoxicated with methylmercury

The effects of methylmercury chloride (MMC) on the degenerative changes in rat brain and cranial nerves were studied. Twelve Wistar rats were divided into two equal groups. The rat model of methylmercury intoxication (MMC gro up) was made by subcutaneously administering 10 mg mercury/kg body weight d aily for 7 days. Control group rats were infused with the same amount of no rmal saline during this period. Magnetic resonance imaging (MRI) measuremen ts were performed before and 14 days after the first MMC administration, us ing a 4.7-T MR system. No significant focal changes were observed on T1- an d T2-weighted MR images regarding the internal structures of the brains of the MMC-intoxicated rats, atrophy of the cerebellum, and dilatation of the arachnoid space around the brain stem of MMC-treated rats, but were demonst rated without edematous change. The apparent diffusion coefficients (ADC) o f the cortex, caudate-putamen, and trigeminal nerve were not significantly different between the MMC-treated and control rats. However, the ADC parall el to the optic nerves were significantly increased in the MMC group, in co ntrast to the unchanged ADC perpendicular to the optic nerves. An electron microscopy study revealed a marked decrease of microtubules and moderate de crease of neurofilaments in the axons of myelinated fibers of optic nerves of the MMC-treated rats. We have thus demonstrated a disturbance in the int egrity of microtubules and neurofilaments as a toxic action of MMC in the r at nervous system in vivo, particularly in the optic nerves. The use of ADC values calculated by diffusion-weighted MRI is a promising approach for th e evaluation of changes in brains and nerves in methylmercury intoxication research. (C) 1999 Academic Press.