Neurotoxicity of ethyl methacrylate in rats.

Ethyl methacrylate (ethyl 2-methyl-2-propenoate, EMA) has been implicated in the development of neurologic impairment following occupational exposure. The potential of EMA to produce neurotoxicity was investigated in adult male Sprague-Dawley rats in two experiments. In the first experiment, animals were administered 100, 200, 400, or 800 mg/kg by daily intraperitoneal (i.p.) injections for 60 d. Control rats received daily i.p. injections of 1 ml saline/kg. Clinical observations, spontaneous motor activity, and performance in the Morris water maze were assessed. Alterations in clinical parameters in the higher dose groups included lethargy, impaired breathing, decreased weight gain, and increased mortality. Alterations in motor activity were observed at 100 mg/kg, a dose that did not cause alterations in clinical parameters, body weight gain, or mortality. There was also a dose-dependent impairment in performance in the Morris water maze. In the second experiment, animals were administered EMA in drinking water at concentrations of 0.1, 0.2, or 0.5% for 60 d. Control rats were administered tap water. Animals were perfused at the termination of exposure and samples of brain, spinal cord, and sciatic nerve were prepared for histological examination. Spongiform alterations were observed in fiber tracts of the forebrain, brainstem, and spinal cord. Clusters of axonal swellings were scattered throughout the dorsal, ventral, and lateral columns of the spinal cord, and typically involved internodal segments of two or three neighboring axons. Shrunken axons with separated myelin lamellae and large axons with thinner than normal myelin sheaths were apparent in the sciatic nerve. The patterns of alterations in the white matter of the spinal cord and the sciatic nerve are consistent with myelinopathy, but additional experiments are necessary to confirm whether oligodendroglia and Schwann cells are the primary sites of injury. In addition to the alterations associated with myelin, there was a decrease in the density of neurons in the ventral horn of the spinal cord. While the observed effects of EMA on the nervous system of rats are consistent with neurologic symptoms of workers exposed to EMA, additional experiments are necessary to determine if the level and route of exposures associated with occupational use produce these impairments in experimental animals.