Dose-dependent neurophysiological and biochemical effects of prolonged vinyltoluene vapor inhalation in rat.

Vinyltoluene is a less volatile homologue of styrene, a neurotoxic chemical. Sixty male Wistar rats were exposed to vinyltoluene vapor at 50, 100 or 300 ppm solvent concentrations 6 h daily, 5 days a week for up to 15 weeks. Twenty control rats were similarly sham exposed. Motor conduction velocity of the tail nerve decreased significantly after exposure for 12 weeks to 100 or 300 ppm and the amplitude of evoked motor action potential decreased also. This effect was reproducible in another series of 15 rats exposed to similar concentrations for 11 weeks. Acid proteinase activity in the cerebral homogenate increased at 8 weeks in 300-ppm rats and at 15 weeks in 100-ppm rats. Succinate dehydrogenase activity was below the control range in all exposed groups. Two small protein fractions appeared in the electrophoretograms of axons taken from exposed rats at the end of the experiment; these fractions occurred near the origin and between the two main fractions of the typical axon pattern. Electrophysiological changes typical of axonal degeneration and a change in the axonal proteins coincided in rats exposed to 100 or 300 ppm of vinyltoluene, while exposure to 50 ppm had no electrophysiological effects.