Inhalation of low concentrations of toluene induces persistent effects on a learning retention task, beam-walk performance, and cerebrocortical size in the rat

The organic solvent toluene is widely used in industry. The threshold limit value for extended occupational exposure to toluene is presently set to 20 0 ppm in the United States. We have investigated the effect of an inhalatio n exposure of 80 ppm for 4 weeks (6 h/day, 5 days/week), followed by a post exposure period of at least 4 weeks, on behavior and brain features in the rat. Toluene exposure appeared to affect spatial memory, since toluene-expo sed rats showed a longer time in the correct quadrant in a Morris swim maze . This effect may indicate that the exposed rats used their praxis strategy longer before they started to look for the platform elsewhere. Toluene-exp osed rats showed trends for increases in both locomotion and rearing behavi ors and a significantly reduced beam-walk performance. The area of the cere bral cortex, especially the parietal cortex, was decreased by B-10% in tolu ene-exposed rats, as shown by magnetic resonance imaging of living rats and autoradiograms of frozen brain sections. The K-D and B-max values of the d opamine D-3 agonist [H-3]PD 128907 were not affected by toluene, as measure d in caudate-putamen and subcortical limbic area using biochemical receptor binding assays and in caudate-putamen and islands of Calleja using quantit ative receptor autoradiography, Hence, previously demonstrated persistent e ffects by toluene on the binding characteristics of radioligands binding to both D-2 and D-3 receptors seem to indicate a persistent effect of toluene selectively on dopamine D-2 receptors, Taken together, the present results indicate that exposure to low concentrations of toluene leads to persisten t effects on cognitive, neurological, and brain-structural properties in th e rat. (C) 2000 Academic Press.