Tolerance and reverse tolerance to toluene inhalation: effects on open-field behavior.

Rats were exposed by inhalation to extremely high concentrations of toluene vapors twice daily for six weeks, as an animal model of organic solvent abuse. At preset intervals during repeated exposure, the rats were exposed to test concentrations of toluene and effects on behavior in an open field were measured. Concentration-effect curves were determined during Weeks 4 to 6 of repeated exposure. Tolerance to toluene was measured as a decreased response to the test exposure and a shift of the concentration-effect curve to the right. Reverse tolerance was measured as an increased response to the test exposure and a shift shift of the concentration-effect curve to the left. Results demonstrated that the effects of repeated exposure to toluene showed behavioral selectivity: tolerance developed to ataxia, hindlimb myoclonus, and inhibition of rearing, whereas reverse tolerance developed to headshakes and increased locomotor activity.