Abusing the volatile organic chemicals

Characterization of an inhaled toluene drug discrimination in mice: effect of exposure conditions and route of administration

The drug discrimination procedure in animals has been extensively utilized to model the abuse related, subjective effects of drugs in humans, but it has seldom been used to examine abused volatile inhalants like toluene. The present study sought to characterize the temporal aspects of toluene's discriminative stimulus as well assess toluene blood concentrations under identical exposure conditions. B6SJLF1/J mice were trained to discriminate 10 min of exposure to 6000 ppm inhaled toluene vapor from air. Toluene vapor concentration dependently substituted for the training exposure condition with longer exposures to equivalent concentrations producing greater substitution than shorter exposures. Toluene's discriminative stimulus effects dissipated completely by 60 min after the cessation of exposure. Injected liquid toluene dose-dependently substituted for toluene vapor as well as augmenting the discriminative stimulus effects of inhaled toluene. Toluene blood concentrations measured under several exposure conditions which produced full substitution were all nearly identical suggesting that the concentration of toluene in the animal tissues at the time of testing determined discriminative performance. These results indicate that the discriminative stimulus effects of inhaled toluene vapor are likely mediated by CNS effects rather than by its pronounced peripheral stimulus effects.

CREB regulation of BK channel gene expression underlies rapid drug tolerance

Pharmacodynamic tolerance is believed to involve homeostatic mechanisms initiated to restore normal neural function. Drosophila exposed to a sedating dose of an organic solvent, such as benzyl alcohol or ethanol, acquire tolerance to subsequent sedation by that solvent. The slo gene encodes BK-type Ca(2+)-activated K(+) channels and has been linked to alcohol- and organic solvent-induced behavioral tolerance in mice, Caenorhabditis elegans (C. elegans) and Drosophila. The cyclic AMP response element-binding (CREB) proteins are transcription factors that have been mechanistically linked to some behavioral changes associated with drug addiction. Here, we show that benzyl alcohol sedation alters expression of both dCREB-A and dCREB2-b genes to increase production of positively acting CREB isoforms and to reduce expression of negatively acting CREB variants. Using a CREB-responsive reporter gene, we show that benzyl alcohol sedation increases CREB-mediated transcription. Chromatin immunoprecipitation assays show that the binding of dCREB2, with a phosphorylated kinase-inducible domain, increases immediately after benzyl alcohol sedation within the slo promoter region. Most importantly, we show that a loss-of-function allele of dCREB2 eliminates drug-induced upregulation of slo expression and the production of benzyl alcohol tolerance. This unambiguously links dCREB2 transcription factors to these two benzyl alcohol-induced phenotypes. These findings suggest that CREB positively regulates the expression of slo-encoded BK-type Ca(2+)-activated K(+) channels and that this gives rise to behavioral tolerance to benzyl alcohol sedation.