Cross-Tolerance Between the Discriminative Stimulus Properties of Ethanol, Diazepam and Pentobarbital

Lytle, Douglas A., Cross-Tolerance Between the Discriminative Stimulus Properties of Ethanol, Diazepam and Pentobarbital. Doctor of Philosophy (Biomedical Sciences), December, 1995, 132 pp., 8 tables, 19 figures, bibliography, 176 titles. Ethanol, benzodiazepine agonists and barbiturates all facilitate GABA-mediated CT flux. The present experiments tested the hypothesis that, because these agents share this common action, tolerance to discriminative stimulus properties of one of these drugs would result in cross-tolerance to the others. Rats were trained to detect either ethanol (EtOH; 1.0 g/kg), the benzodiazepine diazepam, (DZP; 5.6 mg/kg), or the barbiturate pentobarbital (PB; 10.0 mg/kg) from vehicle using a two-lever choice procedure where food was available under a fixed-ration ten schedule of reinforcement. Subsequently, dose-effect curves for EtOH (0.1-1.78 g/kg), DZP (0.56-17.8 mg/kg), or PB (1.0-17.8 mg/kg) were tested before and after chronic administration of EtOH 96.0 g/kg/12hrs for seven days), DZP (20.0 mg/kg/8hrs for seven days), or PB (32.0 mg/kg/8hrs for seven days). The chronic administration of EtOH conferred tolerance to itself in all cases and cross-tolerance to DZP and PB in subjects trained to detect EtOH, but did not confer cross-tolerance to these agents in their respective discriminations. The chronic administration of DZP conferred tolerance to itself substituting for DZP. Although tolerance developed to DZP substituting for PB after treating animals with chronic DZP, this regimen on DZP did not confer tolerance to itself substituting for EtOH. This regimen of DZP failed to confer significant cross-tolerance to either EtOH or PB under any conditions. The chronic administration of PB conferred tolerance to itself substituting for PB. Although tolerance developed to PB substituting for DZP after treating animals with chronic PB, this regimen of PB did not confer tolerance to itself substituting for EtOH. This regimen of PB failed to confer significant cross-tolerance to either EtOH or DZP under any conditions. In summary, EtOH was found to confer cross-tolerance to DZP and PB only in animals trained to detect EtOH. The chronic administrations of DZP and PB failed to confer tolerance to themselves substituting for EtOH. These results are parsimonious with the heterogeneous nature of the GABA receptor. Finally, tolerance to either DZP or PB does not result in cross-tolerance to the discriminative stimulus properties of the other drug. These results suggest that the mechanisms mediating tolerance to BZs and barbiturates are not linked.