Cross-tolerance to phenobarbital following chronic ethanol polydipsia.

Using contingent food pellet delivery, rats were trained on a discriminative motor control task requiring that a force transducer be held steadily within a force band. Motor performance following pre-task doses of phenobarbital (40, 60 or 80 mg/kg) both before and after 4 months fo chronic ethanol polydipsia (mean intake = 11.1 g/kg/kay)indicated the development of cross-tolerance from ethanol to phenobarbital. Days on which saline control injections were given in place of phenobarbital injections (on injection days ethanol was withdrawn 5 hr pre-injection) revealed the development of a mild physical dependence on ethanol at this level of ethanol polydipsia. Chronic ethanol polydipsia did not alter the time course of phenobarbital elimination from the serum, indicating that the cross-tolerance probably was due to central nervous system changes.