Comparison of ethanol, pentobarbital, and phenobarbital using drug vs. drug discrimination training.

Rats learned drug vs. drug (D vs. D) or drug vs. no drug (D vs. N) discriminations in a T-maze shock escape task with various doses of pentobarbital, phenobarbital, or ethanol. Dose-effect curves were obtained for each drug using D vs. N training. After D vs. N training with any one of these drugs, rats made D choices during substitution tests with the other two drugs, suggesting drug interchangeability. D vs. D training also showed that pentobarbital and phenobarbital were virtually indistinguishable from one another. However, ethanol was readily discriminated from pentobarbital, showing that the two drugs differed. The results show the utility of D vs. D training as a method for studying drug differences that may be too small to detect with substitution tests.