Discriminative properties of pentobarbital after repeated noncontingent exposure in gerbils.

Two groups of gerbils were pretreated with pentobarbital (P-barb.) (10 and 20 mg/kg) for 20 days before being subjected to drug discrimination training in a (T-shaped shock-escape maze. The rapidity with which these gerbils acquired the discrimination was compared to that of gerbils that were drug naive until beginning the P-barb.-discrimination training. The acquisition rates of the respective groups did not differ substantially within each dose level (10 and 20 mg/kg), although open-field activity (primarily the rearing scores) differentiated the P-barb.- and vehicle-pretreated animals at both dose levels. The peak effect in rectal temperature, however, was not markedly different after the first and 20th drug exposures, although the temperature effects leveled off earlier during the second recording session. In conclusion, certain parameters (open-field activity) may be changed as a consequence of repeated administrations of P-barb. without a significant parallel loss of the cue or stimulus properties of the drug.