The UCS preexposure effect in taste aversion learning : Tolerance and blocking are drug specific

Following drug preexposure, rats were given taste aversion conditioning in either the pre- exposure environment or the home cage. For animals preexposed to LiCI, only the subjects con- ditioned in the preexposure environment showed the typical Despreexposure effect, that is, an attenuated aversion, an effect consistent with a blocking interpretation of the LiCI-induced pre- exposure effect. On the other hand, all rats preexposed to morphine displayed attenuated aver- sions, independent of the preexposure and conditioning environments. an effect consistent with a pharmacological tolerance explanation of the ues preexposure effect to morphine. The spe- cific mechanism underlying the drug-induced attenuation appears to be drug-dependent.