Attenuation of the aversive and analgesic effects of morphine by repeated administration: Different mechanisms

Rats were repeatedly injected with a low (8 mg/kg) or high (40 mg/kg) dose of morphine during the preexposure phase of the experiment. They then received both taste-aversion training and morphine-induced analgesia assessment. These tasks were presented in the same environment or in a different environment from that associated with the drug during preexposure. Morphine preexposure attenuated morphine-induced taste aversion conditioning, whether …