Pre-drug cues modulate morphine tolerance, striatal c-Fos, and AP-1 DNA binding

To evaluate the molecular mechanisms that mediate the effect of learning on morphine tolerance in rats, we examined striatal c-Fos, and c-Jun protein expression, and AP-1 DNA binding. Morphine paired with a conditioned stimulus (CS) led to analgesic tolerance in the presence of the CS. Rats receiving morphine unpaired with the CS displayed significantly less tolerance than paired morphine animals. Striatal c-Fos protein levels and AP-1 DNA …