In the study, researchers trained rats to predict tasty treats by association with a series of sound cues. Researchers then injected mice with both dopamine and opioids, stimulating corresponding circuits in the rats' brains. Both chemicals caused rats to respond to the sound cues with hyperactive desire (i.e., craving) for their upcoming dessert. Opioid chemicals additionally caused rats to feel increased pleasure while indulging their collective sweet tooth. These findings suggest that the brain uses separate signals to indicate desire and pleasure.
A better understanding of the complexities of dopamine and opioid neural circuits, one or both of which are triggered by the majority of addictive drugs, may lend itself to valuable insights into addiction treatment.