Researchers at Duke University School of Medicine are investigating how to keep opioids' pain-relieving benefits while reducing their addictive potential. "Dopamine isn’t enough by itself; opioid reward learning also appears to require a drop in acetylcholine, controlled by a small cholinergic hub.” Because dopamine rises when opioids are taken, scientists have long viewed it as a major driver of opioid reward learning. Earlier studies examining these cholinergic neurons suggested they were not essential for opioid reward learning. The mice no longer developed a preference for a chamber where they received morphine, a widely used measure of reward learning.