Cocaine's rewarding effects are controlled by the opposing actions of the two main cell types in the brain's reward centre, the nucleus accumbens.
The cells differ, in part, in which receptor they express for the neurotransmitter dopamine — D1 or D2. Eric Nestler at the Mount Sinai School of Medicine in New York and his co-workers used engineered mice in which they could activate each of these cell types in the nucleus accumbens using blue light. Mice with enhanced D1 activity showed a preference for cocaine in a behavioural test, whereas those with activated D2 cells had suppressed interest in the drug.
The authors say that the effect involves signalling through a pathway for the protein BDNF. They suggest that an imbalance of D1 and D2 cell activity contributes to cocaine addiction.