When first exposed to cocaine, the adolescent brain launches a strong defensive reaction designed to minimize the drug’s effects. Now two new studies by a Yale team identify key genes that regulate this response. Researchers have shown that vulnerability to cocaine is much higher in adolescence, when the brain is shifting from an explosive growth phase to more settled and refined neural connections. Past studies have shown that the neurons and their synaptic connections in adolescence change shape when first exposed to cocaine through molecular pathway regulated by the gene integrin beta1. In the latest study, researchers report when they knocked out this pathway, mice needed approximately three times less cocaine to induce behavioral changes than mice with an intact pathway. This suggests that the relative strength of the pathway among individuals may explain why some cocaine users end up addicted to the drug.