Cannabis use is a hypothesized gateway to subsequent abuse of other drugs such as heroin. We currently assessed whether Delta-9-tetrahydrocannabinol (THC) exposure during adolescence modulates opiate reinforcement and opioid neural systems in adulthood. Long-Evan male rats received THC (1.5 mg/kg intraperitoneally (i.p.)) or vehicle every third day during postnatal days (PNDs) 28-49. Heroin...