The site of action of addictive drugs is:

Nucleus accumbens has a very high population of dopaminergic neurons that act D3 receptors. This area is found to be associated with reward and addictive behavior. Pneumotaxic center is located in the nucleus parabrachialis and Kolliker-Fuse nucleus in upper pons. Nucleus raphe magnus (medulla) has high density of serotonergic neurons and is a component of descending analgesia system.