The mesolimbic dopaminergic system, encompassing DA neurons originating from the ventral tegmental area (VTA) that project to the nucleus accumbens (NAc) and PFC, has long been recognized as an important pathway mediating behavioral responses to natural rewards as well as drugs of abuse. Essentially, all drugs of abuse enhance extracellular DA in the NAc (Di Chiara and Imperato, 1988) and blocking dopaminergic transmission will attenuate the reinforcing properties of the drug (Corrigall et al., 1992). Furthermore, this DA signal provides convergent information to the system regarding reward expectation and environmental cues related to drug intake (Di Chiara, 1999; Berke and Hyman, 2000). It is not surprising, therefore that drug-induced neural adaptations have been discovered in this circuit and presumably contribute to addiction.
