Dopaminergic mechanisms and brain reward

Abstract

Considerable evidence has shown that brain reward is dependent on the functional integrity of dopamine (DA) neurotransmission within the mesotelencephalic DA system in the brain. Among the many terminal loci of the mesotelencephalic DA system, the nucleus accumbens has been shown to be perhaps the most critically involved in brain reward. Feeding, copulation and electrical self-stimulation of the ventral tegmental area in laboratory rats induce significant increases in extracellular DA overflow in the nucleus accumbens. Laboratory animals self-inject abusable drugs directly into the nucleus accumbens or ventral tegmental area (the latter containing the DA cell bodies which project to the nucleus accumbens). Systemic administration of abusable drugs preferentially enhances extracellular DA overflow in the nucleus accumbens compared to other terminal loci of the mesotelencephalic DA system. Specific lesions of the nucleus accumbens and/or other mesolimbic portions of the mesotelencephalic DA system markedly inhibit the rewarding effects of most abusable drugs. Altogether this evidence suggests an important role for the nucleus accumbens and associated portions of the mesolimbic DA pathway in the mediation of brain reward. However, additional evidence suggests that the mesolimbic DA system also plays an important role in other complex functions such as psychomotor arousal, reward anticipation, consummatory behavior, and craving. The relationship of these other functions to reward is, as yet, unclear.