Subtypes of dopamine receptors involved in the mechanism of reinforcement.

Advancement in the study of receptors for neurotransmitters facilitated the analysis of neural mechanisms underlying reinforcement. Two subtypes of dopamine receptors, D1 and D2, play distinct roles in producing reinforcing effects. Experiments using SCH 23390 suggest that the reinforcing effects of food, water, saccharin, heroin and brain stimulation all critically depend on the activation of D1 dopamine receptors, particularly those in the nucleus accumbens and the ventral tegmental area. Raclopride, a D2 dopamine antagonist, also reduced bar-pressing responses for food, heroin, and brain stimulation. Thus, both D1 and D2 receptors seem to be involved in the reinforcement mechanisms. There were some differences between D1 and D2 dopamine antagonists in the manner of reducing operant responding. It appears that D1 receptors are related to the efficacy of reinforcements while D2 receptors are related to the type of reinforcers.