The dopamine systems in the brain, functional classification of different dopamine receptors

Dopamine (DA) acts as a neurotransmitter in the central nervous system. The main part of the DA cell bodies are localized in the ventral mesencephalon and their axons run together in the medial forebrain bundle before diverging to different terminal areas in the forebrain, like the nucleus caudatus-putamen, nucleus accumbens, septum, amygdala, and several cortical areas like the cingulate, pyriform, entorhinal and prefrontal cortices. The functions of the dopamine systems are discussed in terms of how dopamine can modulate the functions of the area it innervates. Changes in dopaminergic transmission may be found after animals have been exposed to stress. This has implications for the discussion of whether a changed dopaminergic transmission in schizophrenia is a cause to, or a consequence of the disease. Both theories proposing a single localized anatomical site of action for the antipsychotic effect of neuroleptic drugs as well as those implicating a general effect on a number of different regions have been put forward. It is now widely accepted that there exists two classes of DA receptors, the D-1 and D-2 receptors, which have different physiological, and therefore proposed to have different clinical, characteristics. Other research implies however that a subpopulation of D-2 receptors is most important for the antipsychotic effect.