Dopamine receptor diversity: Anatomy, function, and relevance to Parkinson’s disease

The importance of dopamine in the motor functions of the striatum is evident in Parkinson’s disease (PD). The striatum controls motor activity by processing the flow of information arising from the cerebral cortex and projecting via direct and indirect pathways to the output nuclei of the basal ganglia. The degenerative loss of dopamine is a hallmark of this disease and leads to severe motor impairments that are relieved by dopamine agonists. However, dopamine plays a role not only in the execution of complex movement, but also in higher-order cognitive processes, including motor planning and sequencing, motor learning, and motivational drive and affect. Of the biogenic amine neurotransmitters, dopamine has been the best studied in the central nervous system (CNS). The actions of dopamine are segregated in different neural circuits. For example, dopamine in the nigrostriatal pathway is involved in the generation and execution of voluntary movement. In this function, dopamine is a prime modulator of various other basal ganglia neurotransmitters, including gamma-aminobutyric acid (GABA), acetylcholine, glutamate, enkephalin, and substance P. Dopamine in the mesolimbic pathway plays a role in the control of various cognitive functions, including drive, reinforcement, attention, and in the addiction to psychostimulants.