DA receptors belong to the G-protein coupled receptors superfamily, and are prominent in the vertebrate central nervous system (CNS) as well as the peripheral nervous system (PNS). The neurotransmitter dopamine, a precursor of noradrenaline and adrenaline, is one of the main endogenous catecholamine ligand for DA receptors. There are at least five subtypes of dopamine receptors, D₁, D₂, D₃, D₄, and D₅, based on their sequence homology, pharmacology and functional properties. Several neuropsychiatric disorders are derived from abnormal dopamine receptor signaling and dopaminergic nerve dysfunction.