Pharmacology of Dopamine and Its Receptors

Dopamine (DA) is the major catecholamine neurotransmitter in the brain which regulates multiple functions including the control over voluntary action, reward, circadian rhythm, consciousness, and cognition. The synthesis of DA involves two events, i.e. hydroxylation of L-tyrosine to DOPA catalysed by tyrosine hydroxylase (TH) and further, DOPA gets decarboxylated to final product DA via aromatic L-amino acid decarboxylase (AADC) enzyme. Metabolism involves monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) enzymes, which degrade dopamine finally into 3, 4-Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). DA acts through two different subclasses of receptors including D1-like (D1 and D5) and D2-like (D2, D3 and D4) dopamine receptors. Dopamine performs various functions through its receptors like regulation of growth, reward, sleep, locomotion, emotions, renal functions, gastrointestinal motility, etc. Furthermore, dopaminergic system plays an important role in the pathogenesis of various neurological diseases like Parkinson’s disease (PD), Huntington’s diseases (HD), Alzheimer’s disease (AD), schizophrenia, anxiety, epilepsy, traumatic brain injury (TBI), and multiple sclerosis (MS). Also, high pace discoveries that occurred in the research field pave the way for recent advancements in the dopaminergic system. Currently, with the help of molecular cloning, two D1-like and three D2-like receptor genes have been successfully identified. In the current chapter, various roles of dopamine and dopaminergic receptors have been highlighted but there is still a need to understand a lot of functions and specific roles of the receptors. Hence, the high pace of research along with newly developed advancements in the field of neuroscience and pharmacology will be useful to get more knowledge about dopamine receptor signalling in devastating disorders.