Dopamine: Receptors, Functions, Synthesis, Pathways, Locations and Mental Disorders: Review of Literatures

Dopamine is monoamine neurotransmitter. Dopamine is produced in the dopaminergic neurons in the ventral tegmental area of the substantia nigra, midbrain and the arcuate nucleus of the hypothalamus. In the periphery, dopamine is found in the kidney where it functions to produce renal vasodilation, diuresis, and natriuresis. Dopamine neurons are more widely distributed than those of other monamines and it is found in hypothalamus, olfactory bulb, the midbrain substantia nigra and ventral tegmental area and in the periaqueductal gray and retina. There are five subtypes of dopamine receptors, D1, D2, D3, D4, and D5, which are members of the large G-protein coupled receptor super family. The dopamine receptor subtypes are divided into two major subclasses: types 1 and 5 are similar in structure and drug sensitivity, and these two receptors are referred to as the "D1like" group or class of receptors. Dopamine receptor types 2, 3, and 4 are called the "D2like" group. Dopamine plays central role in pleasurable reward behavior, inhibition of prolactin production (involved in lactation), sleep, mood, attention, learning, behavior, control of nausea and vomiting and pain processing. In addition it also involved in controlling movement, emotion and cognition. Due to extensive localization of dopamine receptor to brain areas and its role in wide range of functions, dopaminergic dysfunction has been implicated in the pathophysiology of schizophrenia, mood disorders, obsessive compulsive disorder (OCD), autism spectrum disorders, attention deficit–hyperactivity disorder (ADHD), tourette's syndrome, substance dependency, Parkinson's disease and other disorders. the D2 receptor, implicating this subtype as an important site of antipsychotic drug action [3,4]. D1 receptor has high affinity for the antagonist SCH 23390 and relatively low affinity for butyrophenones such as haloperidol. D1 receptor activation stimulates cyclic adenosine monophosphate (cAMP) formation, D2 receptor stimulation produces the opposite effect. In addition to the stimulation of adenylate cyclase, D1 receptors may also stimulate phosphoinositide turnover and modulate intracellular calcium levels [1,3]. The D1 receptors are found in high concentration in the hypocampus, caudate, putamen, nucleus accumbens, hypothalamus, substantia nigra pars reticulata, olfactory tubercle and frontal and temporal cortex [3,5]. D1 receptors have been implicated in the cognitive functions of dopamine such as the control of working memory and attention. D1 receptors contribute significantly to the CNS effects of cocaine, suggesting the involvement of other receptors in addition to the D2 receptor, in mediating rewarding effects of drugs of abuse [1,3,5]. D1 and D5 receptors have a higher degree of homology with each other than with the D2–4 subtypes. D5 receptor has 50% homology