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Dopamine

Dopamine

Dopamine receptors are a class of metabotropic G protein-coupled receptors that are prominent in the vertebrate central nervous system (CNS). The neurotransmitter dopamine is the endogenous ligand for dopamine receptors.

Dopamine receptors have key roles in many processes, including the control of motivation, learning, and fine motor movement, as well as modulation of neuroendocrine signaling. Abnormal dopamine receptor signaling and dopaminergic nerve function is implicated in several neuropsychiatric disorders.[1] Thus, dopamine receptors are common neurologic drug targets; antipsychotics are often dopamine receptor antagonists while psychostimulants are typically indirect agonists of dopamine receptors.

Dopamine receptor subtypesEdit

Dopamine receptor agonists (+) and antagonists (-). Specificity is not always perfect. This table is not complete.
D1-like D2-like
D1 D5 D2 D3 D4
Apomorphine + + + + +
Fenoldopam + + + ? +
SKF 38393 + + +
SKF 82958 + +
Dihydrexidine + +
Quinpirole + +
Haloperidol - ? - - ?
Flupentixol - ? - ? ?
Fluphenazine - ? ? ? ?
SCH 23390 - -
Spiperone ? - ? ?
Raclopride - - -
Clozapine - - - - -

There are five subtypes of dopamine receptors, D1, D2, D3, D4, and D5. D1 and D5 receptors are members of the D1-like family of dopamine receptors, whereas the D2, D3 and D4 receptors are members of the D2-like family. There is also some evidence that suggests the existence of possible D6 and D7 dopamine receptors, but such receptors have not been conclusively identified.[2]

D1-like familyEdit

Activation of the D1-like family receptors is coupled to the G protein Gαs, which subsequently activates adenylyl cyclase, increasing the intracellular concentration of the second messenger Cyclic adenosine monophosphate (cAMP). Increased cAMP in neurons is typically excitatory and can induce an action potential by modulating the activity of ion channels.

D1Edit

D5Edit

D2-like familyEdit

D2-like activation is coupled to the G protein Gαi, which subsequently increased phosphodiesterase activity. Phosphodiesterases break down cAMP, producing an inhibitory effect in neurons.

D2Edit

  • D2 ("DRD2", OMIM 126450). There is a short version of D2 (D2Sh) and a long version of D2 (D2Lh):
    • The D2Sh are pre-synaptic situated, having modulatory functions (called autoreceptor, they regulate the neurotransmission by feed-back mechanisms, i.e., synthesis, storage and release of dopamine into the synaptic cleft) .
    • The D2Lh may have the classic function of a post-synaptic receptor, i.e., keep going on the neurotransmission (excitatory or inhibitory) once blocked by a receptor antagonist or stimulated by the endogenous neurotransmitter itself or a synthetic full or partial agonist.

D3Edit

D4Edit

  • D4 ("DRD4", OMIM 126452). D4 has the following variants D4.2, D4.3a, D4.3b, D4.4a, D4.4b, D4.4c, D4.4d, D4.4e, D4.5a, D4.5b, D4.6a, D4.6b, D4.7a, D4.7b, D4.7c, D4.7d, D4.8, D4.10.

Role of dopamine receptors in the central nervous systemEdit

Dopamine receptors control neural signaling that modulates many important behaviors, such as spatial working memory.[3]

Non-CNS dopamine receptorsEdit

Cardio-pulmonary systemEdit

In humans, the pulmonary artery expresses D1, D2, D4, and D5 and receptor subtypes, which may account for vasorelaxive effects of dopamine in the blood.[4] In rats, D1-like receptors are present on the smooth muscle of the blood vessels in most major organs.[5]

D4 receptors have been identified in the atria of rat and human hearts.[6] Dopamine increases myocardial contractility and cardiac output, without changing heart rate, by signaling through dopamine receptors.[2]

Renal systemEdit

Dopamine receptors are present along the nephron in the kidney, with proximal tubule epithelial cells showing the highest density.[5] In rats, D1-like receptors are present on the juxtaglomerular apparatus and on renal tubules, while D2-like receptors are present on the renal tubules, glomeruli, postganglionic sympathetic nerve terminals, and zona glomerulosa cells of the renal cortex.[5] Dopamine signaling affects diuresis and natriuresis.[2]

Dopamine receptors in diseaseEdit

Dysfunction of dopaminergic neurotransmission in the CNS has been implicated in a variety of neuropsychiatric disorders, including Tourette's syndrome,[7] Parkinson's disease,[8] schizophrenia,[7] Attention-deficit hyperactivity disorder,[9] and drug and alcohol dependence.[7][10]

Drug abuseEdit

Dopamine is the primary neurotransmitter involved in the reward pathways in the brain. Thus, drugs that increase dopmamine signaling may produce euphoric effects. Cocaine and methamphetamine—two examples of such drugs—alter the functionality of the dopamine transporter (DAT), the protein responsible for removing dopamine from the neural synapse. When DAT activity is blocked, the synapse floods with dopamine and increases dopaminergic signaling. When this occurs, particularly in the nucleus accumbens,[11] increased D1[10] and D2[11] receptor signaling mediates the "rewarding" stimulus of drug intake.[11]

Genetic hypertensionEdit

Dopamine receptor mutations can cause genetic hypertension in humans.[12] This can occur in animal models and humans with defective dopamine receptor activity, particularly D1.[5]

External links Edit

References Edit

  1. Girault J, Greengard P (2004). The neurobiology of dopamine signaling. Arch Neurol 61 (5): 641-4.
  2. 2.0 2.1 2.2 Contreras F, Fouillioux C, Bolívar A, Simonovis N, Hernández-Hernández R, Armas-Hernandez M, Velasco M (2002). Dopamine, hypertension and obesity. J Hum Hypertens 16 Suppl 1: S13-7.
  3. Williams G, Castner S (2006). Under the curve: critical issues for elucidating D1 receptor function in working memory. Neuroscience 139 (1): 263-76.
  4. Ricci A, Mignini F, Tomassoni D, Amenta F (2006). Dopamine receptor subtypes in the human pulmonary arterial tree. Auton Autacoid Pharmacol 26 (4): 361-9.
  5. 5.0 5.1 5.2 5.3 Hussain T, Lokhandwala M (2003). Renal dopamine receptors and hypertension. Exp Biol Med (Maywood) 228 (2): 134-42.
  6. Ricci A, Bronzetti E, Fedele F, Ferrante F, Zaccheo D, Amenta F (1998). Pharmacological characterization and autoradiographic localization of a putative dopamine D4 receptor in the heart. J Auton Pharmacol 18 (2): 115-21.
  7. 7.0 7.1 7.2 Kienast T, Heinz A (2006). Dopamine and the diseased brain. CNS Neurol Disord Drug Targets 5 (1): 109-31.
  8. Fuxe K, Manger P, Genedani S, Agnati L (2006). The nigrostriatal DA pathway and Parkinson's disease. J Neural Transm Suppl 70: 71-83.
  9. Faraone S, Khan S (2006). Candidate gene studies of attention-deficit/hyperactivity disorder. J Clin Psychiatry 67 Suppl 8: 13-20.
  10. 10.0 10.1 Hummel M, Unterwald E (2002). D1 dopamine receptor: a putative neurochemical and behavioral link to cocaine action. J Cell Physiol 191 (1): 17-27.
  11. 11.0 11.1 11.2 Di Chiara G, Bassareo V, Fenu S, De Luca M, Spina L, Cadoni C, Acquas E, Carboni E, Valentini V, Lecca D (2004). Dopamine and drug addiction: the nucleus accumbens shell connection. Neuropharmacology 47 Suppl 1: 227-41.
  12. Jose P, Eisner G, Felder R (2003). Regulation of blood pressure by dopamine receptors. Nephron Physiol 95 (2): p19-27.
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