Dopamine receptor

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The dopamine receptors are a class of metabotropic G protein-coupled receptors with the neurotransmitter dopamine as their endogenous ligand.

[edit] Dopamine receptor types

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

There are five types of dopamine receptor.

The 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.

D1-like: Activation of the D1-like family receptors is coupled to increases in cAMP and is typically excitatory.
- D1 ("DRD1", Mendelian Inheritance in Man (OMIM) 126449)
- D5 ("DRD5", Mendelian Inheritance in Man (OMIM) 126453)
D2-like: D2-like activation reduces cAMP and is typically inhibitory.
- D2 ("DRD2", Mendelian Inheritance in Man (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) and the D2Lh, which 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.
- D3 ("DRD3", Mendelian Inheritance in Man (OMIM) 126451)
- D4 ("DRD4", Mendelian Inheritance in Man (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.

All are G protein coupled metabotropic receptors, and can be excitatory or inhibitory to the post-synaptic neuron.

In schizophrenics and patients with Tardive dysphrenia, D2 receptors are supposed to exist in higher than normal levels on the dopaminergic mesolimbic pathway, and antipsychotic drugs which aim to block these may cause its upregulation.

In patients with Tourettes Syndrome, studies show that the severity of the patient's tics may be directly correlated with the amount of binding of D2 Dopamine receptors in the Caudate nucleus.