Dopamine

Dopamine is "one of the catecholamine neurotransmitters in the brain. It is derived from tyrosine and is the precursor to norepinephrine and epinephrine. Dopamine is a major transmitter in the extrapyramidal system of the brain, and important in regulating movement. A family of receptors (dopamine receptors) mediate its action."

Dopamine regulates the secretion of prolactin from the anterior pituitary gland. Dopamine is released from specialised neurons of the arcuate nucleus of the hypothalamus into the blood vessels of the median eminence, which transport the dopamine to the pituitary gland where it inhibits prolactin secretion from lactotroph cells.

Physiology

Dopamine plasma membrane transport proteins

Dopamine plasma membrane transport proteins are "sodium chloride-dependent neurotransmitter symporters located primarily on the plasma membrane of dopaminergic neurons. They remove dopamine from the extracellular space by high affinity reuptake into presynaptic terminals and are the target of dopamine uptake inhibitors."

Dopamine receptors

D₁-like receptors

These receptors stimulate adenylate cyclase.

D1 receptors

D5 receptors

D₂-like receptors

These receptors inhibit adenylate cyclase.

Dopamine D2 receptors

Agonists, such as metoclopramide, are used as antiemetics.

Antagonists, such as risperidone and haloperidol, are used to treat schizophrenia.

Blockade of the D2 receptors, which may be predisposed by genetic polymorphisms of the allele, may cause neuroleptic malignant syndrome.

D3 receptors

Agonists of D3, especially nonergot agonists such as pramipexole and ropinirole, may be used to treat Parkinonism and restless legs syndrome.

D4 receptors

Clinical pharmacology

Dopamine agonists

Dopamine agonists are "dugs that bind to and activate dopamine receptors."

Dopamine antagonists

Dopamine antagonists are "drugs that bind to but do not activate dopamine receptors, thereby blocking the actions of dopamine or exogenous agonists. Many drugs used in the treatment of psychotic disorders (antipsychotic agents) are dopamine antagonists, although their therapeutic effects may be due to long-term adjustments of the brain rather than to the acute effects of blocking dopamine receptors. Dopamine antagonists have been used for several other clinical purposes including as antiemetics, in the treatment of Tourette syndrome, and for hiccup. Dopamine receptor blockade is associated with neuroleptic malignant syndrome."

Dopamine uptake inhibitors

Dopamine uptake inhibitors are "drugs that block the transport of dopamine into axon terminals or into storage vesicles within terminals. Most of the adrenergic uptake inhibitors also inhibit dopamine uptake." Dopamine uptake inhibitors affect dopamine plasma membrane transport proteins.

Examples include amphetamines, bupropion, cocaine, and methylphenidate. Some of these drugs are also adrenergic uptake inhibitors.