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.

D1-like receptors
These receptors stimulate adenylate cyclase.
 * D1 receptors
 * D5 receptors

D2-like receptors
These receptors inhibit adenylate cyclase. Agonists, such as metoclopramide, are used as antiemetics.
 * Dopamine D2 receptors

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.

Agonists of D3, especially nonergot agonists such as pramipexole and ropinirole, may be used to treat Parkinonism and restless legs syndrome.
 * D3 receptors
 * D4 receptors