Dopamine

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Classic neurotransmitter; a term which includes acetylcholine, the biogenic amines and the amino acid transmitters. One of the catecholamine neurotransmitter, the two others being epinephrine and norepinephrine.

Catecholamines are organic compounds containing a catechol nucleus (benzene ring with two adjacent hydroxyl substitutions) and an amine group. The catecholamines have transmitter roles both in the CNS and PNS.

Biosynthesis

Phenylalanine and tyrosine are required for the synthesis of catacholamines, including dopamine. Tyrosine is converted into 3,4-dihydroxyphenylalanine (DOPA) by tyrosine hydroxylase (TH). DOPA is then rapidly metabolized to dopamine (DA) by L-aromatic amino acid decarboxylase (AADC).

Storage

Dopamine is stored in vesicles, which accumulate the transmitter by vesicular monoamine transporters (VMAT).

Release

Usually by calcium-dependent exocytosis of the vesicles, but can also occur via two other mechanisms: reversal of the dopamine transporter (DAT) and release from dendrites (in a process that does not appear to involve calcium).

Inactivation

In addition to simple diffusion:

  1. Enzymatic inactivation: monoamine oxidase (MAO) and catechol-0-methyltransferase (COMT).
  2. Neuronal transporters: dopamine transporter (DAT) reuptake the neurotransmitter
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