Dopamine re-uptake and metabolism

Once the dopamine that is released into the synaptic cleft has exerted its action on the various dopamine receptors, these actions have to be terminated to prevent continuous 

After re-uptake by the nerve terminal a part of the released dopamine is converted to dihydroxyphenylacetic acid (DOPAC, 5) by intraneuronal monoamine oxidase (MAO) and aldehyde dehydrogenase (AD). Released dopamine is also converted to homovanillic acid (HVA, 6), probably at an extraneuronal site through the sequential action of catechol-O-methyltransferase (COMT) and MAO. In rat brain, DOPAC is the major metabolite and considerable amounts of DOPAC and HVA are present in sulfate-conjugated as well as free forms.1 

Chart 1.2 Neuronal metabolism of dopamine. Dopamine (1) 3,4-dihydroxyphenyl acetaldehyde (4) 3,4-dihydroxyphenylacetic acid (DOPAC, 5) homovanillic acid (HVA, 6) 3-methoxytyramine (3-MT, 7) 3-methoxy-4-hydroxyphenyl acetaldehyde (8) MAO, monoamine oxidase AD, aldehyde dehydrogenase COMT, catechol-O- 

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