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. Author manuscript; available in PMC: 2009 Oct 1.
Published in final edited form as: Adv Drug Deliv Rev. 2008 Jul 4;60(13-14):1527–1533. doi: 10.1016/j.addr.2008.06.002

Figure 3. Synaptic processing of dopamine (DA).

Figure 3

Following release, DA receptor activation and reuptake by DA transporter (DAT), DA is degraded by two main enzymatic pathways. (1) In the first pathway, MAO (monoamine oxidase) and ALDH (aldehyde dehydrogenase) convert DA into 3,4-dihydroxyphenylacetic acid (DOPAC); this compound is then processed by catechol-O-methyltransferase (COMT) into homovanillic acid (HVA). (2) In the second pathway, COMT metabolizes DA into 3-methoxytyramine (3-MT), which is then converted into HVA by MAO and ALDH.