Figure 2.

Model illustrating the processes of levodopa-dopamine metabolism and uptake. (A) Normal striatum (B) Dopamine-denervated striatum. Note that MAO-A localization is unclear. A study suggests MAO-A is mainly expressed in medium spiny neurons, rather than in axon terminals in the striatum. Serotonergic neurons express MAO-B in their cell bodies, however, it is still unclear whether the neurons express MAO in axon terminals. OCT-3 also exists in neurons, however the specific subtype is unknown. PMAT is illustrated at the astrocyte membrane according to one recent study (see text), although its localization is not certain yet. 3-MT, 3-methoxytyramine; 3-OMD, 3-O-methyldopa; AADC, aromatic amino acid decarboxylase; ALD.DH, aldehyde dehydrogenase; COMT, catechol-O-methyltransferase; D2R, dopamine D2 receptor; DA, dopamine; DAT, dopamine transporter; DCI, dopa-decarboxylase inhibitor; DOPAC, dihydroxyphenylacetic acid; DOPALD, dihydroxyphenylacetaldehyde; DR, dopamine receptor; HVA, homovanillic acid; MAO, monoamine oxidase; NET, norepinephrine transporter, noradrenaline transporter; OCT, organic cation transporter; PMAT, plasma membrane monoamine transporter; SERT, serotonin transporter; VMAT-2, vesicular monoamine transporter-2.