DOPAC, brain levels

Also, harmala alkaloids create effects on monoamine turnover. Postnatal rats administered harmaline (shortly before birth) have elevations in brain levels of the norepinephrine metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG), but decreases in the dopamine and serotonin metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindole acetic acid (5-HIAA) (Okonmah et al. 

Just as the synthesis of DA and NA is similar so is their metabolism. They are both substrates for monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT). In the brain MAO is found in, or attached to, the membrane of the intraneuronal mitochondria. Thus it is only able to deaminate DA which has been taken up into nerve endings and blockade of DA uptake leads to a marked reduction in the level of its deaminated metabolites and in particular DOPAC. The final metabolite, homovanillic... 

Once returned to the presynaptic terminal, dopamine is repackaged into synaptic vesicles via the vesicular monoamine transporter (VMAT) or metabolized to dihydroxyphenylacetic acid (DOPAC) by monoamine oxidase (MAO). Two alternative pathways are available for dopamine catabolism in the synapse, depending on whether the first step is catalyzed by MAO or catechol-O-methyltransferase (COMT). Thus, dopamine can be either deaminated to 3,4-dihydroxyphenylacetic acid (DOPAC) or methylated to 3-methoxytyramine (3-MT). In turn, deamination of 3-MT and methylation of DOPAC leads to homovanillic acid (HVA). In humans, cerebrospinal fluid levels of HVA have been used as a proxy for levels of dopaminergic activity within the brain (Stanley et al. 1985). 

Scatton B, Dennis T, Curet O (1984) Increase in dopamine and DOPAC levels in noradrenergic terminals after electrical stimulation of the ascending noradrenergic pathways. Brain Res 298 193-196. 

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