Brain dialysis: in vivo metabolism of dopamine and serotonin by monoamine oxidase A but not B in the striatum of unrestrained rats.
A dialysis cannula was implanted into rat striatum while the animals were anesthetized, and the area was perfused with Ringer solution while the animals were unanesthetized after at least 3 days following surgery. Concentrations of the metabolites of 3,4-dihydroxyphenylethylamine (DA) and 5-hydroxytryptamine (5-HT) in the perfusate were determined by HPLC with electrochemical detection. Levels of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the perfusate significantly decreased after pargyline administration (50 mg/kg i.p.), which may inhibit not only monoamine oxidase (MAO)-B but also MAO-A in these high doses. The level of the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) also decreased after pargyline treatment, although change in the relative level of 5-HIAA was less than that of DOPAC or HVA. To clarify the mechanisms for the metabolism of monoamines in rat striatum, highly specific MAO-A and -B inhibitors were used in the following experiments. Treatment with l-deprenyl (10 mg/kg), a specific inhibitor for MAO-B, did not cause any statistically significant change in DOPAC, HVA, and 5-HIAA levels. No significant change was found in rat striatal homogenates at 2 h after the same treatment with l-deprenyl. In contrast, low-dose treatment (1 mg/kg) with clorgyline, a specific inhibitor for MAO-A, caused a significant decrease in levels of these three metabolites in both the perfusates and tissue homogenates. In addition to the above three metabolites, the level of 3-methoxytyramine, which is an indicator of the amount of DA released, greatly increased after treatment with a low dose (1 mg/kg) of clorgyline.(ABSTRACT TRUNCATED AT 250 WORDS)
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D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003010:Clorgyline / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000201:enzymology*; D003956:Dialysis; D004298:Dopamine / Q000031:analogs & derivatives / Q000378:metabolism*; D006719:Homovanillic Acid / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D010293:Pargyline / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*
D008996:Monoamine Oxidase Inhibitors; D015102:3,4-Dihydroxyphenylacetic Acid; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D010293:Pargyline; D008995:Monoamine Oxidase; C001746:3-methoxytyramine; D003010:Clorgyline; D004298:Dopamine; D006719:Homovanillic Acid