IDENTIFICATION AND DETERMINATION OF 3,4-DIHYDROXYPHENYLACETALDEHYDE, THE DOPAMINE METABOLITE, IN IN-VIVO DIALYSATE FROM RAT STRIATUM

3,4-Dihydroxyphenylacetic acid (DOPAC) is commonly considered to be th e main dopamine (DA) metabolite produced by monoamine oxidase (MAO); h owever, the initial product of DA oxidation is 3,4-dihydroxy-phenylace taldehyde (DOPALD). Owing to technical difficulties in detecting DOPAL D from a biological matrix, no studies have so far been performed to m easure brain levels of this aldehyde in vivo. In this work, using tran sstriatal microdialysis in freely moving rats, we identified DOPALD by HPLC coupled to a coulometric detector. In chromatograms obtained fro m microdialysis samples, DOPALD appeared as a peak with a retention ti me coincident with that of the standards obtained via enzymatic and ch emical synthesis. On the other hand, DOPALD was undetectable ex vivo f rom rat striatal homogenates. This discrepancy is probably due to the preferential extraneuronal localization together with the high reactiv ity of the aldehyde, which is rapidly removed by the dialysis probe, w hereas the ex vivo procedure allows its condensation and enzymatic con version. Measurement of DOPALD levels as a routine procedure might rep resent a reliable tool to evaluate DA oxidative metabolism directly, i n vivo. Moreover, parallel detection of DOPALD and DOPAC levels in bra in dialysate may make it possible to distinguish between the activity of MAO and aldehyde dehydrogenase. DOPALD, like many endogenous aldehy des, has been shown to be toxic to the cell in which it is formed. The refore, in vivo measurement of DOPALD levels could highlight new aspec ts in the molecular mechanisms underlying both acute neurological insu lts and neurodegenerative diseases.