Overflow of endogenous dopamine and 3,4-dihydroxyphenylacetic acid from tissues of the rat brain, elicited by electrical stimulation, depolarization by potassium and activation of carrier-mediated release.

Overflow of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) from slices of striatum and slices containing the nucleus accumbens of the rat, during spontaneous loss and as elicited by electrical stimulation, depolarization by potassium and carrier-mediated release, in conditions of inhibition of COMT was studied. Levels of dopamine and DOPAC in tissues and in the superfusates were quantified by means of high pressure liquid chromatography with electrochemical detection (HPLC-ECD). Inhibition of neuronal uptake by cocaine (10 mumol/l) or GBR 12909 (100 nmol/l) was found to increase only the spontaneous outflow of dopamine. Electrical stimulation of slices of striatum produced an increase in levels of overflow of dopamine, but not of DOPAC. Inhibition of neuronal uptake during electrical stimulation potentiated the release of dopamine and slightly reduced levels of DOPAC in the effluent. Changes in the electrically-stimulated or potassium-evoked release of dopamine, as a result of blockade or activation of prejunctional dopamine receptors, did not affect levels of DOPAC in the effluent. Release of dopamine, induced through a favourable sodium gradient, was not accompanied by an increased release of DOPAC. The results presented demonstrate that most of the DOPAC does not originate from a recently released pool of dopamine.