MINOR EFFECT OF TOLCAPONE, A CATECHOL-O-METHYLTRANSFERASE INHIBITOR, ON EXTRACELLULAR DOPAMINE LEVELS MODIFIED BY AMPHETAMINE OR PARGYLINE - A MICRODIALYSIS STUDY IN ANESTHETIZED RATS

In vivo microdialysis was used to examine the effects of tolcapone (30 mg/kg) on dopamine metabolism in amphetamine (5 mg/kg) and pargyline (75 mg/kg) treated rats. Amphetamine- or pargyline-induced decreases i n the extracellular dihydroxyphenyl acetic acid (DOPAC) levels were co unteracted by additional tolcapone. Tolcapone also decreased homovanil lic acid effluxes below those caused by amphetamine or pargyline. Howe ver, dopamine effluxes were not further enhanced by additional tolcapo ne. These results show that central metabolism of dopamine can be modu lated by catechol-O-methyltransferase (COMT) inhibition also without e xogenous L-DOPA. However, extracellular dopamine levels are not easily increased.