REGULATION OF STRIATAL AROMATIC L-AMINO-ACID DECARBOXYLASE - EFFECTS OF BLOCKADE OR ACTIVATION OF DOPAMINE-RECEPTORS

Previous experiments have shown that blockade of dopamine D1 or D2 rec eptors by SCH 23390 or pimozide increases aromatic L-amino acid decarb oxylase (AADC) activity in the rat striatum and the mesolimbic system. This study examined whether other dopamine receptor antagonists affec t AADC activity and if there is an interaction between dopamine D1 and D2 receptor blockade on AADC activity. The possible effect of dopamin e receptor agonists on AADC activity has been investigated as well. Ad ministration of cis-flupenthixol (0.5 and 1 mg/kg) increased striatal AADC activity (by 25 and 26% above controls) and similar effects were observed with remoxipride (0.5-4 mg/kg) (by, 18-27% above controls). P retreatment with cycloheximide (10 mg/kg) did not change the increases produced by cis-flupenthixol (0.5 mg/kg). The administration of non-n euroleptic trans-flupenthixol did not change AADC activity. Combined t reatment with SCH 23390 (0.1 mg/kg) and remoxipride (0.5 mg/kg), but n ot combination of SCH 23390 (0.1 mg/kg) and pimozide (0.3 mg/kg), show ed higher increases of AADC activity than by the individual treatments , suggesting an interaction between the effects of the two drugs. Brom ocriptine, but not (-)-quinpirole and d-amphetamine, significantly red uced the striatal AADC activity by 23% at the dose of 10 mg/kg. The re sults further demonstrate that AADC is a regulated enzyme in the rat b rain.