PHENYLALANINE IN THE CAUDATE-NUCLEUS OF DOPAMINE DEPLETED RATS

Dopamine depleting lesions of the substantia nigra result in a reducti on of the striatal accumulation of 2-phenylethylamine following monoam ine oxidase inhibition. It is established that this effect may not be due to a change in availability of aromatic L-amino acid decarboxylase in striatum. Nevertheless, the possibility remains that striatal conc entrations of phenylalanine (the precursor of 2-phenylethylamine) may be altered by dopamine-depleting lesions. The present experiments asse ssed the effects of dopamine depletion induced by 6-OHDA (7 days follo wing 8 mug/4 mul unilateral substantia nigra injection) on striatal co ncentrations of phenylalanine, dopamine, 5-hydroxytryptamine and their metabolites. In addition, the effects of reserpine-induced (10 mg kg- 1, 2h, sc) amine depletion on these striatal levels were also assessed . Under equivalent conditions reserpine is reported to increase striat al accumulation of 2-phenylethylamine. 6-OHDA induced a significant un ilateral depletion of dopamine, DOPAC and HVA and increased 5-HIAA but had no significant effect on phenylalanine levels. Reserpine decrease d dopamine and 5-hydroxytryptamine and increased DOPAC, HVA and 5-HIAA levels, no changes in phenylalanine were observed. This pattern of re sults was also observed when lesioned animals or reserpine-treated ani mals were pretreated with (-)-deprenyl (2 mg kg-1, 2 hr, sc), the trea tment previously used to induce accumulation of 2-phenylethylamine. Th ese data indicate that changes in 2-phenylethylamine previously observ ed under these conditions may not simply be secondary to a change in s triatal phenylalanine concentrations.