An In Vivo Study of Dopamine Release in Striatum: The Effects of Phenylalanine

Abstract

We used intracerebral dialysis to monitor extracellular levels of dopamine and its major metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum of chloralose/urethane-anesthetized rats. Levels of these compounds were determined after intraperitoneal administration of phenylalanine (200, 500, and 1000-mg/kg). A dose of 200 mg phenylalanine per kg (which increases brain tyrosine by more than phenylalanine) increased basal dopamine release by 59{%}, peaking at 75 min. There was no change in basal dopamine release after the 500-mg dose, whereas the 1000-mg/kg dose (which increases brain phenylalanine more than tyrosine) significantly reduced (26{%}) dopamine release. No corresponding changes were observed in the concentrations of DOPAC and HVA with any of the treatments, indicating that changes in brain phenylalanine and tyrosine levels may selectively affect production of the dopamine molecules that are preferentially released into synapses.