BP values were extracted from the t-map (threshold: t=4.2, equivalent to p<0.05, Bonferroni corrected) and a priori identified regions of interest from each individual's coregistered magnetic resonance images. Brain parametric images were generated by calculating raclopride BP at each voxel. On the morning before each scan, subjects ingested, in counter-balanced order, an amino-acid mixture deficient in the catecholamine precursors, phenylalanine, and tyrosine, or a nutritionally balanced mixture. Eight healthy men received two PET scans, both following d-amphetamine, 0.3 mg/kg, p.o., an oral dose known to decrease raclopride BP in ventral striatum. In the present study, we tested the hypothesis that APTD would reduce stimulated dopamine (DA) release, as assessed by positron emission tomography (PET) and changes in raclopride binding potential (BP), a measure of DA D2/D3 receptor availability. Validation studies in animals are encouraging, but direct evidence in human brain is lacking.
Acute phenylalanine/tyrosine depletion (APTD) has been proposed as a new method to decrease catecholamine neurotransmission safely, rapidly, and transiently.
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