Reduction of brain dopamine concentration with dietary tyrosine plus phenylalanine depletion:: An [11C]raclopride PET study

Objective: Extracellular dopamine concentrations were estimated through measurement of [C-11]raclopride binding with positron emission tomography after dietary manipulation of the dopamine precursors tyrosine and phenylalanine. Method: Healthy male subjects were scanned on two occasions: once after receiving a balanced amino acid drink and once after receiving a drink mixture from which tyrosine and phenylalanine were omitted. Results: Dietary tyrosine and phenylalanine depletion increased [C-11]raclopride binding in the striatum by a mean of 6%. The change in [C-11]raclopride binding correlated significantly with the fall in the ratio of tyrosine and phenylalanine to large neutral amino acids. Conclusions: This is the first demonstration of an effect of a dietary manipulation on brain dopamine release in humans. This result provides support for the further investigation of the role of dietary manipulations in the treatment of neuropsychiatric disorders.