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Central dopamine function is reduced by decreasing the availability of the catecholamine precursor, tyrosine, using a tyrosine-free amino acid mixture containing multiple large neutral as well as branched chain amino-acids, which compete with tyrosine for uptake into the brain. Current mixtures are cumbersome to make and administer, and unpalatable to patients and volunteers. Here, we investigate whether individual or limited amino-acid combinations could reduce brain tyrosine levels and hence dopamine function. Measurements of regional brain tyrosine levels, catecholamine and indoleamine synthesis (L-DOPA and 5-HTP accumulation, respectively) were used to identify an effective paradigm to test in neurochemical, behavioral and fos immunocytochemical models. Administration of leucine or isoleucine, or a mixture of leucine, isoleucine, and valine reduced tyrosine and 5-HTP, but not L-DOPA accumulation. A mixture of leucine, valine, and isoleucine supplemented with tryptophan reduced brain tyrosine and L-DOPA, but not 5-HTP. In microdialysis experiments this amino-acid mixture reduced basal and amphetamine-evoked striatal dopamine release, as well as amphetamine-induced hyperactivity. This mixture also reduced amphetamine-induced fos expression in striatal areas. In conclusion, the present study identified a small combination of amino acids that reduces brain tyrosine and dopamine function in a manner similar to mixtures of multiple amino acids. This minimal mixture may have use as a dopamine reducing paradigm in patient and volunteer studies.

Original publication

DOI

10.1038/sj.npp.1300835

Type

Journal

Neuropsychopharmacology

Publication Date

02/2006

Volume

31

Pages

310 - 317

Keywords

3,4-Dihydroxyphenylacetic Acid, 5-Hydroxytryptophan, Amino Acids, Branched-Chain, Amphetamine, Analysis of Variance, Animals, Behavior, Animal, Brain, Brain Chemistry, Catecholamines, Cell Count, Dopamine, Dopamine Agents, Dose-Response Relationship, Drug, Drug Interactions, Immunohistochemistry, Male, Microdialysis, Motor Activity, Oncogene Proteins v-fos, Rats, Rats, Sprague-Dawley, Serotonin, Time Factors, Tyrosine