AN AMINO-ACID MIXTURE DEFICIENT IN PHENYLALANINE AND TYROSINE REDUCESCEREBROSPINAL-FLUID CATECHOLAMINE METABOLITES AND ALCOHOL-CONSUMPTIONIN VERVET MONKEYS

An amino acid mixture devoid of tryptophan, given orally, was previous ly shown to reduce cerebrospinal fluid levels of tryptophan and 5-hydr oxyindoleacetic acid in vervet monkeys, as compared to a control mixtu re containing all essential amino acids, In the present study, we test ed the possibility that a similar amino acid mixture containing trypto phan, but devoid of phenylalanine and tyrosine (the amino acid precurs ors of catecholamine neurotransmitters), would influence dopamine and noradrenaline metabolism. Five hours after the administration of this mixture to vervet monkeys, cerebrospinal fluid levels of homovanillic acid and 3-methoxy-4-hydroxy-phenylethylene glycol were reduced by 27. 4% and 26.9%, respectively. Both effects were statistically significan t. Plasma tyrosine (-30%) and the ratio of tyrosine to the sum of othe r large neutral amino acids (Sigma LNAA) were also significantly reduc ed. The behavioral efficacy of phenylalanine/tyrosine depletion was co mpared with that of tryptophan depletion in a primate model of volunta ry alcohol consumption. All three drinks lowered alcohol consumption, but the effects of the tryptophan-deficient amino acid mixture were no t different from those of the balanced amino acid control. The phenyla lanine/tyrosine-deficient drink differentially lowered alcohol consump tion, consistent with other data in this species and elsewhere implica ting dopamine in the rewarding effects of alcohol.