Dietary amino acid precursors: Effects on central monoamines, aggression, and locomotor activity in the mouse

Behavioral and brain neurochemical changes were assessed in mice maintained on amino acid supplemented 12% protein diets for two and six weeks. Addition of 1,2, or 4% L-phenylalanine increased aggression but only the 1% supplement increased locomotion. Addition of 0.25 or 0.5% L-tryptophan of the basal diet also increased aggression. All behavioral effects were noted after two weeks but not after six weeks on the diets, suggesting the development of behavioral tolerance. All groups of mice gained the same amount of weight on the various diets over a seven-week period and no ill effects were observed. Mice on 16% protein diets displayed only marginal differences in brain concentrations of phenylalanine, tyrosine, tryptophan, dopamine, norepinephrine, serotonin or 5-hydroxyindoleacetic acid. Brain concentrations of tyrosine, phenylalanine and tryptophan were significantly reduced in animals receiving supplements of leucine for two and six weeks. L-phenylalamine supplementation caused marked increases in brain phenylalanine and tyrosine concentrations after two and six weeks. Changes in brain dopamine and 5-hydroxyindoleacetic acid also were noted. Supplements of 0.25, 0.5, and 1.0% L-tryptophan increased brain indoles, and these changes also appeared to be sustained over the six-week period.