Research proposed on this project during the next year will continue to be directed toward examining relationships among dietary amino acid pattern, blood amino acid pattern, brain amino acid pattern and food intake and food preferences. The approach will consist of examining the degree of competition among basic amino acids for uptake into brain slices. From the results of such studies, diets will be devised that are predicted to inhibit the uptake of a basic amino acid into brain. These diets will then be fed to groups of rats to determine whether they result in food intake depression and depressed uptake into brain of the amino acid shown to be depressed in brain slice experiments. In previous studies, addition to diets of amino acids that compete with histidine or tryptophan has been shown to depress food intake and the depression could be prevented by a supplement of tryptophan or histidine. Plasma amino acid concentrations will also be determined. In experiments in which food intake depression is associated with altered brain amino acid pattern, concentrations of neurotransmitters, such as serotonin and norepinephrine, will be determined.