Self-selection of Amino Acid and Protein, and Brain Serotonin Concentration in Rats

Abstract

The effects of intraperitoneally injecting pargyline, which elevates the brain serotonin (5-HT) content, and p-chlorophenylalanine (p-Cl-Phe), which lowers the brain 5-HT content, on food selection in growing rats choosing freely between two diets containing various amounts of amino acid (Val, Thr or Trp) or protein (casein) were investigated. Under the conditions of this experiment, no consistent correlation was observed between the amount of amino acid or protein intake and the plasma ratio of Trp to large neutral amino acids (Trp/LNAA). Also, neither the amino acid nor protein intake under the conditions of the selection paradigm was affected, despite the brain neurotransmitter (5-HT) concentration being markedly altered. These results suggest that the concentration of 5-HT in the whole brain will not regulate the amino acid or protein intake and selection. The behavioral aspect of selection for dietary amino acid or protein appears to be related to the maintenance of amino acid concentrations in the blood and brain within normal limits, regardless of the brain 5-HT level.