Gustatory effectiveness of amino acids in mice: behavioral and neurophysiological studies

Neural responses to L- and D-amino acids were recorded from the chorda tympani in the ddy mouse and their preferences were measured using the two-bottle choice technique. Most of the D- and L-amino acids elicited neural responses above 10-30 mM, but amino acids with basic side chains and their HCl derivatives produced responses at much lower concentrations. Among 19 amino acids examined, 3 D- and 7 L-amino acids were preferred, 5 L-amino acids were avoided and 4 were neutral to mice. The behavioral threshold to initiate either preference or aversion was negatively correlated with the hedonic intensity produced in mice, but not with the neural response threshold. The preference magnitude for L-amino acids at 0.1 M was negatively correlated with both MW and hydrophobicity of side chains. A high positive correlation was noted between preference magnitude in mice and hedonic intensity in humans. The role of molecular properties of amino acids in eliciting sweetness and bitterness is discussed.