Induction of conditioned taste aversion in rats by GABA or other amino acids

GABA included in the diet is known to reduce food intake and growth of rats fed a low protein diet. Experiments were designed to determine if GABA or other small neutral amino acids would affect food intake if they were administered separately from the diet, and if such amino acids could induce a conditioned taste aversion (CTA) to saccharin. Intubated or injected GABA or alpha-aminoisobutyric acid (AIB), a non-metabolizable isomer of GABA, reduced food intake. When rats were fed a low protein diet, IP injection of threonine (2 mmoles/200 g rat) induced CTA but did not depress food intake; serine (3 mmoles/200 g rat) induced CTA and caused only a small reduction in food intake. Another isomer, alpha-amino-n-butyric acid did not affect food intake or induce CTA at the tested concentrations. Adaptation to a high protein diet, which increases enzymatic degradation of many amino acids including GABA and serine, lessened severity of GABA-induced CTA and eliminated that caused by serine. CTA to saccharin can be induced by certain amino acids; the mechanism is unknown but may involve malaise or other adverse sensations.