Learning of gastrointestinal satiety signals

Rats were trained to ingest corn oil emulsion. Such ingestion was accompanied by intragastric injection either of dilute amino acid (e.g., 4.3 mM L-tryptophan) in one group or saline in a second. No significant difference between the two groups was observed at the end of training. However sudden omission of the amino acid led to a large increase in intake, whereas sudden introduction of the amino acid produced no significant change. It seems that signals for the amount of nutrient ingested can be arbitrarily associated with different nutrients and that the value of such satiety signals is not innately fixed in the amount of feeding inhibition exerted.