Essential amino acid deficiency enhances long-term intake but not short-term licking of the required nutrient.

Rats can adjust their nutrient intake in response to nutritional deficiency. This phenomenon has been described extensively for sodium deficiency, whereas other nutrient deficiencies have not been explored thoroughly. Essential amino acid (EAA) deficiency represents a relevant model to describe adaptive changes in behavior resulting from deficiency. The purpose of these experiments was to examine more closely the behavioral responses that occur as a result of lysine (LYS) and threonine (THR) deficiency. Licking to LYS, THR, glycine and distilled water during 10-s trials was measured in control (CON) and EAA-deficient rats. Licking tests were conducted both before and after 23-h intake tests. Although EAA-deficient rats did not show increased licking to the deficient EAA in any of the brief-access tests, in all cases, they did initiate significantly more overall trials than did CON. The EAA-deficient rats also had elevated intake of the deficient EAA in long-duration tests. These findings suggest that LYS or THR deficiency does not emulate the behavioral properties of sodium deficiency in that it does not result in enhanced immediate licking responses to the limiting EAA in brief-access tests. Nevertheless, an appetite is expressed to the relevant EAA in a long-term intake test.