Latent learning about calcium and sodium.

We used the latent-learning paradigm to examine whether replete rats can recognize sodium and calcium and whether they use that knowledge to guide consumption when subsequently mineral deprived. Rats fed a nutritionally complete diet received four pairs of 17-h training trials. During one trial of each pair, the rats drank grape- or cherry-flavored water; during the other, they drank the other flavor mixed with 100 mM CaCl2 (experiment 1), 750 mM NaCl (experiment 2), or 584 mM (20% wt/vol) sucrose (experiment 3). The rats were then fed nutritionally complete, calcium-deficient, or sodium-deficient diet for 3 wk and were given a two-bottle preference test between the two flavors. Relative to rats fed complete diet, calcium-deprived rats had elevated preferences for calcium- and sodium-paired flavors but not sucrose-paired flavors. Sodium-deprived rats had elevated preferences only for sodium-paired flavors. These results provide evidence for the existence of innate calcium and sodium appetites in calcium-deprived rats. They indicate that these distinct appetites are centrally generated behaviors and are not simply due to peripheral alterations in taste perception.