Comparison of preference thresholds for NaCl solution in rats of the Sprague-Dawley and Long-Evans strains.

Rats of the Sprague-Dawley and Long-Evans strains were compared with respect to their preference threshold and preference maximum concentrations for NaCl solution in a two-bottle choice paradigm. The preference threshold for NaCl in rats of the Sprague-Dawley strain occurred when the concentration of NaCl presented was 0.030 M. The preference maximum concentration was 0.10 M. In the case of rats of the Long-Evans strain, a preference threshold concentration was not clearly manifested although the preference maximum concentration was also 0.10 M. Thus, the previously reported lack of an appetite for isotonic NaCl solution in rats of the Long-Evans strain compared to those of the Sprague-Dawley strain is most likely related to the failure of rats of the former strain to discriminate between water and NaCl solution until the concentration of NaCl exceeds 0.15 M. However, at this concentration, both strains rejected NaCl solution in favor of water. In contrast to the results with NaCl solution, rats of the Long-Evans strain appear to have a greater appetite for 5% glucose solution than do those of the Sprague-Dawley strain. Whether this is related to a reduced preference threshold concentration for glucose remains to be tested.