Specificity of acquired aversions to taste qualities in hamsters and rats

Nine groups of rats and 27 groups of hamsters (n = 12/group) each tasted 1 from among 27 different solutions before receiving an ip injection of apomorphine, then were tested for aversions to 4 solutions prototypic of human beings' four taste qualities (S, sucrose; N, NaCl; H, Hcl; Q, quinine hydrochloride). With most of the solutions that are described as sweet by humans employed as a conditional stimulus (CS), the rodents acquired an S aversion (exceptions occurring for some artificial sweeteners). With CSs described as either predominantly salty or sour by humans, the rodents acquired an N aversion in the former case or an H aversion in the latter case; a Q aversion was also acquired with two (including H) of the three CSs described as sour. With most of the CSs described as predominantly bitter or as having a considerable bitter component by humans, the rodents acquired a Q aversion (as well as a weaker H aversion). Considerable parallels among the taste sensations of humans, rats, and hamsters are indicated. Patterns of activity evoked across four classes of peripheral gustatory neurons (those responding best to lingual stimulation with S, N, H, or Q) in rodents when the CSs were applied to the tongue were similar to the patterns of aversions across the four test stimuli for the CSs. This suggests that these four neural channels mediate the sensations evoked by S, N, H, and Q in rats and hamsters, perhaps even in human beings.