Taste aversion learning during successive negative contrast

Abstract

Previous experiments found that acceptance of saccharin by rats was reduced if they had prior experience of sucrose or some other highly palatable solution. This study tested whether such successive negative contrast (SNC) effects involve acquisition of an aversion to the new taste. In three experiments, rats were switched from sucrose exposure in Stage 1 to a less palatable solution containing a new taste in Stage 2. In Experiments 1 and 2, a novel flavor was added to a saccharin solution at the start of Stage 2. In Experiment 1, preference tests revealed a weak aversion to the added vanilla flavor in the Suc-Sacch group, while in Experiment 2 an aversion was found in the Suc-Sacch group to the salty flavor that was used, compared with controls given access either saccharin or water in Stage 1. In Experiment 3, the Suc-Quin group, given quinine solution in Stage 2, displayed a greater aversion to quinine than a Water-Quin control group. These results support the suggestion that taste aversion learning plays a role in the initial suppression of intakes in a qualitative consummatory SNC effect. However, in the light of other evidence, it seems that the unusual persistence of successive negative contrast when rats are switched from sucrose to saccharin is not due to a long-lasting reduction in the value of saccharin.

Keywords: Negative contrast; Rats; Saccharin; Sucrose; Taste aversion.

Fig. 1

Experiment 1. A Mean intakes (±SEM) in Stage 1, in which groups were given either 10% sucrose (n = 12), 0.4% saccharin (n = 10) or water (n = 9) and in Stage 2, in which all groups were given 0.4% saccharin. The latter solution was flavored with 1% vanilla for the first session of Stage 2 (Day 13). B Mean intake (+SEM) of vanilla-flavored saccharin on Day 13

Fig. 2

Experiment 1. Mean preference ratios (+SEM): A Vanilla-flavored water versus unflavored water. B 0.4% saccharin versus 4% maltodextrin

Fig. 3

Experiment 2. A Mean intakes (±SEM) in Stage 1 of 10% sucrose and 0.4% saccharin solutions and in Stage 2 of the saccharin solution by both groups (n = 12). Access to the solutions was limited to 30 min daily in both stages. On Days 13–14, 0.5% NaCl was added to the saccharin solution for both groups. B Mean intake (+SEM) of the compound NaCl and saccharin solution in the first two sessions of Stage 2 (Days 13–14). NB, the NaCl extinction phase had not yet been introduced but group divisions are presented for comparison

Fig. 4

Experiment 2. Mean preference ratios (+SEM) in two-bottle choice tests between: A 0.5% NaCl solution and water; B 0.4% saccharin and 4% maltodextrin. Note. The NaCl extinction phase had not yet occurred, but group divisions are presented for comparison. n.s. = not significant; ***p = .001

Fig. 5

A Mean intake (±SEM) of 0.5% NaCl solution in the Suc-Extn and Sacch-Extn groups and water in the Suc-Non and Sacch-Non groups. B Mean preference ratios (+SEM) in the two-bottle choice test between 0.5% NaCl solution and water. n.s. = not significant

Fig. 6

Experiment 3. A Mean intakes (±SEM) in Stage 1 of 10% sucrose vs. water and in Stage 3 of quinine solution vs. water. B Mean intake (+SEM) of quinine solution in the first two sessions of Stage 2 (Days 13–14; note, groups were not yet divided into the Stage 3 quinine vs. water conditions)

Fig. 7

Mean quinine preferences (+SEM) presented as percentage ratio of quinine versus water intake at two-bottle choice tests. A Test 1 after two sessions (Days 13–14) of quinine exposure (allocation to Stage 3 fluids had not yet occurred), **p = .006. B Test 2 after Stage 3 quinine or water intake, n.s. = not significant (simple effects)