Enhancement of flavor aversion conditioning in weanling but not adult rats by prior conditioning to an odor

In four experiments, we tested the effect of signaled and unsignaled preexposure to the US on conditioning of a taste aversion to saccharin, which was induced by pairing the saccharin (CS) with lithium chloride (US). Rats of two ages were tested, weanlings 21 days old at the time of conditioning and adults 60–80 days old at the time of conditioning. The procedures generally were designed to minimize the deleterious effects of US preexposure on conditioning in adults. In Experiment 1, preexposure to a US signaled by a novel odor (banana) facilitated conditioning in the weanlings but not in the adults. In Experiments 2A and 2B, these results were completely replicated. Only the weanlings were tested in the final experiment, in which it was determined that saccharin-LiCl conditioning was again facilitated by a prior pairing of the banana odor and LiCl, but only if the LiCl doses (.15M or.30 M) were the same for the signaled US preexposure and for the taste-aversion conditioning itself. In all of these experiments, a conditioned aversion to saccharin paired with LiCl was enhanced by prior pairing of an unrelated odor with LiCl, in the weanlings but not the adults. These results agree with others in suggesting that during the first three postnatal weeks rats may have a special disposition for cross-modal transfer.