Cortical and subcortical components of the conditioned saccharin aversion

Cortical mechanisms of the conditioned saccharin aversion were studied in 190 rats by the functional ablation technique. Water deprived animals had 15-min access to water on the familiarization Days 1 and 2. On Day 3 the rats were offered saccharin (0.1%, CS) followed 30 min later by LiCl injection (0.14 M, 2% body weight, UCS). The resulting intoxication caused marked conditioned saccharin aversion leading to reduced saccharin ingestion (by 60–80%) on Day 4. Unilateral cortical spreading depression (CSD) elicited on Days 3 and/or 4 by application of 25% KCl on the same or on opposite hemispheres does not diminish conditioned saccharin aversion in comparison with intact animals. Bilateral CSD elicited after saccharin administration, 15 min before or 5 min after LiCl injection on Day 3, does not prevent the development of conditioned saccharin aversion. On the other hand, forced feeding of saccharin under bilateral CSD elicits conditioned saccharin aversion neither with 30 min nor with 5 min CS-UCS delays although significant conditioned saccharin aversion was observed under forced feeding conditions in normal rats. It is concluded that cerebral cortex is necessary for the initial short-term storage of the indifferent gustatory trace but that the association of this engram with aversive gastrointestinal stimuli can be accomplished without cortical participation.