Kindling increases aversion to saccharin in taste aversion learning

Abstract

Kindling is a model in which an initially subconvulsive electrical stimulation of certain brain areas eventually develops a generalized seizure that produces behavioral and long term neuronal changes. In the present study we evaluated if kindling can modify conditioning taste aversion (CTA). In this paradigm animals acquire aversion to saccharin when it is presented as the conditioned stimulus (CS) followed by an injection of lithium chloride (LiCl) that induces a gastric irritation as the unconditioned stimulus (US). Male Wistar rats were implanted with bipolar electrodes aimed at the right amygdala (AMG) or at the right insular cortex (IC). The animals were stimulated daily until they reached stages 2–4 (intermediate) or until kindling was fully established (three consecutive stage 5 seizures). At least two weeks after kindling stimulation had ceased the animals were deprived of water for 24 h and given 10-min drinking sessions twice a day for 4 days. On day 5 (morning session) tap water was replaced by saccharin solution (0.1%), 20 min later the animals were injected with LiCl (7.5 ml/kg i.p., 0.2 M) to induce gastric malaise or taste aversion. After three more days of baseline consumption, water was substituted by a fresh 0.1% saccharin solution to test the aversion. AMG-kindling delayed the extinction of CTA. Animals with kindling in the IC had a higher retention than the sham kindling group; that is, they drank significantly less saccharin solution than the other groups. The results of the present experiment show that local modification of brain function induced by kindling stimulation can prolong the aversive effects of CTA.