Contextual conditioning with an illness US is attenuated by the antiemeticondansetron

In two experiments, rats received an injection of LiCl before being placed in a distinctive context. The formation of an aversion to the context was e vident in the rats' unwillingness, on a subsequent test trial, to consume a (normally palatable) sucrose solution in that context. Experiment 1 demons trated that the size of the context aversion was reduced in rats that recei ved an injection of the antiemetic ondansetron, a selective 5-HT3 antagonis t, immediately prior to the injection of LiCl. Experiment 2 confirmed this effect and showed it to occur also in rats that received an injection of on dansetron prior to the test trial (thus ruling out an explanation of Experi ment 1 in terms of state-dependency of conditioning). The implications of t hese findings for the development of an animal learning model of the condit ioned side effects experienced by patients undergoing cancer chemotherapy a re considered.