Contextual conditioning with an illness US is attenuated by the antiemetic ondansetron

Abstract

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 evident in the rats' unwillingness, on a subsequent test trial, to consume a (normally palatable) sucrose solution in that context. Experiment 1 demonstrated that the size of the context aversion was reduced in rats that received an injection of the antiemetic ondansetron, a selective 5-HT3 antagonist, 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 ondansetron prior to the test trial (thus ruling out an explanation of Experiment 1 in terms of state-dependency of conditioning). The implications of these findings for the development of an animal learning model of the conditioned side effects experienced by patients undergoing cancer chemotherapy are considered.