Conditioned place aversion based on forced swimming in rats

Forced swimming after the intake of a flavored solution causes aversion to that flavor in rats. The study reported here presents a new finding that forced swimming results in conditioned place aversion. In Experiment 1, a rat's confinement in one of two distinctive chambers—either with vertical stripes on the wall or horizontal stripes—was followed by a 20-min swimming opportunity, while the other chamber did not have this swimming exposure. After the repetitions of these treatments (i.e., the differential conditioning training), a choice preference test was administered, where the rat was given free access to both chambers. The choice test demonstrated that the rats spent less time in the swimming-paired chamber than in the unpaired chamber. Experiment 2 showed that not only a 20-min swimming session but also a 1-min swimming session endowed rats with aversion to the swimming-paired chamber. These results were discussed with regard to the underlying mechanism of swimming-based aversion learning.