Aversion- vs fear-inducing properties of 2,4,5-trimethyl-3-thiazoline, a component of fox odor, in comparison with those of butyric acid.

2,4,5-trimethyl-3-thiazoline (TMT), a component of fox feces, is a widely used odorant to induce innate fear behavior in rats and mice. However, based on the slight acrid smell it was argued that the observed behavioral effects are a result of the aversive and not of the fear-inducing properties of TMT. In the present study, we tried to directly compare the aversive and fear-inducing properties of TMT with those of the aversive control odor butyric acid. We first identified concentrations of butyric acid and TMT that induce similar amounts of avoidance behavior in rats, indicating that these concentrations have similar aversive properties. In a second experiment, these two concentrations were then tested for their ability to induce freezing, a species-specific defensive response. Only TMT but not butyric acid induced freezing in the rats. This supports the hypothesis that TMT indeed has specific fear-inducing properties and that the observed behavioral effects could not simply be reduced to the aversive properties of TMT.