Immediate and long-term effects of novel odors on risk assessment in mice.

The effects novel predator and nonpredator odors on risk assessment and nonagonistic behaviors were investigated in a series of 4 experiments. During initial exposure, a synthetic predator odor proved to be no more effective than sheeps' wool in evoking defensive behaviors among either naive or previously defeated mice. When the mice were tested following 60-min habituation to the odors, the predator odor consistently elicited stronger defensiveness than sheeps' wool. Substitution of a pungent nonpredator odor (citronella) for that of sheeps' wool in Experiment 4 however, elevated levels of risk assessment among habituated mice to those evoked by the predator stimulus. The use of prior habituation trials seems to provide a sensitive procedure for assessing differential responsiveness to odors and should be useful for anxiogenic, but not anxiolytic, experimental manipulations. The data further suggest that odor novelty and intensity are important contributors to heightened levels of antipredator defense.