Abstract
Urine excreted from the common grey wolf (Canis lupus) contains a kairomone, inducing fear-related behaviors in various mammals. Numerous fear-inducing substances activate neurons at the main and/or accessory olfactory bulb (AOB), medial and central amygdala, and hypothalamus. Our previous study showed that the mixture of pyrazine analogues (P-mix) contained in wolf urine induced avoidance and fear-related behaviors in laboratory mice and Hokkaido deer (Cervus nippon yesoensis), a species native to Japan. Exposure to wolf urine or P-mix induced expression of Fos, a marker of neuronal excitation, in the AOB of mice. In the present study, we explored the effects of P-mix on fear-related behaviors and Fos-expression in rats. Exposure to P-mix induced avoidance and immobilization in rats, while that to a mixture of i-amyl acetate, linalool and R(+)-limonene (O-mix), which generate floral and fruity odors, induced avoidance but not immobilization. P-mix but not O-mix increased Fos-immunoreactivity of the AOB, medial and central amygdala, and hypothalamus of rats. The present results suggest that P-mix odor induces unlearned fear-related behaviors in rats.
Highlights
Prey animals are equipped with sensory systems for predator detection
We examined the Fos-immunoreactive structure at the accessory olfactory bulb (AOB), medial amygdala (MeA), medial division of central amygdaloid nucleus (CeM), and hypothalamus after exposure to P-mix to explore whether P-mix induces neuronal excitation in these brain regions of the rats
Tukey-Kramer's post-hoc testing indicated that the density of Fos-ir cells at the MeA after exposure to P-mix was higher than that without P-mix or after exposure to O-mix. These results indicate that P-mix induces excitation of neurons at the medial amygdala of rats
Summary
Prey animals are equipped with sensory systems for predator detection Predator odors such as cat odor, trimethyl thiazoline (TMT), which is a component of fox feces, and ferret odor induce fear-related behaviors in rats (Wallace and Rosen, 2000; Dielenberg et al, 2001; Blanchard et al, 2001; Roseboom et al, 2007). Analysis of the feces of the gray wolf shows that the diets of these animals are diverse and include smaller prey species such as rodents in addition to ungulates (Stahler et al, 2006). This suggests that rodents are afraid of wolves. We identified pyrazine derivatives in wolf urine that induced fear-related responses in mice and Hokkaido deer (Cervus nippon yesoensis), a species native to Japan (Osada et al, 2013; 2014; 2015)
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