Strain differences in mouse response to odours of predators

Sexually mature male mice of three different strains (CD-1 outbred, CBA, and C57BI/6J inbred) were exposed in an arena to a small black cylinder (35 mm film container), filled with faeces of either a mouse predator (red fox, Vulpes vulpes) or a non-predator (rabbit, Oryctolagus cuniculus) during a 3 min test. Control animals were given an empty container. Locomotor activity and behavioural responses in the arena were scored. Hot-plate response (50 ± 0.5°C) was measured 15 min before and immediately after exposure to the odour. Responses to predators were found to be strain-specific. In CD-1 and C57 mice, latency of approach to the small cylinder increased while contacts with it decreased upon fox odour exposure. In CBA mice, fox odour caused an increase of defensive burying and sniffing, and a decrease of rearing. Odour exposure did not affect grooming, digging, or wall rearing in any of the strains. Hot-plate analgesia was also unaffected. The observed strain differences in the defensive response, interpreted as evolutionary adaptive anti-predatory strategies, seem to confirm the suggested origin of the two inbred strains used.