Ethoexperimental studies of behaviour in wild and laboratory mice

The laboratory mouse is the most frequently used laboratory animal in biomedical research today. This thesis deals with behavioural studies of risk assessment in mice as a means of assessing emotional reactivity. The long-term objective of this work is to find relevant behavioural measures in relation to animal welfare. We were interested in increasing our knowledge about the natural baseline of risk assessment behaviours and therefore the idea of comparing behavioural strategies between wild mice and laboratory mice was realised. A novel environment elicits exploratory motivation in the mouse and entails a trade-off conflict between the possibility of locating important resources and the risk of encountering unidentified dangers. Using a battery of tests, Concentric Square Field, Open Field and Elevated Plus Maze, differences in behavioural strategies of exploration and risk assessment were studied. Wild-derived house mice (Mus musculus musculus) were contrasted with domesticated mice of the inbred strains BALB/c and C57BL/6. Taken together, differences in behavioural strategies between wild and laboratory mice were mainly quantitative, however specific behavioural profiles in relation to risk assessment and emotional reactivity were recorded. Wild mice differed from both laboratory strains mainly in an unwillingness to enter open areas. The BALB/c mice generally avoided risk areas and showed a high risk assessment while C57BL/6 mice were more explorative, demonstrating a higher rate of risk taking and performing little risk assessment. No major sex differences were found in the behaviours related to risk assessment and emotional reactivity. However, sex differences were more pronounced in Wild and C57BL/6 mice than in BALB/c mice. In the Light/Dark test, strain was a greater factor than home cage environment (enriched/non-enriched) in terms of risk assessment, emotional reactivity and inter individual variance . Risk assessment was also investigated in a novel test of predator exposure, the Rat Exposure Test. The results were in contrast to the previous findings, as C57BL/6 mice showed more risk assessment, avoidance behaviour and active defence than BALB/c mice in response to the rat. This discrepancy suggest a difference between the responsiveness to novelty or novel places compared to the anti-predator response, at least in these two inbred strains. Moreover, it supports the notion that the environmental features of the test arena, familiarity of the environment and type of aversive stimuli may have a large impact on emotional reactivity and that the strain of the mouse is an important factor in how the situation is perceived. It is concluded that risk assessment is a sensitive marker for emotional reactivity in laboratory mice but that a multivariate approach is necessary for a thorough characterisation in terms of animal welfare