Change in locomotor activity pattern in mice: a model for recognition of distress?

Recognition and assessment of pain and distress is made by observing common clinical and behavioural signs. Observation usually occurs during a limited period of time and results can be biased by interpretation of an individual observer. To improve objective assessment of distress we studied the locomotor activity pattern of mice during a 24-h interval. As a reference compound, Freund's complete adjuvant (FCA) was used. Mice were injected intraperitoneally with different doses FCA (0, 0.1, 0.2 and 0.5 ml) and observed for 5 to 7 days. Animals did not appear to be in pain and seemed to have a normal activity and behaviour pattern at first sight, however FCA induced a dose-dependent decrease of body weight. Open field activity (total distance run) measured during a limited period of time was not altered as a result of FCA. However, nocturnal activity was dose dependently decreased during the first 3 to 4 nights after treatment with FCA. The data presented indicate that using locomotor activity patterns over 24 h might be a useful adjunct and an objective approach to assess distress.