Use of spontaneous behaviour measures to assess pain in laboratory rats and mice: How are we progressing?

The understanding and recognition of pain in laboratory rats and mice has advanced considerably in recent times. However, there is evidence that despite these advances, analgesics are still relatively underutilised in these species. One possible contributing influence to this is the difficulty in assessing pain reliably and objectively in these prey species. This review presents the current scientific knowledge on behavioural methods of pain assessment in laboratory rats and mice. The focus is on measures of spontaneous behaviour, since these will find greatest utility in clinical pain management.A range of behavioural pain assessment tools are discussed and difficulties in study interpretation are highlighted. Such methods include locomotor activity, pain specific behaviour identification and the novel facial pain recognition methods developed more recently. Practical problems associated with the techniques are discussed and gaps in the scientific knowledge are identified. A substantial body of information on behavioural signs of acute pain has been collected. Developing awareness and attention to this amongst research workers would improve its application to practice. However, use of techniques for objective measurement can be laborious, subject to variability and confounded by experimental procedures. The increased availability of automated behavioural monitoring systems will reduce these concerns, but it still remains imperative that researchers perform behavioural pilot studies to elucidate behaviours of interest specific to their animal model.Few murine studies of behavioural pain assessment have been performed and this is an area that needs further investigation. Additionally, whilst acute post-operative pain scales in rats have been fairly well-characterised, these should be tested in different acute pain models to determine their reproducibility. Few tools for assessment of chronic pain, such as that arising from inflammatory or neoplastic disease, exist in both of the species examined. Pain-specific behavioural identification is the more widely tested method in the face of chronic pain. However, studies to date have yielded few reliable and consistent behaviours indicative of this category of pain. This is an area in which future studies and funding should be directed, given the significant number of laboratory animals that are likely to experience such pain states. Greater collaboration between ethologists and scientists using animal models should be established in order to improve animal welfare and advance scientific knowledge in this area.