Advancing pain research and animal welfare: focusing on the Rat Grimace Scale and reporting standards

There is growing interest in the use of non-evoked spontaneous behaviours to assess pain in animals. A tool that measures such behaviours is the Rat Grimace Scale (RGS), a validated facial expression pain scale consisting of four “action units”: orbital tightening, nose/cheek flattening, ear changes and whisker changes.  The strengths and limitations of the RGS are not fully explored. One limitation of the RGS (using the standard scoring method) is its time- and labour-intensive nature (video recording and manual image extraction are required). A primary goal of my research was to evaluate the feasibility of real-time RGS scoring. To accomplish this, the standard and real-time assessment methods were compared. It was found that both scoring methods were comparable and demonstrated the utility of real-time RGS scoring. This provides evidence that the RGS may be utilised not only as a research tool, but a useful clinical and welfare tool as well. A further goal was to explore the use of the RGS in a visceral and chronic pain model. The RGS was hence tested in a dextran sulfate sodium (DSS) colitis model. Two other behavioural tools (burrowing and the composite behaviour score [CBS]) were also evaluated. These behavioural tools were compared to the Disease Activity Index (DAI), a common tool assessing disease severity in colitis models. The RGS and DAI scores increased and decreased concurrently. This study demonstrates that the RGS can be applied to assess chronic visceral pain and may be used to assess the mechanisms of different pain types. The need for training prior to RGS scoring was explored by assessing the rater reliability after receiving training or no training (scoring of multiple images only). This study demonstrates that training is beneficial; training improved scoring reliability and reduced variability. This was not observed in raters who received no training. Additionally, trained raters could still score reliably four years later. Therefore, this study demonstrates the need for new raters to be trained in RGS use to improve reliability. Lastly, this thesis explores whether the publication of the ARRIVE (Animal Research: Reporting of In Vivo Experiments) guidelines improved the reporting standards of animal studies. This study found that reporting standards had not improved meaningfully, and the standard of reporting was no better in papers published in journals that support the ARRIVE guidelines. Therefore, this highlights the need for the enforcement or refinement of ARRIVE guidelines to ensure meaningful improvement of reporting standards. Overall, this thesis demonstrates the utility of the RGS as a practical pain assessment tool, with real-time application and the ability to assess chronic visceral pain. It highlights the need for raters to be trained prior to RGS scoring. Lastly, it demonstrates that the implementation of reporting standards in line with the ARRIVE guidelines are low, and enforcement may be required to ensure widespread application. It is the hope that these studies will encourage the use of the RGS and other non-evoked spontaneous behavioural pain assessment tools and will improve reporting standards in medical literature that advance pain research.

Keyphrases: Grimace scale, Facial expression, Pain, Animal behaviour, Tool development, Affective state, Animal models, ARRIVE guidelines, Reporting standard, Expression faciale