The assessment of pain using facial expressions in laboratory mice, rats, rabbits and macaques

Facial expressions are routinely used to assess emotions such as pain in humans, especially in the non-verbal (e.g. cognitively impaired and neonates). Recently, the work of Langford et al. (2010) has demonstrated that mice exhibit facial expressions in response to a range of routine nociceptive tests. If these facial expressions are a direct response to pain, then this may offer a new method of assessing pain in animals. The assessment of pain using facial expressions may overcome some of the limitations associated with current best practice of using behaviour. The administration of opioid analgesia itself does not appear to induce changes in facial expressions, confounding the assessment of pain. Facial expressions may be more directly related to the emotional rather than sensory component of pain, and it is the emotional component that is the most critical. In assessing facial expressions we could take advantage of our natural tendency to look at face, which could increase the effectiveness of this method. The assessment of pain using facial expressions should be less time consuming to undertake, allowing effective indicators to be identified for more procedures and species. Our aim is to investigate whether facial expressions can be objectively and reliably used to measure post-procedure pain in a range of laboratory animal species either alone, or in conjunction with other techniques. Initially we will assess whether facial expressions in mice change following procedures associated with both acute (e.g. post-surgical) and chronic (e.g. neoplasia) pain. Once we have successfully validated the use of facial expressions for assessing post-surgical pain in mice we will assess whether a similar approach can be used to assess post-surgical pain in other species, including rats, rabbits and macaques. It is important to note that we currently have no objective method of assessing post-operative pain in non-human primates. We will demonstrate that facial expressions can: (1) Assess post-procedural pain as well as responses to nociceptive testing in mice; (2) Overcome the limitations associated with behavioural pain assessment; (3) Rapidly and objectively score pain in a variety of species; (4) Potentially be a more sensitive measure of pain; (5) Determine the duration and severity of post-procedural pain by correlating them with behavioural indicators of pain in a range of species; (6) Potentially assess the affective component of pain in animals; (7) Evaluate the efficacy of methods to alleviate pain (e.g. analgesic administration), and to develop and apply more humane endpoints.

• Featured in Genetics Magazine: Gene editing and the 3Rs: 20 years of pioneering better science
• Resources: Grimace scales
• Research Review 2013: Using facial expressions of pain in animals
• Engagement Activities: A taste of Pint of Science 2019
• Engagement Activities: British Science Festival 2014