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

Worldwide millions of laboratory animals undergo potentially painful procedures as part of essential scientific research. In order for this pain to be relieved we must be able to effectively recognise it and to assess its severity. Although we have made considerable advances in the effective assessment of animal pain our current methods have major limitations that urgently need to be overcome: (1) Effective indicators of pain have been identified for a very limited range of painful procedures in a small number of laboratory animal species, because developing and applying the methods are very time consuming; (2) Current methods may only measure an animals? physical reaction to pain rather than how it makes them ?feel?. In humans, how we feel about our pain is more important than our physical reaction to it; (3) Some routinely used painkillers (e.g. morphine-like drugs) cause changes in commonly used indicators of pain that are similar to those seen in response to pain; (4) We seem to focus on the face of animals when trying to assess their pain, but almost all of the currently used indicators of pain are not observed in the face.

The assessment of facial expressions exhibited in response to pain may offer a solution to these limitations. Facial expressions are often used in assessments of pain and other emotional states in humans, particularly in those who are unable to communicate verbally (e.g. newborn babies). We will investigate whether facial expressions can effectively be used to measure pain in animals following potentially painful procedures and whether this approach is an improvement on current techniques. We will develop and apply measurement of facial expressions in several different species. We will use it, together with existing methods, to assess the duration and severity of pain after different procedures. We will also test whether facial expressions can be use to evaluate the effectiveness of methods to alleviate pain (e.g. painkiller administration) and to develop and apply more humane endpoints.

Initially we will assess whether facial expressions in mice change following procedures associated with both acute (e.g. post-surgical) and chronic (e.g. cancer) pain. We will then assess whether a similar approach can be used to assess post-surgical pain in 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.

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.