The Assessment of Post-Vasectomy Pain in Mice Using Behaviour and the Mouse Grimace Scale

et al. (2012) The Assessment of Post-Vasectomy Pain in Mice Using Behaviour and the Mouse Grimace Scale. PLoS ONE 7(4): e35656. doi:10.1371/journal.pone.0035656 The Assessment of Post-Vasectomy Pain in Mice Using Behaviour and the Mouse Grimace Scale Matthew C. Leach 0 Kristel Klaus 0 Amy L. Miller 0 Maud Scotto di Perrotolo 0 Susana G. Sotocinal 0 Paul A. Flecknell 0 Weidong Le, Baylor College of Medicine, Jiao Tong University School of Medicine, United States of America 0 1 Institute of Neuroscience and Comparative Biology Centre, Newcastle University , Newcastle upon Tyne , United Kingdom , 2 Department of Psychology and Alan Edwards Centre for Research on Pain, McGill University , Montreal, Quebec , Canada Background: Current behaviour-based pain assessments for laboratory rodents have significant limitations. Assessment of facial expression changes, as a novel means of pain scoring, may overcome some of these limitations. The Mouse Grimace Scale appears to offer a means of assessing post-operative pain in mice that is as effective as manual behavioural-based scoring, without the limitations of such schemes. Effective assessment of post-operative pain is not only critical for animal welfare, but also the validity of science using animal models. Methodology/Principal Findings: This study compared changes in behaviour assessed using both an automated system (''HomeCageScan'') and using manual analysis with changes in facial expressions assessed using the Mouse Grimace Scale (MGS). Mice (n = 6/group) were assessed before and after surgery (scrotal approach vasectomy) and either received saline, meloxicam or bupivacaine. Both the MGS and manual scoring of pain behaviours identified clear differences between the pre and post surgery periods and between those animals receiving analgesia (20 mg/kg meloxicam or 5 mg/kg bupivacaine) or saline post-operatively. Both of these assessments were highly correlated with those showing high MGS scores also exhibiting high frequencies of pain behaviours. Automated behavioural analysis in contrast was only able to detect differences between the pre and post surgery periods. Conclusions: In conclusion, both the Mouse Grimace Scale and manual scoring of pain behaviours are assessing the presence of post-surgical pain, whereas automated behavioural analysis could be detecting surgical stress and/or postsurgical pain. This study suggests that the Mouse Grimace Scale could prove to be a quick and easy means of assessing post-surgical pain, and the efficacy of analgesic treatment in mice that overcomes some of the limitations of behaviourbased assessment schemes. - Funding: Dr. Leach was supported by the NC3Rs (www.nc3rs.org.uk), the BBSRC (www.bbsrc.ac.uk) and the Wellcome Trust (www.wellcome.ac.uk). Ms. Scotto received support from AFSTAL (www.afstal.com) and Laboratory Animals Ltd (www.lal.org.uk). Dr. Miller was supported by the NC3Rs (www.nc3rs.org.uk). The animals used in this study were donated by Charles River (www.criver.com). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have read the journals policy and have the following conflicts. The commercial organizations AFSTAL (the French Laboratory Animal Science Association) and Laboratory Animals Ltd provided financial support for Ms. Scotto in the form of a training scholarship. The commercial organization Charles River UK donated the animals used in the study. This does not alter the authors adherence to all the PLoS ONE policies on sharing data and materials. Legislation governing the use of animal in biomedical research requires that any unnecessary pain or distress is avoided or alleviated (e.g. European Directive EU 2010/63). Successful implementation of effective pain management strategies in animals requires accurate assessment of post-surgical/procedural pain. Such assessments are also essential for evaluating animal models used in the development of novel analgesics. Behaviour-based assessments of pain have been developed for both rats and mice following surgery and other traumatic procedures, and use either the appearance of abnormal behaviours [14], or the change in the frequency of normal behaviour patterns [5] to score pain. The latter approach has the advantage of enabling automated as well as manual behavioural assessments to be conducted, and has been recommended in expert reports [6]. Despite the obvious advantages of using behaviour to assess pain in animals, there remain a number of limitations. The non-specific (i.e. nonanalgesic) effects of many commonly used opioids (e.g. buprenorphine, morphine) can confound behavioural assessments by causing marked behavioural changes in normal, pain-free rodents (e.g. altered activity, increased grooming etc.) that can overlap with those considered to be associated with pain [7]. These changes in overall activity levels could also influence the exhibition abnormal behaviours, so extending this problem to both types of behavioural assessment. The specific behavioural responses to painful stimuli may also vary markedly following different surgical or other painful procedures. Currently such behaviours have been identified for a very limited range of procedures in a small number of laboratory animal species, e.g. abdominal-based procedures in rats, mice and rabbits [24]. A more fundamental issue relates to the underlying assumption that behavioural responses reflect an animals integrated response to external stimuli and relate directly to its internal state. However, they may simply reflect the response to the sensory afferent barrage associated with tissue damage (nociceptive input), and not reflect the affective component of pain (how pain makes animals feel) [8,9]. It is this affective component that is most relevant from a welfare perspective (as recognised in humans). The recently described approach of using facial expressions to assess pain [9] may overcome many of these difficulties. The authors demonstrate that mice undergoing routine rodent nociceptive tests exhibit characteristic changes in facial expressions. Based on these expressions the authors have developed the Mouse Grimace Scale (MGS), which has been used to score pain intensity [9]. In this study, morphine administration induced no change in facial expressions in normal (pain-free) laboratory mice, suggesting no confounding influence of opioid analgesia. Preliminary data from Langford et al. [9] also raises the possibility that facial expression could indicate the affective component of pain in animals as it does in humans. Lesioning of the rostral anterior insula (implicated in the affective component of pain in humans) prevented changes in facial expression but not abdominal writhing (the behavioural marker of abdominal pain or nociception). In addition, using facial expressions to assess pain should be less time consuming to apply than (...truncated)