Methods Used and Application of the Mouse Grimace Scale in Biomedical Research 10 Years on: A Scoping Review

Abstract

The Mouse Grimace Scale (MGS) was developed 10 years ago as a method for assessing pain through the characterisation of changes in five facial features or action units. The strength of the technique is that it is proposed to be a measure of spontaneous or non-evoked pain. The time is opportune to map all of the research into the MGS, with a particular focus on the methods used and the technique’s utility across a range of mouse models. A comprehensive scoping review of the academic literature was performed. A total of 48 articles met our inclusion criteria and were included in this review. The MGS has been employed mainly in the evaluation of acute pain, particularly in the pain and neuroscience research fields. There has, however, been use of the technique in a wide range of fields, and based on limited study it does appear to have utility for pain assessment across a spectrum of animal models. Use of the method allows the detection of pain of a longer duration, up to a month post initial insult. There has been less use of the technique using real-time methods and this is an area in need of further research.

Preclinical models of deep craniofacial nociception and temporomandibular disorder pain

“…The grimace scales could identify characteristics of the facial expression associated with nociception, which have been considered to represent a measure of the affective responses to pain in the rodents [ 211 ]. The grimace scales adapt that scoring to utilize facial features as indicators to assess pain, and are correlated with deep craniofacial pain in the rodents [ 151 ].…”

The neurobiology of pain and facial movements in rodents: Clinical applications and current research

“…The pain scales developed and now applied in veterinary medicine began with rodents due to their importance in studies of diverse pathologies for biomedical research purposes ( Figure 3 ), which involved both spontaneous or induced pain ( 11 ). They were also derived with clinical application in mind due to the challenges in evaluating negative states like pain in rodents ( 160 ). Their development has been based on taking images of animals with and without pain by video recording or using still photos, with or without the use of software such as the “Rodent Face Finder,” which automatically selects specific frames where the face of the rodent can be seen clearly ( 151 ).…”

“…Although these values likely need further investigation and validation ( 162 , 168 ). In general most studies of grimace scales in rodents have employed models where pain was expected to be momentary or acute in nature (from a few minutes to several days) and this is where the strongest evidence for their utility exists ( 160 ). However, there is limited evidence of their utility in manifestations of chronic, neuropathic, and orthopedic pain which are expected to be more chronic in nature and that can implicate pain-related stress ( 169 ).…”

Glycinergic Modulation of Pain in Behavioral Animal Models

“…For example, conditioned place preference experiments can determine if an analgesic drug is perceived as rewarding, indicating an overall improvement in the experience of the rodent ( King et al, 2009 ). The grimace scale enables the study of spontaneous pain which experimenters can gauge by observing the facial language in rodents, resembling the approach to human pain treatment ( Langford et al, 2010 ; Whittaker et al, 2021 ). Additionally, tests such as gait analyses and mechanical conflict-avoidance assays can be used to determine ongoing pain behaviors in a non-evoked manner ( Harte et al, 2016 ; Deuis et al, 2017 ; Sadler et al, 2022 ).…”