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The Rat Grimace Scale: A partially automated method for quantifying pain in the laboratory rat via facial expressions

Susana G Sotocinal1, Robert E Sorge1, Austin Zaloum1, Alexander H Tuttle1, Loren J Martin1, Jeffrey S Wieskopf1, Josiane CS Mapplebeck1, Peng Wei2, Shu Zhan3, Shuren Zhang3, Jason J McDougall3, Oliver D King2 and Jeffrey S Mogil1*

Author Affiliations

1 Dept. of Psychology and Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC H3A 1B1, Canada

2 Boston Biomedical Research Institute, Watertown, MA 02472 USA

3 Dept. of Physiology and Pharmacology, University of Calgary, Calgary, AB T2N 4N1, Canada

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Molecular Pain 2011, 7:55  doi:10.1186/1744-8069-7-55

Published: 29 July 2011


We recently demonstrated the utility of quantifying spontaneous pain in mice via the blinded coding of facial expressions. As the majority of preclinical pain research is in fact performed in the laboratory rat, we attempted to modify the scale for use in this species. We present herein the Rat Grimace Scale, and show its reliability, accuracy, and ability to quantify the time course of spontaneous pain in the intraplantar complete Freund's adjuvant, intraarticular kaolin-carrageenan, and laparotomy (post-operative pain) assays. The scale's ability to demonstrate the dose-dependent analgesic efficacy of morphine is also shown. In addition, we have developed software, Rodent Face Finder®, which successfully automates the most labor-intensive step in the process. Given the known mechanistic dissociations between spontaneous and evoked pain, and the primacy of the former as a clinical problem, we believe that widespread adoption of spontaneous pain measures such as the Rat Grimace Scale might lead to more successful translation of basic science findings into clinical application.