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      The grimace scale reliably assesses chronic pain in a rodent model of trigeminal neuropathic pain

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          Highlights

          • Facial expressions were analyzed after constriction injury of infraorbital nerve.

          • The grimace score reliably assesses ongoing pain in a this model.

          • The grimace score can be used in both rats and mice with trigeminal neuropathic pain.

          Abstract

          The limited success in translating basic science findings into effective pain management therapies reflects, in part, the difficulty in reliably assessing pain in experimental animals. This shortcoming is particularly acute in the field of chronic, ongoing pain. Quantitative analysis of facial expressions—the grimace score—was introduced as a promising tool, however, it is thought to reliably assess only pain of short or medium duration (minutes to hours). Here, we test the hypothesis that grimace scores are a reliable metric of ongoing neuropathic pain, by testing the prediction that chronic constriction injury of the infraorbital nerve (CCI-ION) will evoke significant increases in grimace scale scores. Mice and rats were subjected to CCI-ION, and tested for changes in mechanical hypersensitivity and in grimace scores, 10 or more days after surgery. Both rats and mice with CCI-ION had significantly higher grimace scores, and significantly lower thresholds for withdrawal from mechanical stimuli applied to the face, compared to sham-operated animals. Fentanyl reversed the changes in rat grimace scale scores, suggesting that these scores reflect pain perception. These findings validate the grimace scale as a reliable and sensitive metric for the assessment of ongoing pain in a rodent model of chronic, trigeminal neuropathic pain.

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          Most cited references35

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          A call for transparent reporting to optimize the predictive value of preclinical research.

          The US National Institute of Neurological Disorders and Stroke convened major stakeholders in June 2012 to discuss how to improve the methodological reporting of animal studies in grant applications and publications. The main workshop recommendation is that at a minimum studies should report on sample-size estimation, whether and how animals were randomized, whether investigators were blind to the treatment, and the handling of data. We recognize that achieving a meaningful improvement in the quality of reporting will require a concerted effort by investigators, reviewers, funding agencies and journal editors. Requiring better reporting of animal studies will raise awareness of the importance of rigorous study design to accelerate scientific progress.
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            How to Do Random Allocation (Randomization)

            Purpose To explain the concept and procedure of random allocation as used in a randomized controlled study. Methods We explain the general concept of random allocation and demonstrate how to perform the procedure easily and how to report it in a paper.
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              An overview of animal models of pain: disease models and outcome measures.

              Pain is ultimately a perceptual phenomenon. It is built from information gathered by specialized pain receptors in tissue, modified by spinal and supraspinal mechanisms, and integrated into a discrete sensory experience with an emotional valence in the brain. Because of this, studying intact animals allows the multidimensional nature of pain to be examined. A number of animal models have been developed, reflecting observations that pain phenotypes are mediated by distinct mechanisms. Animal models of pain are designed to mimic distinct clinical diseases to better evaluate underlying mechanisms and potential treatments. Outcome measures are designed to measure multiple parts of the pain experience, including reflexive hyperalgesia measures, sensory and affective dimensions of pain, and impact of pain on function and quality of life. In this review, we discuss the common methods used for inducing each of the pain phenotypes related to clinical pain syndromes as well as the main behavioral tests for assessing pain in each model. Understanding animal models and outcome measures in animals will assist in translating data from basic science to the clinic. Copyright © 2013 American Pain Society. Published by Elsevier Inc. All rights reserved.
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                Author and article information

                Contributors
                Journal
                Neurobiol Pain
                Neurobiol Pain
                Neurobiology of Pain
                Elsevier
                2452-073X
                01 November 2017
                August 2017
                01 November 2017
                : 2
                : 13-17
                Affiliations
                [a ]Program in Toxicology, University of Maryland School of Medicine, Baltimore, MD, USA
                [b ]Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
                [c ]Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
                [d ]Department of Advanced Oral Sciences and Therapeutics, School of Dentistry, Baltimore, MD, USA
                Author notes
                [* ]Corresponding author at: Department of Anatomy & Neurobiology, University of Maryland School of Medicine, 20 Penn Street, Room S251, Baltimore, MD 21201, USA. akeller@ 123456som.umaryland.edu
                Article
                S2452-073X(17)30022-3
                10.1016/j.ynpai.2017.10.001
                5808980
                29450305
                53a87043-d81e-40ed-8c28-70d32db93e6e
                © 2017 The Authors

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                History
                : 5 October 2017
                : 24 October 2017
                : 29 October 2017
                Categories
                Original Research Article

                chronic pain,constriction nerve injury,behavior,pain metrics

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