Review article
Pros and Cons of Clinically Relevant Methods to Assess Pain in Rodents

https://doi.org/10.1016/j.neubiorev.2019.03.009Get rights and content

Highlights

  • Translational research requires the use of relevant preclinical pain models and assessment tools.

  • Clinically relevant behavioral tests should focus on restoring function by reducing pathological pain in the absence of disruptive side effects.

  • Grimace, Operant Behavior, Wheel Running, Burrowing, Nesting, Home Cage Monitoring, Gait Analysis, CPP and CPA are described.

  • Analysis of the advantages and limitations of these tests will help researchers identify appropriate tests for their particular goal.

Abstract

The primary objective of preclinical pain research is to improve the treatment of pain. Decades of research using pain-evoked tests has revealed much about mechanisms but failed to deliver new treatments. Evoked pain-tests are often limited because they ignore spontaneous pain and motor or disruptive side effects confound interpretation of results. New tests have been developed to focus more closely on clinical goals such as reducing pathological pain and restoring function. The objective of this review is to describe and discuss several of these tests. We focus on: Grimace Scale, Operant Behavior, Wheel Running, Burrowing, Nesting, Home Cage Monitoring, Gait Analysis and Conditioned Place Preference/ Aversion. A brief description of each method is presented along with an analysis of the advantages and limitations. The pros and cons of each test will help researchers identify the assessment tool most appropriate to meet their particular objective to assess pain in rodents. These tests provide another tool to unravel the mechanisms underlying chronic pain and help overcome the translational gap in drug development.

Introduction

The ultimate goal of pain research is to develop better treatments to reduce suffering and restore function in chronic pain patients. The problem is that current treatments do not adequately manage chronic pain (Borsook et al., 2014). Barriers to effective treatment include inadequate efficacy of current pharmacological therapies, unpleasant or dangerous side effects that limit dosing, the development of tolerance and dependence with repeated administration, fear of addiction, limited knowledge about how pain is coded, and difficulties assessing the social, emotional, and cognitive aspects of pain. The promise of animal research is to improve understanding of the biological mechanisms underlying pain and the endogenous systems that provide pain relief. Advances in our knowledge of how molecular mechanisms and neural circuits differ between different pain conditions (e.g. evoked vs. spontaneous pain; protective vs. pathological pain; deep tissue vs cutaneous pain) will enhance pain treatment by identifying novel targets. Clinically relevant pain assessment techniques will be especially useful in identifying molecular targets and neural circuits that can be used to guide development of more effective treatments. Using appropriate animal models of pain and thoughtful interpretation of the measures will allow the screening of novel compounds for analgesic efficacy. To date, few treatments targeting pain mechanisms in animals have translated to clinical application in chronic pain patients (Mao, 2012; Mogil et al., 2010a).

There are many reasons for the failure of basic research to produce novel treatments. The endpoint for classical stimulus-evoked pain tests that have been used for decades in rodents - von Frey (Frey, 1896), tail flick (D’amour and Smith, 1941), hotplate (O’Callaghan and Holtzman, 1975), and Hargreaves tests (Hargreaves et al., 1988) – is the inhibition of a behavioral response following acute application of a noxious stimulus. In many cases, the stimulus is applied to normal, non-pathological skin. Drugs that inhibit these responses in uninjured animals block normal, protective responses to noxious stimuli. Any treatment that prevents a patient from responding to a hot stove or a blister on the toe puts the patient at risk. An ideal analgesic compound will leave pain-evoked responses intact and reduce pathological pain. The goal of the clinician is to reduce pathological pain so the patient can engage in normal life activities, not to block responses to noxious stimuli. This mismatch between the goal of clinicians to restore function and the aim of preclinical studies to inhibit normal pain-evoked responses has limited drug development.

Pain-evoked tests are also problematic because they can’t distinguish between analgesic and motor or other disruptive side effects. An animal’s lack of response to a noxious stimulus could indicate analgesia, paralysis, sedation, or lack of motivation. Some studies deal with this problem by conducting additional tests to screen for side effects (Morgan et al., 2006), but this is time-consuming and most studies do not include such an analysis. A change in preclinical research from using pain-evoked tests to function based tests would facilitate the identification of drugs that inhibit nociception in the absence of disruptive side effects.

The first step in the alignment of animal research and clinical practice was the development of different chronic pain conditions in laboratory animals (Bennett and Xie, 1988; Hong and Abbott, 1994; Iadarola et al., 1988; Ness and Gebhart, 1988; Schaible and Schmidt, 1985). These studies have advanced animal research from analysis of pain-evoked responses in healthy animals (e.g., hot plate and tail flick tests) to analysis of chronic conditions such as inflammatory and neuropathic pain. The second step in aligning animal research and clinical practice is the use of similar behavioral endpoints. The most common method to assess pain in humans is self-report using visual analog scales, but a number of non-verbal methods that can be used in both humans and animals are also available (Chow et al., 2016; Rabbitts et al., 2014). This review is focused on the pros and cons of behavior measures that can be used to assess clinically relevant pain in both humans and animals.

Our definition of clinical relevance is an animal study that uses a persistent pain condition that occurs in humans and is measured using endpoints that can also be measured in humans. We do not claim, nor do we believe, that only studies that use these criteria are clinically relevant. Clinical relevance depends on the research objective. Pain-evoked tests such as tail withdrawal from hot water may be clinically relevant for studies examining thermal pain mechanisms, but not clinically relevant if the goal is to assess treatments for neuropathic pain. Many pain-evoked tests (e.g., the hot plate & von Frey tests) have been used to assess the analgesic efficacy of drugs to treat pain. These tests have a long history and have contributed much to pain research (Le Bars et al., 2001). However, our more narrow definition of clinical relevance is necessary for the identification of new treatments for chronic pain.

A new generation of clinically relevant pain measures has been developed over the past decade. The tests differ widely, including both pain-evoked and pain-depressed methods. Although some of these tests have been reviewed before (Cobos and Portillo-Salido, 2013; Negus et al., 2006; Tappe-Theodor and Kuner, 2014), our goal is to describe the advantages and disadvantages of these pain measures as a way to facilitate adoption of the best test for the goals of a particular study.

Section snippets

Grimace scale

The Mouse and Rat Grimace Scale have been widely cited as a clinically relevant method to assess nociception. Although grimacing can also be evoked in aggressive or fearful contexts (Defensor et al., 2012), in positive emotional states (Finlayson et al., 2016), and in response to aversive taste experiences (Berridge, 2000), pain grimacing is distinguished by the context and associated behaviors (e.g., orbital tightening, ear position). The method to assess pain grimacing consists of examining

Conclusion

The key to successful research is using tests that match the goals of the study: For example, gait analysis to understand the impact of arthritis on movement, reversal of pain-depressed wheel running for drug development, and CPP to assess the affective component of pain. We do not claim that the tests described in this review are better than other tests, but they do mimic clinical features of pain in unique and important ways. Our goal in describing problems with each test is not to discourage

Acknowledgments

The authors acknowledge funding from the Collaborative Research Center 1158 (SFB1158, Heidelberg Pain Consortium, Germany) from the Deutsche Forschungsgemeinschaft (DFG) to ATT and NIH grant NS095097 to MMM.

References (139)

  • R.M.J. Deacon et al.

    Hippocampal cytotoxic lesion effects on species-typical behaviours in mice

    Behav. Brain Res.

    (2002)
  • R.M.J. Deacon et al.

    Age-dependent and -independent behavioral deficits in Tg2576 mice

    Behav. Brain Res.

    (2008)
  • C.J. Gordon et al.

    Impact of genetic strain on body fat loss, food consumption, metabolism, ventilation, and motor activity in free running female rats

    Physiol. Behav.

    (2016)
  • K. Hargreaves et al.

    A new and sensitive method for measuring thermal nociception in cutaneous hyperalgesia

    Pain

    (1988)
  • B. Hart

    Biological basis of hte behavior of sick animals

    Neurosci. Biobehav. Rev.

    (1988)
  • Y. Hong et al.

    Behavioural effects of intraplantar injection of inflammatory mediators in the rat

    Neuroscience

    (1994)
  • W. Huang et al.

    A clinically relevant rodent model of the HIV antiretroviral drug stavudine induced painful peripheral neuropathy

    Pain

    (2013)
  • C.H. Hung et al.

    Spontaneous chronic pain after experimental thoracotomy revealed by conditioned place preference: morphine differentiates tactile evoked pain from spontaneous pain

    J. Pain

    (2015)
  • M.J. Iadarola et al.

    Enhancement of dynorphin gene expression in spinal cord following experimental inflammation: stimulus specificity, behavioral parameters and opioid receptor binding

    Pain

    (1988)
  • P. Jirkof

    Burrowing and nest building behavior as indicators of well-being in mice

    J. Neurosci. Methods

    (2014)
  • R. Kandasamy et al.

    Home cage wheel running is an objective and clinically relevant method to assess inflammatory pain in male and female rats

    J. Neurosci. Methods

    (2016)
  • R. Kandasamy et al.

    Analysis of inflammation-induced depression of home cage wheel running in rats reveals the difference between opioid antinociception and restoration of function

    Behav. Brain Res.

    (2017)
  • R. Kandasamy et al.

    Depression of home cage wheel running is an objective measure of spontaneous morphine withdrawal in rats with and without persistent pain

    Pharmacol. Biochem. Behav.

    (2017)
  • T. King et al.

    Contribution of afferent pathways to nerve injury-induced spontaneous pain and evoked hypersensitivity

    Pain

    (2011)
  • E.H. Lakes et al.

    Gait analysis methods for rodent models of arthritic disorders: reviews and recommendations

    Osteoarthr. Cartil.

    (2016)
  • W. Lau et al.

    A back translation of pregabalin and carbamazepine against evoked and non-evoked endpoints in the rat spared nerve injury model of neuropathic pain

    Neuropharmacology

    (2013)
  • W. Lau et al.

    A back translation of pregabalin and carbamazepine against evoked and non-evoked endpoints in the rat spared nerve injury model of neuropathic pain

    Neuropharmacology

    (2013)
  • P. Liu et al.

    Ongoing pain in the MIA model of osteoarthritis

    Neurosci. Lett.

    (2011)
  • L.C. Loram et al.

    Behavioural, histological and cytokine responses during hyperalgesia induced by carrageenan injection in the rat tail

    Physiol. Behav.

    (2007)
  • J. Mao

    Current challenges in translational pain research

    Trends Pharmacol. Sci.

    (2012)
  • K.A. McLinden et al.

    Age exacerbates sickness behavior following exposure to a viral mimetic

    Physiol. Behav.

    (2012)
  • J.S. Mogil et al.

    The necessity of animal models in pain research

    Pain

    (2010)
  • E. Navratilova et al.

    Brain circuits encoding reward from pain relief

    Trends Neurosci.

    (2015)
  • T.J. Ness et al.

    Colorectal distension as a noxious visceral stimulus: physiologic and pharmacologic characterization of pseudaffective reflexes in the rat

    Brain Res.

    (1988)
  • A. Okun et al.

    Afferent drive elicits ongoing pain in a model of advanced osteoarthritis

    Pain

    (2012)
  • N. Andrews et al.

    Novel, nonreflex tests detect analgesic action in rodents at clinically relevant concentrations

    Ann. N. Y. Acad. Sci.

    (2011)
  • M. Arras

    Improvement of pain therapy in laboratory mice

    ALTEX

    (2007)
  • R.S. Bains et al.

    Analysis of individual mouse activity in group housed animals of different inbred strains using a novel automated home cage analysis system

    Front. Behav. Neurosci.

    (2016)
  • D. Borsook et al.

    Lost but making progress - Where will new analgesic drugs come from?

    Sci. Transl. Med.

    (2014)
  • D. Bree et al.

    Characterization of the affective component of acute postoperative pain associated with a novel rat model of inguinal hernia repair pain

    CNS Neurosci. Ther.

    (2016)
  • R.G. Brito et al.

    Regular physical activity prevents development of chronic muscle pain through modulation of supraspinal opioid and serotonergic mechanisms

    Pain Rep.

    (2017)
  • Y.-Q. Cai et al.

    Brain circuits mediating opposing effects on emotion and pain

    J. Neurosci.

    (2018)
  • F. Cattaruzza et al.

    Transient receptor potential ankyrin 1 mediates chronic pancreatitis pain in mice

    Am. J. Physiol. Liver Physiol.

    (2013)
  • S. Chow et al.

    Pain assessment tools for older adults with dementia in long-term care facilities: a systematic review

    Neurodegener. Dis. Manag.

    (2016)
  • M.D. Clark et al.

    Evaluation of liposome-encapsulated oxymorphone hydrochloride in mice after splenectomy

    Comp. Med.

    (2004)
  • P.J. Clark et al.

    Genetic influences on exercise-induced adult hippocampal neurogenesis across 12 divergent mouse strains

    Genes Brain Behav.

    (2011)
  • E.J. Cobos et al.

    “Bedside-to-Bench” behavioral outcomes in animal models of pain: beyond the evaluation of reflexes

    Curr. Neuropharmacol.

    (2013)
  • M. Constantinou et al.

    Spatial-temporal gait characteristics in individuals with hip osteoarthritis: a systematic literature review and meta-analysis

    J. Orthop. Sports Phys. Ther.

    (2014)
  • E.D. Costa et al.

    Can grimace scales estimate the pain status in horses and mice? A statistical approach to identify a classifier

    PLoS One

    (2018)
  • F.E. D’amour et al.

    A method for determining loss of pain sensation

    J. Pharmacol. Exp. Ther.

    (1941)
  • Cited by (0)

    View full text