A Review of Pain Assessment Methods in Laboratory Rodents

Abstract

Ensuring that laboratory rodent pain is well managed underpins the ethical acceptability of working with these animals in research. Appropriate treatment of pain in laboratory rodents requires accurate assessments of the presence or absence of pain to the extent possible. This can be challenging some situations because laboratory rodents are prey species that may show subtle signs of pain. Although a number of standard algesiometry assays have been used to assess evoked pain responses in rodents for many decades, these methods likely represent an oversimplification of pain assessment and many require animal handling during testing, which can result in stress-induced analgesia. More recent pain assessment methods, such as the use of ethograms, facial grimace scoring, burrowing, and nest-building, focus on evaluating changes in spontaneous behaviors or activities of rodents in their home environments. Many of these assessment methods are time-consuming to conduct. While many of these newer tests show promise for providing a more accurate assessment of pain, most require more study to determine their reliability and sensitivity across a broad range of experimental conditions, as well as between species and strains of animals. Regular observation of laboratory rodents before and after painful procedures with consistent use of 2 or more assessment methods is likely to improve pain detection and lead to improved treatment and care—a primary goal for improving overall animal welfare.

Grimace Scores: Tools to Support the Identification of Pain in Mammals Used in Research

“…Acute pain serves an evolutionary and adaptive function to signal and avoid potential or actual damage to tissues. This type of pain may result from an injury or surgical wound [ 3 , 4 , 5 ]. Visceral pain is due to the activation of stretch or pressure receptors in visceral organs.…”

“…Unalleviated or poorly treated acute pain can progress to chronic pain. The latter is the result of neuroplastic changes occurring within the nervous system, rendering the body more sensitive to pain and can even create sensations of pain without any external stimuli [ 3 , 4 , 5 , 6 , 7 ]. It is important to be able to manage and assess all types of pain in research mammals and avoid the inadvertent development of chronic pain.…”

“…Using the precautionary principle, animal ethics committees and research staff must acknowledge the potential for pain [ 5 , 10 , 12 , 14 ]. They must also consider the experimental and animal welfare consequences of pain and take steps to ensure pain is adequately managed during procedures [ 3 , 4 , 5 , 15 ]. Regulatory frameworks often apply, as a precaution, the anthropomorphic principle, by which any procedure causing, or expected to cause, pain in humans, may produce pain in animals.…”

“…Conversely, positive emotional states of animals are linked to less experimental variability and more robust experimental results [ 22 , 23 ]. The full spectrum of potential confounders to unmitigated pain is not entirely understood; however, the literature supports that there are experimental and animal welfare benefits in identifying and subsequently treating pain and alleviating negative effects on animals used for research [ 3 , 17 , 19 , 21 , 22 , 23 , 24 ].…”

“…The specificity and sensitivity of a test are also crucial to ensure animals are correctly identified when pain or welfare concerns arise. If the specificity is too low, there is a risk of pain being incorrectly identified, potentially leading to unnecessary interventions such as pain relief or humane euthanasia [ 3 , 7 , 15 , 36 ]. Alternatively, if the sensitivity is too low, experimental animals may reach their threshold for intervention while being inaccurately identified as not painful, therefore remaining in pain possibly even beyond their humane endpoint.…”