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Review
. 2019 Dec 1;69(6):451-467.
doi: 10.30802/AALAS-CM-19-000042. Epub 2019 Dec 20.

A Review of Pain Assessment Methods in Laboratory Rodents

Patricia V Turner  1 , Daniel Sj Pang  2 , Jennifer Ls Lofgren  3
Affiliations
Review

A Review of Pain Assessment Methods in Laboratory Rodents

Patricia V Turner et al. Comp Med. .

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.

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Figures

Figure 1.
Figure 1.
Common methods to assess analgesic efficacy in rodents.
Figure 2.
Figure 2.
Examples of pain-associated behaviors demonstrated after a laparotomy in an adult male Sprague–Dawley rat. (A) Back arch—this behavior is described as a vertical cat-like stretch upward. (B) Writhe - this behavior is described as the contraction of the abdominal muscles (arrow).
Figure 3.
Figure 3.
The Grooming Transfer Test allows indirect assessment of a mouse's grooming behavior. If grooming well, the mouse will transfer the fluorescent signal from the top of their head to additional body locations, and in time, completely groom away from the signal. The latency to progressive grooming scores is increased in mice with unalleviated postlaparotomy pain. Reproduced with permission from AALAS.
Figure 4.
Figure 4.
Burrowing behavior in an adult female Sprague–Dawley placed in a burrowing tube with 2-5 mm gravel.
Figure 5.
Figure 5.
The Rat Grimace Scale (A) Rat depicted with ‘pain’ (left) and with ‘no pain’ (right). The ‘pain’ rat has 1) folded ears that are angled away from the front of the face, 2) partial eye closure, 3) a flattened and elongated nose and 4) whiskers that are bunched together and directed away from the face. The ‘no pain’ rat has 1) rounded ears that face forward, 2) no eye closure, 3) a rounded nose and cheeks and 4) whiskers that are fanned and droopy at ends. (B) Image depicts the face of a normal male Wistar rat with no pain. Its eyes are round and open. Its ears are rounded, facing forward and roughly perpendicular to the top of its head. Its nose and cheeks are rounded with an evident bulge and crease between the nose and cheeks. Lastly, the whiskers are spread apart and droop downward at the ends. (Action unit scores—Eyes: 0, Ears: 0, Nose/cheek: 0, Whiskers: 0). (C) Image depicts an adult male Wistar rat grimacing with orbital tightening, nose/cheek flattening with only a slight crease between the nose and cheeks and straightened whiskers that are pulled toward the cheeks. Its ears are curled and slightly rotated outwards. (Action unit scores—eyes: 1, ears: 1, nose/cheek: 1, whiskers: 1, overall score of 1 [from average of 4 action units]). (D) Image depicts an adult male Wistar rat grimacing with an overall score of 2. It has a tightly closed eyelid. Its nose and cheeks are flattened with the nose appearing elongated. The nose and cheek flatten with no crease evident between them. The whiskers are straightened, bunched together and horizontal to the cheeks. Its ears are rotated outwards and curled inwards. (Action unit scores—eyes: 2, ears: 2, nose/cheek: 2, whiskers: 2). (E) Image depicts an adult male Wistar rat grimacing with an overall score of 1.75. Its eyelids are tightly closed. The ears are curled and rotated away from the front of the rat's face. Its nose and cheeks are flattened with no crease evident between them. The whiskers are straight and pulled toward the cheeks. (Action unit scores—eyes: 2, ears: 2, nose/cheek: 2, whiskers: 1). Illustration by Dr Vivian SY Leung.
Figure 6.
Figure 6.
When given the appropriate amount and material, mice can build a full domed nest and a nest complexity score can be assigned. Reproduced with permission from AALAS.
Figure 7.
Figure 7.
The Nest Consolidation Test allows mice to retrieve one of 4 pieces of nesting material, either with or without an existing nest. The pieces must be consolidated to within a specific distance of one another or within the existing nest. The nest can be built anywhere in the home cage. Reproduced with permission from AALAS.
Figure 8.
Figure 8.
The postsurgical rat on the left (A) received a single analgesic, carprofen, whereas the rat on the right (B) that underwent the same procedure received multimodal analgesia: carprofen and tramadol. When comparing the 2 animals it is clear that the animal that received multimodal analgesia is more alert, paying attention to the observer, and in addition, its fur is lying flat, and its eyes are wide open, all indicating this animal is more comfortable than the rat that only received only carprofen. Reproduced with permission.
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