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. 2019 Mar 5;4(2):e718.
doi: 10.1097/PR9.0000000000000712. eCollection 2019 Mar-Apr.

Performance of behavioral assays: the Rat Grimace Scale, burrowing activity and a composite behavior score to identify visceral pain in an acute and chronic colitis model

Vivian S Y Leung  1 , Marie-Odile Benoit-Biancamano  1 , Daniel S J Pang  1
Affiliations

Performance of behavioral assays: the Rat Grimace Scale, burrowing activity and a composite behavior score to identify visceral pain in an acute and chronic colitis model

Vivian S Y Leung et al. Pain Rep. .

Abstract

Introduction: The Rat Grimace Scale (RGS), a facial expression scale, quantifies the affective component of pain in rats. The RGS was developed to identify acute and inflammatory pain, and applicability in acute and chronic visceral pain is unknown. The dextran sulfate sodium (DSS) colitis model is commonly used in rats, but pain is rarely assessed, instead, disease progression is monitored with the Disease Activity Index (DAI; assessing fecal blood, stool consistency, and weight loss).

Objectives: The aim of this study was to assess whether the RGS and 2 additional behavioral tools (composite behavior score [CBS] and burrowing) could identify pain in an acute and chronic DSS colitis model.

Methods: Male and female Sprague-Dawley rats were block randomized to (1) acute colitis (4 days DSS in drinking water); (2) chronic colitis (4 days DSS, 7 days water, and 3 days DSS); or (3) control (14 days water). Disease Activity Index, RGS, CBS, and burrowing assessments were performed daily.

Results: Rat Grimace Scale scores increased as DAI scores increased during both acute and chronic phases. Burrowing only decreased during the acute phase. By contrast, CBS scores did not increase significantly during either colitis phase.

Conclusions: These data show that the RGS and burrowing did not decrease in a sustained manner during chronic phase visceral pain, and that variables assessed in the DAI are indicative of pain. This suggests that the RGS can be applied to a wider range of pain types and chronicity than originally suggested. These findings increase the application of the RGS as a pain scale and welfare improvement tool.

Keywords: Animal; Facial expression; Ongoing pain; Pain assessment; Pain behavior; Rodent; Spontaneous pain.

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Conflict of interest statement

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

Figures

Figure 1.
Figure 1.
Experimental timeline (DAI, RGS, burrowing, and CBS). Each filled box indicates a habituation or assessment activity for each assessment method. Unfilled boxes indicate when no assessments were performed. During the acute phase, group 1 and group 2 rats were treated with 5% DSS administered in water. Group 1 rats were euthanized at the end of the acute colitis phase. During the water phase (group 2 and controls), no assessments were made. During the chronic phase, group 2 rats were treated with 5% DSS for a second time before euthanasia on day 3. Tissue was harvested for microscopic and macroscopic analysis immediately after euthanasia. BL, baseline; DSS, dextran sulfate sodium.
Figure 2.
Figure 2.
Disease Activity Index scores during the acute and chronic colitis phases. Disease Activity Index scores increased significantly during acute DSS exposure compared with BL and controls on days 3 and 4 (P < 0.0001). Disease Activity Index scores increased significantly during chronic DSS exposure compared with BL on day 0 (before DSS treatment began again) and controls on days 1, 2, and 3 (P < 0.0001). Shaded boxes represent when DSS treatment was given. ****P < 0.0001. Data presented as mean ± SEM. BL, baseline; DSS, dextran sulfate sodium.
Figure 3.
Figure 3.
Rat Grimace Scale (video) scores during the acute and chronic phases. Significant increases from BL were observed on day 4 of the acute phase in group 1 and on days 2 and 3 of the chronic phase in group 2 (P < 0.05). Significant increases from controls were observed on day 4 during the acute phase and on days 2 and 3 during the chronic phase (P < 0.01). Broken horizontal line represents a derived analgesic intervention threshold. Shaded boxes represent DSS treatment phases. *P < 0.05. **P < 0.01. ***P < 0.001. ****P < 0.0001. Data presented as mean ± SEM. BL, baseline; DSS, dextran sulfate sodium.
Figure 4.
Figure 4.
Mean difference in gravel displacement during acute and chronic colitis phases (shaded boxes). During both phases, no significant differences were observed between DSS treated and control rats (P > 0.99). A significant decrease from baseline was observed on day 4 (acute phase; P < 0.05). *P < 0.05. Data presented as mean ± SEM.
Figure 5.
Figure 5.
Summed frequency of 4 behaviours (back arch, stagger/fall, writhe, and twitch) evaluated during the acute phase and the chronic phase (shaded boxes). Differences between groups were identified at BL between group 1 and controls (P < 0.05). Differences within groups (from BL) were not observed. Shaded boxes represent when DSS treatment was given. Data presented as median (10–90 percentile). *P < 0.05. BL, baseline.
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