Figure 2.

Stimulation of nasal mucosa with 2.5% formalin induces painful grimacing in rats. (A) The rat faces showing, from left to right, normal appearance (saline-treated animal), and different severity of painful facial expression in formalin-treated animals (moderate to obvious). In the images, left to right, orbital tightening is the best visible action with following rat grimace scale (RGS) scores ascribable to them: 0, 1, 2. (B) Animals treated with formalin had higher sum of total RGS scores (ƩRGS) assessed every 3 min during the 39 min period after intranasal treatment with formalin, compared to saline or no treatment (3–5 animals per group, mean ± SEM, * p < 0.05 in comparison to non-treated or saline-treated group, one-way ANOVA followed by Newman Keuls post hoc test).