Figure 3.

Intranasal formalin (2.5%, 10 μl) induces bilateral neuronal activation in the caudal part of spinal trigeminal nucleus (TNC), which correlates with painful facial grimacing behavior. (A) Neuronal activation was quantified by c-Fos immunohistochemistry, and subsequent automatic quantification of the number of c-Fos-expressing [c-Fos (+)] neuronal profiles in ipsilateral (ipsi) and contralateral (cont) TNC. (B) The images and quantification are representative of 4 slices per animal, 4 animals per treatment group. Scale bar = 200 µm. Data are represented as mean ± SEM. ***p < 0.001 compared to saline ipsilaterally or contralaterally, ⁺⁺p < 0.01 compared to formalin contralaterally, ANOVA followed by Newman Keuls post hoc test). (C) The painful facial grimacing assessed by rat grimace scale total score, measured every 3-min intervals during 39-min observation period (Ʃ RGS) is significantly correlated with the number of c-Fos positive cells in the ipsilateral TNC (circle, no treatment; square, saline; triangle, formalin; r, Pearson’s correlation coefficient).