Figure 1. Histology of experimentally induced rat pulpitis and iNOS mRNA expression in experimentally induced rat pulpitis. LPS application to the pulp tissue of rat upper incisors for 6 hrs (A,B) caused severe inflammation, and the infiltration of many neutrophils into the pulp tissue can be seen (n = 3). Saline application (C,D) did not induce severe inflammation. Bars in the low-power fields (A,C) and those in the high-power fields (B,D) indicate 500 µm and 80 µm, respectively. iNOS mRNA expression (n = 3 in each group) was evaluated with RT-PCR, and the relative intensity of expression against ß-actin in each experimental period was statistically compared, by ANOVA and Tukey-Kramer tests (p < 0.05), with that in untreated pulp samples. The relative intensities in each period were: 0 ± 0, 0 hr; 0.4 ± 0.21, 3 hrs; 1.0 ± 0.24, 6 hrs; 0.6 ± 0.15, 9 hrs; 0.075 ± 0.03, 12 hrs; and 0 ± 0, 24 hrs (mean ± SD) (E). Competitive RT-PCR on LPS-treated pulp (6 hrs, n = 3) and LPS-treated liver (6 hrs, n = 3) shows that the expression of iNOS mRNA in the LPS-treated pulp is almost the same as that in the LPS-treated liver (F). The same results were observed in 3 separate experiments.