Figure 1. Evidence for poly(ADP-ribose) polymerase (PARP) activation in periodontitis. Immunohistochemical staining of rat gingivomucosal tissue for poly(ADP-ribose) formation, an indicator PARP activation, in healthy control (a), experimental periodontitis (b), and PARP inhibitor PJ34-treated experimental periodontitis (c). Bars = 100 µm. (a) In the gingivomucosal tissue of the control side, only a few poly(ADP-ribose) immunopositive nuclei (arrow) were found in the connective tissue. [The connective tissue-epithelium (E) interfaces are marked by arrowheads.] (b) In the ligated side, there are large numbers of strongly poly(ADP-ribose) immunoreactive nuclei in the subepithelial connective tissue. [The arrowheads indicate the connective tissue-epithelium (E) border.] (c) Treatment with PJ34 attenuated PARP activation in the gingivomucosal tissue of the ligated side (arrows). [The connective tissue-epithelium (E) interfaces are marked by arrowheads.]