FIGURE 13.

Histopathological staining of the nasal cavity in the male rats exposed to the mixture of SM and PG for 2 weeks by aerosol inhalation. Panels (A–C) are the results of exposure groups each defining for control, medium-, and high-dosage treatment, respectively. Panel (D) shows the recovery of high-exposure groups. Note the metaplasia of the respiratory epithelium into squamous cells in (B) and (C) (arrows). Compare these with normal respiratory epithelium composed of ciliated pseudostratified columnar epithelium with goblet cells [arrows in (A) and (D)]. Squamous cell metaplasia occurred in the front of the nasal cavity, but was completely recovered 7 days after exposure was stopped (D). H&E staining. Magnification = ×400 for all images.