Cell death of olfactory receptor neurons in a rat with nasosinusitis infected artificially with Staphylococcus

Nasosinusitis is a common cause of acquired hyposmia or anosmia. To study the apoptotic death of olfactory receptor neurons in nasosinusitis, we made an inflammation model in rat infected with Staphylococcus. The histochemical changes in olfactory epithelium were examined using antibodies against protein gene product 9.5 (PGP 9.5), single-strand DNA (ssDNA), Bcl-2 and Bax that might be involved in the apoptosis of olfactory receptor neurons. The thickness of olfactory epithelium and the number of ssDNA-labeled cells were evaluated in each post-treatment group and the results were analyzed by two-way analysis of variance (ANOVA) and post hoc tests. Hematoxylin-eosin staining showed that a severe inflammatory reaction had occurred on the infected side of the nasal cavity and sinus, but not on the non-infected side. However, apoptosis of olfactory receptor neurons occurred on both sides; the apoptosis on the non-infected side started later and behaved like a shadow curve similarly to the infected side. Repeated measures ANOVA showed significant differences of both the thickness of olfactory epithelium (P < 0.0001) and the number of ssDNA-labeled cells (P = 0.0339) in the epithelium between the infected side and non-infected side comparing treatment, time and their interactions. Bcl-2 and Bax were detected only on the infected side in the early stages. Thus, nasosinusitis induced the apoptosis of olfactory receptor neurons. However, the apoptosis occurred not only on the infected side, but also on the non-infected side with no significant inflammation. The Bcl-2/Bax family seems to play an important role in the apoptosis induced by infection, but not in the apoptosis on the non-infected side. The results suggest that mechanisms of apoptosis of olfactory receptor neurons on the infected side may differ from those on the non-infected side.