OBJECTIVETo study whether apoptosis plays a role in controlling the number of olfactory receptor neurons, so as to reveal the specialty and mystery of neurogenesis.

METHODSUsing terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein nick end labeling (TUNEL) and transmission electron microscopy to detect apoptosis in olfactory mucosa of normal adult rats and damaged olfactory mucosa of 16, 32, 48 hours and 3, 7, 30 days after bulbectomy.

RESULTSIn normal olfactory epithelium, a subpopulation of immature neurons, as well as mature neurons, showed internucleosomal DNA-fragmentation. The number of TUNEL-labeled neurons increased dramatically 32 hours after removal of olfactory bulb. Then it declined quickly and remained at low level. Ultrastructural data of olfactory mucosa showed that the feature of apoptotic neurons was chromatin condensation and cell shrinkage. Besides, some dying cells were characterized by the formation of numerous autophagic vacuoles, and few had some of the features of necrosis but without obvious mitochondrial swelling.

CONCLUSIONSApoptosis might play a role in turnover of the olfactory epithelium and regeneration in adult rats. There might be other two types of neural death through different mechanism.