Increased apoptosis and different regulation of pro-apoptosis protein bax and anti-apoptosis protein bcl-2 in the olfactory bulb of a rat model of depression

Reduced olfactory bulb (OB) volume and olfactory sensitivity have been observed in depressed patients, the exact mechanisms underlying, however, are still unknown. Our previous study found that decreased neurogenesis and pre-synaptic dysfunction in the OB of a rat model of depression may be responsible for the phenomena. Nevertheless, whether the apoptosis would also play a certain role in this process is not clear. In this study, we investigated the apoptosis in the OB of a chronic unpredictable mild stress (CUMS) rat model of depression using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Simultaneously, the pro-apoptosis protein bax and anti-apoptosis protein bcl-2 were detected by Western blot. The results showed that the number of TUNEL-positive cells increased dramatically in the glomerular layer of the OB of the CUMS rats, accompanied with up-regulated expression of bax protein and down-regulated expression of bcl-2 protein. The findings indicate that increased apoptosis may be attributed to explain at some level for the reduced OB volume and olfactory dysfunction in depressed patients. Moreover, the mitochondria-dependent death pathway might be involved in apoptosis in the OB of the CUMS rats.

► TUNEL-positive cells increased in the glomerular layer of the OB of the CUMS rats.
► Up-regulated expression of bax protein was observed in the CUMS rats.
► Down-regulated expression of bcl-2 protein was observed in the CUMS rats.