Abstract
In the present study, we investigated the roles of the efferents and centrifugal afferents in cell survival in the adult rat main olfactory bulb (MOB). Rats underwent unilateral transection of these central connections at the posterior end of the MOB. The effects of the transection were examined by morphological and histochemical methods. In the MOB ipsilateral to the surgery, many degenerating cells were present in both the mitral cell layer (MCL) and GCL at 3 days after surgery. The numbers of degenerating cells in the ipsilateral MOB were 6.4-fold greater in the MCL and 65.8-fold greater in GCL compared to the contralateral MOB. We also obtained essentially the same results by using TUNEL assay (the MCL, 11.8-fold; the GCL, 22.6-fold). Furthermore, the degenerating and TUNEL-positive cells in the ipsilateral MOB were located predominantly in the deep, rather than the superficial, GCL (p<0.0001 for both). Immunohistochemistry for activated caspase-9 further supported the occurrence of apoptotic cell death in the mitral and deeply located granule cells. These results indicate that not only axotomized mitral cells, but also deeply located granule cells that were not directly injured, underwent apoptosis after transection of the central connections, and suggest that the roles of the central connections in cell survival differ among granule cells according to their depth in the GCL. [Jpn J Physiol 55 Suppl:S164 (2005)]
