Maintenance of regional difference in cellular composition of neurospheres derived from adult mouse olfactory bulb.

Neurospheres are potentially good tools to study olfactory neurogenesis. For this purpose, it is necessary to characterize neurospheres derived from the olfactory system. This study is aimed at identifying the regional difference of cellular composition within neurospheres derived from the adult mouse olfactory bulb, and studying whether these characteristics are maintained throughout the long-term culture. Neural cells were obtained from the olfactory bulbs of 8-week-old Balb/c mice and the dissociated cells were cultured in serum-free media containing epidermal growth factor and basic fibroblast growth factor to form neurospheres. These neurospheres were subjected to characterization by confocal microscopy after immunofluorescence staining with nestin, proliferating cell nuclear antigen (PCNA), neuronal cell adhesion molecule (NCAM), glial fibrillary acidic protein (GFAP), O4, and olfactory marker protein (OMP). Confocal microscopy showed that nestin-reactive cells, which are stem cell-like cells, were present at the periphery of neurospheres and PCNA-reactive cells undergoing proliferation were found throughout the neurospheres. Neuronal cell markers, NCAM-reactive cells, were observed at the center of neurospheres while glial cell markers, GFAP- or O4-reactive cells, were present at the periphery of neurospheres. No cells were found to be reactive for OMP, a differentiated olfactory neuron marker. This regional distribution of cells in neurospheres was maintained through 17 passages for a year. The neural lineage of cells showed different distribution within neurospheres and this localization was preserved throughout the culture period. These findings in the neurosphere culture system of the olfactory bulb may help to study olfactory neurogenesis.