Expression of active caspase-3 in mitotic and postmitotic cells of the ratforebrain

Active caspase-3 immunoreactivity was detected in the rat forebrain prolife rative regions at birth and remained high in these areas for about 2 weeks, during which period labeled cells were present centroperipherally across t he olfactory bulb. By the end of the third postnatal week, only a small num ber of immunolabeled cells remained in these forebrain structures. Active c aspase-3 immunolabeling was localized mostly to cell nuclei and co-localize d partially with TuJ1 and NeuN immunoreactivity, but not with glial fibrial ly acidic protein, OX-42, gamma -aminobutyric acid, or terminal deoxynucleo tidyl transferase-mediated nick end labeling (TUNEL)-positive labeling. Act ive caspase-3 and 5-bromo-2 ' -deoxyuridine (BrdU) double-labeled nuclei we re seen in the proliferative regions after 2 hours and in the periglomerula r region of the bulb after 7 days following BrdU injections. Examination of the cells with electron microscopy confirmed that the active caspase-3-con taining nuclei in the proliferative regions often had infoldings and appear ed to be undergoing division. Some of the cells with active caspase-3-label ed nuclei in the bulb had synapses on their somata or dendrites. Labeled de ndritic spines and a few axon terminals were also observed in the olfactory bulb. Taken together, it appears that a wave of active caspase-3-positive cells are dividing in the proliferative zones and then migrating to the bul b as they differentiate into neurons. Therefore, active caspase-3 may play a role in cellular processes such as neuronal differentiation, migration, a nd plasticity, in addition to its role in cell death. (C) 2001 Wiley-Liss, Inc.