The expression of stress-responsive proteins, such as nestin and a 27-kDa heat-shock protein (HSP27), was immunohistochemically examined in order to demonstrate glial responses in the rat olfactory bulb following sensory deprivation. At 3 days to 1 week after sensory deprivation, numerous nestin-expressing cells appeared within the glomerulus of the olfactory bulb. These cells were regarded as reactive astrocytes since they were immunoreactive for glial fibrillary acidic protein and showed hypertrophic features. The glomeruli, in which nestin-immunoreactive astrocytes were localized, were filled with degenerating terminals of olfactory receptor neurons and migrated microglia. A small population of nestin-immunoreactive cells was positive for a proliferating cell marker, Ki67 (8.0-9.7% at 3 days; 3.1-5.0% at 1 week). At 3 weeks, nestin-immunoreactive astrocytes were occasionally detected. At 6 weeks, when the olfactory receptor neurons had completely recovered, no nestin-immunoreactive astrocytes were detected. HSP 27 was also expressed within the glomerular astrocytes and showed a similar spatiotemporal expression pattern to nestin. The present study suggests that reactive astrocytes may be involved in axonal regeneration and synaptic remodeling in the olfactory system, through the recapitulation of developmentally regulated proteins, such as nestin and HSP27.
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