The expression of B-50/GAP-43 and GFAP after bilateral olfactory bulbectomy in rats

In the present study we investigated the effect of a two-stage bilateral lesion of the olfactory bulb (OB) in rats on the regeneration ability of peripheral olfactory neurons and their reinnervation capacity in the spared OB. The outgrowth of newly-generated olfactory axons as well as the maturation of their terminal synaptic field was detected by immunohistochemistry of the growth-associated phosphoprotein B-50/GAP-43. In addition, the glial response to the surgery was monitored by an immunohistochemical marker for astrocytes, glial fibrillary acidic protein (GFAP). In neonatal rats (P3-P5), the right OB was removed, then three months later the contralateral side was ablated. Six days after the second operation the animals were transcardially perfused. Their brains were embedded in paraplast, serially sectioned and processed for histological and immunohistochemical observations. After neonatal OB ablation, homogeneous B-50-immunoreactivity (BIR) was found in the forebrain, olfactory axons and ectopic glomeruli localized in the small OB remnant-like structures and in the regenerated neuroepithelium. A strong GFAP response was revealed in the brain cortex as well as in the newly-formed olfactory axons and glomeruli-like structures of the OB remnants. After adult OB ablation strong BIR was observed in olfactory axons, while remaining glomerular structures were only faintly stained. The neuroepithelium revealed signs of massive degenerative processes with a substantial decrease in BIR. The GFAP-positive astrocytes were scattered throughout the entire OB remnant and were prominent in the glomeruli-like structures and adjacent frontal cortex. In the present study, we applied GAP-43 and GFAP immunohistochemistry to characterize the responses of individual olfactory components after two-stage olfactory bulbectomy. Furthermore, this model of OB ablation characterized by two immunohistochemical markers could elucidate certain molecular mechanisms involved in the regeneration and/or plasticity of the olfactory system.