Regulation of the low affinity receptor for nerve growth factor, p75^NGFR, in the olfactory system of neonatal and adult rat

Using MAb192, a monoclonal antibody to the rat low affinity receptor for nerve growth factor (p75^NGFR), we determined the expression of p75^NGFR in rat neonatal and adult olfactory system. In neonates and adults, we observed discrete p75^NGFR-immunoreactivity (p75^NGFR-ir) in the glomerular layer of the main olfactory bulb. The intensity and organization of glomerular p75^NGFR-ir increased with age. This was in keeping with the general ontogeny of the main olfactory bulb. Generally, granule cells, mitral cells and periglomerular cells of the main olfactory bulb were not specifically stained. However, in early neonates, granule cells close to the lateral olfactory tract exhibited p75^NGFR-ir. Additional specific staining was found in the olfactory receptor neurons of neonatal and adult olfactory neuroepithelium, the olfactory fascicles and in the glomeruli of the accessory olfactory bulb. The intensity, but not the organization, of specific staining in the accessory olfactory bulb increased as the animal matured. We believe that p75^NGFR-ir in the olfactory system is associated with its unique capacity to regenerate its peripheral input to the main olfactory bulb. The presence of p75^NGFR-ir in the accessory olfactory bulb would suggest a broader role for this protein. Here we discuss the implications of these findings with regards to nerve growth factor, other trophic molecules, and their receptors. The data presented provide a foundation for studies involving manipulation of regenerative phenomena while monitoring the expression of neurotrophic factors and their receptors.