B-50/GAP43 Gene Expression in the Rat Olfactory System During Postnatal Development and Aging

The olfactory neuroepithelium exhibits neurogenesis throughout adult life, and in response to lesions, a phenomenon that distinguishes this neural tissue from the rest of the mammalian brain. The newly formed primary olfactory neurons elaborate axons into the olfactory bulb. Thus, denervation and subsequent re-innervation of olfactory bulb neurons may occur throughout life. In this study the authors demonstrate the distribution of the growth-associated phosphoprotein B-50/GAP43 and its mRNA in the olfactory neuroepithelium and olfactory bulb during development and aging. In neonatal rats B-50/GAP43 mRNA was expressed in primary olfactory neurons throughout the olfactory epithelium and in their target neurons in the olfactory bulb, the mitral, juxtaglomerular and tufted cells. In contrast, in adult (7.5 weeks) and aging animals (6 - 18 months of age) B-50/GAP43 mRNA expression was progressively restricted to neurons in the basal region of the neuroepithelium and to some of their target mitral and juxtaglomerular cells in the olfactory bulb. The continuing expression of B-50/GAP43 mRNA in mitral- and juxtaglomerular cells in mature animals is thought to be related to their capacity to respond to continuously changing input from the primary olfactory neurons present in the olfactory neuroepithelium.