Primary olfactory axons form ectopic glomeruli in mice lacking p75NTR

The restricted expression of the low affinity nerve growth factor receptor p75NTR by olfactory ensheathing cells suggests that this molecule is involv ed in the development of the olfactory nerve pathway. To begin to understan d the role of p75NTR, we examined the development of the primary olfactory system in p75NTR(-/-) and wild-type mice. Our results demonstrate that, alt hough p75NTR is not essential for the initial assembly of the olfactory ner ve, it plays an important role in the postnatal maturation of the olfactory bulb. In the absence of p75NTR, there is exuberant growth of some primary olfactory axons into the olfactory bulb. These axons either aberrantly bypa ss the glomerular layer and project into deeper lamina or grow into an abno rmal bleb of tissue protruding from the medial surface of the dorsocaudal o lfactory bulb. These blebs become apparent in neonatal mice and contain axo ns expressing olfactory marker protein that form ectopic glomerular-like tu fts. Histochemical staining with the plant lectin Dolichos biflorus aggluti nin revealed that axons sorted out and selectively converged on glomeruli w ithin these blebs. Our results suggest that p75NTR indirectly influences ax on growth but not glomerular targeting and plays a role in the postnatal ma turation of laminar cytoarchitecture in the olfactory bulb. J. Comp. Neurol . 428:656-670, 2000. (C) 2000 Wiley-Liss, Inc.