Olfactory neuron-specific expression of NeuroD in mouse and human nasal mucosa

Human olfactory neuroepithelium (OE) is situated within the olfactory cleft of the nasal cavity and has the characteristic property of continually reg enerating neurons during the lifetime of the individual. This regenerative ability of OE provides a unique model for neuronal differentiation, but lit tle is known about the structure and biology of human olfactory mucosa. Thu s, to better understand neurogenesis in human OE, we studied the expression of olfactory marker protein (OMP), TrkB and NeuroD in human nasal biopsies and autopsy specimens and compared these data with those obtained from nor mal and regenerating mouse OE. We show that NeuroD and TrkB are coordinatel y expressed in human OE. Thus, by using these markers we have been able to extend the known boundaries of the human OE to include the inferior middle turbinate. In normal mouse OE, TrkB and OMP expression overlap in cells clo sest to the superficial layer, but TrkB is expressed more strongly in the l ower region of this layer. In contrast, NeuroD expression is more basally r estricted in a region just above the globose basal cells. These characteris tic expression patterns of OMP, TrkB and NeuroD were also observed in the r egenerating mouse OE induced by axotomy. These results support a role of Ne uroD and brain-derived neurotrophic factor (BDNF), the preferred ligand for TrkB, in the maintenance of the olfactory neuroepithelium in humans and mi ce.