Thesis Abstracts 2001

Axons of olfactory receptor cells (ORCs) grow from the olfactory epithelium (OE) to the olfactory bulb (OB), where they travel through the olfactory nerve layer (ONL) of the OB, reorganize extensively, and innervate specific synaptic targets in the glomeruli. Within the ONL a unique population of glial cells, the olfactory ensheathing cells (OECs), surround ORC axon fascicles and accompany them to the OB. To better understand the relationship between the OECs and the axon fascicles in the ONL of the adult mouse, we used confocal microscopy and antibodies to the low affinity nerve growth factor receptor p75 (p75), glial fibrillary acidic protein (GFAP), and S-100 to identify glia and olfactory marker protein (OMP) and neuronal cell adhesion molecule (NCAM) to identify ORC. Electron microscopy characterized the ONL ultrastructure. We found that glial processes, in particular those of the OECs, were not uniformly distributed in the ONL. The p75+ OEC processes were largely restricted to the olfactory nerve and the outer ONL sublamina, and oriented parallel to the plane of the OB layers. GFAP+ processes were largely restricted to the inner ONL sublamina, the ONL/GL boundary, and the GL, where they delineated loosely aggregated axon fascicles that entered the glomeruli obliquely. S-100O processes and somata were broadly distributed throughout the ONL; the outer and inner ONL were equivalent in their S-100 staining. Ultrastructural studies supported our immunocytochemical findings suggesting a sublaminar ONL organization. Our data suggest that the differential organization of the ONL may subserve distinct functions; axonal extension may occur predominately in the outermost ONL while glomerular targeting occurs in the the inner sublamina of the ONL.