Ultrastructural study of the primary olfactory pathway in Macaca fascicularis

Abstract

Olfactory ensheathing glial cells (OEGs) interact with a wide repertoire of cell types and support extension of olfactory axons (OAs) within the olfactory pathway. OEGs are thought to exclude OAs from contact with all other cells between the olfactory epithelium and the glomerulus of the olfactory bulb. These properties have lead to testing to determine whether OEGs support axonal growth following transplantation. The cellular interactions of transplanted OEGs will probably resemble those that occur within the normal pathway where interactions between OEGs and fibroblasts are prominent. No previous primate studies have focused on these interactions, knowledge of which is important if clinical application is envisioned. We describe the detailed intercellular interactions of OAs with supporting cells throughout the olfactory epithelium, the lamina propria, the fila olfactoria, and the olfactory nerve layer by using transmission electron microscopy in adult Macaca fascicularis. Patterns of OEG ensheathment and variations of the endo- and perineurium formed by olfactory nerve fibroblasts are described. OAs mainly interacted with horizontal basal cells, OEGs, and astrocytes. At both transitional ends of the pathway seamless intercellular interactions were observed, and fibroblast processes were absent. Perineurial cells produced surface basal lamina; however, endoneurial, epineurial, and meningeal fibroblasts did not. Perineurial cells contained intermediate filaments and were distinct from other fibroblasts and meningeal cells. OAs had direct contacts with astrocytes near the glia limitans. The properties of OEGs differed depending on whether astrocytic or fibroblastic processes were present. This indicates the importance of the cellular milieu in the structure and function of OEGs in primates.

The glycoprotein fibulin‐3 regulates morphology and motility of olfactory ensheathing cells in vitro

“…The intimate relationship between blood vessels and nerve in the primary olfactory pathway (Herrera et al, 2005;Okada and Schraufnagel, 2002) strongly implies that similar molecular mechanisms were adopted by both systems to facilitate growth of blood vessels and nerves. However, the expression of both angiogenesis-promoting and -inhibiting factors in OECs also suggests that there is direct glial control of angiogenic microvessel sprouting in the olfactory nerve in response to OSN degeneration and replenishment.…”

Morphofunctional Adaptations of the Olfactory Mucosa in Postnatally Developing Rabbits

“…Axons of the olfactory cells run close to each other forming small intraepithelial fascicles which, on piercing the basal lamina, become entrapped by processes of olfactory ensheathing cells (Williams, 1995;Field et al, 2003;Nomura et al, 2004). On reaching the lamina propria, the fascicles progressively group together to form large axon bundles, which eventually pierce the cribriform plate of the ethmoid bone to reach the olfactory bulb glomeruli where connections are established with central relay cells (Meisami, 1989;Williams, 1995;Herrera et al, 2005;Levine and Marcillo, 2008). Through vertically oriented ducts, the Bowman's glands deliver secretions to the surface of the OE that form the environment for dissolving odorants and allowing their diffusion to the sensory receptor sites (Getchell and Getchell, 1992;Williams, 1995).…”

Molecular composition of tight and adherens junctions in the rat olfactory epithelium and fila

“…The lamina propria (LP) contains the olfactory glands (OG), and fascicles of the FO. Ultrastructural investigations have documented the presence of TJs and AJs in the OE and OG in various species (e.g., Menco 1980;Moran et al 1982;Mendoza 1993;Herrera et al 2005). In freeze-fracture studies, diVerential structural characteristics of TJs between the cell types were described and were suggested to be related to TJ dynamics (Menco 1980).…”

“…Ultrastructural analyses of FOs in diVerent species using transmission electron microscopy did not report the presence of conspicuous TJs between OEC processes (Field et al 2003;Herrera et al 2005). TJs between the olfactory nerve Wbroblasts (ONF), speciWc cells surrounding larger FO fascicles in the LP up to their passage through the pia into the olfactory nerve layer (ONL) of the olfactory bulb (OB), were described (Field et al 2003;Herrera et al 2005). ZO1-immunoreactivity was documented immunocytochemically in the FO periphery (Miragall et al 1994).…”