Endocytic pathways in the olfactory and vomeronasal epithelia of the mouse: Ultrastructure and uptake of tracers

Abstract

Mammalian olfactory neurons possess a well-developed system of endocytic vesicles, endosomes, and lysosomes in their dendrites and perikarya. Vomeronasal neurons are similar and also contain much perikaryal agranular endoplasmic reticulum (AER). Olfactory supporting cells contain endocytic vesicles and endosomes associated closely with abundant fenestrated AER, and vesicles and numerous large dense vacuoles are present basally. Vomeronasal supporting cells have little AER, and few dense vacuoles occur in their bases. In olfactory neurons, ultrastructural tracers (0.08% horseradish peroxidase, thorium dioxide, ferritin) are endocytosed by olfactory receptor endings and transported to the cell body, where their movement is halted in lysosomes. Higher concentrations (1%) of horseradish peroxidase penetrate olfactory receptor plasma membranes and intercellular junctions. In olfactory supporting cells, endocytosed tracers pass through endosomes to accumulate in dense basal vacuoles. These observations indicate that olfactory sensory membranes are rapidly cycled and that endocytosed materials are trapped within the epithelium. It is proposed that in the olfactory epithelium, endocytosis presents redundant odorants to the enzymes of the supporting cell AER to prevent their accumulation, whereas in the vomeronasal epithelium the receptor cells carry out this activity.

B Cell Response to Herpesvirus Infection of the Olfactory Neuroepithelium

“…In contrast, the olfactory epithelium lies above and behind the respiratory epithelium, so the NALT is not immediately between it and the nasopharyngeal duct. Also, the olfactory cilia are nonmotile, so olfactory mucus turnover is slow and may depend on endocytosis by sustentacular cells (41). Thus, probably few olfactory epithelial antigens reach the NALT.…”

β-Arrestin2-Mediated Internalization of Mammalian Odorant Receptors

“…Redistribution of ␤-arrestin2 to the cilia could precede its accumulation in the dendritic knob, depending on where cilia or dendritic knob arrestin binds to the activated OR. Because coated vesicle-mediated transport of ORs to the base of the cilium is likely compromised because of the limited space between axonemal microtubules and the ciliary membrane, internalization of the receptor-arrestin complex via clathrin-coated vesicles could only occur in the dendritic knob, in which coated pits invaginate and numerous endocytic vesicles exist (Bannister and Dodson, 1992). Interestingly, although endocytosis has not been described as a main pathway to shut off phototransduction in photoreceptor outer segments, endocytic compartments and activity have been described in the inner segments (Cotter, 1989), and light induces internalization of rhodopsin and phosphorylated arrestin into rod cells bodies (Reme et al, 1999;Chuang et al, 2004).…”

Ligand-specific induction of endocytosis in taste receptor cells

“…In other chemosensory cells, as for example the sensory neurons in the olfactory and vomeronasal organs of mice, the structure of the endocytic machinery has been studied and demonstrated to be an uptake of ferritin molecules (Bannister and Dodson, 1992). In…”