Abstract
BackgroundIn the past, ciliated receptor neurons, basal cells, and supporting cells were considered the principal components of the main olfactory epithelium. Several studies reported the presence of microvillous cells but their function is unknown. A recent report showed cells in the main olfactory epithelium that express the transient receptor potential channel TrpM5 claiming that these cells are chemosensory and that TrpM5 is an intrinsic signaling component of mammalian chemosensory organs. We asked whether the TrpM5-positive cells in the olfactory epithelium are microvillous and whether they belong to a chemosensory system, i.e. are olfactory neurons or trigeminally-innervated solitary chemosensory cells.ResultsWe investigated the main olfactory epithelium of mice at the light and electron microscopic level and describe several subpopulations of microvillous cells. The ultrastructure of the microvillous cells reveals at least three morphologically different types two of which express the TrpM5 channel. None of these cells have an axon that projects to the olfactory bulb. Tests with a large panel of cell markers indicate that the TrpM5-positive cells are not sensory since they express neither neuronal markers nor are contacted by trigeminal nerve fibers.ConclusionWe conclude that TrpM5 is not a reliable marker for chemosensory cells. The TrpM5-positive cells of the olfactory epithelium are microvillous and may be chemoresponsive albeit not part of the sensory apparatus. Activity of these microvillous cells may however influence functionality of local elements of the olfactory system.
Highlights
In the past, ciliated receptor neurons, basal cells, and supporting cells were considered the principal components of the main olfactory epithelium
In transgenic mice where the TrpM5 promoter drives the expression of green fluorescent protein (GFP), GFP-positive cells are scattered throughout the main olfactory epithelium (Fig. 1)
These fascicles penetrate the basal lamina and form the fila olfactoria. The majority of these TrpM5-GFP-positive olfactory receptor neurons (ORNs) lie in the ventrolateral zone of the main olfactory epithelium (MOE)
Summary
In the past, ciliated receptor neurons, basal cells, and supporting cells were considered the principal components of the main olfactory epithelium. A recent report showed cells in the main olfactory epithelium that express the transient receptor potential channel TrpM5 claiming that these cells are chemosensory and that TrpM5 is an intrinsic signaling component of mammalian chemosensory organs. The main olfactory epithelium (MOE) of mammals was said to contain only basal cells, supporting cells, and ciliated olfactory receptor neurons (ORNs) that utilize OR-type receptor molecules and the canonical Gprotein-coupled transduction pathway via Gαolf, adenylyl cyclase III (ACIII), and cAMP [1]. Braun and Zimmermann [4], utilizing ecto-5'-nucleotidase as a marker, detected microvillous cells in the MOE and suggested a mechanosensory function for these elements. Carr et al reported microvillous (page number not for citation purposes)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
