TRPM5-expressing microvillous cells in the main olfactory epithelium

We show that the GFP-positive microvillous cells were morphologically diversified and scattered throughout the entire MOE. These cells immunoreacted to an antibody against TRPM5, confirming the expression of this ion channel in these cells. In addition, they showed a Ca2+-activated non-selective cation current in electrophysiological recordings. They did not immunoreact to antibodies that label cell markers and elements of the transduction pathways from olfactory sensory neurons and solitary chemosensory cells of the nasal cavity. Further, the TRPM5-expressing cells did not display axon-like processes and were not labeled with a neuronal marker nor did trigeminal peptidergic nerve fibers innervate these cells.We provide morphological and immunocytochemical characterization of the TRPM5-expressing microvillous cells in the main olfactory epithelium. Our data demonstrate that these cells are non-neuronal and in terms of chemosensory transduction do not resemble the TRPM5-expressing olfactory sensory neurons and nasal solitary chemosensory cells.The peripheral olfactory epithelium in mammal is made up of four types of cells, ciliated olfactory sensory neurons (OSNs), basal cells, supporting cells and microvillious cells, which together form a pseudostratified epithelium [1-3]. The olfactory sensory neurons are specialized in detecting diverse odor molecules and transmitting information to the olfactory bulb through their axonal projections [4-6]. Mature OSNs are ciliated bipolar neurons, with cell bodies that are located in the middle layers of the epithelium[1,7-9]. Each of the mature OSNs sends an apical dendrite to the luminal surface where the dendrite terminates in an oval structure, the olfactory knob, bearing approximately 20 cilia where olfactory receptor proteins and the elements of the olfactory transduction cascade are localized [10-12]. A single axon protruding from the basal end of the soma of the OSN penetrates the basal lamina and projects to the olfacto