Histochemical and ultrastructural analyses of the lubrication systems in the olfactory organs of soft-shelled turtle

In general, the nasal cavity of turtles is divided into two chambers: the upper chamber, lined with the olfactory epithelium containing ciliated olfactory receptor cells, and the lower chamber, lined with the vomeronasal epithelium containing microvillous receptor cells. In the nasal cavity of soft-shelled turtles, however, differences between the upper and lower chamber epithelia are unclear due to the presence of ciliated receptor cells in both epithelia. In the olfactory organ of vertebrates, the surface of sensory epithelium is covered with secretory products of associated glands and supporting cells, playing important roles in the olfaction by dissolving odorants and transporting them to the olfactory receptors. Here, the associated glands and supporting cells in the olfactory organ of soft-shelled turtles were analyzed histochemically and ultrastructurally. The upper chamber epithelium possessed associated glands, constituted by cells containing serous secretory granules; whereas, the lower chamber epithelium did not. In the upper chamber epithelium, secretory granules filled the supranuclear region of supporting cells, while most of the granules were distributed near the free border of supporting cells in the lower chamber epithelium. The secretory granules in the supporting cells of both epithelia were seromucous, but alcian blue stained them differently from each other. In addition, distinct expression of carbohydrates was suggested by the differences in lectin binding. These data indicate the quantitative and qualitative differences in the secretory properties between the upper and lower chamber epithelia, suggesting their distinct roles in the olfaction.