The glucose transporter GLUT1 and the tight junction protein occludin in nasal olfactory mucosa.

The nervous cells in the brain and the peripheral nerves are isolated from the external environment by the blood-brain, blood-cerebrospinal fluid and blood-nerve barriers. The glucose transporter GLUT1 mediates the specific transfer of glucose across these barriers. The olfactory system is unique in that its sensory cells, olfactory receptor neurons, are embedded in the nasal olfactory epithelium and send their axons directly to the olfactory bulb of the brain. Only the apical parts of the olfactory receptor neurons are exposed to the lumen, and these serve as sensors for smell. Immunohistochemical examination showed that the tight junction protein occludin was present in the junctions of the olfactory epithelium. Endothelial cells in the blood vessels in the lamina propria of the olfactory mucosa were also positive for occludin. These observations suggest that the olfactory system is guarded from both the external environment and the blood. GLUT1 was abundant in these occludin-positive endothelial cells, suggesting that GLUT1 may serve in nourishing the cells of the olfactory system. Taken together, GLUT1 and occludin may serve as part of the machinery for the specific transfer of glucose in the olfactory system while preventing the non-specific entry of substances.