Visualization of in vivo olfactory uptake and transfer using fluorescein dextran

Nasal administration of a 3 kDa fluorescein dextran (FD3) solution to rats resulted in transcellular absorption across the olfactory epithelium and transfer to the olfactory bulb within 15 min. After entering the lamina propria, FD3 was transferred in the connective tissue surrounding the olfactory nerve bundles to the olfactory bulb of the brain. More FD3 was absorbed across the olfactory epithelium than across the respiratory epithelium and to the nasal associated lymphoid tissue. Further, the amount of FD3 crossing the olfactory epithelium was region-dependent, with higher amounts absorbed in the turbinates than in the nasal septum. Plastic embedding and sectioning followed by fluorescence microscopy, enabled simultaneous visualization of FD3 in the mucosa and olfactory bulb, as well as the opportunity to store the tissue blocks for a prolonged period of time.