Uptake of materials from the nasal cavity into the blood and brain: are we finally beginning to understand these processes at the molecular level?

Substances that enter the nasal cavity can access the bloodstream or central nervous system by processes including receptor cell uptake, transneuronal transport, and paracellular transport. Until recently, the molecular mechanisms by which agents move from the nasal cavity have not been described. Although the full complement of transporter proteins found in the nasal cavity has certainly not yet been identified, several recent observations have advanced this field substantially. We summarize here a representative sample of transporter proteins found in olfactory mucosa and/or nasal respiratory mucosa and the substrates that they transport into the brain and/or bloodstream.