Models for the Transfer of Drugs from the Nasal Cavity to the Central Nervous System

Abstract: The blood-brain barrier restricts the access of many compounds, including therapeutic agents, to the brain. Several human studies indicate that nasal administration of hydrophilic compounds, such as peptides, can bypass the blood-brain barrier. The aims of this thesis were to develop and refine models for this direct nose-to-brain transfer.In a mouse model, [3H]-dopamine was given as a unilateral nasal dose. The resulting radioactivity in the ipsilateral olfactory bulb was significantly higher than that in the contralateral bulb and peaked at 4 h. Tape section autoradiography showed that the radioactivity was concentrated in the olfactory nerve layer and the glomerular layer of the olfactory bulb. The olfactory transfer of dopamine was also studied in vitro. At a lower donor concentration, the mucosal-to-serosal dopamine permeability was higher than the serosal-to-mucosal permeability, but at a higher concentration, the permeability coefficients were similar. Together, these results suggest that the olfactory transfer of dopamine has an active component.Olfactory transfer of fluorescein-labeled dextran through the epithelium and deeper tissues was studied in a rat model, which enabled visualization of the transfer using fluorescence microscopy. Although the epithelial transfer appeared to be mainly intracellular, transfer in the following deeper tissues was extracellular. Without altering the route of uptake, a gellan gum formulation enhanced the uptake of fluorescein dextran. The enhancing effect was considered likely to be the result of an increased residence time in the nasal cavity.In conclusion, dopamine and fluorescein-labeled dextran were identified as suitable model compounds for the study of olfactory drug transfer mechanisms and the influence of drug formulation. Two new in vitro models of olfactory transfer were compared. Also, a rat model, which enabled the visualization of the entire nose-to-brain transfer, was developed.