Introduction: The pia-arachnoid is a critical component of cerebrospinal fluid removal. It covers and invaginates into brain parenchyma and physiologic failure results in hydrocephalus and cerebral edema. The purpose of this study was to characterize the role of arachnoid within brain parenchyma and determine if water flux and solute transport is affected by these intra-parenchymal cells.

Methods: An immortalized arachnoid rat cell line was used to seed 300 µm organotypic rat brain slices of 4-week old rats.  Fluid and tracer transport analyses were conducted following a 7-10 day intraparenchymal growth period.  The development of an arachnoid brain slice model was characterized using diffusion chamber experiments to calculate permeability, diffusion coefficient, and flux.   

Results: Labeled rat arachnoid cells readily penetrated organotypic cultures for up to 10 days. A significant reduction of dye and water flux across arachnoid impregnated brain slices was observed after 3 hours in the diffusion chamber. Permeability decreased in whole brain slices containing arachnoid cells compared to slices without arachnoid cells.  While a significant reduction of dextran across all slices occurred when molecular weights increased from 40 kDA to 70kDA.  

Conclusion:Tracer and small molecule studies show that the presence of arachnoid cells have a significant impact on the movement of water through brain parenchyma. Size differential experiments indicate that between 40 and 70 kDa, the permeability of solute changed substantially, which is an important marker of blood-CSF barrier definition.  We have developed an arachnoid organotypic model that reveals their ability to alter permeability and transport.