Ultrastructural investigation of the meningeal compartment of the blood-cerebrospinal fluid-barrier in rats and cats. A horseradish peroxidase study.

The permeability of the meningeal blood vessels and cellular layers to horseradish peroxidase was studied 5, 10 and 15 minutes following intravasal or intraarachnoidal introduction of the marker. When applied intravasally, the horseradish peroxidase-containing solution easily passed through the walls of all meningeal vessels (dural, pial and the ones traversing the arachnoid space). The cells of the inner dural layer and dural neurotheliun delay the penetration of horseradish peroxidase into the cerebrospinal fluid-filled arachnoid space by 10 min--rats and 15 min--cats. The perivascular leptomeningeal cells and their processes restrict the passage of the marker into the arachnoid space in a similar way. These barrier functions of the leptomeningeal cells and the cells that comprise the interface zone between dura mater and the arachnoid are confirmed by experiments where the marker was injected into the arachnoid space.