Junctions in the meninges and marginal glia

Abstract

The meninges of various mammals were prepared for examination with the electronmicroscope by thin sectioning or freeze-fracturing. Particular attention was given to the distribution of tight junctions in order to determine the basis for the meningeal barrier between the blood circulating in dural vessels and the cerebrospinal fluid in the subarachnoid space. While some dural blood vessels are fenestrated, those in the subarachnoid space are not and their component endothelial cells are joined by an extensive system of tight junctions. An extensive and continuous system of tight junctions was also found in a layer of specialized cells at the border of the arachnoid with the dura. This arachnoid barrier layer is apparently the only basis of the meningeal barrier because often cellular layers in the dura and arachnoid lack tight junctions although they are linked by gap junctions and desmosomes. In particular, tight junctions are lacking at the border of the "subdural space" which is actually a fascial plane within the dura. Tight junctions are also lacking between astrocytes at the surface of the brain but these cells are linked by gap junctions and a new type of intercellular junction. The distribution of these junctions, as well as assemblies of intramembranous particles at the astrocytic border, raises the question whether this layer might have a role in the exchange of certain substances between the brain and cerebrospinal fluid.

Pial arteriole dilation during somatosensory stimulation is not mediated by an increase in CSF metabolites

“…On the other hand, a component of this hypercapnic dilation response may not be sensitive to CSF superfusion. Because pial arterioles are partially invaginated in brain parenchyma (11,12), CO 2 may diffuse not only into CSF but also into parenchyma in contact with these vessels. Pial arterioles may also be exposed to CO 2 released into brain tissue by intracortical arterioles and capillaries.…”

Nanoparticle transport across the blood brain barrier

“…74,76 This enables very short distances between the nearest blood capillary and neuronal cells, 99 which allows a fast delivery of substances after crossing the BBB. Further, the capillaries in the brain are quite different from capillaries found in the peripheral organs.…”

The transport of the anti‐HIV drug, 2′,3′‐didehydro‐3′‐deoxythymidine (D4T), across the blood‐brain and blood‐cerebrospinal fluid barriers

“…The BBB is found at the level of the cerebral capillary endothelium and is associated with the presence of tight junctions, metabolic enzymes, and the lack of intracellular vesicles and endothelial fenestrae (Bertler et al, 1966;Reese & Karnovsky, 1967;Brightman & Reese, 1969;Westergaard & Brightman, 1973;Shivers et al, 1984;Watson et al, 1991). The barrier between blood and CSF is located at the tight junctions of the choroid plexus epithelium and the dura-arachnoid boundary (Brightman & Reese, 1969;Nabeshima et al, 1975;Smith & Shine, 1992). The CSF bathes the exterior surfaces of the brain and ®lls the ventricles.…”