Barrier functions of the leptomeninges: a study of normal meninges and meningiomas in tissue culture.

The anatomical arrangement of the pia mater suggests that it may act as a regulatory interface between cerebrospinal fluid and the surface of the brain and between arterioles within the brain and the surrounding neural tissue. However, the functional aspects of such a barrier are difficult to evaluate in vivo. In the present study, the enzymic content and endocytotic capacities of normal leptomeningeal cells in situ and meningioma cells in confluent tissue culture are examined in relation to barrier functions of meningeal cells. Growth of cells in culture was obtained from human fetal and newborn rat leptomeninges and from 9/13 meningiomas. But, in only two meningiomas were the cultured cells characterized as meningeal in origin by using the strict criteria of desmosomes identified by immunocytochemistry or by electron microscopy. These two tumours had high (8-8.7%) Ki-67 labelling indices. Glutamine synthetase activity is present in normal meninges and in meningioma cells in culture; this enzyme together with catechol-O-methyltransferase could play a role in limiting the diffusion of neurotransmitters into brain tissue. A steady rate of endocytosis of carbon particles and fluorescent latex beads, 0.2-1 microns in diameter, was observed in cultured meningioma cells. Such endocytosis was inhibited by cytochalasin B indicating the active participation of intracellular microfilaments. Similar endocytosis has been observed in normal leptomeninges in vivo. The results of this study suggest that meningioma cells in culture reflect the barrier functions of the pia mater and may be used as a model to further investigate the functions of the pia mater.