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The ependyma is an important protective barrier between the brain and CSF, the brain and blood, and the blood and CSF. This ventricular lining limits the diffusion of blood and CNS components into the CSF and vice versa. Diffusional dynamics and active transport components are altered during brain inflammation and CNS trauma. Tanycytes, a specialized ependymal cell, are involved in neuroendocrine transport functions, and the choroid plexus is the source of 70% of CSF production;1 CSF then travels to the subarachnoid space.2 Cervical lymphatics also contribute to blood-brain barrier (BBB) function and brain immunoreactivity.3
Ependymal cilia coordinate CSF flow; whereas, junctional adhesion molecules and pore proteins are involved in differential transport to and from the CSF.1 Specific transport systems for glutamine, lipoproteins, immunoglobulins and ions are described.4-7 Several empirical formulas are used to assess the transudation and synthesis of immunoglobulins in the CSF with and without BBB damage.8-10 MRI is used to study CSF fluid dynamics in hydrocepehalus and intracranial hypertension.11,12 Radionuclide cisternography (RC), which is also used to study CSF circulation, demonstrates that the main absorption of the CSF is through the
CNS to the blood. RC also shows that cerebral infarction causes intracellular uptake of calcium from the CSF.13,14 Experimental allergic encephalomyelitis as well as stress alter BBB transport and brain penetration of fluorescein and pyridostigmine.15,16 Membrane protein A of the leptomeninges possesses glycan epitopes which facilitate the transport of Escheriria coli and other bacteria across the BBB.17,18

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