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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