The blood - brain barrier is the separation of circulating blood and brain fluid in the central nervous system. (nurturenormally.com)
To try to pin down its role, McCarley and his team first tracked the levels of adenosine by extracting samples of brain fluid from cats throughout normal sleep - wake cycles. (sciencemag.org)
These spaces surround the blood vessels that drain brain fluid and communicate with the lymph system; widening of these VR spaces is seen in the elderly but rarely in the young. (scientificamerican.com)