It seems like an interesting mechanism, that the brain is somehow signalling by modifying CSF which in turn then then activates nerves. The question I have is

It seems like an interesting mechanism, that the brain is somehow signalling by modifying CSF which in turn then then activates nerves. The question I have is mechanistically, how is the brain actually doing that. If CSF sits on the other side of the blood-brain barrier, it doesn't contact brain cells. So you'd have to introduce some other layer of signalling that does communicate between them.