For 10 points, identify this fluid extracted during a lumbar puncture that cushions the brain.
The presence of beta-2 transferrin is a method used to differentiate this substance, whose electrophoresis in MS patients uniquely displays gamma region spikes known as oligoclonal bands. A study linked violent crime with abnormally elevated levels of a certain protein in this substance while its primary synthesis occurs in the choroid plexus. It enters the bloodstream through the venous sinuses, where specialized villi indent the dura mater from the arachnoid and allow this substance's secretion. Analyzed in a serum albumin ratio test, it is separated from the circulatory system by the blood-brain barrier. For 10 points, identify this fluid extracted during a lumbar puncture that cushions the brain.
The presence of beta-2 transferrin is a method used to differentiate this substance, whose electrophoresis in MS patients uniquely displays gamma region spikes known as oligoclonal bands.
{CSF} or {Cerebrospinal} fluid [or, {apparently}, {Liquor cerebrospinalis}, {worst martini variant ever}]