Table 2.

In vivo models of CSF secretion.

Method	Description	Year/reference
CSF drainage method	CSF outflow is collected following the insertion of a needle into the cerebral aqueduct. Once a balanced CSF outflow is reached, the CSF secretion rate is calculated by measuring the CSF volume over time (ml/min).	1932 [43, 118]
Ventriculo-cisternal perfusion	Artificial CSF (aCSF) containing a marker (dextran) is perfused through the lateral ventricles in the brain in anaesthetised live rats. CSF samples are collected from the Cisterna magna and dilution of the marker over time is used to calculate the CSF secretion rate (Fig. 3a).	1970 [119]
Aqueductal method	CSF is drained out of the aqueduct of Sylvius through a cannula. CSF secretion rate is calculated by dividing the collected CSF volume by time taken for collection.	2009 [44, 45]
Radiographic method	A quantity of CSF is removed and an equivalent quantity of air is injected into the lateral brain ventricle. Natural CSF secretion will then compress the air within the ventricle. The CSF secretion rate is calculated by measuring the time of shifting of the air-CSF level.	1969 [120–122]
CSF secretion on the choroid plexus surface	CSF collected from the brain ventricle using a glass pipette determined the role of the choroid plexus in CSF secretion, and calculated the rate of secretion (ml/min).	1960 [123]
Magnetic resonance imaging	Cardiac cycle-related cerebral blood volume variations produce bidirectional oscillatory movement of CSF within the aqueduct of Sylvius. CSF secretion rates is calculated from an estimate of the net flow (difference between CSF inflow and outflow) over one cardiac cycle.	2006 [124–126]