Brain amine metabolism is reflected in cerebral ventricular CSF

The choroid plexuses are suspended within the ventricles and account for approximately 75% of CSF production. The sodium-potassium ATPase operates within the choroidal epithelial cells and moves sodium ions towards the ventricular surface and potassium ions in the direction of the stroma. Water flows into CSF along osmotic gradient produced by sodium pump. The existence of extracellular channels by which brain metabolites could passively diffuse into the ventriculosubarachnoid space suggests an excretory role for CSF. Removal of solutes from the CSF could occur across the choroidal epithelium or arachnoid membrane into the blood. Systematically administered monoamine metabolites do not cross the blood-brain or the blood-CSF barrier. The regional concentrations of amine metabolites in the CSF is in part a reflection of the concentration of catecholamines and indoleamines in the immediately adjacent neuronal parenchyma. In order to illustrate the validity of monoamine metabolite determinations in cerebral ventricular CSF we developed a device which allowed for a continuous third ventricular CSF withdrawal in freely moving (or anesthetized) rats at a constant flow of 1 microliter/min. The elevation of biogenic amine metabolites in CSF by probenecid or their decline by monoamine oxidase inhibition was used to assess the rate of turnover of amines. Pharmacological manipulations (yohimbine, haloperidol, ouabain) resulted in mono-amine metabolite fluctuations in CSF similar to those previously described in brain tissue. Insulin administration caused an abrupt decrease in CSF glucose and elevated dopamine and serotonin metabolites in rats which had no access to food. These studies demonstrate the adaptation of in vivo analysis of CSF in rats but also exemplify the usefulness of monoamine metabolite determination in the CSF as indicators of brain function.