Cerebrospinal fluid may flow out from the brain through the frontal skull base and choroid plexus: a gold colloid and cadaverine injection study in mouse fetus

Purpose: It has been commonly accepted for a long time that the cerebrospinal fluid (CSF) drains into arachnoid granulations from the subarachnoid space to the dural venous sinus unidirectionally. However, recently, periventricular capillaries and lymphatic concepts have been introduced. The CSF moves along the perivascular space and drains into the capillary vessels or meningeal lymphatic tissues. CSF is involved in removing brain waste out of the brain. In this study, we investigated the outflow mechanism of substances in the CSF from the brain. Methods: We investigated the movement of CSF by injection of gold colloid conjugates (2, 40, and 200 nm) into the lateral ventricles of mouse fetuses and evaluated the deposition by silver stain with tissue transparency and electron microcopy. Cadaverine was also injected into the lateral ventricle to determine its movement tract. Results: The gold particle deposition was mainly observed in the frontal skull base. Electron microscopic study showed that the gold particle deposition was observed on the choroid plexus and ependyma in the lateral ventricle and also red blood cells in the heart and liver. Two-nanometer particles were exclusively observed in the liver. Cadaverine injection study demonstrated that cadaverine was observed at the extracranial frontal skull base, choroid plexus, ependymal surface, and perivascular area in the brain white matter. Conclusion: The particles in the CSF were shown to move from the brain to the frontal skull base and also into the blood stream through the choroid plexus in the fetus. The outflow of particles in the CSF may be regulated by molecular size. This new information will contribute to the prevention of brain degeneration due to brain waste deposition.