Perivascular CSF flow in the rat cerebellum

Cerebrospinal fluid (CSF) flow from the subarachnoid space into the cerebellum was studied in rats using Horseradish peroxidase (HRP) injected into the cisterna magna. Animals were sacrificed after 0, 10 or 30 min Transpial diffusion of HRP did not extend beyond the Purkinje cell layer. At all time intervals, perivascular spaces labelled with HRP were observed in cerebellar grey and white matter. In the cerebellar granular layer and white matter, HRP was usually present only in perivascular spaces and the surrounding extracellular space. There was no evidence of a preferential flow towards the fourth ventricle. These results suggest that there is a perivascular pathway for rapid flow of CSF from the subarachnoid space into the perivascular spaces and then into the cerebellar extracellular space. The Purkinje cell layer appears to act as a barrier to diffusion from the pial surface.