Tracer in cisternal cerebrospinal fluid is soon detected in choroid plexus capillaries

Horseradish peroxidase was detected in the choroid plexus capillary 5 min after the onset of a 2 1 2 - min injection of 7.5 μl of 40% solution into the cisterna cerebellomedullaris in mice. Venous capillaries in the capillary beds of circumventricular organs including the choroid plexus were indicated as sites of cerebrospinal fluid absorption.