Chapter 57: Aspects of normal cerebrospinal fluid circulation and circumventricular organs

Abstract

Publisher Summary Uptake into circumventricular organs (CVOs) of horseradish peroxidase (HRP) administered into blood vessels was first demonstrated with the electron microscope in 1968. CVOs and the remainder of the brain gave rise to the idea that the extravasated HRP must be reabsorbed together with the cerebrospinal fluid (CSF) into fenestrated venous capillaries of the same CVOs. Otherwise, as Evans blue in the bloodstained CVOs, extravasated plasma protein would stain the whole brain. On the other hand, arachnoid villi or granulations are believed to be the sites of drainage into the venous system of the CSF, even though these structures are ontogenetically as well as phylogenetically limited to some adult higher mammals. Experimental data strongly suggest that: (1) routes for CSF to drain into the blood circulation are fundamentally through fenestrated venous capillaries of CVOs; (2) arachnoid granulations prevent a sudden CSF pressure rise, which could cause noxious compression of brain tissue; and (3) arachnoid granulations play a role in the immune response.