Introduction

Abstract

Circumventricular organs (CVOs) are found in the brains of all vertebrates. These specialised structures are so named because of their proximity to the ventricles of the brain (Hofer 1958). The mammalian brain has fewer CVOs than the brains of other classes of vertebrates; however, it is clear that CVOs still play important functional roles in mammals. The seven CVOs designated in mammals are the subfornical organ, Organum vasculosum of the lamina terminalis (OVLT), median eminence, pineal gland, subcommissural organ, area postrema (Figure. 1) and choroid plexuses of the lateral, third and fourth ventricles. Although they are quite diverse in their structures and function, common features are their periventricular midline location in the brain, rich vascularisation, altered blood-brain barrier characteristics and atypical ependymal cells.