Extra-Blood-Brain-Barrier Brain Structures

Abstract

Publisher Summary This chapter discusses three extra blood–brain-barrier brain structures that are the area postrema (a.p.), the subcommissural organ (s.c.o.), and the subfornical organ (s.f.o). It presents anatomical, histo- and bio-chemical, pharmacological, and physiological data on the a.p., the s.c.o., and the s.f.o. The area postrema has many morphological similarities to the intercolumnar tubercle and both regions differ from the rest of the ventricular wall. In these two regions, pericapillary glial processes are not closely apposed to the capillary basement membrane. Connective tissue containing collagen fibrils and fibroblasts is seen around the basement membrane. Outside this connective tissue layer is a second basement membrane with glial cells processes applied to it. The subfornical organ or intercolumnar tubercle described by Putnam has many features suggesting that its cytological arrangement is similar to that of the area postrema, but it has received far less attention. Putnam also suggested that it contains nerve cells in the human and monkey. Akert emphasize the relation of the subfornical organ to the septal region. Three main components of the subfornical organ are recognized: the body, a dorsal stalk, and a ventral stalk. The subcommissural organ lacks sinusoid-like blood vessels, and it has a markedly thickened columnar ependymal epithelium.