PMC:2678986 / 7236-9046 JSONTXT

{"project":"2_test","denotations":[{"id":"19176219-15381331-99578268","span":{"begin":1219,"end":1223},"obj":"15381331"},{"id":"19176219-15381331-99578268","span":{"begin":1219,"end":1223},"obj":"15381331"},{"id":"19176219-18680196-99578269","span":{"begin":1359,"end":1363},"obj":"18680196"},{"id":"19176219-18680196-99578269","span":{"begin":1359,"end":1363},"obj":"18680196"},{"id":"19176219-15381331-3576922","span":{"begin":1219,"end":1223},"obj":"15381331"},{"id":"19176219-15381331-3576922","span":{"begin":1219,"end":1223},"obj":"15381331"},{"id":"19176219-18680196-3576923","span":{"begin":1359,"end":1363},"obj":"18680196"},{"id":"19176219-18680196-3576923","span":{"begin":1359,"end":1363},"obj":"18680196"}],"text":"3 Blood–brain and blood–CSF barriers\nSubstances can cross non-barrier capillary walls by a variety of routes, either between the cells of the endothelium (paracellular movement), directly through the cell wall (active transport, facilitated and/or passive diffusion) or through vesicular transport (endocytosis). However, the cerebral capillaries are the site of the blood–brain barrier (BBB) and consequently these three routes are restricted by the presence of tight junctions between the endothelial cells, the lack of intracellular fenestrations in brain endothelial cells, the paucity of endocytotic vesicles as well as by the presence of multiple metabolic enzymes and diverse transport systems (Fig. 1). Thus the entry of anti-HIV drugs/substances by unregulated pathways or by leakage is limited.\nIn addition, the choroid plexus acts as a barrier between the circulating blood and cerebrospinal fluid (CSF) and is also the site of production of the latter. They are located in the lateral, third and fourth ventricles and their barrier function is attributed to the tight junctions between the epithelial cells, in addition to the metabolism and efflux that occurs within the tissue itself (Strazielle et al., 2004). However, the molecular composition of the intercellular junctional complexes and the transporters present at the BBB (Gazzin et al., 2008) differ from that on the blood–CSF barrier, which means that drug movement into the brain varies depending on its main route of entry. Consequently, although the CSF is an accessible body fluid that provides insight into the brain infection and drug penetration, it can also diverge in important ways from the brain itself. An understanding of anti-HIV drug movement across both the BBB and the blood–CSF barrier is therefore of special interest."}