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The blood–CSF barrier explained: when development is not immaturity
Author(s) -
Johansson Pia A.,
Dziegielewska Katarzyna M.,
Liddelow Shane A.,
Saunders Norman R.
Publication year - 2008
Publication title -
bioessays
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.175
H-Index - 184
eISSN - 1521-1878
pISSN - 0265-9247
DOI - 10.1002/bies.20718
Subject(s) - paracellular transport , transcellular , cerebrospinal fluid , tight junction , biology , microbiology and biotechnology , blood–brain barrier , ependyma , permeability (electromagnetism) , immunology , chemistry , neuroscience , central nervous system , genetics , membrane
It is often suggested that during development the brain barriers are immature. This argument stems from teleological interpretations and experimental observations of the high protein concentrations in fetal cerebrospinal fluid (CSF) and decreases in apparent permeability of passive markers during development. We argue that the developmental blood–CSF barrier restricts the passage of lipid‐insoluble molecules by the same mechanism as in the adult (tight junctions) rendering the paracellular pathway an unlikely route of entry. Instead, we suggest that both protein and passive markers are transferred across the epithelium through a transcellular route. We propose that changes in volume of distribution can largely explain the decrease in apparent permeability for passive markers and that developmentally regulated cellular transfer explains changes in CSF protein concentrations. The blood–CSF tight junctions are functionally mature from very early in development, and it appears that transfer from blood into embryonic brain occurs predominately via CSF rather than the vasculature. BioEssays 30:237–248, 2008. © 2008 Wiley Periodicals, Inc.