Microfiberoptic fluorescence photobleaching reveals size-dependent macromolecule diffusion in extracellular space deep in brain

Zsolt Zador, Mazin Magzoub, Songwan Jin, Geoffrey T. Manley, Marios C. Papadopoulos, A. S. Verkman

    Research output: Contribution to journalArticle

    Abstract

    Diffusion in brain extracellular space (ECS) is important for nonsynaptic intercellular communication, extracellular ionic buffering, and delivery of drugs and metabolites. We measured macromolecular diffusion in normally light-inaccessible regions of mouse brain by microfiberoptic epifluorescence photobleaching, in which a fiberoptic with a micron-size tip is introduced deep in brain tissue. In brain cortex, the diffusion of a noninteracting molecule [fluorescein isothiocyanate (FITC)-dextran, 70 kDa] was slowed 4.5 ± 0.5-fold compared with its diffusion in water (Do/D), and was depth-independent down to 800 μm from the brain surface. Diffusion was significantly accelerated (Do/D of 2.9±0.3) in mice lacking the glial water channel aquaporin-4. FITC-dextran diffusion varied greatly in different regions of brain, with Do/D of 3.5 ± 0.3 in hippocampus and 7.4 ± 0.3 in thalamus. Remarkably, Do/D in deep brain was strongly dependent on solute size, whereas diffusion in cortex changed little with solute size. Mathematical modeling of ECS diffusion required nonuniform ECS dimensions in deep brain, which we call "heterometricity, " to account for the size-dependent diffusion. Our results provide the first data on molecular diffusion in ECS deep in brain in vivo and demonstrate previously unrecognized hindrance and heterometricity for diffusion of large macromolecules in deep brain.

    Original languageEnglish (US)
    Pages (from-to)870-879
    Number of pages10
    JournalFASEB Journal
    Volume22
    Issue number3
    DOIs
    StatePublished - Mar 1 2008

    Fingerprint

    Photobleaching
    photobleaching
    extracellular space
    Extracellular Space
    Macromolecules
    Brain
    Fluorescence
    fluorescence
    brain
    isothiocyanates
    dextran
    fluorescein
    solutes
    cortex
    Aquaporin 4
    cell communication
    Aquaporins
    thalamus
    aquaporins
    mice

    Keywords

    • Aquaporin 4
    • Central nervous system

    ASJC Scopus subject areas

    • Agricultural and Biological Sciences (miscellaneous)
    • Biochemistry, Genetics and Molecular Biology(all)
    • Biochemistry
    • Cell Biology

    Cite this

    Microfiberoptic fluorescence photobleaching reveals size-dependent macromolecule diffusion in extracellular space deep in brain. / Zador, Zsolt; Magzoub, Mazin; Jin, Songwan; Manley, Geoffrey T.; Papadopoulos, Marios C.; Verkman, A. S.

    In: FASEB Journal, Vol. 22, No. 3, 01.03.2008, p. 870-879.

    Research output: Contribution to journalArticle

    Zador, Zsolt ; Magzoub, Mazin ; Jin, Songwan ; Manley, Geoffrey T. ; Papadopoulos, Marios C. ; Verkman, A. S. / Microfiberoptic fluorescence photobleaching reveals size-dependent macromolecule diffusion in extracellular space deep in brain. In: FASEB Journal. 2008 ; Vol. 22, No. 3. pp. 870-879.
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