Nanoscale diffusion in the synaptic cleft and beyond measured with time-resolved fluorescence anisotropy imaging.
Neural activity relies on molecular diffusion within nanoscopic spaces outside and inside nerve cells, such as synaptic clefts or dendritic spines. Measuring diffusion on this small scale in situ has not hitherto been possible, yet this knowledge is critical for understanding the dynamics of molecular events and electric currents that shape physiological signals throughout the brain. Here we advance time-resolved fluorescence anisotropy imaging combined with two-photon excitation microscopy to map nanoscale diffusivity in ex vivo brain slices. We find that in the brain interstitial gaps small molecules move on average ~30% slower than in a free medium whereas inside neuronal dendrites this retardation is ~70%. In the synaptic cleft free nanodiffusion is decelerated by ~46%. These quantities provide previously unattainable basic constrains for the receptor actions of released neurotransmitters, the electrical conductance of the brain interstitial space and the limiting rate of molecular interactions or conformational changes in the synaptic microenvironment.
Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
Kaiyu
K
Zheng
Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
Thomas P
TP
Jensen
Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.|Institute of Neuroscience, University of Nizhny Novgorod, 603950 Nizhny Novgorod, Russia.
Leonid P
LP
Savtchenko
Department of Physics, King's College London, Strand, London WC2R 2LS, UK.
James A
JA
Levitt
Department of Physics, King's College London, Strand, London WC2R 2LS, UK.
Klaus
K
Suhling
Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
Dmitri A
DA
Rusakov
D000818:Animals; D001923:Brain Chemistry; D004058:Diffusion; D005454:Fluorescence Polarization; D015200:Fluoroimmunoassay; D018377:Neurotransmitter Agents / Q000032:analysis*; D061848:Optical Imaging; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000737:chemistry / Q000378:metabolism*
D018377:Neurotransmitter Agents