Ionic contrast terahertz near-field imaging of axonal water fluxes

Laboratoire d'Optique et Biosciences, Ecole Polytechnique, Centre National de la Recherche Scientifique Unité Mixte de Recherche 7645, Institut National de la Santé et de la Recherche Médicale U696, 91128 Palaiseau, France

Edited by Erich P. Ippen, Massachusetts Institute of Technology, Cambridge, MA, and approved February 3, 2006 (received for review December 19, 2005)

Abstract

We demonstrate the direct and noninvasive imaging of functional neurons by ionic contrast terahertz near-field microscopy. This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore, neuronal activity results from both a precise control of transient variations in ionic conductances and a much less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed ionic contrast terahertz microscopy technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by temperature change or neurotoxin poisoning. Water influx as small as 20 fl per μm of axonal length can be measured. This technique should then provide grounds for the development of advanced functional neuroimaging methods based on diffusion anisotropy of water molecules.

Footnotes

*To whom correspondence should be addressed. E-mail: guilhem.gallot{at}polytechnique.fr
Author contributions: J.-B.M., M.-P.S., J.-L.M., and G.G. designed research; J.-B.M., M.-P.S., and G.G. performed research; J.-B.M., M.-P.S., and G.G. analyzed data; and J.-B.M., M.-P.S., J.-L.M., and G.G. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviation:

FEM,

finite element method