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Water diffusion in the giant axon of the squid: Implications for diffusion‐weighted MRI of the nervous system
Author(s) -
Beaulieu Christian,
Allen Peter S.
Publication year - 1994
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910320506
Subject(s) - axoplasm , squid , axon , squid giant axon , anisotropy , diffusion , white matter , isotropy , nuclear magnetic resonance , chemistry , biophysics , anatomy , materials science , magnetic resonance imaging , physics , biology , thermodynamics , optics , medicine , ecology , radiology
To clarify the result that marked diffusional anisotropy had been found in nonmyelinated nerve, and in completion of an evaluation of the role of all longitudinal axonal structures, we report NMR measurements of water diffusion in the giant axon of the squid, where diffusional anisotropy is determined by the neurofilamentary structure. The diffusion coefficients of water parallel and perpendicular to the long axis of the squid giant axon at 20°C are (1.61 ± 0.06) × 10 −5 cm 2 s −1 and (1.33 ± 0.09) × 10 −5 cm 2 s −1 , respectively, which yield an anisotropic diffusion ratio of 1.2 2 0.1. Water diffusion in the squid giant axon is therefore quite rapid and nearly isotropic, thus eliminating the possibility of a significant role for the longitudinally oriented neurofilaments in producing diffusional anisotropy within the axoplasm. In conjunction with our work on garfish nerves therefore, only membranes, either as numerous axonal membranes or as myelin (if present), remain to fulfill the role of the primary determinant of anisotropic water diffusion in nerve and in white matter.