Anisotropic and restricted diffusion of water in the sciatic Nerve: A 2H double-quantum-filtered NMR study

The signals of water in the different compartments of rat sciatic nerve are resolved in the ²H double-quantum-filtered NMR spectrum, due to their different quadrupolar splittings and relaxation rates. This resolution allowed the independent measurement of the water diffusion coefficients in the different compartments. The water diffusion in all three compartments, the endoneurium, the epineurium and the axon was found to be anisotropic. Parallel to the nerve fiber the average intraxonal water diffusion coefficient was 1.11 x 10^-5 cm²/sec, while in the perpendicular direction the diffusion is heavily restricted. The average perpendicular diffusion coefficient ranged from 0.29 x 10^-5 cm²/sec to 0.05 x 10^-5 cm²/sec for diffusion times of 7 msec and 50 msec, respectively. Assuming restricted diffusion in nonpermeable cylinders, intra-axonal mean diameters of 6.0, 7.4 and 9.0 μm were obtained for nerves taken from three different rats.