Diffusion of water in rat sciatic nerve measured by 1H pulsed field gradient NMR: compartmentation and anisotropy

Diffusion of water was measured in rat sciatic nerve at 22.5 +/- 0.5 degrees C using the spinecho pulsed-field gradient sequence. Three effective diffusion coefficients (ca. 1.1, 0.23, and 0.02 x 10(-9) m2/s) were obtained at a diffusion time of 10 ms in fresh nerve and they showed minimal orientation dependency. The extracellular water signal was quenched by 10 mM MnCl2, and 10% of the water signal remained. Two diffusion coefficients of water were now observed at a diffusion time of 10 ms. The faster coefficient (65% of the remaining signal) was 0.8 x 10(9) m2/s when the axis of the nerve fiber was set parallel to the gradient (D0), and was 0.3 x 10(9) m2/s when the axis of the nerve fiber was set perpendicular to the gradient (D90). The values of D90 and D0 decreased when the diffusion time was increased from 3 ms to 50 ms. A cylinder diameter of 5.4 microns was obtained on the assumption of restricted diffusion in a cylindrical geometry. This agrees with the average inner diameter of axons in the rat sciatic nerve. The slower diffusion component (0.02 x 10(-9) m2/s, 35% of the remaining signal) did not show orientation or diffusion time dependency, and may be attributed to the intracellular water of the Schwann cell body.