DIFFUSION OF WATER IN RAT SCIATIC-NERVE MEASURED BY H-1 PULSED-FIELD GRADIENT NMR - COMPARTMENTATION AND ANISOTROPY

Diffusion of water was measured in rat sciatic nerve at 22.5+/-0.5 deg rees C using the spin-echo pulsed-field gradient sequence. Three effec tive diffusion coefficients (ca. 1.1, 0.23, and 0.02x10(-9)m(2)/s) wer e obtained at a diffusion time of 10 ms in fresh nerve and they showed minimal orientation dependency. The extracellular water signal was qu enched by 10 mM MnCl2, and 10% of the water signal remained. Two diffu sion coefficients of water were now observed at a diffusion time of 10 ms. The faster coefficient (65% of the remaining signal) was 0.8x10(- 9)m(2)/s when the axis of the nerve fiber was set parallel to the grad ient (D-0), and was 0.3x10(-9)m(2)/s when the axis of the nerve fiber was set perpendicular to the gradient (D-90). The values of D-90 and D -0 decreased when the diffusion time was increased from 3 ms to 50 ms. A cylinder diameter of 5.4 mu m was obtained on the assumption of res tricted diffusion in a cylindrical geometry. This agrees with the aver age inner diameter of axons in the rat sciatic nerve. The slower diffu sion component (0.02x10(-9)m(2)/s, 35% of the remaining signal) did no t show orientation or diffusion time dependency, and may be attributed to the intracellular water of the Schwann cell body.