Structural information in neuronal tissue as revealed by q-space diffusionNMR spectroscopy of metabolites in bovine optic nerve

H-1 NMR diffusion experiments performed on the signal of the metabolites in bovine optic nerve showed that the signal decay due to diffusion is bi-exp onential with a slow and a fast diffusing component. Diffusion was measured as a function of the diffusion time, and the data were analyzed as a funct ion of b and q values. Biexponential fit was used to analyze the data, and the results were compared with the displacement distribution profiles obtai ned from the q-space analysis of the data. This q-space analysis showed tha t the fast diffusing component has a broad displacement distribution and ap pears not to be restricted. On the other hand, the slow diffusing component appears to be highly restricted to milieu in the order of 1-2 mu m. The or ientation of the sample with respect to the axis for which diffusion was me asured affected mainly the relative sizes of the populations of each compon ent, but had only a small effect on the extracted apparent diffusion coeffi cients. These results from both the b and the q value analyses suggest that the slow diffusing component is related to restricted diffusion of these m etabolites in the axonal fibers, while the fast diffusing component represe nts diffusion of metabolites in cells and along the long axis of the nerve fibers. It is concluded that q-space analysis of metabolite diffusion enabl es extraction of structural information about the sample, and that the diff usion of the metabolites in optic nerve is dictated mainly by the cellular medium and microstructure of the tissue. Copyright (C) 1999 John Wiley & So ns, Ltd.