NMR studies in demyelinating and non-demyelinating experimental allergic encephalomyelitis - An approach involving a dehydration procedure

The spinal cords of rats, involved as part of two distinct and reproducible experimental allergic encephalomyelitis animal models, presenting inflamma tory white matter lesions with and without demyelination, were studied in v itro by NMR, before and after a dehydration procedure, in order to characte rize demyelination. All the parameters of the T-1 and T-2 relaxation times were determined, as well as the initial proportion of the very quickly deca ying component of the free induction decay, and the magnetization transfer ratio. The relaxation decays were fitted with the discrete and Contin metho ds. Magnetization transfer ratio measurements permitted fi rst to evaluate the magnetization transfer at the apex, and secondly to decompose the post- irradiation curves into two components: a gaussian and a lorentzian line, w ith their relative proportions and widths. The results presented in this st udy clearly demonstrate that it is not possible to evidence demyelination i n fresh spinal cord preparations by NMR. Hovewer, the dehydration procedure , which was introduced with the aim of reducing the amount of free water in our samples, seems sufficient to enable the detection of demyelination fro m the T-2 relaxation spectra and magnetization transfer data. As a conclusi on, we think that the NMR properties of water protons allow to achieve tiss ue characterization on condition that the parameters concerning free water and its exchanges are eliminated.