NMR Studies in Demyelinating and Non-Demyelinating Experimental Allergic Encephalomyelitis

Abstract

The spinal cords of rats, involved as part of two distinct and reproducible experimental allergic encephalomyelitis animal models, presenting inflammatory white matter lesions with and without demyelination, were studied in vitro by NMR, before and after a dehydration procedure, in order to characterize demyelination. All the parameters of the T₁ and T₂ relaxation times were determined, as well as the initial proportion of the very quickly decaying component of the free induction decay, and the magnetization transfer ratio. The relaxation decays were fitted with the discrete and Contin methods. Magnetization transfer ratio measurements permitted first 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, with their relative proportions and widths. The results presented in this study clearly demonstrate that it is not possible to evidence demyelination in 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 from the T₂ relaxation spectra and magnetization transfer data. As a conclusion, we think that the NMR properties of water protons allow to achieve tissue characterization on condition that the parameters concerning free water and its exchanges are eliminated.