White Matter Fasciculi Research Articles

Isotropic resolution diffusion tensor imaging with whole brain acquisition in a clinically acceptable time.

Our objective was to develop a diffusion tensor MR imaging pulse sequence that allows whole brain coverage with isotropic resolution within a clinically acceptable time. A single-shot, cardiac-gated MR pulse sequence, optimized for measuring the diffusion tensor in human brain, was developed to provide whole-brain coverage with isotropic (2.5 x 2.5 x 2.5 mm) spatial resolution, within a total imaging time of approximately 15 min. The diffusion tensor was computed for each voxel in the whole volume and the data processed for visualization in three orthogonal planes. Anisotropy data were further visualized using a maximum-intensity projection algorithm. Finally, reconstruction of fiber-tract trajectories i.e., "tractography" was performed. Images obtained with this pulse sequence provide clear delineation of individual white matter tracts, from the most superior cortical regions down to the cerebellum and brain stem. Because the data are acquired with isotropic resolution, they can be reformatted in any plane and the sequence can therefore be used, in general, for macroscopic neurological or psychiatric neuroimaging investigations. The 3D visualization afforded by maximum intensity projection imaging and tractography provided easy visualization of individual white matter fasciculi, which may be important sites of neuropathological degeneration or abnormal brain development. This study has shown that it is possible to obtain robust, high quality diffusion tensor MR data at 1.5 Tesla with isotropic resolution (2.5 x 2.5 x 2.5 mm) from the whole brain within a sufficiently short imaging time that it may be incorporated into clinical imaging protocols.

Immunocytochemical characterization of a new marker of fibrous and reactive astrocytes.

A specific monoclonal antiserum (Mab 6.17) inducing a strong immunostaining of the neuromuscular junction has been used to detect the possible occurrence of the corresponding antigen throughout the intact or lesioned central nervous system of adult rats. In intact animals, 6.17-immunolabeling was essentially detected in astrocyte-like structures located in white matter fasciculi of the brain, such as the optic tract, corpus callosum, fornix, and in the white matter of the spinal cord. The astroglial nature of such 6.17-immunolabeled profiles was verified by performing double or triple immunofluorescent labeling with Mab 6.17 and with specific antisera against astrocytic markers, such as S100 protein, glial fibrillary acidic protein and vimentin. In the white matter, all the structures reactive to Mab 6.17 were also reactive to antibodies against S100 protein, glial fibrillary acidic protein and vimentin. On the other hand, astrocytes of the grey matter that were immunoreactive to S100 and glial fibrillary acidic protein but negative to vimentin, were devoid of 6.17-immunoreactivity. After lesions including stab wound through the diencephalon or transection of the spinal cord, a marked increase of 6.17-immunostaining was noted in the regions surrounding the lesions. In these regions, 6.17-immunolabeling was associated with S100-, GFAP- and vimentin-positive astrocytes constituting the glial scar. The ultrastructural localization of 6.17-immunoreactivity indicated that, similar to glial fibrillary acidic protein and vimentin, the recognized antigen was mainly associated with gliofilaments. These observations indicate that, in the central nervous system of adult rats, Mab 6.17 recognizes a molecule associated with gliofilaments, which is essentially associated to reactive astrocytes expressing high levels of vimentin.

Transplantation of oligodendrocyte precursors in the adult demyelinated spinal cord: Migration and remyelination

A demyelinating lesion induced by an injection of lysolecithin into the spinal cord can be partly repaired by oligodendrocyte precursors transplanted at a distance of 6–8 mm from the lesion. Using a non-toxic fluorescent dye (Hoechst 33342) as a cell marker, we demonstrate that transplanted oligodendrocyte precursors from different origins (periventricular zone fragments from newborn mouse and cultured rat oligodendrocyte progenitor cells) can migrate along specific pathways (i.e. white matter fasciculi, ependymal wall, meninges and blood vessels). These cells can be attracted when passing at the vicinity of the lesion as well as differentiate and remyelinate axons with the lesion. Myelin repair thus appears to be the result of distinct successive events: migration, specific attraction, differentiation and myelination. This can occur in both shiverer and normal adult hosts.