Functional redundancy of ventral spinal locomotor pathways.

Identification of long tracts responsible for the initiation of spontaneous locomotion is critical for spinal cord injury (SCI) repair strategies. Pathways derived from the mesencephalic locomotor region and pontomedullary medial reticular formation responsible for fictive locomotion in decerebrate preparations project to the thoracolumbar levels of the spinal cord via reticulospinal axons in the ventrolateral funiculus (VLF). However, white matter regions critical for spontaneous over-ground locomotion remain unclear because cats, monkeys, and humans display varying degrees of locomotor recovery after ventral SCIs. We studied the contributions of myelinated tracts in the VLF and ventral columns (VC) to spontaneous over-ground locomotion in the adult rat using demyelinating lesions. Animals received ethidium bromide plus photon irradiation producing discrete demyelinating lesions sufficient to stop axonal conduction in the VLF, VC, VLF-VC, or complete ventral white matter (CV). Behavior [open-field Basso, Beattie, and Bresnahan (BBB) scores and grid walking] and transcranial magnetic motor-evoked potentials (tcMMEP) were studied at 1, 2, and 4 weeks after lesion. VLF lesions resulted in complete loss or severe attenuation of tcMMEPs, with mean BBB scores of 18.0, and no grid walking deficits. VC lesions produced behavior similar to VLF-lesioned animals but did not significantly affect tcMMEPs. VC-VLF and CV lesions resulted in complete loss of tcMMEP signals with mean BBB scores of 12.7 and 6.5, respectively. Our data support a diffuse arrangement of axons within the ventral white matter that may comprise a system of multiple descending pathways subserving spontaneous over-ground locomotion in the intact animal.

Temporal progression of angiogenesis and basal lamina deposition after contusive spinal cord injury in the adult rat.

After spinal cord injury (SCI), the absence of an adequate blood supply to injured tissues has been hypothesized to contribute to the lack of regeneration. In this study, blood vessel changes were examined in 28 adult female Fischer 344 rats at 1, 3, 7, 14, 28, and 60 days after a 12.5 g x cm NYU impactor injury at the T9 vertebral level. Laminin, collagen IV, endothelial barrier antigen (SMI71), and rat endothelial cell antigen (RECA-1) immunoreactivities were used to quantify blood vessel per area densities and diameters in ventral gray matter (VGM), ventral white matter (VWM), and dorsal columns (DC) at levels ranging 15 mm rostral and caudal to the epicenter. This study demonstrates an angiogenic response, defined as SMI71/RECA-1-immunopositive endothelial cells that colocalize with a robust deposition of basal lamina and basal lamina streamers, 7 days after injury within epicenter VGM. This angiogenesis diminishes concurrent with cystic cavity formation. GAP43- and neurofilament- (68 kDa and 210 kDa) immunopositive fiber outgrowth was associated with these new blood vessels by day 14. Between 28 and 60 days after injury, increases in SMI71-immunopositive blood vessel densities were observed in the remaining VWM and DC with a corresponding increase in vessel diameters up to 15 mm rostral and caudal to the epicenter. This second angiogenesis within VWM and DC, unlike the acute response observed in VGM, did not correspond to any previously described changes in locomotor behaviors in this model. We propose that therapies targeting angiogenic processes be directed at the interval between 3 and 7 days after SCI.