The role of glias in the chronic spinal cord compression (in reference to neural survival and plasticity)

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We investigated the morphology of spinal accessory motoneurons and immunoreactivity to neurotrophins, brain-derived neurotropic factor (BDNF) and neutotrophin (NT)-3, as well as the presence of reactive astrocytosis in 30 tip-toe walking Yoshimura (twy) mice that develop calcification at C1-C2 vertebral level compressing the spinal cord. At the level of compression, the area of neuronal soma and total length of dendrites of WGA-HRP-labelled accessory motoneurons in the medial cell pool decreased significantly with decrement in motoneuron population, when compared to controls. In contrast, at site rostral to the compressive lesion, enlargement of the neuron soma and dendritic elongation were significant and associated with increased motoneuron population and decreased transverse area of the cord at the compressive level, At this site, enhanced BDNF and NT-3 immunoreactivities were evident in the anterior horn cells. In mice with more severe compression, astrocyte-like cells showing BDNF immunoreactivity became abundant and axons in the anterior column demonstrated marked NT-3 immunoreactivity. Our results suggest increased functional activity of anterior horn cells at levels rostral to the site of compression.We speculate that the presence of BDNF and NT-3 in neurons as well as astrocyte-like cells is proportionate to the severity of chronic mechanical compression and may contribute to the heterotropic neuronal reserve and survival.