Environmental factors involved in axonal regeneration following spinal cord transection in rats.

A recent study of a rat model treated with grafted collagen filament (CF) after spinal cord transection showed dramatic recovery of motor function but did not report on the acute-stage phenomenon. In the present study, we describe molecular and histological aspects of the axonal regeneration process during the acute stage following spinal cord transection. The spinal cord of 8-week-old rats was completely transected, and a scaffold of almost the same size as the resected portion was implanted in the gap. Changes in the mRNA expression of four neurotrophic factors [nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), NT-3, and glial cell-derived neurotrophic factor (GDNF)] were analyzed after 72 h. The expression of BDNF and NT-3 mRNA increased significantly in the CF-grafted group compared to the nongrafted group. Immunostaining for BDNF and NT-3 revealed that cells positive for these neurotrophic factors extended along the collagen filaments in the CF-grafted group. Similarly, astrocytes extended into the collagen filament scaffold together with the neurotrophic factors and partly across a border line. These findings indicate that collagen filament helps to reduce scar tissue, supports the expression of neurotrophic factors, and serves as a scaffold for the outgrowth of regenerating axons.