Expression of Neurotrophins After Experimental Spinal Cord Injury

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BDNF and NT-3, members of the NGF family of trophic factors, have multiple functions including a role in the promotion of neuronal survival and nerve fiber elongation in both the CNS and the PNS.We assessed the expression of endogenous BDNF and NT-3 following an experimentally-induced compression injury to the spinal cord. Expression of BDNF mRNA was increased following the spinal cord injury ; reaching maximum levels 24 hr after the injury. Expression of BDNF mRNA returned to the levels observed in sham-operated control antimals within 3 days of the injury. In contrast, NT-3 mRNA was up-regulated 1 week after the injury and reached to the peak level 2 weeks after the trauma. Using the in situ hybridization technique, we observed a wide distribution of BDNF and NT-3 expression amongst the different cell types in the spinal cord including motor and sensory neurons, and in glial cells, including astrocytes and oligodendrocytes. These results suggest that BDNF is synthesized in both neurons and glial cells during the acute response to injury to the spinal cord, functioning in a mainly neuroprotective role. This is followed by a later phase of NT-3 expression in neurons and glial cells, functioning in a restorative capacity. Especially, NT-3 expression in oligodendrocytes in the later phase suggests that this factor supports restration of long tracts.