Directing Axon Regeneration after Spinal Cord Injury

Many Strategies have attempted to promote axonal regeneration from descending axons after spinal cord injury (Sd). These include administration of neurotrophic factors, transplants of fetal tissue, Schwann cells, stem cells or genetically modified cells to secrete trophic factor, reduce inhibitory effect around the lesion area, as well as increasing the intrinsic growth potential of the axons. Although these treatments show some axonal regeneration and functional recovery, regeneration from supraspinal axons is still limited. All these studies suggest that a single approach may not be enough. In this proposal, we will use a combined strategy to examine the hypothesis that increasing the intrinsic growth ability of axons (using Rolipram), reducing glial-scar inhibitors (using Chase) and creating a growth supportive pathway (using neurotrophins) caudal to the lesion site will not only enhance axon regeneration, but also promote longer-distance growth as well as promote functional recovery. A unilateral hemisection will be made at the third cervical level of adult rats to completely damage the half of the spinal cord. Rolipram, a drug which can increase the level of neuronal cAMP and thus, the neuron's ability to grow, will be delivered for 2 weeks by using a minipump. Chondroitinase (Chase), an enzyme that reduces the inhibitory nature of chondroitin sulfate proteoglycans (CSPGs) found in the scar around the lesion, will be injected at the lesion site. Multiple injections of lentivirus encoding BDNF, NT-3 or (}DNF will be used to create a growth supportive pathway caudal to the lesion site. Four weeks after SCI, bioS dextran amine (BDA) will be injected at the red nucleus contralateral to the lesion side to label rubrospinal axons (RST). One week after BDA injection, regeneration of supraspinal axons will be examined by using BDA staining for RST, or using immunocytochemical staining for raphespinal and coerulospinal tracts. Behavioral tests will also be done throughout these experiments to monitor functional recovery. These experiments are designed to examine if combining three treatments that work independently will enhance regeneration and functional recovery better than any of these treatments alone.