We have developed a new in vitro model of the glial scar in which inhibitory CS-PG in a crude gradient more closely resembles that which occurs in vivo after injury. Classic dystrophic endballs form at the tips of adult sensory axons that become trapped within the gradient. We can now ask, for the first time, a variety of basic questions concerning the biology of the dystrophic growth cone. Three important questions we wish to pursue in aim 1 are: (A) whether the dystrophic state is a peculiarity of adult neurons, (B) whether CNS neurons would respond similarly to the PG gradient environment and, (C) whether dendrites respond differently to the inhibitory gradient than do axons. Finally, (D) we would like to know what molecular changes occur in would- be dystrophic axons that are induced to regrow across the potently inhibitory rim of the gradient via a new combinatorial regeneration stimulating strategy. Our ultimate goal is to devise an optimal strategy in vitro that can be used to overcome growth cone dystrophy and stimulate axon regeneration past the glial scar in vivo.
In aim 2, preliminary in vivo results based on a successful regeneration promoting strategy using our in vitro gradient model, have shown evidence that a combination of chronic sterile inflammation induced in the DRG prior to root crush, plus chondroitinase application to the root entry zone at the time of crush, can foster robust regeneration of sensory axons into the spinal cord. We hypothesize that a similar strategy may foster sensory fiber regeneration in a more clinically relevant post-injury model. We propose to study the functional efficacy of these fibers.
In aim 3, we will utilize a novel microlesion model of the cingulum in which one can make the smallest lesion possible but still clearly identify only those axons that have been severed and have potentially regenerated. With the microlesion model, we can use the micropipette, that cuts the axons, to inject bridge building cells or other factors upon withdrawal of the pipette from the brain. Preliminary evidence shows that injection of chondroitinase combined with immature astroglia can stimulate regeneration clearly past the lesion. None-the-less, once past the lesion the fibers only grow short distances. Using this model we hypothesize that by also driving the intrinsic growth potential of the regenerating neurons at the vicinity of their cell body, regeneration will be significantly enhanced.
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