, 2010). A hypothetical advantage

of using GFP as a neuronal tracer rather than transported dyes is the fact that GFP reputedly moves through the cell through passive diffusion rather than axonal transport, and is not accordingly vulnerable to artifacts associated with injury-related changes in axonal transport. That is, rates of axonal transport increase after neural injury, and greater tracer labeling in an axon may reflect accelerated transport Fulvestrant mouse rather than true structural change; GFP may not be subject to this potential artifact. Viral vectors expressing GFP may also be employed elegantly to study the effects of genetic manipulation of axonal growth. For example, we have utilized an AAV vector coding for a candidate regeneration-associated gene that also expresses the GFP reporter; a neuron that incorporates the AAV vector will

both express the candidate gene and label that neuron’s axon with GFP. This ATM Kinase Inhibitor molecular weight allows specific assessment of a gene effect on growth only in transduced neurons, potentially enhancing the sensitivity to detect an effect on growth (Löw et al., 2010). Transgenic mice can be a very useful model for examining the role of specific genes in axonal growth after adult injury. Several points must be considered when interpreting results from these models, however.

First, genes that are deleted in neural development may perturb development of spinal pathways, leading to uncertainties regarding interpretation of results after adult injury. For example, early post-natal deletion of PTEN enhanced CST growth after spinal cord injury (Liu et al., 2010); however, deletion at this stage, while the CST is developing, could have altered the anatomy of its spinal projections with the result that partial lesion models in the adult failed to remove aberrant axon projections. Accordingly, a precise survey of the anatomy of the CST Idoxuridine projection in adult unlesioned PTEN-deletion mice was required to confirm that axons were not in locations that would be inadvertently spared (Liu et al., 2010). Another caveat of transgenic mouse models in regeneration research is the possibility that developmental compensation may occur for loss of the targeted gene, leading to erroneous conclusions regarding the role of the deleted gene. Finally, a caveat to studies of axon regeneration in mice is a unique wound healing response that occurs at the lesion site, which results in a contracted, cell-rich lesion (Zhang et al., 1996) rather than a large, cystic lesion cavity. Accordingly, it remains to be seen whether manipulations that enable axon growth in mice will also be effective in other species.