s in the L4, L5 and L6 DRGs from three rats, 44% of those neurons were GFP-positive. Interestingly, the GFP-labeled neurons were predominantly of large to medium size. Out of all the GFP-positive profiles in the DRG, 38% were large, 41% were medium and only 21% were small. Conversely, out of all the neuronal profiles, GFP was observed in 100%, 52% and 20% in large, medium and small profiles respectively. Double immunofluorescence study revealed that over 80% of the GFP-positive neurons were co-labeled with NF200, a marker for myelinated fibers. A small portion of transduced neurons are co-labeled with nociceptor markers such as TRPV1, CGRP and IB4. In the spinal cord, GFP was detected in abundance at the lumbar level, and to a much less degree at the thoracic or cervical level. The spinal GFP immunoreactivity was mostly present in the deeper dorsal horn, dorsal columns and nerve roots attached. GFP was also observed 
in the ventral horn and white matter, although the labeling intensity was much lower. In the dorsal horn, the fibrous pattern and minimal co-labeling with spinal cord neuN suggested the major source of GFP was primary afferents. There was a preferential co-labeling of GFP with NF200 but not IB4 or CGRP in the spinal cord dorsal horn. In addition, GFP was observed in the sciatic nerves and the nerve terminals in the plantar skin of the hind paw. AAV5-mediated knockdown of mTOR expression A similar preference for large-diameter DRG neurons by AAV8 and AAV9 was observed in our pilot study, while the transduction efficacy of AAV5 was evidently the most consistent and outstanding among the three AAVs. We therefore selected AAV5 in the following siRNA studies. PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22187127 Two siRNAs targeting mTOR and one control siRNA targeting luciferase were constructed as GSK343 web short-hairpin RNAs downstream of a U6 promoter. The vectors also encoded a GFP gene driven by a phosphoglycerate kinase promoter. GFP-alone vector or si-Luc vector treatment did not alter the mTOR level in the lumbar DRGs, compared to the naive control. However, a significant reduction of mTOR was observed in the lumbar DRG homogenates in rats treated with either of the mTOR siRNA vectors at two week following the IT administration. The two vectors exhibited similar potency and induced a comparable degree of mTOR knockdown. Confocal immunohistochemistry revealed that the pattern of GFP expression driven by the PGK promoter is similar to that driven by the CMV promoter. Strong GFP expression is predominantly present in large to medium-diameter neurons and preferentially co-localized with NF200. mTOR labeling is intact in rats treated with the control si-Luc vector and present in most if not all neurons. As a result, extensive co-labeling of mTOR and GFP was observed. The level of mTOR was greatly reduced in DRG neurons from rats received si-TOR or si-TOR’ vectors and the co-labeling of mTOR with GFP was profoundly reduced. The down-regulation of mTOR is not observed in the lumbar spinal cord or DRGs from thoracic or cervical levels. Interestingly but unexpectedly, the knockdown of mTOR was not confined to GFP-positive neurons. A significant portion of nociceptors, which did not express detectable GFP, also exhibited reduced mTOR labeling after the si-TOR treatment. This prompted us to further examine the time course of mTOR knockdown in a correlation with the expression of GFP. We found that unlike GFP, which was detectable In Vivo DRG Gene Knockdown Mediated by AAV5 beginning at 2 weeks