2 month survival). As discussed, silencing of hSNCA using mir30-SNCA ameliorated some toxic effects observed in hSNCA-expressing MK0683 order rats. Of these positive hSNCA gene silencing effects, the protection against the hSNCA-induced forelimb deficit is of particular interest because it appears to be due specifically to silencing hSNCA in DA terminals in the ST. At 2 months after injection, expression of hSNCA in the ST correlated with the deficit in contralateral forelimb use. Possible correlation of these measures was not assessed at 1 month because the survival time for all rats in this portion

of the study was 2 months. hSNCA mRNA may have been silenced either at the terminals or in the cell body, thereby reducing transport of hSNCA mRNA to the ST. Our data suggest that the presence of hSNCA with either silencing vector induces loss of TH fibers in the ST. Importantly, hSNCA gene silencing promotes a partial selleck kinase inhibitor recovery from this initial toxic effect on TH-IR fibers in the ST, which is not observed in the AAV-NS control group. This partial

protection of TH-IR fibers in rats where hSNCA was silenced also correlates with the recovery in forelimb behavior between 1 and 2 months in this group. These findings are in agreement with our previous study in which a hSNCA-specific shRNA was used to silence hSNCA. In that study, not only was there a protection of forelimb use, but click here data from fluorogold tract tracing suggested that hSNCA gene silencing promoted sprouting of new nigrostriatal fibers from surviving nigral DA neurons (Khodr et al., 2011). Sprouting may also have occurred in the current study, although we cannot rule out the possibility that partial recovery in

TH protein in ST also contributed to behavioral improvement. Although hSNCA gene silencing with mir30-SNCA exhibited positive effects, the observed negative effects exclude the current dose of mir30-SNCA from further preclinical development. The negative effects may have been due to expression of the silencing construct or to viral dose. Toxicity on midbrain DA neurons due to high viral loads or high transgene expression also has been observed by others. Ulusoy et al. (2009) observed that high titer AAV5 vectors expressing either an shRNA or GFP induced loss of DA neurons, as well as microglial activation, and Koprich et al., 2010 and Koprich et al., 2011 observed that high titer AAV1/2 expressing GFP induced loss of SN neurons. However, in the current study, differences were observed between rats injected with AAV-hSNCA and AAV-mir30-hSNCA and rats injected with AAV-hSNCA and AAV-NS even though both groups received similar doses of vectors. Moreover, effects were significantly better in rats in which hSNCA was silenced compared to NS control rats.