NR1 is an essential subunit of the N-methyl-D-aspartate (NMDA) receptor, which at the spinal level is involved in injuryinduced pain hypersensitivity and morphine tolerance. An in vitro luciferase assay was used to identify candidate and control (inactive) short interfering RNA (siRNA) sequences that are expressed by a recombinant adeno-associated virus (rAAV) plasmid. rAAV vectors targeting the NR1 subunit were prepared that express active or control (mismatch) siRNA sequences and injected into the mouse spinal cord dorsal horn (SCDH). Three weeks after vector administration, green fluorescent protein labeling of the ipsilateral SCDH confirmed the spatial localization of the viral transduction. Active siRNAs resulted in a 60 to 75% knockdown of NR1 mRNA and protein in the area of the virus injection. The spatial knockdown persisted for at least 6 months after a single administration of the vector. Neither the active nor the mismatch siRNAs resulted in cellular toxicity as measured by nuclear staining and cell integrity. The vectorderived knockdown of NR1 expression in SCDH did not alter acute thermal or mechanical stimulus paw-withdrawal thresholds. However, the vector-derived siRNA prevented the mechanical allodynia measured at 24 and 48 h after injection into the paw of the inflammatory agent, Complete Freund's adjuvant. These results demonstrate that vector-derived siRNAs can be used to produce an in vivo spatial knockdown of the expression and function of the NMDA receptor that is confined to the ipsilateral SCDH. Vector-derived siRNAs may have therapeutic potential for the management of injury-induced pain resulting from the activation of NMDA receptors in the SCDH.RNA interference (RNAi) is an evolutionarily conserved mechanism for silencing gene expression by targeted degradation of mRNA. Because it allows a sequence-specific inhibition of gene expression, it is being widely applied in biology, including in vivo applications (Fire et al., 1998;Dorsett and Tuschl, 2004;Dykxhoorn et al., 2006).RNAi is often more potent and longer lasting than other nucleic acid-based approaches and, compared to gene targeting by homologous recombination, is less expensive and timeconsuming and not limited to a particular mammalian species (i.e., the mouse) (Dorsett and Tuschl, 2004;Dykxhoorn et al., 2006). A key feature of this approach is that small doublestranded RNAs (small interfering RNAs, siRNAs) are generated by the action of an RNase-III-like enzyme called Dicer from a larger double-stranded RNA precursor or from short hairpin (sh) RNAs, which can be expressed from plasmids or viral vectors (Lieberman et al., 2003;Dorsett and Tuschl, 2004). mRNA degradation occurs when the antisense strand of the siRNA directs the RNA-induced silencing complex that contains the RNA endonuclease Ago2 to cleave the complementary sequence of the target mRNA (Dykxhoorn et al., 2006). Silencing by RNAi is typically incomplete-a knockdown rather than a knockout. Similar to other nucleic acidbased methods, any gene is a potential ...