DOR-immunoreactivity in the dorsal horn of the spinal cord after vehicle, siRNA or mismatch (MM) RNA treatment. The immunoreactivity of DOR was predominantly found in laminae I/II of the dorsal horn. The immunolabeling was significantly lower in tissue from siRNA treated rats. Tissues taken 72 hours after the last siRNA injection (siRNA recovery) show similar level of immunoreactivity for DOR when compared with vehicle or MM RNA controls. Each image is representative of multiple sections from 3 rats per treatment group.