Microglia are principal immune cells in the central nervous system. After peripheral nerve injury, spinal microglia participate in the development of neuropathic pain by transforming from resting to reactive states. However, no evidence directly addresses the microglial role in the initiation or maintenance of neuropathic pain. Recently developed transgenic mice (CX3CR1CreER/+:R26iDTR/+) enable us to ablate CX3CR1-positive cells including microglia in a controllable fashion. Our pilot experiments found that depletion of CX3CR1-positive cells completely reversed the neuropathic pain, while selective microglia ablation partially reduced pain hypersensitivities after peripheral nerve injury. Based on these exciting results, we hypothesize that resident microglia in the spinal cord are critical i the initiation but not maintenance of neuropathic pain. We will test this hypothesis by determining: (1) the function of CX3CR1-positive cells in the initiation and maintenance of neuropathic pain; (2) the role of resident microglia and peripheral macrophages in neuropathic pain; and (3) the spinal and brain microglia in neuropathic pain. The results obtained from this proposal will pinpoint the temporal and spatial resolution of microglia/macrophages in the development of neuropathic pain. The current proposal is the first attempt to use microglial ablation approaches to study neuropathic pain, with the aim of evaluating microglia as a potential therapeutic target for the treatment of neuropathic pain. This study will advance our understanding of microglial mechanism of neuropathic pain. The mechanism may also serve as a common model to address the role of microglia in the pathogenesis of various neurological diseases, such as multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's diseases, ischemic stroke, and epilepsy.