PROJECT SUMMARY Chronic pain is a serious condition which is produced and maintained by a variety of different mechanisms, many of which remain poorly understood This has led to difficulties in providing effective treatments. One key mechanism underlying chronic pain conditions, such as nociplastic pain, is central sensitization in which plastic changes at the level of the spinal cord contribute to and maintain hypernociception. To add further complexity, we have found that different mechanisms underlie the acute, transition, and chronic phases of central sensitization in our model of nociplastic pain. In order to better understand, and therefore successfully treat, chronic pain conditions, the mechanisms underlying these three phases, as well as resolution of chronic pain, must be elucidated. Already, I have shown that excitation of capsaicin-sensitive afferents attenuates the response of sGABAn to low-intensity synaptic stimulation. Furthermore, I have shown that spinal microglia and inflammation mediate the chronic phase of central sensitization underlying a nociplastic pain state. In the F99 phase of the proposed project, I will further characterize the neuronal circuitry underlying the acute and maintenance phases of central sensitization, focusing on 1) how nociceptor activation and subsequent release of reactive oxygen species impair Aβ-fiber-evoked sGABAn activation in the acute phase, 2) whether such impairment allows low-threshold afferent inputs to activate spinal microglia to drive the transition phase, and 3) if reactive microglia and inflammatory mediators maintain the impairment in the chronic phase. In the K00 phase, I will move to a prominent pain research laboratory to investigate the mechanisms by which pro-resolution lipid mediators, such as resolvins, are dysregulated in pain conditions, and their effect on nociceptive circuitry. Additionally, I will investigate how resolvins and the circuitry which they effect may be manipulated to convert chronic pain back to resolving pain. Overall, the proposed project will provide key understanding of the chronification and resolution of nociceptive neural circuit sensitization. These will ultimately reveal new therapeutic targets, allowing for the development of better pain treatments.