Project summary Chronic pain is a highly prevalent and impactful condition. It persists past the time expected for normal tissue healing from an acutely painful event, suggesting plasticity is occurring within the central nervous system to perpetuate the pain experience. Furthermore, there are several conditions known to occur in the absence of any tissue injury, such as fibromyalgia and tension-type headaches. Collectively, these conditions are referred to as nociplastic pain syndromes. The broad goal of this proposal is to identify regions within the central nervous system that exhibit plasticity in response to chronic pain. To model chronic pain, I will employ the partial sciatic nerve ligation (pSNL). I will focus my investigation on the parabrachial nucleus (PBN), a hub for the relay of aversive sensory information. My preliminary data suggests that the population of neurons expressing Calca within the PBN exhibits an increase in neuronal activity acutely following chronic pain induction, however this activity does not persist through the entire chronic pain experience. Additionally, silencing the PBN Calca population prevents pSNL driven pain and chronically stimulating this population produces pain that persists beyond stimulus cessation. Together this information informs my central hypothesis that PBN Calca neurons are involved in the initiation and perpetuation of chronic pain. To test this hypothesis, I will both manipulate Calca neurons and observe their activity during chronic pain. The experiments detailed in Aim 1 will probe whether PBN Calca neurons are involved in maintaining the chronic pain experience by assessing whether transient inhibition of PBN Calca neurons will ameliorate pSNL driven pain. Aim 2 will explore how much and what type of stimulation is required for the manifestation of persistent pain driven by PBN Calca neurons. This aim will also determine whether expression of the Calca gene is required for the manifestation of chronic pain. Finally, in Aim 3 I will observe the activity of PBN Calca neurons preceding and following the induction of chronic pain via calcium imaging. This will reveal when PBN Calca neurons exhibit increased activity during a chronic pain experience. Collectively, these experiments will delineate the role Calca neurons play in the manifestation and perpetuation of chronic pain. This work will further our understanding of how chronic pain conditions arise and persist in the absence of a driving injury and may suggest a target for novel pain therapies.