Chronic pain and mood disorders are highly comorbid, particularly in patients with a history of early life stress (ELS) or trauma. In patients with Urologic Chronic Pelvic Pain Syndromes (UCPPS), the severity of ELS has been associated with a centralized pain phenotype with patients reporting greater widespread pain and negative mood, and reduced likelihood of symptom improvement. Neuroimaging studies revealed functional connectivity changes that may specifically predispose UCPPS patients with ELS to greater symptom burden and comorbidity. ELS has also been correlated with reductions in hippocampal gray matter volume and increased DNA methylation on stress-responsive genes, particularly in patients with major depressive disorder, a common comorbidity of UCPPS. The hippocampus negatively regulates the hypothalamic-pituitary-adrenal (HPA) axis, which mediates the stress response and is often altered in patients with centralized pain disorders. Voluntary exercise is an effective treatment for most mood and centralized pain disorders and significantly increases hippocampal neurogenesis and has been shown to impact epigenetic modifications. Our mouse model of ELS using neonatal maternal separation (NMS) demonstrates urogenital hypersensitivity, increased bladder output, widespread allodynia, impaired reward behaviors, and evidence of altered hippocampal regulation of the HPA axis. These outcomes can be exacerbated by acute exposure to water avoidance stress (WAS) in adulthood and attenuated by voluntary wheel running. Here we provide preliminary evidence of reduced hippocampal gray matter volume, DNA methylation, and blunted neurochemical signals following WAS, suggesting that reduced hippocampal integrity may be driving the NMS-related outcomes, similar to what has been observed in clinical populations. Our central hypothesis is that ELS-induced changes in the hippocampus can be modified by increasing physical activity, thereby attenuating urogenital and widespread hypersensitivity. We will test this hypothesis in two specific aims. Our first specific aim will determine whether increasing physical activity can prevent structural and neurochemical changes in the hippocampus and susceptibility to acute stress exposure in NMS mice. Our second specific aim will determine the impact of DNA methylation in the hippocampus on NMS-related outcomes and whether this process can be attenuated by increasing physical activity. At the completion of this project we will have gained novel and important information on the impact of ELS on hippocampal integrity, which we have identified as a potential integrator of centralized pain and comorbid mood disorders. Determining how increasing voluntary physical activity impacts ELS-related hippocampal and sensitivity changes will provide further evidence for the use of exercise as a powerful non-pharmacologic therapeutic intervention for treating UCPPS patients with a history of ELS and possibly preventing the development of symptoms in at-risk populations.
Experiencing early life stress or trauma increases the likelihood of developing chronic pain and mood disorders later in life. This is in part due to structural, neurochemical, and epigenetic changes within the brain that regulate the response to stress and the perception of pain. We will determine if increasing physical activity can attenuate these central changes and reduce stress-induced symptom exacerbation.
