Receptor-mediated dysfunction of satellite glia and uninjured sensory neurons as a novel link between referred neuropathic pain and bladder disease - PROJECT SUMMARY Referred pain is both understudied in research and poorly understood in the clinic, particularly for patients with bladder disease. Bladder pain can significantly lessen quality of life, which is amplified by unacknowledged or improperly treated pain from the skin. Diagnosis of referred bladder or somatic pain is obfuscated by a lack of obvious pathology, exacerbating the challenges of finding effective therapeutic approaches. Though the root cause of such referred pain is unknown, it likely relies on visceral and skin afferent interactions, termed viscerosomatic crosstalk. Mechanisms of referred pain attributed to the spinal cord fail to explain why patients with pelvic pain have sensory innervation loss of the lower limb skin that is diagnostic for neuropathic pain. Preliminary data shows that mechanical hypersensitivity in hind paws of mice with bladder inflammation closely resembles nerve injury phenotypes and reflect patient experiences of lower limb sensitivity from bladder inflammation or nerve damage. In the peripheral nervous system, dorsal root ganglia (DRG) neurons are widely diverse in function and in innervating tissue, where injured and uninjured neurons, and their surrounding satellite glia, undergo changes after injury that drive pain. Viscerosomatic crosstalk between uninjured bladder or somatic neurons in DRG could be causing referred pain, but there is a dearth of information about bladder neuron crosstalk in the DRG. Retrograde neuronal tracing studies confirming DRG can co-housing both bladder and hind paw skin sensory neurons strongly support this possibility. The proposed research will test the hypothesis that viscerosomatic crosstalk in DRG after injury results in hyperexcitable physiological responses of the uninjured circuit, mediated by functional changes in their sensory neurons and altered signaling with satellite glia. To do this, neurophysiology experiments will utilize intact DRGs to maintain local communication between neurons and satellite glia, including a novel ex vivo preparation that leaves the mouse sensory circuit from the hind paw skin to the spinal cord intact. Together with molecular assays of protein expression, experiments will determine the mechanisms driving activation of tracer-labeled uninjured neurons by probing activation of satellite glia and two key membrane receptors, transient potential channel V member 1 (TRPV1), also known as the capsaicin receptor, and Purinocepter 3 (P2X3), a widely studied adenosine triphosphate receptor, both of which are poorly understood in referred pain that results from bladder inflammation or nerve injury. Aim 1 is designed to investigate how uninjured hind paw neurons are physiologically altered after acrolein-induced cystitis, and the possibility that these alterations are mediated by changes in TRPV1 or P2X3. Aim 2 will explore how uninjured bladder sensory neurons are affected by Spared Nerve Injury, a robust model of lower limb neuropathic pain. Collectively, these data will help elucidate sensory neuron crosstalk in DRG as a new biological mechanism underlying referred pain in patients with bladder disease and provide a starting point for improved diagnosis and novel, effective therapeutic approaches.
