Book Description

The urinary bladder relies on complex and interconnected neural circuits in the peripheral and central nervous systems to properly coordinate micturition. Local sensory signals in the bladder produce neurochemical changes that are relayed and integrated to allow a switch from the storage phase to the elimination phase of the micturition reflex. These local signals can result from mechanical distension that occurs during bladder filling or can be the result of maladaptive neurotransmission due to noxious stimuli and/or inflammation. The latter occurs frequently in individuals with a chronic pain pathology called interstitial cystitis (IC)/bladder pain syndrome (BPS). Patients with IC/BPS typically present with persistent pelvic pain and severe urinary frequency/urgency that cannot be explained by identifiable causes (e.g.: bacterial, viral, fungal). Though the etiology is unknown, IC/BPS patient symptoms are associated with the breakdown of the uroepithelial barrier and neurogenic inflammation that results in the sensitization of peripheral and central nervous system circuits. In this dissertation, we identify two distinct neurochemical mediators that we have found are important for urinary bladder function and dysfunction using cyclophosphamide (CYP)-induced cystitis, a bladder-centric, chemically inducible, animal model for IC/BPS. The first aim examines vascular endothelial growth factor (VEGF) signaling with its main receptor, VEGF receptor 2 (VEGFR2). High expression of VEGF in the bladder has previously been implicated in increased afferent nerve sensitization and pelvic pain in rodents and humans. Using open-outlet conscious cystometry to measure voiding function, we found changes in bladder function outcomes after blocking VEGF/VEGFR2 signaling using a potent VEGFR2 antagonist in naïve rats and rats treated with acute and chronic CYP. To further elucidate the contribution of VEGF signaling in bladder inflammation, we used RT-qPCR to quantify the presence of VEGF alternative splice variant gene expression in different layers of the urinary bladder (urothelium and detrusor) and the lumbosacral dorsal root ganglia, and spinal cord. We observed changes in VEGF isoform gene expression in these tissues dependent on the duration of CYP-treatment (acute vs. chronic). The second aim examines the role of mechanotransduction in urinary bladder function and dysfunction, with a particular emphasis on Piezo1, a non-selective calcium (Ca2+) permeable ion channel. Using a non-invasive, natural voiding assay, we established a role for Piezo1 activation in increased bladder voiding frequency in naïve (no CYP) rats. On a molecular level, we used RT-qPCR to quantify the gene expression of several mechanosensitive channels and found consistent upregulation in the bladder after chronic CYP-induced cystitis. In addition, we measured urothelial Ca2+ activity following Piezo1 activation and found a CYP-dependent increase in Ca2+ network activity. Lastly, we assessed changes in tight junction gene expression following in vivo Piezo1 activation and found that several urothelial tight junction genes are downregulated. These results underscore the multifaceted signaling within the urinary bladder in normal, and especially in pathological, conditions. Using a multidisciplinary approach, we identified two mediators that contribute to voiding function and dysfunction. Future treatments for IC/BPS will certainly be individualized and will not be a one size fits all approach. Therefore, research into the numerous neurochemical mediators that contribute to IC/BPS is paramount to understanding and treating the functional bladder impairments experienced by patients.