Peripheral Contributions to Bladder Hypersensitivity

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Many disorders of urinary bladder sensation, which is common in interstitial cystitis, bladder outlet obstruction, and bladder over activity, including idiopathic detrussor instability, are characterized by pain and discomfort and enhanced sensitivity to stimuli (i.e., bladder hypersensitivity). Inflammation is present in many, but not all major bladder disorders and interstitial cystitis, for example, often presents without demonstrable organic cause (i.e., there is no apparent mechanical, biochemical or inflammatory condition to explain the symptoms). Visceral hypersensitivity thus can differ from somatic hyperalgesia, which is typically associated with tissue injury and inflammation. Because the anatomical organization of innervation and adequate noxious stimuli for the viscera are unlike the innervation and adequate noxious stimuli in the somatic realm, peripheral mechanisms of visceral hypersensitivity differ from those of somatic hyperalgesia and are not well understood. The long term objective of this research program is to understand peripheral mechanisms of bladder hypersensitivity. The current application proposes to establish functional relevance of stimuli and treatments before subsequent examination of peripheral contributions to the development of bladder hypersensitivity. The peripheral receptors to be examined for contributions to bladder hypersensitivity include ASIC3, TRPV1, P2X2-3 and PAR2, all of which have been implicated in visceral hypersensitivity. For each of these receptors, in normal and hypersensitive conditions (e.g., cyclophosphamide-induced cystitis), we will study: 1) their contribution to bladder voiding and reflex micturition to functionally evaluate bladder hypersensitivity, 2) mechano- and chemo-sensitivity of pelvic nerve and lumbar splanchnic nerve fiber terminals in the bladder using an in vitro bladder-nerve preparation, and 3) whole cell currents and excitability of bladder sensory neurons, identified by content of retrograde tracer. The overall hypothesis is that these four ligand-gated ion channels contribute to mechano-transduction in the urinary bladder. We also hypothesize that protons and/or endogenous mediators (e.g., ATP,mast cell tryptase) contribute to bladder hypersensitivity and can do so even in the absence of frank tissue damage, which is relevant to interstitial cystitis and other so-called "functional" visceral disorders.