Bladder afferent nerves are composed by myelinated Aδ- and unmyelinated C-fibers. During the storage phase of urine, distention of the bladder has long been considered to evoke afferent activity via Aδ-fibers connected in series with the smooth muscle fibers. In contrast, a previous study in cats revealed that more than 90% of C-fibers do not respond to normal bladder distension, being so called "silent" fibers. However, at least in rats, C-fibers can respond to normal bladder distension like Aδ-fibers, although they may also fulfill a potentially different role in the bladder sensory function in response to abnormal stimuli.
The symptoms of overactive bladder (OAB) or interstitial cystitis (IC) are believed to be commonly related to the sensory (afferent) function. In our laboratory, a direct measuring technique of mechanosensitive single-unit afferent activities of the primary bladder nerves in the rat has been established, and we have investigated the direct effects of drugs (anticholinergics, β3-adrenoceptor agonists, α1-adrenoceptor antagonists, PDE type5 inhibitors, etc.) on the bladder afferent function.
In this symposium, we will show some of our results and propose a possible additional action on sensory pathway of drugs as therapeutic agents for OAB or IC.

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