Purpose-Afferent nerve firing has been linked to spontaneous bladder contractions in a number of lower urinary tract pathologies and it may lead to urgency and incontinence. Using optical mapping, single unit recording and tension measurements we investigated the correlation between afferent nerve firing and spontaneous bladder contractions in spinal cord transected mice.Materials and Methods-Bladder-nerve preparations (bladder sheets and the associated L6-S2 pelvic nerves) were dissected from normal and spinal cord transected mice showing overactivity on cystometry and opened along the ventral aspect from base to dome. Bladder sheets were mounted horizontally in a temperature regulated chamber to simultaneously record Ca 2+ transients across the mucosal surface, single unit afferent nerve firing and whole bladder tension.Results-Single unit afferent fibers were identified by probing their receptive fields. Fibers showed a graded response to von Frey stimulation and a frequency of afferent firing that increased as a function of the degree of stretch. Optical maps of Ca 2+ transients in control bladders demonstrated multiple initiation sites that resulted in high frequency, low amplitude spontaneous contractions. Alternatively in maps of the bladders of spinal cord transected mice Ca 2+ transients arose from 1 or 2 focal sites, resulting in low frequency, high amplitude contractions and concomitant afferent firing.Conclusions-Large amplitude, spontaneous bladder contractions evoke afferent nerve activity, which may contribute to incontinence. Keywords urinary bladder; spinal cord injuries; urinary incontinence; neurons, afferent; muscular contraction Spontaneous bladder contractions have been shown to decrease in frequency but increase in magnitude in a number of lower urinary tract pathologies, including outlet obstruction 1 and SCT. 2 These contractions may underlie abnormal increases in intravesical pressure, resulting in urgency, frequency and urge incontinence. 3 This activity may originate in the central nervous system 4 or in detrusor smooth muscle. 5 Alternatively it may originate in the urothelial/ suburothelial region. It has been suggested that the urothelial release of acetylcholine and ATP interacts with lamina propria myofibroblasts to drive spontaneous activity. 6,7 In the rat increases in the amplitude of spontaneous contractions have been noted after SCT. 2 This activity was initiated at a focal site near the bladder dome and it spread over the detrusor in a coordinated fashion. In normal bladders spontaneous contractions originate at multiple Copyright © 2009 Afferent nerves convey sensory information from the bladder to the central nervous system. These nerves comprise myelinated Aδ fibers that are primarily located in detrusor smooth muscle and unmyelinated C fibers that spread through all of the layers of the bladder wall. 8 In the bladder 4 types of afferent nerves have been described, including serosal, muscular, muscular-mucosal and mucosal, of which 63% are muscular. 9 Afferents...

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Studies in humans and rodents suggest that colon inflammation promotes urinary bladder hypersensitivity and, conversely, that cystitis contributes to colon hypersensitivity, events referred to as cross-organ sensitization. To investigate a potential peripheral mechanism, we examined whether cystitis alters the sensitivity of pelvic nerve colorectal afferents. Male C57BL/6 mice were treated with cyclophosphamide (CYP) or saline, and the mechanosensitive properties of single afferent fibers innervating the colorectum were studied with an in vitro preparation. In addition, mechanosensitive receptive endings were exposed to an inflammatory soup (IS) to study sensitization. Urinary bladder mechanosensitive afferents were also tested. We found that baseline responses of stretch-sensitive colorectal afferents did not differ between treatment groups. Whereas IS excited a proportion of colorectal afferents CYP treatment did not alter the magnitude of this response. However, the number of stretch-sensitive fibers excited by IS was increased relative to saline-treated mice. Responses to IS were not altered by CYP treatment, but the proportion of IS-responsive fibers was increased relative to saline-treated mice. In bladder, IS application increased responses of muscular afferents to stretch, although no differences were detected between saline- and CYP-treated mice. In contrast, their chemosensitivity to IS was decreased in the CYP-treated group. Histological examination revealed no changes in colorectum and modest edema and infiltration in the urinary bladder of CYP-treated mice. In conclusion, CYP treatment increased mechanical sensitivity of colorectal muscular afferents and increased the proportion of chemosensitive colorectal afferents. These data support a peripheral contribution to cross-organ sensitization of pelvic organs.

Fry CH, Young JS, Jabr RI, McCarthy C, Ikeda Y, Kanai AJ. Modulation of spontaneous activity in the overactive bladder: the role of P2Y agonists. Am J Physiol Renal Physiol 302: F1447-F1454, 2012. First published February 22, 2012 doi:10.1152/ajprenal.00436.2011Spinal cord transection (SCT) leads to an increase in spontaneous contractile activity in the isolated bladder that is reminiscent of an overactive bladder syndrome in patients with similar damage to the central nervous system. An increase in interstitial cell number in the suburothelial space between the urothelium and detrusor smooth muscle layer occurs in SCT bladders, and these cells elicit excitatory responses to purines and pyrimidines such as ATP, ADP, and UTP. We have investigated the hypothesis that these agents underlie the increase in spontaneous activity. Rats underwent lower thoracic spinal cord transection, and their bladder sheets or strips, with intact mucosa except where specified, were used for experiments. Isometric tension was recorded and propagating Ca 2ϩ and membrane potential (Em) waves were recorded by fluorescence imaging using photodiode arrays. SCT bladders were associated with regular spontaneous contractions (2.9 Ϯ 0.4/min); ADP, UTP, and UDP augmented the amplitude but not their frequency. With strips from such bladders, a P2Y 6-selective agonist (PSB0474) exerted similar effects. Fluorescence imaging of bladder sheets showed that ADP or UTP increased the conduction velocity of Ca 2ϩ /Em waves that were confined to regions of the bladder wall with an intact mucosa. When transverse bladder sections were used, Ca 2ϩ /Em waves originated in the suburothelial space and propagated to the detrusor and urothelium. Analysis of wave propagation showed that the suburothelial space exhibited properties of an electrical syncitium. These experiments are consistent with the hypothesis that P2Y-receptor agonists increase spontaneous contractile activity by augmenting functional activity of the cellular syncitium in the suburothelial space.spinal cord injury; spontaneous contraction; Ca 2ϩ waves; ADP THE OVERACTIVE BLADDER IN patients is associated with spontaneous transient increases in pressure that occur particularly during filling and, if sufficiently severe, contribute to lower urinary tracts symptoms of frequency, urgency, and incontinence (1). The origins of this common pathology are unclear but can be mimicked in animals in which the bladder outflow is artificially obstructed or the spinal cord is transected (SCT; T8 -T9) (12). Whole rat bladders from an SCT model demonstrate large, regular contractions (ϳ2/min) that coincide with waves of raised intracellular Ca 2ϩ and depolarization (E m ) propagating across the surface but originating from one or very few foci. This is in contrast to normal animals where more frequent (5-10/min), low-amplitude contractions are associated with multiple Ca 2ϩ /E m foci (12,14). The detrusor layer of the bladder wall contributes the bulk of tissue and hence most of the Ca 2ϩ /E m signals, but an in...

Previous studies in rat and mouse documented that a subpopulation of dorsal root ganglion (DRG) neurons innervating non-visceral tissues express tyrosine hydroxylase (TH). Here we studied whether or not mouse DRG neurons retrogradely traced with Fast Blue (FB) from colorectal or urinary bladder also express immunohistochemically detectable TH. The lumbar sympathetic chain (LSC) and major pelvic ganglion (MPG) were included in the analysis. Previously characterized antibodies against TH, norepinephrine transporter type 1 (NET-1) and calcitonin gene-related peptide (CGRP) were used. On average, 14% of colorectal and 17 % of urinary bladder DRG neurons expressed TH and spanned virtually all neuronal sizes, although more often in the medium-sized to small ranges. Also, they were more abundant in lumbosacral than thoracolumbar DRGs, and often coexpressed CGRP. We also detected several TH-immunoreactive (IR) colorectal and urinary bladder neurons in the LSC and the MPG, more frequently in the former. No NET-1-IR neurons were detected in DRGs, whereas the majority of FB-labeled, TH-IR neurons in the LSC and MPG coexpressed this marker (as did most other THIR neurons not labeled from the target organs). TH-IR nerve fibers were detected in all layers of the colorectum and the urinary bladder, with some also reaching the basal mucosal cells. Most TH-IR fibers in these organs lacked CGRP. Taken together, we show: 1) that a previously undescribed population of colorectal and urinary bladder DRG neurons expresses TH, often CGRP but not NET-1, suggesting absence of a noradrenergic phenotype; and 2) that TH-IR axons/terminals in colon or urinary bladder, naturally expected to derive from autonomic sources, could also originate from sensory neurons.