Altered distribution of interstitial cells and innervation in the rat urinary bladder following spinal cord injury

Urinary dysfunction after spinal cord injury: Comparing outcomes after thoracic spinal transection and contusion in the rat

Spinal cord injury (SCI) above the lumbosacral spinal cord induces loss of voluntary control over micturition. Spinal cord transection (SCT) was the gold standard method to reproduce SCI in rodents, but its translational value is arguable and other experimental SCI methods need to be better investigated, including spinal cord contusion (SCC). At present, it is not fully investigated if urinary impairments arising after transection and contusion are comparable. To explore this, we studied bladder-reflex activity and lower urinary tract (LUT) and spinal cord innervation after SCT and different severities of SCC. Severe-contusion animals presented a longer spinal shock period and the tendency for higher residual volumes, followed by SCT and mild-contusion animals. Urodynamics showed that SCT animals presented higher basal and peak bladder pressures. Immunostaining against growth-associated protein-43 (GAP43) and calcitonin gene-related peptide (CGRP) at the lumbosacral spinal cord demonstrated that afferent sprouting is dependent on the injury model, reflecting the severity of the lesion, with a higher expression in SCT animals. In LUT organs, the expression of GAP43, CGRP cholinergic (vesicular acetylcholine transporter (VAChT)) and noradrenergic (tyrosine hydroxylase (TH)) markers was reduced after SCI in the LUT and lumbosacral cord, but only the lumbosacral expression of VAChT was dependent on the injury model. Overall, our findings demonstrate that changes in LUT innervation and function after contusion and transection are similar but result from distinct neuroplastic processes at the lumbosacral spinal cord. This may impact the development of new therapeutic options for urinary impairment arising after spinal cord insult.

Neurogenic Lower Urinary Tract Dysfunction in Spinal Dysraphism: Morphological and Molecular Evidence in Children

Spinal dysraphism, most commonly myelomeningocele, is the typical cause of a neurogenic lower urinary tract dysfunction (NLUTD) in childhood. The structural changes in the bladder wall in spinal dysraphism already occur in the fetal period and affect all bladder wall compartments. The progressive decrease in smooth muscle and the gradual increase in fibrosis in the detrusor, the impairment of the barrier function of the urothelium, and the global decrease in nerve density, lead to severe functional impairment characterized by reduced compliance and increased elastic modulus. Children present a particular challenge, as their diseases and capabilities evolve with age. An increased understanding of the signaling pathways involved in lower urinary tract development and function could also fill an important knowledge gap at the interface between basic science and clinical implications, leading to new opportunities for prenatal screening, diagnosis, and therapy. In this review, we aim to summarize the evidence on structural, functional, and molecular changes in the NLUTD bladder in children with spinal dysraphism and discuss possible strategies for improved management and for the development of new therapeutic approaches for affected children.

Spinal Cord Injury Causes Marked Tissue Rearrangement in the Urethra-Experimental Study in the Rat

Traumatic spinal cord injury (SCI) results in the time-dependent development of urinary impairment due to neurogenic detrusor overactivity (NDO) and detrusor-sphincter-dyssynergia (DSD). This is known to be accompanied by massive changes in the bladder wall. It is presently less clear if the urethra wall also undergoes remodelling. To investigate this issue, female rats were submitted to complete spinal transection at the T8/T9 level and left to recover for 1 week and 4 weeks. To confirm the presence of SCI-induced NDO, bladder function was assessed by cystometry under urethane anesthesia before euthanasia. Spinal intact animals were used as controls. Urethras were collected and processed for further analysis. Following thoracic SCI, time-dependent changes in the urethra wall were observed. Histological assessment revealed marked urethral epithelium reorganization in response to SCI, as evidenced by an increase in epithelial thickness. At the muscular layer, SCI resulted in strong atrophy of the smooth muscle present in the urethral sphincter. Innervation was also affected, as evidenced by a pronounced decrease in the expression of markers of general innervation, particularly those present in sensory and sympathetic nerve fibres. The present data show an evident impact of SCI on the urethra, with significant histological rearrangement, accompanied by sensory and sympathetic denervation. It is likely that these changes will affect urethral function and contribute to SCI-induced urinary dysfunction, and they deserve further investigation.

Transient receptor potential vanilloid type 4 (TRPV4) in urinary bladder structure and function

Bladder pain syndrome (BPS)/interstitial cystitis (IC) is a urologic, chronic pelvic pain syndrome characterized by pelvic pain, pressure, or discomfort with urinary symptoms. Symptom exacerbation (flare) is common with multiple, perceived triggers including stress. Multiple transient receptor potential (TRP) channels (TRPA1, TRPV1, TRPV4) expressed in the bladder have specific tissue distributions in the lower urinary tract (LUT) and are implicated in bladder disorders including overactive bladder (OAB) and BPS/IC. TRPV4 channels are strong candidates for mechanosensors in the urinary bladder and TRPV4 antagonists are promising therapeutic agents for OAB. In this perspective piece, we address the current knowledge of TRPV4 distribution and function in the LUT and its plasticity with injury or disease with an emphasis on BPS/IC. We review our studies that extend the knowledge of TRPV4 in urinary bladder function by focusing on (i) TRPV4 involvement in voiding dysfunction, pelvic pain, and non-voiding bladder contractions in NGF-OE mice; (ii) distention-induced luminal ATP release mechanisms and (iii) involvement of TRPV4 and vesicular release mechanisms. Finally, we review our lamina propria studies in postnatal rat studies that demonstrate: (i) the predominance of the TRPV4+ and PDGFRα+ lamina propria cellular network in early postnatal rats; (ii) the ability of exogenous mediators (i.e., ATP, TRPV4 agonist) to activate and increase the number of lamina propria cells exhibiting active Ca2+ events; and (iii) the ability of ATP and TRPV4 agonist to increase the rate of integrated Ca2+ activity corresponding to coupled lamina propria network events and the formation of propagating wavefronts.

Imatinib Mesylate Reduces Voiding Frequency in Female Mice With Acute Cyclophosphamide-Induced Cystitis

Lamina propria interstitial cells that express the tyrosine kinase receptor, platelet-derived growth factor receptor alpha (PDGFRα) may play a role in urinary sensory signaling. Imatinib mesylate, also referred to as imatinib, is a tyrosine kinase inhibitor that can inhibit PDGFRα and has been widely used in urological research. We evaluated the functional effects of imatinib administration (via oral gavage or intravesical infusion) with two different experimental designs (prevention and treatment), in a cyclophosphamide (CYP)-induced cystitis (acute, intermediate, and chronic), male and female rodent model using conscious cystometry and somatic sensitivity testing. Imatinib significantly (0.0001 ≤ p ≤ 0.05) decreased voiding frequency and increased bladder capacity in acute CYP-induced cystitis, by the prevention (females) and treatment (females and males) designs. Imatinib was not effective in preventing or treating intermediate or chronic CYP-induced cystitis in either sex. Interestingly, in the prevention experiments, imatinib administration increased (0.0001 ≤ p ≤ 0.01) voiding frequency and decreased bladder capacity in control mice. However, in the treatment experiments, imatinib administration decreased (0.01 ≤ p ≤ 0.05) voiding frequency and increased bladder capacity in control mice. Bladder function improvements observed with imatinib treatment in acute CYP-induced cystitis mice remained and additionally improved with a second dose of imatinib 24 hours after CYP treatment. Imatinib administration did not affect pelvic somatic sensitivity in female mice with acute CYP-induced cystitis. Our studies suggest that (1) imatinib improves bladder function in mice with acute CYP-induced cystitis with a prevention and treatment design and (2) interstitial cells may be a useful target to improve bladder function in cystitis.

Imatinib Mesylate Reduces Neurotrophic Factors and pERK and pAKT Expression in Urinary Bladder of Female Mice With Cyclophosphamide-Induced Cystitis

Imatinib mesylate is a tyrosine kinase inhibitor that inhibits platelet-derived growth factor receptor (PDGFR)-α, -β, stem cell factor receptor (c-KIT), and BCR-ABL. PDGFRα is expressed in a subset of interstitial cells in the lamina propria (LP) and detrusor muscle of the urinary bladder. PDGFRα + interstitial cells may contribute to bladder dysfunction conditions such as interstitial cystitis/bladder pain syndrome (IC/BPS) or overactive bladder (OAB). We have previously demonstrated that imatinib prevention via oral gavage or treatment via intravesical infusion improves urinary bladder function in mice with acute (4 hour, h) cyclophosphamide (CYP)-induced cystitis. Here, we investigate potential underlying mechanisms mediating the bladder functional improvement by imatinib using a prevention or treatment experimental design. Using qRT-PCR and ELISAs, we examined inflammatory mediators (NGF, VEGF, BDNF, CCL2, IL-6) previously shown to affect bladder function in CYP-induced cystitis. We also examined the distribution of phosphorylated (p) ERK and pAKT expression in the LP with immunohistochemistry. Imatinib prevention significantly (0.0001 ≤ p ≤ 0.05) reduced expression for all mediators examined except NGF, whereas imatinib treatment was without effect. Imatinib prevention and treatment significantly (0.0001 ≤ p ≤ 0.05) reduced pERK and pAKT expression in the upper LP (U. LP) and deeper LP (D. LP) in female mice with 4 h CYP-induced cystitis. Although we have previously demonstrated that imatinib prevention or treatment improves bladder function in mice with cystitis, the current studies suggest that reductions in inflammatory mediators contribute to prevention benefits of imatinib but not the treatment benefits of imatinib. Differential effects of imatinib prevention or treatment on inflammatory mediators may be influenced by the route and frequency of imatinib administration and may also suggest other mechanisms (e.g., changes in transepithelial resistance of the urothelium) through which imatinib may affect urinary bladder function following CYP-induced cystitis.

The urethra in continence and sensation: Neural aspects of urethral function

AIMS

Traditionally, the urethra has been considered a mere conduit to guide urine from the bladder to the external side of the body. Building evidence indicates that the urethra may directly influence bladder function via mechanisms restricted to the lower urinary tract (LUT).

METHODS

Here, we discuss the tissue arrangement of the urethra and addressed the contribution of new paraneuronal cells to LUT function. We also briefly reviewed two frequent LUT pathologies associated with urethral dysfunction.

RESULTS

Continence depends on an intact and functional urethral sphincter, composed of smooth, and striated muscle fibers and regulated by somatic and autonomic fibers. Recent studies suggest the existence of an urethro-vesical reflex that also contributes to normal LUT function. Indeed, the urethral lumen is lined by a specialized epithelium, the urothelium, in the proximal urethra. In this region, recent evidence demonstrates the presence of specific paraneuronal cells, expressing the neurotransmitters acetylcholine and serotonin. These cells are in close proximity of nerve fibers coursing in the lamina propria and are able to release neurotransmitters and rapidly induce detrusor contractions, supporting the existence of an urethro-vesical crosstalk.

CONCLUSION

The mechanism underlying the fast communication between the urethra and thebladder are beginning to be understood and should involve the interaction between specificepithelial cells and fibres innervating the urethral wall. It is likely that this reflex should bealtered in pathological conditions, becoming an attractive therapeutic target.

Contractile function of detrusor smooth muscle from children with posterior urethral valves - The role of fibrosis

INTRODUCTION

Posterior urethral valves (PUV) is the most common cause of congenital bladder outflow obstruction with persistent lower urinary tract and renal morbidities. There is a spectrum of functional bladder disorders ranging from hypertonia to bladder underactivity, but the aetiology of these clinical conditions remains unclear.

AIMS AND OBJECTIVES

We tested the hypothesis that replacement of detrusor muscle with non-muscle cells and excessive deposition of connective tissue is an important factor in bladder dysfunction with PUV. We used isolated detrusor samples from children with PUV and undergoing primary or secondary procedures in comparison to age-matched data from children with functionally normal bladders. In vitro contractile properties, as well as passive stiffness, were measured and matched to histological assessment of muscle and connective tissue. We examined if a major pathway for fibrosis was altered in PUV tissue samples.

METHODS

Isometric contractions were measured in vitro in response to either stimulation of motor nerves to detrusor or exposure to cholinergic and purinergic receptor agonists. Passive mechanical stiffness was measured by rapid stretching of the tissue and recording changes to muscle tension. Histology measured the relative amounts of detrusor muscle and connective tissue. Multiplex quantitative immunofluorescence labelling using five epitope markers was designed to determine cellular pathways, in particular the Wnt-signalling pathway, responsible for any changes to excessive deposition of connective tissue.

RESULTS AND DISCUSSION

PUV tissue showed equally reduced contractile function to efferent nerve stimulation or exposure to contractile agonists. Passive muscle stiffness was increased in PUV tissue samples. The smooth muscle:connective tissue ratio was also diminished and mirrored the reduction of contractile function and the increase of passive stiffness. Immunofluorescence labelling showed in PUV samples increased expression of the matrix metalloproteinase, MMP-7; as well as cyclin-D1 expression suggesting cellular remodelling. However, elements of a fibrosis pathway associated with Wnt-signalling were either reduced (β-catenin) or unchanged (c-Myc). The accumulation of extracellular matrix, containing collagen, will contribute to the reduced contractile performance of the bladder wall. It will also increase tissue stiffness that in vivo would lead to reduced filling compliance.

CONCLUSIONS

Replacement of smooth muscle with fibrosis is a major contributory factor in contractile dysfunction in the hypertonic PUV bladder. This suggests that a potential strategy to restore normal contractile and filling properties is development of the effective use of antifibrotic agents.

Establishment of animal model manifested as bladder neurogenic changes generated by bilateral pelvic nerve injury in male rats

PURPOSE

To establish a male rat model of neurogenic bladder after bilateral pelvic nerve injury (BPNI) and investigate the factors associated with onset of neurogenic bladder.

METHODS

Twenty-four 8-week-old male Sprague-Dawley rats were randomly divided into three groups (n = 8 rats per group). Rats in 4-week and 8-week nerve injury group underwent BPNI, while rats in the sham group underwent a sham operation. Bladder functional analysis were performed and then bladders tissues were harvested for morphological examination and investigating the mRNA expression levels of target genes in all rats.

RESULTS

The bladder weight significantly increased in rats following BPNI. Functional analysis revealed non-voiding contractions and decreased detrusor contractility following BPNI, manifested as elevated post-void residual and bladder capacity while reduced maximum voiding pressure and voiding efficiency. The collagen area in bladder tissue and mRNA expression levels of target genes significantly increased at 4 or 8 weeks post-BPNI except Smad3. At 4 weeks post-BPNI, expression levels of vesicular acetylcholine transporter were reduced, then returned to baseline at 8 weeks. Expression levels of tyrosine hydroxylase were reduced at both 4 and 8 weeks post-BPNI.

CONCLUSIONS

A neurogenic bladder animal model was successfully established by performing BPNI in male rats, characterized by impaired voiding function, bladder detrusor fibrosis, and reduced neurotransmitter release.

Fibrosis and the bladder, implications for function ICI-RS 2017

AIMS

Most benign bladder pathologies are associated with an increase of extracellular matrix (ECM-fibrosis) and may progress from formation of stiffer matrix to a more compliant structure. The aims were to summarize current knowledge of the origins of bladder fibrosis and consequences in bladder function.

METHODS

A meeting at the International Consultation on Incontinence Research Society 2017 congress discussed the above aims and considered paradigms to reduce the extent of fibrosis. Discussants based their arguments on the basis of their own expertise, supplemented by review of the literature through PubMed. Proposals for future work were derived from the discussion.

RESULTS

Altered urodynamic compliance when ECM deposition is increased is mirrored by changes in the elastic modulus of isolated tissue, whether compliance is decreased or increased. No changes to compliance or fibrosis have been reported after botulinum toxin injections. Several paracrine and autocrine agents increase ECM deposition, the role of TGF-β was particularly emphasized. None of these agents has a net long-term effect on detrusor contractility and the reduction of contractile performance with increased ECM is due solely to a loss of detrusor mass. Several strategies to reduce fibrosis were described, ranging from potential therapeutic roles for vitamin-D or endostatin, manipulation of intracellular pathways that mediate myofibroblast differentiation and the potential role of the anti-fibrotic hormone relaxin. An understanding of epigenetic regulation of ECM deposition was also considered.

CONCLUSIONS

The conclusion that reduced bladder contractile function with increased fibrosis is due largely to the replacement of detrusor with ECM offers a way forward for future research to consider approaches that will restore bladder function by reducing ECM deposition.

Spontaneous synaptic drive in detrusor smooth muscle: computational investigation and implications for urinary bladder function

The detrusor, a key component of the urinary bladder wall, is a densely innervated syncytial smooth muscle tissue. Random spontaneous release of neurotransmitter at neuromuscular junctions (NMJs) in the detrusor gives rise to spontaneous excitatory junction potentials (SEJPs). These sub-threshold passive signals not only offer insights into the syncytial nature of the tissue, their spatio-temporal integration is critical to the generation of spontaneous neurogenic action potentials which lead to focal contractions during the filling phase of the bladder. Given the structural complexity and the contractile nature of the tissue, electrophysiological investigations on spatio-temporal integration of SEJPs in the detrusor are technically challenging. Here we report a biophysically constrained computational model of a detrusor syncytium overlaid with spatially distributed innervation, using which we explored salient features of the integration of SEJPs in the tissue and the key factors that contribute to this integration. We validated our model against experimental data, ascertaining that observations were congruent with theoretical predictions. With the help of comparative studies, we propose that the amplitude of the spatio-temporally integrated SEJP is most sensitive to the inter-cellular coupling strength in the detrusor, while frequency of observed events depends more strongly on innervation density. An experimentally testable prediction arising from our study is that spontaneous release frequency of neurotransmitter may be implicated in the generation of detrusor overactivity. Set against histological observations, we also conjecture possible changes in the electrical activity of the detrusor during pathology involving patchy denervation. Our model thus provides a physiologically realistic, heuristic framework to investigate the spread and integration of passive potentials in an innervated syncytial tissue under normal conditions and in pathophysiology.

Spontaneous Activity and the Urinary Bladder

The urinary bladder has two functions: to store urine, when it is relaxed and highly compliant; and void its contents, when intravesical pressure rises due to co-ordinated contraction of detrusor smooth muscle in the bladder wall. Superimposed on this description are two observations: (1) the normal, relaxed bladder develops small transient increases of intravesical pressure, mirrored by local bladder wall movements; (2) pathological, larger pressure variations (detrusor overactivity) can occur that may cause involuntary urine loss and/or detrusor overactivity. Characterisation of these spontaneous contractions is important to understand: how normal bladder compliance is maintained during filling; and the pathophysiology of detrusor overactivity. Consideration of how spontaneous contractions originate should include the structural complexity of the bladder wall. Detrusor smooth muscle layer is overlain by a mucosa, itself a complex structure of urothelium and a lamina propria containing sensory nerves, micro-vasculature, interstitial cells and diffuse muscular elements.Several theories, not mutually exclusive, have been advanced for the origin of spontaneous contractions. These include intrinsic rhythmicity of detrusor muscle; modulation by non-muscular pacemaking cells in the bladder wall; motor input to detrusor by autonomic nerves; regulation of detrusor muscle excitability and contractility by the adjacent mucosa and spontaneous contraction of elements of the lamina propria. This chapter will consider evidence for each theory in both normal and overactive bladder and how their significance may vary during ageing and development. Further understanding of these mechanisms may also identify novel drug targets to ameliorate the clinical consequences of large contractions associated with detrusor overactivity.

Urothelial Senescence in the Pathophysiology of Diabetic Bladder Dysfunction-A Novel Hypothesis

Diabetic bladder dysfunction (DBD) is a well-recognized and common symptom affecting up to 50% of all diabetic patients. DBD has a broad range of clinical presentations ranging from overactive to underactive bladder symptoms that develops in middle-aged to elderly patients with long standing and poorly controlled diabetes. Low efficacy of current therapeutics and lifestyle interventions combined with high national healthcare costs highlight the need for more research into bladder dysfunction pathophysiology and novel treatment options. Cellular senescence is an age-related physiologic process in which cells undergo irreversible growth arrest induced by replicative exhaustion and damaging insults. While controlled senescence negatively regulates cell proliferation and promotes tissue regeneration, uncontrolled senescence is known to result in tissue dysfunction through enhanced secretion of inflammatory factors. This review presents previous scientific findings and current hypotheses that characterize diabetic bladder dysfunction. Further, we propose the novel hypothesis that cellular senescence within the urothelial layer of the bladder contributes to the pro-inflammatory/pro-oxidant environment and symptoms of diabetic bladder dysfunction. Our results show increased cellular senescence in the urothelial layer of the bladder; however, whether this phenomenon is the cause or effect of DBD is unknown. The urothelial layer of the bladder is made up of transitional epithelia specialized to contract and expand with demand and plays an active role in transmission by modulating afferent activity. Transition from normal functioning urothelial cells to secretory senescence cells would not only disrupt the barrier function of this layer but may result in altered signaling and sensation of bladder fullness; dysfunction of this layer is known to result in symptoms of frequency and urgency. Future DBD therapeutics may benefit from targeting and preventing early transition of urothelial cells to senescent cells.

Involvement of TRPM4 in detrusor overactivity following spinal cord transection in mice

Transient receptor potential cation channel subfamily M member 4 (TRPM4) has been shown to play a key role in detrusor contractility under physiological conditions. In this study, we investigated the potential role of TRPM4 in detrusor overactivity following spinal cord transection (SCT) in mice. TRPM4 expression and function were evaluated in bladder tissue with or without the mucosa from spinal intact (SI) and SCT female mice (T8-T9 vertebra; 1-28 days post SCT) using PCR, western blot, immunohistochemistry, and muscle strip contractility techniques. TRPM4 was expressed in the urothelium (UT) and detrusor smooth muscle (DSM) and was upregulated after SCT. Expression levels peaked 3-7 days post SCT in both the UT and DSM. Pharmacological block of TRPM4 with the antagonist, 9-Phenanthrol (30 μM) greatly reduced spontaneous phasic activity that developed after SCT, regardless of the presence or absence of the mucosa. Detrusor overactivity following spinal cord injury leads to incontinence and/or renal impairment and represents a major health problem for which current treatments are not satisfactory. Augmented TRPM4 expression in the bladder after chronic SCT supports the hypothesis that TRPM4 channels play a role in DSM overactivity following SCT. Inhibition of TRPM4 may be beneficial for improving detrusor overactivity in SCI.

Rhythmic Calcium Events in the Lamina Propria Network of the Urinary Bladder of Rat Pups

The lamina propria contains a dense network of cells, including interstitial cells (ICs), that may play a role in bladder function by modulating communication between urothelium, nerve fibers and smooth muscle or acting as pacemakers. Transient receptor potential vanilloid 4 (TRPV4) channels allow cation influx and may be involved in sensing stretch or chemical irritation in urinary bladder. Urothelium was removed from rats (P0-Adult), cut into strips, and loaded with a Ca²⁺ fluorescent dye (Fluo-2 AM leak resistant or Cal 520) for 90 min (35-37°C) to measure Ca²⁺ events. Ca²⁺ events were recorded for a period of 60 seconds (s) in control and after drug treatment. A heterogeneous network of cells was identified at the interface of the urothelium and lamina propria of postnatal rat pups, aged ≤ postnatal (P) day 21, with diverse morphology (round, fusiform, stellate with numerous projections) and expressing platelet-derived growth factor receptor alpha (PDGFRα)- and TRPV4-immunoreactivity (IR). Ca²⁺ transients occurred at a slow frequency with an average interval of 30 ± 8.6 s. Waveform analyses of Ca²⁺ transients in cells in the lamina propria network revealed long duration Ca²⁺ events with slow upstrokes. We observed slow propagating waves of activity in the lamina propria network that displayed varying degrees of coupling. Application of the TRPV4 agonist, GSK1016790 (100 nM), increased the duration of Ca²⁺ events, the number of cells with Ca²⁺ events and the integrated Ca²⁺ activity corresponding to propagation of activity among cells in the lamina propria network. However, GSK2193874 (1 μM), a potent antagonist of TRPV4 channels, was without effect. ATP (1 μM) perfusion increased the number of cells in the lamina propria exhibiting Ca²⁺ events and produced tightly coupled network activity. These findings indicate that ATP and TRPV4 can activate cells in the laminar propria network, leading to the appearance of organized propagating wavefronts.

PACAP/Receptor System in Urinary Bladder Dysfunction and Pelvic Pain Following Urinary Bladder Inflammation or Stress

Complex organization of CNS and PNS pathways is necessary for the coordinated and reciprocal functions of the urinary bladder, urethra and urethral sphincters. Injury, inflammation, psychogenic stress or diseases that affect these nerve pathways and target organs can produce lower urinary tract (LUT) dysfunction. Numerous neuropeptide/receptor systems are expressed in the neural pathways of the LUT and non-neural components of the LUT (e.g., urothelium) also express peptides. One such neuropeptide receptor system, pituitary adenylate cyclase-activating polypeptide (PACAP; Adcyap1) and its cognate receptor, PAC1 (Adcyap1r1), have tissue-specific distributions in the LUT. Mice with a genetic deletion of PACAP exhibit bladder dysfunction and altered somatic sensation. PACAP and associated receptors are expressed in the LUT and exhibit neuroplastic changes with neural injury, inflammation, and diseases of the LUT as well as psychogenic stress. Blockade of the PACAP/PAC1 receptor system reduces voiding frequency in preclinical animal models and transgenic mouse models that mirror some clinical symptoms of bladder dysfunction. A change in the balance of the expression and resulting function of the PACAP/receptor system in CNS and PNS bladder reflex pathways may underlie LUT dysfunction including symptoms of urinary urgency, increased voiding frequency, and visceral pain. The PACAP/receptor system in micturition pathways may represent a potential target for therapeutic intervention to reduce LUT dysfunction.

Distribution of interstitial cells of Cajal in the bladders of fetal rats with retinoic acid induced myelomeningocele

OBJECTIVE

Myelomeningocele (MMC) is one of the most common reason of neurogenic bladder dysfunction in children. Although neurogenic bladder dysfunction occurrence is related with bladder innervation, also there are some changes seen in the smooth muscle and neural cells of the bladder. Interstitial cells of Cajal (ICC) are the pacemaker cells found in organs with peristaltic activity. Although it has been shown that ICC are diminished in the rat urinary bladder with traumatic spinal cord injury, there is no data about ICC in fetal rat bladders with MMC. This study has been conducted to investigate the ICC in the bladders of fetal rats with retinoic acid induced MMC.

MATERIALS AND METHODS

Time dated pregnant Wistar albino rats were divided into 3 groups. In MMC group, dams were fed with gavage solution containing 60 mg/kg all-trans retinoic acid dissolved in olive oil on 10. embryologic day. Sham group animals were fed only olive oil. Control group dams were fed with standard rat chow. Fetuses were delivered by cesarean section and harvested on 22. embryologic day. MMC was identified by observing MMC sacs at the back of the fetuses. Distribution of ICCs were evaluated using immunohistochemical staining.

RESULTS

ICCs were found in all groups, which have the same morphological features that had been described earlier in the gastrointestinal tract and the bladder. The density of the ICC in the MMC group was found to be significantly decreased when compared with the control and the sham groups (p<0.05).

CONCLUSION

The density of the ICC in the urinary bladder decreased in the neurogenic bladder developed in MMC.

Research Findings on Overactive Bladder

Several physiopathologic conditions lead to the manifestation of overactive bladder (OAB). These conditions include ageing, diabetes mellitus, bladder outlet obstruction, spinal cord injury, stroke and brain injury, Parkinson's disease, multiple sclerosis, interstitial cystitis, stress and depression. This review has discussed research findings in human and animal studies conducted on the above conditions. Several structural and functional changes under these conditions have not only been observed in the lower urinary tract, but also in the brain and spinal cord. Significant changes were observed in the following areas: neurotransmitters, prostaglandins, nerve growth factor, Rho-kinase, interstitial cells of Cajal, and ion and transient receptor potential channels. Interestingly, alterations in these areas showed great variation in each of the conditions of the OAB, suggesting that the pathophysiology of the OAB might be different in each condition of the disease. It is anticipated that this review will be helpful for further research on new and specific drug development against OAB.

The role of brain-derived neurotrophic factor (BDNF) in the development of neurogenic detrusor overactivity (NDO)

Neurogenic detrusor overactivity (NDO) is a well known consequence of spinal cord injury (SCI), recognizable after spinal shock, during which the bladder is areflexic. NDO emergence and maintenance depend on profound plastic changes of the spinal neuronal pathways regulating bladder function. It is well known that neurotrophins (NTs) are major regulators of such changes. NGF is the best-studied NT in the bladder and its role in NDO has already been established. Another very abundant neurotrophin is BDNF. Despite being shown that, acting at the spinal cord level, BDNF is a key mediator of bladder dysfunction and pain during cystitis, it is presently unclear if it is also important for NDO. This study aimed to clarify this issue. Results obtained pinpoint BDNF as an important regulator of NDO appearance and maintenance. Spinal BDNF expression increased in a time-dependent manner together with NDO emergence. In chronic SCI rats, BDNF sequestration improved bladder function, indicating that, at later stages, BDNF contributes NDO maintenance. During spinal shock, BDNF sequestration resulted in early development of bladder hyperactivity, accompanied by increased axonal growth of calcitonin gene-related peptide-labeled fibers in the dorsal horn. Chronic BDNF administration inhibited the emergence of NDO, together with reduction of axonal growth, suggesting that BDNF may have a crucial role in bladder function after SCI via inhibition of neuronal sprouting. These findings highlight the role of BDNF in NDO and may provide a significant contribution to create more efficient therapies to manage SCI patients.

Calcium signalling in Cajal-like interstitial cells of the lower urinary tract

Interstitial cells of Cajal (ICC) serve several critical physiological roles in visceral smooth muscle organs, including acting as electrical pacemakers to modulate phasic contractile activity and as intermediaries in motor neurotransmission. The major roles of ICC have been described in the gastrointestinal tract, however, ICC-like cells (ICC-LC) can also be found in other visceral organs, including those of the lower urinary tract (LUT), where they provide similar functions, acting as electrical pacemakers and as intermediary cells involved in the modulation of neurotransmission to adjacent smooth muscle cells. The physiological functions of ICC-LC, in particular their role as pacemakers, relies on their ability to generate transient and propagating intracellular Ca(2+) events. The role of ICC-LC as pacemakers and neuromodulators in the LUT is increasingly apparent and the study of their intracellular Ca(2+) dynamics will provide a better understanding of their role in LUT excitability.

Interstitial cells: regulators of smooth muscle function

Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.

Anoctamin-1 in the juvenile rat urinary bladder

Purpose

To investigate presence, location and functional role of calcium-activated chloride channel (CaCC) Anoctamin-1 (Ano1) in rat urinary bladder.

Materials and Methods

Bladders from 3 week old Wistar rats were studied. End-point PCR on total mRNA was used to assess the expression of Ano1. Immunofluorescent labelling of whole mount bladder tissue imaged with confocal microscope allowed localization of Ano1 and vimentin immunopositive cells. The effects of CaCC blockers: niflumic acid (NFA) (3,10,30 µM) and 5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) (10, 30 µM) on spontaneous phasic contractile activity of intact (with mucosa) and denuded (without mucosa) detrusor strips were measured under isometric tension in organ baths (n = 141, N = 60).

Results

Ano1 expression was found at mRNA level in mucosa and detrusor layers. Confocal microscopy revealed presence of Ano1 immunopositive cells in mucosa and in detrusor layers; a subpopulation of vimentin positive cells expressed Ano1. Both chloride channel blockers reduced the amplitude and frequency of phasic contractions in denuded and intact strips.

Conclusions

Ano1 is expressed in rat urinary bladder and is present in cells sharing markers with interstitial cells. CaCC blockers reduced phasic activity of the bladder tissue. Ano1 is expressed in the bladder and plays a role in its spontaneous phasic contractile activity.

Do we understand any more about bladder interstitial cells?-ICI-RS 2013

AIMS

To present a brief review on discussions from "Do we understand any more about lower urinary tract interstitial cells?" session at the 2013 International Consultation on Incontinence-Research Society (ICI-RS) meeting in Bristol, UK.

METHODS

Discussion focused on bladder interstitial cell (IC) subtypes, their localization and characterization, and communication between themselves, the urothelium, and detrusor smooth muscle. The role of ICs in bladder pathologies and new methods for studying ICs were also addressed.

RESULTS

ICs have been studied extensively in the lower urinary tract and have been characterized based on comparisons with ICs of Cajal in the gastro-intestinal tract. In fetal bladders it is believed that ICs drive intrinsic contractions to expel urine through the urachus. These contractions diminish postpartum as bladder innervation develops. Voiding in human neonates occurs when filling triggers a spinal cord reflex that contracts the detrusor; in rodents, maternal stimulation of the perineum triggers voiding. Following spinal cord injury, intrinsic contractions, and spinal micturition reflexes develop, similar to those seen during neonatal development. These enhanced contractions may stimulate nociceptive and mechanosensitive afferents contributing to neurogenic detrusor overactivity and incontinence. The IC-mediated activity is believed to be initiated in the lamina propria by responding to urothelial factors. These IC may act syncytially through gap junction coupling and modulate detrusor activity through unknown mechanisms.

CONCLUSION

There has been a great deal of information discovered regarding bladder ICs, however, many of their (patho)physiological functions and mechanisms are still unclear and necessitates further research. Neurourol. Urodynam. 33:573-576, 2014. © 2014 Wiley Periodicals, Inc.

Control of urinary drainage and voiding

Urine differs greatly in ion and solute composition from plasma and contains harmful and noxious substances that must be stored for hours and then eliminated when it is socially convenient to do so. The urinary tract that handles this output is composed of a series of pressurizable muscular compartments separated by sphincteric structures. With neural input, these structures coordinate the delivery, collection, and, ultimately, expulsion of urine. Despite large osmotic and chemical gradients in this waste fluid, the bladder maintains a highly impermeable surface in the face of a physically demanding biomechanical environment, which mandates recurring cycles of surface area expansion and increased wall tension during filling, followed by rapid wall compression during voiding. Afferent neuronal inflow from mucosa and submucosa communicates sensory information about bladder fullness, and voiding is initiated consciously through coordinated central and spinal efferent outflow to the detrusor, trigonal internal sphincter, and external urethral sphincter after periods of relative quiescence. Provocative new findings suggest that in some cases, lower urinary tract symptoms, such as incontinence, urgency, frequency, overactivity, and pain may be viewed as a consequence of urothelial defects (either urothelial barrier breakdown or inappropriate signaling from urothelial cells to underlying sensory afferents and potentially interstitial cells). This review describes the physiologic and anatomic mechanisms by which urine is moved from the kidney to the bladder, stored, and then released. Relevant clinical examples of urinary tract dysfunction are also discussed.

The mouse cyclophosphamide model of bladder pain syndrome: tissue characterization, immune profiling, and relationship to metabotropic glutamate receptors

Abstract Painful bladder syndrome/Interstitial cystitis (PBS/IC) is a chronic disorder characterized clinically by recurring episodes of pelvic pain and increased urination frequency, significantly impairing patients' quality of life. Despite this, there is an unmet medical need in terms of effective diagnostics and treatment. Animal models are crucial in this endeavor. Systemic chronic administration of cyclophosphamide (CYP) in mice has been proposed as a relevant preclinical model of chronic bladder pain. However, molecular mechanisms underlying the pathogenesis of this model are lacking. Here, we show that mice, subjected to repetitive systemic injections of CYP, developed mild inflammatory response in bladder tissue characterized by submucosal edema, moderate increase in proinflammatory cytokine gene expression, and mastocytosis. No signs of massive inflammatory infiltrate, tissue hemorrhages, mucosal ulcerations and urothelium loss were observed. Instead, CYP treatment induced urothelium hyperplasia, accompanied by activation of proliferative signaling cascades, and a decrease in the expression of urothelium-specific markers. Metabotropic glutamate (mGlu) receptors have been implicated in chronic pain disorders. CYP administration induced differential changes in mGlu receptors mRNA levels in bladder tissue, without affecting gene expression at spinal cord level, pointing to the potential link between peripheral mGlu receptors and inflammation-induced bladder malfunction and hyperalgesia. Taken together, these data indicate that chronic CYP treatment in mice is a model of PBS mostly relevant to the major, nonulcerative subtype of the syndrome, characterized by a relatively unaltered mucosa and a sparse inflammatory response. This model can help to elucidate the pathogenetic mechanisms of the disease.

Functional innervation of Guinea-pig bladder interstitial cells of cajal subtypes: neurogenic stimulation evokes in situ calcium transients

Several populations of interstitial cells of Cajal (ICC) exist in the bladder, associated with intramural nerves. Although ICC respond to exogenous agonists, there is currently no evidence of their functional innervation. The objective was to determine whether bladder ICC are functionally innervated. Guinea-pig bladder tissues, loaded with fluo-4AM were imaged with fluorescent microscopy and challenged with neurogenic electrical field stimulation (EFS). All subtypes of ICC and smooth muscle cells (SMC) displayed spontaneous Ca²⁺-oscillations. EFS (0.5 Hz, 2 Hz, 10 Hz) evoked tetrodotoxin (1 µM)-sensitive Ca²⁺-transients in lamina propria ICC (ICC-LP), detrusor ICC and perivascular ICC (PICC) associated with mucosal microvessels. EFS responses in ICC-LP were significantly reduced by atropine or suramin. SMC and vascular SMC (VSM) also responded to EFS. Spontaneous Ca²⁺-oscillations in individual ICC-LP within networks occurred asynchronously whereas EFS evoked coordinated Ca²⁺-transients in all ICC-LP within a field of view. Non-correlated Ca²⁺-oscillations in detrusor ICC and adjacent SMC pre-EFS, contrasted with simultaneous neurogenic Ca²⁺ transients evoked by EFS. Spontaneous Ca²⁺-oscillations in PICC were little affected by EFS, whereas large Ca²⁺-transients were evoked in pre-EFS quiescent PICC. EFS also increased the frequency of VSM Ca²⁺-oscillations. In conclusion, ICC-LP, detrusor ICC and PICC are functionally innervated. Interestingly, Ca²⁺-activity within ICC-LP networks and between detrusor ICC and their adjacent SMC were synchronous under neural control. VSM and PICC Ca²⁺-activity was regulated by bladder nerves. These novel findings demonstrate functional neural control of bladder ICC. Similar studies should now be carried out on neurogenic bladder to elucidate the contribution of impaired nerve-ICC communication to bladder pathophysiology.

Bladder interstitial cells: an updated review of current knowledge

The field of bladder research has been energized by the study of novel interstitial cells (IC) over the last decade. Several subgroups of IC are located within the bladder wall and make structural interactions with nerves and smooth muscle, indicating integration with intercellular communication and key physiological functions. Significant progress has been made in the study of bladder ICs' cellular markers, ion channels and receptor expression, electrical and calcium signalling, yet their specific functions in normal bladder filling and emptying remain elusive. There is increasing evidence that the distribution of IC is altered in bladder pathophysiologies suggesting that changes in IC may be linked with the development of bladder dysfunction. This article summarizes the current state of the art of our knowledge of IC in normal bladder and reviews the literature on IC in dysfunctional bladder.

Characterization of the early proliferative response of the rodent bladder to subtotal cystectomy: a unique model of mammalian organ regeneration

Subtotal cystectomy (STC; surgical removal of ∼75% of the rat urinary bladder) elicits a robust proliferative response resulting in complete structural and functional bladder regeneration within 8-weeks. The goal of these studies was to characterize the early cellular response that mediates this regenerative phenomenon, which is unique among mammalian organ systems. STC was performed on eighteen 12-week-old female Fischer F344 rats. At 1, 3, 5 and 7-days post-STC, the bladder was harvested 2-hours after intraperitoneal injection of bromodeoxyuridine (BrdU). Fluorescent BrdU labeling was quantified in cells within the urothelium, lamina propria (LP), muscularis propria (MP) and serosa. Cell location was confirmed with fluorescently co-labeled cytokeratin, vimentin or smooth muscle actin (SMA), to identify urothelial, interstitial and smooth muscle cells, respectively. Expression of sonic hedgehog (Shh), Gli-1 and bone morphogenic factor-4 (BMP-4) were evaluated with immunochemistry. Three non-operated rats injected with BrdU served as controls. Less than 1% of cells in the bladder wall were labeled with BrdU in control bladders, but this percentage significantly increased by 5-8-fold at all time points post-STC. The spatiotemporal characteristics of the proliferative response were defined by a significantly higher percentage of BrdU-labeled cells within the urothelium at 1-day than in the MP and LP. A time-dependent shift at 3 and 5-days post-STC revealed significantly fewer BrdU-labeled cells in the MP than LP or urothelium. By 7-days the percentage of BrdU-labeled cells was similar among urothelium, LP and MP. STC also caused an increase in immunostaining for Shh, Gli-1 and BMP-4. In summary, the early stages of functional bladder regeneration are characterized by time-dependent changes in the location of the proliferating cell population, and expression of several evolutionarily conserved developmental signaling proteins. This report extends previous observations and further establishes the rodent bladder as an excellent model for studying novel aspects of mammalian organ regeneration.