Innervation of the detrusor muscle bundle in neurogenic detrusor overactivity

Low-Dose Cyclophosphamide Induces Nerve Injury and Functional Overactivity in the Urinary Bladder of Rats

Aim: This research aimed to investigate the neurotoxicity of low-dose cyclophosphamide (CYP) on the urinary bladder of rats by in vivo and in vitro studies. Methods: To establish CYP-induced cystitis rat model, rats were treated with three intraperitoneal injections of CYP (25 mg/kg) in a week. During treatment, the up-down method was used to assess the mechanical withdrawal threshold. On day 8, urodynamic test and bladder smooth muscle contractility study, including the contraction of bladder strips to electrical field stimulation (EFS, 2-64 Hz), carbachol (CCh, 10^-8-10^-5 M) and KCl (120 mM), were performed to evaluate the function of bladder function. Body weight and bladder weight were also recorded. Morphometric analysis using an optical microscope and transmission electron microscope was performed to observe the changes of microstructure and submicrostructure of the bladder. The major pelvic neurons were isolated and treated with acrolein (the main CYP metabolite) to assess apoptosis in vitro. RT-PCR assays were used to quantify the mRNA expression levels of Nlrp6, Asc, Casp11 and Casp1 in bladder tissues and primary neurons. Results: After CYP injections, the body weights decreased, but the bladder weights increased in the model group. The mechanical withdrawal threshold of the cystitis model remained at a low level. The morphometric analysis suggested bladder inflammation and neuroinflammation in the bladder of the cystitis rat model. Urodynamic test revealed that, the amplitude, the pressure baseline, the peak pressure and pressure threshold of model rats significantly increased after CYP treatment. The muscle strips of model rats exhibited significantly higher contractility caused by EFS and CCh than the controls. Apoptotic cells appeared at the highest concentration group (100 μM acrolein) after 6 h of acrolein incubation in apoptosis assay of primary neurons. The mRNA expression levels of Nlrp6 and Casp11 were significantly increased in the cystitis rat model and in the acrolein-treated neurons. Conclusions: Low-dose CYP treatment was confirmed to induce nerve injury, which leading to bladder pain and overactive bladder in female rats, and the up-regulation of Nlrp6 and Casp11 may contribute to these pathological changes.

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.

The Botulinum Treatment of Neurogenic Detrusor Overactivity: The Double-Face of the Neurotoxin

Botulinum neurotoxin (BoNT) can counteract the highly frequent involuntary muscle contractions and the uncontrolled micturition events that characterize the neurogenic detrusor overactivity (NDO) due to supra-sacral spinal cord lesions. The ability of the toxin to block the neurotransmitter vesicular release causes the reduction of contractions and improves the compliance of the muscle and the bladder filling. BoNT is the second-choice treatment for NDO once the anti-muscarinic drugs have lost their effects. However, the toxin shows a time-dependent efficacy reduction up to a complete loss of activity. The cellular mechanisms responsible for BoNT effects exhaustion are not yet completely defined. Similarly, also the sites of its action are still under identification. A growing amount of data suggest that BoNT, beyond the effects on the efferent terminals, would act on the sensory system recently described in the bladder mucosa. The specimens from NDO patients no longer responding to BoNT treatment displayed a significant increase of the afferent terminals, likely excitatory, and signs of a chronic neurogenic inflammation in the mucosa. In summary, beyond the undoubted benefits in ameliorating the NDO symptomatology, BoNT treatment might bring to alterations in the bladder sensory system able to shorten its own effectiveness.

Pharmacological modulation of the spatiotemporal disposition of micromotions in the intact resting urinary bladder of the rabbit; their pattern is under both myogenic and autonomic control

OBJECTIVES

To explore and characterize the disposition and dynamics of micromotions in the wall of the intact resting teradotoxinized urinary bladder of the rabbit before and after the administration of adrenergic and cholinergic pharmaceutical agents.

METHODS

Spatiotemporal maps and related intravesical pressure were used to analyse propagating patches of contractions (PPCs) and their component individual myogenic contractions [propagating individual contractions (PICs)] in the wall of the tetradotoxinized urinary bladder.

RESULTS

The bladder wall exhibited two contractile states that were of similar frequencies to those of the two types of electrophysiological discharge described in previous studies; the first, in which cyclic PPCs predominated, the second in which small irregular PICs predominated. The addition of carbachol increased the size, frequency, speed and distance of propagation of PPCs, whereas the addition of isoprenaline temporarily halted the incorporation of PICs into PPCs, and reduced patch size and total area undergoing contraction. The RhoA kinase (ROCK) inhibitor Y-27632 reduced both largest patch index and mean patch size. Both carbenoxolone and ROCK inhibition decreased the duration of PPCs. Carbenoxolone also prolonged duration and accelerated PPC propagation velocity. The authors postulate that these differences arise from differing effects of these agents on myocytes and interstitial cells within the stress environment of the bladder, influencing the development, coordination and propagation of PPCs.

CONCLUSIONS

The timings and structure of spontaneous micromotions in the wall of the isolated bladder change when it is treated with sympathetic/parasympathetic agonists and with myogenically active agents. Correspondingly, disorders of bladder wall contraction may result from disorders of either neurogenic or myogenic signalling and may be amenable to treatment with combinations of agents that influence both.

Nerve sprouting and neurogenic inflammation characterize the neurogenic detrusor overactive bladder of patients no longer responsive to drug therapies

Urothelium and Lamina Propria (LP) are considered an integrate sensory system which is able to control the detrusor activity. Complete supra-sacral spinal cord lesions cause Neurogenic Detrusor Overactivity (NDO) whose main symptoms are urgency and incontinence. NDO therapy at first consists in anti-muscarinic drugs; secondly, in intra-vesical injection of botulinum toxin. However, with time, all the patients become insensitive to the drugs and decide for cystoplastic surgery. With the aim to get deeper in both NDO and drug's efficacy lack pathogenesis, we investigated the innervation, muscular and connective changes in NDO bladders after surgery by using morphological and quantitative methodologies. Bladder innervation showed a significant global loss associated with an increase in the nerve endings located in the upper LP where a neurogenic inflammation was also present. Smooth muscle cells (SMC) anomalies and fibrosis were found in the detrusor. The increased innervation in the ULP is suggestive for a sprouting and could condition NDO evolution and drug efficacy length. Denervation might cause the SMC anomalies responsible for the detrusor altered contractile activity and intra-cellular traffic and favour the appearance of fibrosis. Inflammation might accelerate these damages. From the clinical point of view, an early anti-inflammatory treatment could positively influence the disease fate.

Increased autophagy contributes to impaired smooth muscle function in neurogenic lower urinary tract dysfunction

AIMS

To explore whether autophagy plays a role in the remodeling of bladder smooth muscle cells (SMCs) in children with neurogenic lower urinary tract dysfunction (NLUTD), we investigated the effect of autophagy in NLUTD in the paediatric population.

METHODS

Bladder biopsies were taken from children with NLUTD and healthy donors as controls. Samples were labeled with the SMC markers calponin, smoothelin, and the autophagy proteins LC3, ATG5, and Beclin1. The contractile ability of bladder derived SMCs was investigated.

RESULTS

ATG5 gene and protein was upregulated in NLUTD muscle tissue compared to normal bladder. NLUTD muscle exhibited a punctated immunostaining pattern for LC3 in a subset of the SMCs, confirming the accumulation of autophagosomes. Pronounced elevation of ATG5 in the SMC in NLUTD tissue was associated with a downregulation of the key contractile proteins smoothelin and calponin. Pharmacological blocking of autophagy completely stopped the cells growth in normal bladder SMCs. Inhibition of autophagy in the NLUTD SMCs, with already elevated levels of ATG5, resulted in a reduction of ATG5 protein expression to the basal level found in normal controls.

CONCLUSIONS

Our study suggests that autophagy is an important factor affecting the remodeling of SMCs and the alteration of functionality in bladder smooth muscle tissue in the NLUTD. Since autophagy can be influenced by oral medication, this finding might lead to novel strategies preventing the deterioration of NLUTD muscle.

Pathophysiology of the underactive bladder

Underactive bladder (UAB), which has been described as a symptom complex suggestive of detrusor underactivity, is usually characterized by prolonged urination time with or without a sensation of incomplete bladder emptying, usually with hesitancy, reduced sensation on filling, and slow stream often with storage symptoms. Several causes such as aging, bladder outlet obstruction, diabetes mellitus, neurologic disorders, and nervous injury to the spinal cord, cauda equine, and peripheral pelvic nerve have been assumed to be responsible for the development of UAB. Several contributing factors have been suggested in the pathophysiology of UAB, including myogenic failure, efferent and/or afferent dysfunctions, and central nervous system dysfunction. In this review article, we have described relationships between individual contributing factors and the pathophysiology of UAB based on previous reports. However, many pathophysiological uncertainties still remain, which require more investigations using appropriate animal models.

Characteristics of the mechanosensitive bladder afferent activities in relation with microcontractions in male rats with bladder outlet obstruction

We investigated the characteristics of bladder mechanosensitive single-unit afferent activities (SAAs) in rats with a bladder outlet obstruction (BOO) and their relationship with bladder microcontractions. Male Wistar rats were divided into Sham and BOO groups. Four or 10 days after the surgery, rats were anesthetized with urethane. The SAAs of Aδ- or C-fibers from the L6 dorsal roots were recorded during bladder filling. The BOO group showed a higher number of microcontractions and lower SAAs of Aδ-fibers compared with those of the Sham group. These findings were significant at day 10 post-operatively. In contrast, SAAs of C-fibers were not significantly different between the groups at either day 4 or 10. In the BOO group at day 10, the SAAs of both Aδ- and C-fibers at the “ascending” phase of microcontractions were significantly higher than those at the other phases (descending or stationary), and a similar tendency was also observed at day 4. Taken together, during bladder filling, the bladder mechanosensitive SAAs of Aδ-fibers were attenuated, but SAAs of both Aδ- and C-fibers were intermittently enhanced by propagation of microcontractions.

Stem Cells in Functional Bladder Engineering

Conditions impairing bladder function in children and adults, such as myelomeningocele, posterior urethral valves, bladder exstrophy or spinal cord injury, often need urinary diversion or augmentation cystoplasty as when untreated they may cause severe bladder dysfunction and kidney failure. Currently, the gold standard therapy of end-stage bladder disease refractory to conservative management is enterocystoplasty, a surgical enlargement of the bladder with intestinal tissue. Despite providing functional improvement, enterocystoplasty is associated with significant long-term complications, such as recurrent urinary tract infections, metabolic abnormalities, stone formation, and malignancies. Therefore, there is a strong clinical need for alternative therapies for these reconstructive procedures, of which stem cell-based tissue engineering (TE) is considered to be the most promising future strategy. This review is focused on the recent progress in bladder stem cell research and therapy and the challenges that remain for the development of a functional bladder wall.

The potential role of unregulated autonomous bladder micromotions in urinary storage and voiding dysfunction; overactive bladder and detrusor underactivity

The isolated bladder shows autonomous micromotions, which increase with bladder distension, generate sensory nerve activity, and are altered in models of urinary dysfunction. Intravesical pressure resulting from autonomous activity putatively reflects three key variables; the extent of micromotion initiation, distances over which micromotions propagate, and overall bladder tone. In vivo, these variables are subordinate to the efferent drive of the central nervous system. In the micturition cycle storage phase, efferent inhibition keeps autonomous activity generally at a low level, where it may signal 'state of fullness', whilst maintaining compliance. In the voiding phase, mass efferent excitation elicits generalised contraction (global motility initiation). In lower urinary tract dysfunction, efferent control of the bladder can be impaired, for example due to peripheral 'patchy' denervation. In this case, loss of efferent inhibition may enable unregulated micromotility, and afferent stimulation, predisposing to urinary urgency. If denervation is relatively slight, the detrimental impact on voiding may be low, as the adjacent innervated areas may be able to initiate micromotility synchronous with the efferent nerve drive, so that even denervated areas can contribute to the voiding contraction. This would become increasingly inefficient the more severe the denervation, such that ability of triggered micromotility to propagate sufficiently to engage the denervated areas in voiding declines, so the voiding contraction increasingly develops the characteristics of underactivity. In summary, reduced peripheral coverage by the dual efferent innervation (inhibitory and excitatory) impairs regulation of micromotility initiation and propagation, potentially allowing emergence of overactive bladder and, with progression, detrusor underactivity.

Physiological and pathophysiological implications of micromotion activity in urinary bladder function

'Micromotions' is a term signifying the presence of localized microcontractions and microelongations, alongside non-motile areas. The motile areas tend to shift over the bladder surface with time, and the intravesical pressure reflects moment-by-moment summation of the interplay between net contractile force generated by micromotions and general bladder tone. Functionally, the bladder structure may comprise modules with variable linkage, which supports presence of localized micromotions (no functional linkage between modules), propagating contractions (where emergence of linkage allows sequential activation) and the shifting of micromotions over time. Detrusor muscle, interstitial cells and intramural innervation have properties potentially relevant for initiating, coordinating and modulating micromotions. Conceptually, such activity could facilitate the generation of afferent activity (filling state reporting) in the absence of intravesical pressure change and the ability to transition to voiding at any bladder volume. This autonomous activity is an intrinsic property, seen in various experimental contexts including the clinical setting of human (female) overactive bladder. 'Disinhibited autonomy' may explain the obvious micromotions in isolated bladders and perhaps contribute clinically in neurological disease causing detrusor overactivity. Furthermore, any process that could increase the initiation or propagation of microcontractions might be anticipated to have a functional effect, increasing the likelihood of urinary urgency and detrusor overactivity respectively. Thus, models of bladder outlet obstruction, neurological trauma and ageing provide a useful framework for detecting cellular changes in smooth muscle, interstitial cells and innervation, and the consequent effects on micromotions.

Alterations of the myovesical plexus of the human overactive detrusor

Objectives. The human bladder shows spontaneous autonomous activity. Detrusor overactivity could be seen as a consequence of exaggerated autonomous activity. Interstitial cells (ICs) play a potential role in coordination of autonomous activity. As it is suggested that changes in ICs coexist with detrusor overactivity (DO), we investigated possible alterations to human bladder ICs. Methods. Biopsies were obtained from 23 patients and were categorized into four groups: genuine stress incontinence (without DO) (n = 5), neurogenic disease with DO (n = 6), bladder outlet obstruction with DO (n = 6), or idiopathic DO (n = 6). Specimens were processed to investigate expression of N-cadherin and PGP9.5. N-cadherin expression was semiquantitatively analyzed and correlated to PG9.5 expression and bladder wall morphology. Results. The population of cells expressing N-cadherin is altered in the overactive detrusor, making no difference between the sources of DO. Punctate distribution of morphological changes was found and downregulation of PGP9.5 expression seemed to coexist with upregulation of N-cadherin expression in the detrusor layer. Conclusions. The population of N-cadherin+ cells of the interstitial compartment of the human bladder has the ability to proliferate. As this proliferation seems to coexist with denervation, it could be possible that a highly developed network of interstitial cells replaces the loss of innervation in overactive detrusor.

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

Changes in the distribution of interstitial cells (IC) are reportedly associated with dysfunctional bladder. This study investigated whether spinal cord injury (SCI) resulted in changes to IC subpopulations (vimentin-positive with the ultrastructural profile of IC), smooth muscle and nerves within the bladder wall and correlated cellular remodelling with functional properties. Bladders from SCI (T8/9 transection) and sham-operated rats 5 weeks post-injury were used for ex vivo pressure–volume experiments or processed for morphological analysis with transmission electron microscopy (TEM) and light/confocal microscopy. Pressure-volume relationships revealed low-pressure, hypercompliance in SCI bladders indicative of decompensation. Extensive networks of vimentin-positive IC were typical in sham lamina propria and detrusor but were markedly reduced post-SCI; semi-quantitative analysis showed significant reduction. Nerves labelled with anti-neurofilament and anti-vAChT were notably decreased post-SCI. TEM revealed lamina propria IC and detrusor IC which formed close synaptic-like contacts with vesicle-containing nerve varicosities in shams. Lamina propria and detrusor IC were ultrastructurally damaged post-SCI with retracted/lost cell processes and were adjacent to areas of cellular debris and neuronal degradation. Smooth muscle hypertrophy was common to SCI tissues. In conclusion, IC populations in bladder wall were decreased 5 weeks post-SCI, accompanied with reduced innervation, smooth muscle hypertrophy and increased compliance. These novel findings indicate that bladder wall remodelling post-SCI affects the integrity of interactions between smooth muscle, nerves and IC, with compromised IC populations. Correlation between IC reduction and a hypercompliant phenotype suggests that disruption to bladder IC contribute to pathophysiological processes underpinning the dysfunctional SCI bladder.

Impact of partial urethral obstruction on bladder function: time-dependent changes and functional correlates of altered expression of Ca²⁺ signaling regulators

In animal models of partial urethral obstruction (PUO), altered smooth muscle function/contractility may be linked to changes in molecules that regulate calcium signaling/sensitization. PUO was created in male rats, and urodynamic studies were conducted 2 and 6 wk post-PUO. Cystometric recordings were analyzed for the presence or absence of nonvoiding contractions [i.e., detrusor overactivity (DO)]. RT-PCR and Western blots were performed on a subpopulation of rats to study the relationship between the expression of RhoA, L-type Ca(2+) channels, Rho kinase-1, Rho kinase-2, inositol 1,4,5-trisphosphate, ryanodine receptor, sarco(endo)plasmic reticulum Ca(2+)-ATPase 2 and protein kinase C (PKC)-potentiated phosphatase inhibitor of 17 kDa, and urodynamic findings in the same animal. Animals displayed DO at 2 (38%) and 6 wk (43%) post-PUO, increases were seen in in vivo pressures at 2 wk, and residual volume at 6 wk. Statistical analysis of RT-PCR and Western blot data at 2 wk, during the compensatory phase of detrusor hypertrophy, documented that expression of molecules that regulate calcium signaling and sensitization was consistently lower in obstructed rats without DO than those with DO or control rats. Among rats with DO at 2 wk, linear regression analysis revealed positive correlations between in vivo pressures and protein and mRNA expression of several regulatory molecules. At 6 wk, in the presence of overt signs of bladder decompensation, no clear or consistent alterations in expression of these same targets were observed at the protein level. These data extend prior work to suggest that molecular profiling of key regulatory molecules during the progression of PUO-mediated bladder dysfunction may shed new light on potential biomarkers and/or therapeutic targets.

Effects of botulinum toxin type a in the bladder wall of children with neurogenic bladder dysfunction: a comparison of histological features before and after injections

PURPOSE

Botulinum toxin type A has gained popularity in urology. Most reported studies have been in adults at urology centers and most have addressed long-term safety. Since botulinum toxin type A treatment for neurogenic bladder dysfunction requires repeat injections, verifying that such treatment does not induce fibrosis in children seems essential.

MATERIALS AND METHODS

The study was approved by the institutional review board and patients were enrolled after we obtained written consent. Patients with neurogenic bladder dysfunction not responding to conventional treatment (anticholinergics and clean intermittent catheterization) were treated with 10 IU/kg botulinum toxin type A up to a maximum of 300 IU. Endoscopic cold cup biopsies were obtained from the posterolateral bladder wall 1.5 to 2 cm above the ureteral orifice. Bladder wall findings were categorized into 3 groups, including inflammatory infiltration, edema and fibrosis. Each criterion was then graded as mild or severe and analyzed by Fisher's exact test (p <0.05).

RESULTS

A total of 46 bladder wall biopsies were obtained from 40 patients 2 to 18 years old. Biopsies were evaluated in groups 1 and 2, including group 1-20 from patients with no botulinum toxin type A injection and group 2-20 after botulinum toxin type A injection. Group 2 was subdivided into group 3-10 biopsies after 1 injection and group 4-10 after multiple injections. Six patients underwent biopsy twice, that is before the first and second treatments. Histological changes were present in all biopsies. When comparing groups 1 and 2, there was no statistically significant difference in inflammation and edema. However, there was a significant difference in fibrosis between groups 1 and 4 (p <0.05) with apparently decreased fibrosis after multiple injections.

CONCLUSIONS

In our experience repeat botulinum toxin type A injections into the detrusor in children do not lead to increased fibrosis in the bladder wall. This study confirms the long-term safety of botulinum toxin type A in the pediatric population.

The integrative physiology of the bladder

Normal bladder function is complex, resulting from the co-operative interaction of numerous regulatory cell types, of which the interstitial cells and the peripheral neurones are particularly interesting. Collectively, these comprise the myovesical plexus, which appears to confer structural and functional characteristics on the bladder loosely akin to those of the gut. These include functional modularity, which gives rise to the potential for localised and propagating peristalsis-like movements in the bladder wall according to the prevailing physiological conditions. Localised modular activity during filling may contribute to normal generation of sensation and exaggerated modular activity may give rise to urinary urgency. Enhanced co-ordination of modular activity occurs in various models of detrusor overactivity; it leads to surges of contraction over a large part of the bladder wall, generating phasic changes in intravesical pressure. During voiding, the myovesical plexus sustains detrusor contraction at the behest of the brainstem, monitoring state of bladder fullness as it does so, as a guide to the required duration for which it has to keep up the effort. Accordingly, the bladder wall itself may house structures which render the bladder the effector level in a hierarchy of lower urinary tract regulation. Dysfunction in these vital regulatory structures is an underestimated factor in the pathophysiology of clinical bladder problems.

A survey of commonalities relevant to function and dysfunction in pelvic and sexual organs

Micturition, defecation and sexual function are all programmed through spinal reflexes that are under descending control from higher centres. Interaction between these reflexes can clearly be perceived, and evidence is accumulating the dysfunction in one reflex is often associated with dysfunction in another. In this article, we describe some of the basic properties and neural control of the smooth muscles mediating the reflexes, reviewing the common features that underlie these reflex functions, and what changes may be responsible for dysfunction. We propose that autonomic control within the pelvis predisposes pelvic and sexual organs to crosstalk, with the consequence that diseases and conditions of the pelvis are subject to convergence on a functional level. It should be expected that disturbance of the function of one system will inevitably impact adjacent systems.

Role of gap junctions in spontaneous activity of the rat bladder

Increased gap junction expression in lamina propria myofibroblasts and urothelial cells may be involved in detrusor overactivity, leading to incontinence. Immunohistochemistry was used to compare connexin (Cx) 26, 43, and 45 expression in the bladders of neonatal, adult, and spinal cord-transected rats, while optical imaging was used to map the spread of spontaneous activity and the effects of gap junction blockade. Female adult Sprague-Dawley rats were deeply anesthetized, a laminectomy was performed, and the spinal cord was transected (T8/T9). After 14 days, their bladders and those of age-matched adults (4 mo old) and neonates (7-21 day old) were excised and studied immunohistochemically using frozen sections or optically using whole bladders stained with voltage- and Ca(2+)-sensitive dyes. The expression of Cx26 was localized to the urothelium, Cx43 to the lamina propria myofibroblasts, and Cx45 to the detrusor smooth muscle. While the expression of Cx45 was comparable in all bladders, the expression of Cx43 and Cx26 was increased in neonate and transected animals. In the bladders of adults, spontaneous activity was initiated at multiple sites, resulting in a lack of coordination. Alternatively, in neonate and transected animals spontaneous activity was initiated at a focal site near the dome and spread in a coordinated fashion throughout the bladder. Gap junction blockade (18beta-glycyrrhetinic acid, 1 microM) abolished this coordinated activity but had no effect on the uncoordinated activity in adult bladders. These data suggest that coordinated spontaneous activity requires gap junction upregulation in urothelial cells and lamina propria myofibroblasts.

Sensory collaterals, intramural ganglia and motor nerves in the guinea-pig bladder: evidence for intramural neural circuits

The afferent output from the bladder is important for triggering micturition. This study identifies different types of afferent nerve and explores the connections of their collateral fibres on intramural ganglia and potential ganglionic targets. The experiments were performed on tissues from male guinea-pigs (n=16). Fibres positive for choline acetyl transferase (ChAT(+)) were found to originate close to the urothelium, to transit the sub-urothelial interstitial cell layer and to pass into the lamina propria. A different population of fibres, immunopositive for calcitonin gene-related peptide (CGRP), capsaicin receptors or neurofilament protein (NF), were seen to intertwine with the ChAT(+) fibres in the lamina propria. The ChAT(+) fibres did not express NF. Ganglia with ChAT(+) and NF(+) neurones were found in the lamina propria and muscle. ChAT(+) fibres, with pronounced terminal varicosities, were present on the nerve cell bodies. Two types were noted: NF(+) terminals and those with little or no NF (NF(-)) suggesting that their origins were the ChAT(+) afferent collaterals and the adjacent ganglia. Fibres containing CGRP or substance P were seen on the ganglionic cells. alpha1B adrenergic receptors were also found on the neurones indicative of adrenergic synapses. Thus, the ganglia had multiple inputs. Different types of ChAT(+) nerves were seen in the muscle: NF(+) and NF(-). The ChAT(+)/NF(+) nerves may represent a ganglionic output to the muscle. This complex neuronal network may therefore represent the elements generating and modulating bladder sensations. The role of such a scheme in bladder pathology and the therapeutic sites of action of anticholinergic and sympathomimetic drugs are discussed.

Quantification of bladder smooth muscle orientation in normal and spinal cord injured rats

Spinal cord injuries (SCI) often lead to severe bladder dysfunctions. Our previous studies have demonstrated that following SCI, rat bladder wall tissue became hypertrophied, significantly more compliant, and changed its mechanical behavior from orthotropic to isotropic. In order to elucidate the link between the tissue microstructure and mechanical properties of the wall, we have developed a novel semi-automated image analysis method to quantify smooth muscle bundle orientation and mass fraction in the bladder wall tissues from normal and 10 day-post-SCI rats. Results of the present study revealed that there were significant (p < 0.05) increases in smooth muscle area fractions as well as significantly (p < 0.001) fewer cell nuclei per muscle area in the SCI groups compared to the normal groups. Furthermore, while the normal rat bladders exhibited predominant smooth muscle orientation only in the longitudinal direction, the SCI rat bladders exhibited smooth muscles oriented in both the circumferential and longitudinal directions. These results provide first evidence that bladder smooth muscle cells exhibit hypertrophy rather than hyperplasia and developed a second, orthogonal orientation of smooth muscle bundles following SCI. The results of the present study corroborate our previous mechanical anisotropy data and provide the basis for development of structure-based constitutive models for urinary bladder wall tissue.

Trypanosoma cruzi infection induced changes in the innervation, structure and function of the murine bladder

PURPOSE

The involvement of the lower urinary tract in chronic Chagas' disease has received little attention. Therefore, we investigated pathology and functional alterations in the bladder of Trypanosoma cruzi infected mice.

MATERIALS AND METHODS

CD1 mice were infected with 5 x 10 T. cruzi trypomastigotes of the Brazil strain of T. cruzi. At day 100 after infection bladder structure and function were examined by pathological evaluation, magnetic resonance imaging and cystometric studies.

RESULTS

The bladder in infected mice weighed more and were large, dilated, deformed, friable and thin walled compared with control mice. Magnetic resonance imaging confirmed these observations. Inflammation, fibrosis and ganglionitis was observed. Cystometric studies revealed that baseline, threshold and micturition pressures were increased in infected mice. Bladder overactivity and decreased bladder compliance were also noted in infected mice. There were no detectable differences in bladder capacity, micturition volume or residual volume between infected and uninfected mice.

CONCLUSIONS

Bladder abnormalities may be a more common clinical sequelae of T. cruzi infection than previously appreciated.

Elementary purinergic Ca2+ transients evoked by nerve stimulation in rat urinary bladder smooth muscle

The translation of nerve transmission to Ca2+ signals in urinary bladder smooth muscle (UBSM) is incompletely understood. Thus, we sought to characterize Ca2+ signals in strips of UBSM loaded with the Ca2+-sensitive fluorescent dye, fluo-4, using laser scanning confocal microscopy. Two types of Ca2+ signals occurred spontaneously and could be evoked with field stimulation: large, rapid, global Ca2+ transients termed 'global Ca2+ flashes', and much smaller, localized Ca2+ transients. Global Ca2+ flashes were inhibited by the L-type voltage-dependent Ca2+ channel (VDCC) inhibitor, diltiazem and with P2X receptor blockade. Simultaneous intracellular recordings and Ca2+ measurements indicated that these events are caused by Ca2+ influx through VDCCs during action potentials. Small, local Ca2+ transients occurred spontaneously, and their frequency could be elevated with field stimulation. Atropine, an inhibitor of muscarinic receptors, did not affect these local Ca2+ transients. However, the desensitizing P2X receptor agonist alpha,beta-methylene ATP, and the purinergic antagonist, suramin, effectively inhibited the local Ca2+ transients. The frequency of these 'purinergic Ca2+ transients' was increased about 7-fold by a 10 s stimulus train (1 Hz). The amplitude, duration at one-half amplitude and the spatial spread of the evoked purinergic Ca2+ transients were F/F(o) = 2.4 +/- 0.13, 111.7 +/- 9.3 ms and 14.0 +/- 1.0 microm2, respectively. Tetrodotoxin inhibited evoked purinergic Ca2+ transients, indicating that they were dependent on nerve fibre activation. Purinergic Ca2+ transients were not dependent on VDCC activity. Neither 2-APB, an inhibitor of inositol 1,4,5-triphosphate (Ins(1,4,5)P3) (IP3)-induced Ca2+ release, nor ryanodine inhibited the purinergic Ca2+ transients. We have identified two novel Ca2+ signals in rat UBSM. Large, rapid, global Ca2+ flashes that represent Ca2+ influx through VDCCs during action potentials, and local, purinergic Ca2+ transients that represent Ca2+ entry through P2X receptors. Our results indicate that purinergic Ca2+ transients evoked by release of ATP from nerve varicosities are elementary signals in the process of nerve-smooth muscle communication.

Nerve regeneration: might this be the only solution for functional problems of the urinary tract?

PURPOSE OF REVIEW

To assess the potential role of nerve regeneration in restoring urinary tract function, the rapidly developing and exciting area of central and peripheral nerve repair and regeneration is reviewed, with particular reference to papers in which animal models of nerve damage resulting in urogenital dysfunction have been used. The difficulties and potential of these techniques for therapeutic application to human subjects with functional problems of the urinary tract are discussed.

RECENT FINDINGS

Methods for encouraging regeneration of cut axons and directed growth in the inhibitory environment of the central nervous system are being extensively explored. The recent discovery of the potential of olfactory ensheathing cells has proved a significant advance. Olfactory ensheathing cells are a type of glial cell which can be harvested from the olfactory mucosa. Transplantation of these cells, in conjunction with a biodegradable synthetic nerve guide or conduit, has been shown to restore urinary tract function after spinal cord injury. Artificial, biodegradable conduits have also restored bladder and spermatic duct function after sympathetic nerve damage. Other adjuvants facilitating the process of axonal recovery include the use of neurotrophins to accelerate and guide the formation of new nerve-fibre growth.

SUMMARY

These revolutionary technologies may, in the future, provide a means of treating urinary tract dysfunction with some types of aetiology, including acute spinal cord injury, and injury to nerves following pelvic surgery. It is, however, less likely that these treatments will be used successfully in the near future in patients in which the neural damage is long term, or associated with death of post-ganglionic neurons.