Activation of muscarinic receptors in rat bladder sensory pathways alters reflex bladder activity

Pathology and physiology of acid-sensitive ion channels in the bladder

Acid-sensitive ion channels (ASICs) are sodium-permeable channels activated by extracellular acidification. They can be activated and trigger the inward flow of Na+ when the extracellular environment is acidic, leading to membrane depolarization and thus inducing action potentials in neurons. There are four ASIC genes in mammals (ASIC1-4). ASIC is widely expressed in humans. It is closely associated with pain, neurological disorders, multiple sclerosis, epilepsy, migraines, and many other disorders. Bladder pain syndrome/interstitial cystitis (BPS/IC) is a specific syndrome characterized by bladder pain. Recent studies have shown that ASICs are closely associated with the development of BPS/IC. A study revealed that ASIC levels are significantly elevated in a BPS/IC model. Additionally, researchers have reported differential changes in ASICs in the bladders of patients with neurogenic lower urinary tract dysfunction (NLUTD) caused by spinal cord injury (SCI). In this review, we summarize the structure and physiological functions of ASICs and focus on the mechanisms by which ASICs mediate bladder disease.

Rapid-Onset, Short-Duration Induction of Colorectal Contractions in Anesthetized, Adult, Male Rats

Substantial clinical and preclinical evidence indicates that transient receptor potential vanilloid 1 (TRPV1) receptors are expressed on terminals of colorectal chemoreceptors and mechanoreceptors and are involved in various rectal hypersensitivity disorders with common features of colorectal overactivity. These stimulatory properties of TRPV1 receptors on colorectal function suggested that brief stimulation of TRPV1 might provide a means of pharmacologically activating the colorectum to induce defecation in patients with an "unresponsive" colorectum. The current studies explored the basic features of TRPV1 receptor-induced contractions of the colorectum in anesthetized rats with and without acute spinal cord injury (aSCI). Cumulative concentration-response curves to intrarectal (IR) capsaicin (CAP) solutions (0.003%-3.0%) were performed in anesthetized aSCI and spinal intact rats. CAP produced an "inverted U," cumulative concentration-response curve with a threshold for inducing colorectal contractions at 0.01% and a peak response at 0.1% and slight decreases in responses up to 3%. Decreases in responses with concentrations >0.1% are due to a rapid desensitization (i.e., ≤30 minutes) of TRPV1 receptors to each successive dose. Desensitization appeared fully recovered within 24 hours in spinal intact rats. Colorectal contractions were completely blocked by atropine, indicating a reflexogenic activation of parasympathetic neurons, and responses were completely unaffected by a neurokinin 2 receptor antagonist, indicating that release of neurokinin A from afferent terminals and subsequent direct contractions of the smooth muscle was not involved. IR administration of three other TRPV1 receptor agonists produced similar results as CAP. SIGNIFICANCE STATEMENT: Individuals with spinal cord injury often lose control of defecation. Time-consuming bowel programs using digital stimulation of the rectum are used to empty the bowel. This study shows that intrarectal administration of the transient receptor potential vanilloid 1 (TRPV1) receptor agonist, capsaicin, can induce rapid-onset, short-duration colorectal contractions capable of inducing defecation in spinal cord injured and intact rats. Therefore, TRPV1 agonists show promise as potential therapeutics to induce defecation in individuals with neurogenic bowel.

Moxibustion attenuates neurogenic detrusor overactivity in spinal cord injury rats by inhibiting M2/ATP/P2X3 pathway

PURPOSE

Activation of muscarinic receptors located in bladder sensory pathways is generally considered to be the primary contributor for driving the pathogenesis of neurogenic detrusor overactivity following spinal cord injury. The present study is undertaken to examine whether moxibustion improves neurogenic detrusor overactivity via modulating the abnormal muscarinic receptor pathway.

MATERIALS AND METHODS

Female Sprague-Dawley rats were subjected to spinal cord injury with T9-10 spinal cord transection. Fourteen days later, animals were received moxibustion treatment for one week. Urodynamic parameters and pelvic afferents discharge were measured. Adenosine triphosphate (ATP) content in the voided cystometry fluid was determined. Expressions of M2, M3, and P2X3 receptors in the bladder mucosa were evaluated.

RESULTS

Moxibustion treatment prevented the development of detrusor overactivity in spinal cord injury rats, with an increase in the intercontraction interval and micturition pressure threshold and a decrease in afferent activity during filling. The expression of M2 was markedly suppressed by moxibustion, accompanied by a reduction in the levels of ATP and P2X3. M2 receptor antagonist methoctramine hemihydrate had similar effects to moxibustion on bladder function and afferent activity, while the M2-preferential agonist oxotremorine methiodide abolished the beneficial effects of moxibustion.

CONCLUSION

Moxibustion is a potential candidate for treating neurogenic bladder overactivity in a rat model of spinal cord injury, possibly through inhibiting the M2/ATP/P2X3 pathway.

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.

Evaluation of Choline and Acetylcholine Levels in Responders and Nonresponders to Anticholinergic Therapy for Overactive Bladder Syndrome

OBJECTIVE

This study aimed to determine whether levels of choline (Ch) and acetylcholine (Ach) differ between responders and nonresponders to anticholinergic therapy.

METHODS

Patients prescribed an anticholinergic were evaluated using the Overactive Bladder Symptom Score; Medical, Epidemiologic and Social Aspects of Aging and Incontinence Questionnaire; and Incontinence Impact Questionnaire-7. A 1-day voiding diary and a urine sample were collected. After treatment for 12 weeks, the questionnaires were administered and 1-day voiding diary was completed. Levels of Ach and Ch were measured by liquid chromatography with tandem mass spectrometry. Subjects were divided into responders and nonresponders. Wilcoxon rank sum test and Fisher exact test were used to express differences between groups. Spearman ρ correlation coefficient was used to determine the relationship between Ach and Ch and symptom severity, patient demographics, and questionnaire scores.

RESULTS

Thirty-one women were included in the analysis. The treatment response rate was 48.8%. The median age was 67 years (interquartile range, 50-76 years), and median body mass index was 32.3 kg/m2 (27.5-40.6 kg/m2), with 41.2% having an additional complaint of stress incontinence. There were no significant differences in symptom severity or questionnaire scores between groups.The median Ch and Ach levels were higher in responders (28.6 vs 9.2 μL, P = 0.04) and (83.1 vs 18.7 nL, P = 0.02), respectively. Levels of both Ch and Ach had moderate positive correlations with the Medical, Epidemiologic and Social Aspects of Aging and Incontinence Questionnaire urgency urinary incontinence score (ρ = 0.533 [P = 0.002] and ρ = 0.453 [P = 0.01], respectively).

CONCLUSION

In women with overactive bladder, urinary Ach and Ch levels are higher in responders to anticholinergic therapy compared with nonresponders.

Functional atropine sensitive purinergic responses in the healthy rat bladder

While acetylcholine is regarded to be the main directly contractile transmitter substance in the urinary bladder, interactions with other transmitters likely occur. Presently, the interplay between purinergic and cholinergic signalling was investigated to unravel the involvement of the urothelium and efferent neurons in the functionally important purinergically evoked release of acetylcholine in vitro. Functional characterization of receptor subtypes involved in this interplay was also performed. In vitro organ bath experiments with electrical field stimulation (EFS) or administration of agonist were performed in the absence and presence of the neurotoxin tetrodotoxin (TTX; 5 × 10^-7 M) and/or receptor antagonists, in intact and urothelium-denuded full thickness rat bladder strip preparations. Interestingly, functional contractions to ATP (10^-6-10^-3 M) remained unaffected by TTX, but were significantly lowered in the presence of the muscarinic antagonist atropine (10^-6 M). However, in urothelium-denuded strip preparations, this latter phenomenon was not present and the ATP response remained unaltered. To rule out purinergic interference caused by break-down of ATP, experiments were performed in which the stable ATP-analogue αβMeATP (10^-7-10^-5 M) gave rise to functional atropine-sensitive contractions. Furthermore, contractions to ATP were not affected by P2Y6 purinoceptor blockade (by MRS2578; 10^-7, 10^-5 M), nor were relaxatory responses to ATP sensitive to atropine, PPADS (3 × 10^-5 M) or αβMeATP. Lastly, relaxations to ADP (10^-6-10^-3 M) or NECA (10^-8-10^-5 M) were unaltered by the presence of atropine. To conclude, purinergic functional contractile, but not relaxatory, responses are supported by the cholinergic transmitter system in vitro, through non-neuronal mechanisms in the urothelium. Involved purinoceptors are of the P2X-subtype, most likely P2X1 and/or P2X3.

In vivo paracrine effects of ATP-induced urothelial acetylcholine in the rat urinary bladder

Mechanical stretch of the urothelium induces the release of ATP that activates bladder afferent nerves. In the rat urinary bladder, ATP is also a contractile co-transmitter in the parasympathetic innervation. In isolated preparations, ATP evokes a urothelial release of acetylcholine that substantially contributes to ATP-evoked contractile responses. Currently we aimed to further examine the interactions of ATP and acetylcholine in the rat urinary bladder in two in vivo models. In the whole bladder preparation, atropine reduced ATP-evoked responses by about 50% in intact but denervated bladders, while atropine had no effect after denudation of the urothelium. In a split bladder preparation, reflex-evoked responses of the contralateral half were studied by applying stimuli (agonists or stretch) to the ipsilateral half. Topical administration of ATP and methacholine as well as of stretch induced contralateral reflex-evoked contractions. While topical administration of atropine ipsilaterally reduced the ATP- and stretch-induced contralateral contractions by 27 and 39%, respectively, the P2X purinoceptor antagonist PPADS reduced them by 74 and 84%. In contrary, the muscarinic M2-(M4)-selective receptor antagonist methoctramine increased the responses by 38% (ATP) and 75% (stretch). Pirenzepine (M1-selective antagonist) had no effect on the reflex. In vitro, in the absence of the reflex, methoctramine did not affect the ATP-induced responses. It is concluded that urothelial ATP potently induces the micturition reflex and stimulates urothelial release of acetylcholine. Acetylcholine subsequently acts on afferents and on the detrusor muscle. While muscarinic M2 and/or M4 receptors in the sensory innervation exert inhibitory modulation, muscarinic M3 receptors cause excitation.

Methylglyoxal, a Reactive Glucose Metabolite, Induces Bladder Overactivity in Addition to Inflammation in Mice

Diabetic bladder dysfunction (DBD) is one of the most common complication of diabetes. Methylglyoxal (MGO), a highly reactive dicarbonyl compound formed as a by-product of glycolysis, is found at high levels in plasma of diabetic patients. Here, we explored the effects of chronic administration of MGO on micturition pattern (cystometry) and bladder contractility in vitro in healthy male C57/BL6 mice. Methylglyoxal was given at 0.5% in drinking water for 4 weeks. Exposure to MGO led to bladder tissue disorganization, edema of lamina propria, partial loss of urothelium and multiple leukocyte infiltrates. Filling cystometry revealed significant increases of micturition frequency and number of non-voiding contractions (NVCs) in the MGO group, clearly indicating an overactive bladder profile. Bladder contractions induced by electrical-field stimulation (EFS) and carbachol were significantly higher in the MGO group, while the muscarinic M₂ and M₃ mRNA expressions remained unchanged between groups. Additionally, MGO exposure induced upregulation of TRPA1 and down-regulation of TRPV1 and TRPV4 in bladder tissues. Methylglyoxal did not change the mRNA expression of the advanced glycation end products receptor (RAGE), but markedly increased its downstream NF-κB - iNOS signaling. The mRNA expression of cyclooxygenase-2 (COX-2) and reactive-oxygen species (ROS) levels remained unchanged. Altogether, our data show that 4-week MGO intake in mice produces an overactive bladder phenotype in addition to bladder inflammation and increased NF-kB/iNOS signaling. TRPA1 up-regulation and TRPV1/TRPV4 down-regulation may account for the MGO-induced bladder overactivity. Scavengers of MGO could be an option to ameliorate bladder dysfunction in diabetic conditions.

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.

Single onabotulinumtoxinA 200U dose improved clinical symptoms but not urothelial dysfunction in neurogenic detrusor overactivity due to spinal cord injury

OBJECTIVE

To evaluate the changes in urothelial dysfunction protein expressions in bladder after onabotulinumtoxin injection and correlate that with clinical outcomes in spinal cord injury (SCI) patients.

METHODS

Twenty-six patients with neurogenic detrusor overactivity (NDO) and urinary incontinence due to suprasacral SCI were treated with onabotulinumtoxinA 200U detrusor injection. Urodynamic studies and bladder biopsies were obtained at baseline, 3, and 6 months after treatment. Biopsy tissues were investigated for E-cadherin, zonula occludens-1 (ZO-1), mast cell activity, and urothelial cell apoptosis, sensory protein expression including purinergic receptor P2X3, endothelial NOS, inducible NOS, β3-adrenoceptors, and muscarinic receptors M2 and M3. Differences in functional protein expression between controls and SCI patients and between successful and failed treatment groups were analyzed.

RESULTS

SCI patients had significantly lower E-cadherin, higher mast cell activity, increased apoptosis, decreased M3 and eNOS expressions than the controls at baseline. Of the 26 patients, 17 (65%) showed improvement in bladder capacity by >50% at 3 months; however, improvement declined by 6 months after treatment. The urothelial expression of E-cadherin and ZO-1 increased at 3 months but had declined at 6 months. The urothelial sensory protein expression did not change significantly after treatment. M3 receptor density was significantly decreased in SCI patients at baseline and patients with treatment success 3 months after injection (p = 0.01).

CONCLUSION

A single injection of onabotulinumtoxinA 200U improved clinical symptoms but did not significantly alter urothelial sensory protein expression. The results imply that a single 200U onabotulinumtoxinA dose might not be adequate for urothelial dysfunction in NDO. IRB: TCGH 098-53.

The Mystery of the Interstitial Cells in the Urinary Bladder

Intrinsic mechanisms to restrain smooth muscle excitability are present in the bladder, and premature contractions during filling indicate a pathological phenotype. Some investigators have proposed that c-Kit⁺ interstitial cells (ICs) are pacemakers and intermediaries in efferent and afferent neural activity, but recent findings suggest these cells have been misidentified and their functions have been misinterpreted. Cells reported to be c-Kit⁺ cells colabel with vimentin antibodies, but vimentin is not a specific marker for c-Kit⁺ cells. A recent report shows that c-Kit⁺ cells in several species coexpress mast cell tryptase, suggesting that they are likely to be mast cells. In fact, most bladder ICs labeled with vimentin antibodies coexpress platelet-derived growth factor receptor α (PDGFRα). Rather than an excitatory phenotype, PDGFRα⁺ cells convey inhibitory regulation in the detrusor, and inhibitory mechanisms are activated by purines and stretch. PDGFRα⁺ cells restrain premature development of contractions during bladder filling, and overactive behavior develops when the inhibitory pathways in these cells are blocked. PDGFRα⁺ cells are also a prominent cell type in the submucosa and lamina propria, but little is known about their function in these locations. Effective pharmacological manipulation of bladder ICs depends on proper identification and further study of the pathways in these cells that affect bladder functions.

Urothelium update: how the bladder mucosa measures bladder filling

AIM

This review critically evaluates the evidence on mechanoreceptors and pathways in the bladder urothelium that are involved in normal bladder filling signalling.

METHODS

Evidence from in vitro and in vivo studies on (i) signalling pathways like the adenosine triphosphate pathway, cholinergic pathway and nitric oxide and adrenergic pathway, and (ii) different urothelial receptors that are involved in bladder filling signalling like purinergic receptors, sodium channels and TRP channels will be evaluated. Other potential pathways and receptors will also be discussed.

RESULTS

Bladder filling results in continuous changes in bladder wall stretch and exposure to urine. Both barrier and afferent signalling functions in the urothelium are constantly adapting to cope with these dynamics. Current evidence shows that the bladder mucosa hosts essential pathways and receptors that mediate bladder filling signalling. Intracellular calcium ion increase is a dominant factor in this signalling process. However, there is still no complete understanding how interacting receptors and pathways create a bladder filling signal. Currently, there are still novel receptors investigated that could also be participating in bladder filling signalling.

CONCLUSIONS

Normal bladder filling sensation is dependent on multiple interacting mechanoreceptors and signalling pathways. Research efforts need to focus on how these pathways and receptors interact to fully understand normal bladder filling signalling.

Autonomic Receptor-mediated Regulation of Production and Release of Nitric Oxide in Normal and Malignant Human Urothelial Cells

In the urinary bladder, the main source of NO seems to be the urothelium and the underlying suburothelium. In this study, we aimed to characterize how receptors in the human urothelium regulate the production and release of NO. For this, we cultured two human urothelial cell lines - the normal immortalized cell line UROtsa and the malignant cell line T24. These were treated with an array of agonists and antagonists with affinity for adrenergic, muscarinic and purinergic receptors. The production of NO and expression of nitric oxide synthase (NOS) was studied by immunocytochemistry and Western blotting. The amount of released NO was measured indirectly by detecting nitrite using amperometry and a Griess reaction kit. The results showed that NO, endothelial NOS and inducible NOS were predominantly produced and expressed in the close vicinity of the nucleus in untreated human urothelial cells. Upon treatment with a beta-adrenoceptor agonist, but not any of the other agonists or antagonists, the pattern of NO production changed, showing a more even production throughout the cytosol. The pattern of expression of endothelial NOS changed in a similar way upon dobutamine treatment. The release of nitrite, as a measurement of NO, increased after treatment with dobutamine from 0.31 ± 0.029 to 1.97 ± 0.18 nmol and 0.80 ± 0.12 to 3.27 ± 0.24 nmol in UROtsa and T24, respectively. In conclusion, our results show that the expression of NOS and production of NO as well as the release of NO from human urothelial cells is regulated by beta-adrenoceptor activation.

Nerve growth factor release from the urothelium increases via activation of bladder C-fiber in rats with cerebral infarction

AIMS

There are some reports that bladder C-fibers are partially involved in detrusor overactivity in patients with brain lesions. We investigated the contribution of bladder C-fiber to decreased bladder capacity in rats with cerebral infarction.

METHODS

Cerebral infarction was induced under halothane anesthesia by left middle cerebral artery occlusion with 4-0 nylon thread in female Sprague-Dawley rats. Intramural amounts of ATP and prostaglandin E₂ , in vivo and in vitro ATP, NGF, and prostaglandin E₂ release from the distended bladder urothelium, and changes in mRNA expressions of sensor molecules and receptors were monitored 6 h after the occlusion. Cystometry was performed in rats with or without resiniferatoxin pretreatment.

RESULTS

Overexpression of sensor molecule, transient receptor potential vanilloid-type channel 1, acid-sensing ion channel 2, purinergic receptors P2X₃ , and M₂ /M₃ muscarinic receptors was found in the bladder. These changes were accompanied by increases in ATP and NGF release from the urothelium. In contrast, when bladder C-fibers were desensitized by resiniferatoxin, no increase in NGF release from the urothelium was found either in vivo or in vitro. There was no difference in the percentage decrease in bladder capacity between cerebral infarction rats pretreated with resiniferatoxin and cerebral infarction rats without pretreatment.

CONCLUSIONS

Results indicate that expression of sensor molecules in the bladder is altered by distant infarction in the brain. ATP and NGF release from the urothelium also increased. NGF release was related to activation of bladder C-fibers. Bladder C-fibers might not contribute much to decreased bladder capacity caused by cerebral infarction.

Urothelial ATP signaling: what is its role in bladder sensation?

AIM

Bladder functional disorders are common health problems; however, their pathologies are poorly understood. Adenosine triphosphate (ATP) released from the urothelium has been suggested to have an essential role in the micturition reflex, and its involvement in bladder functional disorders has been intensively investigated. Here, we review the latest advances in research on urothelial ATP signaling.

METHODS

We reviewed research articles on the role of the urothelium and urothelial ATP release in bladder function.

RESULTS

Mice lacking purinergic receptors have been reported to exhibit marked bladder hyporeflexia. Based on this observation, it was commonly believed, according to the widely held ATP urothelial signaling theory, that stretch-induced urothelial ATP release mediates the sensation of bladder filling via purinergic receptors. However, recent studies employing novel experimental methods and approaches have demonstrated that there are no significant differences in bladder function between wild-type and purinergic receptor knockout mice under physiological conditions. Nonetheless, under pathological conditions, inhibition of purinergic receptors has been shown to improve bladder hyperactivity. Moreover, enhanced urothelial ATP release has been reported in patients with bladder functional disorders.

CONCLUSIONS

Recently, conflicting evidence has led us to question the role of urothelial ATP signaling in normal micturition reflex. In contrast, under pathological conditions, it seems likely that enhanced urothelial ATP signaling mediates bladder hyperactivity. These recent findings suggest that the urothelial ATP signaling pathway is a potential therapeutic target for bladder functional disorders.

Overactive bladder in children

Overactive bladder (OAB) is a ubiquitous syndrome that is defined by urinary urgency with, or without urinary incontinence. OAB is observed in all parts of the world, with a prevalence of 5-12% in children (5-10 years of age) and a prevalence of 0.5% in older adolescents (16-18 years of age). Published data indicate that around a third of children with OAB are likely to become adults with similar complaints. Studies in children and in adults with OAB indicate that these individuals are more likely to also have anxiety, depression and attention deficit problems, and that appropriate treatment of these comorbidities can often improve the patient's OAB symptoms. Furthermore, data from twin studies and familial surveys seem to indicate a genetic component of OAB. Pharmacological treatments of OAB in children have improved in the past 5 years, moving beyond anticholinergic agents and including the off-label use of α-blockers, β3-agonists and intravesical botulinum toxin. Use of several different electrical stimulation techniques is also effective, both as first-line treatments, and for patients with treatment-refractory symptoms. Overall the outlook of children with OAB seems to be improving, with a greater understanding of the pathophysiology of this syndrome. Treatment modalities that target the source of the underlying problem, especially in children, are likely to provide the best patient outcomes.

The Role of the Mucosa in Normal and Abnormal Bladder Function

The internal face of the detrusor smooth muscle wall of the urinary bladder is covered by a mucosa, separating muscle from the hostile environment of urine. However, the mucosa is more than a very low permeability structure and offers a sensory function that monitors the extent of bladder filling and composition of the urine. The mucosa may be considered as a single functional structure and comprises a tight epithelial layer under which is a basement membrane and lamina propria. The latter region itself is a complex of afferent nerves, blood vessels, interstitial cells and in some species including human beings a muscularis mucosae. Stress on the bladder wall through physical or chemical stressors elicits release of chemicals, such as ATP, acetylcholine, prostaglandins and nitric oxide that modulate the activity of either afferent nerves or the muscular components of the bladder wall. The release and responses are graded so that the mucosa forms a dynamic sensory structure, and there is evidence that the gain of this system is increased in pathologies such as overactive bladder and bladder pain syndrome. This system therefore potentially provides a number of drug targets against these conditions, once a number of fundamental questions are answered. These include how is mediator release regulated; what are the intermediate roles of interstitial cells that surround afferent nerves and blood vessels; and what is the mode of communication between urothelium and muscle - by diffusion of mediators or by cell-to-cell communication?

Influence of urothelial or suburothelial cholinergic receptors on bladder reflexes in chronic spinal cord injured cats

The effects of intravesical administration of a muscarinic receptor agonist (oxotremorine-M, OXO-M) and antagonist (atropine methyl nitrate, AMN) and of a nicotinic receptor agonist (nicotine) and antagonist (hexamethonium, C₆) on reflex bladder activity were investigated in conscious female chronic spinal cord injured (SCI) cats using cystometry. OXO-M (50μM) decreased bladder capacity (BC) for triggering micturition contractions, increased maximal micturition pressure (MMP), increased frequency and area under the curve of pre-micturition contractions (PMC-AUC). Nicotine (250μM) decreased BC, increased MMP, but did not alter PMC-AUC. The effects of OXO-M on BC and PMC-AUC were suppressed by intravesical administration of AMN (50-100μM), and the effects of nicotine were blocked by hexamethonium (1mM). Antagonists infused intravesically alone did not alter reflex bladder activity. However, AMN (0.2mg/kg, subcutaneously) decreased PMC-AUC. 8-OH-DPAT (0.5mg/kg, s.c.), a 5-HT_1A receptor agonist, suppressed the OXO-M-induced decrease in BC but not the enhancement of PMC-AUC. These results indicate that activation of cholinergic receptors located near the lumenal surface of the bladder modulates two types of reflex bladder activity (i.e., micturition and pre-micturition contractions). The effects may be mediated by activation of receptors on suburothelial afferent nerves or receptors on urothelial cells which release transmitters that can in turn alter afferent excitability. The selective action of nicotine on BC, while OXO-M affects both BC and PMC-AUC, suggests that micturition reflexes and PMCs are activated by different populations of afferent nerves. The selective suppression of the OXO-M effect on BC by 8-OH-DPAT without altering the effect on PMCs supports this hypothesis. The failure of intravesical administration of either AMN or hexamethonium alone to alter bladder activity indicates that cholinergic receptors located near the lumenal surface do not tonically regulate bladder reflex mechanisms in the SCI cat.

Combination therapy with β3 -adrenoceptor agonists and muscarinic acetylcholine receptor antagonists: Efficacy in rats with bladder overactivity

OBJECTIVE

To investigate the efficacy of combination therapy of a selective β3 -adrenoceptor agonist (mirabegron) and muscarinic acetylcholine receptor antagonists (a selective muscarinic acetylcholine receptor2 antagonist: methoctramine hemihydrate or a selective muscarinic acetylcholine receptor3 antagonist; 4-DAMP) compared with monotherapy of either agent in rats with oxotremorine methiodide (a non-selective muscarinic acetylcholine receptor agonist)-induced bladder overactivity.

METHODS

Cystometry was carried out in conscious female rats with intravesical instillation of oxotremorine methiodide (200 μmol/L). Either mirabegron (0.3-3 mg/kg), methoctramine (0.1-1 mg/kg) or 4-DAMP (0.03-0.3 mg/kg) was cumulatively applied intravenously. Also, the effects of combined application of mirabegron (3 mg/kg) plus methoctramine (1 mg/kg) or 4-DAMP (0.3 mg/kg) on cystometric parameters were compared with those of single-agent monotherapy.

RESULTS

Intravesical instillation of oxotremorine methiodide induced bladder overactivity, as evidenced by decreases in threshold pressure and bladder capacity. In oxotremorine methiodide-treated rats, single application of mirabegron (1, 3 mg/kg), methoctramine (0.3, 1 mg/kg) or 4-DAMP (0.1, 0.3 mg/kg) decreased baseline pressure and increased bladder capacity. In addition, reductions in threshold pressure and maximal voiding pressure were also seen after the administration of 4-DAMP (0.3 mg/kg). The combined treatment of mirabegron plus 4-DAMP induced a larger increase in bladder capacity compared with monotherapy of either drug, whereas there were no significant changes in cystometric parameters between the combination therapy of mirabegron plus methoctramine and monotherapy of either drug.

CONCLUSION

These results suggest that the combination therapy of β3 -adrenoceptor agonists plus muscarinic acetylcholine receptor3 antagonists is more effective compared with monotherapy for the treatment of bladder overactivity. In contrast, the efficacy of β3 -adrenoceptor agonists might not be increased by the addition of muscarinic acetylcholine receptor2 antagonists.

Effects of nicotinic receptor agonists on bladder afferent nerve activity in an in vitro bladder-pelvic nerve preparation

Effects of nicotinic receptor agonists (epibatidine and nicotine) on mechano-sensitive bladder afferent nerve (MS-BAN) activity were studied in an in vitro bladder-pelvic afferent nerve preparation. MS-BAN activity was induced by isotonic distention of the bladder at pressures of 10-40 cmH2O. The effect of epibatidine varied according to the concentration, route of administration and the intravesical pressure stimulus. Epibatidine (300-500 nM) administered in the perfusate to the serosal surface of the bladder decreased distension evoked afferent firing by 30-50% depending on the bladder pressure. However these concentrations also produced an immediate increase in tonic afferent firing in the empty bladder. Lower concentrations (50-100 nM) elicited weaker and more variable effects. The inhibitory effects were blocked by bath application of mecamylamine (150 µM) a nicotinic receptor antagonist. Bath application of nicotine (20 µM) elicited similar effects. Intravesical administration of epibatidine (500 nM) significantly increased MS-BAN firing by 15-30%; while lower concentrations (200-300 nM) were ineffective. This facilitatory effect of epibatidine was blocked by intravesical administration of mecamylamine (250 µM). Electrical stimulation on the surface of the bladder elicited action potentials (AP) in BAN. Bath application of epibatidine (300 nM) or nicotine (20 µM) did not change either the voltage threshold or the area of evoked AP. These results indicate that nicotinic agonists: (1) enhance MS-BAN activity originating at afferent receptors near the urothelium, (2) inhibit MS-BAN activity originating at afferent receptors located at other sites in the bladder, (3) directly excite unidentified afferents, (4) do not alter afferent axonal excitability.

Authentic role of ATP signaling in micturition reflex

Adenosine triphosphate (ATP) is a signaling molecule that regulates cellular processes. Based on previous studies of bladder function over the past decade, bladder ATP signaling was thought to have an essential role in the normal micturition reflex. In this study, we performed detailed analyses of bladder function in purinergic receptor-deficient mice using the automated voided stain on paper method and video-urodynamics. Unexpectedly, a lack of P2X₂ or P2X₃ receptors did not affect bladder function under normal physiological conditions, indicating that bladder ATP signaling is not essential for normal micturition reflex. In contrast, we found that lipopolysaccharide (LPS) induced markedly high levels of ATP release from the urothelium. In addition, LPS-induced rapid bladder hyperactivity was attenuated in P2X₂^−/− and P2X₃^−/− mice. Contrary to the previous interpretation, our present findings indicate that bladder ATP signaling has a fundamental role in the micturition reflex, especially in bladder dysfunction, under pathological conditions. Therefore, the bladder ATP signaling pathway might be a highly promising therapeutic target for functional bladder disorders. This study newly defines an authentic role for bladder ATP signaling in the micturition reflex.

Anatomy and physiology of the lower urinary tract

Functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. Neural control of micturition is organized as a hierarchic system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brainstem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brainstem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily during the early postnatal period, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults cause re-emergence of involuntary micturition, leading to urinary incontinence. The mechanisms underlying these pathologic changes are discussed.

M2muscarinic receptors inhibit cell proliferation and migration in urothelial bladder cancer cells

The role of muscarinic receptors in several diseases including cancer has recently emerged. To evaluate the hypothesis that muscarinic acetylcholine receptors may play a role in bladder cancer as well as in other tumor types, we investigated their expression in bladder tumor specimens. All examined samples expressed the M1, M2 and M3 receptor subtypes. We also found that the level of M2 transcripts, but not those of M1 or M3, significantly increased with the tumor histologic grade. In view of these results, we proceeded to investigate whether the M2 agonist Arecaidine had any effect on in vitro cell growth and migration of T24 cells, a bladder tumor cell line expressing the muscarinic receptors, including the M2 subtype. We observed that Arecaidine significantly reduced T24 and 5637 cell proliferation and migration in a concentration dependent manner. The silencing of M2 receptor by siRNA in T24 and 5637 cell lines showed the inability of Arecaidine (100 μM) to inhibit cell proliferation after 48 hours, whereas the use of M1 and M3 antagonists in T24 appeared not to counteract the Arecaidine effect, suggesting that the inhibition of cell proliferation was directly dependent on M2 receptor activation. These data suggest that M2 muscarinic receptors may play a relevant role in bladder cancer and represent a new attractive therapeutic target.

Investigating detrusor muscle concentrations of oxybutynin after intravesical delivery in an ex vivo porcine model

Intravesical oxybutynin is highly effective in the treatment of overactive bladder. Traditionally the mechanism of action was explained by antagonism of muscarinic receptors located in the detrusor, however evidence now suggests antimuscarinics may elicit their effect by modifying afferent pathways in the mucosal region. This study aimed to investigate the bladder wall distribution of oxybutynin in an ex vivo setting providing tissue - layer specific concentrations of drug achieved after intravesical delivery. Whole ex vivo porcine bladders were intravesically instilled with 0.167 mg mL(-1) oxybutynin solution. After 60 min, tissue samples were excised, serially sectioned parallel to the urothelial surface and extracted drug quantified. Drug distribution into the urothelium, lamina propria and detrusor was determined. Oxybutynin permeated into the bladder wall at a higher rate than other drugs previously investigated (apparent transurothelial Kp = 1.36 × 10(-5) cm s(-1) ). After 60 min intravesical instillation, concentrations achieved in the urothelium (298.69 μg g(-1) ) and lamina propria (43.65 μg g(-1) ) but not the detrusor (0.93 μg g(-1) ) were greater than reported IC50 values for oxybutynin. This work adds to the increasing body of evidence suggesting antimuscarinics elicit their effects via mechanisms other than direct inhibition of detrusor contraction.

Purinergic signalling in the urinary bladder

It is well established that in most species, exocytotic vesicular release of ATP from parasympathetic neurons contributes to contraction of the bladder. However, ATP is released not only from parasympathetic nerves, but also from the urothelium. During bladder filling, the urothelium is stretched and ATP is released from the umbrella cells thereby activating mechanotransduction pathways. ATP release can also be induced by various mediators present in the urine and and/or released from nerves or other components of the lamina propria. Urothelial release of ATP is mainly attributable to vesicular transport or exocytosis and, to a smaller extent, to pannexin hemichannel conductive efflux. After release, ATP acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex and to mediate the sensation of bladder filling and urgency. ATP also acts on suburothelial interstitial cells/myofibroblasts generating an inward Ca(2+) transient that via gap junctions could provide a mechanism for long-distance spread of signals from the urothelium to the detrusor muscle. ATP release can be affected by urological diseases, e.g., interstitial cystitis and both the mechanisms of release and the receptors activated by ATP may be targets for future drugs for treatment of lower urinary tract disorders.

Laser-capture microdissection for analysis of cell type-specific gene expression of muscarinic receptor subtypes in the rat bladder with cyclophosphamide-induced cystitis

PURPOSE

This study examined whether the laser-capture microdissection (LCM) method can achieve separation of urothelial cells from detrusor cells or superficial urothelial cells from intermediate/basal urothelial cells, using α-smooth muscle actin (SMA) and cytokeratin 20 (CK20). In addition, we investigated the changes in expression of muscarinic receptors in laser-captured urothelial and detrusor cells in rats with chronic cystitis.

METHODS

Female SD rats were injected with cyclophosphamide (75 mg/kg) intraperitoneally at day 1, 4, 7 and 10 to induce chronic cystitis. Saline was injected in the same protocol for controls. Bladder specimens were cut at 8 μm thickness, fixed in 70% ethanol and lightly stained by hematoxylin and eosin, and then superficial urothelium, intermediate/basal urothelium and detrusor muscles were laser-captured separately. Real-time PCR was performed to examine expressions of α-SMA, CK20, muscarinic 2 receptors (M2R) and muscarinic 3 receptors (M3R).

RESULTS

The expression of α-SMA mRNA in detrusor muscle cells was 200 times higher than that in urothelial cells in controls. CK20 mRNA expression in apical urothelial cells was 55 times more than that in detrusor muscle and four times more than that in intermediate/basal urothelial cells. Expressions of M2R and M3R mRNA were increased in urothelial cells and decreased in detrusor muscles following chronic cystitis.

CONCLUSIONS

The LCM could be useful for tissue collection of detrusor muscle and different layers of urothelial cells with minimal contamination of other cell types, and cell type-specific changes in molecular expression could accurately be analyzed. Increased expression of urothelial MR might enhance urothelial-afferent interactions to induce bladder overactivity/pain conditions associated with bladder inflammation.

Pannexin 1 channels mediate the release of ATP into the lumen of the rat urinary bladder

KEY POINTS

ATP is released through pannexin channels into the lumen of the rat urinary bladder in response to distension or stimulation with bacterial endotoxins. Luminal ATP plays a physiological role in the control of micturition because intravesical perfusion of apyrase or the ecto-ATPase inhibitor ARL67156 altered reflex bladder activity in the anaesthetized rat. The release of ATP from the apical and basolateral surfaces of the urothelium appears to be mediated by separate mechanisms because intravesical administration of the pannexin channel antagonist Brilliant Blue FCF increased bladder capacity, whereas i.v. administration did not. Intravesical instillation of small interfering RNA-containing liposomes decreased pannexin 1 expression in the rat urothelium in vivo and increased bladder capacity. These data indicate a role for pannexin-mediated luminal ATP release in both the physiological and pathophysiological control of micturition and suggest that urothelial pannexin may be a viable target for the treatment of overactive bladder disorders.

ABSTRACT

ATP is released from the bladder epithelium, also termed the urothelium, in response to mechanical or chemical stimuli. Although numerous studies have described the contribution of this release to the development of various bladder disorders, little information exists regarding the mechanisms of release. In the present study, we examined the role of pannexin channels in mechanically-induced ATP release from the urothelium. PCR confirmed the presence of pannexin 1 and 2 mRNA in rat urothelial tissue, whereas immunofluorescence experiments localized pannexin 1 to all three layers of the urothelium. During continuous bladder cystometry in anaesthetized rats, inhibition of pannexin 1 channels using carbenoxolone (CBX) or Brilliant Blue FCF (BB-FCF) (1-100 μm, intravesically), or by using intravesical small interfering RNA, increased the interval between voiding contractions. Intravenous administration of BB-FCF (1-100 μg kg(-1) ) did not alter bladder activity. CBX or BB-FCF (100 μm intravesically) also decreased basal ATP concentrations in the perfusate from non-distended bladders and inhibited increases in ATP concentrations in response to bladder distension (15 and 30 cmH2 O pressure). Intravesical perfusion of the ATP diphosphohydrolase apyrase (2 U ml(-1) ), or the ATPase inhibitor ARL67156 (10 μm) increased or decreased reflex bladder activity, respectively. Intravesical instillation of bacterial lipopolysaccharides (LPS) (Escherichia coli 055:B5, 100 μg ml(-1) ) increased ATP concentrations in the bladder perfusate, and also increased voiding frequency; these effects were suppressed by BB-FCF. These data indicate that pannexin channels contribute to distension- or LPS-evoked ATP release into the lumen of the bladder and that luminal release can modulate voiding function.

Neural control of the lower urinary tract

This article summarizes anatomical, neurophysiological, pharmacological, and brain imaging studies in humans and animals that have provided insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract. The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. The neural control of micturition is organized as a hierarchical system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brain stem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brain stem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary micturition, leading to urinary incontinence. Neuroplasticity underlying these developmental and pathological changes in voiding function is discussed.

Pelvic organ cross-sensitization to enhance bladder and urethral pain behaviors in rats with experimental colitis

Neural cross-sensitization has been postulated as a mechanism underlying overlaps of chronic pelvic pain disorders such as bladder pain syndrome/interstitial cystitis (BPS/IC) and irritable bowel syndrome (IBS). Animals with experimental colitis have been used to study the underlying mechanisms for overlapped pelvic pain symptoms, and shown to exhibit bladder overactivity evidenced by frequent voiding; however, it has not directly been evaluated whether pain sensation derived from the lower urinary tract is enhanced in colitis models. Also, the cross-sensitization between the colon and urethra has not been studied previously. In the present study, we therefore investigated pain behaviors induced by nociceptive stimuli in the lower urinary tract and the involvement of C-fiber afferent pathways using rats with colitis induced by intracolonic application of 2,4,6-trinitrobenzenesulfonic acid (TNBS). In TNBS-induced colitis rats at 10 days, intravesical application of resiniferatoxin (RTx) induced a significantly greater number of episodes of both licking and freezing behaviors, which were reduced by capsaicin-sensitive C-fiber afferent desensitization. Histochemical studies using fluorescent dye tracers injected into the colon, bladder or urethra showed that dichotomized afferent neurons comprised 6.9-14.5% of L1, L6 and S1 dorsal root ganglion (DRG) neurons innervating the colon or the lower urinary tract. Transient receptor potential vanilloid 1 (TRPV1) mRNA expression was significantly increased in, the bladder, urethra and S1 DRG in colitis rats. An increase in myeloperoxidase (MPO) activity was found in the colon, but not in the bladder or urethra after intracolonic TNBS treatment. These results indicate that TNBS-induced colitis increased pain sensitivity in the bladder and urethra via activation of C-fiber afferent pathways due to colon-to-bladder and colon-to-urethral cross-sensitization, suggesting the contribution of pelvic organ cross-sensitization mechanisms to overlapped pain symptoms in BPS/IC and IBS.

Alterations in nerve-evoked bladder contractions in a coronavirus-induced mouse model of multiple sclerosis

BACKGROUND

Patients with neurodegenerative diseases such as multiple sclerosis, Parkinson's, and Alzheimer's often present with lower urinary tract symptoms (LUTS, urinary frequency, urgency, nocturia and retention) resulting from damage to the peripheral and central nervous systems. These studies were designed to examine the changes in the function of the bladder that may underlie neurogenic bladder dysfunction using a mouse model of demyelination in the CNS.

METHODS

Bladders from 12 week old male C57BL/6J mice with coronavirus-induced encephalomyelitis (CIE, a chronic, progressive demyelinating disease model of human MS), and age-matched controls, were cut into 5-7 strips and suspended in physiological muscle baths for tension measurement in response to agonists and electric field stimulation (EFS). Experiments were performed on intact and denuded (with mucosa removed) bladder strips.

RESULTS

The maximum effect of EFS was not significantly different between CIE and control bladders. Nerve-evoked EFS contractions (tetrodotoxin-sensitive) were blocked by a combination of atropine (cholinergic antagonist) and α,β-methylene ATP (an ATP analog that desensitizes purinergic receptors). In response to EFS, the α,β-methylene ATP-resistant (cholinergic) component of contraction was significantly reduced, while the atropine-resistant (purinergic) component was significantly increased in CIE bladders. Removal of the mucosa in CIE bladders restored the cholinergic component. Bethanechol (muscarinic receptor agonist) potency was significantly increased in CIE bladders.

CONCLUSIONS

Our data demonstrate a deficit in the nerve-evoked cholinergic component of contraction that is not due to the ability of the smooth muscle to respond to acetylcholine. We conclude that neurodegenerative bladder dysfunction in this model of multiple sclerosis may be due, in part, to pathologic changes in the mucosa that causes suppression of muscarinic receptor-mediated contractile response and augmentation of purinergic response of the underlying muscle. Further studies utilizing CIE mice should help elucidate the pathological changes in the mucosa resulting from demyelination in the CNS.

Signalling molecules in the urothelium

The urothelium was long considered to be a silent barrier protecting the body from the toxic effects of urine. However, today a number of dynamic abilities of the urothelium are well recognized, including its ability to act as a sensor of the intravesical environment. During recent years several pathways of these urothelial abilities have been proposed and a major part of these pathways includes release of signalling molecules. It is now evident that the urothelium represents only one part of the sensory web. Urinary bladder signalling is finely tuned machinery of signalling molecules, acting in autocrine and paracrine manner, and their receptors are specifically distributed among different types of cells in the urinary bladder. In the present review the current knowledge of the formation, release, and signalling effects of urothelial acetylcholine, ATP, adenosine, and nitric oxide in health and disease is discussed.

Purinergic signalling in the urinary tract in health and disease

Purinergic signalling is involved in a number of physiological and pathophysiological activities in the lower urinary tract. In the bladder of laboratory animals there is parasympathetic excitatory cotransmission with the purinergic and cholinergic components being approximately equal, acting via P2X1 and muscarinic receptors, respectively. Purinergic mechanosensory transduction occurs where ATP, released from urothelial cells during distension of bladder and ureter, acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex, via low threshold fibres, and nociception, via high threshold fibres. In human bladder the purinergic component of parasympathetic cotransmission is less than 3 %, but in pathological conditions, such as interstitial cystitis, obstructed and neuropathic bladder, the purinergic component is increased to 40 %. Other pathological conditions of the bladder have been shown to involve purinoceptor-mediated activities, including multiple sclerosis, ischaemia, diabetes, cancer and bacterial infections. In the ureter, P2X7 receptors have been implicated in inflammation and fibrosis. Purinergic therapeutic strategies are being explored that hopefully will be developed and bring benefit and relief to many patients with urinary tract disorders.

Combination of foot stimulation and tolterodine treatment eliminates bladder overactivity in cats

AIMS

To determine whether transcutaneous foot stimulation combined with a lower dose tolterodine would inhibit bladder overactivity more effectively than either treatment alone.

METHODS

Cystometrograms were performed on α-chloralose anesthetized cats (N = 6) by infusing 0.25% acetic acid (AA) to induce bladder overactivity. Foot stimulation (5 Hz) was applied at 2 and 4 times the threshold (T) intensity in volts (i.e., 2T or 4T) for inducing toe movement to inhibit bladder overactivity. Cumulative doses of tolterodine (0.003-0.3 mg/kg, i.v.) were also administered to determine the effect of combination treatment.

RESULTS

AA irritation of the bladder significantly (P < 0.0001) reduced bladder capacity to 23.6 ± 7.1% of saline control capacity. Foot stimulation alone at 2T and 4T inhibited bladder overactivity and significantly (P < 0.0001) increased bladder capacity to 50.7 ± 6.8% and 79.0 ± 11.6% of saline control, respectively. Tolterodine alone at 0.3 mg/kg significantly (P < 0.05) increased bladder capacity to 65.6 ± 15.5% of saline control. However, when tolterodine at a threshold dose (0.3 mg/kg) was combined with foot stimulation, the bladder capacity was significantly (P < 0.05) increased to 86.2 ± 6.2% and 107.9 ± 10.6% by 2T and 4T stimulation, respectively. Complete inhibition of bladder overactivity could be achieved at a lower tolterodine dose (0.1 mg/kg) when combined with 4T stimulation (97.0 ± 11.2% of saline control). The amplitude of micturition contraction was not changed by tolterodine treatment.

CONCLUSIONS

This study suggests a novel, efficacious, non-invasive therapy by combining foot stimulation with a lower dose tolterodine to treat bladder overactivity. It also provides the first objective evidence supporting an additive therapeutic benefit of neuromodulation and antimuscarinic combination treatment.

Highlights in basic autonomic neuroscience: contribution of the urothelium to sensory mechanisms in the urinary bladder

Urothelial cells in the urinary bladder express neural properties including: (1) release of neurotransmitters and neurotrophic factors, (2) expression of neurotransmitter receptors and ion channels, and (3) sensitivity to mechanical and chemical stimuli. These properties have focused attention on the possible contribution of the urothelium to the storage and emptying functions of the bladder. In addition chemicals released from urothelial cells can affect the excitability of adjacent afferent nerves and this interaction can be affected by pathological conditions. This raises the possibility that abnormal urothelial-afferent interactions may contribute to bladder dysfunctions and therefore be a target for drug therapy.

Sex differences in the physiology and pharmacology of the lower urinary tract

Sexual dimorphism is not only noticed in the prevalence of many diseases, but also in multiple physiological functions in the body. This review has summarized findings from published literature on the sex differences of the pathophysiology and pharmacology of the lower urinary tract (LUT) of humans and animals. Sex differences have been found in several key areas of the LUT, such as overactive bladder, expression and function of neurotransmitter receptors in the bladder and urethra, and micturition patterns in humans and animals. It is anticipated that this review will not only evoke renewed interest for further research on the mechanism of sex differences in the pathophysiology of the LUT (especially for overactive bladder), but might also open up the possibilities for gender-based drug development by pharmaceutical industries in order to find separate cures for men and women with diseases of the LUT.

Alteration in TRPV1 and Muscarinic (M3) receptor expression and function in idiopathic overactive bladder urothelial cells

AIM

To examine function of both cholinergic (muscarinic) and TRPV1 receptors in human bladder urothelial (HBUC) from non-neurogenic overactive bladder (OAB) patients as compared to control subjects.

METHODS

Primary HBUC cultures were derived from cystoscopic biopsies from OAB and control subjects. Muscarinic and TRPV1 function was assessed by acetylcholine (5 μm) or capsaicin (0.5 μm) evoked ATP release, measured by luciferase assay. Overall, expression of TRPV1 and muscarinic M3 receptors in bladder urothelial cells was accomplished using western immunoblotting.

RESULTS

Our findings revealed that the response to acetylcholine in OAB HBUC cultures (which was blocked by the nonselective muscarinic antagonist, atropine methyl nitrate or AMN) was not significantly different than from controls. The acetylcholine M3 receptor was slightly decreased as compared to control. In contrast, OAB HBUC cultures exhibited a capsaicin hypersensitivity and augmented release of ATP (3.2 fold higher), which was blocked by the antagonist capsazepine. The increase in capsaicin sensitivity correlated with increased urothelial TRPV1 expression.

CONCLUSION

Though characterized in a small number of subjects, augmented release of urothelial-derived transmitters such as ATP could 'amplify' signalling between and within urothelial cells and nearby afferent nerves.

Adenosine receptor antagonism suppresses functional and histological inflammatory changes in the rat urinary bladder

Cyclophosphamide (CYP) induces an interstitial cystitis-like inflammation. The resulting bladder dysfunction has been associated with increased release of adenosine-5'-triphosphate (ATP), structural bladder wall changes and contractile impairment. Due to the inflammatory modulatory effects of purines it was presently wondered if pre-treatment with P1 and P2 purinoceptor antagonists affect the CYP-induced alterations. Rats were pre-treated with saline or antagonists for five days, and 60 h before the in vitro functional examination the rats were administered either saline or CYP. Histological examination revealed CYP-induced bladder wall thickening largely depending on submucosal enlargement, mast cell invasion of the detrusor muscle, increase in muscarinic M5 receptor expression and macrophage migration inhibitory factor (MIF) occurrence in large parts of the urothelium. Functionally, methacholine- and ATP-evoked contractions were smaller in urinary bladders from CYP-treated rats. Pre-treatment with the P2 purinoceptor antagonist suramin and the P1A2B antagonist PSB1115 did not to any great extent affect the CYP-induced changes. The P1A1 antagonist DPCPX, however, abolished the difference of methacholine-evoked contractions between saline- and CYP-treated rats. ATP-evoked contractions were reduced in control after the DPCPX pre-treatment, but not in cystitis. The functional observations for DPCPX were supported by its suppression of CYP-induced submucosal thickening, muscarinic M5 receptor expression and, possibly, detrusor mast cell infiltration and the spread of urothelial MIF occurrence. Thus, P1A1 is an important pro-inflammatory receptor in the acute CYP-induced cystitis and a P1A1 blockade during the initial phase may suppress CYP-induced cystitis. P1A1 purinoceptors seem to regulate contractility in healthy and in inflamed rat urinary bladders.

Nitric oxide modulates bladder afferent nerve activity in the in vitro urinary bladder-pelvic nerve preparation from rats with cyclophosphamide induced cystitis

Effects of a nitric oxide (NO) donor (SNAP), NO substrate (l-arginine), and NO synthase inhibitor (l-NAME) on bladder afferent nerve (BAN) activity were studied in an in vitro bladder-pelvic nerve preparation from untreated or cyclophosphamide (CYP) treated rats. Distension of the bladder induced phasic bladder contractions (PBC) that were accompanied by multiunit afferent firing. Intravesical administration of SNAP (2mM) which did not change the amplitude of PBC significantly decreased peak afferent firing from 79 ± 15 spikes/s to 44 ± 8 spikes/s in CYP pretreated but not untreated preparations. In CYP treated preparations SNAP also decreased by 33-55% BAN firing induced by isotonic distension of the bladder at 10-40 cmH(2)O pressures. Electrical stimulation on the surface of the bladder elicited action potentials (AP) in BAN. SNAP significantly increased the voltage threshold by 75% (p<0.05) and decreased by 45% (p<0.05) the area of the AP evoked at submaximal stimulus intensity. Bath application of SNAP (2mM) or l-arginine (50mM) elicited similar inhibitory effects on the distension evoked BAN firing. The effects of l-arginine were blocked by bath application of l-NAME (20mM). l-NAME alone did not alter BAN firing. In preparations from normal rats SNAP or l-arginine did not alter BAN activity. These results suggest that exogenous as well as endogenously generated NO depresses the excitability of sensitized but not normal BAN and that NO may have an antinociceptive function and modulate bladder hyperactivity induced by pathological conditions.