Sex-related differences in activity of lower urinary tract in response to intravesical acid irritation in decerebrate unanesthetized mice

Bladder-colon chronic cross-sensitization involves neuro-glial pathways in male mice

BACKGROUND

Irritable bowel syndrome and bladder pain syndrome often overlap and are both characterized by visceral hypersensitivity. Since pelvic organs share common sensory pathways, it is likely that those syndromes involve a cross-sensitization of the bladder and the colon. The precise pathophysiology remains poorly understood.

AIM

To develop a model of chronic bladder-colon cross-sensitization and to investigate the mech-anisms involved.

METHODS

Chronic cross-organ visceral sensitization was obtained in C57BL/6 mice using ultrasound-guided intravesical injections of acetic acid under brief isoflurane anesthesia. Colorectal sensitivity was assessed in conscious mice by measuring intracolonic pressure during isobaric colorectal distensions. Myeloperoxidase, used as a marker of colorectal inflammation, was measured in the colon, and colorectal permeability was measured using chambers. c-Fos protein expression, used as a marker of neuronal activation, was assessed in the spinal cord (L6-S1 level) using immunohistochemistry. Green fluorescent protein on the fractalkine receptor-positive mice were used to identify and count microglia cells in the L6-S1 dorsal horn of the spinal cord. The expression of NK1 receptors and MAPK-p38 were quantified in the spinal cord using western blot.

RESULTS

Visceral hypersensitivity to colorectal distension was observed after the intravesical injection of acetic acid vs saline (P < 0.0001). This effect started 1 h post-injection and lasted up to 7 d post-injection. No increased permeability or inflammation was shown in the bladder or colon 7 d post-injection. Visceral hypersensitivity was associated with the increased expression of c-Fos protein in the spinal cord (P < 0.0001). In green fluorescent protein on the fractalkine receptor-positive mice, intravesical acetic acid injection resulted in an increased number of microglia cells in the L6-S1 dorsal horn of the spinal cord (P < 0.0001). NK1 receptor and MAPK-p38 levels were increased in the spinal cord up to 7 d after injection (P = 0.007 and 0.023 respectively). Colorectal sensitization was prevented by intrathecal or intracerebroventricular injections of minocycline, a microglia inhibitor, by intracerebroventricular injection of CP-99994 dihydrochloride, a NK1 antagonist, and by intracerebroventricular injection of SB203580, a MAPK-p38 inhibitor.

CONCLUSION

We describe a new model of cross-organ visceral sensitization between the bladder and the colon in mice. Intravesical injections of acetic acid induced a long-lasting colorectal hypersensitivity to distension, mediated by neuroglial interactions, MAPK-p38 phosphorylation and the NK1 receptor.

Expandable and implantable bioelectronic complex for analyzing and regulating real-time activity of the urinary bladder

Underactive bladder or detrusor underactivity (DUA), that is, not being able to micturate, has received less attention with little research and remains unknown or limited on pathological causes and treatments as opposed to overactive bladder, although the syndrome may pose a risk of urinary infections or life-threatening kidney damage. Here, we present an integrated expandable electronic and optoelectronic complex that behaves as a single body with the elastic, time-dynamic urinary bladder with substantial volume changes up to ~300%. The system configuration of the electronics validated by the theoretical model allows conformal, seamless integration onto the urinary bladder without a glue or suture, enabling precise monitoring with various electrical components for real-time status and efficient optogenetic manipulation for urination at the desired time. In vivo experiments using diabetic DUA models demonstrate the possibility for practical uses of high-fidelity electronics in clinical trials associated with the bladder and other elastic organs.

Blockade of Acid-Sensing Ion Channels Increases Urinary Bladder Capacity With or Without Intravesical Irritation in Mice

We conducted this study to examine whether acid-sensing ion channels (ASICs) are involved in the modulation of urinary bladder activity with or without intravesical irritation induced by acetic acid. All in vivo evaluations were conducted during continuous infusion cystometry in decerebrated unanesthetized female mice. During cystometry with a pH 6.3 saline infusion, an i.p. injection of 30 μmol/kg A-317567 (a potent, non-amiloride ASIC blocker) increased the intercontraction interval (ICI) by 30% (P < 0.001), whereas vehicle injection had no effect. An intravesical acetic acid (pH 3.0) infusion induced bladder hyperactivity, with reductions in ICI and maximal voiding pressure (MVP) by 79% (P < 0.0001) and 29% (P < 0.001), respectively. A-317567 (30 μmol/kg i.p.) alleviated hyperreflexia by increasing the acid-shortened ICI by 76% (P < 0.001). This dose produced no effect on MVP under either intravesical pH condition. Further analysis in comparison with vehicle showed that the increase in ICI (or bladder capacity) by the drug was not dependent on bladder compliance. Meanwhile, intravesical perfusion of A-317567 (100 μM) had no effect on bladder activity during pH 6.0 saline infusion cystometry, and drug perfusion at neither 100 μM nor 1 mM produced any effects on bladder hyperreflexia during pH 3.0 acetic acid infusion cystometry. A-317567 has been suggested to display extremely poor penetrability into the central nervous system and thus to be a peripherally active blocker. Taken together, our results suggest that blockade of ASIC signal transduction increases bladder capacity under normal intravesical pH conditions and alleviates bladder hyperreflexia induced by intravesical acidification and that the site responsible for this action is likely to be the dorsal root ganglia.

Best practices for cystometric evaluation of lower urinary tract function in muriform rodents

AIMS

Rodent cystometry has provided valuable insights into the impact of the disease, injury, and aging on the cellular and molecular pathways, neurologic processes, and biomechanics of lower urinary tract function. The purpose of this white paper is to highlight the benefits and shortcomings of different experimental methods and strategies and to provide guidance on the proper interpretation of results.

METHODS

Literature search, selection of articles, and conclusions based on discussions among a panel of workers in the field.

RESULTS

A range of cystometric tests and techniques used to explore biological phenomena relevant to the lower urinary tract are described, the advantages and disadvantages of various experimental conditions are discussed, and guidance on the practical aspects of experimental execution and proper interpretation of results are provided.

CONCLUSIONS

Cystometric evaluation of rodents comprises an extensive collection of functional tests that can be performed under a variety of experimental conditions. Decisions regarding which approaches to choose should be determined by the specific questions to be addressed and implementation of the test should follow standardized procedures.

P2Y6-deficiency increases micturition frequency and attenuates sustained contractility of the urinary bladder in mice

The role of the P2Y₆ receptor in bladder function has recently attracted a great deal of attention in lower urinary tract research. We conducted this study to determine contributions of the P2Y₆ receptor in lower urinary tract function of normal phenotypes by comparing P2Y₆-deficient mice and wild-type mice. In in vivo experiments, P2Y₆-deficient mice had more frequent micturition with smaller bladder capacity compared to wild-type mice; however, there was no difference between these groups in bladder-filling pressure/volume relationships during cystometry under decerebrate, unanaesthetized conditions. Analysis of in vivo bladder contraction revealed significant difference between the 2 groups, with P2Y₆-deficient mice presenting markedly shorter bladder contraction duration but no difference in peak contraction pressure. However, analysis of in vitro experiments showed no P2Y₆ involvements in contraction and relaxation of bladder muscle strips and in ATP release by mechanical stimulation of primary-cultured urothelial cells. These results suggest that the P2Y₆ receptor in the central nervous system, dorsal root ganglion, or both is involved in inhibition of bladder afferent signalling or sensitivity in the pontine micturition centre and that the receptor in the detrusor may be implicated in facilitation to sustain bladder contraction force.

Muro-Neuro-Urodynamics; a Review of the Functional Assessment of Mouse Lower Urinary Tract Function

Background: Mouse urodynamic tests are fundamental to understanding normal lower urinary tract (LUT) function. These experiments also contribute to our understanding of neurological dysfunction, pathophysiological processes, and potential mechanisms of therapy.

Objectives: Systematic assessment of published evidence on urodynamics, advantages and limitations of different urodynamic measurements in mice, and consideration of potential implications for the clinical field.

Methods: A search using specific search-terms for urodynamic studies and mice was conducted on PubMed (from inception to 1 July 2016).

Results: We identified 55 studies examining or describing mouse neuro-urodynamics. We summarize reported features of mouse urodynamic function deriving from frequency-volume chart (FVC) measurements, voiding spot assays, filling cystometry, and pressure-flow studies. Similarly, an influence of the diurnal cycle on voiding is observed in mice and should be considered when interpreting rodent urodynamic studies, especially FVC measurements and voiding spot assays. Anaesthesia, restraint conditions, or filling rate influence mouse neuro-urodynamics. Mouse cystometric studies have observed intravesical pressure oscillations that accompany urine flow, attributed to high frequency opening and closing of the urethra. This characterization is not seen in other species, except rats. In contrast to human clinical urodynamics, the terminology of these examinations has not been standardized although many rodent urodynamic studies have been described.

Conclusion: Mice have many anatomical and physiological similarities to humans and they are generally cost effective, and allow investigation of the effects of aging because of their short lifespan. There are some differences between mouse and human urodynamics. These must be considered when interpreting LUT function in mice, and translational value of murine disease models.

Sex-dependent expression of TRPV1 in bladder arterioles

Transient receptor potential vanilloid type 1 (TRPV1) is a major nociceptive ion channel implicated in bladder physiology and/or pathophysiology. However, the precise expression of TRPV1 in neuronal vs. nonneuronal bladder cells is uncertain. Here we used reporter mouse lines (TRPV1-Cre:tdTomato and TRPV1^PLAP-nlacZ) to map expression of TRPV1 in postnatal bladder. TRPV1 was not detected in the urothelium, however, we found marked expression of TRPV1 lineage in sensory nerves, and surprisingly, in arterial/arteriolar smooth muscle (ASM) cells. Tomato fluorescence was prominent in the vesical arteries and in small-diameter (15-40 μm) arterioles located in the suburothelial layer with a near equal distribution in bladder dome and base. Notably, arteriolar TRPV1 expression was greater in females than in males and increased in both sexes after 90 days of age, suggesting sex hormone and age dependency. Analysis of whole bladder and vesical artery TRPV1 mRNA revealed a similar sex and developmental dependence. Pharmacological experiments confirmed functional TRPV1 protein expression; capsaicin increased intracellular Ca²⁺ in ∼15% of ASM cells from wild-type female bladders, but we observed no responses to capsaicin in bladder arterioles isolated from TRPV1-null mice. Furthermore, capsaicin triggered arteriole constriction that was rapidly reversed by the TRPV1 antagonist, BCTC. These data show that predominantly in postpubertal female mice, bladder ASM cells express functional TRPV1 channels that may act to constrict arterioles. TRPV1 may therefore play an important role in regulating the microcirculation of the female bladder, and this effect may be of significance during inflammatory conditions.

Urothelial ATP exocytosis: regulation of bladder compliance in the urine storage phase

The bladder urothelium is more than just a barrier. When the bladder is distended, the urothelium functions as a sensor to initiate the voiding reflex, during which it releases ATP via multiple mechanisms. However, the mechanisms underlying this ATP release in response to the various stretch stimuli caused by bladder filling remain largely unknown. Therefore, the aim of this study was to elucidate these mechanisms. By comparing vesicular nucleotide transporter (VNUT)-deficient and wild-type male mice, we showed that ATP has a crucial role in urine storage through exocytosis via a VNUT-dependent mechanism. VNUT was abundantly expressed in the bladder urothelium, and when the urothelium was weakly stimulated (i.e. in the early filling stages), it released ATP by exocytosis. VNUT-deficient mice showed reduced bladder compliance from the early storage phase and displayed frequent urination in inappropriate places without a change in voiding function. We conclude that urothelial, VNUT-dependent ATP exocytosis is involved in urine storage mechanisms that promote the relaxation of the bladder during the early stages of filling.

γEpithelial Na(+) Channel (γENaC) and the Acid-Sensing Ion Channel 1 (ASIC1) expression in the urothelium of patients with neurogenic detrusor overactivity

OBJECTIVE

To investigate the expression of two types of cation channels, γEpithelial Na(+) Channel (γENaC) and the Acid-Sensing Ion Channel 1 (ASIC1), in the urothelium of controls and in patients affected by neurogenic detrusor overactivity (NDO). In parallel, urodynamic parameters were collected and correlated to the immunohistochemical results.

PATIENTS SUBJECTS AND METHODS

Four controls and 12 patients with a clinical diagnosis of NDO and suprasacral spinal cord lesion underwent urodynamic measurements and cystoscopy. Cold-cup biopsies were frozen and processed for immunohistochemistry and Western Blot. Spearman's correlation coefficient between morphological and urodynamic data was applied. One-way anova followed by Newman-Keuls multiple comparison post hoc test was applied for Western Blot results.

RESULTS

In the controls, γENaC and ASIC1 were expressed in the urothelium with differences in their cell distribution and intensity. In patients with NDO, both markers showed consistent changes either in cell distribution and labelling intensity compared with the controls. A significant correlation between a higher intensity of γENaC expression in the urothelium of patients with NDO and lower values of bladder compliance was detected.

CONCLUSIONS

The present findings show important changes in the expression of γENaC and ASIC1 in NDO human urothelium. Notably, while the changes in γENaC might impair the mechanosensory function of the urothelium, the increase of ASIC1 might represent an attempt to compensate for the excess in local sensitivity.

Functional roles of TRPV1 and TRPV4 in control of lower urinary tract activity: dual analysis of behavior and reflex during the micturition cycle

The present study used a dual analysis of voiding behavior and reflex micturition to examine lower urinary tract function in transient receptor potential vanilloid (TRPV)1 knockout (KO) mice and TRPV4 KO mice. In metabolic cage experiments conducted under conscious conditions (i.e., voluntary voiding behavior), TRPV4 KO mice showed a markedly higher voiding frequency (VF; 19.3 ± 1.2 times/day) and a smaller urine volume/voiding (UVV; 114 ± 9 μl) compared with wild-type (WT) littermates (VF: 5.2 ± 0.5 times/day and UVV: 380 ± 34 μl). Meanwhile, TRPV1 KO mice showed a similar VF to WT littermates (6.8 ± 0.5 times/day) with a significantly smaller UVV (276 ± 20 μl). Water intake among these genotypes was the same, but TRPV4 KO mice had a larger urine output than the other two groups. In cystometrogram experiments conducted in decerebrate unanesthetized mice (i.e., reflex micturition response), no differences between the three groups were found in any cystometrogram variables, including voided volume, volume threshold for inducing micturition contraction, maximal voiding pressure, and bladder compliance. However, both TRPV1 KO and TRPV4 KO mice showed a significant number of nonvoiding bladder contractions (NVCs; 3.5 ± 0.9 and 2.8 ± 0.7 contractions, respectively) before each voiding, whereas WT mice showed virtually no NVCs. These results suggest that in the reflex micturition circuit, a lack of either channel is involved in NVCs during bladder filling, whereas in the forebrain, it is involved in the early timing of urine release, possibly in the conscious response to the bladder instability.

Combination of bladder ultrasonography and novel cystometry method in mice reveals rapid decrease in bladder capacity and compliance in LPS-induced cystitis

Various animal models have been used in research into bladder dysfunction, and in vivo cystometry is a common method to analyze bladder function in animals. However, it is rather difficult to perform reliably in small animals. Transabdominal bladder ultrasonography combined with cystometry in urethane-anesthetized mice have revealed physical inhibition of bladder wall movement by a bladder catheter conventionally placed in the bladder apex. For reliable evaluation of mouse lower urinary tract function, we established a novel cystometry method in which a catheter was placed in the bladder anterior wall, in combination with bladder ultrasonography. This new method allowed the bladder to be well distended (i.e., larger maximum bladder capacity, lower pressure threshold, higher voided volume, and higher bladder compliance compared with conventional methods), which reflected more spontaneous voiding than conventional cystometry methods. We also demonstrated the usefulness of bladder ultrasonography for analysis of mouse bladder function, especially bladder dynamics, maximum bladder capacity, and post-voiding residual volume. We analyzed bladder functional changes in lipopolysaccharide (LPS)-induced cystitis by combining bladder ultrasonography and this new cystometry method. Bladder ultrasonography revealed a rapid decrease in bladder capacity, and cystometry showed a rapid decrease in voided volume due to intravesical LPS instillation. This new cystometry method also revealed a rapid decrease in bladder compliance caused by LPS instillation, which was not detectable by conventional methods. The combination of ultrasonography and the new cystometry method may become a powerful tool for analysis of mouse bladder function and could contribute to the development of new treatments for bladder dysfunction.

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.

Effects of urethane on reflex activity of lower urinary tract in decerebrate unanesthetized rats

Effects of urethane on lower urinary tract function were examined in decerebrate unanesthetized rats. During single slow infusion (0.04 ml/min) cystometrograms (CMGs), urethane (0.3 g/kg) increased micturition pressure threshold (PT) by 73%, postvoid residual volume (RV) by 425%, and decreased voiding efficiency (VE) by 57%, but did not change maximal voiding pressure (MVP), closing peak pressure (CPP), bladder compliance, bladder contraction duration (BCD), or volume threshold (VT) for inducing micturition. Lower doses (0.01-0.1 g/kg) did not alter any parameter. During continuous fast infusion (0.21 ml/min) CMGs, urethane at doses of 0.6-1.2 g/kg (iv) markedly decreased CPP by 69-85%, whereas only the largest dose (1.2 g/kg iv) decreased MVP and external urethral sphincter electromyogram activity by 42 and by 80%, respectively. Doses of 0.001-0.6 g/kg did not alter the intercontraction interval and BCD. Taken together, these results suggest that urethral activity, which is essential for efficient voiding, is more sensitive to the suppressive effect of urethane than afferent or efferent mechanisms controlling the bladder. The threshold dose of MK-801 (0.3 mg/kg), an NMDA antagonist, required to decrease MVP and increase VT in urethane (1.2 g/kg)-anesthetized rats, only increased VT in rats treated with a subanesthetic dose of urethane (0.3 g/kg), suggesting a higher sensitivity of the afferent vs. efferent limb of the micturition reflex pathway to urethane-MK-801 interactions. Because effects of urethane persisted after removal of the forebrain, they must be mediated by actions on the brain stem, spinal cord, or peripheral nervous system.

The use of cystometry in small rodents: a study of bladder chemosensation

The lower urinary tract (LUT) functions as a dynamic reservoir that is able to store urine and to efficiently expel it at a convenient time. While storing urine, however, the bladder is exposed for prolonged periods to waste products. By acting as a tight barrier, the epithelial lining of the LUT, the urothelium, avoids re-absorption of harmful substances. Moreover, noxious chemicals stimulate the bladder's nociceptive innervation and initiate voiding contractions that expel the bladder's contents. Interestingly, the bladder's sensitivity to noxious chemicals has been used successfully in clinical practice, by intravesically infusing the TRPV1 agonist capsaicin to treat neurogenic bladder overactivity. This underscores the advantage of viewing the bladder as a chemosensory organ and prompts for further clinical research. However, ethical issues severely limit the possibilities to perform, in human subjects, the invasive measurements that are necessary to unravel the molecular bases of LUT clinical pharmacology. A way to overcome this limitation is the use of several animal models. Here we describe the implementation of cystometry in mice and rats, a technique that allows measuring the intravesical pressure in conditions of controlled bladder perfusion. After laparotomy, a catheter is implanted in the bladder dome and tunneled subcutaneously to the interscapular region. Then the bladder can be filled at a controlled rate, while the urethra is left free for micturition. During the repetitive cycles of filling and voiding, intravesical pressure can be measured via the implanted catheter. As such, the pressure changes can be quantified and analyzed. Moreover, simultaneous measurement of the voided volume allows distinguishing voiding contractions from non-voiding contractions. Importantly, due to the differences in micturition control between rodents and humans, cystometric measurements in these animals have only limited translational value. Nevertheless, they are quite instrumental in the study of bladder pathophysiology and pharmacology in experimental pre-clinical settings. Recent research using this technique has revealed the key role of novel molecular players in the mechano- and chemo-sensory properties of the bladder.

Rodent models for urodynamic investigation

Rodents, most commonly rats, mice, and guinea pigs are widely used to investigate urinary storage and voiding functions, both in normal animals and in models of disease. An often used methodology is cystometry. Micturitions in rodents and humans differ significantly and this must be considered when cystometry is used to interpret voiding in rodent models. Cystometry in humans requires active participation of the investigated patient (subject), and this can for obvious reasons not be achieved in the animals. Cystometric parameters in rodents are often poorly defined and do not correspond to those used in humans. This means that it is important that the terminology used for description of what is measured should be defined, and that the specific terminology used in human cystometry should be avoided. Available disease models in rodents have limited translational value, but despite many limitations, rodent cystometry may give important information on bladder physiology and pharmacology. The present review discusses the principles of urodynamics in rodents, techniques, and terminology, as well as some commonly used disease models, and their translational value.

Functional roles of TRPV1 channels in lower urinary tract irritated by acetic acid: in vivo evaluations of the sex difference in decerebrate unanesthetized mice

Sex-specific differences in activity of the lower urinary tract (LUT) responding to acid irritation in mice have been revealed. This study, using continuous infusion cystometry with acetic acid (AA; pH 3.0), was conducted to examine whether the transient receptor potential vanilloid type 1 (TRPV1) channels expressed in the mouse LUT are involved in the sex difference in functional responses of the bladder and urethra to irritation. No differences were found between effects of capsazepine (a TRPV1 blocker; 100 μM) and those of its vehicle on any of the cystometric changes by intravesical AA in either female or male mice. However, capsazepine eliminated the acid-induced sex differences in parameters associated with bladder contraction phase (i.e., maximal voiding pressure, closing peak pressure, 2nd-phase contraction, bladder contraction duration), whereas capsazepine did not affect those in parameters associated with bladder-filling period (i.e., intercontraction interval, actual collecting time). In males, capsazepine reduced the number of bladder contractions accompanying fluid dribbling at 2nd-phase contraction, which is indicative of the urethral response to irritation, whereas in females it increased the number. Together, these results suggest the possibilities that TRPV1 channels in the bladder and urethra are involved in the sex difference in the LUT response to acid irritation and that these participate, e.g., via “cross talk” between the bladder and urethra, in the fine-tuning of intravesical pressure (or bladder emptying) at the bladder contraction phase under irritated LUT conditions but not in sensing for bladder filling during the storage period, although the contribution of the mechanism may be small.

Sex differences in the expression profile of acid-sensing ion channels in the mouse urinary bladder: a possible involvement in irritative bladder symptoms

OBJECTIVE

To investigate the expressions and sex differences of acid-sensitive ion channels (i.e. ASIC and transient receptor potential channel V1, TRPV1; both key receptors for extracellular protons that might underlie the acid-evoked pain perception) and other nociceptive ion channels in the mouse bladder.

MATERIALS AND METHODS

Mucosa and muscle layers of the urinary bladder were separately taken from male and female mice. The gene expressions of ASIC subunits, TRPV1, TRPA1 and TRPM8 were quantified using real-time reverse transcriptase-polymerase chain reaction. The localization of ASIC protein was explored using immunohistochemistry. Continuous-filling cystometry was used to examine the effects of capsazepine, a TRPV1 blocker, on the bladder response to acetic acid.

RESULTS

ASIC1 was the dominant ASIC subunit expressed in bladder epithelium, whereas both ASIC1 and ASIC2 were expressed in bladder smooth muscle. ASIC3 expression was much less abundant, but localized in the subepithelial region. In the mucosa, the ASIC1 gene was more highly expressed in male than in female mice, whereas the expression level of ASIC2 in the bladder muscle was higher in female than in male mice. The expression of TRPV1 in the bladder showed a sex difference (male < female), but it was much lower than ASIC genes. Furthermore, the intravesical administration of 100 microm capsazepine showed no effect on bladder irritation by acetic acid. TRPA1 and TRPM8 did not show sex differences in their expression.

CONCLUSION

The expression of ASIC subunit in the bladder was abundant and showed significant sex differences. Thus, ASICs might be involved in the sex difference in the bladder response to acidic irritation.