Detrusor expulsive strength is preserved, but responsiveness to bladder filling and urinary sensitivity is diminished in the aging mouse

The prevalence of urinary symptoms increases with age and is a significant source of distress, morbidity, and expense in the elderly. Recent evidence suggests that symptoms in the aged may result from sensory dysfunction, rather than abnormalities of detrusor performance. Therefore, we employed a pressure/flow multichannel urethane-anesthetized mouse cystometry model to test the hypothesis that in vivo detrusor performance does not degrade with aging. Secondarily, we sought to evaluate sensory responsiveness to volume using pressure-volume data generated during bladder filling. Cystometric data from 2-, 12-, 22-, and 26-mo-old female C57BL6 mice were compared. All 2- and 12-mo-old mice, 66% of 22-mo-old mice, and 50% of 26-mo-old mice responded to continuous bladder filling with periodic reflex voiding. Abdominal wall contraction with voiding had a minimal contribution to expulsive pressure, whereas compliance pressure was a significant contributor. Maximum bladder pressure, estimated detrusor pressure, detrusor impulse (pressure-time integral), as well as indices of detrusor power and work, did not decrease with aging. Bladder precontraction pressures decreased, compliance increased, and nonvoiding contraction counts did not change with increasing age. Intervoid intervals, per-void volumes, and voiding flow rates increased with age. Calculations approximating wall stress during filling suggested loss of bladder volume sensitivity with increasing age. We conclude that aging is associated with an impaired ability to respond to the challenge of continuous bladder filling with cyclic voiding, yet among responsive animals, voiding detrusor contraction strength does not degrade with aging in this murine model. Furthermore, indirect measures suggest that bladder volume sensitivity is diminished. Thus, changes in homeostatic reserve and peripheral and/or central sensory mechanisms may be important contributors to aging-associated changes in bladder function.     

Quantifying whole bladder biomechanics using the novel pentaplanar reflected image macroscopy system

Optimal bladder compliance is essential to urinary bladder storage and voiding functions. Calculated as the change in filling volume per change in pressure, bladder compliance is used clinically to characterize changes in bladder wall biomechanical properties that associate with lower urinary tract dysfunction. But because this method calculates compliance without regard to wall structure or wall volume, it gives little insight into the mechanical properties of the bladder wall during filling. Thus, we developed Pentaplanar Reflected Image Macroscopy (PRIM): a novel ex vivo imaging method to accurately calculate bladder wall stress and stretch in real time during bladder filling. The PRIM system simultaneously records intravesical pressure, infused volume, and an image of the bladder in five distinct visual planes. Wall thickness and volume were then measured and used to calculate stress and stretch during filling. As predicted, wall stress was nonlinear; only when intravesical pressure exceeded ~ 15 mmHg did bladder wall stress rapidly increase with respect to stretch. This method of calculating compliance as stress vs stretch also showed that the mechanical properties of the bladder wall remain similar in bladders of varying capacity. This study demonstrates how wall tension, stress and stretch can be measured, quantified, and used to accurately define bladder wall biomechanics in terms of actual material properties and not pressure/volume changes. This method is especially useful for determining how changes in bladder biomechanics are altered in pathologies where profound bladder wall remodeling occurs, such as diabetes and spinal cord injury.

     

Hypercompliant Apical Membranes of Bladder Umbrella Cells

Urinary bladder undergoes dramatic volume changes during filling and voiding cycles. In the bladder the luminal surface of terminally differentiated urothelial umbrella cells is almost completely covered by plaques. These plaques (500 to 1000 nm) are made of a family of proteins called uroplakins that are known to form a tight barrier to prevent leakage of water and solutes. Electron micrographs from previous studies show these plaques to be interconnected by hinge regions to form structures that appear rigid, but these same structures must accommodate large changes in cell shape during voiding and filling cycles. To resolve this paradox, we measured the stiffness of the intact, living urothelial apical membrane and found it to be highly deformable, even more so than the red blood cell membrane. The intermediate cells underlying the umbrella cells do not have uroplakins but their membranes are an order of magnitude stiffer. Using uroplakin knockout mouse models we show that cell compliance is conferred by uroplakins. This hypercompliance may be essential for the maintenance of barrier function under dramatic cell deformation during filling and voiding of the bladder.     

Hypercompliant Apical Membranes of Bladder Umbrella Cells

Urinary bladder undergoes dramatic volume changes during filling and voiding cycles. In the bladder the luminal surface of terminally differentiated urothelial umbrella cells is almost completely covered by plaques. These plaques (500 to 1000 nm) are made of a family of proteins called uroplakins that are known to form a tight barrier to prevent leakage of water and solutes. Electron micrographs from previous studies show these plaques to be interconnected by hinge regions to form structures that appear rigid, but these same structures must accommodate large changes in cell shape during voiding and filling cycles. To resolve this paradox, we measured the stiffness of the intact, living urothelial apical membrane and found it to be highly deformable, even more so than the red blood cell membrane. The intermediate cells underlying the umbrella cells do not have uroplakins but their membranes are an order of magnitude stiffer. Using uroplakin knockout mouse models we show that cell compliance is conferred by uroplakins. This hypercompliance may be essential for the maintenance of barrier function under dramatic cell deformation during filling and voiding of the bladder.     

Sexually dimorphic micturition in rats: relationship of perineal muscle activity to voiding pattern

In the present study we examined the possibility that striated muscle activity may underlie sexually dimorphic micturition in rats. Micturition dynamics, the gross anatomy of the external urethral sphincter, and the participation of the striated perineal muscles in micturition were compared in urethane-anesthetized adult male and female rats. Bladder contraction characteristics, particularly the magnitude of bladder high-frequency pressure waves during voiding, differed between sexes. Dissections indicated that the sphincter was more extensive and thicker in males than in females. Electromyography showed that in both sexes the sphincter discharged in bursts that correlated with the rising phase of high-frequency bladder pressure oscillations. Regional differences in discharge pattern were seen in the sphincters of males, with the proximal part of the sphincter showing components activated during bladder filling. Bulbospongiosus, ischiocavernosus, and cremaster muscles also were activated during bladder contraction in males. In both sexes transection of the motor branch of the lumbosacral plexus eliminated the bladder high-frequency oscillations and reduced voided volume. Neurectomy did not affect bladder pressure but reduced voiding efficiency by 45% in males. In females the bladder pressure was dramatically decreased, but voiding efficiency only decreased by 24%. Our findings suggest that, in rats, striated perineal muscles contribute to the sexually dimorphic micturition. Activity of the dimorphic perineal muscles may regulate genital and urinary urethra expulsive functions, helping to expel seminal plug and fluids through the long urethra in the male.     

Effect of naftopidil,an alpha1D/A-adrenoceptor antagonist,on the urinary bladder in rats with spinal cord injury

AimsAlpha_1D-adrenoceptors (α_1D-ARs) located in the spinal cord are involved in the control of lower urinary tract function. In order to clarify the effect of α_1D-ARs on storage function in the spinal cord, we examined the effect of oral administration and intrathecal injection of the α_1D/A-AR antagonist, naftopidil, on bladder activity, as well as the effect of naftopidil on bladder wall histology, in female rats with spinal cord injury (SCI).Main methodsAdult female Sprague–Dawley rats with Th9–10 spinal cord transection were used. In SCI rats with or without 5 mg/day of naftopidil for 4 weeks, bladder activity was examined via continuous cystometry. In other SCI rats, bladder activity was examined before and after intrathecal injection of naftopidil. In addition, bladder wall histology was compared between SCI rats with or without oral administration of naftopidil for 4 weeks.Key findingsOral administration of naftopidil decreased the number of non-voiding contractions (NVCs). Intrathecal injection of naftopidil prolonged the interval between voiding contractions, decreased the maximum voiding contraction pressure and the number of NVCs, and increased bladder capacity without affecting the residual urine volume. Oral administration of naftopidil also decreased bladder wall fibrosis.SignificanceThe α_1D/A-AR antagonist naftopidil might act on the bladder and spinal cord to improve detrusor hyperreflexia in the storage state in SCI female rats. Naftopidil also suppressed bladder wall fibrosis, suggesting that it may be effective for the treatment of neurogenic lower urinary tract dysfunction after SCI.     

Evaluation of voiding dysfunction and measurement of bladder volume

When evaluating patients with voiding dysfunction, noninvasive tests such as uroflowmetry and measurement of postvoid residual urine volume (PVR) can help to determine whether additional testing is warranted. PVR can be measured by 2 methods: catheterization or bedside bladder ultrasonography. Although both methods have advantages, the convenience, efficiency, and safety of bladder ultrasound makes its use beneficial in a wide variety of populations, including hospitalized patients, children, and the elderly. More recently, bladder ultrasound has been used for other procedures, such as suprapubic aspiration, evaluation of intravesical masses, and to determine bladder wall thickness and bladder wall mass, both of which have been associated with outflow obstruction.     

MRI image-based FE modelling of the pelvis system and bladder filling

In this study, high-resolution magnetic resonance imaging was performed in the transaxial, coronal and sagittal planes to provide comprehensive structural details of the bladder and surrounding systems. Detailed finite-element (FE) models that were specific to each participant were developed by rendering the images, and the process of bladder filling was simulated. The overall model of bladder deformation was compared with repeated images of the filled bladder that were obtained using computed tomography to validate the FE models. The relationship between the changes in the key dimensions of the bladder and the increase in bladder volume during the filling process was also investigated. The numerical results showed that the bladder dimensions increased linearly with its volume during the filling process and the predicted coefficients are comparable to some of the published clinical results.     

Modulation of the visceromotor reflex by a lumbosacral ventral root avulsion injury and repair in rats

Increased abdominal muscle wall activity may be part of a visceromotor reflex (VMR) response to noxious stimulation of the bladder. However, information is sparse regarding the effects of cauda equina injuries on the VMR in experimental models. We studied the effects of a unilateral L6-S1 ventral root avulsion (VRA) injury and acute ventral root reimplantation (VRI) into the spinal cord on micturition reflexes and electromyographic activity of the abdominal wall in rats. Cystometrogram (CMG) and electromyography (EMG) of the abdominal external oblique muscle (EOM) were performed. All rats demonstrated EMG activity of the EOM associated with reflex bladder contractions. At 1 wk after VRA and VRI, the duration of the EOM EMG activity associated with reflex voiding was significantly prolonged compared with age-matched sham rats. However, at 3 wk postoperatively, the duration of the EOM responses remained increased in the VRA series but had normalized in the VRI group. The EOM EMG duration was normalized for both VRA and VRI groups at 8-12 wk postoperatively. CMG recordings show increased contraction duration at 1 and 3 wk postoperatively for the VRA series, whereas the contraction duration was only increased at 1 wk postoperatively for the VRI series. Our studies suggest that a unilateral lumbosacral VRA injury results in a prolonged VMR to bladder filling using a physiological saline solution. An acute root replantation decreased the VMR induced by VRA injury and provides earlier sensory recovery.     

Pressure overload alters stress-strain properties of the developing chick heart

As a first step in investigating a control mechanism regulating stress and/or strain in the embryonic heart, this study tests the hypothesis that passive mechanical properties of left ventricular (LV) embryonic myocardium change with chronically increased pressure during the chamber septation period. Conotruncal banding (CTB) created ventricular pressure overload in chicks from Hamburger-Hamilton (HH) stage 21 (HH21) to HH27, HH29, or HH31. LV sections were cyclically stretched while biaxial strains and force were measured. Wall architecture was assessed with scanning electron microscopy. In controls, porosity-adjusted stress-strain relations decreased significantly from HH27 to HH31. CTB at HH21 resulted in significantly stiffer stress-strain relations by HH27, with larger increases at HH29 and HH31, and nearly constant wall thickness. Strain patterns, hysteresis, and loading-curve convergence showed few differences after CTB. Trabecular extent decreased with age, but neither extent nor porosity changed significantly after CTB. The stiffened stress-strain relations and constant wall thickness suggest that mechanical load may play a regulatory role in this response.     

Adjustable passive stiffness in mouse bladder: regulated by Rho kinase and elevated following partial bladder outlet obstruction

Detrusor smooth muscle (DSM) contributes to bladder wall tension during filling, and bladder wall deformation affects the signaling system that leads to urgency. The length-passive tension (L-T(p)) relationship in rabbit DSM can adapt with length changes over time and exhibits adjustable passive stiffness (APS) characterized by a L-T(p) curve that is a function of both activation and strain history. Muscle activation with KCl, carbachol (CCh), or prostaglandin E(2) at short muscle lengths can increase APS that is revealed by elevated pseudo-steady-state T(p) at longer lengths compared with prior T(p) measurements at those lengths, and APS generation is inhibited by the Rho Kinase (ROCK) inhibitor H-1152. In the current study, mouse bladder strips exhibited both KCl- and CCh-induced APS. Whole mouse bladders demonstrated APS which was measured as an increase in pressure during passive filling in calcium-free solution following CCh precontraction compared with pressure during filling without precontraction. In addition, CCh-induced APS in whole mouse bladder was inhibited by H-1152, indicating that ROCK activity may regulate bladder compliance during filling. Furthermore, APS in whole mouse bladder was elevated 2 wk after partial bladder outlet obstruction, suggesting that APS may be relevant in diseases affecting bladder mechanics. The presence of APS in mouse bladder will permit future studies of APS regulatory pathways and potential alterations of APS in disease models using knockout transgenetic mice.     

Ex vivo deformations of the urinary bladder wall during whole bladder filling: Contributions of extracellular matrix and smooth muscle

As the complete understanding of urinary bladder function requires knowledge of organ level deformations, we conducted ex vivo studies of surface strains of whole bladders during controlled filling. The surface strains derived from displacements of surface markers applied to the posterior surface of excised rat bladders were tracked under slow filling with pressure and volume simultaneously recorded in the passive and completely inactivated states (i.e. with and without smooth muscle tone, respectively). Bladders evaluated in the passive state exhibited spontaneous contractions and larger average peak pressures (16.7 mmHg compared to 6.4 mmHg in the inactive state). Overall, the bladders exhibited anisotropic deformations and were stiffer in the circumferential direction, with average peak stretch values of ～2.3 and ～1.9 in the longitudinal and circumferential directions, respectively, for both states. Although bladders in the passive state were stiffer, they had similar average peak areal stretches of 4.3 in both states. However, differences early in the filling process as a result of a loss in smooth muscle tone in the inactive state resulted in longitudinal lengthening of 36%. Idealizing the bladder as a prolate spheroid, we estimated the wall stress–strain relation during filling and demonstrated that the intact bladder exhibited the classic stress–stretch relation, with a significantly protracted low stress region and peak stresses of 36 and 51 kPa in the longitudinal and circumferential directions, respectively. The present study fills a major gap in the urinary bladder biomechanics literature, wherein knowledge of the pressure–volume–wall stress–wall strain relation was explored for the first time in a functioning organ ex vivo.     

Electrostimulation: a future treatment option for patients with neurogenic urodynamic disorders?

This paper provides an overview of electrical stimulation of the nervous system as a treatment option for urodynamic dysfunction and of some of the recent results in this field. The set-up used in our studies for improved bladder filling in spinal cord injured patients by conditional stimulation of the dorsal penile/clitoral nerve is a highly efficient way to limit neurogenic detrusor overactivity and increase bladder capacity. Ongoing studies suggest that recording of bladder nerve activity is stable over time and may be a technique for chronic monitoring of bladder activity. Bladder emptying exploiting an anodal blocking technique permits bladder emptying without simultaneous urethral-perineal contraction, thus enabling a physiological voiding pattern in one continuous sequence. In patients with supraspinal lesions, deep brain electrical stimulation is established only as treatment for a subgroup of patients suffering from Parkinson's disease. Yet, with improved electrode designs and increased clinical experience and experimental results, probably other groups of patients may be candidates for deep brain stimulation. In our study in pigs there was a trend towards increased bladder capacity and compliance in response to stimulation, which is encouraging as several neurological diseases are accompanied by overactive bladder with reduced capacity.     

Mechanical analysis of the development of left ventricular aneurysms

The left ventricle is modelled as a spherical shell with an infarcted wall segment. The mechanics of the circumstances causing this infarcted segment to develop into an aneurysm is presented. Both the wall stresses and deformations are worked out for aneurysms developing from infarcts of different sizes and percentages of wall damage. The governing equations consist of incompressibility relations, force-equilibrium relations and stress-strain relations. Newton Raphson technique is used to solve these nonlinear simultaneous algebraic equations, for the values of the myocardial stresses in the infarcted segment and the bulge values, in terms of the ventricular geometry and the damage extent (expressed in terms of the damage angle and percentage of wall damage). The results indicate that in general it is innermost layer which is severely stressed and that in the rupture of the ventricle the critical factor involved is the percentage of infarct thickness rather than the angle of damage.     

Changes in the rheological properties of blood vessel tissue remodeling in the course of development of diabetes.

Rheological properties of blood vessels are expected to change in disease process if the structure of the vessel wall changes. This is illustrated in diabetes, which can be induced in rat by a single injection of Streptozocin. One of the rheological properties of the blood vessel is the stress-strain relationship. The nonlinear stress-strain relationship of arteries is best expressed as derivations of a strain-energy function. In this paper, the stress-strain relations are measured and the coefficients in the strain energy function of arteries are determined for diabetic and control rats. The meaning of these coefficients are explained. The influence of diabetes on the elastic property of the arteries is expressed by the changes of these coefficients. A point of departure of the present paper from all other blood vessel papers published so far is that all strains used here are referred to the zero-stress state of the arteries, whereas all other papers refer strains to the no-load state. The existence of a large difference between the zero-stress state and no-load state of arteries is one of our recent findings. We have explained that the use of zero-stress state as a basis of strain measurements reveals that the in vivo circumferential stress distribution is quite uniform in the vessel wall at the homeostatic condition. It also makes the strain energy function much more accurate than those in which the residual stress is ignored. Using these new results, the stress and strain distribution in normal and diabetic arteries are presented.     

Role of pudendal afferents in voiding efficiency in the rat

The reciprocal activities of the bladder and external urethral sphincter (EUS) are coordinated by descending projections from the pontine micturition center but are subjected to modulation by peripheral afferent inputs. Transection of the somatic pudendal nerve innervating the striated EUS decreases voiding efficiency and increases residual urine in the rat. The reduction in voiding efficiency was attributed to the lack of phasic bursting activity of the EUS following denervation. However, transection of the pudendal nerve also eliminates somatic sensory feedback that may play a role in voiding. We hypothesized that feedback from pudendal afferents is required for efficient voiding and that the loss of pudendal sensory activity contributes to the observed reduction in voiding efficiency following pudendal nerve transection. Quantitative cystometry in urethane anesthetized female rats following selective transection of pudendal nerve branches, following chemical modulation of urethral afferent activity, and following neuromuscular blockade revealed that pudendal nerve afferents contributed to efficient voiding. Sensory feedback augmented bladder contraction amplitude and duration, thereby increasing the driving force for urine expulsion. Second, sensory feedback was necessary to pattern appropriately the EUS activity into alternating bursts and quiescence during the bladder contraction. These findings demonstrate that the loss of pudendal sensory activity contributes to the reduction in voiding efficiency observed following pudendal nerve transection, and illustrate the importance of urethral sensory feedback in regulating bladder function.     

Aging and urinary control: Alterations in the brain–bladder axis

Age-associated alterations in bladder control affect millions of older adults, with a heavy burden added to families both economically and in quality of life. Therapeutic options are limited with poor efficacy in older adults, lending to a growing need to address the gaps in our current understanding of urinary tract aging. This review summarizes the current knowledge of age-associated alterations in the structure and function of the brain–bladder axis and identifies important gaps in the field that have yet to be addressed. Urinary aging is associated with decreased tissue responsiveness, decreased control over the voiding reflex, signaling dysfunction along the brain–bladder axis, and structural changes within the bladder wall. Studies are needed to improve our understanding of how age affects the brain–bladder axis and identify genetic targets that correlate with functional outcomes.     

Urinary bladder function in conscious rat pups: a developmental study

Cystometric studies of bladder function in anesthetized neonatal rats have suggested specific changes in urodynamic parameters that coincide with the development of a mature bladder-to-bladder micturition reflex. Here, we used a conscious cystometry model that avoids the potentially confounding effects of anesthesia to characterize voiding patterns and urodynamic parameters during early postnatal development in healthy rat pups. Cystometry was performed on postnatal day (P)0, 3, 7, 14, and 21 rats with continuous intravesical instillation of NaCl via a bladder catheter. Micturition cycles were analyzed with respect to voiding pattern, nonvoiding contractions, infused volume, and basal, filling, threshold, and micturition pressures. Reproducible micturition patterns were obtained from all age groups. The time from stimulation to contraction was significantly longer (P ≤ 0.001) in ≤1-wk-old rats (～10 s) than that in older rats (～3 s). An interrupted voiding pattern was observed in ≤10-day-old subgroups. Micturition pressure progressively increased with age (from 21.77 ± 1.92 cmH(2)O at P0 to 35.47 ± 1.28 cmH(2)O at P21, P ≤ 0.001), as did bladder capacity. Nonvoiding contractions were prominent in the P3 age group (amplitude: 4.6 ± 1.3 cmH(2)O, frequency: ～4.0 events/100 s). At P7, the pattern of spontaneous contractions became altered, acquiring a volume-related character that persisted in a less prominent manner through P21. Bladder compliance increased with age, i.e., maturation. In conclusion, conscious cystometry in rat pups resulted in reproducible micturition cycles that yielded consistent data. Our results revealed immature voiding and prolonged micturition contractions during the first 10 neonatal days and provide evidence for age-related changes in urodynamic parameters.     

The motion of the left ventricle—III

We use the concept of a layered wall, where each separate layer is to be homogeneous, isotropic, and incompressible, to derive stress-strain relations for the middle layer muscle ring at the transverse midsection of the left ventricle; a convenient method of formulation is that based on the elastic potential function. The hoop or circumferential stress in all three layers is found using dimensional and mechanical parameters derived earlier. The various parameters are expressed as Fourier series so that their behavior over a complete ventricular cycle is known analytically. The cases of simple elongation and what we termcurvilinear simple elongation are considered for the middle layer muscle ring strain, and the resulting stress-strain relations are derived. The results are compared with an incompressible rubber-like material known as a Mooney material.     

The influence of ovariectomy and estrogen replacement on voiding patterns and detrusor muscarinic receptor affinity in the rat

A rat model of ovariectomy-induced voiding dysfunction was established and the effects of ovariectomy and subsequent estrogen replacement on the affinity of muscarinic receptors in the rat bladder were determined. Voiding frequency and spatial distribution patterns were documented in sham-operated (control), and ovariectomized (placebo- or estrogen-treated) rats. The ovariectomized rats had a significantly different urinating pattern, i.e. higher voiding frequency and less peripheral voiding than the sham-operated group, suggestive of urge incontinence. Using this model of voiding dysfunction, negative logs of dissociation constants of carbachol of the rat detrusor muscarinic receptors were then determined indirectly using the Furchgott's double-reciprocal method. Receptor affinities were not significantly different in all groups compared to control females. In conclusion, a model of ovariectomy-induced voiding dysfunction in ovariectomized rats was established, where bladder dysfunction occurred with no significant changes in the affinity of muscarinic receptors.