Neurophysiology of micturition and continence

Clarification of the Innervation of the Bladder, External Urethral Sphincter and Clitoris: A Neuronal Tracing Study in Female Mongrel Hound Dogs

Many studies examining the innervation of genitourinary structures focus on either afferent or efferent inputs, or on only one structure of the system. We aimed to clarify innervation of the bladder, external urethral sphincter (EUS) and clitoris. Retrograde dyes were injected into each end organ in female dogs. Spinal cord, mid-bladder, and spinal, caudal mesenteric, sympathetic trunk and pelvic plexus ganglia were examined for retrograde dye-labeled neurons. Neurons retrogradely labeled from the bladder were found primarily in L7-S2 spinal ganglia, spinal cord lateral zona intermedia at S1-S3 levels, caudal mesenteric ganglia, T11-L2 and L6-S2 sympathetic trunk ganglia, and pelvic plexus ganglia. The mid-bladder wall contained many intramural ganglia neurons labeled anterogradely from the pelvic nerve, and intramural ganglia retrogradely labeled from dye labeling sites surrounding ureteral orifices. Neurons retrogradely labeled from the clitoris were found only in L7 and S1 spinal ganglia, L7-S3 spinal cord lateral zona intermedia, and S1 sympathetic trunk ganglia, and caudal mesenteric ganglia. Neurons retrogradely labeled from the EUS were found in primarily at S1 and S2 spinal ganglia, spinal cord lamina IX at S1-S3, caudal mesenteric ganglia, and S1-S2 sympathetic trunk ganglia. Thus, direct inputs from the spinal cord to each end organ were identified, as well as multisynaptic circuits involving several ganglia, including intramural ganglia in the bladder wall. Knowledge of this complex circuitry of afferent and efferent inputs to genitourinary structures is necessary to understand and treat genitourinary dysfunction. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

Neurogenic mechanisms in bladder and bowel ageing

The prevalence of both urinary and faecal incontinence, and also chronic constipation, increases with ageing and these conditions have a major impact on the quality of life of the elderly. Management of bladder and bowel dysfunction in the elderly is currently far from ideal and also carries a significant financial burden. Understanding how these changes occur is thus a major priority in biogerontology. The functions of the bladder and terminal bowel are regulated by complex neuronal networks. In particular neurons of the spinal cord and peripheral ganglia play a key role in regulating micturition and defaecation reflexes as well as promoting continence. In this review we discuss the evidence for ageing-induced neuronal dysfunction that might predispose to neurogenic forms of incontinence in the elderly.

Neural control of lower urinary tract and targets for pharmacological therapy

Studies on the physiology and pharmacology of the lower urinary tract have brought new information and concepts about the complex neural control of micturition. There are many mechanisms, some proven and others not yet completely understood, in which pharmacological agents may act facilitating the filling, storage, and emptying of the bladder. This review describes the peripheral innervation and the main pathways involved in lower urinary tract control. It also presents potential targets for the treatment of voiding dysfunctions.

Serious periventricular white matter injury has a significant effect on the voiding pattern of preterm infants

AIM

To evaluate the effect of serious periventricular white matter injury (PWMI) on the voiding patterns of preterm infants.

METHODS

Free voiding was continuously observed for eight hours in 19 preterm infants with serious PWMI and 16 infants without PWMI. The infants had a gestational age of 32-35 weeks and a postnatal age of 9-15 days. Voiding frequency, voided volume, postvoid residual volume, empty voiding, awake voiding and interrupted voiding were recorded and compared between the two groups of infants.

RESULTS

The voiding frequency ((5.1 ± 1.0) vs. (7.0 ± 1.1)), awake voiding percentage ((23 ± 11)% vs. (42 ± 7)%) and empty voiding percentage (lower quartile = 16% vs. 28%, median = 20% vs. 33%, upper quartile = 28% vs. 40%) were significantly lower, while the voided volume ((19.9 ± 6.6) mL vs.(15.9 ± 5.3) mL)and postvoid residual volume (lower quartile = 1 mL. vs. 0 mL., median = 3 mL. vs. 2 mL., upper quartile = 3 mL. vs. 2 mL.) were significantly higher in the injured preterm infants, compared with the healthy infants (p < 0.05).

CONCLUSION

Serious PWMI has a significant effect on the voiding pattern of preterm infants, and the senior nerve centre plays a role in the voiding reflex of preterm infants.

Urethral flow-responsive afferents in the cat sacral dorsal root ganglia

Although sensory feedback from the urethra plays an integral role in the regulation of lower urinary tract function, little is known about the properties of flow-responsive primary afferent neurons. The purpose of this study was to characterize the activity of sacral afferents that responded to fluid flow through the urethra. Single neuron action potentials were recorded extracellularly from the S1 and S2 dorsal root ganglia in eight cats anesthetized with α-chloralose. 21 of 116 cells responded to urethral flow but not to mechanical palpation of the perineum, 22 responded to both urethral flow and palpation, and 27 responded to palpation only. 34 of the 43 flow-responsive cells exhibited a firing response to 10 ml flow boluses that could be fit using a power function: FR(t)=a×(t)(b)+c, where FR is firing rate, t is time, and a, b and c are constants. In all 34 cells the 'b' term was negative, indicating that the firing rate slowed over the time course of the urethral flow. In 16 of the 24 cells that were recorded during at least four different flow rates, a power function provided a good fit of the relationship between firing rate and flow rate: FR(flow)=k×(flow)(p)+q, where k, p and q are constants. In each of these 16 cells the 'p' term was positive, indicating that the firing rate tended to increase with increases in flow rate. These are the first data to characterize the properties of flow-responsive afferents in the cat, and reveal properties that parallel those of other afferents.

Mechanisms of action of sacral neuromodulation

The lower urinary tract dysfunction encompasses voiding, postvoiding, and storage symptoms. Conventional treatment modalities include pharmacotherapy and behavioural therapy. Sacral neuromodulation (SNM) is a safe and minimally invasive treatment modality that has recently gained wide acceptance in the management of urinary urge incontinence, urge frequency, and nonobstructive urinary retention, in particular, among those patients with conditions refractory to conventional methods. We searched multiple electronic databases through June 30, 2009 for eligible studies. We examined published clinical and experimental studies concerning the mechanisms of action of SNM. In the first part of the manuscript, we describe the anatomy and functions of the lower urinary tract including the reflexes involved in its functions and then review the pathophysiology of major types of the lower urinary tract dysfunction. In the second part, we discuss different ways for SNM to control various types of voiding dysfunction. The lower urinary tract dysfunctions affect millions of people worldwide and have a severe impact on their quality of life. SNM offers a safe and minimally invasive modality in the treatment of voiding dysfunctions, especially in patients with conditions refractory to conventional therapies.

A guide to continence assessment for community nurses

Problems with continence are common in older people, therefore quality continence assessment advice and follow up are essential in providing a high standard of care. Many older people can be helped to regain some measure of control over their continence. Continence assessment can often focus on containment rather than cure. This is a sad state of affairs which adversely affects patients' well being. This article explains how continence assessment enables the nurse to assess and treat continence issues and improve quality of life.

Sacral neuromodulation in lower urinary tract dysfunction

Vesico-urethral dysfunction is a major problem in daily medical practice due to its psychological disturbances, its social costs and its high impact on quality of life. Recently, sacral neuromodulation, namely the electrical stimulation of the sacral nerves, appears to have become an alternative for radical bladder surgery particularly in cases of idiopathic bladder overactivity. The mechanism of action is only partially understood but it seems to involve a modulation in the spinal cord due to stimulation of inhibitory interneurons. Temporary sacral nerve stimulation is the first step. It comprises the temporary application of neuromodulation as a diagnostic test to determine the best location for the implant and to control the integrity of the sacral root. If test stimulation is successful, a permanent device is implanted. This procedure is safe in experienced hands. So-called idiopathic bladder overactivity still the major indication for this technique. Patients not likely to benefit from the procedure were those with complete or almost complete spinal lesions, but incomplete spinal lesions seemed to be a potential indication. This technique is now also indicated in the case of idiopathic chronic retention and chronic pelvic pain syndrome. When selection is performed, more than three-quarters of the patients showed a clinically significant response with 50% or more reduction in the frequency of incontinent episodes, but the results vary according to the author's mode of evaluation. From the economic point of view, the initial investment in the device is amortized in the mid-term by savings related to lower urinary tract dysfunction. Finally, this technique requires an attentive follow-up and adjustments to the electric parameters so as to optimize the equilibrium between the neurological systems.

Agrin becomes concentrated at neuroeffector junctions in developing rodent urinary bladder

The formation of somatic neuromuscular junctions in skeletal muscle is regulated by an extracellular matrix protein called agrin. Here, we have examined the expression and localization of agrin during development of the rodent urinary bladder, as a first step to examining its possible role at autonomic neuroeffector junctions in smooth muscle. We have found that agrin is expressed on the surface of developing smooth muscle cells and in the basement membrane underlying the urothelium. More importantly, agrin is progressively concentrated at parasympathetic varicosities during postnatal development and is present at virtually all junctions in mature muscle. Reverse transcription/polymerase chain reaction analysis has shown that pelvic ganglion neurons that innervate the bladder express LN/z8 agrin, whereas bladder smooth muscle expresses LN/z- agrin. Together, these results demonstrate that nerve and/or muscle agrin becomes localized at cholinergic parasympathetic varicosities in smooth muscle, where it could play a role in the maturation of the neuroeffector junction.

Bladder-anal reflex

AIMS

The purposes of this study were to evaluate the bladder-anal reflex (BAR) latency in asymptomatic women and determine the pathway of the reflex using selective anesthesia and neuromuscular block.

METHODS

Urinary incontinence, voiding dysfunction, and pelvic organ prolapse are common problems in women. Evaluation of pelvic nerve function often augments the clinical assessment of these women. Urethral-anal and clitoral-anal reflex testing have been reported as methodologies to assess patients with neurogenic disorders. A bladder-anal reflex is also obtainable but has not been reported previously in the literature. Twenty-two subjects and two patients were recruited for evaluation of the BAR.

RESULTS

This study has allowed us to estimate reference ranges for BAR latency and threshold. We defined the upper limit of these reference ranges as two standard deviations above their respective means. For the BAR latency, the upper limit of the reference range is 91 msec. Any latency value above this limit should be considered abnormal. The upper limit for the BAR threshold reference range is 37.7 mA. Lower thresholds are not thought to be clinically meaningful due to the presence of several low sensory thresholds in this asymptomatic normal population.

CONCLUSIONS

The BAR was obtainable in asymptomatic women and compatible with known anatomy and innervation of the lower urinary tract.

Urinary symptoms in Parkinson's disease: prevalence and associated factors

The authors present a cross-sectional study involving 61 patients with idiopathic Parkinson's disease (PD) who were consecutively examined and compared to a control group with 74 subjects. Only patients who fulfilled the standard diagnostic criteria for PD and whose brain magnetic resonance imaging was normal were included. The objective of the study was to evaluate the prevalence of inferior urinary tract symptoms in PD and to study the possible association between clinical factors to urinary dysfunction. ln the patient group, 39.3% presented urinary symptoms when compared to 10.8% in the control group. All symptomatic patients presented irritative symptoms. The most common irritative symptom PD was nocturia, followed by frequency and urinary incontinence. Around 25% of the patients presented functional obstructive symptoms determined by the disease. The most frequent obstructive symptom was incomplete emptying of the bladder. Only the age of the patients and control group were correlated with urinary dysfunction.

Separate urinary bladder and external urethral sphincter neurons in the central nervous system of the rat: simultaneous labeling with two immunohistochemically distinguishable pseudorabies viruses

This work examines the distribution, in the central nervous system, of virus-labeled neurons from the rat urinary bladder and the external urethral sphincter simultaneously within the same tissue sections. Two immunohistochemically distinct pseudorabies virus strains were injected into male Sprague--Dawley rats (approximately 280 g). One virus was injected into the bladder and the other into the external urethral sphincter. After incubation intervals of 2, 2.5 and 3 days, sections from the spinal cord and brain were treated immunohistochemically to detect cells which were labeled separately by each virus or were labeled by both viruses. The major result of these experiments is that each strain of virus labeled a separate population of neurons and that some neurons were labeled by both strains. In the lumbosacral cord, 3 days post-infection, neurons labeled by virus from the external urethral sphincter were found in Onuf's nucleus, the dorsal gray commissure, and the superficial dorsal horn. Neurons labeled by virus from the urinary bladder were found in the L6--S1 and L1--L2 spinal cord segments within the dorsal gray commissure, the intermediolateral area and the superficial dorsal horn. Double-labeled interneurons were mainly located in the dorsal gray commissure although some were also found in the intermediolateral area and the superficial dorsal horn. In the medulla, external urethral sphincter neurons and bladder neurons and double-labeled neurons were found in the reticular region and the raphe. More rostrally, bladder neurons were located in the pontine micturition center and external urethral sphincter neurons were found in the locus coeruleus and subcoeruleus. A very small number of double-labeled neurons were found in the pontine micturition center and the locus coeruleus or subcoeruleus.

Neuroprosthetic applications of electrical stimulation

Neural prostheses are a developing technology that use electrical activation of the nervous system to restore function to individuals with neurological impairment. Neural prostheses function by electrical initiation of action potentials in nerve fibers that carry the signal to an endpoint where chemical neurotransmitters are released, either to affect an end organ or another neuron. Thus, in principle, any end organ under neural control is a candidate for neural prosthetic control. Applications have included stimulation in both the sensory and motor systems and range in scope from experimental trials with single individuals to commercially available devices. Outcomes of motor system neural prostheses include restoration of hand grasp and release in quadriplegia, restoration of standing and stepping in paraplegia, restoration of bladder function (continence, micturition) following spinal cord injury, and electrophrenic respiration in high-level quadriplegia. Neural prostheses restore function and provide greater independence to individuals with disability.

Regulation of urinary bladder smooth muscle contractions by ryanodine receptors and BK and SK channels

This study examines the roles of voltage-dependent Ca(2+) channels (VDCC), ryanodine receptors (RyRs), large-conductance Ca(2+)-activated K(+) (BK) channels, and small-conductance Ca(2+)-activated K(+) (SK) channels in the regulation of phasic contractions of guinea pig urinary bladder smooth muscle (UBSM). Nisoldipine (100 nM), a dihydropyridine inhibitor of VDCC, abolished spontaneous UBSM contractions. Ryanodine (10 microM) increased contraction frequency and thereby integrated force and, in the presence of the SK blocker apamin, had a greater effect on integrated force than ryanodine alone. Blocking BK (iberiotoxin, 100 nM) or SK (apamin, 100 nM) channels increased contraction amplitude and duration but decreased frequency. The contractile response to iberiotoxin was more pronounced than to apamin. The increases in contraction amplitude and duration to apamin were substantially augmented with ryanodine pretreatment. These results indicate that BK and SK channels have prominent roles as negative feedback elements to limit UBSM contraction amplitude and duration. RyRs also appear to play a significant role as a negative feedback regulator of contraction frequency and duration, and this role is influenced by the activity of SK channels.

Assessment and investigations for urinary incontinence

Assessment of a woman complaining of urinary incontinence includes full urological, gynaecological, medical, surgical and drug histories. General, neurological, abdominal and pelvic examinations are undertaken and with the history, enable a presumptive diagnosis to be formulated. Investigations for incontinence should be selected to suit the individual woman's need. Non-specialist investigations include urine testing, completion of a urinary diary and symptom score, pad testing, measurement of residual urine volume and biochemical tests. Specialist investigations include uroflowmetry, conventional and ambulatory cystometry, urethral pressure profilometry and measurement of urethral electrical conductance and leak point pressure. Imaging using ultrasound, X-ray, magnetic resonance or isotopes is sometimes indicated. While neurophysiological testing has little clinical application, cystourethroscopy is of value in various subgroups of women. Thorough assessment and appropriate investigation together result in an accurate diagnosis which in turn allows appropriate treatment for urinary incontinence to be initiated.

Diagnosis and management of urinary retention

Failure to empty the urinary bladder completely can be attributed to failure of detrusor contractile function, inappropriate outlet resistance, or both. For each of these mechanisms, anatomic, neurogenic, and end-organ (myogenic or idiopathic) abnormalities are possible. The approach to urinary retention involves systematic consideration of neurogenic, obstructive, and functional causes and requires understanding of the neurophysiology and pharmacology of micturation.

Isoprostane 8-epi PGF2alpha, a product of oxidative stress, is synthesized in the bladder and causes detrusor smooth muscle contraction

Isoprostane 8-epi PGF2alpha is a product of oxidative stress that causes potent smooth muscle contraction. Its production increases in conditions associated with oxidative stress such as in diabetes, smoking, and aging. The aim was to study whether the urinary bladder synthesizes isoprostane 8-epi PGF2alpha and releases to the urine and whether isoprostane 8-epi PGF2alpha causes bladder smooth muscle contraction. Urine samples were obtained transurethrally from 12 male New Zealand white rabbits for measurement of isoprostane 8-epi PGF2alpha levels. To examine whether bladder synthesizes isoprostane 8-epi PGF2alpha, both ureters were ligated, then the bladder was washed 5 times by filling and emptying with normal saline. Bladder was refilled with normal saline, and at 5 minutes a bladder washout sample was taken. After this, the bladder was contracted by nerve stimulation periodically for 30 minutes, and then another washout sample was taken. Strips of bladder tissues were processed for study of isoprostane 8-epi PGF2alpha production in tissue culture chambers and for isometric tension measurements in the organ bath. Enzyme immunoassay (EIA) revealed a remarkable amount of isoprostane 8-epi PGF2alpha in the rabbit urine. EIA of washout samples showed that the bladder synthesizes isoprostane 8-epi PGF2alpha and its production increases with nerve stimulation-induced contractions. EIA of samples from the tissue culture media showed that bladder strips synthesize isoprostane 8-epi PGF2alpha in vitro. Electrical field stimulation (EFS) significantly increased the synthesis and release of isoprostane 8-epi PGF2alpha by the bladder strips. In the organ bath, isoprostane 8-epi PGF2alpha caused concentration-dependent contraction of bladder tissue. While the threshold contraction required smaller concentration of isoprostane 8-epi PGF2alpha (3 nmol) than carbachol (10 nmol), the amplitude of contraction to carbachol was greater than isoprostane 8-epi PGF2alpha. Our studies show that the rabbit bladder synthesizes isoprostane 8-epi PGF2alpha and releases it to the urine. Production of isoprostane 8-epi PGF2alpha in the bladder increases with nerve stimulation-induced contraction. Exogenous isoprostane 8-epi PGF2alpha causes significant bladder smooth muscle contraction. Our findings necessitate further studies to evaluate the possible role of oxidative stress and increased isoprostane 8-epi PGF2alpha production in bladder dysfunction. Neurourol. Urodynam. 19:43-51, 2000.

Bladder afferent pathway and spinal cord injury: possible mechanisms inducing hyperreflexia of the urinary bladder

Lower urinary tract dysfunction is a common problem in patients with spinal cord injury (SCI). Since the coordination of the urinary bladder and urethra is controlled by the complex mechanisms in spinal and supraspinal neural pathways, SCI rostral to the lumbosacral level disrupts voluntary and supraspinal control of voiding and induces a considerable reorganization of the micturition reflex pathway. Following SCI, the urinary bladder is initially areflexic. but then becomes hyperreflexic because of the emergence of a spinal micturition reflex pathway. Recent electrophysiologic and histologic studies in rats have revealed that chronic SCI induces various phenotypic changes in bladder afferent neurons such as: (1) somal hypertrophy along with increased expression of neurofilament protein; and (2) increased excitability due to the plasticity of Na+ and K+ ion channels. These results have now provided detailed information to support the previous notion that capsaicin-sensitive, unmyelinated C-fiber afferents innervating the urinary bladder change their properties after SCI and are responsible for inducing bladder hyperreflexia in both humans and animals. It is also suggested that the changes in bladder reflex pathways following SCI are influenced by neural-target organ interactions probably mediated by neurotrophic signals originating in the hypertrophied bladder. Thus, increased knowledge of the plasticity in bladder afferent pathways may help to explain the pathogenesis of lower urinary tract dysfunctions after SCI and may provide valuable insights into new therapeutic strategies for urinary symptoms in spinal cord-injured patients.

Leaky urothelium and/or vesical ischemia enable urinary potassium to cause idiopathic urgency/frequency syndrome and urge incontinence

Urine contains up to 10 times more potassium (K+) than blood plasma. Hence, extracellular K+ concentration of the bladder wall can increase secondary to a leaky urothelium (GAG layer deficiency) and/or vesical ischemia (reduced washout) at low filling volumes. Consequent sensory afferentiated excitation/depolarization of the detrusor leads to urgency/frequency and facilitates the onset of 'uninhibited' contractions. This feature, in association with a weak rhabdosphincter, causes urge incontinence. The non-neuromuscular (non-reflexive) origin explains refractoriness to any neurotransmitted inhibition. Even successful interference with contractility (Ca2+) leaves depolarization unaffected. Accordingly, comparative cystometry (saline versus 0.2 M KCl) is recommended in order to comprise better former falsely under-diagnosed 'normals' as well as former undiscovered urge incontinence, and thus indications for bladder neck surgery as well as neuromuscular drug treatment. Future first-line therapy in idiopathic storage disorders should be directed to the GAG layer, vesical blood flow (K+ washout) and the rhabdosphincter.