Neuropeptides and neurotransmitter-synthesizing enzymes in intrinsic neurons of the human urinary bladder

The differences in the anatomy of the thoracolumbar and sacral autonomic outflow are quantitative

PURPOSE

We have re-evaluated the anatomical arguments that underlie the division of the spinal visceral outflow into sympathetic and parasympathetic divisions.

METHODOLOGY

Using a systematic literature search, we mapped the location of catecholaminergic neurons throughout the mammalian peripheral nervous system. Subsequently, a narrative method was employed to characterize segment-dependent differences in the location of preganglionic cell bodies and the composition of white and gray rami communicantes.

RESULTS AND CONCLUSION

One hundred seventy studies were included in the systematic review, providing information on 389 anatomical structures. Catecholaminergic nerve fibers are present in most spinal and all cranial nerves and ganglia, including those that are known for their parasympathetic function. Along the entire spinal autonomic outflow pathways, proximal and distal catecholaminergic cell bodies are common in the head, thoracic, and abdominal and pelvic region, which invalidates the "short-versus-long preganglionic neuron" argument. Contrary to the classically confined outflow levels T1-L2 and S2-S4, preganglionic neurons have been found in the resulting lumbar gap. Preganglionic cell bodies that are located in the intermediolateral zone of the thoracolumbar spinal cord gradually nest more ventrally within the ventral motor nuclei at the lumbar and sacral levels, and their fibers bypass the white ramus communicans and sympathetic trunk to emerge directly from the spinal roots. Bypassing the sympathetic trunk, therefore, is not exclusive for the sacral outflow. We conclude that the autonomic outflow displays a conserved architecture along the entire spinal axis, and that the perceived differences in the anatomy of the autonomic thoracolumbar and sacral outflow are quantitative.

Development and Assessment of Herpes Simplex Virus Type 1 (HSV-1) Amplicon Vectors with Sensory Neuron-Selective Promoters

Background: Neurogenic detrusor overactivity (NDO) is a severe pathological condition characterized by involuntary detrusor contractions leading to urine leakage. This condition is frequent after spinal cord injury (SCI). Gene therapy for NDO requires the development of vectors that express therapeutic transgenes driven by sensory neuron-specific promoters. The aim of this study was to develop and assess tools for the characterization of sensory neuron-specific promoters in dorsal root ganglia (DRG) neurons after transduction with herpes simplex virus type 1 (HSV-1)-based amplicon defective vectors. Methods: The HSV-1 vector genome encoded two independent transcription cassettes: one expressed firefly luciferase (FLuc) driven by different promoters’ candidates (rTRPV1, rASIC3, rCGRP, or hCGRP), and the other expressed a reporter gene driven by an invariable promoter. The strength and selectivity of promoters was assessed in organotypic cultures of explanted adult DRG, or sympathetic and parasympathetic ganglia from control and SCI rats. Results: The rCGRP promoter induced selective expression in the DRG of normal rats. The rTRPV-1 promoter, which did not display selective activity in control rats, induced selective expression in DRG explanted from SCI rats. Conclusions: This study provides a methodology to assess sensory neuron-specific promoters, opening new perspectives for future gene therapy for NDO.

Prenatal development of sympathetic innervation of the human pancreas

BACKGROUND

The sympathetic nervous system plays an important role in the regulation of pancreatic exocrine and endocrine secretion. The results of experimental studies also demonstrate the involvement of the sympathetic nervous system in the regulation of endocrine cell differentiation and islet formation during the development of the pancreas. However, the prenatal development of sympathetic innervation of the human pancreas has not yet been studied.

MATERIAL AND METHODS

Pancreatic autopsy samples from 24 human fetuses were examined using immunohistochemistry with antibodies to tyrosine hydroxylase (TH). The density, concentration, and size (width, length, perimeter and area) of the TH-positive sympathetic nerves were compared in four developmental periods: pre-fetal (8-11 weeks post conception (w.p.c.), n = 6), early fetal (13-20 gestational weeks (g.w.), n = 7), middle fetal (21-28 g.w., n = 6) and late fetal (29-40 g.w., n = 5) using morphometric methods and statistical analysis (Multiple Comparisons p values). Double immunofluorescence with antibodies to TH and either insulin or glucagon and confocal microscopy were applied to analyze the interaction between the sympathetic nerves and endocrine cells, and the co-localization of TH with hormones.

RESULTS

TH-positive sympathetic nerves were detected in the fetal pancreas starting from the early stages (8 w.p.c.). The developmental dynamics of sympathetic nerves was follows: from the pre-fetal period, the amount of TH-positive nerves gradually increased and their branching occurred reaching the highest density and concentration in the middle fetal period, followed by a decrease in these parameters in the late fetal period. From the 14th g.w. onwards, thin TH-positive nerve fibers were mainly distributed in the vicinity of blood vessels and around the neurons of intrapancreatic ganglia, which is similar in adults. There were only rare TH-positive nerve fibers adjacent to acini or located at the periphery of some islets. The close interactions between the TH-positive nerve fibers and endocrine cells were observed in the neuro-insular complexes. Additionally, non-neuronal TH-containing cells were found in the pancreas of fetuses from the pre-fetal and early fetal periods. Some of these cells simultaneously contained glucagon.

CONCLUSIONS

The results demonstrate that sympathetic innervation of the human pancreas, including the formation of perivascular and intraganglionic nerve plexuses, extensively develops during prenatal period, while some processes, such as the formation of sympathetic innervation of islet capillaries, may occur postnatally. Non-neuronal TH-containing cells, as well as the interactions between the sympathetic terminals and endocrine cells observed in the fetal pancreas may be necessary for endocrine pancreas development in humans.

Somatostatin immunoreactivity within the urinary bladder nerve fibers and paracervical ganglion urinary bladder projecting neurons in the female pig

The study was designed to examine the distribution and chemical coding of somatostatin-immunoreactive (SOM-IR) nerve fibers supplying the urinary bladder wall and to establish the distribution and immunohistochemical characteristics of the subpopulation of paracervical ganglion (PCG) SOM-IR neurons projecting to this organ in female pigs. The PCG-urinary bladder projecting neurons (PCG-UBPN) were visualized with retrograde neuronal tracer Fast Blue (FB). Double-labeling immunohistochemistry performed on cryostat sections from the urinary bladder wall revealed that the greatest density of SOM-IR nerve fibers was found in the muscle layer and around blood vessels, a moderate number of these nerve terminals supplied the submucosa and only single SOM-IR axons were encountered beneath the urothelium. In all the investigated sections the vast majority of SOM-IR nerve fibers were immunopositive to vesicular acetylcholine transporter (VAChT) and many SOM-IR axons contained immunoreactivity to neuropeptide Y (NPY). Approximately 65 % of FB-positive (FB+) PCG-UBPN were immunoreactive to SOM. Moreover, PCG FB+/SOM + nerve cells were simultaneously immunoreactive to choline acetyltransferase (ChAT; 64.6 ± 0.6 %), NPY (59.7 ± 1.2 %), neuronal nitric oxide synthase (nNOS; 46.1 ± 0.7 %), vasoactive intestinal polypeptide (VIP; 29.9 ± 2.2 %), Leu⁵-enkephalin (L-ENK; 19.5 ± 6.3 %), dopamine β-hydroxylase (DβH; 14.9 ± 1.9 %) or pituitary adenylate cyclase-activating polypeptide (PACAP; 14.8 ± 2.4 %). The present study reveals the extensive expression of SOM in both the nerve fibres supplying the porcine urinary bladder wall and the PCG neurons projecting to this organ, indicating an important regulatory role of SOM in the control of the urinary bladder function.

The diversity of neuronal phenotypes in rodent and human autonomic ganglia

Selective sympathetic and parasympathetic pathways that act on target organs represent the terminal actors in the neurobiology of homeostasis and often become compromised during a range of neurodegenerative and traumatic disorders. Here, we delineate several neurotransmitter and neuromodulator phenotypes found in diverse parasympathetic and sympathetic ganglia in humans and rodent species. The comparative approach reveals evolutionarily conserved and non-conserved phenotypic marker constellations. A developmental analysis examining the acquisition of selected neurotransmitter properties has provided a detailed, but still incomplete, understanding of the origins of a set of noradrenergic and cholinergic sympathetic neuron populations, found in the cervical and trunk region. A corresponding analysis examining cholinergic and nitrergic parasympathetic neurons in the head, and a range of pelvic neuron populations, with noradrenergic, cholinergic, nitrergic, and mixed transmitter phenotypes, remains open. Of particular interest are the molecular mechanisms and nuclear processes that are responsible for the correlated expression of the various genes required to achieve the noradrenergic phenotype, the segregation of cholinergic locus gene expression, and the regulation of genes that are necessary to generate a nitrergic phenotype. Unraveling the neuron population-specific expression of adhesion molecules, which are involved in axonal outgrowth, pathway selection, and synaptic organization, will advance the study of target-selective autonomic pathway generation.

Octodon degus, a new model to study the agonist and plexus-induced response in the urinary bladder

Urinary bladder function consists in the storage and controlled voiding of urine. Translational studies require animal models that match human characteristics, such as Octodon degus, a diurnal rodent. This study aims to characterize the contractility of the detrusor muscle and the morphology and code of the vesical plexus from O. degus. Body temperature was measured by an intra-abdominal sensor, the contractility of detrusor strips was evaluated by isometric tension recording, and the vesical plexus was studied by electrical field stimulation (EFS) and immunofluorescence. The animals showed a diurnal chronotype as judged from core temperature. The myogenic contractile response of the detrusor muscle to increasing doses of KCl reached its maximum (31.04 mN/mm²) at 60 mM. In the case of cumulative dose-response of bethanecol, the maximum response (37.42 mN/mm²) was reached at 3.2 × 10^-4 M. The response to ATP was clearly smaller (3.8 mN/mm²). The pharmacological dissection of the EFS-induced contraction identified ACh and sensory fibers as the main contributors to this response. The neurons of the vesical plexus were located mainly in the trigone area, grouped in big and small ganglia. Out of them, 48.1 % of the neurons were nitrergic and 62.7 % cholinergic. Our results show functional and morphological similarities between the urinary bladder of O. degus and that of humans.

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.

Characterization of axons expressing the artemin receptor in the female rat urinary bladder: a comparison with other major neuronal populations

Artemin is a member of the glial cell line-derived neurotrophic factor (GDNF) family that has been strongly implicated in development and regeneration of autonomic nerves and modulation of nociception. Whereas other members of this family (GDNF and neurturin) primarily target parasympathetic and nonpeptidergic sensory neurons, the artemin receptor (GFRα3) is expressed by sympathetic and peptidergic sensory neurons that are also the primary sites of action of nerve growth factor, a powerful modulator of bladder nerves. Many bladder sensory neurons express GFRα3 but it is not known if they represent a specific functional subclass. Therefore, our initial aim was to map the distribution of GFRα3-immunoreactive (-IR) axons in the female rat bladder, using cryostat sections and whole wall thickness preparations. We found that GFRα3-IR axons innervated the detrusor, vasculature, and urothelium, but only part of this innervation was sensory. Many noradrenergic sympathetic axons innervating the vasculature were GFRα3-IR, but the noradrenergic innervation of the detrusor was GFRα3-negative. We also identified a prominent source of nonneuronal GFRα3-IR that is likely to be glial. Further characterization of bladder nerves revealed specific structural features of chemically distinct classes of axon terminals, and a major autonomic source of axons labeled with neurofilament-200, which is commonly used to identify myelinated sensory axons within organs. Intramural neurons were also characterized and quantified. Together, these studies reveal a diverse range of potential targets by which artemin could influence bladder function, nerve regeneration, and pain, and provide a strong microanatomical framework for understanding bladder physiology and pathophysiology.

Experimental colitis triggers the release of substance P and calcitonin gene-related peptide in the urinary bladder via TRPV1 signaling pathways

Clinical data provide evidence of high level of co-morbidity among genitourinary and gastrointestinal disorders characterized by chronic pelvic pain. The objective of this study was to test the hypothesis that colonic inflammation can impact the function of the urinary bladder via activation of TRPV1 signaling pathways followed by alterations in gene and protein expression of substance P (SP) and calcitonin gene-related peptide (CGRP) in sensory neurons and in the bladder. Inflammation was induced by intracolonic instillation of trinitrobenzene sulfonic acid (TNBS, 12.5mg/kg), and desensitization of TRPV1 receptors was evoked by intracolonic resiniferatoxin (RTX, 10(-)(7)M). mRNA and protein concentrations of CGRP and SP were measured at 3, 5 and 30 days. RTX instillation in the colon caused 3-fold up-regulation of SP mRNA in the urinary bladder at day 5 (n=7, p ≤ 0.05) followed by 35-fold increase at day 30 (n=5, p ≤ 0.05). Likewise, TNBS colitis triggered 15.8-fold up-regulation of SP mRNA 1 month after TNBS (n=5, p ≤ 0.05). Desensitization of colonic TRPV1 receptors prior to TNBS abolished SP increase in the urinary bladder. RTX led to 4.3-fold increase of CGRP mRNA at day 5 (n=7, p ≤ 0.05 to control) in the bladder followed by 28-fold increase at day 30 post-RTX (n=4, p ≤ 0.05). Colitis did not alter CGRP concentration during acute phase; however, at day 30 mRNA level was increased by 17.8 ± 6.9-fold (n=5, p ≤ 0.05) in parallel with 4-fold increase in CGRP protein (n=5, p ≤ 0.01) in the detrusor. Protein concentration of CGRP in the spinal cord was diminished by 45-65% (p ≤ 0.05) during colitis. RTX pretreatment did not affect CGRP concentration in the urinary bladder; however, it caused a reduction in CGRP release from lumbosacral DRG neurons during acute phase (3 and 5 days post-TNBS). Our results clearly demonstrate that colonic inflammation triggers the release of pro-inflammatory neuropeptides SP and CGRP in the urinary bladder via activation of TRPV1 signaling mechanisms enunciating the neurogenic nature of pelvic organ cross-sensitization.

Neural control of the lower urinary tract: peripheral and spinal mechanisms

This review deals with individual components regulating the neural control of the urinary bladder. This article will focus on factors and processes involved in the two modes of operation of the bladder: storage and elimination. Topics included in this review include: (1) The urothelium and its roles in sensor and transducer functions including interactions with other cell types within the bladder wall ("sensory web"), (2) The location and properties of bladder afferents including factors involved in regulating afferent sensitization, (3) The neural control of the pelvic floor muscle and pharmacology of urethral and anal sphincters (focusing on monoamine pathways), (4) Efferent pathways to the urinary bladder, and (5) Abnormalities in bladder function including mechanisms underlying comorbid disorders associated with bladder pain syndrome and incontinence.

Changes in bladder innervation in a mouse model of Alzheimer's disease

AIM

The aims of this study were to compare the structure of bladders from a transgenic mouse model of Alzheimer's disease with age matched control animals and to explore the idea that any structural differences might be related to functional bladder changes associated with the condition.

MATERIALS AND METHODS

Two groups of mice were used. Transgenic animals in which the murine Amyloid Precursor Protein (APP) gene has been partly replaced by the human APP including both the Swedish and London mutations and that overexpress a mutant of the human Presenilin 1 gene (PS1M146L) driven by the PDGF promoter. The transgenic mice (App(SL)/PS1(M146L)) aged 24+/-3 months were used. The second group was an age matched control group of C57 black mice. The bladders from each group were isolated, fixed in 4% paraformaldehyde and prepared for immunohistochemistry. Antibodies to the vesicular acetylcholine transporter (VAChT) and neuronal nitric oxide synthase (nNOS) were used to identify neural structures.

RESULTS

Cholinergic nerves (VAChT(+)) were observed in the inner and outer muscle bundles of App(SL)/PS1(M146L) and control mice. No major differences were noted in the distribution of these fibres. In contrast, there was a distinct difference in the innervation of the sub-urothelial layer. In App1(SL)/PS1(M146L) mice there were numerous VAChT and nNOS positive fibres in sharp contrast to the paucity of similar nerves in control animals. VAChT and nNOS did not appear to co-localise in the same nerve fibres within the lamina propria. Pairs of nerve fibres, nNOS(+) and VAChT(+), were observed to be intertwined and run in close proximity. A particularly unusual feature of the App(SL)/PS1(M146L) mouse bladder was the presence of neurones within the bladder wall. These nerve cell bodies were seen in all App(SL)/PS1(M146L) mouse bladders. The neurones could be found singly or in small ganglion like groups of cells and were located in all layers of the bladder wall (sub-urothelium, in the lamina propria adjacent to the inner muscle and within the inner muscle and outer muscle layers). No nerve cells or small ganglia were noted in any of the control bladders studied.

CONCLUSIONS

There are structural differences in the bladders of App(SL)/PS1(M146L) mice compared to control animals. These differences are associated with sub-urothelial nerves which, because of their location, are likely to be sensory fibres. This may lead to a changed sensory processing from the App(SL)/PS1(M146L) bladders. The physiological role of the intra-mural neurones and ganglia is not known. It is speculated that they may be associated with peripheral motor/sensory mechanisms linked to the generation and modulation of sensation.

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

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

The effects of a new selective beta3-adrenoceptor agonist (GW427353) on spontaneous activity and detrusor relaxation in human bladder

OBJECTIVE

To examine the effects of a new selective beta3-adrenoceptor agonist, GW427353 on human detrusor function, as beta2- and beta3-adrenoceptors have been identified in the bladder, and can mediate detrusor relaxation, but beta3-adrenoceptors are less widely distributed and beta3-adrenoceptor agonists should have the therapeutic advantage of producing fewer treatment side-effects.

PATIENTS AND METHODS

'Normal' human detrusor was retrieved from 12 patients (mean age 56 years) at cystectomy and from organ donors. Detrusor strips (4 x 1 x 1 mm) were mounted in superfused organ baths. Tone was induced with carbachol (5 x 10(-7)m) before applying either a nonselective beta-adrenoceptor agonist (isoprenaline) or GW427353 (with or without the beta3-adrenoceptor antagonist, SR59230A). In addition, the effect of GW427353 was tested on intrinsic nerve-evoked smooth muscle contraction over time. Effects on spontaneous activity were also recorded.

RESULTS

GW427353 produced significant relaxation at concentrations of >10(-7)m; isoprenaline produced a significant effect from 10(-6)m, but otherwise both agonists had similar effects. The addition of SR59230A (10(-7)m), produced partial inhibition of the GW427353 response. GW427353 at 10(-6)m significantly reduced spontaneous activity within 10 min of incubation, and at higher concentrations (>5 x 10(-6)m) inhibited detrusor contractions evoked by electrical field stimulation.

CONCLUSION

Neuropathic bladder dysfunction is characterized by increased spontaneous activity and involuntary detrusor contractions, which can result in urinary frequency, urgency, nocturia and incontinence. The novel feature of GW427353 is the ability to suppress spontaneous activity and produce significant relaxation in human detrusor tissue at low concentrations, whilst also inhibiting evoked detrusor contractions at higher concentrations.

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

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

Expression of neuronal nitric oxide synthase (nNOS) and nitric-oxide-induced changes in cGMP in the urothelial layer of the guinea pig bladder

The urothelium plays a sensory role responding to deformation of the bladder wall; this involves the release of adenosine trisphosphate (ATP) and nitric oxide (NO), which affect afferent nerve discharge and bladder sensation. The urothelial cells responsible for producing ATP and NO and the cellular targets, other than afferent nerves, for ATP and NO remain largely unexplored. Sub-urothelial interstitial cells (SU-ICs) lie immediately below the urothelium and respond to NO with a rise in cGMP. To determine which cells might target SU-ICs by producing NO, areas of dome, lateral wall and base wall were treated with isobutyl-methyl-xanthine, exposed to the NO donor diethylamino NONOate and then fixed for immunohistochemistry. Surface urothelial cells (SUCs) in the base and dome expressed neuronal nitric oxide synthase (nNOS), whereas those in the lateral wall did not. Distinct populations of SUCs were present in the bladder base. SUCs with significant amounts of nNOS lay adjacent to cells with low levels of nNOS. In specific base regions, the few SUCs present contained nNOS within discrete intracellular particles. In the basal urothelial cell (BUC) layer of the lateral wall, nNOS-positive (NOS(+)) BUCs neither showed an elevation in cGMP in response to NO, nor expressed the beta1 sub-unit of soluble guanylate cyclase, protein kinase I or protein kinase II. Thus, they produced but did not respond to NO. The BUC layer also stained for the stem cell factor c-Kit suggesting its involvement in urothelial cell development. No NOS(+) BUCs were present in the SUC-sparse region in the bladder base. Exogenous NO produced an elevation in cGMP in SUCs and SU-ICs. The distribution and proportion of these target cells varied between the dome, lateral wall and base. cGMP(+) SU-ICs were present as a dense layer in the bladder base but were rarely seen in the lateral wall, which contained nNOS(+) BUCs. No nNOS(+) BUCs and cGMP(+) SU-ICs were apparent in the dome. The degree of complexity in nNOS distribution and NO target cells is therefore greater than has previously been described and may reflect distinct physiological functions that have yet to be identified.

cGMP-generating cells in the bladder wall: identification of distinct networks of interstitial cells

OBJECTIVE

To identify cells which might contribute to the complex physiological responses of the guinea-pig bladder, and specifically to describe the distribution and types of cell in the bladder wall of the guinea pig which respond to nitric oxide (NO) with an increase in intracellular cGMP, i.e. putative interstitial cells (ICs).

MATERIALS AND METHODS

The whole bladder was removed from 11 male guinea pigs killed by cervical dislocation. Sections of the bladder wall, from the dome lateral wall and base, were isolated and incubated separately in Krebs' solution at 36 degrees C, gassed with 95% O(2) and 5% CO(2), and containing 1 mmol/L of the nonspecific phosphodiesterase inhibitor isobutyl-methyl-xanthene. Individual pieces of tissue were then exposed to 100 micromol/L of the NO donor NONOate for 10 min; control tissues remained in Krebs' solution. Tissues were then fixed in 4% paraformaldehyde and processed for immunohistochemistry. cGMP and neuronal NO synthase (nNOS) were subsequently visualized using appropriate primary and secondary antibodies.

RESULTS

Cells responding to NO with an increase in cGMP were detected in the dome, lateral wall and base, with positive cells in the thin outer surface of the wall (muscle coat), associated with muscle bundles in an outer layer of muscle, and in a region immediately beneath the urothelium. These cells (not urothelium, smooth muscle or vascular) are described as interstitial cells. Superficial urothelial umbrella cells were apparent and were strongly cGMP-positive. A high density of interstitial cells was associated with muscle bundles on the outer aspects of the wall, while few cells were detected on inner bundles. Thus there appeared to be two distinct types of muscle, inner and outer, with no obvious orientation of the fibres in each layer. Both muscle groups contained fibres expressing nNOS. In the outer muscle layer most of these fibres co-localized with cGMP, suggesting that different populations of nerves innervate each layer. There were more nNOS-positive fibres in the base of the bladder than in the dome. Three populations of cGMP-positive interstitial cells were associated with the outer muscle layer; cells in the outer surface (muscle coat interstitial cells, MC-ICs), cells on the surface of the bundles (superficial, SM-ICs) and cells within the muscle bundles (intramuscular, IM-ICs). The IM-ICs form a network in close apposition to the smooth muscle cells while the SM-ICs may connect adjacent muscle bundles and connect to the MC-ICs. Thus, there is a network linking potentially the muscle cells in the outer muscle bundles. cGMP-positive cells were also detected in the suburothelial layer (suburothelial, SU-ICs) which had a different structure to the cells associated with muscle, had a oval cell bodies with bifurcating processes and appeared to form a complex network; they were prevalent in the base and virtually absent in the dome.

CONCLUSIONS

There are structures within the bladder wall that can be identified and categorized by the ability of the constituent cells to increase intracellular cGMP in response to NO; these cells have been defined as ICs. Two distinct networks were identified, one associated with the outer muscle layers and another lying immediately beneath the urothelium, predominantly in the base of the bladder. The functions of these cells and networks are unknown; their possible roles in complex motor activity, urothelial signalling and bladder pathophysiology are discussed.

The autonomous bladder: a view of the origin of bladder overactivity and sensory urge

Incontinence and the generation of excessive sensory urges are common problems that can seriously influence the quality of life of both men and women. The underlying causes have in some instances been associated with uncontrolled bladder activity. However, the mechanisms generating such activity are still poorly understood and pharmacological tools to control it remain relatively ineffective. There are no effective treatments for bladder overactivity possibly because the bladder mechanisms are not understand or targeted. The purpose of this short review is to raise questions and re-visit ideas from some older possibly forgotten and neglected publications, but which may shed new light on this problem.

Modulation of autonomous contractile activity in the isolated whole bladder of the guinea pig

OBJECTIVE

To investigate the actions of the nonhydrolysable analogue of ATP, alpha,beta-methylene ATP (alpha,beta-MATP) and the sensory peptide, substance P, on the phasic activity generated by muscarinic stimulation in the isolated whole bladder. Isolated bladder can generate complex contractions resulting in phasic rises in intravesical pressure (the autonomous bladder): activity thought to underlie nonmicturition activity in vivo and which may be important in generating bladder sensations.

MATERIALS AND METHODS

Experiments were conducted on whole isolated bladders from female guinea pigs (270-300 g). Bladders were cannulated via the urethra, suspended in a heated chamber containing oxygenated solution at 33-36 degrees C and intravesical pressure recorded. All drugs were added to the solution bathing the abluminal surface of the bladder.

RESULTS

When alpha,beta-MATP (30-3000 nmol/L) or substance P (30-300 nmol/L) was added to resting bladders there were small rises in intravesical pressure (<2 cmH2O). However, in the presence of phasic activity generated by exposing the bladder to the muscarinic agonist arecaidine (100-300 nmol/L) or the nicotinic ligand lobeline (10-30 micromol/L) similar or lower concentrations of alpha,beta-MATP or substance P produced more dramatic effects: alpha,beta-MATP and substance P (both at 100 nmol/L) activated a rise in basal pressure of > 15 cmH2O and increased the frequency of the phasic activity. On removing alpha,beta-MATP or substance P, there was a slowing of phasic activity indicative of an inhibitory mechanism.

CONCLUSION

In addition to direct effects on smooth muscle the agonists alpha,beta-MATP and substance P appear to be potent regulators of the mechanisms generating phasic activity. A developing concept is that the mechanisms responsible for generating phasic activity underlie nonmicturition activity are the target for excitatory and inhibitory inputs. Regulating such activity may be a factor in generating or modifying bladder sensation. Inappropriate or exaggerated phasic activity could underpin the pathological changes which cause the overactive bladder, thus adding another hypothesis to the neurogenic and myogenic hypotheses of bladder overactivity, i.e. that of the autonomous bladder.

Noradrenaline inhibits autonomous activity in the isolated guinea pig bladder

OBJECTIVE

To investigate the actions of noradrenaline and the specific alpha-adrenergic agonists cirazoline (alpha1) and UK14304 (alpha2), and beta-receptor agonists formoterol (beta2) and BRL37344 (beta3) on the phasic activity induced by muscarinic stimulation on the isolated guinea pig bladder, as the physiological significance of this activity is unknown but it may underlie non-micturition contractions (NMCs, which can be inhibited by sympathetic nerve stimulation) and the generation of bladder sensations.

MATERIALS AND METHODS

All experiments were conducted using whole isolated bladders from female guinea pigs (270-300 g). Bladders were cannulated via the urethra and suspended in a heated chamber containing oxygenated Tyrode's solution at 33-35 degrees C and the intravesical pressure recorded. All drugs were added to the solution bathing the abluminal surface.

RESULTS

Exposure to noradrenaline reduced the amplitude and frequency of the phasic activity. When noradrenaline was washed off there was a transient increase in frequency. There was marked desensitization with repeated applications of noradrenaline. Applying the specific beta3-agonist BRL37344 reduced the amplitude of the phasic activity while formoterol, a specific beta2-agonist, had no effect. Cirazoline, a specific alpha1-agonist, reduced the amplitude of the responses and significantly reduced the frequency of the phasic activity. UK14304, a specific alpha2-agonist, had no effect. Stimulation of the hypogastric nerve to the guinea pig bladder generates contractions. Prolonged nerve stimulation at low frequency (6.5 Hz) generated phasic rises in intravesical pressure which were inhibited by noradrenaline. Using short (5 s) periods of stimulation noradrenaline inhibited nerve-mediated contractions at all frequencies but was more effective at <10 Hz.

CONCLUSION

These experiments show that sympathomimetic stimulation in the isolated whole bladder results primarily in an inhibition of phasic activity, but also a stimulation. Two receptor subtypes appear to be involved in the inhibition, alpha1 and beta3, suggesting that there may be many sites of action. These results are discussed in terms of the possible physiological significance of phasic activity and the potential importance of its inhibition, in the context of the causes of pathological changes in the bladder, particularly those associated with bladder overactivity, and the pharmacological approach to the alleviation of clinical symptoms.

Physiology of female micturition

Micturition is a dynamic physiologic process consisting of alternating storage and expulsion phases and is accomplished by complex interactions among innervation, smooth muscle, connective tissue, urothelium and supportive structures. Although our current understanding of the anatomy and physiology of the lower urinary tract is far from complete, intensive research over the last decade has dramatically improved our appreciation of the neural, biomechanical, biochemical, and morphologic properties of the bladder and urethra, as well as the hormonal influences and unique pelvic and perineal anatomy of women. Continued research related to the physiology of female micturition promises to offer new insights into the complex bladder-urethral interactions and to provide a basis for developing better management strategies for a variety of voiding dysfunctions in women.

Tachykinins as modulators of the micturition reflex in the central and peripheral nervous system

In the normal urinary bladder, tachykinins (TKs) are expressed in a population of bladder nociceptors that is sensitive to the excitatory and desensitizing effects of capsaicin (i.e., capsaicin-sensitive primary afferent neurons (CSPANs)). Several endobiotics or xenobiotics excite CSPANs and release TKs and other mediators at both the peripheral and spinal cord level. The peripheral release of TKs determines a set of responses (known as neurogenic inflammation) that includes vasodilatation, plasma protein extravasation, smooth muscle contraction and stimulation of afferent nerves. Following chronic inflammation, both immune cells and capsaicin-resistant sensory neurons can de novo express TKs: whether these pools of TKs are releasable and contribute to inflammatory processes is presently unsettled. At the spinal cord level, the release of TKs contributes in determining an altered pattern of vesicourethral reflexes in response to nociceptive stimulation of the bladder by conveying: (a) the afferent transmission to supraspinal sites, and (b) descending or sensory inputs to the sacral parasympathetic nucleus (SPN). Recent evidence also attribute a synergetic role of TKs in the supraspinal modulation of the sensory arm of the micturition reflex. The overall available information suggests that TK receptor antagonists may affect bladder motility/reflexes which occur during different pathological states, while having little influence on the normal motor bladder function.

Model of peripheral autonomous modules and a myovesical plexus in normal and overactive bladder function

Normal bladder function is controlled by the central nervous system (CNS) and any peripheral contribution to bladder control is believed to be small. Nevertheless, anatomically and functionally, such a contribution might exist. Taking account of this evidence, we propose that the detrusor muscle is arranged into modules, which are circumscribed areas of muscle active during the filling phase of the micturition cycle. These modules might be controlled by a peripheral myovesical plexus, consisting of intramural ganglia and interstitial cells. Detrusor overactivity is the occurrence of abnormal increases in pressure during bladder filling, which the patient cannot inhibit. This disorder is thought to be a consequence of abnormal expression of the micturition reflex or changes in the properties of the smooth muscle. We propose that detrusor overactivity results from exaggerated symptomatic expression of peripheral autonomous activity, resulting from a shift in the balance of excitation and inhibition in smooth muscle modules. These structures responsible for origin and spread of peripheral autonomous activity could be targeted to help develop new therapeutic strategies.

Structural and functional denervation of human detrusor after spinal cord injury

The bladder receives an extensive nerve supply that is predominantly cholinergic, but several putative transmitters are present, some of which are colocalized. Previous studies have shown increased levels of sensory nerves, reduced inhibitory transmitters, and structural and functional changes in the excitatory input in unstable bladder conditions. The present study compared the end-organ nerve supply to the bladder in spinal cord injury (SCI) with uninjured controls. Acetylcholinesterase histochemistry and double-label immunofluorescence were used to investigate neurotransmitter content, with confocal laser scanning microscopy to assess colocalization. Organ bath studies provided functional correlates for the structural changes in the excitatory innervation. Control samples had dense innervation of the detrusor containing a diverse range of transmitters. Hyperreflexic SCI samples showed patchy denervation, and areflexic SCI samples were diffusely denervated. Vasoactive intestinal polypeptide-, neuropeptide Y-, neuronal nitric oxide synthase-, and galanin-immunoreactive nerve fibers were reduced from frequent or moderately frequent to infrequent or very infrequent in SCI. Calcitonin gene-related peptide-immunoreactive fibers were infrequent in controls and SCI samples. Patterns of colocalization were unchanged, but significantly fewer fibers expressed more than one transmitter. The subepithelial plexus was markedly reduced and several of the smaller coarse nerve trunks showed no immunoreactivity to the transmitters assessed. There was no reduction in sensitivity to electrical field stimulation of intrinsic nerves in SCI, but the maximum force generated by each milligram of bladder tissue and the peak force as a proportion of the maximum carbachol contraction were significantly reduced and the responses were protracted. There was no significant functional atropine-resistant neuromuscular transmission in controls or SCI. The reported findings have clinical implications in the management of chronic SCI and development of new treatments.

Evaluation and treatment of children with neurogenic bladders

The evaluation and treatment of children with neurogenic bladders can be difficult because of the complexity of the neurologic deficit and the subjectivity of the history and physical exam. The primary emphasis of the physicians caring for these children should be to preserve renal function and facilitate continence when possible. As knowledge of both normal and abnormal lower urinary-tract dynamics increases, so does the ability to care for children with abnormal bladder dynamics caused by various neurologic conditions. With recent advancements in medical and surgical treatment of the neurogenic bladder, most children can maintain adequate renal function and attain urinary continence. This article reviews the pertinent innervation, anatomy, and physiology of the lower urinary tract, and discusses current evaluation and treatment of children with neurogenic bladders.

Tyrosine hydroxylase and vesicular acetylcholine transporter are coexpressed in a high proportion of intramural neurons of the human neonatal and child urinary bladder

Autonomic ganglia of the human pelvic plexus contain sympathetic and parasympathetic neurons which innervate the internal reproductive organs and the lower urinary tract while the urinary bladder also receives innervation from small intramural ganglia embedded in the detrusor muscle. Previous studies have used the immunocytochemical demonstration of tyrosine hydroxylase (TH), either alone or in combination with dopamine beta-hydroxylase, to identify noradrenergic neurons in these ganglia. However until recently a reliable marker for cholinergic neurons in the human autonomic nervous system was not available since antibodies to choline acetyltransferase do not react in this tissue. The present immunohistochemical study has used an antibody to human vesicular acetylcholine transporter (VAChT) to identify cholinergic neurons in the pelvic plexus and intramural bladder ganglia in a series of specimens from human male neonates and children. Immunostaining for TH was also carried out on the same sections and the results showed that while the vast majority of pelvic ganglion neurons were either cholinergic or noradrenergic (as seen by the presence of VAChT or TH respectively), approximately 50% of the neurons in the intramural ganglia were labeled with both immunomarkers. The presence of TH in cholinergic neurons may be due to the immaturity of the tissues examined since previous data on intramural bladder ganglia in the adult have shown that a much smaller proportion of the neurons contain TH than was observed in the present study. It is concluded that the presence of TH alone cannot be regarded as a specific marker for noradrenergic neurons in the genitourinary system of the human neonate and child.

Changes in bladder tone during filling: pharmacological aspects

The mechanism by which the bladder maintains a low pressure during filling has not yet been established. Myogenic and neural factors have been suggested, although their relative importance has not been settled. There is an ongoing thoracolumbar sympathetic outflow to the lower urinary tract during filling, and noradrenaline, released from adrenergic nerves and acting through stimulation of beta-adrenoceptors (beta 2 and beta 3), may relax the bladder, due to a relative dominance of beta- over alpha-adrenoceptors in the detrusor. Non-adrenergic, non-cholinergic mediators, such as nitric oxide and vasoactive intestinal polypeptide have been suggested to relax the detrusor during filling; there is no compelling evidence to support these proposals. Unidentified relaxant factors may be released from the bladder. Their existence and possible importance need to be further documented. Although it is widely accepted that there is no sacral parasympathetic outflow to the bladder during filling, antimuscarinic drugs increase, and anticholinesterase inhibitors decrease bladder capacity, suggesting an ongoing acetylcholine (ACh) mediated stimulation of detrusor tone. If this is correct, agents inhibiting ACh release should be expected to contribute to bladder relaxation during filling. Inhibition of ACh release can be obtained by stimulation of various receptors on cholinergic nerves, including alpha 2-adrenoceptors, receptors for neuropeptide Y and galanin, or by antagonism of neuronal 5-HT4 receptors. Whether any of these mechanisms is of importance for bladder relaxation during filling, or whether they can be targets for pharmacological therapeutic interventions, remains to be established.

The C fibre reflex of the cat urinary bladder

1. Reflexes evoked in bladder parasympathetic neurones by electrical stimulation of bladder C afferent fibres were studied in cats anaesthetized with alpha-chloralose. The responses were compared with the ordinary micturition reflex evoked by low-threshold Adelta afferents from bladder mechanoreceptors and mediated by a spino-ponto-spinal reflex pathway. 2. The bladder was catheterized for fluid instillations and pressure recordings. Efferent reflex discharges were recorded from the cut central end of a small distal bladder branch of the pelvic nerve. The remaining bladder pelvic nerve branches were stimulated electrically close to the bladder. 3. Stimulation at C afferent intensity evoked a late reflex discharge in bladder pelvic efferents in all animals. The response was centrally mediated, had a latency of 150-250 ms, and was much weaker after stimulation on the contralateral nerve. 4. The bladder C fibre reflex differed in several functional aspects from the ordinary Adelta micturition reflex. It could be evoked at a low rate of stimulation, with an empty bladder and no background activity from bladder mechanoreceptors. In this situation, the normal Adelta micturition reflex is not elicited. The C fibre reflex also survived an acute spinalization at a low thoracic level. 5. The C fibre reflex was strongly inhibited by dorsal clitoris or dorsal penis nerve stimulation, an effect that was maintained after spinalization. It was facilitated by bladder or urethra exposure to cold and menthol, stimuli that activate specific cold-sensitive receptors associated with unmyelinated C afferents. 6. It is concluded that the central pathway of the C fibre reflex is spinal and partly separate from that of the ordinary micturition reflex. These observations are in keeping with the clinical finding that a bladder cooling reflex can be elicited in patients with disturbed descending control of the bladder.

Smooth muscle of the bladder in the normal and the diseased state: pathophysiology, diagnosis and treatment

The smooth muscle of the normal bladder wall must have some specific properties. It must be very compliant and able to reorganise itself during filling and emptying to accommodate the change in volume without generating any intravesical pressure, but whilst maintaining the normal shape of the bladder. It must be capable of synchronous activation to generate intravesical pressure at any length to allow voiding. The cells achieve this through spontaneous electrical activity combined with poor electrical coupling between cells, and a dense excitatory innervation. In the diseased state, alterations of the smooth muscle may lead to failure to store or failure to empty properly. The diseased states discussed are bladder instability and diabetic neuropathy. Bladder instability is characterised urodynamically by uninhibitable rises in pressure during filling, and is seen idiopathically and in association with bladder outflow obstruction and neuropathy. In diabetic neuropathy, many of the smooth muscle changes are a consequence of diuresis, but there is evidence for alterations in the sensory arm of the micturition reflex. In the unstable bladder, additional alterations of the smooth muscle are seen, which are probably caused by the patchy denervation that occurs. The causes of this denervation are not fully established. Nonsurgical treatment of instability is not yet satisfactory; neuromodulation has some promise, but is expensive, and the mechanisms poorly understood. Pharmacological treatment is largely through muscarinic receptor blockade. Drugs to reduce the excitability of the smooth muscle are being sought, since they may represent a better pharmacological option.

Heme oxygenase and NO-synthase in the human prostate--relation to adrenergic, cholinergic and peptide-containing nerves

In the human prostate, the distribution of heme oxygenase (HO-1 and HO-2)-, nitric oxide synthase (NOS)-, and tyrosine hydroxylase (TH)-immunoreactive (IR), acetylcholine-esterase (AChE)-positive, and some peptidergic nerve structures was investigated. Cell bodies and nerve fibers within coarse nerve trunks expressed HO-1-, HO-2-, NOS-, TH-, and vasoactive intestinal polypeptide (VIP)-immunoreactivities, and were AChE-positive, but, as revealed by confocal microscopy. HO- and NOS-immunoreactivities were found in separate nerves. Along strains of smooth muscle, intraglandular septa, and around acini, HO-1-, NOS-, and VIP-IR nerves, and AChE-positive fibers were observed. Double immunostaining showed that NOS- and VIP-immunoreactivities were generally co-localized in varicose nerve terminals. Some TH-IR terminals had profiles that were similar, but not identical, to those of NOS-, HO-1-, or VIP-IR terminals. NPY-IR nerves were similarly distributed as VIP- and NOS-IR fibers, and were found in rich amounts. Calcitonin gene-related peptide (CGRP)-IR nerves were few compared to other nerve populations studies. NOS- and CGRP-IR terminals had similar profiles, but the immunoreactivities were not co-localized. Nitric oxide and electrical stimulation of nerves relaxed noradrenaline-contracted preparations of prostatic stroma. Inhibition of synthesis of nitric oxide abolished the electrically induced relaxations. VIP had small relaxant effects, whereas carbon monoxide was without effect on noradrenaline-contracted strips. The innervation pattern and the functional effects suggest that the L-arginine/nitric oxide pathway may have a role in the control of human prostatic smooth muscle activity and/or in secretory neurotransmission. A physiological role of carbon monoxide in the prostate remains to be established.