Roles of glutamatergic and serotonergic mechanisms in reflex control of the external urethral sphincter in urethane-anesthetized female rats

Functional mapping of the lower urinary tract by epidural electrical stimulation of the spinal cord in decerebrated cat model

Several neurologic diseases including spinal cord injury, Parkinson's disease or multiple sclerosis are accompanied by disturbances of the lower urinary tract functions. Clinical data indicates that chronic spinal cord stimulation can improve not only motor function but also ability to store urine and control micturition. Decoding the spinal mechanisms that regulate the functioning of detrusor (Detr) and external urethral sphincter (EUS) muscles is essential for effective neuromodulation therapy in patients with disturbances of micturition. In the present work we performed a mapping of Detr and EUS activity by applying epidural electrical stimulation (EES) at different levels of the spinal cord in decerebrated cat model. The study was performed in 5 adult male cats, evoked potentials were generated by EES aiming to recruit various spinal pathways responsible for LUT and hindlimbs control. Recruitment of Detr occurred mainly with stimulation of the lower thoracic and upper lumbar spinal cord (T13-L1 spinal segments). Responses in the EUS, in general, occurred with stimulation of all the studied sites of the spinal cord, however, a pronounced specificity was noted for the lower lumbar/upper sacral sections (L7-S1 spinal segments). These features were confirmed by comparing the normalized values of the slope angles used to approximate the recruitment curve data by the linear regression method. Thus, these findings are in accordance with our previous data obtained in rats and could be used for development of novel site-specific neuromodulation therapeutic approaches.

Mental health problems, stressful life events and new-onset urinary incontinence in primary school-age children: a prospective cohort study

Emotional/behaviour problems and exposure to stressful life events are thought to contribute to new onset of urinary incontinence (UI) amongst children who have attained bladder control. However, very few prospective studies have examined these associations. We assessed whether mental health problems and stressful life events were associated with subsequent new onset in UI using multivariable logistic regression in a prospective UK cohort (n = 6408). Mothers provided information on their child's symptoms of common mental disorders (Development and Wellbeing Assessment, 7 years), stressful life events (7-8 years) and wetting (day and night, 9 years). There was strong evidence that separation anxiety symptoms were associated with new-onset UI in the fully adjusted model (OR (95% CI) = 2.08 (1.39, 3.13), p < 0.001). Social anxiety, attention-deficit hyperactivity disorder and oppositional defiant disorder symptoms were associated with new-onset UI, but these associations attenuated following adjustment for child developmental level and earlier emotional/behaviour problems. There was weak evidence for a sex interaction with stressful life events (p = 0.065), such that females experiencing more stressful life events were at higher risk of new-onset UI (fully adjusted model OR (95% CI) = 1.66 (1.05, 2.61), p = 0.029), but there was no association in males (fully adjusted model OR (95% CI) = 0.87 (0.52, 1.47), p = 0.608). These results suggest that separation anxiety and stressful life events in girls may lead to an increase in UI.

The pathophysiology of Post SSRI Sexual Dysfunction - Lessons from a case study

BACKGROUND

Although Post-SSRI Sexual Dysfunction (PSSD) has finally been recognized by the European Medicines Agency as a medical condition that can outlast discontinuation of SSRI and SNRI antidepressants, this condition is still largely unknown by patients, doctors, and researchers, and hence, poorly understood, underdiagnosed, and undertreated.

OBJECTIVE

Becoming familiar with the symptomatology of PSSD and understanding the underlying mechanisms and treatment options.

METHOD

We applied a design thinking approach to innovation to 1) provide insights into the medical condition as well as the personal needs and pains of a targeted patient; and 2) generate ideas for new solutions from the perspective of this particular patient. These insights and ideas informed a literature search on the potential pathophysiological mechanisms that could underlie the patient's symptoms.

RESULTS

The 55-year-old male patient developed symptoms of low libido, delayed ejaculation, erectile dysfunction, 'brain zaps', overactive bladder and urinary inconsistency after discontinuation of the SNRI venlafaxine. In many of these symptoms a dysregulation in serotonergic activity has been implicated, with an important role of 5-HT_1A receptor downregulation and possible downstream effects on neurosteroid and oxytocin systems.

CONCLUSIONS

The clinical presentation and development of symptoms are suggestive of PSSD but need further clinical elaboration. Further knowledge of post-treatment changes in serotonergic - and possibly noradrenergic - mechanisms is required to improve our understanding of the clinical complaints and to inform appropriate treatment regimes.

Liberation of Serotonin Is Not Unaffected by Acetylcholine in Rat Hippocampus

Purpose

Raised cerebral titers of acetylcholine have notable links with storage symptomatology related to lower urinary tract symptoms. The hippocampus contributes to the normal control of continence in the majority of instances (circuit 3). Owing to synaptic connections with other nerve cells, acetylcholine affects the micturition pathway via the liberation of additional cerebral neurotransmitters. Despite the fact that cerebral serotonin is a key inhibitor of reflex bladder muscle contractions, the influence of acetylcholine on its liberation is poorly delineated. The current research was conducted in order to explore the role of acetylcholine in serotonin liberation from sections of rat hippocampus in order to improve the comprehension of the relationship between cholinergic and serotonergic neurons.

Methods

Hippocampal sections from 6 mature male Sprague-Dawley rats were equilibrated over a 30-minute period in standard incubation medium so as to facilitate [³H]5-hydroxytryptamine (5-HT) uptake. The cerebral neurotransmitter, acetylcholine, was applied to the sections. Aliquots of drained medium solution were utilized in order to quantify the radioactivity associated with [³H]5-HT liberation; any alterations in this parameter were noted.

Results

When judged against the controls, [³H]5-HT liberation from the hippocampal sections remained unaltered following the administration of acetylcholine, implying that this agent has no inhibitory action on this process.

Conclusions

Serotonin liberation from murine hippocampal sections is unaffected by acetylcholine. It is postulated that the bladder micturition reflex responds to acetylcholine through its immediate cholinergic activity rather than by its influence on serotonin release. These pathways are a promising target for the design of de novo therapeutic agents.

Serotonin Discharge Regulation by Additional Neurotransmitters of Rat Hippocampus Associated With the Continence Central Circuit

Purpose

The lower urinary tract is believed to be centrally regulated with the involvement of a range of neurotransmitters. The parasympathetic excitatory input to the urinary bladder is suppressed when the serotonergic system is activated, and thereby voiding is blocked. In healthy people, continence is usually underpinned by hippocampal formation (circuit 3). In order to advance knowledge of how serotoninergic neurons and additional nerve fibers were correlated, the purpose of the present work was to research how the discharge of serotonin from hippocampal slices was affected by different neurotransmitters in rat models.

Methods

The adopted procedure involved administration of the central neurotransmitters acetylcholine, norepinephrine, dopamine, N-methyl-D-aspartate (NMDA), gamma-aminobutyric acid (GABA), glycine, and neuropeptide Y as well as monitoring of the alterations in the discharge of [³H]5-hydroxytryptamine (5-HT). Furthermore, to determine whether the effect of the neurotransmitters was influenced by interneuron, tetrodotoxin was also employed.

Results

Acetylcholine (10^-5M) did not alter [³H]5-HT discharge, whereas more 5-HT was discharged from the hippocampal slices of rats under stimulation by norepinephrine (10^-5M) as well as dopamine (10^-5M) and tetrodotoxin (10^-6M) did not inhibit the discharge. By contrast, tetrodotoxin inhibited the discharge of [³H]5-HT that was exacerbated by NMDA (10^-4M). Meanwhile, compared to control, GABA (10^-5M), glycine (10^-5M), or neuropeptide Y (10^-6M) did not alter the [³H]5-HT discharge.

Conclusions

From the research findings, it can be concluded that 5-HT discharge from rat hippocampus is enhanced by norepinephrine and dopamine through direct effect on the 5-HT neuronal terminal. By contrast, 5-HT discharge is intensified by NMDA by activating interneurons.

Delivery of the 5-HT2A Receptor Agonist, DOI, Enhances Activity of the Sphincter Muscle during the Micturition Reflex in Rats after Spinal Cord Injury

Simple Summary

Spinal cord injury often disrupts connections between the brain and spinal cord leading to a plethora of health complications, including bladder dysfunction. Spinal cord injured patients are left with symptoms such as a leaky bladder (the inability to hold their urine), frequent urinary tract infections, and potential kidney failure. However, previous studies have shown that manipulation of serotoninergic receptors can improve urinary performance following spinal cord injury. In the current study, we sought to explore how stimulation of a specific serotonergic receptor subtype can significantly enhance bladder function in spinal cord injured rats. To do so, we utilized spinal cord injured female rats that underwent various bladder performance evaluations combined with pharmacological intervention of a specific serotonergic subtype. Additionally, the primary site of action was investigated to determine effects elicited during various administration routes (e.g., directly into the cord, into the femoral vein, or into the skin). Stimulation of this receptor subtype, regardless of delivery route, improved activity of the external urethral sphincter and detrusor-sphincter coordination in spinal cord injured rats. Collectively, the results of these experiments have the potential to provide vital guidance for the development of therapeutic strategies to alleviate urinary dysfunction following spinal cord injury.

Abstract

Traumatic spinal cord injury (SCI) interrupts spinobulbospinal micturition reflex pathways and results in urinary dysfunction. Over time, an involuntary bladder reflex is established due to the reorganization of spinal circuitry. Previous studies show that manipulation of serotonin 2A (5-HT_2A) receptors affects recovered bladder function, but it remains unclear if this receptor regulates the activity of the external urethral sphincter (EUS) following SCI. To elucidate how central and peripheral serotonergic machinery acts on the lower urinary tract (LUT) system, we employed bladder cystometry and EUS electromyography recordings combined with intravenous or intrathecal pharmacological interventions of 5-HT_2A receptors in female SCI rats. Three to four weeks after a T10 spinal transection, systemic and central blockage of 5-HT_2A receptors with MDL only slightly influenced the micturition reflex. However, delivery of the 5-HT_2A receptor agonist, DOI, increased EUS tonic activity and elicited bursting during voiding. Additionally, subcutaneous administration of DOI verified the enhancement of continence and voiding capability during spontaneous micturition in metabolic cage assays. Although spinal 5HT_2A receptors may not be actively involved in the recovered micturition reflex, stimulating this receptor subtype enhances EUS function and the synergistic activity between the detrusor and sphincter to improve the micturition reflex in rats with SCI.

Choice of cystometric technique impacts detrusor contractile dynamics in wistar rats

The objective of the current animal study was to investigate factors contributing to the different phases of the cystometrogram (CMG) in order to address disparities in research data reported in the current literature. Three experiments in 20 female Wistar rats were designed to investigate (1) the effects of anesthesia on the contractile pattern of the bladder during micturition; (2) the impact of the physical characteristics of the CMG technique upon the accuracy of intra-vesical pressure recordings; and (3) identification of physiological and methodological factors associated with the emptying and rebound phases during CMG. Variables tested included awake versus urethane-anesthetized conditions, use of a single catheter for both filling and intra-vesical pressure (Pves) recording versus a separate two catheter approach, and comparisons between ureter, bladder dome, and urethral catheter placements. Both awake and anesthetized conditions contributed to variations in the shape and magnitude of the CMG pressure curves. In addition, catheter size, acute incision of the bladder dome for catheter placement, use of the same catheter for filling and Pves recordings, as well as the placement and positioning of the tubing, all contributed to alterations of the physiological properties and characteristic of the various CMG phases, including the frequent occurrence of an artificial rebound during the third phase of micturition. The present results demonstrate how different experimental conditions lead not only to variability in Pves curves, but consistency of the measurements as well, which needs to be accounted for when interpreting CMG outcome data.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Central pattern generators in the brainstem and spinal cord: an overview of basic principles, similarities and differences

Central pattern generators (CPGs) are generally defined as networks of neurons capable of enabling the production of central commands, specifically controlling stereotyped, rhythmic motor behaviors. Several CPGs localized in brainstem and spinal cord areas have been shown to underlie the expression of complex behaviors such as deglutition, mastication, respiration, defecation, micturition, ejaculation, and locomotion. Their pivotal roles have clearly been demonstrated although their organization and cellular properties remain incompletely characterized. In recent years, insightful findings about CPGs have been made mainly because (1) several complementary animal models were developed; (2) these models enabled a wide variety of techniques to be used and, hence, a plethora of characteristics to be discovered; and (3) organizations, functions, and cell properties across all models and species studied thus far were generally found to be well-preserved phylogenetically. This article aims at providing an overview for non-experts of the most important findings made on CPGs in in vivo animal models, in vitro preparations from invertebrate and vertebrate species as well as in primates. Data about CPG functions, adaptation, organization, and cellular properties will be summarized with a special attention paid to the network for locomotion given its advanced level of characterization compared with some of the other CPGs. Similarities and differences between these networks will also be highlighted.

Transsynaptic tracing to dissect supraspinal serotonergic input regulating the bladder reflex in rats

AIMS

This study was designed to determine specific cell groups of the raphe nuclei (RN) that give rise to supraspinal serotonergic projections regulating the bladder reflex.

METHODS

Anesthetized rats underwent surgery to open the abdomen and expose the bladder. A total of 6 µL transsynaptic neuronal tracer pseudorabies virus (PRV-152), encoding for green fluorescent protein (GFP), was injected into the bladder detrusor. After 72 or 96 h, animals were perfused and the brain was dissected for processing transverse and sagittal sections. Subsequently, fluorescent immunohistochemistry for GFP and Serotonin (5-hydroxytryptamine [5-HT]) was performed in the brain sections. Under the microscope, each RN subset was characterized individually from caudal to rostral according to the atlas. GFP⁺ or GFP/5-HT double labeled neurons in each subset were quantified for statistical analysis.

RESULTS

At 72-h post-infection, very few GFP⁺ or GFP/5-HT double-labeled neurons appeared in the brainstem and beyond. In contrast, many labeled neurons were found at these levels after 96 h. Quantitative analysis showed that the majority of infected 5-HT⁺ neurons were located in the pallidus, obscurus, and magnus nuclei. Conversely, very few infected neurons were found in other raphe subsets, that is the pontis, median, dorsal, or linear nuclei. Overall, the raphe magnus had the highest number of GFP-labeled and GFP/5-HT double-labeled cells.

CONCLUSIONS

The caudal subsets of RN, especially the raphe magnus, are the main sources of serotonergic input to the lower spinal cord controlling bladder activity.

Novel Neurostimulation of Autonomic Pelvic Nerves Overcomes Bladder-Sphincter Dyssynergia

The disruption of coordination between smooth muscle contraction in the bladder and the relaxation of the external urethral sphincter (EUS) striated muscle is a common issue in dysfunctional bladders. It is a significant challenge to overcome for neuromodulation approaches to restore bladder control. Bladder-sphincter dyssynergia leads to undesirably high bladder pressures, and poor voiding outcomes, which can pose life-threatening secondary complications. Mixed pelvic nerves are potential peripheral targets for stimulation to treat dysfunctional bladders, but typical electrical stimulation of pelvic nerves activates both the parasympathetic efferent pathway to excite the bladder, as well as the sensory afferent pathway that causes unwanted sphincter contractions. Thus, a novel pelvic nerve stimulation paradigm is required. In anesthetized female rats, we combined a low frequency (10 Hz) stimulation to evoke bladder contraction, and a more proximal 20 kHz stimulation of the pelvic nerve to block afferent activation, in order to produce micturition with reduced bladder-sphincter dyssynergia. Increasing the phase width of low frequency stimulation from 150 to 300 μs alone was able to improve voiding outcome significantly. However, low frequency stimulation of pelvic nerves alone evoked short latency (19.9–20.5 ms) dyssynergic EUS responses, which were abolished with a non-reversible proximal central pelvic nerve cut. We demonstrated that a proximal 20 kHz stimulation of pelvic nerves generated brief onset effects at lower current amplitudes, and was able to either partially or fully block the short latency EUS responses depending on the ratio of the blocking to stimulation current. Our results indicate that ratios >10 increased the efficacy of blocking EUS contractions. Importantly, we also demonstrated for the first time that this combined low and high frequency stimulation approach produced graded control of the bladder, while reversibly blocking afferent signals that elicited dyssynergic EUS contractions, thus improving voiding by 40.5 ± 12.3%. Our findings support advancing pelvic nerves as a suitable neuromodulation target for treating bladder dysfunction, and demonstrate the feasibility of an alternative method to non-reversible nerve transection and sub-optimal intermittent stimulation methods to reduce dyssynergia.

Mapping and neuromodulation of lower urinary tract function using spinal cord stimulation in female rats

Spinal cord epidural stimulation (SCS) represents a form of neuromodulation for the management of spasticity and pain. This technology has recently emerged as a new approach for potentially augmenting locomotion and voiding function in humans and rodents after spinal cord injury. However, the effect of SCS on micturition has not been studied extensively. Here, SCS was first applied as a direct stimulus onto individual segmental levels of the lumbar spinal cord in rats to map evoked external urethral sphincter (EUS) electromyography activity and SCS-induced voiding contractions. SCS of L2-3 inhibited EUS tonic activity, and SCS on L3 (L3/SCS) inhibited EUS tonic activity and elicited EUS bursting. In contrast, SCS of L1 and L4-6 evoked EUS tonic contractions, which resembled the urethral guarding reflex during bladder storage. Next, the effects of a bilateral pelvic nerve crush (PNC) injury on urodynamic function were examined at 14 days post-operatively. The PNC injury resulted in decreased voiding efficiency and maximum intravesical pressure, whereas the post-voiding residual volume was increased, suggestive of an underactive bladder. Finally, L3/SCS was performed to induce a voiding contraction and enable voiding in rats with a PNC injury. Voiding efficiency was significantly increased, and the residual volume was decreased by L3/SCS in rats after the PNC injury. We conclude that L3/SCS may be used to induce micturition reflexes in a partially filled bladder, reduce urethral resistance, and augment bladder emptying after PNC injury.

Effect of 5-HT7 receptor agonist, LP-211, on micturition following spinal cord injury in male rats

BACKGROUND AND PURPOSE

Central and peripheral 5-hydroxytryptamine (5-HT) receptors play a critical role in regulation of micturition reflex. The aim of this study was to evaluate effect of a 5-HT7 receptor agonist, LP-211 (N-(4-cyanophenylmethyl)-4-(2-diphenyl)-1-piperazinehexanamide) on micturition reflex in acute spinal cord-injured (SCI) rats during infusion of vehicle into the bladder.

METHODS

SCI was induced by compressing T10 segment using an aneurysm clip, extradurally in male rats. Following two weeks, LP-211 doses (0.003-0.3 mg/kg) were administered cumulatively (intraperitoneally, i.p.) with 20 min interval. The 5-HT7 antagonist, SB-269970 ((R)-3-[2-[2-(4-Methylpiperidin-1-yl) ethyl] pyrrolidine-1-sulfonyl] phenol hydrochloride), was administered after achievement of LP-211 dose-response. A cystometric study was performed 2 weeks after spinal crushing in all the animals. Cystometric variables consisting of micturition volume (voided volume), residual volume (volume remaining in the bladder after voiding), and bladder capacity (micturition volume plus residual volume). Voiding efficiency was calculated as the percent of micturition volume to bladder capacity.

FINDINGS

Intact and sham-operated rats showed few significant changes in micturition reflex. SCI rats responded to LP-211 (0.003-0.3, mg/kg, i.v.) with dose-dependent increases in bladder capacity, and residual volume. In this treatment group, LP-211 induced significant dose-dependent increases in micturition volume, resulting in significant increases in voiding efficiency (P<0.001) compared to intact and sham-operated rats, SB-269970 (0.1 mg/kg, i.v.) completely reversed the LP-211-induced changes on micturition volume and voiding efficiency was decreased significantly.

CONCLUSION

The 5-HT7 receptors activation by LP-211 facilitated the micturition reflex. Furthermore, 5-HT7 receptors do seem to play an important role in physiological regulation of micturition, and as a result, may represent a new strategy to improve voiding efficiency after SCI in patients in the future perspective.

Does pharmacological activation of 5-HT1A receptors improve urine flow rate in female rats?

The role of 5-HT1A receptors in regulating voiding functions remains unclear, particularly regarding the urine flow rate (UFR) during voiding. This study examined the effects of 5-HT1A receptors on regulating urethral functions in female rats and investigated underlying modulatory mechanisms. Intravesical pressure (IVP), external urethral sphincter-electromyography (EUS-EMG), and UFR were simultaneously recorded during continuous transvesical infusion to examine the effects of a 5-HT1A receptor agonist (8-OH-DPAT) and antagonist (WAY-100635) on bladder and urethral functions. In addition, this study evaluated the independent roles of urethral striated and smooth muscles in the UFR in rats after a neuromuscular blockade (NMB) treatment and bilateral hypogastric nerve transection. Our results revealed that 8-OH-DPAT significantly increased the maximal UFR but reduced the mean UFR. This discrepancy may be because 8-OH-DPAT markedly increased the maximal UFR during the initial segment of the flow duration and subsequently induced an approximately zero level of long oscillatory waves during the remaining flow duration. Thus the mean UFR was reduced because of the prolonged approximately zero level of the UFR. However, paralyzing the EUS with an NMB agent, 8-OH-DPAT, significantly increased the maximal and mean UFRs because the prolonged zero level of the oscillatory UFR did not continue. These results support the hypothesis that the increased UFR in female rats during voiding is due to the induction of urethral smooth muscle relaxation by 8-OH-DPAT. This paper provides a detailed understanding of the role of 5-HT1A receptors in controlling the UFR in female rats.

Noradrenergic Mechanisms Controlling Urethral Smooth and Striated Muscle Function in Urethral Continence Reflex in Rats

OBJECTIVES

To investigate the role of noradrenergic pathways in the urethral continence reflex during abdominal compression in rats.

METHODS

Under urethane anesthesia, urethral baseline pressure (UBP) and urethral pressure response (UPR) during momentary abdominal compression using a 100 g weight was measured using a transurethral microtransducer-tipped catheter placed at the middle urethra in Sprague-Dawley female rats. Following intravenous (i.v.) application of hexamethonium or α-bungarotoxin to block urethral smooth or striated muscle function, respectively, the effects of terazosin, an α1 -adrenoceptor (AR) antagonist (0.3 mg/kg, i.v.), medetomidine, an α2 -AR agonist (0.3 mg/kg, i.v.) or nisoxetine, a norepinephrine reuptake inhibitor (1 mg/kg, i.v.) followed by terazosin on UBP and UPR were examined.

RESULTS

After hexamethonium pretreatment, terazosin did not alter UBP or UPR, whereas medetomidine significantly decreased UPR by 28% without UBP changes. Nisoxetine significantly increased UPR by 64%, which was eliminated by terazosin, but UBP was not altered by nisoxetine. After α-bungarotoxin pretreatment, UBP and UPR were significantly decreased by terazosin or medetomidine. Nisoxetine induced significant increases in UBP and UPR by 16 and 15%, respectively, which were antagonized by terazosin.

CONCLUSION

These results suggest that: the baseline activity and reflex contraction of urethral smooth muscle are decreased by α1 -AR inhibition or α2 -AR stimulation; the reflex contraction of urethral striated muscle is decreased by α2 -AR stimulation, but not by α1 -AR inhibition; and nisoxetine increases baseline and reflex activity of smooth muscle in addition to striated muscle reflex activity by α1 -AR stimulation. These findings will be useful to understand nerve-mediated urethral closure mechanisms.

Serotonergic regulation of distention-induced ATP release from the urothelium

Serotonin [5-hydroxytryptamine (5-HT)] is involved in both motor and sensory functions in hollow organs, especially in the gastrointestinal tract. However, the involvement of 5-HT in visceral sensation of the urinary bladder remains unknown. Because distention-induced ATP release from the urothelium plays an essential role in visceral sensation of the urinary bladder, we investigated the regulation of urothelial ATP release by the 5-HT signaling system. RT-PCR and immunohistochemical analyses of the urothelium revealed specific expression of 5-HT_1D and 5-HT₄ receptors. The addition of 5-HT did not affect urothelial ATP release without bladder distention, but it significantly reduced distention-induced ATP release by physiological pressure during urine storage (5 cmH₂O). The inhibitory effect of 5-HT on distention-elicited ATP release was blocked by preincubation with the 5-HT_1B/1D antagonist GR-127935 but not by the 5-HT₄ antagonist SB-204070. mRNA encoding tryptophan hydroxylase 1 was detected in the urinary bladder by nested RT-PCR amplification, and l-tryptophan or the selective serotonin reuptake inhibitor citalopram also inhibited ATP release, indicating that 5-HT is endogenously synthesized and released in the urinary bladder. The addition of GR-127935 significantly enhanced the distention-elicited ATP release 40 min after distention, whereas SB-204070 reduced the amount of ATP release 20 min after distention. These data suggest that 5-HT₄ facilitates the distention-induced ATP release at an earlier stage, whereas 5-HT_1D inhibits ATP release at a later stage. The net inhibitory effect of 5-HT indicates that the action of 5-HT on the urothelium is mediated predominantly by 5-HT_1D.

Regulatory Effects of 5-Hydroxytryptamine Receptors on Voiding Function

A growing body of evidence suggests that 5-hydroxytryptamine (5-HT; serotonin) has both physiological and pathological functions in the lower urinary tract. A wide variety of 5-HT receptor subtypes are variably expressed in different organs, both peripheral and central. On urinary bladder smooth muscle, 5-HT1A, 5-HT2, 5-HT3, and 5-HT7 subtypes could function as postjunctional receptors. Postjunctional 5-HT2 receptors induce detrusor contraction of the bladder body. 5-HT1A is suggested to have a similar effect to 5-HT2, while 5-HT3 might suppress detrusor contraction evoked by direct muscle stimulation. Postjunctional 5-HT7 is reported to induce relaxation of the bladder neck, which might be required for efficient voiding. 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT7 subtypes also could act as prejunctional receptors in autonomic excitatory nerve terminals. 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT7 subtypes facilitate the neurogenic contraction of the detrusor by enhancing cholinergic or purinergic transmission, whereas 5-HT1A receptors might inhibit the release of acetylcholine in the detrusor. Furthermore, 5-HT1D could be involved in the suppression of ATP release from the urothelium, aiding visceral sensation of the urinary bladder. In the central pathways controlling the micturition reflex, 5-HT1A, 5-HT2A, and 5-HT7 are involved in regulation of bladder and urethral sphincter activities. Their functions, especially that of 5-HT1A, vary in a species- and site (spinal or supraspinal)- dependent manner. In addition to urinary bladder, 5-HT could be involved in prostate contraction and cell proliferation. Evidence indicates that 5-HT receptor subtypes may be novel therapeutic targets for lower urinary tract symptoms.

FUNDING

Grants-in-Aid for Scientific Research (C) (KAKENHI 23590707, 24590722, and 26460694) from the Japan Society for the Promotion of Science.

Anatomy and physiology of the lower urinary tract

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

Sex differences in neonatal and young adult rat lower urinary tract function caused by bladder reduction

INTRODUCTION

Pediatric urinary incontinence has been proposed as a cause for adult urinary incontinence, yet animal models mimic the findings of overactive bladder more closely than dysfunctional voiding. We used the bladder reduction (BR) model to study the effects of early external urethral sphincter (EUS) dysfunction on the maturation of lower urinary tract function in neonatal and young adult rats of both sexes.

OBJECTIVE

To determine long-term alterations in bladder and EUS function in young adult rats caused by neonatal BR.

MATERIALS AND METHODS

46 Sprague-Dawley rats underwent BR and 52 underwent sham surgery at 1 week of age. At 3, 6, and 9 weeks of life, cystometry was carried out, 8-OH-DPAT (serotonergic receptor agonist) and WAY 100,635 (serotonergic receptor antagonist) were administered intravenously. Pressure threshold (PT), volume threshold (VT), storage tonic AUC, contraction area under the curve (AUC), EUS burst amplitude and burst duration were measured at baseline and after administration of serotonergic agents.

RESULTS

PT increased in 3-week BR females compared with shams (31.1 vs. 22.7 cm H2O, p < 0.01), in conjunction with less efficient EUS emptying, as burst amplitude was suppressed (BR 0.04 vs. sham 0.07 mV, p < 0.05). VT subsequently increased in 9-week BR females compared with shams (0.81 vs. 0.36 mL, p < 0.05). Although 3-week BR males also experienced suppressed burst amplitude (BR 0.17 vs. sham 0.28 mV, p < 0.05), they showed no difference in PT at 3 weeks or VT at 9 weeks compared with sham males. The burst amplitude returned to normal in 6- and 9-week BR animals of both sexes, confirming a spontaneous recovery of EUS function over time. The thresholds for voiding in male rats are not as sensitive to early changes in EUS function compared with female rats. The response to serotonergic agents was identical between BR and sham animals. In the female animals, 8-OH-DPAT increased storage tonic AUC and burst duration, whereas in male animals, 8-OH-DPAT increased contraction AUC, burst amplitude, and burst duration. WAY 100,635 reversed the enhancements of EUS function caused by 8-OH-DPAT.

CONCLUSIONS

BR caused a temporary impairment of EUS emptying at 3 weeks of life, similar to dysfunctional voiding, while serotonergic agonists remained effective at enhancing EUS emptying in BR animals. Although EUS emptying spontaneously improved, the increase in VT in female young adult rats suggests that timely treatment of EUS dysfunction is required to decrease the risk of long-term bladder dysfunction.

Spinal stimulation of the upper lumbar spinal cord modulates urethral sphincter activity in rats after spinal cord injury

After spinal cord injury (SCI), the neurogenic bladder is observed to develop asynchronous bladder and external urethral sphincter (EUS) contractions in a condition known as detrusor-sphincter dyssnergia (DSD). Activation of the EUS spinal controlling center located at the upper lumbar spinal cord may contribute to reduce EUS dyssynergic contractions and decrease urethral resistance during voiding. However, this mechanism has not been well studied. This study aimed at evaluating the effects of epidural stimulation (EpS) over the spinal EUS controlling center (L3) in combination with a serotonergic receptor agonist on EUS relaxation in naive rats and chronic (6-8 wk) T8 SCI rats. Cystometrogram and EUS electromyography (EMG) were obtained before and after the intravenous administration of 5HT-1A receptor agonist and antagonist. The latency, duration, frequency, amplitude, and area under curve of EpS-evoked EUS EMG responses were analyzed. EpS on L3 evoked an inhibition of EUS tonic contraction and an excitation of EUS intermittent bursting/relaxation correlating with urine expulsion in intact rats. Combined with a 5HT-1A receptor agonist, EpS on L3 evoked a similar effect in chronic T8 SCI rats to reduce urethral contraction (resistance). This study examined the effect of facilitating the EUS spinal controlling center to switch between urine storage and voiding phases by using EpS and a serotonergic receptor agonist. This novel approach of applying EpS on the EUS controlling center modulates EUS contraction and relaxation as well as reduces urethral resistance during voiding in chronic SCI rats with DSD.

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.

Influence of serotonergic mechanisms on the urine flow rate in male rats

This study extensively examined the role of a 5-HT(1A) receptor in controlling voiding function in anesthetized male rats. A simultaneous recording of the intravesical pressure (IVP), external urethral sphincter (EUS)-electromyography (EMG), and urine flow rate (UFR) during continuous cystometry was used. 8-Hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), a 5-HT(1A) receptor agonist, significantly improved the voiding efficiency, as detected by increases in the evoked contraction amplitude, EUS burst period, and silent period, and decreases in the volume threshold, pressure threshold, and residual volume. Interestingly, the UFR during voiding was reduced by 8-OH-DPAT, as evidenced by decreases in the maximal UFR and mean UFRs of the voiding period, spike duration, and interspike interval. Conversely, treating rats with WAY-100635, a 5-HT(1A) antagonist, produced effects opposite to those produced by 8-OH-DPAT. These findings suggest that 8-OH-DPAT improved the voiding efficiency by enhancing the detrusor contractile ability and prolonging EUS burst period, which would compensate for the lower UFR, resulting from urethral smooth muscle contractions and longer EUS silent periods during voiding. The present study contributes to our understanding of the role of 5-HT(1A) receptors in controlling the urine flow rate in male rats.

Preclinical evidence supporting the clinical development of central pattern generator-modulating therapies for chronic spinal cord-injured patients

Ambulation or walking is one of the main gaits of locomotion. In terrestrial animals, it may be defined as a series of rhythmic and bilaterally coordinated movement of the limbs which creates a forward movement of the body. This applies regardless of the number of limbs-from arthropods with six or more limbs to bipedal primates. These fundamental similarities among species may explain why comparable neural systems and cellular properties have been found, thus far, to control in similar ways locomotor rhythm generation in most animal models. The aim of this article is to provide a comprehensive review of the known structural and functional features associated with central nervous system (CNS) networks that are involved in the control of ambulation and other stereotyped motor patterns-specifically Central Pattern Generators (CPGs) that produce basic rhythmic patterned outputs for locomotion, micturition, ejaculation, and defecation. Although there is compelling evidence of their existence in humans, CPGs have been most studied in reduced models including in vitro isolated preparations, genetically-engineered mice and spinal cord-transected animals. Compared with other structures of the CNS, the spinal cord is generally considered as being well-preserved phylogenetically. As such, most animal models of spinal cord-injured (SCI) should be considered as valuable tools for the development of novel pharmacological strategies aimed at modulating spinal activity and restoring corresponding functions in chronic SCI patients.

Sexually dimorphic urethral activity in response to pharmacological activation of 5-HT1A receptors in the rat

In this study, we examined the possibility that 5-HT1A receptors may underlie sexually dimorphic mechanisms affecting the regulation of urethral functions in anesthetized rats. Simultaneous recordings of intravesical pressure under isovolumetric conditions, external urethral sphincter-electromyography, and urethral perfusion pressure were used to examine the effects of a 5-HT1A receptor agonist [8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT)] and antagonist (WAY-100635) on bladder and urethral functions. This research also evaluated the effects of 8-OH-DPAT and α-bungarotoxin (a neuromuscular blockade agent) on urethral continence using leak point pressure testing, and the distribution of 5-HT1A receptors in the lower urinary tract was assessed by immunohistochemistry. The serotonergic mechanism that controls the urinary bladder and external urethral sphincter-electromyography activity showed no significant sexual differences, but urethral activity in urethral perfusion pressure and leak point pressure values exhibited some sexual differences. 8-OH-DPAT enhanced urethral pressure during continence in rats of both sexes, but the drug elevated the pressure during voiding in male rats and reduced it in female rats. The distribution of 5-HT1A receptors in the spinal cord also showed some sexual differences. The present study contributes to our understanding of the role of 5-HT1A receptors in physiological and immunohistochemical properties of urethral smooth muscle in rats of different sexes. These findings may be a basis for the future development of pharmacotherapies for stress urinary incontinence in men.

Coadministration of low-dose serotonin/noradrenaline reuptake inhibitor (SNRI) duloxetine with α 2-adrenoceptor blockers to treat both female and male mild-to-moderate stress urinary incontinence (SUI)

BACKGROUND

Female urinary incontinence is a relatively common disorder affecting women in different age groups, with significant prevalence amounts of stress-related subtype (stress urinary incontinence, SUI). Various neurotransmitters/neuromodulators - particularly both the glutamatergic and GABA-ergic ones - are involved in micturition/urinary continence nerve centre-based control, where Onuf's nucleus plays an important functional role under the adiuvant serotoninergic/ noradrenergic influences.

OBJECTIVES

To outline, deriving them from the literature review, the SUI therapeutic implications of SNRI (serotonin-noradrenaline reuptake inhibitors) particularly of the duloxetine, though displaying its full therapeutic dose (40 mg twice/day)-related side effects and, therefore, highlighting recent issues concerning novel drug administration modalities to avoid such adverse events. EMERGING KNOWLEDGES: Intriguing studies in SUI animal models have shown that co-administration of duloxetine low dose with α 2-adrenoceptor antagonists - given the α 2-adrenoceptor inhibition-induced enhancement of duloxetine effectiveness on the urethral rhabdospincter-can avoid the duloxetine-related adverse events though perspectively reaching, in perspective translational clinical applications, the awaited beneficial effects for women suffering from intrinsic rhabdosphincter deficiency-based mild-to-moderate SUI as well as, in men, to treat post-prostatectomy mild SUI.

Serotonergic 5-HT(1A) receptor agonist (8-OH-DPAT) ameliorates impaired micturition reflexes in a chronic ventral root avulsion model of incomplete cauda equina/conus medullaris injury

Trauma to the thoracolumbar spine commonly results in injuries to the cauda equina and the lumbosacral portion of the spinal cord. Both complete and partial injury syndromes may follow. Here, we tested the hypothesis that serotonergic modulation may improve voiding function after an incomplete cauda equina/conus medullaris injury. For this purpose, we used a unilateral L5-S2 ventral root avulsion (VRA) injury model in the rat to mimic a partial lesion to the cauda equina and conus medullaris. Compared to a sham-operated series, comprehensive urodynamic studies demonstrated a markedly reduced voiding efficiency at 12 weeks after the VRA injury. Detailed cystometrogram studies showed injury-induced decreased peak bladder pressures indicative of reduced contractile properties. Concurrent external urethral sphincter (EUS) electromyography demonstrated shortened burst and prolonged silent periods associated with the elimination phase. Next, a 5-HT(1A) receptor agonist, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), was administered intravenously at 12 weeks after the unilateral L5-S2 VRA injury. Both voiding efficiency and maximum intravesical pressure were significantly improved by 8-OH-DPAT (0.3-1.0 mg/kg). 8-OH-DPAT also enhanced the amplitude of EUS tonic and bursting activity as well as duration of EUS bursting and silent period during EUS bursting. The results indicate that 8-OH-DPAT improves voiding efficiency and enhances EUS bursting in rats with unilateral VRA injury. We conclude that serotonergic modulation of the 5-HT(1A) receptor may represent a new strategy to improve lower urinary tract function after incomplete cauda equina/conus medullaris injuries in experimental studies.

Effect of ovariectomy on external urethral sphincter activity in anesthetized female rats

PURPOSE

The postmenopausal hypoestrogen condition is associated with various lower urinary tract dysfunctions, including frequency, urgency, stress urinary incontinence and recurrent urinary infection. We determined whether hypoestrogen induced lower urinary tract dysfunction after ovariectomy is also associated with an alteration in external urethral sphincter activity.

MATERIALS AND METHODS

Bilateral ovariectomy was performed in female Sprague-Dawley® rats and sham operated rats served as controls. Transvesical cystometry and external urethral sphincter electromyogram activity were monitored 4, 6 and 12 weeks after sham operation or bilateral ovariectomy and at 6 weeks in bilaterally ovariectomized rats treated with estrogen.

RESULTS

The micturition reflex was elicited in sham operated and bilaterally ovariectomized, urethane anesthetized animals. Post-void residual urine increased and voiding efficiency decreased in rats with 4 to 12 weeks of bilateral ovariectomy. The silent period of external urethral sphincter electromyogram activity was shortened significantly and progressively at increased times after bilateral ovariectomy. These effects were prevented by estradiol treatment.

CONCLUSIONS

As evidenced by shortening of the external urethral sphincter electromyogram silent period in ovariectomized rats, the disruption of coordination between the external urethral sphincter and the detrusor muscle could decrease urine outflow and in turn voiding efficiency. Estrogen replacement reverses these changes, suggesting that the central pathways responsible for detrusor-sphincter coordination are modulated by gonadal hormones.

Effect of a 5-HT1A receptor agonist (8-OH-DPAT) on external urethral sphincter activity in a rat model of pudendal nerve injury

Although serotonergic agents have been used to treat patients with stress urinary incontinence, the characteristics of the external urethral sphincter (EUS) activity activated by 5-HT receptors have not been extensively studied. This study examined the effects of the 5-HT(1A) receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), on the EUS-electromyography and resistance of the urethra in a rat model with bilateral pudendal nerve injury (BPNI). Two measurements were utilized to assess the effects of the drug on bladder and urethral functions: the simultaneous recordings of transvesical pressure under isovolumetric conditions [isovolumetric intravesical pressure (IVP)] and urethral perfusion pressure, and the simultaneous recordings of IVP during continuously isotonic transvesical infusion with an open urethra (isotonic IVP) and EUS-electromyography. This study also evaluated the urethral continence using leak point pressure testing. The urethral perfusion pressure and leak point pressure measurements of BPNI rats reveal that 8-OH-DPAT significantly increased urethral resistance during the bladder storage phase, yet decreased resistance during the voiding phase. The entire EUS burst period was significantly prolonged, within which the average silent period increased and the frequency of burst discharges decreased. 8-OH-DPAT also improved the voiding efficiency, as evidenced by the detection of decreases in the contraction amplitude and residual volume, with increases in contraction duration and voided volume. These findings suggest that 8-OH-DPAT not only improved continence function, but also elevated the voiding function in a BPNI rat model.

Role of vasopressin V1A receptor in the urethral closure reflex in rats

An enhanced urethral closure reflex via the spinal cord is related to urethral resistance elevation during increased abdominal pressure. However, with the exception of monoamines, neurotransmitters modulating this reflex are not understood. We investigated whether the vasopressin V1A receptor (V1AR) is involved in the urethral closure reflex in urethane-anesthetized female rats. V1AR mRNA was highly expressed among the vasopressin receptor family in the total RNA purified from lamina IX in the spinal cord L6–S1 segment. In situ hybridization analysis of the spinal L6–S1 segment confirmed that these positive signals from the V1ARs were only detected in lamina IX. Intrathecally injected Arg8-vasopressin (AVP), an endogenous ligand, significantly increased urethral resistance during an intravesical pressure rise, and its effect was blocked by the V1AR antagonist. AVP did not increase urethral resistance in rats in which the pelvic nerves were transected bilaterally. Urethral closure reflex responses to the intravesical pressure rise increased by up to threefold compared with the baseline response after AVP administration in contrast to no increase by vehicle. In addition, intravenously and intrathecally injected V1AR antagonists decreased urethral resistance. These results suggest that V1AR stimulation in the spinal cord enhances the urethral closure reflex response, thereby increasing urethral resistance during an abdominal pressure rise and that V1AR plays a physiological role in preventing urine leakage.

Neural control of the female urethral and anal rhabdosphincters and pelvic floor muscles

The urethral rhabdosphincter and pelvic floor muscles are important in maintenance of urinary continence and in preventing descent of pelvic organs [i.e., pelvic organ prolapse (POP)]. Despite its clinical importance and complexity, a comprehensive review of neural control of the rhabdosphincter and pelvic floor muscles is lacking. The present review places historical and recent basic science findings on neural control into the context of functional anatomy of the pelvic muscles and their coordination with visceral function and correlates basic science findings with clinical findings when possible. This review briefly describes the striated muscles of the pelvis and then provides details on the peripheral innervation and, in particular, the contributions of the pudendal and levator ani nerves to the function of the various pelvic muscles. The locations and unique phenotypic characteristics of rhabdosphincter motor neurons located in Onuf's nucleus, and levator ani motor neurons located diffusely in the sacral ventral horn, are provided along with the locations and phenotypes of primary afferent neurons that convey sensory information from these muscles. Spinal and supraspinal pathways mediating excitatory and inhibitory inputs to the motor neurons are described; the relative contributions of the nerves to urethral function and their involvement in POP and incontinence are discussed. Finally, a detailed summary of the neurochemical anatomy of Onuf's nucleus and the pharmacological control of the rhabdosphincter are provided.

Pelvic floor muscles and the external urethral sphincter have different responses to applied bladder pressure during continence

OBJECTIVES

To determine the functional innervation of the pelvic floor muscles (PFM) and whether there is PFM activity during an external pressure increase to the bladder in female rats.

METHODS

Thirty-one female adult virgin Sprague-Dawley rats received an external increase in bladder pressure until urinary leakage was noted while bladder pressure was recorded (leak point pressure [LPP]) under urethane anesthesia. Six of the rats underwent repeat LPP testing after bilateral transection of the levator ani nerve. Another 6 rats underwent repeat LPP testing after bilateral transection of the pudendal nerve. Simultaneous recordings of PFM (pubo- and iliococcygeus muscles), electromyogram (EMG), and external urethral sphincter (EUS) EMG were recorded during cystometry and LPP testing.

RESULTS

Thirteen rats (42%) showed tonic PFM EMG activity during filling cystometry. Eighteen rats (58%) showed no tonic PFM EMG activity at baseline, but PFM EMG could be activated by pinching the perineal skin. This activity could be maintained unless voiding occurred. The external increase in bladder pressure caused significantly increased EUS EMG activity as demonstrated by increased amplitude and frequency. However, there was no such response in PFM EMG. LPP was not significantly different after levator ani nerve transection, but was significantly decreased after pudendal nerve transection.

CONCLUSIONS

PFM activity was not increased during external pressure increases to the bladder in female rats. Experimental designs using rats should consider this result. The PFM, unlike the EUS, does not contribute to the bladder-to-urethra continence reflex. PFM strengthening may nonetheless facilitate urinary continence clinically by stabilizing the bladder neck.

Role of 5-HT1A receptors in control of lower urinary tract function in anesthetized rats

The role of 5-hydroxytryptamine (5-HT) 1A (5-HT1A) receptors in lower urinary tract function was examined in urethane-anesthetized female Sprague-Dawley rats. Bladder pressure and the external urethral sphincter electromyogram (EUS EMG) activity were recorded during continuous-infusion transvesical cystometrograms (TV-CMGs) to allow voiding and during transurethral-CMGs (TU-CMGs) which prevented voiding and allowed recording of isovolumetric bladder contractions. 8-Hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, decreased volume threshold (VT) for initiating voiding and increased contraction amplitude (CA) during TU-CMGs but decreased CA during TV-CMGs. 8-OH-DPAT prolonged EUS bursting as well as the intrabursting silent periods (SP) during voiding. N-[2-[4-(2-methoxyphenyl)-1- piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamine trihydrochloride (WAY-100635), a 5-HT1A antagonist, increased VT, increased residual volume, markedly decreased voiding efficiency, decreased the amplitude of micturition contractions recorded under isovolumetric conditions, and decreased the SP of EUS bursting. These results indicate that activation of 5-HT1A receptors by endogenous 5-HT lowers the threshold for initiating reflex voiding and promotes voiding function by enhancing the duration of EUS relaxation, which should reduce urethral outlet resistance.

Anatomical tracer injections into the lower urinary tract may compromise cystometry and external urethral sphincter electromyography in female rats

Physiological and anatomical investigations are commonly combined in experimental models. When studying the lower urinary tract (LUT), it is often of interest to perform both urodynamic studies and retrogradely labeled neurons innervating the peripheral target organs. However, it is not known whether the use of anatomical tracers for the labeling of, e.g. spinal cord neurons may interfere with the interpretation of the physiological studies on micturition reflexes. We performed cystometry and external urethral sphincter (EUS) electromyography (EMG) under urethane anesthesia in adult female rats at 5-7 days after injection of a 5% fluorogold (FG) solution or vehicle into the major pelvic ganglia (MPG) or the EUS. FG and vehicle injections into the MPG and EUS resulted in decreased voiding efficiency. MPG injections increased the duration of both bladder contractions and the inter-contractile intervals. EUS injections decreased EUS EMG bursting activity during voiding as well as increased both the duration of bladder contractions and the maximum intravesical pressure. In addition, the bladder weight and size were increased after either MPG or EUS injections in both the FG and vehicle groups. We conclude that the injection of anatomical tracers into the MPG and EUS may compromise the interpretation of subsequent urodynamic studies and suggest investigators to consider experimental designs, which allow for physiological assessments to precede the administration of anatomical tracers into the LUT.

Role of spinal serotonergic pathways in sneeze-induced urethral continence reflex in rats

To clarify the role of spinal serotonergic mechanisms in preventing stress urinary incontinence (SUI) during sneezing, we investigated the effect of intrathecal (it) application of 8-OH-DPAT (a 5-HT(1A) agonist), mCPP (a 5-HT(2B/2C) agonist), and fluoxetine (a serotonin reuptake inhibitor) using a rat model that can examine the neurally evoked continence reflex during sneezing. Amplitudes of urethral pressure responses during sneezing (A-URS), urethral baseline pressure (UBP) at the midurethra, and sneeze-induced leak point pressure (S-LPP) were measured in normal female adult rats and rats with SUI induced by vaginal distention (VD). In normal rats, 8-OH-DPAT decreased A-URS by 48.9%, whereas mCPP increased A-URS by 33.6%. However, A-URS was not changed after fluoxetine. 8-OH-DPAT, mCPP, or fluoxetine did not alter UBP. The effect of 8-OH-DPAT and mCPP was antagonized by WAY-100635 (it), a selective 5-HT(1A) antagonist, and RS-102221 (it), a selective 5-HT(2C) antagonist, respectively. Fluoxetine in the presence of WAY-100635 did not change either A-URS or UBP, but fluoxetine in the presence of RS-102221 decreased A-URS. In VD rats, S-LPP was decreased by 14.6 cmH2O after 8-OH-DPAT, whereas it was increased by 12.8 cmH2O after mCPP. However, S-LPP was not changed after fluoxetine. These results indicate that activation of 5-HT(2C) receptors enhances the active urethral closure reflex during sneezing at the spinal level, whereas 5-HT(1A) inhibits it and that no apparent changes in the sneeze-induced continence reflex after fluoxetine treatment are due to coactivation of excitatory 5-HT(2C) receptors and inhibitory 5-HT receptors other than the 5-HT(1A) subtype. Thus, activation of excitatory 5-HT receptor subtypes such as 5-HT(2C) could be effective for the treatment of SUI.

Role of alpha2-adrenoceptors and glutamate mechanisms in the external urethral sphincter continence reflex in rats

PURPOSE

We investigated the role of alpha(2)-adrenoceptors and glutamate mechanisms in the urethral continence reflex in response to abdominal pressure increases.

MATERIALS AND METHODS

Under urethane anesthesia external urethral sphincter electromyogram activity was evaluated in spinal cord transected (T8-T9) female rats during lower abdominal wall compression before and after intravenous application of test drugs. The effects of the N-methyl-D-aspartate glutamate receptor antagonist MK-801 (Sigma) or the alpha(2)-adrenoceptor agonist medetomidine (Tocris Cookson, Ellisville, Missouri) (each 0.03, 0.3 and 3 mg/kg intravenously) on external urethral sphincter activity were examined. A 0.3 mg/kg intravenous dose of the alpha(2)-adrenoceptor antagonist idazoxan (Sigma) was then administered before or after the application of 1 mg/kg MK-801 intravenously. In addition, 0.3 mg/kg idazoxan were administered intravenously following the application of 1 mg/kg of the serotonin/norepinephrine reuptake inhibitor duloxetine (Kemprotec, Middlesbrough, United Kingdom) intravenously.

RESULTS

MK-801 and medetomidine dose dependently decreased external urethral sphincter activity. Idazoxan significantly increased external urethral sphincter activity by 64% but the increase in activity after idazoxan was abolished by MK-801. On the other hand, idazoxan did not reverse the inhibitory effects of MK-801. In addition, idazoxan significantly potentiated the duloxetine effects on external urethral sphincter activity by 120%.

CONCLUSIONS

These results indicate that 1) glutamate is a major excitatory neurotransmitter in the urethral continence reflex response to abdominal pressure increases, 2) alpha(2)-adrenoceptor activation suppresses external urethral sphincter activity, probably via presynaptic inhibition of glutamate release and 3) the effects of serotonin/norepinephrine reuptake inhibitors are enhanced by alpha(2)-adrenoceptor inhibition. Therefore, alpha(2)-adrenoceptor antagonists could be beneficial for treating stress urinary incontinence.

The neural control of micturition

Micturition, or urination, occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. The neural circuitry that controls this process is complex and highly distributed: it involves pathways at many levels of the brain, the spinal cord and the peripheral nervous system and is mediated by multiple neurotransmitters. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary or reflex micturition, leading to urinary incontinence. This is a major health problem, especially in those with neurological impairment. Here we review the neural control of micturition and how disruption of this control leads to abnormal storage and release of urine.

Effect of duloxetine, a norepinephrine and serotonin reuptake inhibitor, on sneeze-induced urethral continence reflex in rats

We investigated the effect of duloxetine, a norepinephrine (NE) and serotonin (5-HT) reuptake inhibitor, on the neurally evoked urethral continence reflex induced by sneezing in rats. To clarify the role of noradrenergic and serotonergic mechanisms in preventing stress urinary incontinence (SUI) during sneezing, we examined the effect of duloxetine followed by intrathecal (it) methiothepin maleate (5-HT receptor and alpha1-adrenoceptor antagonist) or terazosin or idazoxan (selective alpha1- and alpha2-adrenoceptor antagonists, respectively). Amplitude of urethral pressure responses during sneezing (A-URS), urethral baseline pressure (UBP) at the midurethra, and sneeze-induced leak point pressure (S-LPP) were measured in normal adult female rats and rats with SUI induced by vaginal distension (VD). In normal and VD rats, intravenous application of duloxetine (1 mg/kg) increased A-URS by 35% and 34% and UBP by 21% and 34%, respectively. Sneezing-induced fluid leakage from the urethral orifice was observed in VD rats but not in normal rats. S-LPP was increased from 39.1 to 92.2 cmH2O by intravenous duloxetine in incontinent VD rats. Duloxetine-mediated enhancement of A-URS was inhibited by terazosin but not methiothepin maleate (it). In addition, simultaneous intrathecal application of methiothepin and terazosin induced a reduction in A-URS during sneezing, which was not increased by intravenous duloxetine. However, the reduced A-URS after intrathecal application of methiothepin and terazosin returned to the control level when duloxetine (iv) was applied after intrathecal idazoxan administration. These results indicate that duloxetine can prevent SUI by facilitating noradrenergic and serotonergic systems in the spinal cord to enhance the sneeze-induced active urethral closure mechanism.

Nicotine-activated descending facilitation on spinal NMDA-dependent reflex potentiation from pontine tegmentum in rats

This study was conducted to investigate the possible neurotransmitter that activates the descending pathways coming from the dorsolateral pontine tegmentum (DPT) to modulate spinal pelvic-urethra reflex potentiation. External urethra sphincter electromyogram (EUSE) activity in response to test stimulation (TS, 1/30 Hz) and repetitive stimulation (RS, 1 Hz) on the pelvic afferent nerve of 63 anesthetized rats were recorded with or without microinjection of nicotinic cholinergic receptor (nAChR) agonists, ACh and nicotine, to the DPT. TS evoked a baseline reflex activity with a single action potential (1.00 ± 0.00 spikes/stimulation, n = 40), whereas RS produced a long-lasting reflex potentiation (16.14 ± 0.96 spikes/stimulation, n = 40) that was abolished by d-2-amino-5-phosphonovaleric acid (1.60 ± 0.89 spikes/stimulation, n = 40) and was attenuated by 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxaline (7.10 ± 0.84 spikes/stimulation, n = 40). ACh and nicotine microinjections to DPT both produced facilitation on the RS-induced reflex potentiation (23.57 ± 2.23 and 28.29 ± 2.36 spikes/stimulation, P < 0.01, n = 10 and 20, respectively). Pretreatment of selective nicotinic receptor antagonist, chlorisondamine, reversed the facilitation on RS-induced reflex potentiation caused by nicotine (19.41 ± 1.21 spikes/stimulation, P < 0.01, n = 10) Intrathecal WAY-100635 and spinal transection at the T1level both abolished the facilitation on reflex potentiation resulting from the DPT nicotine injection (12.86 ± 3.13 and 15.57 ± 1.72 spikes/stimulation, P < 0.01, n = 10 each). Our findings suggest that activation of nAChR at DPT may modulate N-methyl-d-aspartic acid-dependent reflex potentiation via descending serotonergic neurotransmission. This descending modulation may have physiological/pathological relevance in the neural controls of urethral closure.

Re-established micturition reflexes show differential activation patterns after lumbosacral ventral root avulsion injury and repair in rats

Previous studies have demonstrated that an acute implantation of lesioned lumbosacral ventral roots into the rat conus medullaris (CM) results in functional reinnervation of the lower urinary tract (LUT). Although the root implantation procedure results in a return of reflexive micturition, voiding efficiency (VE) remains incompletely recovered. Here, we performed a detailed urodynamic analysis of cystometry and external urethral sphincter (EUS) electromyography (EMG) recordings to determine underlying mechanisms for the incompletely recovered VE. For this purpose, adult female rats were studied at 12 weeks after a bilateral L5-S2 ventral root avulsion injury followed by an acute surgical implantation of the avulsed L6 and S1 ventral roots into the CM (n=6). Age-matched sham-operated rats (n=6) were included for control purposes. Compared to sham-operated controls, rats of the implanted series showed 1) reflex bladder contractions with a significantly shortened urine expulsion phase, 2) markedly decreased phasic EUS EMG activity during micturition, and 3) a pronounced bladder-sphincter dys-coordination, as demonstrated by a significantly delayed onset of the switch from low-amplitude tonic EUS EMG activity to either phasic EUS EMG activity or a large-amplitude tonic EUS EMG activity during the urine expulsion phase. Our findings provide a mechanistic explanation for the incomplete recovery of the VE following implantation of avulsed ventral roots into the spinal cord. Our future studies will aim to increase successful axonal regeneration in attempts to augment the recovery of the LUT after cauda equina injury and repair.

Effect of exogenous glutamate and N-Methyl-D-aspartic acid on spontaneous activity of isolated human ureter

OBJECTIVES

While the neurotransmitter role of glutamate in the gastrointestinal tract has been shown, its effects on smooth muscle of the human ureter have not previously been investigated. In our study we have investigated the effects of exogenous glutamate on the spontaneous activity of isolated human ureter, taken from 14 adult patients after nephrectomy.

METHODS

The segment of ureter, excised 3 cm distal from the pyeloureteral junction, was isolated in an organ bath. Both longitudinal tension and intraluminal pressure of the segment were recorded simultaneously.

RESULTS

Glutamate administered in the lumen of the isolated ureteral segments (7.8 x 10(-7) M/L-3.5 x 10(-2) M/L) was ineffective. When added to the isolated organ bath from the serous side of the ureteral segment, glutamate (7.9 x 10(-6) M/L-10.6 x 10(-3) M/L) and N-Methyl-D-aspartic acid (NMDA) (9.1 x 10(-8) M/L-3.1 x 10(-5) M/L) produced a concentration-dependent increase in spontaneous activity of the isolated preparations, while kainic acid (6.3 x 10(-8) M/L-10.5 x 10(-5) M/L) and (+/-)-trans-1-Aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD) (7.7 x 10(-8) M/L -6.5 x 10(-5) M/L) were ineffective.

CONCLUSIONS

The results of our study suggest that an excitatory neurotransmitter glutamate stimulates spontaneous activity of the human ureter through activation of NMDA ionotropic receptors, located on smooth muscle cells or intramural nerve fibers.

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.

Descending facilitation of spinal NMDA-dependent reflex potentiation from pontine tegmentum in rats

This study was conducted to investigate whether dorsolateral pontine tegmentum stimulation modulates spinal reflex potentiation (SRP) and whether serotonergic neurotransmission is involved in such a modulation. Reflex activities of the external urethra sphincter (EUS) electromyogram in response to a test stimulation (TS; 1/30 Hz) or repetitive stimulation (RS; 1 Hz) on the pelvic afferent nerve in 35 anesthetized rats were recorded with/without synchronized train pontine stimulation (PS; 300 Hz, 30 ms) and/or intrathecal administrations of 10 μl of 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxaline (NBQX; 100 μM), d-2-amino-5-phosphonovalerate (APV; 100 μM), N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY 100635; 100 μM), and 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT; 100 μM). The TS evoked a single action potential (1.00 ± 0.00 spikes/stimulation), while the RS produced a long-lasting SRP (16.12 ± 1.59 spikes/stimulation) that was abolished by APV (1.57 ± 0.29 spikes/stimulation) and was attenuated by NBQX (7.42 ± 0.57 spikes/stimulation). Synchronized train PS with RS (PS+RS) produced facilitation in RS-induced SRP (25.17 ± 2.21 spikes/stimulation). Intrathecal WAY 100635 abolished the facilitation in SRP as a result of the synchronized PS (14.66 ± 1.58 spikes/stimulation). On the other hand, intrathecal 8-OH-DPAT elicited facilitation in the RS-induced SRP (25.16 ± 1.05 spikes/stimulation) without synchronized PS. Our findings suggest that dorsolateral pontine tegmentum may modulate N-methyl-d-aspartic acid-dependent SRP via descending serotonergic neurotransmission. This descending modulation may have physiological/pharmacological relevance in the neural controls of urethral closure.

Spinal glutamatergic NMDA-dependent cyclic pelvic nerve-to-external urethra sphincter reflex potentiation in anesthetized rats

The purposes of this study were to investigate whether the pelvic nerve-to-external urethra sphincter (EUS) reflex potentiation can be induced under physiological conditions and to determine whether glutamatergic neurotransmission is involved in the reflex potentiation. Stimulation-evoked reflex activities, during rhythmic bladder contractions caused by a continuous saline infusion, in 21 anesthetized rats were recorded with/without the intrathecal administration of 10 μl of CNQX (a glutamatergic AMPA receptor antagonist; 100 μM) and APV( a glutamatergic NMDA receptor antagonist; 100 μM). Reflex activities became potentiated following the increment of intravesical pressure (IVP) during the storage phase (2.39 ± 0.28 spikes/mmHg, n = 21) and the ascending period of the voiding phase (1.46 ± 0.35 spikes/mmHg, n = 21) and decreased following the decrement of IVP during the descending period of the voiding phase (1.50 ± 0.33 spikes/mmHg, n = 21). Although it is characterized by a low IVP, a postvoiding reflex potentiation in stimulation-evoked activities was elicited at the critical period after a voiding contraction had just finished (23.95 ± 8.96 spikes/mmHg, n = 21). The slope of the regression line of evoked activities vs. the IVP during the storage phase was significantly ( P < 0.01) higher than that of the ascending and descending periods of the voiding phase, but there was no statistical difference between the ascending and the descending periods ( P > 0.05). In addition, the slope of the regression line of posttetanic reflex potentiation was significantly higher than that of the storage phase ( P < 0.01). All the slopes of the regression lines decreased after intrathecal CNQX administration (from 3.15 ± 0.44, 2.10 ± 0.57, 2.13 ± 0.53, and 21.30 ± 3.41 to 0.83 ± 0.31, 0.74 ± 0.12, 0.76 ± 0.12, and 4.31 ± 3.71 spikes/mmHg in storage, ascending and descending period of the voiding phase, and postvoiding potentiation, respectively; all P < 0.01, n = 10). The slopes of the regression lines became almost horizontal after intrathecal APV administration (from 3.15 ± 0.44, 2.10 ± 0.57, 2.13 ± 0.53, and 21.30 ± 3.41 to 0.16 ± 0.12, 0.21 ± 0.07, 0.18 ± 0.05, and 0.23 ± 0.76 spikes/mmHg in storage, ascending and descending period of voiding phase, and postvoiding potentiation, respectively; all P < 0.01, n = 10). Our results suggest that a potentiation in the pelvic nerve-to-EUS reflex can be induced under physiological conditions and the glutamatergic mechanism appears to be involved in this reflex potentiation.

Spinal glutamatergic NMDA-dependent pelvic nerve-to-external urethra sphincter reflex potentiation caused by a mechanical stimulation in anesthetized rats

The current study investigates whether the spinal pelvic nerve-to-external urethra sphincter (EUS) reflex potentiation can be induced by a mechanical stimulation and whether the glutamatergic mechanism is involved in yielding such a reflex potentiation. The external urethra sphincter electromyogram (EUSE) activity, evoked by a single or by repetitive pelvic nerve stimulation, in 30 anesthetized rats was recorded with/without bladder saline distension. Without saline distension (0 cmH2O), a single pulse nerve stimulation evoked a single action potential in the reflex activity, whereas repetitive pelvic stimulation and saline distension (6∼20 cmH2O) both elicited a long-lasting reflex potentiation (20.05 ± 3.21 and 75.01 ± 9.87 spikes/stimulation, respectively). The saline distension-induced pelvic nerve-to-EUS reflex potentiation was abolished by d-2-amino-5-phosphonovalerate [APV; a glutamatergic N -methyl-d-aspartic acid (NMDA) receptor antagonist; 100 μM, 10 μl, 1.72 ± 0.31 spikes/stimulation] and attenuated by 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxaline [NBQX; a glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA) receptor antagonist; 100 μM, 10 μl, 26.16 ± 7.27 spikes/stimulation], but was not affected by bicuculline (a GABAergic antagonist; 100 μM, 10 μl, 53.62 ± 15.54 spikes/stimulation). Intrathecal administration of glutamate (31.12 ± 8.25 spikes/stimulation, 100 μM, 10 μl) and NMDA (26.25 ± 4.12 spikes/stimulation, 100 μM, 10 μl) both induced a long-lasting pelvic nerve-to-EUS reflex potentiation without saline distension, which was similar to the findings observed from saline distension only. The duration of the contraction wave of the urethra was elongated by the saline distension-induced pelvic nerve-to-EUS reflex potentiation, whereas the peak pressure of the contraction wave was not affected. Our findings suggest that saline distension in the bladder elicits a pelvic nerve-to-EUS reflex potentiation and the glutamatergic mechanism contributes to the presence of such a reflex potentiation.