Alteration by urethane of glutamatergic control of micturition

Reflex voiding in rat occurs at consistent bladder volume regardless of pressure or infusion rate

AIMS

The central nervous system (CNS) regulates lower urinary tract reflexes using information from sensory afferents; however, the mechanisms of this process are not well known. Pressure and volume were measured at the onset of the guarding and micturition reflexes across a range of infusion rates to provide insight into what the CNS is gauging to activate reflexes.

METHODS

Female Sprague Dawley rats were anesthetized with urethane for open outlet cystometry. A set of 10 infusion rates (ranging 0.92-65.5 mL/h) were pseudo-randomly distributed across 30 single-fill cystometrograms. Bladder pressure and external urethral sphincter electromyography were used for the determination of the onset of the micturition and guarding reflexes, respectively. The bladder volume at the onset of both reflexes was estimated from the total infusion rate during a single fill.

RESULTS

In response to many single-fill cystometrograms, there was an increased volume the bladder could store without a significant increase in pressure. Volume was adjusted for this effect for the analysis of how pressure and volume varied with infusion rate at the onset of the micturition and guarding reflexes. In 25 rats, the micturition reflex was evoked at similar volumes across all infusion rates, whereas the pressure at micturition reflex onset increased with increasing infusion rates. In 11 rats, the guarding reflex was evoked at similar pressures across infusion rates, but the volume decreased with increasing infusion rates.

CONCLUSIONS

These results suggest that the CNS is interpreting volume from the bladder to activate the micturition reflex and pressure from the bladder to activate the guarding reflex.

Mid-lumbar (L3) epidural stimulation effects on bladder and external urethral sphincter in non-injured and chronically transected urethane-anesthetized rats

Recent pre-clinical and clinical spinal cord epidural stimulation (scES) experiments specifically targeting the thoracolumbar and lumbosacral circuitries mediating lower urinary tract (LUT) function have shown improvements in storage, detrusor pressure, and emptying. With the existence of a lumbar spinal coordinating center in rats that is involved with external urethral sphincter (EUS) functionality during micturition, the mid-lumbar spinal cord (specifically L3) was targeted in the current study with scES to determine if the EUS and thus the void pattern could be modulated, using both intact and chronic complete spinal cord injured female rats under urethane anesthesia. L3 scES at select frequencies and intensities of stimulation produced a reduction in void volumes and EUS burst duration in intact rats. After chronic transection, three different subgroups of LUT dysfunction were identified and the response to L3 scES promoted different cystometry outcomes, including changes in EUS bursting. The current findings suggest that scES at the L3 level can generate functional neuromodulation of both the urinary bladder and the EUS in intact and SCI rats to enhance voiding in a variety of clinical scenarios.

Assessing Neurogenic Lower Urinary Tract Dysfunction after Spinal Cord Injury: Animal Models in Preclinical Neuro-Urology Research

Neurogenic bladder dysfunction is a condition that affects both bladder storage and voiding function and remains one of the leading causes of morbidity after spinal cord injury (SCI). The vast majority of individuals with severe SCI develop neurogenic lower urinary tract dysfunction (NLUTD), with symptoms ranging from neurogenic detrusor overactivity, detrusor sphincter dyssynergia, or sphincter underactivity depending on the location and extent of the spinal lesion. Animal models are critical to our fundamental understanding of lower urinary tract function and its dysfunction after SCI, in addition to providing a platform for the assessment of potential therapies. Given the need to develop and evaluate novel assessment tools, as well as therapeutic approaches in animal models of SCI prior to human translation, urodynamics assessment techniques have been implemented to measure NLUTD function in a variety of animals, including rats, mice, cats, dogs and pigs. In this narrative review, we summarize the literature on the use of animal models for cystometry testing in the assessment of SCI-related NLUTD. We also discuss the advantages and disadvantages of various animal models, and opportunities for future research.

Age-associated bladder and urethral coordination impairment and changes in urethral oxidative stress in rats

AIMS

We examined age-associated changes in bladder and urethral coordination involving the nitric oxide (NO)/soluble guanylyl cyclase (sGC) system, which induces urethral smooth muscle relaxation, and urethral ischemic/oxidative stress changes in rats.

MAIN METHODS

Sixteen female Sprague-Dawley rats were divided into young (3 months old) and middle-aged (12-15 months old) groups. Urethral activity was evaluated by simultaneously recording intravesical pressure under isovolumetric conditions and urethral perfusion pressure (UPP) under urethane anesthesia. Sodium nitroprusside (SNP, 0.1 mg/kg), an NO donor, and BAY 41-2272, a novel NO-independent stimulator of sGC (0.1 mg/kg), were administered intravenously to both groups. N-nitro-l-arginine methyl ester hydrochloride (l-NAME, 100 mg/kg) was also injected intravenously, to inhibit NO synthase activity in both groups. Staining for the ischemic marker, hypoxia-inducible factor-1α (HIF-1α), and the oxidative stress markers, 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA), was performed on tissue sections of the urethra, in both groups.

KEY FINDINGS

Baseline UPP and UPP changes were significantly lower in middle-aged rats than in young rats. After administration of SNP and BAY 41-2272, baseline UPP and UPP nadir were significantly decreased in both groups. After administration of l-NAME, UPP change/bladder contraction amplitude in young rats was still lower than at baseline but was completely restored to control levels in middle-aged rats. Immunoreactivity of HIF-1α, 8-OHdG, and MDA was higher in middle-aged rats than in young rats.

SIGNIFICANCE

Age-associated ischemic and oxidative stress in the urethra might be correlated with impairment of the NO/sGC system and with coordination of the bladder and urethra.

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.

The long-lasting post-stimulation inhibitory effects of bladder activity induced by posterior tibial nerve stimulation in unanesthetized rats

Tibial nerve stimulation (TNS) is one of the neuromodulation methods used to treat an overactive bladder (OAB). However, the treatment mechanism is not accurately understood owing to significant differences in the results obtained from animal and clinical studies. Thus, this study was aimed to confirm the response of bladder activity to the different stimulation frequencies and to observe the duration of prolonged post-stimulation inhibitory effects following TNS. This study used unanesthetized rats to provide a closer approximation of the clinical setting and evaluated the changes in bladder activity in response to 30 min of TNS at different frequencies. Moreover, we observed the long-term changes of post-stimulation inhibitory effects. Our results showed that bladder response was immediately inhibited after 30 min of 10 Hz TNS, whereas it was excited at 50 Hz TNS. We also used the implantable stimulator to observe a change in duration of the prolonged post-stimulation inhibitory effects of the TNS and found large discrepancies in the time that the inhibitory effect lasted after stimulation between individual animals. This study provides important evidence that can be used to understand the neurophysiological mechanisms underlying the bladder inhibitory response induced by TNS as well as the long-lasting prolonged post-stimulation effect.

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.

Effects of silodosin and tadalafil on bladder dysfunction in spontaneously hypertensive rats: Possible role of bladder blood flow

OBJECTIVES

To investigate the effects of an alpha1-adrenoceptor antagonist, silodosin, or a phosphodiesterase type 5 inhibitor, tadalafil, on bladder overactivity in spontaneously hypertensive rats.

METHODS

Twelve-week-old male spontaneously hypertensive rats were perorally administered silodosin (100 µg/kg), tadalafil (2 or 10 mg/kg) or vehicle once daily for 6 weeks. Wistar rats were used as normotensive controls and were treated with the vehicle. At 18-weeks-old, the effects of silodosin or tadalafil on blood pressure, bladder blood flow, urodynamic parameters (i.e. micturition frequency, urine output, inter-contraction interval, maximum voiding pressure, single voided volume and post-voiding residual urine volume), and bladder tissue levels of malondialdehyde, interleukin-6 and tumor necrosis factor-alpha were measured.

RESULTS

A significant increase in blood pressure, micturition frequency and bladder tissue levels of malondialdehyde, interleukin-6 and tumor necrosis factor-alpha was noted in spontaneously hypertensive rats. The single voided volume, bladder capacity and bladder blood flow were significantly lower in the spontaneously hypertensive rats than in the Wistar rats. Treatment with silodosin and the higher dose of tadalafil improved the urodynamic parameters, bladder blood flow and bladder tissue levels of malondialdehyde in the spontaneously hypertensive rats without affecting the blood pressure and bladder tissue levels of interleukin-6 and tumor necrosis factor-alpha.

CONCLUSIONS

Treatment with silodosin or tadalafil might improve hypertension-related bladder overactivity, as shown in spontaneously hypertensive rats through an improvement in the bladder blood flow and bladder tissue levels of oxidative stress.

Micturition video thermography in awake, behaving mice

BACKGROUND

Our understanding of the neural circuits controlling micturition and continence is constrained by a paucity of techniques for measuring voiding in awake, behaving mice.

NEW METHOD

To facilitate progress in this area, we developed a new, non-invasive assay, micturition video thermography (MVT), using a down-facing thermal camera above mice on a filter paper floor.

RESULTS

Most C57B6/J mice void infrequently, with a stereotyped behavioral sequence, and usually in a corner. The timing of each void is indicated by the warm thermal contrast of freshly voided urine. Over the following 10-15 min, urine cools to ∼3 °C below the ambient temperature and spreads radially in the filter paper. By measuring the area of cool contrast comprising this "thermal void spot," we can derive the initially voided volume. Thermal videos also reveal mouse behaviors including a home-corner preference apart from void spots, and a stereotyped, seconds-long pause while voiding.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

MVT is a robust, non-invasive method for measuring the timing, volume, and location of voiding. It improves on an existing technique, the void spot assay, by adding timing information, and unlike the cystometrogram preparation, MVT does not require surgical catheterization. Combining MVT with current neuroscience techniques will improve our understanding of the neural circuits that control continence, which is important for addressing the growing number of patients with urinary incontinence as the population ages.

Emotional Stress Facilitates Micturition Reflex: Possible Inhibition by an α1-Adrenoceptor Blocker in the Conscious and Anesthetized State

Purpose

To test the hypothesis that naftopidil prolongs intercontraction intervals in rats undergoing chronic stress as observed in previous animal models, voiding behavior and bladder function were measured and analyzed.

Methods

Female Sprague-Dawley rats weighing 200–230 g were exposed to repeated variate stress (RVS) for 1 week, chronic variable mild stress for 2 weeks, or simple mild stress for 1 week. Voiding behavior was assessed in metabolic cages. Voiding frequency and urine output were measured, and changes of these values were compared for the different types of stress. Micturition reflex was analyzed using unconscious cystometry. Naftopidil was administered orally at 30 mg/kg/day for 2 weeks.

Results

Unexpectedly, no stress-exposed rats exhibited increased micturition frequency compared to the normal nonstressed control. However, intercontraction intervals were shortened with each type of stress in the unconscious condition, especially by RVS (P<0.01). Naftopidil prolonged the shortened intervals.

Conclusions

Although voiding behavior appears approximately normal in rats chronically exposed to emotional stress, internal bladder function can be affected. With anesthesia, micturition intervals were moderately shortened by emotional stress and clearly improved by naftopidil. Therefore, naftopidil appears to act at the spinal level at least.

Preserved Adrenal Function After Lumbar Spinal Cord Transection Augments Low Pressure Bladder Activity in the Rat

Spinal cord injury (SCI) disconnects supraspinal micturition centers from the lower urinary tract resulting in immediate and long-term changes in bladder structure and function. While cervical and high thoracic SCI have a greater range of systemic effects, clinical data suggest that those with lower (suprasacral) injuries develop poorer bladder outcomes. Here we assess the impact of SCI level on acute changes in bladder activity. We used two SCI models, T3 and L2 complete transections in male Wistar rats, and compared bladder pressure fluctuations to those of naïve and bladder-denervated animals. By 2 days after L2 transection, but not T3 transection or bladder denervation, small amplitude rhythmic contractions (1 mmHg, 0.06 Hz) were present at low intravesical pressures (<6 mmHg); these were still present 1 month following injury, and at 3 months, bladders from L2 SCI animals were significantly larger than those from T3 SCI or naïve animals. Low-pressure contractions were unaffected by blocking ganglionic signaling or bladder denervation at the time of measurements. L2 (and sham surgery) but not T3 transection preserves supraspinal adrenal control, and by ELISA we show lower plasma adrenal catecholamine concentration in the latter. When an adrenalectomy preceded the L2 transection, the aberrant low-pressure contractions more closely resembled those after T3 transection, indicating that the increased bladder activity after lumbar SCI is mediated by preserved adrenal function. Since ongoing low-pressure contractions may condition the detrusor and exacerbate detrusor-sphincter dyssynergia, moderating bladder catecholamine signaling may be a clinically viable intervention strategy.

Angiotensin II, a stress-related neuropeptide in the CNS, facilitates micturition reflex in rats

BACKGROUND AND PURPOSE

We investigated the effects of centrally administered stress-related neuropeptide, angiotensin II, on the micturition reflex and the downstream signalling pathways in rats.

EXPERIMENTAL APPROACH

Male Wistar rats were anaesthetized with urethane for cystometry before and after i.c.v. administration of vehicle or angiotensin II (30 pmol). Muscimol (a GABA_A receptor agonist) or baclofen (a GABA_B receptor agonist) was i.c.v. administered 30 min before or 15 min after central angiotensin II administration. Telmisartan [an angiotensin II type 1 (AT₁ ) receptor antagonist], valsartan (an AT₁ receptor antagonist), PD123319 (an AT₂ receptor antagonist), U-73122 (a PLC inhibitor), chelerythrine chloride (a PKC inhibitor), apocynin (a NADPH oxidase inhibitor) or tempol (an antioxidant) was centrally administered 30 min before central angiotensin II administration.

KEY RESULTS

Centrally administered angiotensin II significantly shortened the intercontraction interval and decreased the voided volume and bladder capacity without altering the maximum voiding pressure, post-voiding residual urine volume or voiding efficacy. Muscimol, baclofen, telmisartan, valsartan, U-73122, chelerythrine chloride, apocynin or tempol pretreatment significantly suppressed the reduction in intercontraction interval induced by central angiotensin II. Post-treatment with muscimol or baclofen also ameliorated the decrease in intercontraction interval induced by central angiotensin II.

CONCLUSIONS AND IMPLICATIONS

Angiotensin II in the CNS facilitates micturition reflex by inhibiting central GABAergic activity and activating the AT₁ receptor/PLC/PKC/NADPH oxidase/superoxide anion pathway.

Glutamatergic Mechanisms Involved in Bladder Overactivity and Pudendal Neuromodulation in Cats

The involvement of ionotropic glutamate receptors in bladder overactivity and pudendal neuromodulation was determined in α-chloralose anesthetized cats by intravenously administering MK801 (a NMDA receptor antagonist) or CP465022 (an AMPA receptor antagonist). Infusion of 0.5% acetic acid (AA) into the bladder produced bladder overactivity. In the first group of 5 cats, bladder capacity was significantly (P < 0.05) reduced to 55.3±10.0% of saline control by AA irritation. Pudendal nerve stimulation (PNS) significantly (P < 0.05) increased bladder capacity to 106.8 ± 15.0% and 106.7 ± 13.3% of saline control at 2T and 4T intensity, respectively. T is threshold intensity for inducing anal twitching. MK801 at 0.3 mg/kg prevented the increase in capacity by 2T or 4T PNS. In the second group of 5 cats, bladder capacity was significantly (P < 0.05) reduced to 49.0 ± 7.5% of saline control by AA irritation. It was then significantly (P < 0.05) increased to 80.8±13.5% and 79.0±14.0% of saline control by 2T and 4T PNS, respectively. CP465022 at 0.03-1 mg/kg prevented the increase in capacity by 2T PNS and at 0.3-1 mg/kg prevented the increase in capacity by 4T PNS. In both groups, MK801 at 0.3 mg/kg and CP465022 at 1 mg/kg significantly (P < 0.05) increased the prestimulation bladder capacity (about 80% and 20%, respectively) and reduced the amplitude of bladder contractions (about 30 and 20 cmH₂O, respectively). These results indicate that NMDA and AMPA glutamate receptors are important for PNS to inhibit bladder overactivity and that tonic activation of these receptors also contributes to the bladder overactivity induced by AA irritation.

Comparison of spinal cord contusion and transection: functional and histological changes in the rat urinary bladder

OBJECTIVE

To compare the effect of complete transection (tSCI) and contusion spinal cord injury (cSCI) on bladder function and bladder wall structure in rats.

MATERIALS AND METHODS

A total of 30 female Sprague-Dawley rats were randomly divided into three equal groups: an uninjured control, a cSCI and a tSCI group. The cSCI group underwent spinal cord contusion, while the tSCI group underwent complete spinal cord transection. At 6 weeks post-injury, 24-h metabolic cage measurement and conscious cystometry were performed.

RESULTS

Conscious cystometry analysis showed that the cSCI and tSCI groups had significantly larger bladder capacities than the control group. The cSCI group had significantly more non-voiding detrusor contractions than the tSCI group. Both injury groups had more non-voiding contractions compared with the control group. The mean threshold pressure was significantly higher in the tSCI group than in the control and cSCI groups. The number of voids in the tSCI group was lower compared with the control group. Metabolic cage analysis showed that the tSCI group had larger maximum voiding volume as compared with the control and cSCI groups. Vesicular acetylcholine transporter/smooth muscle immunoreactivity was higher in the control than in the cSCI or tSCI rats. The area of calcitonin gene-related peptide staining was smaller in the tSCI group than in the control or cSCI groups.

CONCLUSIONS

Spinal cord transection and contusion produce different bladder phenotypes in rat models of SCI. Functional data suggest that the tSCI group has an obstructive high-pressure voiding pattern, while the cSCI group has more uninhibited detrusor contractions.

Limited Functional Effects of Subacute Syngeneic Bone Marrow Stromal Cell Transplantation after Rat Spinal Cord Contusion Injury

Cell transplantation might be one means to improve motor, sensory, or autonomic recovery after traumatic spinal cord injury (SCI). Among the different cell types evaluated to date, bone marrow stromal cells (BMSCs) have received considerable interest due to their potential neuroprotective properties. However, uncertainty exists whether the efficacy of BMSCs after intraspinal transplantation justifies an invasive procedure. In the present study, we analyzed the effect of syngeneic BMSC transplantation following a moderate to severe rat spinal cord injury. Adult Fischer 344 rats underwent a T9 contusion injury (200 kDy) followed by grafting of GFP-expressing BMSCs 3 days postinjury. Animals receiving a contusion injury without cellular grafts or an injury followed by grafts of syngeneic GFP-expressing fibroblasts served as control. Eight weeks post-transplantation, BMSC-grafted animals showed only a minor effect in one measure of sensorimotor recovery, no significant differences in tissue sparing, and no changes in the recovery of bladder function compared to both control groups in urodynamic measurements. Both cell types survived in the lesion site with fibroblasts displaying a larger graft volume. Thus, contrary to some reports using allogeneic or xenogeneic transplants, subacute intraparenchymal grafting of syngeneic BMSCs has only a minor effect on functional recovery.

Autonomic consequences of spinal cord injury

Spinal cord injury (SCI) results not only in motor and sensory deficits but also in autonomic dysfunctions. The disruption of connections between higher brain centers and the spinal cord, or the impaired autonomic nervous system itself, manifests a broad range of autonomic abnormalities. This includes compromised cardiovascular, respiratory, urinary, gastrointestinal, thermoregulatory, and sexual activities. These disabilities evoke potentially life-threatening symptoms that severely interfere with the daily living of those with SCI. In particular, high thoracic or cervical SCI often causes disordered hemodynamics due to deregulated sympathetic outflow. Episodic hypertension associated with autonomic dysreflexia develops as a result of massive sympathetic discharge often triggered by unpleasant visceral or sensory stimuli below the injury level. In the pelvic floor, bladder and urethral dysfunctions are classified according to upper motor neuron versus lower motor neuron injuries; this is dependent on the level of lesion. Most impairments of the lower urinary tract manifest in two interrelated complications: bladder storage and emptying. Inadequate or excessive detrusor and sphincter functions as well as detrusor-sphincter dyssynergia are examples of micturition abnormalities stemming from SCI. Gastrointestinal motility disorders in spinal cord injured-individuals are comprised of gastric dilation, delayed gastric emptying, and diminished propulsive transit along the entire gastrointestinal tract. As a critical consequence of SCI, neurogenic bowel dysfunction exhibits constipation and/or incontinence. Thus, it is essential to recognize neural mechanisms and pathophysiology underlying various complications of autonomic dysfunctions after SCI. This overview provides both vital information for better understanding these disorders and guides to pursue novel therapeutic approaches to alleviate secondary complications.

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

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

Comparison of the effects of β3 -adrenoceptor agonism on urinary bladder function in conscious, anesthetized, and spinal cord injured rats

AIMS

To compare the dose effect relationship of a selective β3 -adrenoceptor agonist (CL-316,243) on cystometric parameters in anesthetized and conscious rats and to evaluate its effect in a model of neurogenic bladder overactivity induced by spinal cord injury (SCI).

METHODS

Experiments were performed in anesthetized and conscious normal rats and in conscious rats after complete transection at the T8 level of the spinal cord. The jugular vein and urinary bladder were catheterized and the bladder infused with saline. CL-316,243 was tested intravenously at 0.01, 0.03, and 0.1 mg/kg in anesthetized and conscious rats and at 0.01 mg/kg in sham and SCI rats. Intravesical pressure was recorded for 1 hr following drug administration. Intercontraction interval (ICI), amplitude of micturition (AM), micturition frequency (MF) and non-voiding contractions (NVC) were analyzed.

RESULTS

In anesthetized and conscious normal rats, CL-316,243 significantly increased ICI in a dose-dependent manner. In anesthetized rats, AM was significantly decreased at all doses tested whereas in conscious rats, a significant decrease (-19 ± 6%) in AM was only observed at the highest dose (0.1 mg/kg). In conscious sham and SCI rats, CL-316,243 significantly increased ICI (42 ± 17% and 49 ± 17%, respectively) and decreased MF without affecting AM. In SCI rats, CL-316,243 reduced the frequency of NVC (-53 ± 14%) without significant effects on amplitude.

CONCLUSIONS

The current results suggest that anesthesia can alter the effects of β3 -adrenoceptor agonists in experimental models. In addition, this is the first demonstration that stimulation of β3 -adrenoceptors can produce decreases in micturition frequency and NVC in SCI rats without affecting AM.

Roles of the spinal glutamatergic pathway activated through α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and its interactions with spinal noradrenergic and serotonergic pathways in the rat urethral continence mechanisms

AIMS

To investigate the role of the glutamatergic pathway and its relationship to noradrenergic and serotonergic pathways in modulation of the urethral continence reflex during sneezing in rats.

METHODS

In female Sprague-Dawley rats under urethane anesthesia, the effects of an α-amino-3-hydroxy-5-meth-ylisoxazole-4-propionic acid (AMPA) glutamate receptor antagonist, a norepinephrine reuptake inhibitor and a serotonin [5-hydeoxytripitamine (5-HT)]2B/2C agonist on the amplitude of urethral responses during sneezing (AURS), urethral baseline pressure (UBP), and sneeze-induced leak point pressure (S-LPP) were investigated.

RESULTS

Intrathecal application (i.t.) of NBQX disodium salt (an AMPA receptor antagonist) decreased AURS dose-dependently by approximately 60% without affecting UBP and caused stress urinary incontinence (SUI) during sneezing in 60% of normal rats. Nisoxetine (i.t.), a norepinephrine reuptake inhibitor, and mCPP (i.t.), a 5-HT(2B/2C), agonist increased AURS, and NBQX (i.t.) abolished these excitatory effects of nisoxetine (i.t.) and mCPP (i.t.), whereas nisoxetine (i.t.) and mCPP (i.t.) did not enhance AURS in the presence of NBQX (i.t.).

CONCLUSION

These results indicate that the glutamatergic pathway acting through AMPA receptors plays a crucial role on the active urethral closure reflex during sneezing at the spinal level, and noradrenergic and serotonergic pathways modulate the reflex via the spinal glutamatergic system in rats.

Herpes simplex virus vector-mediated gene transfer of kynurenine aminotransferase improves detrusor overactivity in spinal cord-injured rats

Detrusor overactivity threatens the renal function of patients with spinal cord injury. Suppressing N-methyl-D-aspartate receptors is known to improve detrusor overactivity in rats with spinal cord injury, whereas kynurenic acid, the endogenous antagonist of N-methyl-D-aspartate receptors, is irreversibly synthesized by kynurenine aminotransferases (KATs). In this study, we investigated whether replication-defective herpes simplex virus vector-mediated gene transfer of human KAT II could treat detrusor overactivity by injecting the vectors into the rat bladder wall 1 week after spinal cord injury. Three weeks after injection, we evaluated the cystometry and gene expression of KAT II in L6-S1 dorsal root ganglia. The results showed that the vectors are transported to L6-S1 dorsal root ganglia and upregulate the expression of KAT II, and that they also improve the detrusor overactivity and voiding efficiency. We also proved that N-methyl-D-aspartate receptors were blocked by kynurenic acid in the extracellular solution or the vector-mediated gene transfer of KAT II in cultured rat neurons of L6-S1 dorsal root ganglia by whole-cell patch clamp to explore the mechanisms of gene therapy. Therefore, replication-defective herpes simplex virus vector-mediated KAT II inhibits detrusor overactivity in spinal cord-injured rats, possibly by suppressing N-methyl-D-aspartate receptors in bladder afferent pathways.

Synergistic effects of loxoprofen and glycine on the micturition reflex in conscious rats

We examined the inhibitory effects of loxoprofen, a cyclooxygenase inhibitor, and glycine, a major inhibitory neurotransmitter, on the micturition reflex in conscious rats and hypothesized that these drugs would interact synergistically to inhibit micturition. Voiding behaviors were assessed using a metabolic cage. Oral loxoprofen decreased the urinary frequency, and only a high dose(10 mg/kg) significantly reduced the voided volume. With cystometry, intravenous loxoprofen(0.1-3 mg/kg) and glycine (30 and 100 mg/kg) prolonged the intercontraction intervals (ICI) in adose-dependent manner, but did not change the maximum voiding pressure (MVP) in conscious rats. The combination of loxoprofen (3 mg/kg) and glycine (100 mg/kg) strongly prolonged the ICI more than with either drug alone. The lowest dose of loxoprofen (0.1 mg/kg) and glycine(30 mg/kg) did not affect either the ICI or the MVP, but their combination resulted in a significant increase in the ICI. These results suggest that the combined administration of loxoprofen and glycine produced a synergistic inhibitory effect on the micturition reflex.

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

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

Rodent models for urodynamic investigation

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

Role of supraspinal and spinal α1-adrenergic receptor subtypes in micturition reflex in conscious rats

α1-Adrenergic receptor subtypes are widely distributed in the central nervous system and are involved in autonomic functions such as micturition. We investigated the presence and the role of supraspinal and/or spinal α1-adrenergic receptors in modulating the micturition reflex in conscious female Wistar rats. The expression of α1-adrenergic receptor subtypes in rat brain and lumbosacral spinal cord was studied using RT-PCR. Continuous-infusion cystometrograms were obtained in conscious rats, and α1-adrenergic receptor antagonists were administered via intracerebroventricular or intrathecal routes. The mRNA expression of α1A-, α1B-, and α1D-adrenergic receptors was detected in rat brain (midbrain and pons) and lumbosacral spinal cord (dorsal and ventral parts of spinal cord). In addition, intracerebroventricular injection of the α1-adrenergic receptor antagonist tamsulosin (1–10 μg), the selective α1A-adrenergic receptor antagonist silodosin (1–10 μg), and the selective α1D-adrenergic receptor antagonist BMY 7378 (1–10 μg) significantly prolonged the intercontraction interval (ICI) but did not alter maximum voiding pressure (MVP). Although intrathecal injection of BMY 7378 (0.0001–10 μg) did not affect ICI, tamsulosin and silodosin prolonged ICI in a dose-dependent manner. MVP was significantly reduced by intrathecal injection of tamsulosin (10 μg) but not by silodosin or BMY 7378 (0.0001–10 μg). Supraspinal α1A- and α1D-adrenergic receptors are apparently important for the regulation of reflex-bladder activity in conscious rats. Noradrenergic projection from the brain stem to the lumbosacral spinal cord may promote the afferent limb rather than the efferent limb of the micturition reflex pathway via α1A-adrenergic receptors.

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.

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

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

Brain switch for reflex micturition control detected by FMRI in rats

The functions of the lower urinary tract are controlled by complex pathways in the brain that act like switching circuits to voluntarily or reflexly shift the activity of various pelvic organs (bladder, urethra, urethral sphincter, and pelvic floor muscles) from urine storage to micturition. In this study, functional magnetic resonance imaging (fMRI) was used to visualize the brain switching circuits controlling reflex micturition in anesthetized rats. The fMRI images confirmed the hypothesis based on previous neuroanatomical and neurophysiological studies that the brain stem switch for reflex micturition control involves both the periaqueductal gray (PAG) and the pontine micturition center (PMC). During storage, the PAG was activated by afferent input from the urinary bladder while the PMC was inactive. When bladder volume increased to the micturition threshold, the switch from storage to micturition was associated with PMC activation and enhanced PAG activity. A complex brain network that may regulate the brain stem micturition switch and control storage and voiding was also identified. Storage was accompanied by activation of the motor cortex, somatosensory cortex, cingulate cortex, retrosplenial cortex, thalamus, putamen, insula, and septal nucleus. On the other hand, micturition was associated with: 1) increased activity of the motor cortex, thalamus, and putamen; 2) a shift in the locus of activity in the cingulate and insula; and 3) the emergence of activity in the hypothalamus, substantia nigra, globus pallidus, hippocampus, and inferior colliculus. Understanding brain control of reflex micturition is important for elucidating the mechanisms underlying neurogenic bladder dysfunctions including frequency, urgency, and incontinence.

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

Sex-related differences in lower urinary tract (LUT) activity responding to intravesical infusion of diluted acetic acid (A/A, pH 3.0) were investigated during cystometrograms in decerebrate unanesthetized mice. A/A produced a decrease of intercontraction intervals in both female and male animals, and the extent of the decrease in male mice was much less than in female mice [19 ± 5% ( P = 0.03) vs. 65 ± 5% ( P = 0.03); n = 6 for each], exhibiting a marked difference between the two groups in response to acid irritation of the LUT ( P = 0.002). A/A reduced maximal voiding pressure (MVP) (19 ± 4%, P = 0.03) but had no effect on pressure threshold for inducing voiding contraction (PT) ( P = 0.56) in females, whereas A/A did not change MVP ( P = 1.00) but increased PT (16 ± 4%, P = 0.03) in males. A/A decreased bladder compliances of female and male mice in a similar fashion (44 ± 10% vs. 24 ± 7%, P = 0.03 for each). In male mice, A/A produced persistent dribbling of fluid after voiding contraction phase, which was virtually not seen in females. The present study demonstrates the differences between female and male mice in response to noxious stimulation in the LUT: the female bladder is more sensitive to the acid irritation, while the male urethra is more irritable to the noxious stimulus. Identification of mechanisms underlying sex-specific characteristics might be helpful for elucidating pathogenesis of painful bladder syndrome.

Differential effects of urethane and isoflurane on external urethral sphincter electromyography and cystometry in rats

Urethane is a common and often preferred anesthetic agent for urodynamic recordings in rats, but its use is often restricted to terminal procedures because of a prolonged duration of action and potentially toxic effects. When urodynamic recordings are part of survival procedures in rodent experimental models, inhalation anesthetics, such as isoflurane, are frequently used and generally well tolerated. In this study, we compared the effects of urethane and isoflurane on lower urinary tract function. For this purpose, adult female rats were anesthetized by subcutaneous administration of urethane (n=6) or by inhalation of isoflurane (n=5). Micturition reflexes were assessed by concurrent cystometrogram and external urethral sphincter (EUS) electromyography (EMG) recordings to determine bladder contractile properties, EUS activation patterns, and the coordination between bladder contractions and EUS activation. Compared with urethane, isoflurane reduced frequency of bursts, firing frequency, and amplitude of EUS EMG activity during voiding as well as the EUS EMG amplitude during the bladder filling phase. Isoflurane also prolonged the bladder intercontractile intervals. Other several key functional aspects of the bladder contractile properties as well as the coordination between bladder contractions were not different between the two experimental groups. We conclude that micturition reflexes were differentially affected by isoflurane and urethane. Specifically, isoflurane exhibited a significant suppression of the EUS EMG activity and prolonged the bladder intercontractile intervals compared with urethane. We suggest that these anesthetic properties be taken into consideration during the experimental design and interpretation of urodynamic recordings in rodent models.

Penile erection and micturition events triggered by electrical stimulation of the mesopontine tegmental area

The cholinergic neurons in the laterodorsal tegmental nucleus (LDT) play a crucial role in the regulation of rapid eye movement (REM) sleep. Because penile erection occurs during REM sleep, the involvement of the LDT in penile erection was examined in unanesthetized head-restrained rats. To detect penile erection, corpus spongiosum of the penis (CSP) pressure was measured through a telemetric device with simultaneous bulbospongiosum (BS) muscle EMG recording through stainless wires. Electrical stimulation in and around the LDT induced the following three CSP pressure patterns: 1) a full erection pattern indistinguishable from the nonevoked or spontaneous erection, characterized by a slow increase in CSP pressure with additional sharp CSP peaks associated with BS muscle bursts, 2) a muscular pattern characterized by sharp CSP pressure peaks but in the absence of a vascular component, i.e., without an increase in baseline CSP pressure, and 3) a mixed-type response characterized by high-frequency CSP pressure peaks followed by a full erection response. Full erections were evoked in and around the LDT, including more medially and ventrally. The sites for inducing mixed-type events were intermingled with the sites that triggered full erections in the anterior half of the LDT, whereas they were separated in the posterior half. The sites for muscular responses were lateral to the sites for full erections. Finally, a CSP pressure response identical to micturition was evoked in and around the Barrington's nucleus and in the dorsal raphe nucleus. These results suggest that the LDT and surrounding region are involved in the regulation of penile erection. Moreover, different anatomical areas in the mesopontine tegmentum may have specific roles in the regulation of penile erection and micturition.

Time course of neuroanatomical and functional recovery after bilateral pudendal nerve injury in female rats

The pudendal nerve innervates the external urethral sphincter (EUS) and is among the tissues injured during childbirth, which may lead to symptoms of stress urinary incontinence (SUI). To understand the mechanisms of injury and repair, urethral leak-point pressure (LPP) was measured 4 days, 2 wk, or 6 wk after bilateral pudendal nerve crush. Morphometric changes in the distal nerve and EUS were examined by light and electron microscopy. To determine whether recovery resulted from pudendal neuroregeneration, LPP was measured before and after pudendal nerve transection 2 wk after nerve crush. LPP was significantly decreased 4 days after pudendal nerve crush compared with sham-injured animals as well as 2 or 6 wk after nerve crush. LPP was not significantly different 2 or 6 wk after nerve crush compared with sham-injured animals, suggesting that urethral function had returned to normal. Four days after pudendal nerve crush, the EUS branch of the pudendal nerve distal to the injury site showed evidence of nerve degeneration and the EUS appeared disrupted. Two weeks after nerve crush, the distal nerve and EUS both showed evidence of both nerve degeneration and recovery. Two weeks after nerve crush, LPP was significantly decreased after nerve transection. Six weeks after nerve injury, evidence of neuroregeneration was observed in the pudendal nerve and the EUS. This study has demonstrated that functional recovery and neuroregeneration are significant 2 wk after nerve crush, although by anatomical assessment, recovery appears incomplete, suggesting that 2 wk represents an early time point of initial neuroregeneration.

Effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats

OBJECTIVE

To investigate the effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats.

MATERIALS AND METHODS

The effects of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, on bladder and urethral activities were evaluated by infusion cystometrography (CMG) and urethral perfusion pressure under isovolumetric conditions in awake or urethane-anaesthetized rats. L-NAME was administered intravenously (i.v.), intrathecally (i.t.), intracerebroventriculary (i.c.v.) or intravesically in normal rats or rats pre-treated with resiniferatoxin, a potent C-fibre afferent neurotoxin.

RESULTS

L-NAME injected i.v. decreased the intercontraction interval (ICI) in the awake but increased it in the anaesthetized rats. L-NAME injected i.t. increased the ICI in both states and these effects were not apparent after pre-treatment with resiniferatoxin. L-NAME injected i.c.v. decreased the ICI in the awake but increased i.t. in the anaesthetized rats. Intravesical L-NAME decreased the ICI in the awake but not in the anaesthetized rats. L-NAME administered i.v., but not i.t. or i.c.v., increased bladder contraction during CMG. Under isovolumetric conditions, L-NAME administered i.v., but not i.t. or i.c.v., reduced the urethral relaxation without changing bladder contraction.

CONCLUSIONS

These results indicate that spinal NO release facilitates the mechanoceptive C-fibres, and this facilitatory effect is masked by supraspinal (possibly forebrain) and local inhibitory effects of NO during the micturition reflex in awake rats. Urethane seems to inhibit the supraspinal and local inhibitory effects of NO, resulting in unmasking the facilitatory effect of NO in the spinal cord and brain stem. During the voiding phase, urethral relaxation depends on the peripheral but not the central NO system.

Characterization and restoration of altered inhibitory and excitatory control of micturition reflex in experimental autoimmune encephalomyelitis in rats

Multiple sclerosis (MS) is characterized by inflammatory lesions throughout the central nervous system. Spinal cord inflammation correlates with many neurological defecits. Most MS patients suffer from micturition dysfunction with urinary incontinence and difficulty in emptying the bladder. In experimental autoimmune encephalomyelitis (EAE) induced in female Lewis rats, a model of MS, we investigated at distinct clinical severity scores the micturition reflex by cystometrograms. All rats presenting symptomatic EAE suffered from micturition reflex alterations with either detrusor areflexia or hyperactivity. During pre-symptomatic EAE, a majority of rats presented with detrusor areflexia, whereas at onset of clinical EAE, detrusor hyperactivity was predominant. During progression of EAE, detrusor areflexia and hyperactivity were equally expressed. Bladder hyperactivity was suppressed by activation of glycine and GABA receptors in the lumbosacral spinal cord with an order of potency: glycine > GABA(B) > GABA(A). Detrusor areflexia was transformed into detrusor hyperactivity by blocking glycine and GABA receptors. Spinalization abolished bladder activity in rats presenting detrusor hyperactivity and failed to induce activity in detrusor areflexia. Altogether, the results reveal an exaggerated descending excitatory control in both detrusor reflex alterations. In detrusor areflexia, a strong segmental inhibition dominates this excitatory control. As in treatment of MS, electrical stimulation of sacral roots reduced detrusor hyperactivity in EAE. Blockade of glycine receptors in the lumbosacral spinal cord suppressed the stimulation-induced inhibitory effect. Our data help to better understand bladder dysfunction and treatment mechanisms to suppress detrusor hyperactivity in MS.

Functional reinnervation of the rat lower urinary tract after cauda equina injury and repair

Conus medullaris and/or cauda equina forms of spinal cord injury commonly result in a permanent loss of bladder function. Here, we developed a cauda equina injury and repair rodent model to investigate whether surgical implantation of avulsed lumbosacral ventral roots into the spinal cord can promote functional recovery of the lower urinary tract. Adult female rats underwent sham surgery (n = 6), bilateral L5-S2 ventral root avulsion (VRA) injury (n = 5), or bilateral L5-S2 VRA followed by an acute implantation of the avulsed L6 and S1 ventral roots into the conus medullaris (n = 6). At 12 weeks after operation, the avulsed group demonstrated urinary retention, absence of bladder contractions and external urethral sphincter (EUS) electromyographic (EMG) activation during urodynamic recordings, increased bladder size, and retrograde death of autonomic and motoneurons in the spinal cord. In contrast, the implanted group showed reduced urinary retention, return of reflexive bladder voiding contractions coincident with EUS EMG activation, anatomical reinnervation of the EUS demonstrated by retrograde neuronal labeling, normalization of bladder size, and a significant neuroprotection of both autonomic and motoneurons. In addition, a positive correlation between motoneuronal survival and voiding efficiency was observed in the implanted group. Our results show that implantation of avulsed lumbosacral ventral roots into the spinal cord promotes reinnervation of the urinary tract and return of functional micturition reflexes, suggesting that this surgical repair strategy may also be of clinical interest after conus medullaris and cauda equina injuries.

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

This study was conducted to examine reflex mechanisms that mediate urinary bladder and external urethral sphincter (EUS) coordination in urethane-anesthetized female Sprague-Dawley rats. We investigated the properties of EUS reflexes elicited by electrical stimulation of pelvic nerve afferent axons (pelvic-EUS reflex). The changes in the reflexes induced by bladder distension and administration of agonists or antagonists for glutamatergic or serotonergic receptors were examined. The reflexes consisted of an early response (ER, 18- to 22-ms latency) and a late, long-duration (>100-ms latency) response (LR), which consisted of bursts of activity at 20- to 160-ms interburst intervals. In a few experiments, a reflex with an intermediate (40- to 70-ms) latency was also identified. With the bladder empty, the ER, but not the LR, was detected in the majority of experiments. The LR was markedly enhanced when the bladder was distended. The ER remained, but the LR was abolished, after spinal cord transection at T8-T9. The ER and LR were significantly decreased 75 and 35%, respectively, by the N-methyl-D-aspartate receptor antagonist MK-801 (0.3 mg/kg iv), but only decreased 18 and 14%, respectively, by the alpha-amino-5-methylisoxazole-4-propionate receptor antagonist LY-215490 (3 mg/kg iv). The serotonin (5-HT1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (1 mg/kg iv) enhanced spontaneous EUS activity and the pelvic-EUS reflex. WAY-100635 (0.1-1 mg/kg iv), a 5-HT1A antagonist, reversed the effect of 8-hydroxy-2-(di-n-propylamino)-tetralin and suppressed EUS activity and the pelvic-EUS reflex. These results indicate that glutamatergic and serotonergic mechanisms are important in the reflex pathways underlying bladder- sphincter coordination in rats.

Mechanisms underlying the recovery of lower urinary tract function following spinal cord injury

The lower urinary tract has two main functions, the storage and periodic expulsion of urine, which are regulated by a complex neural control system in the brain and lumbosacral spinal cord. This neural system coordinates the activity of two functional units in the lower urinary tract: (1) a reservoir (the urinary bladder) and (2) an outlet (consisting of bladder neck, urethra and striated muscles of the pelvic floor). During urine storage the outlet is closed and the bladder is quiescent, thereby maintaining a low intravesical pressure over a wide range of bladder volumes. During micturition the outlet relaxes and the bladder contracts to promote the release of urine. This reciprocal relationship between bladder and outlet is generated by visceral reflex circuits, some of which are under voluntary control. Experimental studies in animals indicate that the micturition reflex is mediated by a spinobulbospinal pathway passing through a coordination center (the pontine micturition center) located in the rostral brainstem. This reflex pathway is in turn modulated by higher centers in the cerebral cortex that are presumably involved in the voluntary control of micturition. Spinal cord injury at cervical or thoracic levels disrupts voluntary control of voiding as well as the normal reflex pathways that coordinate bladder and sphincter functions. Following spinal cord injury, the bladder is initially areflexic but then becomes hyperreflexic due to the emergence of a spinal micturition reflex pathway. Studies in animals indicate that the recovery of bladder function after spinal cord injury is dependent in part on plasticity of bladder afferent pathways and the unmasking of reflexes triggered by capsaicin-sensitive C-fiber bladder afferent neurons. The plasticity is associated with changes in the properties of ion channels and electrical excitability of afferent neurons, and appears to be mediated in part by neurotrophic factors released in the spinal cord and the peripheral target organs.

Effects of dextromethorphan on in vitro contractile responses of mouse and rat urinary bladders

PURPOSE

Dextromethorphan (DXM) is a cough-suppressing ingredient in a variety of over-the-counter cough and cold medications. Dextromethorphan elevates the threshold for coughing primarily through a central mechanism. At doses recommended for treating coughs the drug is safe and effective. At much higher doses, DXM produces dissociative effects similar to those of phencyclidine and ketamine. Opioid analgesics structurally related to DXM also inhibit bladder contractions and produce urinary retention through a non-opioid mechanism. This study evaluated the direct effects of DXM on in vitro contractile responses of rat and mouse urinary bladders.

METHODS

Male rats and mice were anaesthetized and their bladders removed. Bladder strips were suspended in 15 ml oxygenated Tyrode's solution containing glucose. Bladder strip contractions were evoked by field stimulation (FS), carbachol or elevated KCl concentrations and contractile responses recorded. The strips were then exposed to 3 microM (DXM) for 30 min and re-stimulated. This sequence was repeated at 10, 30, and 100 microM DXM.

RESULTS

(a) The rat bladder generated significantly greater tension than the mouse bladder. (b) Dextromethorphan produced a dose-dependent inhibition of the response to FS that was approximately equal for rat and mouse bladders. FS at 8 or 32 Hz was significantly more sensitive to DXM inhibition than 2 Hz. (c) The response to carbachol was more sensitive to inhibition by DXM than the responses to FS or KCl.

CONCLUSIONS

These results demonstrate that DXM inhibits bladder contractions in vitro and that mouse and rat bladders are affected to approximately the same extent.

Effect of injury severity on lower urinary tract function after experimental spinal cord injury

Lower urinary tract dysfunction is a serious burden for patients following spinal cord injury. Patients are usually limited to treatment with urinary drainage catheters, which can lead to repeated urinary tract infections and lower quality of life. Most of the information previously obtained regarding lower urinary tract function after spinal cord injury has been in completely transected animals. After thoracic transection in the rat, plasticity of local lumbosacral spinal circuitry establishes a "reflex bladder," which results in partial recovery of micturition, albeit with reduced voiding efficiency. Since at least half of cord-injured patients exhibit neurologically incomplete injury, rat models of clinically relevant incomplete contusion injury have been developed. With respect to lower urinary tract function, recent anatomical and physiological studies have been performed after incomplete thoracic contusion injury. The results show greater recovery of lower urinary tract function that varies inversely with the severity of the initial trauma and is positively correlated with time after injury. Recovery, as measured by coordination of the bladder with the external urethral sphincter, occurs between 1 and 4 weeks after spinal cord injury. It is associated with normalization of: serotonin immunoreactivity and glutamate receptor subunit mRNA expression in the dorsolateral nucleus that innervates the external urethral sphincter muscle, the response to glutamatergic pharmacological probes administered at the lumbosacral spinal cord level, and c-Fos activation patterns in the lumbar spinal cord. Understanding the mechanisms involved in this recovery will provide a basis for enhancing lower urinary tract function in patients after incomplete spinal cord injury.

Abdominal muscle activity during voiding in female rats with normal or irritated bladder

The aims of the present study were to determine in female rats whether abdominal muscle discharges during normal voiding and to describe the effect of bladder irritation on this visceromotor activity. The sensory pathway of this reflex was also determined. Electromyograms (EMGs) indicated that in awake rats, the abdominal muscle was consistently activated during spontaneous voiding and during voiding induced by saline infusion. Similarly, in anesthetized animals, the muscle discharged during urine expulsion. The abdominal EMG activity was not abolished by hypogastric (Hgnx) or sensory pudendal neurectomy (SPdnx). SPdnx dramatically decreased the intercontraction interval and voided volume. Acetic acid infusion reduced the intercontraction interval and increased bladder contraction duration. It also reduced the pressure threshold for evoking the abdominal EMG response and increased the EMG duration and amplitude. Although SPdnx and Hgnx modified some urodynamic parameters, they did not reverse the acetic acid effect on EMG activity. Thus the afferents activating the visceromotor reflex during normal voiding and the increased reflex in response to acetic acid are probably both carried by the pelvic nerve. Abdominal muscle activity induced by bladder distension has been considered to be a pain marker. However, we conclude that in female rats, the abdominal muscle is reflexively activated during physiological urine expulsion. On the other hand, bladder irritation is marked by an exaggeration of this abdominal visceromotor reflex.

Reflexes evoked by electrical stimulation of afferent axons in the pudendal nerve under empty and distended bladder conditions in urethane-anesthetized rats

This study examined reflex mechanisms that mediate urinary bladder and external urethral sphincter (EUS) coordination in female Sprague-Dawley urethane-anesthetized rats under empty and distended bladder conditions. The bladder was distended either by a small balloon or a saline filled catheter inserted through the body of the bladder. Stimulation of the entire pudendal nerve elicited short latency (8-12 ms) responses in the EUS and short (3-8 ms) and long latency responses (16-20 ms) in contralateral pudendal nerve. The long latency pudendal-pudendal reflex was reduced by 36.7% in area during bladder distension with the balloon catheter. However, there was no significant change in the area of pudendal-EUS reflex during bladder distension. Peak amplitudes of both reflexes were reduced 32% by bladder distension. The effects of glutamatergic receptor antagonists on the reflexes were also examined. MK 801 (0.3-5mg/kg, i.v.), an N-methyl-d-aspartate glutamatergic receptor antagonist, markedly depressed the pudendal-pudendal reflex, but LY 215490 (3mg/kg, i.v.), an alpha-amino-5-methyl isoxazole-4-propionate antagonist, had a minimal inhibitory effect. Both glutamatergic receptor antagonists significantly suppressed the pudendal-EUS reflex. These results indicate that the EUS is innervated by multiple pathways and that glutamatergic excitatory transmission is important in the neural mechanisms underlying bladder-sphincter coordination in the rat.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.