Effects of WAY100635, a selective 5-HT1A-receptor antagonist on the micturition-reflex pathway in the rat

Upregulated 5-HT1A Receptors Regulate Lower Urinary Tract Function in Rats after Complete Spinal Cord Injury

Spinal cord injury (SCI) above the lumbosacral level often leads to dysfunction of the lower urinary tract (LUT) including detrusor hyper-reflexia, wherein bladder compliance is low, baseline pressures are increased, and filling is accompanied by numerous non-voiding contractions (NVCs) referred to as neurogenic detrusor overactivity. Here, we investigate the expression levels of the serotonin 1A (5-HT1A) receptor in segments both rostral and caudal to the injured site, as well as the effects on micturition of blocking 5-HT1A receptor using pharmacological interventions in spinally intact rats or T8 complete SCI rats. The activities of detrusor and external urethral sphincter (EUS) were assessed with the rats in a conscious condition. Adult female rats were divided into two groups: (1) sham control (T8 laminectomy only) and (2) T8 complete spinal cord transection. The observation period was 2 months after the original SCI. In Western blot analyses, we identified significant upregulation of the 5-HT1A receptor in the T10-L2 and L6/S1 segments after chronic complete SCI. In pharmacological studies, a dose-response study of the 5-HT1A receptor antagonist, WAY100635, indicated alterations in detrusor and EUS activities in spinally intact rats. Interestingly, blocking the 5-HT1A receptor alone resulted in inhibitory effects on NVCs with a reduced number and decreased amplitude, but in an increased interval between NVCs in SCI rats. In addition, the duration of EUS bursting was also significantly increased by WAY100635. These inhibitory effects of WAY100635 on NVCs were diminished by subsequent application of a beta-adrenergic blocker (propranolol). The reduction of NVCs observed by WAY100635 may be the result of blocking the constitutive activities of the 5-HT1A receptor but activating the beta-adrenergic sympathetic pathway, which in turn relaxes bladder activity. Together, the neuroplasticity of the 5-HT1A receptor can be a potential therapeutic target for treatment of bladder dysfunction after SCI.

Role of Descending Serotonergic Fibers in the Development of Pathophysiology after Spinal Cord Injury (SCI): Contribution to Chronic Pain, Spasticity, and Autonomic Dysreflexia

As the nervous system develops, nerve fibers from the brain form descending tracts that regulate the execution of motor behavior within the spinal cord, incoming sensory signals, and capacity to change (plasticity). How these fibers affect function depends upon the transmitter released, the receptor system engaged, and the pattern of neural innervation. The current review focuses upon the neurotransmitter serotonin (5-HT) and its capacity to dampen (inhibit) neural excitation. A brief review of key anatomical details, receptor types, and pharmacology is provided. The paper then considers how damage to descending serotonergic fibers contributes to pathophysiology after spinal cord injury (SCI). The loss of serotonergic fibers removes an inhibitory brake that enables plasticity and neural excitation. In this state, noxious stimulation can induce a form of over-excitation that sensitizes pain (nociceptive) circuits, a modification that can contribute to the development of chronic pain. Over time, the loss of serotonergic fibers allows prolonged motor drive (spasticity) to develop and removes a regulatory brake on autonomic function, which enables bouts of unregulated sympathetic activity (autonomic dysreflexia). Recent research has shown that the loss of descending serotonergic activity is accompanied by a shift in how the neurotransmitter GABA affects neural activity, reducing its inhibitory effect. Treatments that target the loss of inhibition could have therapeutic benefit.

Improvement of lower urinary tract function by a selective serotonin 5-HT1A receptor agonist, NLX-112, after chronic spinal cord injury

Spinal cord injury (SCI) above the lumbosacral level results in lower urinary tract dysfunction, including (1) detrusor hyperreflexia, wherein bladder compliance is low, and (2) a lack of external urethral sphincter (EUS) control, leading to detrusor-sphincter dyssynergia (DSD) with poor voiding efficiency. Experimental studies in animals have shown a dense innervation of serotonergic (5-HT) fibers and multiple 5-HT receptors in the spinal reflex circuits that control voiding function. Here, we investigated the efficacy of NLX-112 (a.k.a. befiradol or F13640), in regulating lower urinary tract function after T8 contusive SCI in rats. NLX-112 is a very potent, highly-selective, and fully efficacious 5-HT_1A receptor agonist, which has been developed for the treatment of L-DOPA-induced dyskinesia in Parkinson's disease patients. We performed urodynamics tests and external urethral sphincter electromyogram recordings to assess lower urinary tract function while NLX-112 was infused through the femoral vein in rats with chronic complete SCI or contusive SCI. The dose response studies indicated that NLX-112 was able to improve voiding behavior by regulating both detrusor and EUS activity. These included improvements in voiding efficiency, reduction of detrusor hyperactivity, and phasic activity of EUS during the micturition period. In addition, the application of a selective 5-HT_1A receptor antagonist, WAY100635, reversed the improved detrusor and EUS activity elicited by NLX-112. In summary, the current data suggest that pharmacological activation of 5-HT_1A receptors by NLX-112 may constitute a novel therapeutic strategy to treat neurogenic bladder after SCI.

Effect of 5-HT2A receptor antagonist ketanserin on micturition in male rats

OBJECTIVES

This study aimed to investigate the effects of ketanserin on micturition mediated via the 5-HT_2A receptor in the motoneuron nucleus of the Lumbosacral cord, as reflected in high frequency oscillations (HFOs) of intravesical pressure and the external urethral sphincter electromyogram (EUS-EMG) in anesthetized male rats. METHODS：: Male Sprague-Dawley rats were used. Cystometry and EUS-EMG were performed in all rats under urethane anesthesia to examine the variations after successive intrathecal (i.t.) administration of various doses of ketanserin into the lumbosacral cord. Immunofluorescence staining and Western blotting were made to observe the distribution of 5-HT2 A and -2C receptors in the lumbosacral cord motor neurons.

RESULTS

Compared to the controls, ketanserin-treated rats showed a declined trend of dose-dependent manner in the HFOs, in accordance with the variation of EUS-EMG, while decreased micturition volume, voiding efficiency, and increased post-void residual volume was only observed at the dose of 0.1 mg/kg. The effects of ketanserin on the HFO and EUS-EMG activity were partially or completely reversed by the 5-HT_2A/2C receptor agonist, DOI. Meanwhile, immunofluorescence staining and Western blot analysis showed that immunoreactivity of 5-HT_2A receptor was higher than that of 5-HT_2C, labeling in the lumbosacral cord motoneurons.

CONCLUSIONS

The intrathecally administrated 5-HT_2A receptor antagonist ketanserin can weaken the EUS bursting activity, decrease HFOs, and reduce voiding efficiency as dose dependently. The effects of ketanserin on micturition may be mainly mediated via the 5-HT_2A receptors in the motoneuron nucleus of the lumbosacral cord.

The serotonin (5-hydroxytryptamine) 5-HT7 receptor is up-regulated in Onuf's nucleus in rats with chronic spinal cord injury

OBJECTIVES

To examine the effect of intrathecal (i.t.) serotonin (5-hydroxytryptamine) 5-HT₇ agonist administration on voiding function in the urethane-anesthetised rat, and the change in 5-HT₇ receptor (5-HT₇ R) expression in the lumbosacral cord Onuf's nucleus after spinal cord injury (SCI).

MATERIALS AND METHODS

In all, 32 female Sprague-Dawley (SD) rats were equally divided into a spinally intact (SI) group and SCI group (n = 16 each). At 8 weeks after transection, half of the rats underwent continuous cystometry under urethane anaesthesia, and the 5-HT₇ R-selective agonist LP44 was given (i.t.). The remaining rats were used for pseudorabies (PRV) retrograde tracing, immunofluorescence, and Western Blot.

RESULTS

LP44 administered i.t. had no effect in the SI rats. In SCI rats, LP44 (1-30 μg/kg) induced significant dose-dependent increases in micturition volume, voiding efficiency, number of high-frequency oscillations per micturition; and decreases in residual volume, bladder capacity, peak bladder pressure, threshold pressure and non-voiding contractions. The 5-HT₇ R antagonist, SB-269970 (10 μg/kg), partially reversed LP44-induced changes. Using PRV retrograde tracing and immunofluorescence, 5-HT₇ Rs were found in the L6-S1 spinal cord Onuf's nucleus in both SI and SCI rats, but the expression was significantly greater in the SCI rats. Western blot showed significantly more 5-HT₇ Rs in the ventral L6-S1 spinal cord in SCI rats.

CONCLUSION

A 5-HT₇ R agonist, given i.t., improved voiding efficiency in urethane-anesthetised SCI rats, and the 5-HT₇ R was significantly up-regulated in the lumbosacral cord Onuf's nucleus. If valid for humans, these findings suggest that the 5-HT₇ R could be a target for therapeutic interventions.

Investigational Drug Therapies for Overactive Bladder Syndrome: The Potential Alternatives to Anticolinergics

Background

Overactive bladder is a high prevalent and quality of life affecting disease. The mainstay of the medical therapy is represented by antimuscarinic drugs, but their side effects markedly affect patient compliance and prompt studies on novel investigational drugs.

Methods

A systematic literature search of peer-reviewed papers and meeting abstracts published by December 2008 was performed. PubMed databank was searched for original English articles, by using the following search terms: “overactive bladder” or “detrusor overactivity” or “urinary incontinence” and “treatment”, alone and linked to any potential molecular target or novel drug cited in the literature.

Results

Effective alternative pharmacological treatments are currently scarce, but many new promising compounds are emerging which target key molecular pathways involved in micturition control. The most promising potential therapeutic targets include central nervous system GABAergic inhibitory pathway, dopaminergic and serotoninergic systems, b-adrenoceptors and cAMP metabolism, nonadrenergic-noncholinergic mechanisms such as purinergic and neuropeptidergic systems, vanilloid receptor, bladder sensory nervous terminals, nonneuronal bladder signalling systems including urothelium and interstitial cells, prostanoids, Rho-kinase and different subtypes of potassium and calcium channels.

Conclusions

Despite the enormous amount of new biologic insight, very few novel pharmacological therapies seems to have passed the proof-of-concept clinical stage. The ultimate clinical utility of new drugs will depend on the ability to exploit tissue-specific differences and disease-related changes in molecular expression/function and to improve storage phase dysfunctions without interfering with the emptying phase. Further preclinical investigations and controlled clinical trials are urgently needed in this challenging field.

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.

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.

Innovative pharmacotherapies for women with overactive bladder: where are we now and what is in the pipeline?

INTRODUCTION AND HYPOTHESIS

The impressive prevalence of overactive bladder (OAB) and the relevant limitations of current treatments urge the need for novel therapeutic approaches.

METHODS

A systematic literature and web search was performed to identify investigational drugs that entered the early and late phases of clinical development for women with OAB symptoms.

RESULTS

Approved pharmacological therapies for OAB (antimuscarinics, beta-3 agonists, and botulinum toxin) are evolving with the development of alternative administration methods, combination strategies, and novel compounds, expected to improve effectiveness, bladder selectivity, and dose flexibility. A wealth of investigational compounds, developed with both public and companies' indoor nonclinical disease-oriented studies, entered the early and late stages of clinical development in the last decade. Most non-anticholinergic compounds in ongoing clinical trials target central and peripheral neurotransmitter receptors involved in neurological modulation of micturition, nonadrenergic-noncholinergic mechanisms, cyclic nucleotide metabolism, different subtypes of ion channels or peripheral receptors of prostaglandins, vanilloids, vitamin D3, and opioids. Fascinating advances are ongoing also in the field of genetic therapy.

CONCLUSIONS

New pharmaceutical formulations and drug combinations are expected to be available in the next decade in order to overcome the limitations of current drugs for OAB. Although proof-of-concept, patient-oriented studies yielded disappointing results for several tentative drugs, a lot of clinical research is ongoing that is expected to provide clinicians with novel therapeutic agents in the near future.

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.

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.

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.

Models for sensory neurons of dorsal root ganglia and stress urinary incontinence

AIMS

To discuss (1) animal models for investigating bladder afferent pathways from the spinal cord to the brain and (2) animal models of stress urinary incontinence (SUI) with a special emphasis on functional and histopathological characteristics of each model.

METHODS

Literature review of spinal mechanisms of bladder afferent pathways and animal models of SUI.

RESULTS

Electrophysiological studies in the rat using pelvic nerve stimulation and recording of evoked potentials in the periaqueductal gray (PAG) prove to be a valuable tool to examine spinal mechanisms of bladder afferent pathways. Animal models of SUI in the rat include vaginal distention as simulated birth trauma, pudendal nerve crush or transection, urethral sphincter injury by electrocauterization, transabdominal urethrolysis, periurethral botulinum-A toxin injection, and pubo-urethral ligament transection. Functional and histopathological changes in the continence mechanism after injury are different between models.

CONCLUSIONS

Using animal models for sensory neurons, intrathecal and intravenous administration of certain drugs can be tested whether they affect the bladder afferent pathways from the spinal cord to the PAG. Animal models of SUI can serve as a tool to develop new pharmacologic therapies or periurethral injection therapies using stem cell implants.

Improving voiding efficiency in the diabetic rat by a 5-HT1A serotonin receptor agonist

AIMS

Serotonin affects micturition in the normal rat through actions not only on ascending and descending spinal pathways and supraspinal centers but also on the lumbosacral spinal cord level. The selective 5-HT1A receptor agonist, 8-OH-DPAT((R)-(+)-8-hydroxy-2-(di-n-propylamino) tetralin), reversed detrusor-sphincter dyssynergia (DSD) in the spinal cord injury (SCI) rat. Rats with experimental diabetes mellitus (DM) have been shown to have both bladder and urethral dysfunction during reflex voiding. We therefore examined the effects of 8-OH-DPAT on micturition in DM rats.

METHODS

Female Sprague-Dawley rats were used. DM was induced by an intraperitoneal injection of streptozotocin (STZ, 65 mg/kg) and a cystometric study was performed 8 weeks post-injection. External urethral sphincter electromyography (EUS-EMG) was also measured. The 5-HT1A antagonist WAY-100635(N-tert-butyl-3-(4-(2-methoxyphenyl)-piperazin-1-yl)-2-phenylpropanamide) was administered after each 8-OH-DPAT dose-response.

RESULTS

Compared to controls, DM rats had a higher bladder capacity, residual volume, and a lower voiding efficiency. In DM rats, 8-OH-DPAT (3-1,000 µg/kg, i.v.) induced significant dose-dependent increases in micturition volume, and decreases in residual volume, resulting in increases in voiding efficiency. During the micturition, there was a dose-dependent increased phasic EUS activity correlated with the improved voiding efficiency. WAY-100635 (300 µg/kg, i.v.) reversed the 8-OH-DPAT-induced changes.

CONCLUSIONS

Both the bladder voiding efficiency and the periodic EUS activity were decreased in DM rats. 5-HT1A receptor agonism promoted periodic EUS activity, thereby improving voiding efficiency. Whether or not these results may have implications for the future treatment of voiding dysfunction in DM patients remains to be studied.

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.

Investigation of the role of 5-HT2 receptor subtypes in the control of the bladder and the urethra in the anaesthetized female rat

BACKGROUND AND PURPOSE

Micturition is controlled by central 5-HT-containing pathways. 5-HT2 receptors have been implicated in this system especially in control of the urethra, which is a drug target for treating urinary incontinence. This study investigates the role of each of the three subtypes of this receptor with emphasis on sphincter regulation.

EXPERIMENTAL APPROACH

Recordings of urethral and bladder pressure, external urethral sphincter (EUS) EMG, as well as the micturition reflex induced by bladder distension along with blood pressure and heart rate were made in anaesthetized rats. The effects of agonists and antagonists for 5-HT2 receptor subtypes were studied on these variables.

KEY RESULTS

The 5-HT2C agonists Ro 60-0175, WAY 161503 and mCPP, i.v., activated the EUS, increased urethral pressure and inhibited the micturition reflex. The effects of Ro 60-0175 on the EUS were blocked by the 5-HT2C antagonist SB 242084 and the 5-HT2A antagonists, ketanserin and MDL 100907. SB 242084 also blocked the inhibitory action on the reflex, while the 5-HT2B antagonist RS 127445 only blocked the increase in urethral pressure. The 5-HT2A receptor agonist DOI given i.v. or i.t. but not i.c.v. activated the EUS.

CONCLUSIONS AND IMPLICATIONS

5-HT2A/2C receptors located in the sacral spinal cord activate the EUS, while central 5-HT2C receptors inhibit the micturition reflex and 5-HT2B receptors, probably at the level of the urethra, increase urethral smooth muscle tone. Furthermore, 5-HT2B and 5-HT2C receptors do not seem to play an important role in the physiological regulation of micturition.

Effect of selective antagonists of group I metabotropic glutamate receptors on the micturition reflex in rats

OBJECTIVE

To investigate the role of Group I metabotropic glutamate (mGlu) receptor subtypes on reflex-induced micturition in anaesthetized and conscious rats using selective mGlu1 (NPS 2407 and R214127) and mGlu5 (MPEP, MTEP, and SIB1893) allosteric antagonists.

MATERIALS AND METHODS

The affinity of the compounds at mGlu1 and mGlu5 receptor subtypes was evaluated by displacement of tritiated R214127 and MPEP, respectively, from rat brain tissue. Effects of intravenous (i.v.) administration of the compounds on isovolumic bladder contractions were evaluated in anaesthetized rats. Effects of MPEP and NPS 2407 on bladder filling and voiding were evaluated by cystometry using saline or diluted (0.2%) acetic acid (MPEP only) infusion of bladders in conscious rats.

RESULTS

Binding studies confirmed the selectivity of the mGlu1 (NPS 2407 and R214127) and mGlu5 (MPEP, MTEP, and SIB1893) compounds. Isovolumic bladder contractions were blocked after i.v. administration of all compounds. However, the mGlu5 antagonists were generally more potent than mGlu1 antagonists. In conscious rats with bladders infused with saline, MPEP dose-dependently and significantly increased bladder capacity starting from oral administration of 10 mg/kg. Oral administration of NPS 2407 (up to 30 mg/kg) did not induce consistent changes in bladder capacity or micturition pressure. MPEP (10 mg/kg, orally) was also evaluated in conscious rats with bladders infused with diluted acetic acid. In this model, MPEP reduced bladder instability counteracting the decrease of bladder volume capacity induced by acetic acid. There were no consistent effects on bladder contractility.

CONCLUSIONS

The results indicate that i.v. and oral administration of selective mGlu5 antagonists, but not those selective for the mGlu1 subtype, have a marked inhibitory effect on reflex micturition pathways in the rat.

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.

Emerging pharmacological targets in overactive bladder therapy: experimental and clinical evidences

Antimuscarinics are the mainstay of the medical therapy for overactive bladder, but their side effects and often modest success have prompted studies on novel pharmacological approaches. In this paper, we give a systematic literature review of peer-reviewed papers on the subject. Effective nonantimuscarinic treatments are currently scarce, but many new promising compounds are emerging, which target key molecular pathways involved in micturition control. The most promising potential therapeutic targets include: nervous GABAergic, glycinergic, dopaminergic, and serotonergic systems; b-adrenoceptors and cAMP metabolism; nonadrenergic-noncholinergic mechanisms such as purinergic and neuropeptidergic systems; vanilloid receptors; bladder afferent nerves; nonneuronal bladder signaling systems including urothelium and interstitial cells; prostanoids; Rho-kinase; and different subtypes of potassium and calcium channels. Despite the enormous amount of new biologic insight, very few drugs with mechanism of action other than antimuscarinics have passed as yet the proof-of-concept stage. Further preclinical and clinical studies are urgently needed in this rapidly moving field.

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.

Effect of Gosha-Jinki-Gan, a Blended Herbal Medicine, on Bladder Activity in Rats

PURPOSE

We investigated the effect of the blended herbal medicine Gosha-jinki-gan on bladder activity and the autonomic nervous system in rats.

MATERIALS AND METHODS

A total of 42 female rats were divided into a control diet group of 21 and a Gosha-jinki-gan diet group of 21. Rats in the control diet group were fed a standard diet, while animals in the Gosha-jinki-gan were fed a special diet containing 1.08% Gosha-jinki-gan (TJ107, Tsumura Co., Tokyo, Japan). After 4 weeks 28 rats, including 14 in the control and 14 in the Gosha-jinki-gan group, underwent continuous cystometry with physiological saline or 0.1% acetic acid solution and bladder activity was recorded. The remaining 14 rats were anesthetized with halothane, and body weight, serum amino acid (glutamate and glycine) and plasma monoamine (noradrenaline, adrenaline, dopamine and serotonin) levels were measured.

RESULTS

The amplitude of bladder contraction on continuous cystometry with physiological saline was lower in the Gosha-jinki-gan diet group than in the control diet group, and plasma dopamine and serotonin levels were also lower in the Gosha-jinki-gan group. When cystometry was done with 0.1% acetic acid, the interval between bladder contractions was shortened in the control and Gosha-jinki-gan groups. However, the interval and duration of bladder contractions were longer in the Gosha-jinki-gan than in the control group.

CONCLUSIONS

These results suggest that Gosha-jinki-gan inhibits bladder activity by maintaining the balance of the sympathetic and parasympathetic nervous systems at a low level.

Activation of the external urethral sphincter central pattern generator by a 5-HT(1A) receptor agonist in rats with chronic spinal cord injury

We recently demonstrated that treatment with the 5-HT(1A/7) receptor agonist [(R)-(+)-8-hydroxy-2-di-n-propylamino]tetralin (8-OH-DPAT) increases bladder capacity in chloralose-anesthetized female cats with chronic spinal cord injury. In the current study, we investigated the effects of 8-OH-DPAT on bladder capacity and external urethral sphincter (EUS) activity in urethane-anesthetized female rats (initial body mass 175-200 g) with chronic spinal cord injury (transsection at T10). Cystometric study took place 8-12 wk posttranssection. Intravesical pressure was monitored in urethane-anesthetized rats with a transvesical catheter, and EUS activity was assessed electromyographically. Spinal cord injury disrupts phasic activity of the EUS, resulting in decreased voiding efficiency and increased residual volume. 8-OH-DPAT induced a dose-dependent decrease in bladder capacity (the opposite of its effect in chronic spinal cord-injured cats) with an increase in micturition volume and decrease in residual volume resulting from improvement in voiding efficiency. The unexpected improvement in voiding efficiency can be explained by the 8-OH-DPAT-induced emergence of phasic EUS relaxation. Phasic EUS relaxation was also altered by 8-OH-DPAT in spinally intact rats, whereas the 5-HT(1A) receptor antagonist N-tert-butyl-3-[4-(2-methoxyphenyl)-piperazin-1-yl]-2-phenylpropanamide (WAY-100635), on its own, was without effect. It remains to be determined when phasic relaxation is restored after spinal cord injury, and indeed whether it is ever truly lost or is only temporarily separated from excitatory input.

The role of central 5-hydroxytryptamine (5-HT, serotonin) receptors in the control of micturition

At present the most investigated 5-HT receptor that has been shown to play a role in the control of micturition is the 5-HT(1A) receptor followed by 5-HT(7), 5-HT(2) and 5-HT(3) receptors. Most experiments focus on the control these receptors have on the parasympathetic outflow to the bladder and the somatic outflow to the external urethral sphincter (EUS) in the rat. Furthermore, 5-HT(1A) and 5-HT(7) receptors have been identified as having an excitatory physiological role in the control of bladder function. 5-HT(1A) receptors act, at least in the rat, at both a spinal (probably a heteroreceptor) and supraspinal (probably an autoreceptor) level, while 5-HT(7) receptors only act at a supraspinal level. Additionally, in the rat, 5-HT administered at a spinal or supraspinal site has an excitatory action, although earlier experiments have shown that activating 5-HT-containing brain areas causes inhibition of the bladder. Recent experiments have also indicated that blockade of the 5-HT(1A) receptor pathway shows rapid tolerance. However, no data exist for the development of tolerance for the 5-HT(7) receptor pathway. Neither receptor seems to play a role in the control of the urethra. Regarding 5-HT(2) receptors, activation of this receptor subtype inhibits micturition, and this inhibitory action may occur at a spinal, supraspinal or both levels. Although no physiological role for 5-HT(2C) receptors can yet be identified, 5-HT(2C) receptors have been implicated in the proposed supraspinal tonically active 5-HT(1A) autoreceptor (negative feedback) pathway. This proposition reconciles the data that central 5-HT-containing pathways are inhibitory to micturition, while 5-HT(1A) receptors, although inhibitory to adenylyl cyclase, have an excitatory function. This is because activation of 5-HT(1A) autoreceptors reduces the release of 5-HT thus reducing the activation of the 5-HT(2C) receptors, which are inhibitory in the control of micturition (disinhibition). Furthermore, 5-HT(2A) receptors in the rat and 5-HT(2C) receptors in the guinea pig cause activation of the EUS. In this respect, 5-ht(5A) receptors have also been identified in Onuf's nucleus, the site of somatic motoneurones controlling this sphincter. In the cat there is very little evidence to indicate that 5-HT receptors are involved in micturition except under pathological conditions in which activation of 5-HT(1A) receptors causes inhibition of micturition. Interestingly, under such conditions 5-HT(1A) receptors cause excitation of the EUS. Nevertheless, spinal 5HT(3) receptors have been implicated in the physiological control of micturition in the cat, but not yet in the rat. Overall, the data support the view that 5-HT receptors are important in the control of micturition. However, many more studies are required to fully understand these roles and why there are such species differences.

Serotonergic drugs and spinal cord transections indicate that different spinal circuits are involved in external urethral sphincter activity in rats

Lower urinary tract function is regulated by spinal and supraspinal reflexes that coordinate the activity of the urinary bladder and external urethral sphincter (EUS). Two types of EUS activity (tonic and bursting) have been identified in rats. This study in urethane-anesthetized female rats used cystometry, EUS electromyography, spinal cord transection (SCT) at different segmental levels, and analysis of the effects of 5-HT(1A) receptor agonist (8-OH-DPAT) and antagonist (WAY100635) drugs to examine the origin of tonic and bursting EUS activity. EUS activity was elicited by bladder distension or electrical stimulation of afferent axons in the pelvic nerve (pelvic-EUS reflex). Tonic activity evoked by bladder distension was detected in spinal cord-intact rats and after acute and chronic T8-9 or L3-4 SCT but was abolished after L6-S1 SCT. Bursting activity was abolished by all types of SCT except chronic T8-9 transection. 8-OH-DPAT enhanced tonic activity, and WAY100635 reversed the effect of 8-OH-DPAT. The pelvic-EUS reflex consisted of an early response (ER) and late response (LR) when the bladder was distended in spinal cord-intact rats. ER remained after acute or chronic T8-9 and L3-4 SCT, but was absent after L6-S1 SCT. LR occurred only in chronic T8-9 SCT rats where it was enhanced or unmasked by 8-OH-DPAT. The results indicate that spinal serotonergic mechanisms facilitate tonic and bursting EUS activity. The circuitry for generating different patterns of EUS activity appears to be located in different segments of the spinal cord: tonic activity at L6-S1 and bursting activity between T8-9 and L3-4.

Impaired micturition reflex caused by acute selective dorsal or ventral root(s) rhizotomy in anesthetized rats

PURPOSE

To clarify the contributions of parasympathetic inputs and outputs to the micturition reflex.

MATERIALS AND METHODS

Intra-vesical pressure (IVP), external urethral sphincter electromyogram (EMG), pelvic afferent nerve activities (PANA), and pelvic efferent nerve activities (PENA) as well as the time-derived IVP (dIVP, an index of bladder contractility) were evaluated in intact and acute dorsal or ventral root(s) rhizotomized (DRX and VRX, respectively) rats.

RESULTS

In DRX rats, when compared with that in intact stage, the voiding frequency was decreased (75 +/- 15% of intact, P < 0.05, n = 8), while the threshold pressure to trigger voiding contractions was significantly increased (187 +/- 75% of intact, P < 0.05, n = 8). In addition, several insufficient contractions (5.3 +/- 3.5 contractions/voiding, P < 0.05, n = 8) occurred in ahead of each voiding contraction. On the other hand, in VRX rats, the peak and rebound IVP were significantly decreased (90 +/- 3.5% and 75 +/- 11.3% of intact, P < 0.01, n = 8), while the threshold pressure was not affected (102 +/- 11% of intact, P = NS, n = 8). The time-derived parameters were significantly decreased in VRX (peak dIVP, 78 +/- 10.2%, rebound dIVP, 75 +/- 15.6%, minimal dIVP, 68 +/- 14% of intact, P < 0.01, n = 8) but only peak dIVP was decreased (85 +/- 11% of intact, P < 0.01, n = 8) in DRX rats.

CONCLUSION

Acute selective DRX and VRX rat can be an animal model to investigate peripheral neural control in micturition functions.

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.

Animal models in urological disease and sexual dysfunction

There are several conditions associated with dysfunction of the lower urinary tract or which result in a reduction in the ability to engage in satisfactory sexual function and result in significant bother to sufferers, partners and/or carers. This review describes some of the animal models that may be used to discover safe and effective medicines with which to treat them. While alpha adrenoceptor antagonists and 5-alpha-reductase inhibitors deliver improvement in symptom relief in benign prostatic hyperplasia sufferers, the availability of efficacious and well-tolerated medicines to treat incontinence is less well served. Stress urinary incontinence (SUI) has no approved medical therapy in the United States and overactive bladder (OAB) therapy is limited to treatment with muscarinic antagonists (anti-muscarinics). SUI and OAB are characterised by high prevalence, a growing ageing population and a strong desire from sufferers and physicians for more effective treatment options. High patient numbers with low presentation rates characterizes sexual dysfunction in men and women. The introduction of Viagra in 1998 for treating male erectile dysfunction and the success of the phosphodiesterase type 5 inhibitor class (PDE5 inhibitor) have indicated the willingness of sufferers to seek treatment when an effective alternative to injections and devices is available. The main value of preclinical models in discovering new medicines is to predict clinical outcomes. This translation can be established relatively easily in areas of medicine where there are a large number of drugs with different underlying pharmacological mechanisms in clinical usage. However, apart from, for example, the use of PDE5 inhibitors to treat male erectile dysfunction and the use of anti-muscarinics to treat OAB, this clinical information is limited. Therefore, current confidence in existing preclinical models is based on our understanding of the biochemical, physiological, pathophysiological and psychological mechanisms underlying the conditions in humans and how they are reflected in preclinical models. Confidence in both the models used and the pharmacological data generated is reinforced if different models of related aspects of the same disorder generate confirmatory data. However, these models will only be fully validated in retrospect once the pharmacological agents they have helped identify are tested in humans.

Integrative control of the lower urinary tract: preclinical perspective

Storage and periodic expulsion of urine is regulated by a neural control system in the brain and spinal cord that coordinates the reciprocal activity of two functional units in the lower urinary tract (LUT): (a) a reservoir (the urinary bladder) and (b) an outlet (bladder neck, urethra and striated muscles of the urethral sphincter). Control of the bladder and urethral outlet is dependent on three sets of peripheral nerves: parasympathetic, sympathetic and somatic nerves that contain afferent as well as efferent pathways. Afferent neurons innervating the bladder have A-delta or C-fibre axons. Urine storage reflexes are organized in the spinal cord, whereas voiding reflexes are mediated by a spinobulbospinal pathway passing through a coordination centre (the pontine micturition centre) located in the brainstem. Storage and voiding reflexes are activated by mechanosensitive A-delta afferents that respond to bladder distension. Many neurotransmitters including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide and neuropeptides are involved in the neural control of the LUT. Injuries or diseases of the nervous system as well as disorders of the peripheral organs can produce LUT dysfunctions including: (1) urinary frequency, urgency and incontinence or (2) inefficient voiding and urinary retention. Neurogenic detrusor overactivity is triggered by C-fibre bladder afferent axons, many of which terminate in the close proximity to the urothelium. The urothelial cells exhibit 'neuron-like' properties that allow them to respond to mechanical and chemical stimuli and to release transmitters that can modulate the activity of afferent nerves.

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.

CNS involvement in overactive bladder: pathophysiology and opportunities for pharmacological intervention

The pathophysiology of overactive bladder (OAB) syndrome is complex, and involves both peripheral and CNS factors. Several CNS disorders are associated with OAB, e.g. stroke, spinal cord injury, Parkinson's disease and multiple sclerosis, and in each disorder the pathophysiology of OAB can be multifactorial. Irrespective of cause or pathophysiology of OAB, antimuscarinic drugs are the first line of pharmacological treatment. However, adverse effects and limited efficacy makes alternative therapeutic principles desirable. Most alternative drugs used for the treatment of OAB have a peripheral site of action, mainly affecting efferent or afferent neurotransmission or the detrusor muscle itself. New targets for pharmacological intervention may be found in the CNS. Several CNS transmitters/transmitter systems are known to be involved in micturition control, but few drugs with a defined CNS site of action (e.g. baclofen, imipramine and duloxetine) have been used for the treatment of voiding disorders. GABA, glutamate, opioid, serotonin, noradrenaline (norepinephrine), and dopamine receptors and mechanisms are known to influence micturition, and drugs influencing these systems could potentially be developed for the treatment of OAB. Preclinical studies in different animal models have shown that modulation of normal micturition and detrusor overactivity by drugs acting within the spinal cord or supraspinally is possible. Promising results have been obtained in such models, e.g. with drugs interfering with GABA mechanisms, serotonin 5-HT1A receptors, mu-opioid receptors and alpha-adrenoreceptors. However, considering the limited predictability of existing animal models for efficacy in humans, positive proof of concept studies in humans are mandatory. Such studies are scarce and further investigations are needed.

Evidence for the involvement of central 5-HT7 receptors in the micturition reflex in anaesthetized female rats

(1) The effects of the selective 5-HT7 receptor antagonists SB-269970 (3-300 microg kg-1; n=5-6) and SB-656104 (30 microg kg-1; n=5) administered centrally (i.c.v.) were investigated on the 'micturition reflex' in the urethane anaesthetized female rat. (2) In cystometric recordings, SB-269970 caused significant increases in volume of 58+/-15 and 138+/-33% and pressure of 140+/-46 and 149+/-60% thresholds at 10 and 30 microg kg-1. These changes were associated with significant decreases in distension-induced bladder contraction of 62+/-14 and 60+/-11%, respectively. However, there was no change in residual volume. At the higher doses, SB-269970 blocked the micturition reflex. SB-656104 had similar effects to SB-269970 but in addition significantly increased the residual volume. (3) SB-269970 (10 microg kg-1; n=5) given i.v. had no effect on the micturition reflex. (4) SB-269970 (30 microg kg-1; n=4) given intrathecally (i.t.) had no effect on micturition reflex, although the selective 5-HT1A receptor antagonist WAY-100635 given i.t. after SB-269970 caused a significant increase in the volume threshold. (5) Using an isovolumetric method in which urethral changes were measured, SB-269970 (30 microg kg-1; n=4; i.c.v.) failed to have any effect on these urethral-evoked changes although they significantly reduced the amplitude of the bladder contraction. (6) These data demonstrate that 5-HT7 receptors located supraspinally in the rat are involved in the control of micturition.

Role of protein kinase C in central muscarinic inhibitory mechanisms regulating voiding in rats

To evaluate the role of protein kinase C in central muscarinic mechanisms regulating voiding, cystometry was performed in conscious rats. Oxotremorine methiodide, a muscarinic agonist was injected i.c.v. in a dose (0.1 microg/rat) shown previously to alter voiding function. Oxotremorine methiodide was also tested after i.c.v. injection of chelerythrine chloride (a protein kinase C inhibitor, 2 microg/rat) or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7, a protein kinase inhibitor, 5 nmol/rat). In untreated rats, oxotremorine methiodide elicited a bimodal response consisting of an initial increase in bladder capacity, maximal voiding pressure, pressure threshold and post voiding intravesical pressure, but reduced voiding efficiency and bladder compliance. The second response consisted of a decrease in bladder capacity and bladder compliance, increases in maximal voiding pressure and post voiding intravesical pressure, but no change in pressure threshold or voiding efficiency. However, approximately 20 min after pre-treatment with chelerythrine chloride or H-7 in doses that did not alter voiding function, oxotremorine methiodide decreased bladder capacity, increased maximal voiding pressure, but did not change pressure threshold or voiding efficiency. These results indicate that inhibitory and facilitatory muscarinic mechanisms in the brain that control voiding function involve different second messenger systems. Inhibitory mechanisms which are blocked by chelerythrine chloride or H-7 must involve protein kinase C and normally be inactive because the protein kinase inhibitors alone did not alter voiding. On the other hand, facilitatory muscarinic mechanisms which previous studies showed were tonically active are not mediated by chelerythrine chloride or H-7 sensitive signaling pathways.

Current and future pharmacological treatment for overactive bladder

PURPOSE

Urinary incontinence and overactive bladder are important and common conditions that have received little general medical attention. We reviewed the magnitude and impact of these conditions, and discuss pharmacotherapy as well as new drugs under investigation.

MATERIALS AND METHODS

The main emphasis of this review is pharmacological therapy for the bladder. We discuss currently available agents, drugs under development and pharmacological targets that would be suitable targets for treating overactive bladder. Drugs such as duloxetine that target not bladder smooth muscle, but rather central nervous system control of the micturition reflex are undergoing clinical trials. We also discuss intravesical therapy and alternative drug delivery methods, such as intravesical capsaicin and botulinum toxin, with special emphasis on approaches to modulate bladder afferent nerve function for preventing overactive bladder.

RESULTS

There are many advantages to advanced drug delivery systems, including long-term therapeutic efficacy, decreased side effects and improved patient compliance. Future speculation such as gene therapy holds great promise for overactive bladder because it is possible to access all genitourinary organs via endoscopy and other minimally invasive techniques that are ideally suited for gene therapy.

CONCLUSIONS

Traditional anticholinergic therapies are limited in their effectiveness. There is great hope for future research regarding voiding dysfunction and urinary incontinence through a focus on afferent nerve intervention for preventing overactive bladder.

5-Hydroxytryptamine receptors, especially the 5-HT4 receptor, in guinea pig urinary bladder

The function of 5-hydroxytryptamine (5-HT) receptors, especially the 5-HT4 receptor, in the urinary bladder were examined in preparations isolated from the guinea pig by in vitro receptor autoradiography and determinations of mechanical activity and acetylcholine (ACh) release. Specific [125I]SB207710 binding sites were detected evenly throughout the urinary bladder. 5-HT (3 x 10(-8)-10(-4) M) caused contractions of strips of the urinary bladder, in a concentration dependent manner. Ketanserin antagonized the 5-HT-induced contractions, while granisetron and SB204070 antagonized the contractions induced by high concentrations of 5-HT. Atropine inhibited the contractions induced by high concentrations of 5-HT. Ketanserin prevented the 5-HT-induced contractions in the presence of atropine, but granisetron and SB204070 did not affect the contractions under such a condition. 5-HT enhanced the electrically-stimulated (5 Hz, 0.5 ms) outflow of [3H]acetylcholine from strips preloaded with [3H]choline, and the enhancement was antagonized by granisetron and SB204070. Thus, the contractile response to 5-HT was mediated by activations of 5-HT2, 5-HT3 and 5-HT4 receptors. The 5-HT2 receptor may be a property of high affinity to 5-HT and located on the smooth muscle cells. The 5-HT4 as well as 5-HT3 receptor may be a property of low affinity to 5-HT and located on the cholinergic neurons.

Treatment of the overactive bladder: possible central nervous system drug targets

The well-known side effects of antimuscarinic drugs have focused interest on other modalities of treatment of the overactive bladder. To effectively control bladder activity, identification of suitable targets for pharmacologic intervention is necessary. Such targets may be found in the central nervous system (CNS) or peripherally. Several CNS transmitters may modulate voiding, but few drugs with a defined CNS site of action have been developed for treatment of voiding disorders. Drugs affecting gamma-aminobutyric acid, opioid, serotonin, noradrenaline, dopamine, or glutamatergic receptors and mechanisms are known to influence micturition, and potentially such drugs could be developed for clinical use. However, a selective action on the lower urinary tract may be difficult to obtain.