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

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.

Liposomal formulations of oxybutynin and resiniferatoxin for the treatment of urinary diseases: improvement of drug tolerance upon intravesical

The use of liposomes for drug release has demonstrated to be a promising therapeutic platform for biomedical applications. In this study, intravesical administration of OXI (1.5 mM) and RTX (100 nM) was used to compare histological changes caused in Wistar female rats by the drugs both unloaded and loaded in liposomes. After instillation of formulations by intravesical catheter, bladders were removed and histological analysis carried out at pre-determined time intervals over a period of 60 days. Urinalysis was performed to verify the presence of infection and of liposomes. Results showed that RTX caused a higher bladder damage, with inflammatory reaction that reached all bladder layers. After 60 days, RTX-treated group showed urothelial alterations, collagen replacement by fibrosis and also abdominal adherence, but not the OXI-treated group. At the end of the assay, the liposomal-treated groups showed a minimal inflammatory reaction and significantly increased bladder size. Moreover, urinalysis confirmed the presence of liposomes in rat urine. RTX promoted higher bladder damage than OXI. Intravesical administration of liposomal OXI or RTX formulations minimized inflammatory reaction, with an extended drug effect on bladders. After a single intravesical administration, liposomes were found in rat urine samples after 60 days.

The clinical pharmacology of the medical treatment for overactive bladder in adults

INTRODUCTION

Overactive bladder is a prevalent symptom complex that affects the patient's quality of life. Any disruption between the neuronal micturition pathway can lead to bladder overactivity. Neurogenic causes, myogenic causes, aging, bladder outlet obstruction, sex, and psychological factors are some of the factors contributing to bladder overactivity. The complaint of any symptoms of OAB, which is highly prevalent and affects overall QOL, often needs therapeutic interventions. When conservative therapy methods fail, the addition of medications is recommended. The most commonly used agents for the treatment of OAB are antimuscarinic drugs. New classes of drugs, such as beta-3 agonists, have enriched our pharmacologic armamentarium.

AREAS COVERED

In this review, with a special focus on oral pharmacological treatments, we discussed the definition, etiology, symptoms, diagnosis, and management of OAB.

EXPERT OPINION

OAB is a multifactorial condition with every patient presenting with a different collection of symptoms and signs. Medical therapies should be given in conjunction with behavioral therapies. Using high or low doses, flexible doses, and stopping or changing the medications are interchangeable strategies based on the level of treatment efficacy and patient satisfaction.

Serotonergic mechanisms in spinal cord injury

Spinal cord injury (SCI) is a tragic event causing irreversible losses of sensory, motor, and autonomic functions, that may also be associated with chronic neuropathic pain. Serotonin (5-HT) neurotransmission in the spinal cord is critical for modulating sensory, motor, and autonomic functions. Following SCI, 5-HT axons caudal to the lesion site degenerate, and the degree of axonal degeneration positively correlates with lesion severity. Rostral to the lesion, 5-HT axons sprout, irrespective of the severity of the injury. Unlike callosal fibers and cholinergic projections, 5-HT axons are more resistant to an inhibitory milieu and undergo active sprouting and regeneration after central nervous system (CNS) traumatism. Numerous studies suggest that a chronic increase in serotonergic neurotransmission promotes 5-HT axon sprouting in the intact CNS. Moreover, recent studies in invertebrates suggest that 5-HT has a pro-regenerative role in injured axons. Here we present a brief description of 5-HT discovery, 5-HT innervation of the CNS, and physiological functions of 5-HT in the spinal cord, including its role in controlling bladder function. We then present a comprehensive overview of changes in serotonergic axons after CNS damage, and discuss their plasticity upon altered 5-HT neurotransmitter levels. Subsequently, we provide an in-depth review of therapeutic approaches targeting 5-HT neurotransmission, as well as other pre-clinical strategies to promote an increase in re-growth of 5-HT axons, and their functional consequences in SCI animal models. Finally, we highlight recent findings signifying the direct role of 5-HT in axon regeneration and suggest strategies to further promote robust long-distance re-growth of 5-HT axons across the lesion site and eventually achieve functional recovery following SCI.

Pharmacology and Therapeutic Potential of the 5-HT7 Receptor

It is well-documented that serotonin (5-HT) exerts its pharmacological effects through a series of 5-HT receptors. The most recently identified member of this family, 5-HT₇, was first identified in 1993. Over the course of the last 25 years, this receptor has been the subject of intense investigation, and it has been demonstrated that 5-HT₇ plays an important role in a wide range of pharmacological processes. As a result of these findings, modulation of 5-HT₇ activity has been the focus of numerous drug discovery and development programs. This review provides an overview of the roles of 5-HT₇ in normal physiology and the therapeutic potential of this interesting drug target.

Brain serotoninergic nervous system is involved in bombesin-induced frequent urination through brain 5-HT7 receptors in rats

BACKGROUND AND PURPOSE

Psychological stress exacerbates symptoms of urinary bladder dysfunction; however, the underlying brain mechanisms are unclear. We have demonstrated that centrally administered bombesin, a stress-related neuropeptide, facilitates the rat micturition reflex. Brain bombesin-like peptides modulate the serotoninergic nervous system activity under stress conditions; therefore, we examined whether brain 5-HT is involved in the bombesin-induced increased frequency of urination in urethane-anaesthetised male Sprague-Dawley rats.

EXPERIMENTAL APPROACH

Evaluation of intercontraction intervals (ICI) and maximal voiding pressure (MVP) during cystometrograms were started 1 h before i.c.v. administration of bombesin or i.c.v. pretreatment with the 5-HT receptor antagonists.

KEY RESULTS

Bombesin (0.03 nmol per animal, i.c.v.) significantly reduced ICI without affecting MVP. The bombesin-induced response was significantly suppressed by acute depletion of brain 5-HT, which was induced by pretreatment with p-chlorophenylalanine, a 5-HT synthesis inhibitor. Bombesin at a lower dose (0.01 nmol per animal, i.c.v.) showed no significant effect on ICI, while it significantly reduced ICI in the presence of WAY-100635 (5-HT_1A receptor antagonist, 0.1 or 0.3 μg per animal, i.c.v.), which can block the negative feedback control of 5-HT release. Bombesin (0.03 nmol per animal)-induced ICI reduction was significantly attenuated by SB269970 (5-HT₇ receptor antagonist, 0.1 or 0.3 μg per animal, i.c.v.) but not by ritanserin (5-HT₂ receptor antagonist, 0.3 or 1 μg per animal, i.c.v.).

CONCLUSIONS AND IMPLICATIONS

The brain serotoninergic nervous system is involved in the facilitation of the rat micturition reflex induced by bombesin-like peptides at least in part through brain 5-HT₇ receptors.

Escitalopram-Associated Acute Urinary Retention in Elderly Men With Known or Latent Benign Prostatic Hyperplasia: A Case Series

Lower urinary tract outflow dysfunction is frequent in older men and a potential cause of serious complications such as acute urinary retention (AUR). Drug-induced AUR has only rarely been reported with selective serotonin reuptake inhibitors including escitalopram; reported cases had no history of urinary outflow dysfunction. We herein report the development of AUR after the introduction of escitalopram at a standard dose in 3 male patients with previously diagnosed or unknown/latent and nonsymptomatic benign prostatic hyperplasia. Urinary retention receded after escitalopram discontinuation in 2 cases but led to emergent prostatectomy in the third. This case series highlights escitalopram's potential association with AUR in elderly men with known or latent benign prostatic hyperplasia. Further studies are warranted to investigate whether compromised or marginal urinary outflow should be considered a contraindication for treatment with escitalopram.

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

BACKGROUND AND PURPOSE

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

METHODS

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

FINDINGS

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

CONCLUSION

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

Serotonergic regulation of distention-induced ATP release from the urothelium

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

Regulatory Effects of 5-Hydroxytryptamine Receptors on Voiding Function

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

FUNDING

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

Expression of 5-Hydroxytryptamine Receptors in Human Urinary Bladders with Benign Prostatic Hyperplasia

INTRODUCTION

This study investigated the mRNA expression pattern and distribution of 5-hydroxytryptamine (5-HT) receptors 5-HT2A, 5-HT2B, 5-HT3A, 5-HT4, and 5-HT7 within the urothelium and detrusor of normal bladder tissue and in the urothelium of bladders from patients with benign prostatic hyperplasia (BPH).

METHODS

Normal urinary bladder specimens were obtained from 13 patients undergoing radical cystectomy due to bladder cancer (normal group) and BPH specimens were obtained from 27 benign prostatic obstruction patients receiving transurethral prostatectomy or retropubic prostatectomy. Receptor subtype mRNA expression was determined by real-time reverse transcription polymerase chain reaction on urothelium, detrusor, and whole mucosal preparations. Receptor distribution was determined by immunohistochemistry.

RESULTS

In normal tissues, expressions of 5-HT2B and 5-HT7 receptor mRNAs in the urothelium, detrusor, and whole mucosa were greater than the average expression for all receptor subtype mRNAs. 5-HT2B receptor protein was distributed in the apical urothelium and among the detrusor smooth muscle layers. In contrast, the 5-HT7 receptors were within the urothelium middle cell layers and detrusor smooth muscle cells. The expression pattern of each 5-HT receptor subtype mRNA within the BPH urothelium was similar to that in the normal urothelium. The expression level of 5-HT2A receptor mRNA in the BPH group was significantly lower than the normal group; however, the expressions of both 5-HT3A and 5-HT7 mRNAs were significantly higher. The expressions of both 5-HT2B and 5-HT4 mRNAs were not significantly different between the normal and BPH groups.

CONCLUSION

In normal urinary bladders, the expressions of both 5-HT2B and 5-HT7 mRNAs were higher compared to the 5-HT2A, 5-HT3A, and 5-HT4 mRNAs. The distributions of 5-HT2B and 5-HT7 receptors were different in the urothelium and detrusor layers. The 5-HT3A and 5-HT7 receptor mRNAs in the BPH group were significantly higher compared to the normal urothelium, while the 5-HT2A mRNA was significantly lower.

FUNDING

Asahi Kasei Pharma Corporation.

Serotonin modulation of macrophage polarization: inflammation and beyond

Macrophages display a ample plethora of effector functions whose acquisition is promoted by the surrounding cytokine and cellular environment. Depending on the stimulus, macrophages become specialized ("polarized") for either pathogen elimination, tissue repair and wound healing or immunosuppression. This "polarization" versatility allows macrophages to critically contribute to tissue homeostasis, as they promote initiation and resolution of inflammatory responses. As a consequence, deregulation of the tissue macrophage polarization balance is an etiological agent of chronic inflammation, autoimmune diseases, cancer and even obesity and insulin resistance. In the present review we describe current concepts on the molecular basis and the patho-physiological implications of macrophage polarization, and describe its modulation by serotonin (5-HT), a neurotransmitter that regulates inflammation and tissue repair via a large set of receptors (5-HTR1-7). 5-HT modulates the phenotypic and functional polarization of macrophages, and contributes to the maintenance of an anti-inflammatory state mainly via 5-HTR2B and 5-HTR7, whose activation has a great impact on macrophage gene expression profile. The identification of 5-HTR2B and 5-HTR7 as functionally-relevant polarization markers suggests their therapeutic value in inflammatory pathologies as well as their potential involvement in linking the immune and nervous systems.

The effect of the 5-HT7 serotonin receptor agonist, LP44, on micturition in rats with chronic spinal cord injury

AIMS

To better understand the effects of the selective 5-HT7 receptor agonist 4-[2-(Methylthio)phenyl]-N-(1,2,3,4-tetrahydro-1-naphthalenyl)-1-piperazinehexanamide hydrochloride (LP44) on micturition in spinal cord injury (SCI) rats.

METHODS

Female Sprague-Dawley rats weighing 200-275 g were used. SCI was produced in 8 of the 16 rats by transection at the T10 level; cystometric study occurred 8-12 weeks post-transection. Intravesical pressure was monitored in urethane-anesthetized animals via a transvesical catheter. The selective 5-HT7 antagonist (R)-3-[2-[2-(4-Methylpiperidin-1-yl)ethyl]pyrrolidine-1-sulfonyl] phenol hydrochloride (SB-269970) was administered after each LP44 dose-response curve (all drugs were administered intravenously, i.v).

RESULTS

Compared to controls, SCI rats had a higher bladder capacity and residual volume, and a lower voiding efficiency. In SCI rats, LP44 (0.003-0.3 mg/kg, i.v) induced significant dose-dependent increases in micturition volume, significant dose-dependent decreases in residual volume, resulting in significant increases in voiding efficiency. CMG measurements showed a dose-dependent increase of the high-frequency oscillation (HFO) activity, including the number of small oscillation per voiding. This was correlated with the improved voiding efficiency. SB-269970 (0.1 mg/kg, i.v) partially or completely reversed all LP44-induced changes.

CONCLUSIONS

HFOs seems to be correlated with external urethral sphincter (EUS) bursting activity during voiding. Both the bladder voiding efficiency and the periodic EUS activity were decreased in SCI rats. 5-HT7 receptor agonist can enhance HFO activity, thereby improving voiding efficiency. Whether or not these results may have implications for the future treatment of voiding dysfunction in SCI patients remains to be studied.

Effect of methysergide on pudendal inhibition of micturition reflex in cats

The role of 5-HT2 and opioid receptors in pudendal inhibition of bladder activity induced by intravesical infusion of saline or 0.25% acetic acid (AA) was investigated in anesthetized cats using methysergide (a 5-HT2 receptor antagonist) and naloxone (an opioid receptor antagonist). AA irritated the bladder and significantly (P<0.0001) reduced bladder capacity to 27.0 ± 7.4% of saline control capacity. Pudendal nerve stimulation (PNS) at multiples of the threshold (T) intensity for inducing anal sphincter twitching restored bladder capacity to 60.1 ± 8.0% at 1-2T (P<0.0001) and 92.2 ± 14.1% at 3-4T (P=0.001) of the saline control capacity. Methysergide (0.03-1mg/kg, i.v.) suppressed low intensity (1-2T) PNS inhibition but not high intensity (3-4T) inhibition, and also significantly (P<0.05) increased control bladder capacity at the dosage of 0.3-1mg/kg. During saline infusion without AA irritation, PNS significantly increased bladder capacity to 150.8 ± 9.9% at 1-2T (P<0.01) and 180.4 ± 16.6% at 3-4T (P<0.01) of the saline control capacity. Methysergide (0.1-1 mg/kg) significantly (P<0.05) increased saline control bladder capacity and suppressed PNS inhibition at the dosage of 0.03-1mg/kg. After methysergide treatment (1 mg/kg), naloxone significantly (P<0.05) reduced control bladder capacity during AA infusion but had no effect during saline infusion. Naloxone also had no influence on PNS inhibition. These results suggest that 5-HT2 receptors play a role in PNS inhibition of reflex bladder activity and interact with opioid mechanisms in micturition reflex pathway. Understanding neurotransmitter mechanisms underlying pudendal neuromodulation is important for the development of new treatments for bladder disorders.

Role of serotonin receptors in regulation of contractile activity of urinary bladder in rabbits

OBJECTIVE

To evaluate the role of different serotonin (5-hydroxytryptamine [5-HT]) receptor subtypes on urinary bladder contraction, pharmacologic analysis of electromotor activity (EMA) variation was performed using a rabbit bladder model.

MATERIALS AND METHODS

Measurements of EMA were performed on 3 urinary bladder portions: top, body, and trigone. The experiments were performed on 24 Shinshilla rabbits of both sexes, 5-6 months old, and weighing 2.5-4.0 kg. The bladder was isolated. Noninvasive electrodes were superimposed on the surface of the top, body, and trigone of the bladder. Contact between the electrode tips and the bladder surface was achieved. The bladder EMA was measured using bipolar silver electrodes for extracellular recordings.

RESULTS

The stimulation of the serotoninergic fibers and parasympathetic nerve resulted in increased bladder EMA frequency and amplitude (72% and 25%, respectively). The increase in bladder EMA was prevented by administration of selective inhibitors of serotonin receptor subtypes such as droperidol, spiperone, and sumatriptan. Exogenous serotonin administered to the rabbits after vagus nerve excitation increased the typical EMA of the bladder body smooth muscle.

CONCLUSION

The serotoninergic system has been widely implicated in the control of urinary bladder function. In the present study, we have demonstrated that preganglionic fibers and ganglionic serotoninergic neurons, expressing the 5-HT3 and 5-HT4 receptors, and the effector smooth muscle cells, expressing 5-HT1 and 5-HT2 receptors, are actively involved in the regulation of the bladder contractile activity in rabbits.

Effect of mirabegron, a novel β3-adrenoceptor agonist, on bladder function during storage phase in rats

Mirabegron, a selective β(3)-adrenoceptor agonist, facilitates urine storage function by exerting a relaxing effect on bladder smooth muscle. Here, we investigated the effect of mirabegron on bladder function during the storage phase. We assessed the effect of mirabegron on the resting intravesical pressure in anesthetized rats and also tested antimuscarinics (oxybutynin and tolterodine) under the same experimental conditions. Mirabegron dose-dependently decreased the resting intravesical pressure, while oxybutynin and tolterodine showed no statistically significant effects on resting intravesical pressure. We also investigated the effect of mirabegron on bladder function using cystometry technique in conscious rats with bladder outlet obstruction. While mirabegron dose-dependently decreased the frequency of nonvoiding contractions, considered an index of abnormal response in bladder storage, no significant effects were noted on the amplitude of nonvoiding contractions, micturition pressure, threshold pressure, voided volume, residual volume, or bladder capacity. Neither oxybutynin nor tolterodine affected the frequency of nonvoiding contractions; however, oxybutynin increased residual volume and tended to decrease voided volume in a dose-dependent manner, and tolterodine dose-dependently decreased voided volume. Taken together, these results shed light on the suggestion of mirabegron as a therapeutic agent, compared with antimuscarinics, with its most prominent effect being the facilitation of bladder storage.

Pathophysiology of overactive bladder

Overactive bladder (OAB) is a common disorder that negatively affects the quality of life of our patients and carries a large socioeconomic burden. According to the International Continence Society, it is characterized as urinary urgency, with or without urge incontinence, usually, with frequency and nocturia in the absence of causative infection. The pathophysiology of this disease entity varies between neurogenic, myogenic, or idiopathic factors. This paper provides a review of the contemporary theories behind the pathophysiology of OAB.

RhoBTB3 interacts with the 5-HT7a receptor and inhibits its proteasomal degradation

The 5-hydroxytryptamine (5-HT)7 receptor is the most recently identified serotonin receptor and is involved in a wide variety of central nervous system (CNS) functions, namely circadian rhythm, REM sleep, depression, thermoregulation, obsessive-compulsive disorder (OCD), anxiety, schizophrenia, epilepsy, nociception, migraine, sensation-seeking behavior, impulsivity, learning and memory. These numerous (patho)physiological processes of the CNS, in which the 5-HT7 receptor is involved, most likely reflect a diverse set of signaling pathways arising from this receptor. In order to reveal new interaction partners and possibly new signaling and/or trafficking pathways, we performed a yeast two-hybrid screening, using the C-terminal tail of the 5-HT7a receptor as bait and an adult-human brain cDNA library as prey. In this way we identified RhoBTB3 as a new interaction partner of the 5-HT7a receptor. By means of co-immunoprecipitation we were able to confirm the interaction between full length 5-HT7a receptor and RhoBTB3 in HEK293T cells. Subsequent domain mapping of this interaction revealed that not only the C-terminal tail, but also the third intracellular loop of the 5-HT7a receptor is involved. In addition, immunofluorescence microscopy showed clear co-localization between the 5-HT7a receptor and RhoBTB3 at the plasma membrane and in the endoplasmic reticulum. Despite the fact that RhoBTB3 has been shown to interact with Cul3, which in turn interacts with the E3 ubiquitin ligase, Roc1, we show here that RhoBTB3 neither recruits Cul3/Roc1 to the 5-HT7a receptor nor does it mediate ubiquitination of this receptor. Instead, we demonstrate that RhoBTB3 strongly inhibits proteasomal degradation of the 5-HT7a receptor.

The 5-HT(7) receptor in learning and memory

The 5-HT(7) receptor is a more recently discovered G-protein-coupled receptor for serotonin. The functions and possible clinical relevance of this receptor are not yet fully understood. The present paper reviews to what extent the use of animal models of learning and memory and other techniques have implicated the 5-HT(7) receptor in such processes. The studies have used a combination of pharmacological and genetic tools targeting the receptor to evaluate effects on behavior and cellular mechanisms. In tests such as the Barnes maze, contextual fear conditioning and novel location recognition that involve spatial learning and memory there is a considerable amount of evidence supporting an involvement of the 5-HT(7) receptor. Supporting evidence has also been obtained in studies of mRNA expression and cellular signaling as well as in electrophysiological experiments. Especially interesting are the subtle but distinct effects observed in hippocampus-dependent models of place learning where impairments have been described in mice lacking the 5-HT(7) receptor or after administration of a selective antagonist. While more work is required, it appears that 5-HT(7) receptors are particularly important in allocentric representation processes. In instrumental learning tasks both procognitive effects and impairments in memory have been observed using pharmacological tools targeting the 5-HT(7) receptor. In conclusion, the use of pharmacological and genetic tools in animal studies of learning and memory suggest a potentially important role for the 5-HT(7) receptor in cognitive processes.

Role of the 5-HT7 receptor in the central nervous system: from current status to future perspectives

Pharmacological and genetic tools targeting the 5-hydroxytryptamine (5-HT)7 receptor in preclinical animal models have implicated this receptor in diverse (patho)physiological processes of the central nervous system (CNS). Some data obtained with 5-HT7 receptor knockout mice, selective antagonists, and, to a lesser extent, agonists, however, are quite contradictory. In this review, we not only discuss in detail the role of the 5-HT7 receptor in the CNS but also propose some hypothetical models, which could explain the observed inconsistencies. These models are based on two novel concepts within the field of G protein-coupled receptors (GPCR), namely biphasic signaling and G protein-independent signaling, which both have been shown to be mediated by GPCR dimerization. This led us to suggest that the 5-HT7 receptor could reside in different dimeric contexts and initiate different signaling pathways, depending on the neuronal circuitry and/or brain region. In conclusion, we highlight GPCR dimerization and G protein-independent signaling as two promising future directions in 5-HT7 receptor research, which ultimately might lead to the development of more efficient dimer- and/or pathway-specific therapeutics.

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.

The 5-HT7 receptor and disorders of the nervous system: an overview

RATIONALE

The 5-HT(7) receptor is a more recently discovered G-protein-coupled receptor for serotonin. The functions and possible clinical relevance of this receptor are not yet fully understood.

OBJECTIVE

The present paper reviews to what extent the use of animal models of human psychiatric and neurological disorders have implicated the 5-HT(7) receptor in such disorders. The studies have used a combination of pharmacological and genetic tools targeting the receptor to evaluate effects on behavior.

RESULTS

Models of anxiety and schizophrenia have yielded mixed results with no clear role for the 5-HT(7) receptor described in these disorders. Some data are available for epilepsy, migraine, and pain but it is still very early to draw any definitive conclusions. There is a considerable amount of evidence supporting a role for the 5-HT(7) receptor in depression. Both blockade and inactivation of the receptor have resulted in an antidepressant-like profile in models of depression. Supporting evidence has also been obtained in sleep studies. Especially interesting are the augmented effects achieved by combining antidepressants and 5-HT(7) receptor antagonists. The antidepressant effect of amisulpride has been shown to most likely be mediated by the 5-HT(7) receptor.

CONCLUSIONS

The use of pharmacological and genetic tools in preclinical animal models strongly supports a role for the 5-HT(7) receptor in depression. Indirect evidence exists showing that 5-HT(7) receptor antagonism is clinically useful in the treatment of depression. Available data also indicate a possible involvement of the 5-HT(7) receptor in anxiety, epilepsy, pain, and schizophrenia.

5-hydroxytryptamine induced relaxation in the pig urinary bladder neck

BACKGROUND AND PURPOSE

5-Hydroxytryptamine (5-HT) is one of the inhibitory mediators in the urinary bladder outlet region. Here we investigated mechanisms involved in 5-HT-induced relaxations of the pig bladder neck.

EXPERIMENTAL APPROACH

Urothelium-denuded strips of pig bladder were mounted in organ baths for isometric force recordings of responses to 5-HT and electrical field stimulation (EFS).

KEY RESULTS

After phenylephrine-induced contraction, 5-HT and 5-HT receptor agonists concentration-dependently relaxed the preparations, with the potency order: 5-carboxamidotryptamine (5-CT) > 5-HT = RS67333 > (+/-)-8-hydroxy-2-dipropylaminotetralinhydrobromide > m-chlorophenylbiguanide > alpha-methyl-5-HT > ergotamine. 5-HT and 5-CT relaxations were reduced by the 5-HT(7) receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulphonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride and potentiated by (S)-N-tert-butyl-3-(4-(2-methoxyphenyl)-piperazin-1-yl)-2-phenylpropanamide dihydrochloride (WAY 100135) and cyanopindolol, 5-HT(1A) and 5-HT(1A/1B) receptor antagonists respectively. Inhibitors of 5-HT(1B/1D), 5-HT(2), 5-HT(2B/2C), 5-HT(3), 5-HT(4), 5-HT(5A) and 5-HT(6) receptors failed to modify 5-HT responses. Blockade of monoamine oxidase A/B, noradrenergic neurotransmission, alpha-adrenoceptors, muscarinic and purinergic receptors, nitric oxide synthase, guanylate cyclase and prostanoid synthesis did not alter relaxations to 5-HT. Inhibitors of Ca(2+)-activated K(+) and ATP-dependent K(+) channels failed to modify 5-HT responses but blockade of neuronal voltage-gated Na(+)-, Ca(2+)- and voltage-gated K(+) (K(v))-channels potentiated these relaxations. Adenylyl cyclase activation and cAMP-dependent protein kinase (PKA) inhibition potentiated and reduced, respectively, 5-HT-induced responses. Under non-adrenergic, non-cholinergic, non-nitrergic conditions, EFS induced neurogenic, frequency-dependent, relaxations which were resistant to WAY 100135 and cyanopindolol.

CONCLUSIONS AND IMPLICATIONS

5-HT relaxed the pig urinary bladder neck through muscle 5-HT(7) receptors linked to the cAMP-PKA pathway. Prejunctional 5-HT(1A) receptors and K(v) channels modulated 5-HT-induced relaxations whereas postjunctional K(+) channels were not involved in such responses. 5-HT(7) receptor antagonists could be useful in the therapy of urinary incontinence produced by intrinsic sphincter deficiency.

5-HT7 receptor deletion enhances REM sleep suppression induced by selective serotonin reuptake inhibitors, but not by direct stimulation of 5-HT1A receptor

5-HT(7) receptors are involved in REM sleep and possibly in mood disorders. REM sleep suppression and antidepressant-like behavior is observed in 5-HT(7)(-/-) mice and in rats treated with 5-HT(7) receptor antagonists. We recently demonstrated that pharmacological blockade of 5-HT(7) receptors enhances REM sleep suppression and antidepressant-like behavior induced by citalopram in rodents. It has been hypothesized that the effect of citalopram on sleep is essentially mediated by the activation of 5-HT(1A) receptors. The present study investigates the impact of 5-HT(7) receptor gene deletion on the effect of various reuptake inhibitors on REM sleep and probes the role of 5-HT(1A) receptors in this response. Three SSRIs (citalopram, fluoxetine and paroxetine) but not the tricyclic antidepressant desipramine had a significantly stronger REM sleep suppressive effect in 5-HT(7)(-/-) mice compared to 5-HT(7)(+/+) mice. In contrast, REM sleep was similarly reduced in 5-HT(7)(+/+) mice and 5-HT(7)(-/-) mice after treatment with the 5-HT(1A) receptor agonist ipsapirone. Furthermore, both 5-HT(7)(+/+) and 5-HT(7)(-/-) mice displayed the same increase in REM sleep duration produced by the 5-HT(1A) receptor antagonist WAY-100635. These findings indicate that 5-HT(7) receptor deletion augments the effect of various SSRIs on REM sleep suppression and that this effect is distinct from those mediated via 5-HT(1A) receptors.

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.

Involvement of central 5-HT7 receptors in modulation of cardiovascular reflexes in awake rats

This study evaluated the role of 5-HT7 receptors within the central nervous system in modulating cardiovascular responses to the activation of chemo-, baro- and cardiopulmonary reflexes and in the regulation of mean arterial pressure and heart rate, using intracisternal (i.c.) application of the selective 5-HT7 receptor antagonist SB-269970 in awake rats. Experiments were performed on male Wistar rats (300-320 g). At 4 days before the experiment, rats were anesthetized and placed in a stereotaxic frame implantation of a guide cannula in the direction of the cisterna magna to be used for microinjection of saline or SB-269970 (100 microg/kg). On the day before the experiments a femoral artery and vein were cannulated to record arterial pressure and heart rate and to inject drugs to activate cardiovascular reflexes, respectively. The chemo-, baro- and cardiopulmonary reflexes were activated in different experimental groups before and after i.c. injection of saline or SB-269970. The antagonism of 5-HT7 receptors reduced: (a) the pressor (50+/-4 vs. 19+/-9 mm Hg) and bradycardic (-247+/-13 vs. -69+/-27 bpm) responses to chemoreflex activation; (b) the fall in MAP (-54+/-4 vs. -20+/-6 mm Hg) and the bradycardia (-294+/-12 vs. -98+/-34 bpm) in response to cardiopulmonary reflex activation; and (c) the gain of the baroreflex (-2.3+/-0.1 to -0.9+/-0.2 bpm/mm Hg). Intracisternal application of SB-269970 increased significantly baseline MAP in those rats previously submitted to the activation of a cardiovascular reflex but in naïve rats produced no changes in the baseline MAP were observed. The fact that cardiovascular responses to all reflexes tested were attenuated by the antagonism of 5-HT7 receptors suggests that brainstem 5-HT7 receptors brainstem facilitate the processing of the autonomic responses to cardiovascular reflex activation and that a 5-HT-containing pathway to the brainstem provides a normalizing input during challenges produced by cardiovascular reflex activation which seems to be mediated by 5-HT7 receptors.

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.

Effects of electrical stimulation of the raphe area on the micturition reflex in cats

The raphe nucleus has a variety of physiological functions, including emotion, regulation of skeletal muscle motoneurons, spinal transmission of nociceptive signals, sleep, respiration, gastric motility, and cardiovascular function. Recent evidence has shown that centrally administered serotonin has modulatory effects on micturition function, and that decreased brain serotonin might underlie depression and an overactive bladder. We applied high-frequency stimulation (HFS; 0.2-ms duration, 100 Hz) in the raphe nucleus and the adjacent midline area in 20 supracollicular decerebrate cats, which mostly elicited inhibition of the micturition reflex. The effective amplitude of the electrical stimulation for evoking inhibitory responses was less than 50 muA. We also examined single neuronal activities in the raphe nucleus in response to isovolumetric spontaneous micturition reflexes. In total, 79 neurons were recorded in the raphe nucleus that were related to urinary storage/micturition cycles. Of the neurons recorded, the most common were tonic storage neurons (48%), followed by tonic micturition neurons (28%), phasic storage neurons (18%), and phasic micturition neurons (6%). In addition to the tonic/phasic as well as storage/micturition classification, the neurons showed diverse discharge patterns: augmenting, constant and decrementing, with the constant discharge pattern being most common. Among neurons in the raphe nucleus, the neurons with a decrementing discharge pattern were concentrated in the rostral portion, whereas the augmenting and constant neurons existed diffusely. The storage and micturition neurons were intermingled in the rostral portion, whereas they were separate in the caudal portion. In conclusion, the results of the present study indicate that HFS of the raphe area inhibits the micturition reflex and that there are micturition-related neuronal firings in the raphe area in cats, suggesting that the raphe nucleus is involved in neural control of micturition.

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.

Serotoninergic receptors in the anteroventral preoptic region modulate the hypoxic ventilatory response

Hypothalamus is a site of integration of the hypoxic and thermal stimuli on breathing and there is evidence that serotonin (5-HT) receptors in the anteroventral preoptic region (AVPO) mediate hypoxic hypothermia. Once 5-HT is involved in the hypoxic ventilatory response (HVR), we investigated the participation of the 5-HT receptors (5-HT1, 5-HT2 and 5-HT7) in the AVPO in the HVR. To this end, pulmonary ventilation (V(E)) of rats was measured before and after intra-AVPO microinjection of methysergide (a 5-HT1 and 5-HT2 receptor antagonist), WAY-100635 (a 5-HT1A receptor antagonist) and SB-269970 (a 5-HT7 receptor antagonist), followed by 60 min of hypoxia exposure (7% O2). Intra-AVPO microinjection of vehicles or 5-HT antagonists did not change V(E) during normoxic conditions. Exposure of rats to 7% O2 evoked typical hypoxia-induced hyperpnea after vehicle microinjection, which was not affected by methysergide. WAY-100635 and SB-269970 treatment caused an increased HVR, due to a higher tidal volume. Therefore, the current data provide the evidence that 5-HT acting on 5-HT1A and 5-HT7 receptors in the AVPO exert an inhibitory modulation on the HVR.

Effect of 5-HT depletion on cardiovascular vagal reflex sensitivity in awake and anesthetized rats

Antagonism of central 5-HT1A and 5-HT7 receptors inhibits reflex-evoked vagal bradycardias indicating that 5-HT is released during these reflexes. The present experiments examined the effect of 5-HT depletion with para-chlorophenylalanine (p-CPA) on the cardiac vagal baroreflex and cardiopulmonary reflex in awake and anesthetized rats. Immunocytochemistry and neurochemical detection showed that p-CPA depleted the brainstem of 5-HT, but not of norepinephrine or dopamine. Depletion of 5-HT was associated with an increase in mean arterial pressure (MAP) in awake rats. This difference was abolished by anesthesia, which reduced MAP in both groups of animals. The baroreflex gain, whether calculated from the rise in pressure induced by phenylephrine or the fall in pressure evoked by sodium nitroprusside, was significantly attenuated in depleted rats compared to controls. This attenuation of the baroreflex gain was unaffected by subsequent anesthesia. 5-HT depletion also attenuated the cardiopulmonary reflex vagal bradycardias but this only reached statistical significance when the rats were anesthetized. The data support the view that 5-HT is released in the reflex activation of the cardiac vagal pathway.

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.

Characterization of 5-HT7-receptor-mediated gastric relaxation in conscious dogs

We aimed to evaluate the gastric relaxant capacity of the 5-HT(1/7)-receptor agonist 5-carboxamidotryptamine (5-CT) in conscious dogs and to clarify the mechanism of action by use of selective antagonists, vagotomy, and in vitro experiments. A barostat enabled us to monitor the intragastric volume in response to different treatments (intravenously administered) before and after supradiaphragmatic vagotomy [results presented as the maximum volume change after treatment (mean; n = 5-11)]. In vitro experiments were performed with isolated muscle strips cut from four different stomach regions of the vagotomized dogs [results were fitted to the operational model of agonism to determine the efficacy parameter tau (n = 5)]. 5-CT (0.5-10 microg/kg) caused a dose-dependent gastric relaxation (29-267 ml) that was completely blocked by the selective 5-HT(7)-receptor antagonist SB-269970 (50 microg/kg). After vagotomy, the relaxation to 10 microg/kg 5-CT was significantly less pronounced (73 vs. 267 ml; P < 0.05) but still blocked by SB-269970, whereas the response to the nitric oxide donor nitroprusside was similar to that before vagotomy (178 vs. 218 ml). In vitro, 5-CT concentration dependently inhibited the PGF(2alpha)-contracted muscle strips before and after vagotomy. Although before and after vagotomy the response in every region was mediated by 5-HT(7) receptors (apparent affinity dissociation constant: SB-269970, 8.2-8.6 vs. 8.3-8.6, respectively), the response after vagotomy was less efficacious (log tau: 1.9 to 0.5 vs. 1.4 to -0.1). The results indicate that the 5-CT-induced proximal stomach relaxation in conscious dogs before and after vagotomy is mediated via 5-HT(7) receptors. The decreased efficacy of 5-CT in vitro after vagotomy is probably related to vagotomy-induced changes in receptor density or coupling efficiency and provides a possible explanation for the decreased in vivo response to 5-CT after vagotomy.

Recent advances in basic science for overactive bladder

PURPOSE OF REVIEW

Detrusor overactivity is a relatively common yet embarrassing symptom complex with significant impact on quality of life. The mainstay of current pharmacological treatment involves the use of muscarinic receptor antagonists, but their therapeutic effectiveness is limited by a combination of limited efficacy and troublesome side effects and has recently been challenged by Herbison et al. Recognition of the limitations of existing therapy has started the search for pharmacotherapeutic agents acting on alternative pathways underlying detrusor overactivity with the intention of improving storage symptoms of urgency, frequency and urge incontinence.

RECENT FINDINGS

Recent research has suggested that several transmitters may modulate bladder storage. However, no agents currently available, acting via mechanisms other than muscarinic receptors have entered clinical practice so far. It is clear that far from being a passive container for urine, the urothelium is a crucial area within the bladder wall and its functions are complex and only now beginning to be appreciated. The release of several neurotransmitters from urothelium in response to distension and its action on receptors on sensory neurons is being increasingly recognized. The role for this afferent stimulation on the micturition reflex is gradually gaining importance in the pathophysiology of detrusor overactivity.

SUMMARY

In this article, the recent developments in basic science related to the pathogenesis and pharmacological basis for future drug targets for effective management of overactive bladder are discussed.

Involvement of serotoninergic receptors in the anteroventral preoptic region on hypoxia-induced hypothermia

Hypoxia causes a regulated decrease in body temperature (Tb). There is circumstantial evidence that the neurotransmitter serotonin (5-HT) in the anteroventral preoptic region (AVPO) mediates this response. However, which 5-HT receptor(s) is (are) involved in this response has not been assessed. Thus, we investigated the participation of the 5-HT receptors (5-HT1, 5-HT2, and 5-HT7) in the AVPO in hypoxic hypothermia. To this end, Tb of conscious Wistar rats was monitored by biotelemetry before and after intra-AVPO microinjection of methysergide (a 5-HT1 and 5-HT2 receptor antagonist, 0.2 and 2 microg/100 nL), WAY-100635 (a 5-HT(1A) receptor antagonist, 0.3 and 3 microg/100 nL), and SB-269970 (a 5-HT7 receptor antagonist, 0.4 and 4 micro/100 nL), followed by 60 min of hypoxia exposure (7% O2). During the experiments, the mean chamber temperature was 24.6 +/- 0.7 degrees C (mean +/- SE) and the mean room temperature was 23.5 +/- 0.8 degrees C (mean +/- SE). Intra-AVPO microinjection of vehicle or 5-HT antagonists did not change Tb during normoxic conditions. Exposure of rats to 7% of inspired oxygen evoked typical hypoxia-induced hypothermia after vehicle microinjection, which was not affected by both doses of methysergide. However, WAY-100635 and SB-269970 treatment attenuated the drop in Tb in response to hypoxia. The effect was more pronounced with the 5-HT7 antagonist since both doses (0.4 and 4 microg/0.1 microL) were capable of attenuating the hypothermic response. As to the 5-HT(1A) antagonist, the attenuation of hypoxia-induced hypothermia was only observed at the higher dose. Therefore, the present results are consistent with the notion that 5-HT acts on both 5-HT(1A) and 5-HT7 receptors in the AVPO to induce hypothermia, during hypoxia.

Differential inverse agonist efficacies of SB-258719, SB-258741 and SB-269970 at human recombinant serotonin 5-HT7 receptors

Recombinant 5-hydroxytryptamine 5-HT7 receptors are known to express constitutive, i.e., agonist-independent activity. Nonselective ligands, like methiothepin, ritanserin or clozapine behave as full inverse agonists at 5-HT7 receptors. The aim of the present study was to evaluate the degree of inverse agonist activity of three selective 5-HT7 receptor antagonists ((R)-3,N-dimethyl-N-[1-methyl-3-(4-methyl-piperidin-1-yl)propyl]benzene sulfonamide or SB-258719, R-(+)-1-(toluene-3-sulfonyl)-2-[2-(4-methylpiperidin-1-yl)ethyl]-pyrrolidine or SB-258741 and (R)-3-(2-(2-(4-methylpiperidin-1-yl)ethyl)-pyrrolidine-1-sulfonyl)-phenol or SB-269970) in the same model. cAMP accumulation was measured in intact Chinese hamster ovary (CHO) cells expressing human recombinant 5-HT7a receptors. In these cells, 5-HT stimulated cAMP levels and a series of ligands antagonized the effect of 5-HT with a 5-HT7 receptor-like profile. SB-258719 had no inverse agonist activity, SB-258741 behaved as a partial inverse agonist and SB-269970 was a quasi-full inverse agonist (as compared to methiothepin). The inverse agonist effect of SB-269970 was antagonized in a concentration-dependent manner by SB-258719. The widespread spectrum of inverse agonist activities shown by these compounds should help assessing the physiological relevance of constitutive 5-HT7 receptor activity in native tissues.

Vagal control of the heart: central serotonergic (5-HT) mechanisms

Cardiac vagal preganglionic neurones (CVPNs) are located within the dorsal vagal nucleus (DVN) and the nucleus ambiguus (nA). In mammals, CVPNs within the nA have small myelinated axons and mediate major chronotropic effects, those in the DVN have non-myelinated axons and mediate smaller chronotropic, dromotropic and inotropic effects. Numerous studies demonstrate important influences of serotonin (5-HT) at multiple sites controlling autonomic outflows including the nucleus tractus solitarius (NTS) where cardiorespiratory afferent fibres terminate, and the CVPNs and rostral ventrolateral medulla (RVLM), the location of sympathetic premotor neurones. We have demonstrated roles for some of the numerous 5-HT receptor subtypes (5-HT1, 5-HT2, 5-HT3, 5-HT4 and 5-HT7) in brainstem regions involved in cardiac control. Intracisternal application of selective ligands was used to study the effect of 5-HT receptors on heart rate and its reflex control. Further electrophysiological studies were also carried out to delineate their location and the mechanisms of action of these ligands. Blocking 5-HT1A receptors attenuated bradycardias evoked by stimulating baroreceptor and cardiopulmonary afferents but not arterial chemoreceptors, whereas antagonizing 5-HT7 receptors markedly attenuated all these reflex bradycardias. Within the DVN, nA and NTS, activation of 5-HT1A receptors could excite or inhibit neurones. In the NTS 5-HT2 receptors also had variable effects; 5-HT2B receptors excite and 5-HT2C receptors inhibit. Antagonism of 5-HT3 receptors attenuated upper airway and cardiopulmonary reflex bradycardias; this is compatible with data showing that 5-HT3 receptors excite DVN and NTS neurones by a glutamate-dependent mechanism. The origin of the glutamate (neuronal or glial) remains unresolved but glia are a possibility as baroreceptor-sensitive NTS neurones receive few direct 5-HT-containing synaptic contacts. Thus, 5-HT plays a critical role in the control of vagal outflow to the heart; however, why so many different receptors are involved, and their relative functional roles, remains unresolved.

Pre- and postsynaptic localization of the 5-HT7 receptor in rat dorsal spinal cord: Immunocytochemical evidence

Several lines of evidence indicate that 5-HT7 receptors are involved in pain control at the level of the spinal cord, although their mechanism of action is poorly understood. To provide a morphological basis for understanding the action of 5-HT on this receptor, we performed an immunocytochemical study of 5-HT7 receptor distribution at the lumbar level. 5-HT7 immunolabelling is localized mainly in the two superficial laminae of the dorsal horn and in small and medium-sized dorsal root ganglion cells, which is consistent with a predominant role in nociception. In addition, moderate labelling is found in the lumbar dorsolateral nucleus (Onuf's nucleus), suggesting involvement in the control of pelvic floor muscles. Electron microscopic examination of the dorsal horn revealed three main localizations: 1) a postsynaptic localization on peptidergic cell bodies in laminae I-III and in numerous dendrites; 2) a presynaptic localization on unmyelinated and thin myelinated peptidergic fibers (two types of axon terminals are observed, large ones, presumably of primary afferent origin, and smaller ones partially from intrinsic cells; this presynaptic labelling represents 60% and 22% of total labelling in laminae I and II, respectively); and 3) 16.9% of labelling in lamina I and 19.8% in lamina II are observed in astrocytes. Labeled astrocytes are either intermingled with neuronal elements or make astrocytic "feet" on blood vessels. In dendrites, the labelling is localized on synaptic differentiations, suggesting that 5-HT may act synaptically on the 5-HT7 receptor. This localization is compared with other 5-HT receptor localizations, and their physiological consequences are discussed.

Central 5-HT7 receptors are critical for reflex activation of cardiac vagal drive in anaesthetized rats

5-Hydroxytryptamine (5-HT; serotonin)-containing neurones contribute to reflex activation of parasympathetic outflow in a number of species, but the 5-HT receptors mediating these effects have yet to be fully determined. The present experiments demonstrate that central 5-HT7 receptors are involved in the vagal bradycardia evoked during the cardiopulmonary reflex, baroreflexes and the chemoreflex, as well as other autonomic changes caused by these reflexes. The experiments examined the effects of the selective 5-HT7 receptor antagonists SB-269970 and SB-656104 on these reflexes. For the cardiopulmonary reflex, when compared to time-matched vehicle control experiments, intracisternal application of SB-269970 (30-300 microg kg(-1), i.c.) dose-dependently attenuated the evoked bradycardia. At the highest dose, SB-269970 also attenuated the reflex hypotension and sympathoinhibition. The structurally different 5-HT7 receptor antagonist SB-656104 (100 microg kg(-1), i.c.) similarly attenuated the reflex bradycardia and hypotension. SB-269970 (100 microg kg(-1), i.c.) also attenuated the bradycardias evoked by electrical stimulation of aortic nerve afferents and the baroreflex evoked by the pressor response to phenylephrine (3-25 microg kg(-1), i.v.). The gain of the baroreflex was also significantly attenuated (0.15 +/- 0.06 versus 0.34 +/- 0.06 ms mmHg(-1)). Finally, SB-269970 (100 microg kg(-1), i.c.) significantly attenuated both the bradycardia and sympathoexcitation evoked by the chemoreflex. These data indicate that central 5-HT7 receptors play an important facilitatory role in the reflex activation of vagal outflow to the heart.

8-OH-DPAT acts on both 5-HT1A and 5-HT7 receptors to induce hypothermia in rodents

Studies using selective drugs and knockout mice have demonstrated that the 5-HT(7) receptor plays an instrumental role in serotonin-induced hypothermia. There is also evidence supporting an involvement of the 5-HT(1A) receptor, although mainly from studies using 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT(1A/7) receptor agonist. Here we studied the effects of 8-OH-DPAT and selective antagonists for the 5-HT(1A) and 5-HT(7) receptors on body temperature in rats, wild-type (5-HT(7)(+/+)) mice and knockout (5-HT(7)(-/-)) mice. At lower doses (0.3-0.6 mg/kg, i.p.), 8-OH-DPAT decreased body temperature in 5-HT(7)(+/+) mice but not in 5-HT(7)(-/-) mice. At a higher dose (1 mg/kg, i.p.) 8-OH-DPAT induced hypothermia in both 5-HT(7)(-/-) and 5-HT(7)(+/+) mice. The 5-HT(1A) receptor antagonist (S)-N-tert-butyl-3-(4-(2-methoxyphenyl)piperazine-1-yl)-2-phenylpropanamide (WAY-100135) (10 mg/kg, i.p.) inhibited the effect of 8-OH-DPAT at all doses in rats and mice. In 5-HT(7)(+/+) mice the selective 5-HT(7) receptor antagonist (R)-3-(2-(2-(4-methylpiperidin-1-yl)-ethyl)pyrrolidine-1-sulfonyl)phenol (SB-269970) (10 mg/kg, i.p.) fully inhibited the hypothermia induced by 0.3 mg/kg 8-OH-DPAT, but not that of higher doses. In rats, SB-269970 caused a 60% inhibition of the hypothermia induced by 0.3 mg/kg 8-OH-DPAT. Thus, both 5-HT(7) and 5-HT(1A) receptors are involved in a complex manner in thermoregulation, with the 5-HT(7) receptor being more important at lower, possibly more physiological, concentrations.

Involvement of 5-hydroxytryptamine (HT)7 receptors in the 5-HT excitatory effects on the rat urinary bladder

OBJECTIVE

To investigate the in vitro and in vivo effects of 5-hydroxytryptamine (5-HT) on the rat urinary bladder and to characterize the receptors involved in mediating these pharmacological effects by using selective antagonists.

MATERIALS AND METHODS

Female Wistar rats (250-350 g) were used for all studies. In vitro, detrusor muscle strips were mounted between two platinum electrodes in organ baths filled with a modified Krebs' solution bubbled with 95% O(2) and 5% CO(2) at 37 degrees C. After equilibration and a contraction to 80 mmol/L KCl, strips were exposed to electrical field stimulation for 30 min and incubated with the antagonist or vehicle for a further 30 min, then a 5-HT concentration-response curve (CRC) was obtained. In vivo, rats were anaesthetized with pentobarbital, and the ureters and urethra ligated, the bladder catheterized and infused with saline. 5-HT (3-100 microg/kg intravenous) dose-dependently increased intravesical pressure (IVP). After administering 5-HT at 30 microg/kg three times at 10 min intervals (controls), one dose of antagonist was perfused for 5 min and, after a further 5 min, 30 microg/kg 5-HT was tested again. This cycle was repeated four times using increasing doses of the antagonist to be tested.

RESULTS

In vitro, 5-HT (0.01-100 micromol/L) induced a concentration-dependent enhancement of the neurogenic response, with a mean (sd) pEC(50) of 6.36 (0.15) and E(max) of 41.1 (4.6)% KCl (eight rats). In unstimulated tissues, 5-HT induced no contractile effect. Selective 5-HT(4), 5-HT(3) and 5-HT(1A) receptor antagonists had no effect on the 5-HT potentiating effects. The potentiating effect of 5-HT was antagonized by mesulergine at 0.3 micromol/L, R(+)lisuride at 0.3 micromol/L and the selective 5-HT(7) receptor antagonist SB-258741 at 0.3 micromol/L. In vivo, in anaesthetized rats, IVP increases induced by repeated doses of 30 microg/kg 5-HT were reproducible. R(+)lisuride (3-100 microg/kg) dose-dependently inhibited the 5-HT-induced increase of IVP. At the maximum dose tested, R(+)lisuride almost totally inhibited the 5-HT effect.

CONCLUSIONS

In rat isolated detrusor muscle the 5-HT(7) receptor antagonists SB-258741, R(+)lisuride and mesulergine blocked the 5-HT potentiating effect with the expected potency. Moreover, in anaesthetized rats, R(+)lisuride abolished 5-HT effects on IVP at doses that antagonize physiological effects known to be mediated by 5-HT(7) receptor activation in several animal species. These results suggest the involvement of 5-HT(7) receptors in the modulation of rat bladder contraction both in vitro and in vivo.

New pharmacologic targets for the treatment of the overactive bladder: an update

Although currently available antimuscarinic agents are the standard of care for overactive bladder (OAB), they are limited by certain side effects, particularly dry mouth and constipation. Research aimed at discovering new therapies for OAB has resulted in the identification of some promising drugs. Investigations of pharmacologic targets in the central nervous system (CNS) have yielded encouraging results with several agents, including tramadol and gabapentin. Further investigation may show that drugs acting at serotonergic and noradrenergic CNS sites are clinically useful as therapies for OAB. Some peripherally acting drugs, such as resiniferatoxin and botulinum toxin, have already been proved to be of clinical value. However, development of other agents that block afferent or efferent nerve impulses in the bladder through activity at vanilloid, purinergic, or opioid-like receptor sites may result in clinically useful drugs.