Involvement of 5-HT3 receptors in pudendal inhibition of bladder overactivity in cats

Sexual dimorphic impacts of systemic vincristine on lower urinary tract function

Vincristine (VCR) is one of the most common chemotherapy agents used in pediatric oncology. Despite the well-known VCR-induced peripheral neuropathy, potential impacts of VCR on lower urinary tract (LUT) function remain poorly defined. We investigated the effects of systemic VCR exposure in childhood on LUT function by using juvenile mice treated with VCR (4 mg/kg) or saline and evaluated at 5 weeks later. VCR induced a decreased urinary frequency with increased functional bladder capacity and non-void contractions. There were no changes in detrusor contractility between the groups. VCR exposure caused sexual dimorphic changes; in females, increased intravesical pressure at micturition and downregulations of a major player in bladder afferent firing, Htr3b, in the bladders, and Cav1.2 in the lumbosacral dorsal root ganglia (Ls-DRG), while male mice displayed increases in bladder compliance and detrusor activity, upregulations of IL-2, Trpa1 and Itga1 in the bladders and neuroinflammation-related genes, P2×4, P2×7, IL-2 and CD68 in the Ls-DRG. These results suggest that that systemic VCR exposure caused sensory neuropathy via sex-dimorphic mechanisms, leading to altered LUT function. These changes might clinically present as gender-specific signs or symptoms of LUT dysfunction, and follow-up urological assessment may be of benefit for pediatric cancer patients treated with VCR.

Superficial peroneal neuromodulation of nonobstructive urinary retention induced by prolonged pudendal afferent activity in cats

The purpose of this study is to determine whether superficial peroneal nerve stimulation (SPNS) can improve nonobstructive urinary retention (NOUR) induced by prolonged pudendal nerve stimulation (PNS). In this exploratory acute study using eight cats under anesthesia, PNS and SPNS were applied by nerve cuff electrodes. Skin surface electrodes were also used for SPNS. A double lumen catheter was inserted via the bladder dome for bladder infusion and pressure measurement and to allow voiding without a physical urethral outlet obstruction. The voided and postvoid residual (PVR) volumes were also recorded. NOUR induced by repetitive (4-13 times) application of 30-min PNS significantly (P < 0.05) reduced voiding efficiency by 49.5 ± 16.8% of control (78.3 ± 7.9%), with a large PVR volume at 208.2 ± 82.6% of control bladder capacity. SPNS (1 Hz, 0.2 ms) at 1.5-2 times threshold intensity (T) for inducing posterior thigh muscle contractions was applied either continuously (SPNSc) or intermittently (SPNSi) during cystometrograms to improve the PNS-induced NOUR. SPNSc and SPNSi applied by nerve cuff electrodes significantly (P < 0.05) increased voiding efficiency to 74.5 ± 18.9% and 67.0 ± 15.3%, respectively, and reduced PVR volume to 54.5 ± 39.0% and 88.3 ± 56.0%, respectively. SPNSc and SPNSi applied noninvasively by skin surface electrodes also improved NOUR similar to the stimulation applied by a cuff electrode. This study indicates that abnormal pudendal afferent activity could be a pathophysiological cause for the NOUR occurring in Fowler's syndrome and a noninvasive superficial peroneal neuromodulation therapy might be developed to treat NOUR in patients with Fowler's syndrome.

Functional constipation induces bladder overactivity associated with upregulations of Htr2 and Trpv2 pathways

Bladder and bowel dysfunction (BBD) is a common yet underdiagnosed paediatric entity that describes lower urinary tract symptoms (LUTS) accompanied by abnormal bowel patterns manifested as constipation and/or encopresis. LUTS usually manifest as urgency, urinary frequency, incontinence, and urinary tract infections (UTI). Despite increasing recognition of BBD as a risk factor for long-term urinary tract problems including recurrent UTI, vesicoureteral reflux, and renal scarring, the mechanisms underlying BBD have been unclear, and treatment remains empirical. We investigated how constipation affects the lower urinary tract function using a juvenile murine model of functional constipation. Following four days of functional constipation, animals developed LUTS including urinary frequency and detrusor overactivity evaluated by awake cystometry. Physiological examination of detrusor function in vitro using isolated bladder strips, demonstrated a significant increase in spontaneous contractions without affecting contractile force in response to electrical field stimulation, carbachol, and KCl. A significant upregulation of serotonin receptors, Htr2a and Htr2c, was observed in the bladders from mice with constipation, paralleled with augmented spontaneous contractions after pre-incubation of the bladder strips with 0.5 µM of serotonin. These results suggest that constipation induced detrusor overactivity and increased excitatory serotonin receptor activation in the urinary bladder, which contributes to the development of BBD.

Bladder underactivity induced by prolonged pudendal afferent activity in cats

The purpose of this study was to determine the effects of pudendal nerve stimulation (PNS) on reflex bladder activity and develop an animal model of underactive bladder (UAB). In six anesthetized cats, a bladder catheter was inserted via the urethra to infuse saline and measure pressure. A cuff electrode was implanted on the pudendal nerve. After determination of the threshold intensity (T) for PNS to induce an anal twitch, PNS (5 Hz, 0.2 ms, 2 T or 4 T) was applied during cystometrograms (CMGs). PNS (4-6 T) of 30-min duration was then applied repeatedly until bladder underactivity was produced. Following stimulation, control CMGs were performed over 1.5-2 h to determine the duration of bladder underactivity. When applied during CMGs, PNS (2 T and 4 T) significantly (P < 0.05) increased bladder capacity while PNS at 4 T also significantly (P < 0.05) reduced bladder contraction amplitude, duration, and area under contraction curve. Repeated application of 30-min PNS for a cumulative period of 3-8 h produced bladder underactivity exhibiting a significantly (P < 0.05) increased bladder capacity (173 ± 14% of control) and a significantly (P < 0.05) reduced contraction amplitude (50 ± 7% of control). The bladder underactivity lasted more than 1.5-2 h after termination of the prolonged PNS. These results provide basic science evidence supporting the proposal that abnormal afferent activity from external urethral/anal sphincter could produce central inhibition that underlies nonobstructive urinary retention (NOUR) in Fowler's syndrome. This cat model of UAB may be useful to investigate the mechanism by which sacral neuromodulation reverses NOUR in Fowler's syndrome.

Neuromodulatory effects of pudendal nerve stimulation on bladder hypersensitivity are present in opioid-pretreated rats

BACKGROUND AND OBJECTIVES

Bilateral electrical pudendal nerve stimulation (bPNS) reduces bladder hypersensitivity in rat models and anecdotally reduces pain in humans with pelvic pain of urologic origin. Concomitant opioids are known to alter responses to neuromodulation in some systems. So prior to the development of a clinical trial for purposes of regulatory approval, the preclinical interaction between opioids and stimulation effectiveness was examined.

METHODS

Bladder hypersensitivity was produced by neonatal bladder inflammation in rat pups coupled with a second inflammatory insult as an adult. Morphine was administered acutely (1-4 mg/kg intraperitoneal) or chronically (5 mg/kg subcutaneously daily for 2 weeks prior to the terminal experiment). bPNS consisted of bilateral biphasic electrical stimulation of the mixed motor/sensory component of the pudendal nerves. Visceromotor responses (VMR; abdominal muscle contractile responses to urinary bladder distension (UBD)) were used as nociceptive endpoints.

RESULTS

Morphine produced a dose-dependent inhibition of VMRs to UBD that was naloxone reversible. bPNS resulted in statistically significant inhibition of VMRs to UBD in hypersensitive rats that had received acute or chronic subcutaneous morphine injections.

CONCLUSIONS

This study suggests that inhibitory effects of bPNS can still be evoked in subjects who are receiving opioid therapy, thus giving guidance to potential clinical trials seeking regulatory approval for the treatment of chronic bladder pain.

Sympathetic afferents in the hypogastric nerve facilitate nociceptive bladder activity in cats

This study in α-chloralose-anesthetized cats revealed a role of hypogastric nerve afferent axons in nociceptive bladder activity induced by bladder irritation using 0.25% acetic acid (AA). In cats with intact hypogastric and pelvic nerves, AA irritation significantly ( P < 0.05) reduced bladder capacity to 45.0 ± 5.7% of the control capacity measured during a saline cystometrogram (CMG). In cats with the hypogastric nerves transected bilaterally, AA irritation also significantly ( P < 0.05) reduced bladder capacity, but the change was significantly smaller (capacity reduced to 71.5 ± 10.6% of saline control, P < 0.05) than that in cats with an intact hypogastric nerve. However, application of hypogastric nerve stimulation (HGNS: 20 Hz, 0.2 ms pulse width) to the central end of the transected nerves at an intensity (16 V) strong enough to activate C-fiber afferent axons facilitated the effect of AA irritation and further ( P < 0.05) reduced bladder capacity to 48.4 ± 7.4% of the saline control. This facilitation by HGNS was effective only at selected frequencies (1, 20, and 30 Hz) when the stimulation intensity was above the threshold for activating C-fibers. Tramadol (an analgesic agent) at 3 mg/kg iv completely blocked the nociceptive bladder activity and eliminated the facilitation by HGNS. HGNS did not alter non-nociceptive bladder activity induced by saline distention of the bladder. These results indicate that sympathetic afferents in the hypogastric nerve play an important role in the facilitation of the nociceptive bladder activity induced by bladder irritation that activates the silent C-fibers in the pelvic nerve.

Spinal mechanisms of pudendal nerve stimulation-induced inhibition of bladder hypersensitivity in rats

Bilateral electrical pudendal nerve stimulation (bPNS) reduces bladder hypersensitivity in rat models of bladder pain and anecdotally reduces pain in humans with pelvic pain of urologic origin. The spinal neurochemical mechanisms of this antinociception are unknown. In the present study, bladder hypersensitivity was produced by neonatal bladder inflammation in rat pups coupled with a second inflammatory insult as an adult. Visceromotor responses (VMRs; abdominal muscle contractions) to urinary bladder distension (UBD) were used as a nociceptive endpoint under urethane-isoflurane anesthesia. bPNS consisted of bilateral biphasic electrical stimulation of the mixed motor/sensory component of the pudendal nerves. Following determination of the inhibitory effect of bPNS on VMRs, pharmacological antagonists were administered via an intrathecal catheter onto the lumbosacral spinal cord and bPNS effects on VMRs redetermined. bPNS resulted in statistically significant inhibition of VMRs to UBD in hypersensitive rats that was statistically reduced by the intrathecal administration of methysergide, WAY100636, CGP35348 and strychnine but was unaffected by naloxone, bicuculline, phentolamine, ondansetron and normal saline. This study suggests that inhibitory effects of bPNS may include serotonergic, GABA-B-ergic and glycinergic mechanisms suggesting the potential for interaction of the neuromodulatory effect with concommitant drug therapies.

Serotonin Receptor 5-HT3A Affects Development of Bladder Innervation and Urinary Bladder Function

The autonomic and sensory nervous systems are required for proper function of all visceral organs, including the lower urinary tract (LUT). Despite the wide prevalence of bladder dysfunction, effective treatment options remain limited. Pelvic innervation regenerative strategies are promising, but surprisingly little is known about the molecular factors driving the development of bladder innervation. Given prior evidence that serotonin receptor 5-HT3A is expressed early in LUT development and is an important mediator of adult bladder function, we sought to determine if 5-HT3A is required for the development of autonomic innervation of the bladder. We found that 5-HT3A is expressed early in fetal mouse pelvic ganglia and is maintained through adulthood. Htr3a knockout male mice, but not females, exhibit increased urinary voiding frequency compared to wild type littermates. Analysis of LUT function via anesthetized cystometry revealed decreased voiding efficiency in male Htr3a mutants. Htr3a^−/− mutant animals exhibit a transient disturbance of autonomic neuronal subtype markers (tyrosine hydroxylase and choline acetyl transferase) within the fetal pelvic ganglia, although the imbalance of neuronal subtype markers assayed is no longer apparent in adulthood. Loss of 5-HT3A activity results in a higher density of autonomic and sensory neuronal fibers supplying bladder smooth muscle in both fetal and adult mice. Collectively, our findings highlight 5-HT3A as a critical component in the autonomic control of micturition and identify a novel role for this serotonin receptor in peripheral nervous system development.

Glutamatergic Mechanisms Involved in Bladder Overactivity and Pudendal Neuromodulation in Cats

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

Screening and Optimization of Nerve Targets and Parameters Reveals Inhibitory Effect of Pudendal Stimulation on Rat Bladder Hypersensitivity

BACKGROUND AND OBJECTIVES

Neuromodulation has been reported to reliably improve symptoms of bladder overactivity and sometimes pain. The effect of electrical stimulation of several nerve pathways demonstrated to alter cystometric responses to bladder distension was examined on nociceptive responses in models of bladder hypersensitivity.

METHODS

Bladder hypersensitivity was produced by several published methods including neonatal inflammation, acute inflammation, and chronic stress. Effects of different sites of stimulation (L6 and T13 nerve roots, proximal and distal pudendal nerves [PNs]) on nociceptive reflex responses to urinary bladder distension in urethane-anesthetized female rats were assessed and a parametric analysis of parameters of stimulation was performed.

RESULTS

Bilateral biphasic stimulation of the proximal PNs resulted in statistically significant inhibition of visceromotor and cardiovascular responses to bladder distension in rats made hypersensitive by neonatal bladder inflammation. We found a range of optimal stimulation frequencies (5-10 Hz) which produced robust inhibitory effects when using short pulse widths (100-240 μs). Onset of inhibition was within minutes and persisted for several minutes after the stimulus was discontinued. Use of bilateral PN stimulation in acute inflammation and stress-induced hypersensitivity models as well as unilateral stimulation, very distal PN cutaneous branch stimulation, and stimulation of the T13 and L6 nerve roots all proved ineffective with the parameters used.

CONCLUSIONS

This study suggests that inhibitory effects of bilateral PN stimulation can be evoked in a rodent hypersensitivity model at relatively low frequencies with short pulse widths. The onset of effect is rapid, which suggests the potential for treating episodic pain in painful bladder disorders.

Neurotransmitter Mechanisms Underlying Sacral Neuromodulation of Bladder Overactivity in Cats

OBJECTIVE

To determine the role of opioid, β-adrenergic, and metabotropic glutamate 5 receptors in sacral neuromodulation of bladder overactivity.

MATERIAL AND METHODS

In α-chloralose anesthetized cats, intravesical infusion of 0.5% acetic acid (AA) irritated the bladder and induced bladder overactivity. Electric stimulation (5 Hz, 0.2 ms, 0.16-0.7V) of S1 or S2 sacral dorsal roots inhibited the bladder overactivity. Naloxone, propranolol, or MTEP were given intravenously (i.v.) to determine different neurotransmitter mechanisms.

RESULTS

AA significantly (p < 0.05) reduced bladder capacity to 7.7 ± 3.3 mL from 12.0 ± 5.0 mL measured during saline infusion. S1 or S2 stimulation at motor threshold intensity significantly (p < 0.05) increased bladder capacity to 179.4 ± 20.0% or 219.1 ± 23.0% of AA control, respectively. Naloxone (1 mg/kg) significantly (p < 0.001) reduced the control capacity to 38.3 ± 7.3% and the bladder capacity measured during S1 stimulation to 106.2 ± 20.8% of AA control, but did not significantly change the bladder capacity measured during S2 stimulation. Propranolol (3 mg/kg) significantly (p < 0.01) reduced bladder capacity from 251.8 ± 32.2% to 210.9 ± 33.3% during S2 stimulation, but had no effect during S1 stimulation. A similar propranolol effect also was observed in naloxone-pretreated cats. In propranolol-pretreated cats during S1 or S2 stimulation, MTEP (3 mg/kg) significantly (p < 0.05) reduced bladder capacity and naloxone (1 mg/kg) following MTEP treatment further reduced bladder capacity. However, a significant inhibition could still be induced by S1 or S2 stimulation after all three drugs were administered.

CONCLUSIONS

Neurotransmitter mechanisms in addition to those activating opioid, β-adrenergic, and metabotropic glutamate 5 receptors also are involved in sacral neuromodulation.

Role of µ, κ, and δ opioid receptors in tibial inhibition of bladder overactivity in cats

In α-chloralose anesthetized cats, we examined the role of opioid receptor (OR) subtypes (µ, κ, and δ) in tibial nerve stimulation (TNS)-induced inhibition of bladder overactivity elicited by intravesical infusion of 0.25% acetic acid (AA). The sensitivity of TNS inhibition to cumulative i.v. doses of selective OR antagonists (cyprodime for µ, nor-binaltorphimine for κ, or naltrindole for δ ORs) was tested. Naloxone (1 mg/kg, i.v., an antagonist for µ, κ, and δ ORs) was administered at the end of each experiment. AA caused bladder overactivity and significantly (P < 0.01) reduced bladder capacity to 21.1% ± 2.6% of the saline control. TNS at 2 or 4 times threshold (T) intensity for inducing toe movement significantly (P < 0.01) restored bladder capacity to 52.9% ± 3.6% or 57.4% ± 4.6% of control, respectively. Cyprodime (0.3-1.0 mg/kg) completely removed TNS inhibition without changing AA control capacity. Nor-binaltorphimine (3-10 mg/kg) also completely reversed TNS inhibition and significantly (P < 0.05) increased AA control capacity. Naltrindole (1-10 mg/kg) reduced (P < 0.05) TNS inhibition but significantly (P < 0.05) increased AA control capacity. Naloxone (1 mg/kg) had no effect in cyprodime pretreated cats, but it reversed the nor-binaltorphimine-induced increase in bladder capacity and eliminated the TNS inhibition remaining in naltrindole pretreated cats. These results indicate a major role of µ and κ ORs in TNS inhibition, whereas δ ORs play a minor role. Meanwhile, κ and δ ORs also have an excitatory role in irritation-induced bladder overactivity.

Role of glycine in nociceptive and non-nociceptive bladder reflexes and pudendal afferent inhibition of these reflexes in cats

AIM

This study examined the role of glycinergic transmission in nociceptive and non-nociceptive bladder reflexes and in inhibition of these reflexes by pudendal nerve stimulation (PNS).

METHODS

Cystometrograms (CMGs) were performed in α-chloralose anesthetized cats by intravesical infusion of saline or 0.25% acetic acid (AA) to trigger, respectively, non-nociceptive or nociceptive bladder reflexes. PNS at 2 or 4 times threshold (T) intensity for inducing anal twitch was used to inhibit the bladder reflexes. Strychnine (a glycine receptor antagonist) was administered in cumulative doses (0.001-0.3 mg/kg, i.v.) at 60-120 min intervals.

RESULTS

Strychnine at 0.001-0.3 mg/kg significantly (P < 0.05) increased bladder capacity and reduced contraction amplitude during saline CMGs but did not change these parameters during AA CMGs except at the 0.3 mg/kg dose which increased bladder capacity. Strychnine did not alter PNS inhibition during saline CMGs except at the highest dose at 2T intensity, but significantly (P < 0.05) suppressed PNS inhibition during AA CMGs after 0.001-0.003 mg/kg doses at 2T and 4T intensities. During AA CMGs strychnine (0.3 mg/kg) also unmasked a post-PNS excitatory effect that significantly reduced bladder capacity after termination of PNS.

CONCLUSIONS

Glycinergic inhibitory neurotransmission in the central nervous system plays an unexpected role to tonically enhance the magnitude and reduce the bladder volume threshold for triggering the non-nociceptive bladder reflex. This is attributable to inhibition by glycine of another inhibitory mechanism. Glycine also has a minor role in PNS inhibition of the nociceptive bladder reflex. Neurourol. Urodynam. 35:798-804, 2016. © 2015 Wiley Periodicals, Inc.

Role of the brain stem in tibial inhibition of the micturition reflex in cats

This study examined the role of the brain stem in inhibition of bladder reflexes induced by tibial nerve stimulation (TNS) in α-chloralose-anesthetized decerebrate cats. Repeated cystometrograms (CMGs) were performed by infusing saline or 0.25% acetic acid (AA) to elicit normal or overactive bladder reflexes, respectively. TNS (5 or 30 Hz) at three times the threshold (3T) intensity for inducing toe movement was applied for 30 min between CMGs to induce post-TNS inhibition or applied during the CMGs to induce acute TNS inhibition. Inhibition was evident as an increase in bladder capacity without a change in amplitude of bladder contractions. TNS applied for 30 min between saline CMGs elicited prolonged (>2 h) poststimulation inhibition that significantly (P < 0.05) increased bladder capacity to 30-60% above control; however, TNS did not produce this effect during AA irritation. TNS applied during CMGs at 5 Hz but not 30 Hz significantly (P < 0.01) increased bladder capacity to 127.3 ± 6.1% of saline control or 187.6 ± 5.0% of AA control. During AA irritation, naloxone (an opioid receptor antagonist) administered intravenously (1 mg/kg) or directly to the surface of the rostral brain stem (300-900 μg) eliminated acute TNS inhibition and significantly (P < 0.05) reduced bladder capacity to 62.8 ± 22.6% (intravenously) or 47.6 ± 25.5% (brain stem application). Results of this and previous studies indicate 1) forebrain circuitry rostral to the pons is not essential for TNS inhibition; and 2) opioid receptors in the brain stem have a critical role in TNS inhibition of overactive bladder reflexes but are not involved in inhibition of normal bladder reflexes.

Pioneering drugs for overactive bladder and detrusor overactivity: Ongoing research and future directions

The ongoing research on pioneering drug candidates for the overactive bladder (OAB) aimed to overcome the limitations of currently licensed pharmacotherapies, such as antimuscarinics, β3-adrenergic agents, and botulinum neurotoxin, has been reviewed performing a systematic literature review and web search. The review covers the exploratory agents alternative to available medications for OAB and that may ultimately prove to be therapeutically useful in the future management of OAB patients based on preclinical and early clinical data. It emerges that many alternative pharmacological strategies have been discovered or are under investigation in disease-oriented studies. Several potential therapeutics are known for years but still find obstacles to pass the clinical stages of development, while other completely novel compounds, targeting new pharmacological targets, have been recently discovered and show potential to translate into clinical therapeutic agents for idiopathic and neurogenic OAB syndrome. The global scenario of investigational drugs for OAB gives promise for the development of innovative therapeutics that may ultimately prove effective as first, combined or second-line treatments within a realistic timescale of ten years.

Impact of Bioelectronic Medicine on the Neural Regulation of Pelvic Visceral Function

Neuromodulation elicited by electrical stimulation of peripheral or spinal nerves is a U.S. Food and Drug Administered (FDA)-approved therapy for treating disorders of the pelvic viscera, including urinary urgency, urgency-frequency, nonobstructive urinary retention and fecal incontinence. The technique is also being tested experimentally for its efficacy in treating interstitial cystitis, chronic constipation and pelvic pain. The goal of neuromodulation is to suppress abnormal visceral sensations and involuntary reflexes and restore voluntary control. Although detailed mechanisms underlying the effects of neuromodulation are still to be elucidated, it is generally believed that effects are due to stimulation of action potentials in somatic afferent nerves. Afferent nerves project to the lumbosacral spinal cord, where they release excitatory neurotransmitters that activate ascending pathways to the brain or spinal circuits that modulate visceral sensory and involuntary motor mechanisms. Studies in animals revealed that different types of neuromodulation (for example, stimulation of a sacral spinal root, pudendal nerve or posterior tibial nerve) act by releasing different inhibitory and excitatory neurotransmitters in the central nervous system. In addition, certain types of neuromodulation inhibit visceral smooth muscle by initiating reflex firing in peripheral autonomic nerves or excite striated sphincter muscles by initiating reflex firing in somatic efferent nerves. This report will provide a brief summary of (a) neural control of the lower urinary tract and distal bowel, (b) clinical use of neuromodulation in the treatment of bladder and bowel dysfunctions,

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Propranolol, but not naloxone, enhances spinal reflex bladder activity and reduces pudendal inhibition in cats

This study examined the role of β-adrenergic and opioid receptors in spinal reflex bladder activity and in the inhibition induced by pudendal nerve stimulation (PNS) or tibial nerve stimulation (TNS). Spinal reflex bladder contractions were induced by intravesical infusion of 0.25% acetic acid in α-chloralose-anesthetized cats after an acute spinal cord transection (SCT) at the thoracic T9/T10 level. PNS or TNS at 5 Hz was applied to inhibit these spinal reflex contractions at 2 and 4 times the threshold intensity (T) for inducing anal or toe twitch, respectively. During a cystrometrogram (CMG), PNS at 2T and 4T significantly (P < 0.05) increased bladder capacity from 58.0 ± 4.7% to 85.8 ± 10.3% and 96.5 ± 10.7%, respectively, of saline control capacity, while TNS failed to inhibit spinal reflex bladder contractions. After administering propranolol (3 mg/kg iv, a β₁/β₂-adrenergic receptor antagonist), the effects of 2T and 4T PNS on bladder capacity were significantly (P < 0.05) reduced to 64.5 ± 9.5% and 64.7 ± 7.3%, respectively, of the saline control capacity. However, the residual PNS inhibition (about 10% increase in capacity) was still statistically significant (P < 0.05). Propranolol treatment also significantly (P = 0.0019) increased the amplitude of bladder contractions but did not change the control bladder capacity. Naloxone (1 mg/kg iv, an opioid receptor antagonist) had no effect on either spinal reflex bladder contractions or PNS inhibition. At the end of experiments, hexamethonium (10 mg/kg iv, a ganglionic blocker) significantly (P < 0.05) reduced the amplitude of the reflex bladder contractions. This study indicates an important role of β₁/β₂-adrenergic receptors in pudendal inhibition and spinal reflex bladder activity.

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.

Brain-derived neurotrophic factor in urinary continence and incontinence

Urinary incontinence adversely affects quality of life and results in an increased financial burden for the elderly. Accumulating evidence suggests a connection between neurotrophins, such as brain-derived neurotrophic factor (BDNF), and lower urinary tract function, particularly with regard to normal physiological function and the pathophysiological mechanisms of stress urinary incontinence (SUI) and bladder pain syndrome/interstitial cystitis (BPS/IC). The interaction between BDNF and glutamate receptors affects both bladder and external urethral sphincter function during micturition. Clinical findings indicate reduced BDNF levels in antepartum and postpartum women, potentially correlating with postpartum SUI. Experiments with animal models demonstrate that BDNF is decreased after simulated childbirth injury, thereby impeding the recovery of injured nerves and the restoration of continence. Treatment with exogenous BDNF facilitates neural recovery and the restoration of continence. Serotonin and noradrenaline reuptake inhibitors, used to treat both depression and SUI, result in enhanced BDNF levels. Understanding the neurophysiological roles of BDNF in maintaining normal urinary function and in the pathogenesis of SUI and BPS/IC could lead to future therapies based on these mechanisms.

Does our limited knowledge of the mechanisms of neural stimulation limit its benefits for patients with overactive bladder? ICI-RS 2013

INTRODUCTION

Neural stimulation has become an established minimally invasive treatment for various lower urinary tract symptoms. The results both short- and long-term are encouraging, however, there is still a lack of knowledge of obvious risk factors, which may affect the outcome of treatment. Although neural stimulation has been embraced by healthcare professionals and patients, the exact mechanism by which neural stimulation works is still unclear.

DISCUSSION

A condense review of knowledge available on this topic is presented. Several research questions are raised. Outlines of research studies, both clinical and basic science, are suggested.

CONCLUSIONS

Further studies are necessary to understand mechanism of action of neural stimulation and its implications on treatment outcomes.

Effects of duloxetine and WAY100635 on pudendal inhibition of bladder overactivity in cats

This study was aimed at determining the effect of duloxetine (a serotonin-norepinephrine reuptake inhibitor) on pudendal inhibition of bladder overactivity. Cystometrograms were performed on 15 cats under α-chloralose anesthesia by infusing saline and then 0.25% acetic acid (AA) to induce bladder overactivity. To inhibit bladder overactivity, pudendal nerve stimulation (PNS) at 5 Hz was applied to the right pudendal nerve at two and four times the threshold (T) intensity for inducing anal twitch. Duloxetine (0.03-3 mg/kg) was administered intravenously to determine the effect on PNS inhibition. AA irritation significantly (P < 0.01) reduced bladder capacity to 27.9 ± 4.6% of saline control capacity. PNS alone at both 2T and 4T significantly (P < 0.01) inhibited bladder overactivity and increased bladder capacity to 83.6 ± 7.6% and 87.5 ± 7.7% of saline control, respectively. Duloxetine at low doses (0.03-0.3 mg/kg) caused a significant reduction in PNS inhibition without changing bladder capacity. However, at high doses (1-3 mg/kg) duloxetine significantly increased bladder capacity but still failed to enhance PNS inhibition. WAY100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide; a 5-HT1A receptor antagonist, 0.5-1 mg/kg i.v.) reversed the suppressive effect of duloxetine on PNS inhibition and significantly (P < 0.05) increased the inhibitory effect of duloxetine on bladder overactivity but did not enhance the effect of PNS. These results indicate that activation of 5-HT1A autoreceptors on the serotonergic neurons in the raphe nucleus may suppress duloxetine and PNS inhibition, suggesting that the coadministration of a 5-HT1A antagonist drug might be useful in enhancing the efficacy of duloxetine alone and/or the additive effect of PNS-duloxetine combination for the treatment of overactive bladder symptoms.

Inhibition of bladder overactivity by duloxetine in combination with foot stimulation or WAY-100635 treatment in cats

The purpose of this study was to determine whether duloxetine [a serotonin (5-HT)-norepinephrine reuptake inhibitor] combined with transcutaneous foot stimulation or WAY-100635 (a 5-HT1A antagonist) can enhance inhibition of bladder overactivity in cats. Cystometrograms were performed on eight cats under α-chloralose anesthesia by infusing saline and then 0.25% acetic acid (AA) to induce bladder overactivity. To inhibit bladder overactivity, foot stimulation (5 Hz) was applied via transcutaneous pad electrodes to the right hindfoot at two and four times the threshold intensity for inducing a toe twitch. Duloxetine (0.003-3 mg/kg) was administered intravenously to determine the effect of combination treatment. After the 3 mg/kg dose of duloxetine, WAY-100635 (0.5 mg/kg) was given intravenously. AA irritation significantly (P < 0.0001) reduced bladder capacity to 42.7 ± 7.4% of the saline control capacity. Foot stimulation alone at both two and four times the threshold intensity significantly (P < 0.0001) inhibited bladder overactivity and increased bladder capacity to 66.7 ± 6.3% and 85.7 ± 6.5% of the saline control, respectively. Duloxetine alone dose dependently inhibited bladder overactivity and completely restored bladder capacity to the saline control (109 ± 15.5%) at 3 mg/kg. Although duloxetine combined with foot stimulation did not further enhance inhibition, WAY-100635 (0.5 mg/kg) given after 3 mg/kg duloxetine further increased (P = 0.008) bladder capacity to 162.2 ± 22.5% of the saline control. Although duloxetine and foot stimulation independently inhibited bladder overactivity, combined treatment did not enhance inhibition. Duloxetine combined with WAY-100635, however, synergistically enhanced bladder inhibition, indicating a potential novel treatment for overactive bladder if duloxetine is combined with a 5-HT1A receptor antagonist drug.