Non-NMDA glutamatergic excitatory transmission in the descending limb of the spinobulbospinal micturition reflex pathway of the rat

Acute ampakines increase voiding function and coordination in a rat model of SCI

Neurogenic bladder dysfunction causes urological complications and reduces the quality of life in persons with spinal cord injury (SCI). Glutamatergic signaling via AMPA receptors is fundamentally important to the neural circuits controlling bladder voiding. Ampakines are positive allosteric modulators of AMPA receptors that can enhance the function of glutamatergic neural circuits after SCI. We hypothesized that ampakines can acutely stimulate bladder voiding that has been impaired due to thoracic contusion SCI. Adult female Sprague-Dawley rats received a unilateral contusion of the T9 spinal cord (n = 10). Bladder function (cystometry) and coordination with the external urethral sphincter (EUS) were assessed 5 d post-SCI under urethane anesthesia. Data were compared to responses in spinal-intact rats (n = 8). The 'low-impact' ampakine CX1739 (5, 10, or 15 mg/kg) or vehicle (2-hydroxypropyl-beta-cyclodextrin [HPCD]) was administered intravenously. The HPCD vehicle had no discernible impact on voiding. In contrast, following CX1739, the pressure threshold for inducing bladder contraction, voided volume, and the interval between bladder contractions were significantly reduced. These responses occurred in a dose-dependent manner. We conclude that modulating AMPA receptor function using ampakines can rapidly improve bladder-voiding capability at subacute time points following contusion SCI. These results may provide a new and translatable method for therapeutic targeting of bladder dysfunction acutely after SCI.

Acute ampakines increase voiding function and coordination in a rat model of SCI

Neurogenic bladder dysfunction causes urological complications and reduces the quality of life in persons with spinal cord injury (SCI). Glutamatergic signaling via AMPA receptors is fundamentally important to the neural circuits controlling bladder voiding. Ampakines are positive allosteric modulators of AMPA receptors that can enhance the function of glutamatergic neural circuits after SCI. We hypothesized that ampakines can acutely stimulate bladder voiding that has been impaired due to thoracic contusion SCI. Adult female Sprague Dawley rats received a unilateral contusion of the T9 spinal cord (n=10). Bladder function (cystometry) and coordination with the external urethral sphincter (EUS) were assessed five days post-SCI under urethane anesthesia. Data were compared to responses in spinal intact rats (n=8). The "low impact" ampakine CX1739 (5, 10, or 15 mg/kg) or vehicle (HPCD) was administered intravenously. The HPCD vehicle had no discernable impact on voiding. In contrast, following CX1739, the pressure threshold for inducing bladder contraction, voided volume, and the interval between bladder contractions were significantly reduced. These responses occurred in a dose-dependent manner. We conclude that modulating AMPA receptor function using ampakines can rapidly improve bladder voiding capability at sub-acute time points following contusion SCI. These results may provide a new and translatable method for therapeutic targeting of bladder dysfunction acutely after SCI.

Characterization on Responsiveness of Excitatory Synaptic Transmissions to α1-Adrenoceptor Blockers in Substantia Gelatinosa Neurons Isolated From Lumbo-Sacral Level in Rat Spinal Cords

Purpose

The aim of this study was to characterize the responsiveness of miniature excitatory postsynaptic currents (mEPSCs) to α1-adrenoceptor blockers in substantia gelatinosa (SG) neurons from the spinal cord to develop an explanation for the efficacy of α1-adrenoceptor blockers in micturition dysfunction.

Methods

Male adult Sprague-Dawley rats were used. Blind whole-cell patch-clamp recordings were performed using SG neurons in spinal cord slices. Naftopidil (100μM), tamsulosin (100μM), or silodosin (30μM), α1-adrenoceptor blockers, was perfused. The frequency of mEPSCs was recorded in an SG neuron to which the 3 blockers were applied sequentially with wash-out periods. Individual frequencies in a pair before naftopidil and tamsulosin perfusion were plotted as baseline, and the correlation between them was confirmed by Spearman correlation coefficient; linear regression was then performed. The same procedure was performed before naftopidil and silodosin perfusion. Frequencies of pairs after naftopidil and tamsulosin perfusion and after naftopidil and silodosin perfusion were similarly analyzed. The ratios of the frequencies after treatment to before were then calculated.

Results

After the treatments, Spearman ρ and the slope were decreased to 0.682 from 0.899 at baseline and 0.469 from 1.004 at baseline, respectively, in the tamsulosin group relative to the naftopidil group. In the silodosin group, Spearman ρ and the slope were also decreased to 0.659 from 0.889 at baseline and 0.305 from 0.989 at baseline, respectively, relative to the naftopidil group. Naftopidil significantly increased the ratio of the frequency of mEPSCs compared to tamsulosin and silodosin (P=0.015 and P=0.004, respectively).

Conclusions

There was a difference in responsiveness in the frequency of mEPSCs to α1-adrenoceptor blockers, with the response to naftopidil being the greatest among the α1-adrenoceptor blockers. These data are helpful to understand the action mechanisms of α1-adrenoceptor blockers for male lower urinary tract symptoms in clinical usage.

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.

Autonomic consequences of spinal cord injury

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

Neural control of the lower urinary tract

This article summarizes anatomical, neurophysiological, pharmacological, and brain imaging studies in humans and animals that have provided insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract. The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. The neural control of micturition is organized as a hierarchical system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brain stem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brain stem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary micturition, leading to urinary incontinence. Neuroplasticity underlying these developmental and pathological changes in voiding function is discussed.

Overexpression of corticotropin-releasing factor in Barrington's nucleus neurons by adeno-associated viral transduction: effects on bladder function and behavior

The stress-related neuropeptide, corticotropin-releasing factor (CRF), is prominent in neurons of the pontine micturition center, Barrington's nucleus. These neurons co-innervate spinal preganglionic neurons that control the bladder, and locus coeruleus (LC) neurons that provide norepinephrine innervation throughout the brain. Adeno-associated viral (AAV) vector-mediated transfer of CRF cDNA was used to increase CRF expression in Barrington's nucleus neurons and investigate the impact of a gain of function in Barrington's nucleus spinal and LC projections. AAV transfer of the reverse CRF cDNA sequence served as the control. Bladder urodynamics and behavior were assessed 4 weeks after vector injection into Barrington's nucleus. Rats with bilateral injections of AAV-CRF cDNA into Barrington's nucleus had immunohistochemical evidence of CRF overexpression in neurons and transport to the spinal cord and LC. The bladder : body weight ratio was greater and micturition pressure was less in these rats compared with controls, consistent with an inhibitory influence on bladder function. Other indices of urodynamic function were not altered. CRF innervation of the LC was increased in rats with bilateral Barrington's nucleus injections of AAV-CRF cDNA, and this was associated with increased burying behavior, an endpoint of LC activation by CRF. The results provide immunohistochemical evidence for viral vector-induced CRF overexpression in Barrington's nucleus neurons and underscore the ability of AAV vector-mediated transfer to increase CRF function in selective circuits. The findings support an inhibitory influence of CRF in Barrington's nucleus regulation of the bladder and an excitatory influence on the brain norepinephrine system that translates to behavioral activation.

Social stress-induced bladder dysfunction: potential role of corticotropin-releasing factor

Psychological stress can impact on visceral function with pathological consequences, although the mechanisms underlying this are poorly understood. Here we demonstrate that social stress produces marked changes in bladder structure and function. Male rats were subjected to repeated (7 days) social defeat stress using the resident-intruder model. Measurement of the voiding pattern indicated that social stress produced urinary retention. Consistent with this, bladder size was increased in rats exposed to social stress. Moreover, this was negatively correlated to the latency to assume a subordinate posture, implying an association between passive behavior and bladder dysfunction. In vivo cystometry revealed distinct changes in urodynamic function in rats exposed to social stress, including increased bladder capacity, micturition volume, intermicturition interval, and the presence of non-micturition-related contractions, resembling overactive bladder. In contrast to social stress, repeated restraint (7 days) did not affect voiding, bladder weight, or urodynamics. The stress-related neuropeptide corticotropin-releasing factor (CRF) is present in spinal projections of Barrington's nucleus that regulate the micturition reflex and has an inhibitory influence in this pathway. Social stress, but not restraint, increased the number of CRF-immunoreactive neurons in Barrington's nucleus. Additionally, social stress increased CRF mRNA in Barrington's nucleus. Together, the results imply that social stress-induced CRF upregulation in Barrington's nucleus neurons results in urinary retention and, eventually, bladder dysfunction, perhaps as a visceral component of a behavioral coping response. This mechanism may underlie dysfunctional voiding in children and/or contribute to the development of stress-induced bladder disorders in adulthood.

Effects of selective unilateral dorsal root(s) rhizotomy on micturition reflex in anesthetized rats

PURPOSE

To clarify the contributions of sensory inputs and glutamate transmissions to the spinal micturition reflex.

MATERIALS AND METHODS

Cystometrogram and external urethral sphincter electromyogram activities evaluated the L6 and/or S1 levels.

RESULTS

Changes in intravesicular pressure (IVP) in response to saline infusion (0.1 ml/min) were found after unilateral dorsal root rhizotomy at the L6 level, which showed significant increases in threshold pressure (rhizotomized vs. control: 14.25 +/- 0.82 vs. 8.40 +/- 0.69 cmH(2)O, P < 0.01, n = 28), post-voiding pressure (7.66 +/- 0.56 vs. 5.42 +/- 0.52 cmH(2)O, P < 0.01, n = 28), holding duration (135.06 +/- 23.6 vs. 77.73 +/- 13.56 sec, P < 0.05, n = 28), and inter-contraction interval (140.62 +/- 23.29 vs. 82.40 +/- 13.57 sec, P < 0.05, n = 28). Several (mean = 2.32 +/- 1.31 vs. 0.12 +/- 0.21, P < 0.01, n = 28, P < 0.01, n = 28) non-voiding contractions with gradual increase in IVP were found ahead of voiding contraction after rhizotomy. An additional dorsal root rhizotomy at the ipsilateral S1 level caused further increases in urodynamic parameters (threshold pressure, 18.18 +/- 1.67 cmH(2)O, P < 0.01; post-voiding pressure 8.07 +/- 0.96 cmH(2)O, P < 0.01; holding duration, 211.44 +/- 42.54 sec, P < 0.01; inter-contraction interval, 264.2 +/- 59.99 sec, P < 0.05; non-voiding contractions, 4.41 +/- 2.12, P < 0.01, n = 7). Intrathecal glutamate (100 microM, 10 microl) ameliorated all the pathological conditions induced by unilateral dorsal root rhizotomy at the L6 level in a dose dependent manner (ED(50) = 1.25 +/- 10(-5)). Intrathecal CNQX (6-cyano-7-nitroquinoxaline-2,3-dione; 100 microM, 10 microl) and APV (D-2-amino-5-phosphonovaleric acid; 100 microM, 10 microl) injections after rhizotomy at the L6 level induced disturbances similar to that caused by an additional rhizotomy at ipsilateral S1 level. Wherease, glutamate (100 microM, 10 microl) reversed the disturbances caused by CNQX but showed no effect on that by APV.

CONCLUSIONS

Acute partial sensory deprivation caused acute impaired micturition reflex in rat models. In addition, glutamatergic NMDA and AMPA receptors are important for mediating these impairments in micturition reflex.

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

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

Impact of state of arousal and stress neuropeptides on urodynamic function in freely moving rats

Corticotropin-releasing factor (CRF) is a neurotransmitter in Barrington's nucleus neurons. These neurons can coregulate parasympathetic tone to the bladder (to modulate micturition) and brain noradrenergic activity (to affect arousal). To identify the role of CRF in the regulation of micturition, the effects of CRF agonists and antagonists on urodynamics in the unanesthetized rat were characterized. Rats were implanted with bladder and intrathecal or intraperitoneal catheters under isoflurane anesthesia. Cystometry was performed in the unanesthetized, unrestrained state at least 24 h later. In some cases, cortical electroencephalographic activity (EEG) was recorded simultaneously to assess arousal state. During cystometry, the state of arousal often shifted between waking and sleeping and urodynamic function changed depending on the state. Micturition threshold, bladder capacity, and micturition volume were all increased during sleep. The CRF1/CRF2 receptor agonists CRF and urocortin 2 increased bladder capacity and micturition volume in awake but not in sleeping rats. Conversely, the CRF1 receptor antagonists antalarmin and NBI-30775 increased urinary frequency and decreased bladder capacity in awake rats. The present results demonstrate a profound effect of the state of arousal on urodynamic function and suggest that simultaneous monitoring of EEG and cystometry may provide a useful model for studying nocturnal enuresis and other urinary disorders. In addition, the results provide evidence for an inhibitory influence of CRF in the spinal pathway on micturition. Targeting the CRF system in the spinal cord may provide a novel approach for treating urinary disorders.

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

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

Effects of a calcineurin inhibitor, tacrolimus, on glutamate-dependent potentiation in pelvic-urethral reflex in anesthetized rats

Effects of tacrolimus, a protein phosphatase 2B inhibitor, on the reflex plasticity between the pelvic afferent nerve fibers and the urethra were examined in urethane-anesthetized rats. Repetitive stimulation (1 Hz) induced a potentiation (0.9+/-0.2 and 10.5+/-1.6 spikes in control and repetitive stimulation groups, respectively, P<0.01, N=10) in the activities of the pelvic-urethral reflex. Intrathecal tacrolimus (0.1 mM, 10 microl, bolus) blocked repetitive stimulation-induced potentiation in pelvic-urethral reflex activities (3.2+/-0.9 spikes in tacrolimus group versus 10.5+/-1.6 spikes in repetitive stimulation group, P<0.01, N=10). Glutamate (intrathecal, 0.1 mM, 10 microl, bolus) and N-methyl-D-aspartic acid (intrathecal, 0.1 mM, 10 microl, bolus) both reversed the blocking effects exerted by tacrolimus on repetitive stimulation-induced pelvic-urethral reflex potentiation (15.0+/-1.4 spikes in glutamate group and 11.4+/-1.4 spikes in N-methyl-D-aspartic acid group versus 3.2+/-0.9 spikes in tacrolimus-treated repetitive stimulation group, P<0.01, N=7). In addition, the reversal effect elicited by these two agonists of glutamate receptors showed no statistical difference (P=NS, N=7). All these results demonstrated that tacrolimus could block glutamatergic N-methyl-D-aspartic acid receptor-mediated potentiation in pelvic-urethral reflex activities. This finding may be pathologically relevant in patients who take tacrolimus as immunosuppressant therapy. Whether tacrolimus will induce urine incontinence in such patients or not needs further investigation.

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.

A method for producing overactive bladder in the rat and investigation of the effects of GABAergic receptor agonists and glutamatergic receptor antagonists on the cystometrogram

PURPOSE

We induced radio frequency (RF) lesions in the neuronal pathway leading from the forebrain to the pontine micturition center (PMC) to produce a rat model of bladder overactivity. We studied the effects of gamma-aminobutyric acid agonists (diazepam and baclofen) and glutamate receptor antagonists (MK-801 maleate and GYKI52466 [1-(4-aminophenyl-D-4-methyl-7,8 methylenedioxy-5H-2,3-benzodiazepine] hydrochloride) on the cystometrogram and developed a possible explanation of the neuronal mechanisms underlying RF lesion induced bladder overactivity.

MATERIALS AND METHOD

Seven-week-old male Sprague-Dawley rats were anesthetized with sodium pentobarbital and RF lesions were produced in the nuclei basalis. Five days later bladder contractions were induced by infusing fluid into the bladder and cystometrograms were measured in conscious rats.

RESULTS

The micturition interval (MI) in rats subjected to RF lesioning was significantly shorter than that in sham operated control rats. Diazepam (0.1 and 1 mg/kg intraperitoneally), baclofen (1 mg/kg intravenously) and MK-801 (0.1 and 1 mg/kg intravenously) did not change or shortened MI in control rats but it prolonged MI in lesioned rats. GYKI52466 (0.5 and 1 mg/kg intravenously) weakly prolonged MI in lesioned rats.

CONCLUSIONS

We consider that RF lesioning causes interruption of the inhibitory GABAergic neurons that lead from the forebrain to the PMC. This results in the activation of N-methyl-D-aspartate receptors in the PMC that are involved in the facilitation of voiding.

Supraspinal and spinal alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and N-methyl-D-aspartate glutamatergic control of the micturition reflex in the urethane-anesthetized rat

Effects of i.c.v. and i.t. administration of (3SR,4aRS,6RS,8aRS)-6-[2-(1H-tetrazol-5-yl)ethyl]decahydroisoquinoline-3-carboxylic acid (LY215490), a competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist and MK-801, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist on the micturition reflex were evaluated in urethane-anesthetized rats, to determine if glutamatergic mechanisms in brain as well as spinal cord are important for the control of micturition. I.c.v. or i.t. injection of LY215490 in low doses (0.01-0.03 microg) did not change rhythmic bladder or external urethral sphincter (EUS) electromyogram (EMG) activity during continuous cystometrograms (CMGs; 0.21 ml/min), whereas higher doses (0.1-1 microg) markedly suppressed these responses. During single CMGs (0.04 ml/min), 0.1-1 microg i.c.v. or 0.1-10 microg i.t. doses increased volume threshold and pressure threshold for inducing micturition, and decreased bladder contraction amplitude and voiding efficiency. MK-801 in low doses (0.6 microg i.c.v. or 0.6-1.8 microg for i.t.) did not change bladder contraction amplitude or EUS EMG activity during continuous CMGs, whereas higher doses 6-60 microg markedly suppressed these responses. During single CMGs, MK-801 (6-60 microg i.c.v. or 60 microg i.t.) increased volume threshold and pressure threshold, and decreased voiding efficiency and bladder contraction amplitude. Pretreatment i.c.v. with MK-801 in a dose 1.8 microg which alone had little effect on bladder contraction amplitude and EUS EMG activity, markedly enhanced depressant effects of LY215490 (0.03 microg i.c.v.) on these responses. Administration of same doses of drugs by i.t. route did not elicit a similar synergistic interaction. These data indicate that in urethane-anesthetized rats glutamatergic mechanisms in brain and spinal cord are essential for controlling micturition and that interactions between AMPA and NMDA glutamatergic transmission are important at supraspinal but not spinal sites.

Feed-forward and feedback regulation of bladder contractility by Barrington's nucleus in cats

The purpose of the present study was to clarify how Barrington's nucleus regulates bladder contractility. Single neurones that discharge at higher rates during micturition contraction were recorded from Barrington's nucleus. Spinal-projecting neurones were identified by antidromic stimulation of the spinal cord. Seventy-six spinal-projecting neurones were classified into four types based on the firing patterns displayed during the relaxation phase of the micturition contraction-relaxation rhythm: (1) ramp-tonic neurones displayed a ramp increase in firing throughout the relaxation phase, (2) ramp-silent neurones were silent initially during the relaxation phase and displayed a ramp increase later, (3) flat-tonic neurones fired constantly, and (4) flat-silent neurones displayed little firing, being virtually silent throughout relaxation. During the relaxation phase, discharge volleys from Barrington's nucleus to sacral neurones were estimated to increase exponentially as micturition contraction approached. Twenty-two neurones increased firing even further within 3 s of micturition contraction, suggesting that they are involved in the final stages of initiation of micturition contraction. During micturition contraction, 18 neurones (of which 14 belonged to the ramp-silent class) displayed maximal firing rates before maximal bladder pressures were reached; firing gradually decreased during micturition contraction. Thirty-nine neurones (of which 25 belonged to the ramp-tonic class) displayed constant firing during micturition contraction. This suggests that ramp-silent neurones might be involved in increasing bladder pressure rapidly and strongly via feed-forward regulation, while ramp-tonic neurones might be involved in maintaining high bladder pressure via positive feedback from the bladder afferents. Sixty neurones continued to fire for 1-8 s after the onset of bladder relaxation, suggesting that Barrington's nucleus does not trigger bladder relaxation.

Effects of a selective metabotropic glutamate receptor agonist on the micturition reflex pathway in urethane-anesthetized rats

AIMS

To determine a possible role of metabotropic glutamate receptors in the spinobulbospinal micturition reflex pathway in the rat.

MATERIALS AND METHODS

A selective metabotropic glutamate receptor agonist, trans-(+/-)-1-amino1,3-cyclopentanedicarboxylic acid (trans-ACPD) was administered to the lumbosacral spinal cord via an intrathecal catheter in urethane anesthetized rats. Amplitude of reflex bladder contractions evoked by bladder distension under isovolumetric condition as well as amplitude of bladder contractions elicited by electrical stimulation of the pontine micturition center (PMC) were examined before and after administration of trans-ACPD. The effect of trans-ACPD on the urethral activity during isovolumetric bladder contractions was also examined by monitoring urethral perfusion pressure and electromyography of the external urethral sphincter (EUS-EMG).

RESULTS

Trans-ACPD (3-10 microg) completely inhibited reflex bladder contractions evoked by bladder distension and the duration of inhibition was dose dependent (3 microg: 11.4 +/- 2.8 min, 5 microg: 13.2 +/- 1.3 min, 10 microg: 36.2 +/- 2.4 min). The mean amplitude of bladder contractions evoked by electrical stimulation of the PMC was reduced to 12.6 +/- 2.3% of control by 10 microg of trans-ACPD. In addition, bursting activity of EUS-EMG and corresponding high frequency oscillations of urethral pressure during isovolumetric bladder contractions were completely abolished by 10 microg of trans-ACPD.

CONCLUSIONS

These results indicate that intrathecal administration of a selective metabotropic glutamate receptor agonist to the lumbosacral spinal cord has an inhibitory effect on the spinobulbospinal micturition reflex pathway in urethane-anesthetized rats. This pharmacological action is attributed at least to the inhibitory effect on the descending pathway from the PMC to the lumbosacral spinal cord.

Transient neonatal expression of NR2B/2D subunit mRNAs of the N-methyl-D-aspartate receptor in the parasympathetic preganglionic neurons in the rat spinal cord

Physiological studies have shown that lower urinary tract function is regulated through glutamate receptors at the levels of spinal and supraspinal cord. Of the receptor family, N-methyl-D-aspartate (NMDA) receptors mediate activity-dependent changes of synaptic efficacy, underlying synaptic plasticity and synapse development. To know the ontogenic changes of NMDA receptor expression in the visceromotor system innervating pelvic organs, including the bladder, we employed double labeling technique of retrograde neuronal tracing and in situ hybridization for detecting NMDA subunit mRNAs in preganglionic neurons (PGNs) of the lumbosacral cord. Rats at postnatal day 7 (P7), 14 (P14), 21 (P21), and adult were used. In situ hybridization was conducted using 35S-labeled antisense oligonucleotides specific to mRNAs for NMDA receptor subunits. Hybridizing signals in PGNs were detected by a dark-field microscope equipped fluorescence detector. PGNs showed strong signals for NR1 subunit mRNA at each developmental stage examined. Moderate signals for the NR2B and NR2D subunit mRNAs were found in PGNs at P7. However, their expression levels decreased thereafter, reaching the minimal level in adults. No significant signals for NR2A and NR2C subunit mRNAs were detected at any stages. This temporal pattern of expression suggests a possible involvement of NMDA receptors in the development of micturitional neural circuit through activity-dependent mechanisms.

Bladder contractility-related neurons in Barrington's nucleus: axonal projections to the spinal cord in the cat

Barrington's nucleus projects directly to the sacral parasympathetic nucleus. The purpose of this study was to clarify whether neurons in Barrington's nucleus that increase their firing during bladder contractions project to the spinal cord and, if so, to which level(s) the axon reaches. Single units were recorded in Barrington's nucleus of cat with glass microelectrodes, and the termination level of descending axons was determined by antidromic stimulation of the spinal cord. Thirty-nine neurons projecting to the spinal cord were located in rostral parts of the dorsolateral pontine tegmentum, medial and ventral to the mesencephalic trigeminal tract. This finding is consistent with previous neuronal tracing studies. All neurons increased their firing rates during contraction associated with micturition. In 19 examined neurons, the most caudal level of the descending axon distributed between the L7 and the S3 level. Stimulation of the axon at this most caudal level resulted in antidromic spike latencies ranging between 19.5 msec and 45.0 msec. These antidromic latencies were much smaller than previously reported orthodromic conduction times between neurons in Barrington's nucleus and sacral preganglionic neurons innervating the bladder. The mean conduction velocity of the descending axon from the cell body to the border between Th13 and the L1 ranged between 7.2 m/sec and 27.7 m/sec. The decrease of the mean conduction velocity was observed at the lumbar as well as at the sacral segments, suggesting that axons issue collaterals to the lumbar level as well as to the sacral level.

Altered glutamate receptor function during recovery of bladder detrusor-external urethral sphincter coordination in a rat model of spinal cord injury

Coordination of the bladder detrusor and the external urethral sphincter is a supraspinally controlled reflex that is essential for efficient micturition. This coordination is permanently lost after spinal cord transection but can recover chronically after incomplete spinal cord injury (SCI). As glutamatergic transmission plays a key role in all levels of detrusor-external urethral sphincter coordination, we examined the role of potential alterations in glutamatergic control in its recovery after SCI. Rats were subjected to standardized incomplete contusion injury. Detrusor-external urethral sphincter coordination was evaluated urodynamically at 5 days (subacute) and 8 weeks (chronic) after SCI. Sensitivity of coordinated activation of the external urethral sphincter in response to bladder distension to the alpha -amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid/kainate antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo(f)quinoxaline-7-sulfonamide disodium (NBQX) and to the N-methyl-D-aspartate (NMDA) antagonist R(--3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP) was determined by intrathecal application at the L6 spinal cord level during urodynamic recordings. We found that while detrusor contractions recovered at 5 days after SCI, coordinated activation of the external urethral sphincter was significantly impaired at 5 days and recovered only by 8 weeks. There was no difference in sensitivity of detrusor-external urethral sphincter coordination to NBQX at the subacute or chronic time points. However, external urethral sphincter response to bladder distension was sensitive to a 50% lower dose of CPP at 5 days compared with uninjured rats or chronic recovered SCI rats. Thus, alterations in NMDA receptor function appeared to be involved in recovery of detrusor-external urethral sphincter coordination after incomplete SCI.

Excitatory synaptic currents in lumbosacral parasympathetic preganglionic neurons elicited from the lateral funiculus

Excitatory postsynaptic currents (EPSCs) in parasympathetic preganglionic neurons (PGNs) were examined using the whole cell patch-clamp recording technique in L6 and S1 spinal cord slices from neonatal rats (6-16 days old). PGNs were identified by labeling with retrograde axonal transport of a fluorescent dye (Fast Blue) injected into the intraperitoneal space 3-7 days before the experiment. Synaptic responses were evoked in PGNs by field stimulation of the lateral funiculus (LF) in the presence of bicuculline methiodide (10 microM) and strychnine (1 microM). In approximately 40% of the cells (total, 100), single-shock electrical stimulation of the LF elicited short, relatively constant latency [3.0 +/- 0.1 (SE) ms] fast EPSCs consistent with a monosynaptic pathway. The remainder of the cells did not respond to stimulation. At low intensities of stimulation, the EPSCs often occurred in an all-or-none manner, indicating that they were mediated by a single axonal input. Most cells (n = 33) exhibited only fast EPSCs (type 1), but some cells (n = 8) had fast EPSCs with longer, more variable latency polysynaptic EPSCs superimposed on a slow inward current (type 2). Type 1 fast synaptic EPSCs were pharmacologically dissected into two components: a transient component that was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5 microM), a non-NMDA glutamatergic antagonist, and a slow decaying component that was blocked by 2-amino-5-phosphonovalerate (APV, 50 microM), a NMDA antagonist. Type 2 polysynaptic currents were reduced by 5 microM CNQX and completely blocked by combined application of 5 microM CNQX and 50 microM APV. The fast monosynaptic component of type 1 EPSCs had a linear current-voltage relationship and reversed at a membrane potential of 5.0 +/- 5.9 mV (n = 5), whereas the slow component exhibited a negative slope conductance at holding potentials greater than -20 mV. The type 1, fast synaptic EPSCs had a time to peak of 1.4 +/- 0.1 ms and exhibited a biexponential decay (time constants, 5.7 +/- 0.6 and 38.8 +/- 4.0 ms). In the majority of PGNs (n = 11 of 15 cells), EPSCs evoked by electrical stimulation of LF exhibited paired-pulse inhibition (range; 25-33% depression) at interstimulus intervals ranging from 50 to 120 ms. These results indicate that PGNs receive monosynaptic and polysynaptic glutamatergic excitatory inputs from axons in the lateral funiculus.

Pharmacology of the lower urinary tract

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the urinary bladder, urethra, and external urethral sphincter. This activity is in turn controlled by neural circuits in the brain, spinal cord, and peripheral ganglia. Various neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in the neural regulation of the lower urinary tract. Injuries or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce voiding dysfunctions such as urinary frequency, urgency, and incontinence or inefficient voiding and urinary retention. This chapter will review recent advances in our understanding of the pathophysiology of voiding disorders and the targets for drug therapy.

Pontine regulation of pelvic viscera: pharmacological target for pelvic visceral dysfunctions

The pathophysiology and pharmacological targets of disorders of the bladder and colon have focused predominantly on the periphery. However, these viscera are regulated by the CNS, which, in turn, must integrate their functions with compatible behaviours. This review focuses on the role of the pontine micturition centre, Barrington's nucleus, as a key to this integration. Through its efferent network this pontine centre links parasympathetic preganglionic neurones with forebrain-projecting nuclei, providing an anatomical substrate for coregulation of pelvic visceral and forebrain activity. Disorders characterized by multiple pelvic visceral symptoms and comorbidity with psychiatric disorders (for example functional bowel disorders) might have their roots in dysfunctions of this circuit, which could provide a novel target for pharmacological treatment.

Trigeminovascular nociceptive transmission involves N-methyl-D-aspartate and non-N-methyl-D-aspartate glutamate receptors

Interest in the fundamental mechanisms underlying headache, particularly the pathophysiology of migraine and cluster headache, has lead to the study of the physiology and pharmacology of the trigeminovascular system and its central ramifications. Cats were anaesthetized (60 mg/kg alpha-chloralose, i.p., along with halothane for all surgical procedures) and prepared for physiological monitoring. The animals were placed in a stereotaxic frame and ventilated. A midline craniotomy and C2 laminectomy were performed for access to the superior sagittal sinus and C2 dorsal horn, respectively. The sinus was isolated from the underlying cortex and stimulated electrically after the animals had been paralysed with gallamine (6 mg/kg, i.v.). Units linked to stimulation were recorded with a tungsten-in-glass microelectrode placed in the most caudal part of the trigeminal nucleus, the trigeminocervical complex. Signals from the neurons were amplified, filtered and passed to a microcomputer, where post-stimulus histograms were constructed on-line to analyse the responses to stimulation. Units responded to sagittal sinus stimulation with a typical latency of 8-10 ms. All units studied had a probability of firing of 0.6 or greater. Intravenous injection of the non-competitive N-methyl-D-aspartate receptor antagonist, dizocilpine maleate (4 mg/kg, i.v.), resulted in a substantial and prolonged blockade of firing of units in the trigeminocervical complex. Similarly, administration of the non-N-methyl-D-aspartate excitatory amino acid receptor blocker, GYKI 52466, lead to a dose-dependent inhibition of trigeminovascular-evoked responses in the trigeminocervical complex. These data demonstrate the participation of both N-methyl-D-aspartate- and non-N-methyl-D-aspartate-mediated mechanisms in transmission within the trigeminocervical complex, and suggest a clear preclinical role of glutamatergic mechanisms in primary headache syndromes, such as migraine and cluster headache.

Bladder afferent pathway and spinal cord injury: possible mechanisms inducing hyperreflexia of the urinary bladder

Lower urinary tract dysfunction is a common problem in patients with spinal cord injury (SCI). Since the coordination of the urinary bladder and urethra is controlled by the complex mechanisms in spinal and supraspinal neural pathways, SCI rostral to the lumbosacral level disrupts voluntary and supraspinal control of voiding and induces a considerable reorganization of the micturition reflex pathway. Following SCI, the urinary bladder is initially areflexic. but then becomes hyperreflexic because of the emergence of a spinal micturition reflex pathway. Recent electrophysiologic and histologic studies in rats have revealed that chronic SCI induces various phenotypic changes in bladder afferent neurons such as: (1) somal hypertrophy along with increased expression of neurofilament protein; and (2) increased excitability due to the plasticity of Na+ and K+ ion channels. These results have now provided detailed information to support the previous notion that capsaicin-sensitive, unmyelinated C-fiber afferents innervating the urinary bladder change their properties after SCI and are responsible for inducing bladder hyperreflexia in both humans and animals. It is also suggested that the changes in bladder reflex pathways following SCI are influenced by neural-target organ interactions probably mediated by neurotrophic signals originating in the hypertrophied bladder. Thus, increased knowledge of the plasticity in bladder afferent pathways may help to explain the pathogenesis of lower urinary tract dysfunctions after SCI and may provide valuable insights into new therapeutic strategies for urinary symptoms in spinal cord-injured patients.

Different expressions of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid and N-methyl-D-aspartate receptor subunit mRNAs between visceromotor and somatomotor neurons of the rat lumbosacral spinal cord

The glutamatergic transmission system plays a key role in afferent and efferent pathways involved in micturition. By in situ hybridization combined with retrograde Fast Blue labeling, expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor (GluR-A to -D) and N-methyl-D-aspartate (NMDA) receptor (NR1 and NR2A-D) subunit mRNAs were examined in visceromotor and somatomotor neurons of the rat lumbosacral spinal cord. Parasympathetic preganglionic neurons (PGNs) in the intermediolateral nucleus highly expressed GluR-A and GluR-B subunit mRNAs, with very low levels for GluR-C and GluR-D subunits. As for the NMDA receptor, PGNs were associated with abundant signals for NR1 subunit mRNA, but without any NR2 subunit mRNAs. On the other hand, somatomotor neurons in the ventral horn (dorsolateral nucleus) express all four AMPA receptor subunit mRNAs, showing relatively abundant expressions of GluR-C and GluR-D subunit mRNA compared with PGNs. In addition to high levels of NR1 subunit mRNA, dorsolateral nucleus neurons moderately expressed NR2A and NR2B subunit mRNAs. These results suggest that molecular organization of both AMPA and NMDA receptor channels are distinct between PGNs and dorsolateral nucleus neurons. Considering that native NMDA receptors are heteromeric channels composed of NR1 and NR2 subunits, it seems likely that dorsolateral nucleus neurons, not PGNs, are provided with functional NMDA receptors, which could induce activity-dependent changes in synaptic transmission in the efferent pathway for the lower urinary tract.

Arrhythmias induced by myocardial ischaemia-reperfusion are sensitive to ionotropic excitatory amino acid receptor antagonists

We have investigated the effects of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK801), a non-competitive N-methyl-D-aspartate (NMDA) ionotropic excitatory amino acid receptor antagonist, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA ionotropic excitatory amino acid receptor antagonist, ketamine and memantine, NMDA receptor channel blockers, on ventricular arrhythmias induced by myocardial ischaemia and myocardial ischaemia-reperfusion. Coronary artery occlusion caused 100 +/- 2% ventricular tachycardia, in saline treated group, and 60 +/- 3% ventricular fibrillation. 66 +/- 6% of the animals recovered from ventricular fibrillation, while in 34 +/- 4% of animals the ventricular fibrillation caused mortality. The incidence of ventricular tachycardia, ventricular fibrillation and mortality was not modified by treatment of rats with MK801 (0.3 mg/kg i.v.), CNQX (1 mg/kg i.v.), ketamine (10 mg/kg) and memantine (1.5 mg/kg), injected 5 min prior to occlusion. Reperfusion caused severe arrhythmias which started within 5 +/- 2 s. For instance, in the saline treated group, the incidence of ventricular tachycardia was 100 +/- 5%, while ventricular fibrillation occurred in 87 +/- 3% of the animals and lasted 90 +/- 12 s. The mortality was 62 +/- 6%. The incidence of ventricular tachycardia, ventricular fibrillation and mortality induced by reperfusion was greatly (P < 0.01) reduced in animals treated with MK801 (0.3 mg/kg i.v.), CNQX (1 mg/kg i.v.), ketamine (10 mg/kg) and memantine (1.5 mg/kg), injected 5 min prior to occlusion. Therefore, reperfusion-induced arrhythmias, but not ischaemia-induced arrhythmias, are sensitive to NMDA/non-NMDA ionotropic excitatory amino acid receptor antagonists.

Developmental and injury induced plasticity in the micturition reflex pathway

The storage and periodic elimination of urine are dependent upon neural circuits in the brain and spinal cord that co-ordinate the activity of the urinary bladder, the urethra and the striated urethral sphincter. This study utilized anatomical, electrophysiological and pharmacological techniques to examine: (1) the organization of the parasympathetic excitatory reflex mechanisms that control the urinary bladder of the rat and the cat; and (2) the changes in these reflexes during postnatal development and after spinal cord injury. In normal adult cats and rats, the parasympathetic excitatory input to the bladder is dependent upon a spinobulbospinal reflex pathway that is activated by myelinated (Adelta) bladder afferents and that passes through an integrative center (the pontine micturition center, PMC) in the rostral brain stem. Transneuronal tracing studies using pseudorabies virus as well as physiological methods have revealed that the PMC is located in close proximity to the locus coeruleus. Single unit recordings indicate that neurons in the PMC respond to afferent input from the bladder and are excited prior to or during reflex bladder contractions. Glutamic acid is the major excitatory transmitter in the micturition reflex pathway. Glutamatergic transmission which is mediated by AMPA/kainate and NMDA receptors can be modulated by a variety of other transmitters. In neonatal animals, a spinal micturition reflex is activated by somatic afferent fibers from the perigenital region. This reflex is suppressed during postnatal development, but can be unmasked in adult animals following spinal cord injury. Spinal injury also causes the emergence of a spinal bladder-to-bladder reflex which in the cat is activated by capsaicin-sensitive C-fiber bladder afferents. Patch clamp studies in spinal cord slice preparations indicate that developmental and spinal cord injury induced plasticity in sacral parasympathetic reflex pathways is due in part to alterations in glutamatergic excitatory transmission between interneurons and preganglionic neurons. Changes in the electrical properties of bladder afferent pathways may also contribute to the reorganization of bladder reflexes in paraplegic animals.

A neurologic basis for the overactive bladder

OBJECTIVES

The functions of the lower urinary tract (LUT) to store and periodically release urine are dependent on neural circuits in the brain and spinal cord. This paper reviews the central neural control of micturition and how disruption of this control can lead to bladder overactivity and incontinence.

METHODS

Neuroanatomic, electrophysiologic, and pharmacologic techniques have provided information about the neural circuitry and the neurotransmitters involved in the central nervous control of voiding. Experimental models of neural injury, including spinal cord transection, cerebral infarction, and localized brain lesions, have been studied to identify the mechanisms contributing to the neurogenic overactive bladder.

RESULTS

Normal storage of urine is dependent on 1) spinal reflex mechanisms that activate sympathetic and somatic pathways to the urethral outlet and 2) tonic inhibitory systems in the brain that suppress the parasympathetic excitatory outflow to the urinary bladder. Voiding is mediated by inhibition of sympathetic-somatic pathways and activation of a spinobulbospinal parasympathetic reflex pathway passing through a micturition center in the rostral pons. Damage to the brain can induce bladder overactivity by reducing suprapontine inhibition. Damage to axonal pathways in the spinal cord leads to the emergence of primitive spinal bladder reflexes triggered by C-fiber bladder afferent neurons. The C-fiber afferent neurotoxin capsaicin, administered intravesically, has been useful in treating certain types of neurogenic bladder overactivity.

CONCLUSIONS

The central nervous mechanisms controlling the LUT are organized in the brain and spinal cord as simple on-off switching circuits that are under voluntary control. Damage to central inhibitory pathways or sensitization of peripheral afferent terminals in the bladder can unmask primitive voiding reflexes that trigger bladder overactivity.