Brain control of the lower urinary tract

Reliability of supraspinal correlates to lower urinary tract stimulation in healthy participants - A fMRI study

Previous functional neuroimaging studies provided evidence for a specific supraspinal network involved in lower urinary tract (LUT) control. However, data on the reliability of blood oxygenation level-dependent (BOLD) signal changes during LUT task-related functional magnetic resonance imaging (fMRI) across separate measurements are lacking. Proof of the latter is crucial to evaluate whether fMRI can be used to assess supraspinal responses to LUT treatments. Therefore, we prospectively assessed task-specific supraspinal responses from 20 healthy participants undergoing two fMRI measurements (test-retest) within 5-8 weeks. The fMRI measurements, conducted in a 3T magnetic resonance (MR) scanner, comprised a block design of repetitive bladder filling and drainage using an automated MR-compatible and MR-synchronized infusion-drainage device. Following transurethral catheterization and bladder pre-filling with body warm saline until participants perceived a persistent desire to void (START condition), fMRI was recorded during repetitive blocks (each 15 s) of INFUSION and WITHDRAWAL of 100 mL body warm saline into respectively from the bladder. BOLD signal changes were calculated for INFUSION minus START. In addition to whole brain analysis, we assessed BOLD signal changes within multiple 'a priori' region of interest (ROI), i.e. brain areas known to be involved in the LUT control from previous literature. To evaluate reliability of the fMRI results between visits, we applied different types of analyses: coefficient of variation (CV), intraclass correlation coefficient (ICC), Sørensen-Dice index, Bland-Altman method, and block-wise BOLD signal comparison. All participants completed the study without adverse events. The desire to void was rated significantly higher for INFUSION compared to START or WITHDRAWAL at both measurements without any effect of visit. At whole brain level, significant (p < 0.05, cluster corrected, k ≥ 41 voxels) BOLD signal changes were found for the contrast INFUSION compared to START in several brain areas. Overlap of activation maps from both measurements were observed in the orbitofrontal cortex, insula, ventrolateral prefrontal cortex (VLPFC), and inferior parietal lobe. The two highest ICCs, based on a ROI's mean beta weight, were 0.55 (right insular cortex) and 0.47 (VLPFC). Spatial congruency (Sørensen-Dice index) of all voxels within each ROI between measurements was highest in the insular cortex (left 0.55, right 0.44). In addition, the mean beta weight of the right insula and right VLPFC demonstrated the lowest CV and narrowest Bland and Altman 95% limits of agreement. In conclusion, the right insula and right VLPFC were revealed as the two most reliable task-specific ROIs using our automated, MR-synchronized protocol. Achieving high reliability using a viscero-sensory/interoceptive task such as repetitive bladder filling remains challenging and further endeavour is highly warranted to better understand which factors influence fMRI outcomes and finally to assess LUT treatment effects on the supraspinal level.

Afferent Pathway-Mediated Effect of α1 Adrenergic Antagonist, Tamsulosin, on the Neurogenic Bladder After Spinal Cord Injury

Purpose

The functions of the lower urinary tract (LUT), such as voiding and storing urine, are dependent on complex central neural networks located in the brain, spinal cord, and peripheral ganglia. Thus, the functions of the LUT are susceptible to various neurologic disorders including spinal cord injury (SCI). SCI at the cervical or thoracic levels disrupts voluntary control of voiding and the normal reflex pathways coordinating bladder and sphincter functions. In this context, it is noteworthy that α1-adrenoceptor blockers have been reported to relieve voiding symptoms and storage symptoms in elderly men with benign prostatic hyperplasia (BPH). Tamsulosin, an α1-adrenoceptor blocker, is also considered the most effective regimen for patients with LUT symptoms such as BPH and overactive bladder (OAB).

Methods

In the present study, the effects of tamsulosin on the expression of c-Fos, nerve growth factor (NGF), and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) in the afferent micturition areas, including the pontine micturition center (PMC), the ventrolateral periaqueductal gray matter (vlPAG), and the spinal cord (L5), of rats with an SCI were investigated.

Results

SCI was found to remarkably upregulate the expression of c-Fos, NGF, and NADPH-d in the afferent pathway of micturition, the dorsal horn of L5, the vlPAG, and the PMC, resulting in the symptoms of OAB. In contrast, tamsulosin treatment significantly suppressed these neural activities and the production of nitric oxide in the afferent pathways of micturition, and consequently, attenuated the symptoms of OAB.

Conclusions

Based on these results, tamsulosin, an α1-adrenoceptor antagonist, could be used to attenuate bladder dysfunction following SCI. However, further studies are needed to elucidate the exact mechanism and effects of tamsulosin on the afferent pathways of micturition.

Effects of Panax ginseng on the nerve growth factor expression in testosterone induced benign prostatic hyperplasia

The prostatic hyperplasia in benign prostatic hyperplasia (BPH) leads to obstructive micturition symptoms. Previous studies showed that pontine micturition center (PMC), ventrolateral periaqueductal gray (vlPAG), and medial preopticnucleus (MPA) regions in the brain have been known to regulate the urinary bladder function. The present study shows the influences of Panax ginseng on nerve growth factor (NGF) expressions in PMC, vlPAG, and MPA regions in the brain. Wistar rats were used for the present study. The rats split into four groups; 4 groups (n = 6) in control group, BPH-induced group, BPH-induced and P. ginseng-treated group, and BPH-induced and finasteride-treated group. BPH in rats was induced by testosterone and the animals were evaluated for NGF expression in PMC, vlPAG, and MPA regions in the brain. The NGF expression was identified using immunohistochemistry (IHC). The NGF expression by IHC showed spots with dark brown color. In our results, NGF expressions in PMC, vlPAG, and MPA regions in the brainstem of the BPH-induced group showed increase than the control animal. These increased NGF expressions in three regions were decreased using treatment with P. ginseng (200 mg/kg). These results suggest that P. ginseng has therapeutic effects on the symptoms of BPH and is associated with the regulation of NGF expression in the brain. In conclusion, the administration of P. ginseng helps nerve growth factor activation.

Role of the Anterior Cingulate Cortex in the Control of Micturition Reflex in a Rat Model of Parkinson's Disease

PURPOSE

In the current study we examined dynamic changes in neural activity of the anterior cingulate cortex and the midbrain periaqueductal gray during the micturition reflex in a Parkinson's disease model as well as the effects of direct stimulation of the anterior cingulate cortex on the micturition reflex.

MATERIALS AND METHODS

Electrodes were inserted in the anterior cingulate cortex or the periaqueductal gray. The effects of intravenous administration of the adenosine A2A receptor antagonist ZM24138 on pelvic nerve evoked field potentials were examined. The effect of electrical stimulation of the anterior cingulate cortex was also examined.

RESULTS

Rats with Parkinson's disease showed bladder overactivity as evidenced by a significant decrease in the intercontraction interval compared with sham operated rats. Intravenous administration of ZM24138 increased the intercontraction interval in both groups with the inhibitory effects greater in rats with Parkinson's disease. It dose dependently increased the amplitude of evoked potentials in the anterior cingulate cortex of rats with Parkinson's disease but not in sham operated rats. Intravenous administration of ZM24138 decreased evoked potential amplitude in the periaqueductal gray of both groups with the inhibitory effects greater in Parkinson's disease vs sham operated rats. Electrical stimulation of the anterior cingulate cortex significantly increased the intercontraction interval.

CONCLUSIONS

These results suggest that anterior cingulate cortex neurons have an inhibitory role in bladder control. Neural activity in the anterior cingulate cortex was significantly increased along with suppression of bladder overactivity after ZM241385 administration in the Parkinson's disease model and the stimulation of the anterior cingulate cortex inhibited the micturition reflex. Understanding the roles of the anterior cingulate cortex in the modulation of micturition could provide further insights into the pathophysiology of overactive bladder.

Inhibitory effects of endomorphin-2 on excitatory synaptic transmission and the neuronal excitability of sacral parasympathetic preganglionic neurons in young rats

The function of the urinary bladder is partly controlled by parasympathetic preganglionic neurons (PPNs) of the sacral parasympathetic nucleus (SPN). Our recent work demonstrated that endomorphin-2 (EM-2)-immunoreactive (IR) terminals form synapses with μ-opioid receptor (MOR)-expressing PPNs in the rat SPN. Here, we examined the effects of EM-2 on excitatory synaptic transmission and the neuronal excitability of the PPNs in young rats (24–30 days old) using a whole-cell patch-clamp approach. PPNs were identified by retrograde labeling with the fluorescent tracer tetramethylrhodamine-dextran (TMR). EM-2 (3 μM) markedly decreased both the amplitude and the frequency of the spontaneous and miniature excitatory postsynaptic currents (sEPSCs and mEPSCs) of PPNs. EM-2 not only decreased the resting membrane potentials (RMPs) in 61.1% of the examined PPNs with half-maximal response at the concentration of 0.282 μM, but also increased the rheobase current and reduced the repetitive action potential firing of PPNs. Analysis of the current–voltage relationship revealed that the EM-2-induced current was reversed at −95 ± 2.5 mV and was suppressed by perfusion of the potassium channel blockers 4-aminopyridine (4-AP) or BaCl₂ or by the addition of guanosine 5′-[β-thio]diphosphate trilithium salt (GDP-β-S) to the pipette solution, suggesting the involvement of the G-protein-coupled inwardly rectifying potassium (GIRK) channel. The above EM-2-invoked inhibitory effects were abolished by the MOR selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), indicating that the effects of EM-2 on PPNs were mediated by MOR via pre- and/or post-synaptic mechanisms. EM-2 activated pre- and post-synaptic MORs, inhibiting excitatory neurotransmitter release from the presynaptic terminals and decreasing the excitability of PPNs due to hyperpolarization of their membrane potentials, respectively. These inhibitory effects of EM-2 on PPNs at the spinal cord level may explain the mechanism of action of morphine treatment and morphine-induced bladder dysfunction in the clinic.

Protocol for a prospective neuroimaging study investigating the supraspinal control of lower urinary tract function in healthy controls and patients with non-neurogenic lower urinary tract symptoms

INTRODUCTION

Lower urinary tract symptoms (LUTS) are highly prevalent, cause an enormous economic burden on healthcare systems and significantly impair the quality of life (QoL) of affected patients. The dependence of the LUT on complex central neuronal circuits makes it unique in comparison to other visceral functions, such as the gastrointestinal tract, but also more vulnerable to neurological diseases.

METHODS AND ANALYSIS

This is a prospective neuroimaging study investigating the supraspinal control of LUT function in healthy controls and in patients with non-neurogenic LUTS. The clinical assessment will include medical history, neuro-urological examination, bladder diary, urine analysis, urodynamic investigations, as well as standardised questionnaires regarding LUTS and QoL. The acquisition of neuroimaging data will include structural assessments (T1-weighted imaging and diffusion tensor imaging) as well as functional investigations using blood-oxygen-level dependent sensitive functional MRI (fMRI) in a 3 T MR scanner. The fMRI will be performed during four different bladder tasks using an automated MR-compatible and MR-synchronised pump system. The first three task-related fMRIs will consist of automated, repetitive filling of 100 mL warm (37°C) saline starting with (1) an empty bladder, (2) a low prefilled bladder volume (100 mL) and (3) a high prefilled bladder volume (persistent desire to void). The fourth task-related fMRI will comprise of automated, repetitive filling of 100 mL cold (4-8°C) saline starting with an empty bladder.

ETHICS AND DISSEMINATION

The local ethics committee approved this study (KEK-ZH-Nr. 2011-0346). The findings of the study will be published in peer-reviewed journals and presented at national and international scientific meetings.

TRIAL REGISTRATION NUMBER

This study has been registered at clinicaltrials.gov (http://www.clinicaltrials.gov/ct2/show/NCT01768910).

An animal study to compare the degree of the suppressive effects on the afferent pathways of micturition between tamsulosin and sildenafil

Background

Tamsulosin, an α1-adrenoceptor antagonist, and sildenafil, a phosphodiesterase (PDE) inhibitor, are reported to improve lower urinary tract symptoms including overactive bladder (OAB). This study is aimed at investing the effects of tamsulosin and sildenafil and comparing the degree of the suppressive effects on the afferent pathways of micturition between them using an animal model of OAB, the spontaneously hypertensive rat (SHR).

Results

The cystometric parameters, the basal pressure and duration of bladder contraction, were significantly increased in the SHR group as compared with the Wistar-Kyoto (WKY) group. The intercontraction interval also significantly decreased in the SHR group. In the SHR-Tam 0.01 mg/kg group and the SHR-Sil 1 mg/kg group, however, the basal pressure and duration were significantly reduced and the intercontraction interval was significantly prolonged. Moreover, the degree of the expression of c-Fos and NGF was significantly higher in the SHR group as compared with the WKY group. But it was significantly reduced in the SHR-Tam 0.01 mg/kg group and the SHR-Sil 1 mg/kg group. Furthermore, tamsulosin had a higher degree of effect as compared with sildenafil.

Conclusions

In conclusion, α1-adrenergic receptor antagonists and PDE-5 inhibitors may have an effect in improving the voiding functions through an inhibition of the neuronal activity in the afferent pathways of micturition.

Synaptic connections between endomorphin 2-immunoreactive terminals and μ-opioid receptor-expressing neurons in the sacral parasympathetic nucleus of the rat

The urinary bladder is innervated by parasympathetic preganglionic neurons (PPNs) that express μ-opioid receptors (MOR) in the sacral parasympathetic nucleus (SPN) at lumbosacral segments L6-S1. The SPN also contains endomorphin 2 (EM2)-immunoreactive (IR) fibers and terminals. EM2 is the endogenous ligand of MOR. In the present study, retrograde tract-tracing with cholera toxin subunit b (CTb) or wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) via the pelvic nerve combined with immunohistochemical staining for EM2 and MOR to identify PPNs within the SPN as well as synaptic connections between the EM2-IR terminals and MOR-expressing PPNs in the SPN of the rat. After CTb was injected into the pelvic nerve, CTb retrogradely labeled neurons were almost exclusively located in the lateral part of the intermediolateral gray matter at L6-S1 of the lumbosacral spinal cord. All of the them also expressed MOR. EM2-IR terminals formed symmetric synapses with MOR-IR, WGA-HRP-labeled and WGA-HRP/MOR double-labeled neuronal cell bodies and dendrites within the SPN. These results provided morphological evidence that EM2-containing axon terminals formed symmetric synapses with MOR-expressing PPNs in the SPN. The present results also show that EM2 and MOR might be involved in both the homeostatic control and information transmission of micturition.

Effects of Tamsulosin on Urinary Bladder Function and Neuronal Activity in the Voiding Centers of Rats with Cyclophosphamide-induced Overactive Bladder

PURPOSE

The overactive bladder (OAB) syndrome is characterized by urgency usually with frequency and nocturia. Tamsulosin, α(1)-adrenergic receptor antagonist, is widely used to reduce symptoms of urinary obstruction and prostatic hyperplasia. Tamsulosin can across the blood-brain barrier. We investigated the effects of tamsulosin on the symptoms of OAB in relation to neuronal activity using rats.

METHODS

Adult female Sprague-Dawley rats, weighing 250±10 g (9 weeks old), were used in this study. The animals were divided into five groups (n=8 in each group): control group, OAB-induced group, OAB-induced and 0.01 mg/kg tamsulosin-treated group, OAB-induced and 0.1 mg/kg tamsulosin-treated group, and OAB-induced and 1 mg/kg tamsulosin-treated group. OAB was induced by intraperitoneal injection of cyclophosphamide (75 mg/kg) every third day for 10 days. The rats in the tamsulosin-treated groups orally received tamsulosin once a day for 14 consecutive days at the respective dose of the groups, starting 1 day after the induction of OAB. Cystometry for bladder pressure determination, immunohistochemistry for c-Fos, nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry for nitric oxide synthase (NOS) in the neuronal voiding centers and western blot for inducible NOS in the bladder were conducted.

RESULTS

Cyclophosphamide injection enhanced contraction pressure and time, representing the induction of OAB. Contraction pressure and time were significantly suppressed by tamsulosin treatment. c-Fos and NOS expressions in the neuronal voiding centers were enhanced by induction of OAB. OAB-induced c-Fos and NOS expressions were suppressed by tamsulosin treatment.

CONCLUSIONS

Tamsulosin exerts inhibitory effect on neuronal activation in the neuronal voiding centers of OAB. The present results suggest the possibility that tamsulosin is effective therapeutic modality for ameliorating the symptoms of OAB.

Neural control of the lower urinary and gastrointestinal tracts: supraspinal CNS mechanisms

Normal urinary function is contingent upon a complex hierarchy of CNS regulation. Lower urinary tract afferents synapse in the dorsal horn of the spinal cord and ascend to the midbrain periaqueductal gray (PAG), with a separate nociception path to the thalamus. A spino-thalamo-cortical sensory pathway is present in some primates, including humans. In the brainstem, the pontine micturition center (PMC) is a convergence point of multiple influences, representing a co-ordinating center for voiding. Many PMC neurones have characteristics necessary to categorize the center as a pre-motor micturition nucleus. In the lateral pontine brainstem, a separate region has some characteristics to suggest a "continence center." Cerebral control determines that voiding is permitted if necessary, socially acceptable and in a safe setting. The frontal cortex is crucial for decision making in an emotional and social context. The anterior cingulate gyrus and insula co-ordinate processes of autonomic arousal and visceral sensation. The influence of these centers on the PMC is primarily mediated via the PAG, which also integrates bladder sensory information, thereby moderating voiding and storage of urine, and the transition between the two phases. The parabrachial nucleus in the pons is also important in behavioral motivation of waste evacuation. Lower urinary tract afferents can be modulated at multiple levels by corticolimbic centers, determining the interoception of physiological condition and the consequent emotional motor responses. Alterations in cognitive modulation, descending modulation, and hypervigilance are important in functional (symptom-based) clinical disorders.

Early elimination dysfunction associated with cephalic anomalies: is there a link?

Elimination dysfunction in children can be related to three main aetiologies: 1) spinal cord anomalies, 2) social and environmental disorders, and 3) syndromic elimination disorders. From this last group, we report cases of a previously undescribed combination of elimination disorders and cephalic anomalies symptoms which may constitute a proper entity for which conventional treatments may fail. A comprehensive review of congenital elimination disorders is given.

PATIENTS AND METHODS

Six patients (four boys, two girls) presenting with early elimination dysfunction associated with cephalic anomalies were assessed and treated between 1994 and 2005. None presented with identified lower urinary tract obstruction or spinal cord anomalies. Follow up ranged between 5.5 and 11.5 (mean 6.7) years.

RESULTS

All six had early elimination disorders, represented by urine retention, urinary tract infections, constipation and soiling. All had facial dysmorphy and cerebral anomalies with developmental delay of varying severity. All had a dilated urinary tract, with severe vesicoureteral reflux in five and one megaureter without reflux. All had abnormal renal isotope scans, two associated with chronic renal failure. The family medical history was significant in some cases. Treatment included early urinary diversion, and there was a high failure rate for ureteral reimplantation.

CONCLUSION

The combination of congenital elimination dysfunction with facial anomalies, developmental retardation, cephalic anomalies, abnormal urinary tracts, without identified spinal cord disorders or lower urinary tract obstruction, may represent a defined population of children. Identification may lead to early elimination support measures including temporary bladder diversion, Mitrofanoff diversion, alpha blockers and bowel transit medications.

Neurophysiology in neurourology

The bladder has only two essential functions. It stores and periodically empties liquid waste. Yet it is unique as a visceral organ, allowing integrated volitional and autonomous control of continence and voiding. Normal function tests the integrity of the nervous system at all levels, extending from the neuroepithelium of the bladder wall to the frontal cortex of the brain. Thus, dysfunction is common with impairment of either the central or peripheral nervous system. This monograph presents an overview of the neural control of the bladder as it is currently understood. A description of pertinent peripheral anatomy and neuroanatomy is provided, followed by an explanation of common neurophysiological tests of the lower urinary tract and associated structures, including both urodynamic and electrodiagnostic approaches. Clinical applications are included to illustrate the impact of nervous system dysfunction on the bladder and to provide indications for testing.

Different brain effects during chronic and acute sacral neuromodulation in urge incontinent patients with implanted neurostimulators

OBJECTIVE

To compare changes in regional cerebral blood flow (rCBF), using positron emission tomography (PET), during chronic and acute sacral neuromodulation (SN). SN is an effective long-term treatment for chronic urge incontinence due to urinary bladder hyperactivity, as sensory nerves, spinal and supraspinal structures are probably responsible for the action of SN. It is not known which brain areas are involved, and the optimum benefit of SN is not immediate, suggesting that induced plasticity of the brain is necessary.

PATIENTS AND METHODS

Brain activity was measured in two groups: 12 urge incontinent patients (11 women and one man; mean age 52 years) in whom an implanted unilateral S3 nerve neurostimulator had been effective for >6 months (mean time after implantation 4.5 years); and eight urge incontinent patients (seven women and one man; mean age 49 years) in whom the neurostimulator was activated for the first time in the PET scanner.

RESULTS

During SN in chronically implanted patients, there were significant decreases in rCBF in the middle part of the cingulate gyrus, the ventromedial orbitofrontal cortex, midbrain and adjacent midline thalamus, and rCBF increases in the dorsolateral prefrontal cortex. During acute SN in newly implanted patients, there were significant decreases in rCBF the medial cerebellum, and increases in the right postcentral gyrus cortex, the right insular cortex and the ventromedial orbitofrontal cortex. Group analysis between chronic and newly implanted patients showed significant differences in the associative sensory cortex, premotor cortex and the cerebellum, all three involved in learning behaviour.

CONCLUSIONS

These findings suggests that chronic SN influences, presumably via the spinal cord, brain areas previously implicated in detrusor hyperactivity, awareness of bladder filling, the urge to void and the timing of micturition. Furthermore, SN affects areas involved in alertness and awareness. Acute SN modulates predominantly areas involved in sensorimotor learning, which might become less active during the course of chronic SN.

Voluntary pelvic floor muscle control—an fMRI study

Storage and periodic expulsion of urine by the bladder are controlled by central pathways and organized as simple on-off switching circuits. Several reports concerning aspects of micturition control have identified distinct regions in the brainstem, like the pontine micturition center (PMC) and the periaqueductal gray (PAG), as well as the cerebellum, basal ganglia, limbic system, and cortical areas that are organized in a widespread network. The present study focused on the involvement of these specific brain regions in pelvic floor muscle control. Functional magnetic resonance imaging (fMRI) was performed at 3T in 11 healthy women with urge to void due to a filled bladder, who were instructed to either imitate voiding by releasing or to imitate interruption of voiding by contracting pelvic floor muscles. None of the subjects was able to start voiding during the experiments, presumably due to subconscious restraint resulting from the inconvenient situation. Relaxation and contraction of pelvic floor muscles induced strong and similar activation patterns including frontal cortex, sensory-motor cortex, cerebellum, and basal ganglia. Furthermore, well-localized activations in the PMC and the PAG were identified. To our knowledge, this is the first study using fMRI to demonstrate micturition-related activity in these brainstem structures. The presented approach proved to characterize the widespread central network in pelvic floor muscle control. Thus, in patients with voiding dysfunction, fMRI will be useful to elucidate the individual disturbance level.

Bladder dysfunction in Parkinsonism: Mechanisms, prevalence, symptoms, and management

The advent of functional imaging methods has increased our understanding of the neural control of the bladder. This review examines current concepts of the role of brain function in urinary control with particular emphasis on the putative role of dopamine receptors. Dopaminergic mechanisms play a profound role in normal bladder control and the dysfunction of these may result in symptoms of overactive bladder in Parkinsonism. The importance of this nonmotor disorder has been overlooked. We address the problem of bladder dysfunction as it presents to patients and their neurologist. The prevalence of bladder symptoms in Parkinson's disease is high; the most common complaint is nocturia followed by frequency and urgency. In multiple-system atrophy, the combination of urge and urge incontinence and poor emptying may result in a complex combination of complaints. The management of bladder dysfunction in Parkinsonism addresses treatment of overactive detrusor as well as incontinence.

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.

Functional brain imaging and the bladder: New insights into cerebral control over micturition

Mechanisms for cerebral control over the micturition process remain poorly elucidated. The knowledge is based largely on human pathophysiology and data derived from electrophysiologic testing in animals. Recent advances in dynamic functional brain imaging technologies including positron-emission tomography, single photon emission computed tomography, and functional magnetic resonance imaging have allowed new insights into how the human brain regulates this process. This article discusses animal studies, which provided the foundation for our understanding of cerebral control over micturition, and recent human studies, implementing functional brain imaging to enhance our knowledge of this complex phenomenon.