A bladder-to-bladder cooling reflex in the cat

[Noninvasive peripheral magnetic stimulation in the treatment of neurogenic urination disorders in children]

Neurogenic urination disorders in children are often clinically represented by urinary incontinence (UI). The prevalence of UI reaches 8.6%, but tends to decrease in frequency with age. One of the methods of non-drug therapy of UI is extracorporeal magnetic stimulation (ExMI) - a type of non-invasive peripheral magnetic stimulation, which is widely used in adult urological practice. However, the effectiveness of the method in children has not been studied.

OBJECTIVE

To study the effectiveness and safety of ExMI in the rehabilitation of children with neurogenic UI.

MATERIAL AND METHODS

A prospective open randomized comparative clinical trial included 75 children (from 5 years to 16 years and 6 months) with neurogenic UI, who were divided by simple randomization into a main group (n=39), who received a standard rehabilitation and ExMI program for 21 days, and a comparison group (n=36), in which the standard rehabilitation program did not include the use of ExMI.

RESULT AND DISCUSSION

A prospective open randomized comparative study revealed that the clinical effectiveness of the ExMI method in the complex rehabilitation of children with neurogenic UI is 94.8%, which is 25.4% higher than in the comparison group. After treatment, patients in the main group had a noticeable decrease in UI episodes, an increase in the micturition volume, and an improvement in the quality of life. Patients with various background neurological pathology responded to treatment, which indicates the common pathogenetic mechanisms of the development of LUTS in these conditions and the independence of the final effect from the basic diagnosis.

CONCLUSION

The use of the perineal ExMI method in children with neurogenic UI increases the effectiveness of rehabilitation and is a promising and safe direction of rehabilitation treatment.

Relevance of dog as an animal model for urologic diseases

We utilize animal models in urologic research to improve understanding of urinary physiology, determine the etiology of many urologic diseases, and discover and test novel therapeutic interventions. Dogs have a similar urinary tract anatomy and physiology to human and they develop many urologic diseases spontaneously. This chapter offers detailed comparisons of urinary tract anatomy, physiology, and the most common urologic diseases between humans and dogs. Dogs offer a unique opportunity for urologic research because they can be studied in research colonies and in client owned cohorts. Dogs also are among a limited number of non-human species that require continence and socially appropriate urinary behaviors (ex. going to the bathroom outside, training to not have submissive urination, etc.). These features make dogs unique in the animal kingdom and make them an ideal animal model for urologic research.

Overactive Bladder Symptoms Within Nervous System: A Focus on Etiology

Overactive bladder (OAB) is a common debilitating condition characterized by urgency symptoms with detrimental effects on the quality of life and survival. The exact etiology of OAB is still enigmatic, and none of therapeutic approaches seems curative. OAB is generally regarded as a separate syndrome, whereas in clinic, OAB symptoms could be found in numerous diseases of other non-urogenital systems, particularly nervous system. The OAB symptoms in neurological diseases are often poorly recognized and inadequately treated. This review provided a comprehensive overview of recent findings related to the neurogenic OAB symptoms. Relevant neurological diseases could be mainly divided into seven kinds as follows: multiple sclerosis and related neuroinflammatory disorders, Parkinson’s diseases, multiple system atrophy, spinal cord injury, dementia, peripheral neuropathy, and others. Concurrently, we also summarized the hypothetical reasonings and available animal models to elucidate the underlying mechanism of neurogenic OAB symptoms. This review highlighted the close association between OAB symptoms and neurological diseases and expanded the current knowledge of pathophysiological basis of OAB. This may increase the awareness of urological complaints in neurological disorders and inspire robust therapies with better outcomes.

Sophisticated regulation of micturition: review of basic neurourology

The neurological regulation of the lower urinary tract can be viewed separately from the perspective of sensory neurons and motor neurons. First, in the receptors of the bladder and urethra of sensory nerves, sensations are transmitted through the periaqueductal gray matter of the midbrain to the cerebral cortex, and the cerebrum goes through the process of decision-making. Motor neurons are divided into upper motor neurons (UMNs) and lower motor neurons (LMNs). UMNs coordinate storage and micturition in the brain stem so that synergic voiding can occur. LMNs facilitate muscle contractions in the spinal cord. The muscles involved in urinary storage and micturition are innervated by the somatic branches of sympathetic, parasympathetic, and peripheral nerves. Sympathetic nerves are responsible for contractions of urethral smooth muscles, while parasympathetic nerves originate from S2–S4 and are in charge of contractions of the bladder muscle. Somatic nerves originate from the motor neurons in Onuf’s nucleus, which is a specific part of somatic nerves. In this review, we will investigate the structures of the nervous systems related to the lower urinary tract and the regulatory system of innervation for the urinary storage and micturition and discuss the clinical significance and future prospects of neurourological research.

Current View of Diagnosing Small Fiber Neuropathy

Small fiber neuropathy (SFN) is a disorder of the small myelinated Aδ-fibers and unmyelinated C-fibers [5, 6]. SFN might affect small sensory fibers, autonomic fibers or both, resulting in sensory changes, autonomic dysfunction or combined symptoms [7]. As a consequence, the symptoms are potentially numerous and have a large impact on quality of life [8]. Since diagnostic methods for SFN are numerous and its pathophysiology complex, this extensive review focusses on categorizing all aspects of SFN as disease and its diagnosis. In this review, sensitivity in combination with specificity of different diagnostic methods are described using the areas under the curve. In the end, a diagnostic work-flow is suggested based on different phenotypes of SFN.

A Nomogram to Characterize the Severity of Detrusor Overactivity during the Ice Water Test: Description of the Method and Proof of Concept

AIMS

To develop a nomogram with severity categories for detrusor overactivity (DO).

METHODS

By conducting ice water tests (IWT) in 55 patients with Parkinson's disease, we identified criteria to describe characteristics of the detrusor pressure curves: (1) a gradient of Δpdet over Δt at the maximum detrusor pressure and (2) the area under the curve. In a nomogram, 10 severity categories of DO were established: 1 and 2 were assigned to group A (mild), 3 and 4 to group B (moderate) and 5-10 to group C (severe).

RESULTS

In the nomogram, negative IWT (20) appeared in category 1. Positive IWT (35) spread over the categories 1-8, 17 in group A, 11 in group B and 7 in categories 5-10. A relationship of incontinence episodes and nomogram category was observed. The nomogram category was reproducible in repeated IWT. Therapeutic interventions to treat DO lowered the nomogram category.

CONCLUSION

From the relationship of detrusor pressure and time in the IWT, a nomogram with 10 severity categories of DO was developed. First observations show a relationship of nomogram category and the number of incontinence episodes, reproducibility in repeated tests and the representation of effects of therapeutic interventions to treat DO.

Is Detrusor Contraction during Rapid Bladder Filling Caused by Cold or Warm Water? A Randomized, Controlled, Double-Blind Trial

PURPOSE

We investigated whether detrusor contraction during rapid bladder filling is provoked by cold or warm water.

MATERIALS AND METHODS

Patients with neurogenic lower urinary tract dysfunction were included in this randomized, controlled, double-blind trial. At the end of a standard urodynamic investigation patients underwent 2 bladder fillings using a 4C ice water test or a 36C warm water test saline solution at a filling speed of 100 ml per minute. The order was randomly selected, and patients and investigators were blinded to the order. The primary outcome measure was detrusor overactivity, maximum detrusor pressure and maximum bladder filling volume during the ice and warm water tests.

RESULTS

Nine women and 31 men were the subject of data analysis. Neurogenic lower urinary tract dysfunction was caused by spinal cord injury in 33 patients and by another neurological disorder in 7. Irrespective of test order detrusor overactivity occurred significantly more often during the ice water test than during the warm water test (30 of 40 patients or 75% vs 25 of 40 or 63%, p = 0.02). When comparing the ice water test to the warm water test, maximum detrusor pressure was significantly higher and maximum bladder filling volume was significantly lower during the ice water test (each p <0.001). The order of performing the tests (ice water first vs warm water first) had no effect on the parameters.

CONCLUSIONS

Our findings imply that the more frequent detrusor overactivity, higher maximum detrusor pressure and lower bladder filling volume during the ice water test compared to the warm water test were caused by cold water. This underlies the theory of a C-fiber mediated bladder cooling reflex in humans.

[The ice water test and bladder cooling reflex. Physiology, pathophysiology and clinical importance]

BACKGROUND

Urodynamic studies are utilised for identification and follow-up of functional disorders of the lower urinary tract. Provocation tests are used to determine disorders which could not be revealed in standard cystometry. The ice water test is a simple test to identify neurogenic bladder dysfunction and to screen the integrity of the upper motor neuron in neurogenic bladder dysfunction.

OBJECTIVES

Development and significance of the ice water test is presented in this review against the background of physiology and pathophysiology of the lower urinary tract.

MATERIALS AND METHODS

A systematic review of PubMed and ScienceDirect databases was performed in April 2015. No language or time limitation was applied. The following key words and Medical Subject Heading terms were used to identify relevant studies: "ice water test", "bladder cooling reflex", "micturition" and "neuronal control". Review articles and bibliographies of other relevant studies identified were hand searched to find additional studies.

RESULTS

The ice water test is performed by rapid instillation of 4-8 °C cold fluid into the urinary bladder. Hereby, afferent C fibers are activated by cold receptors in the bladder leading to the bladder cooling reflex. It is a spinal reflex which causes an involuntarily contraction of the urinary bladder. The test is normally positive in young infants during the first 4 years of life and become negative with maturation of the central nervous system afterwards by inhibition of the reflex. The damage of the upper motor neuron causes the recurrence of the reflex in the adulthood and indicates spinal and cerebral lesions.

DISCUSSION

The ice water test is utilised to identify lesions of the upper motor neuron. However, in the case of detrusor acontractility the test will always be negative and can not be utilized to distinguish between neurogenic or muscular causes. Furthermore, the test is also positive in a small percentage of cases of non-neurogenic diseases, e.g. in prostate-related bladder outlet obstruction or idiopathic overactive bladder. Although no clear explanation exists, a positive ice water test could be the first sign of an otherwise asymptomatic neurological disease.

CONCLUSIONS

Due to the simple procedure, the ice water test is a reliable possibility to identify neurologic bladder hyperactivity subsequent to standard cystometry.

Anatomy and physiology of the lower urinary tract

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. Neural control of micturition is organized as a hierarchic system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brainstem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brainstem 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 during the early postnatal period, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults cause re-emergence of involuntary micturition, leading to urinary incontinence. The mechanisms underlying these pathologic changes are discussed.

Differential functional brain network connectivity during visceral interoception as revealed by independent component analysis of fMRI TIME-series

Influential theories of brain-viscera interactions propose a central role for interoception in basic motivational and affective feeling states. Recent neuroimaging studies have underlined the insula, anterior cingulate, and ventral prefrontal cortices as the neural correlates of interoception. However, the relationships between these distributed brain regions remain unclear. In this study, we used spatial independent component analysis (ICA) and functional network connectivity (FNC) approaches to investigate time course correlations across the brain regions during visceral interoception. Functional magnetic resonance imaging (fMRI) was performed in thirteen healthy females who underwent viscerosensory stimulation of bladder as a representative internal organ at different prefill levels, i.e., no prefill, low prefill (100 ml saline), and high prefill (individually adapted to the sensations of persistent strong desire to void), and with different infusion temperatures, i.e., body warm (∼37°C) or ice cold (4-8°C) saline solution. During Increased distention pressure on the viscera, the insula, striatum, anterior cingulate, ventromedial prefrontal cortex, amygdalo-hippocampus, thalamus, brainstem, and cerebellar components showed increased activation. A second group of components encompassing the insula and anterior cingulate, dorsolateral prefrontal and posterior parietal cortices and temporal-parietal junction showed increased activity with innocuous temperature stimulation of bladder mucosa. Significant differences in the FNC were found between the insula and amygdalo-hippocampus, the insula and ventromedial prefrontal cortex, and the ventromedial prefrontal cortex and temporal-parietal junction as the distention pressure on the viscera increased. These results provide new insight into the supraspinal processing of visceral interoception originating from an internal organ.

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.

The role of TRPM8 in the Guinea-pig bladder-cooling reflex investigated using a novel TRPM8 antagonist

Patients with overactive bladder often exhibit abnormal bladder contractions in response to intravesical cold saline (positive ice-water test). The molecular entity involved in cold sensation within the urinary bladder is unknown, but a potential candidate is the ion channel, transient receptor potential (melastatin)-8 (TRPM8). The objective of the present study was to investigate the role of TRPM8 in a bladder-cooling reflex evoked in anaesthetised guinea-pigs that is comparable to the positive ice-water test seen in patients. Guinea-pig TRPM8 was cloned from L6 dorsal root ganglia (DRG) and expressed in HEK293 cells. Functional agonist- and cold-induced Ca2+ influx and electrophysiology assays were performed in these cells, and for comparison in HEK293 cells expressing human TRPM8, using a novel TRPM8 antagonist, the S-enantiomer of 1-phenylethyl 4-(benzyloxy)-3-methoxybenzyl (2-aminoethyl) carbamate hydrochloride (PBMC). Potency data from these assays was used to calculate intravenous infusion protocols for targeted plasma concentrations of PBMC in studies on micturition reflexes evoked by intravesical infusion of menthol or cold saline in anaesthetised guinea-pigs. Tissue expression of TRPM8 in guinea-pig bladder, urethra and in dorsal root ganglia neurones traced from the bladder was also investigated. TRPM8 mRNA and protein were detected in L6 dorsal root ganglia, bladder urothelium and smooth muscle. PBMC antagonised in vitro activation of human and guinea-pig TRPM8 and reversed menthol and cold-induced facilitation of the micturition reflex at plasma concentrations consistent with in vitro potencies. The present data suggest that the bladder-cooling reflex in the guinea-pig involves TRPM8. The potential significance of TRPM8 in bladder disease states deserves future investigation.

TRP channels in lower urinary tract dysfunction

Lower urinary tract dysfunction (LUTd) represents a major healthcare problem. Although it is mostly not lethal, associated social disturbance, medical costs, loss of productivity and especially diminished quality of life should not be underestimated. Although more than 15% of people suffer from a form of LUTd to some extent, pathophysiology often remains obscure. In the past 20 years, transient receptor potential (TRP) channels have become increasingly important in this field of research. These intriguing ion channels are believed to be the main molecular sensors that generate bladder sensation. Therefore, they are intensely pursued as new drug targets for both curative and symptomatic treatment of different forms of LUTd. TRPV1 was the first of its class to be investigated. Actually, even before this channel was cloned, it had already been targeted in the bladder, with clinical trials of intravesical capsaicin instillations. Several other polymodally gated TRP channels, particularly TRPM8, TRPA1 and TRPV4, also appear to play a prominent role in bladder (patho)physiology. With this review, we provide a brief overview of current knowledge on the role of these TRP channels in LUTd and their potential as molecular targets for treatment.

Neural mechanisms underlying lower urinary tract dysfunction

This article summarizes anatomical, neurophysiological, and pharmacological studies in humans and animals to provide insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract and alterations in these mechanisms in lower urinary tract dysfunction. 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 bladder, urethra, and external urethral sphincter. During urine storage, the outlet is closed and the bladder smooth muscle is quiescent. When bladder volume reaches the micturition threshold, activation of a micturition center in the dorsolateral pons (the pontine micturition center) induces a bladder contraction and a reciprocal relaxation of the urethra, leading to bladder emptying. During voiding, sacral parasympathetic (pelvic) nerves provide an excitatory input (cholinergic and purinergic) to the bladder and inhibitory input (nitrergic) to the urethra. These peripheral systems are integrated by excitatory and inhibitory regulation at the levels of the spinal cord and the brain. Therefore, injury or diseases of the nervous system, as well as disorders of the peripheral organs, can produce lower urinary tract dysfunction, leading to lower urinary tract symptoms, including both storage and voiding symptoms, and pelvic pain. Neuroplasticity underlying pathological changes in lower urinary tract function is discussed.

Organization of the neural switching circuitry underlying reflex micturition

The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain and spinal cord that coordinates the activity of the bladder and urethral outlet. Experimental studies in animals indicate that urine storage is modulated by reflex mechanisms in the spinal cord, whereas voiding is mediated by a spinobulbospinal pathway passing through a coordination centre in the rostral brain stem. Many of the neural circuits controlling micturition exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. This study summarizes the anatomy and physiology of the spinal and supraspinal micturition switching circuitry and describes a computer model of these circuits that mimics the switching functions of the bladder and urethra at the onset of micturition.

Function and expression pattern of TRPM8 in bladder afferent neurons associated with bladder outlet obstruction in rats

We investigated the function and expression pattern of the transient receptor potential melastatin-8 (TRPM8) in urinary bladder afferent neurons from control and bladder outlet obstruction (BOO) rats. BOO was produced and, after six weeks, the effects of intravesical infusion of menthol, the agonist of TRPM8, were investigated using unanesthetized cystometry. The intravesical infusion of menthol produced an increase in the micturition pressure in both sham surgery and BOO rats. In BOO rats, increased basal and threshold pressure and a decreased micturition interval were observed. Next, the population of TRPM8-positive and the co-expression proportion of TRPM8 with neurochemical markers (NF200 or TRPV1) in the bladder afferent neurons were each compared between the control and BOO rats using retrograde tracing and immunohistochemistry. The population of TRPM8-immunoreactive bladder afferent neurons was larger in BOO rats (3.28±0.43%) than in the control rats (1.33±0.18%). However, there were no statistical differences between the control and BOO rats in the co-expression proportion of neither TRPM8-NF200 (84.1±4.3% vs 79.7±2.7%, p=0.41) nor TRPM8-TRPV1 (33.3±3.6% vs 40.8±2.6%, p=0.08) in the bladder afferent neurons. The present results suggest that the neuronal input through TRPM8-positive bladder afferent neurons are augmented after BOO, however, the neurochemical phenotype of the up-regulated TRPM8-positive bladder afferent neurons is not changed after BOO.

Antimuscarinic effects on current perception threshold: a prospective placebo control study

AIMS

To evaluate the effect of Tolterodine on urethral and bladder afferent nerves in women with detrusor overactivity (DO) in comparison to placebo, by studying the changes in the current perception threshold (CPT).

METHODS

Women with overactive bladder symptoms and idiopathic DO were recruited and randomized in a double-blind manner between placebo and tolterodine extended release. All women underwent CPT testing of the bladder and urethra using a Neurometer constant current stimulator. CPT values were determined at three frequencies, including 2,000 Hz (corresponding to Aβ-fibers), 250 Hz (corresponding to Aδ-fibers), and 5 Hz (corresponding to C fibers) before and 7 days on treatment. CPT values before and on treatment were compared using a Wilcoxon Signed Rank test.

RESULTS

Twenty women (mean age 46 years) were studied. There was no statistical difference between the two groups in terms of age, ethnicity, severity of symptoms and pre-treatment CPT values. Only in the tolterodine group there was a significantly increased CPT value at 5 and 250 Hz upon both urethral and bladder stimulation after 1 week of treatment. When compared with placebo, women taking tolterodine had significantly increased Bladder CPT values at 5 Hz (P-value <0.05). The electrical stimulation with 5 Hz was described as urgency.

CONCLUSIONS

This is a randomized placebo control study evaluating the effect of antimuscarinics on sensory nerve function in women with DO. Our results support the animal studies that antimuscarinics have an effect on sensory function.

Plasticity in reflex pathways to the lower urinary tract following spinal cord injury

The lower urinary tract has two main functions, storage and periodic expulsion of urine, that 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 external urethra sphincter). During urine storage the outlet is closed and the bladder is quiescent to maintain a low intravesical pressure. During micturition the outlet relaxes and the bladder contracts to promote efficient release of urine. This reciprocal relationship between bladder and outlet is generated by 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 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 function. Following spinal cord injury the bladder is initially areflexic but then becomes hyperreflexic due to the emergence of a spinal micturition reflex pathway. However the bladder does not empty efficiently because coordination between the bladder and urethral outlet is lost. Studies in animals indicate that dysfunction of the lower urinary tract after spinal cord injury is dependent in part on plasticity of bladder afferent pathways as well as reorganization of synaptic connections in the spinal cord. Reflex 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/or the peripheral target organs.

Basic bladder neurophysiology

Maintenance of normal lower urinary tract function is a complex process that requires coordination between the central nervous system and the autonomic and somatic components of the peripheral nervous system. This article provides an overview of the basic principles that are recognized to regulate normal urine storage and micturition, including bladder biomechanics, relevant neuroanatomy, neural control of lower urinary tract function, and the pharmacologic processes that translate the neural signals into functional results. Finally, the emerging role of the urothelium as a sensory structure is discussed.

Overactive bladder is not only overactive but also hypersensitive

OBJECTIVES

To evaluate differences in bladder filling sensations and current perception threshold (CPT) values between patients with and without overactive bladder (OAB), and to further investigate the correlation between CPT values and voiding patterns in OAB patients.

METHODS

Detrusor overactivity and bladder volumes at first sensation of bladder filling, first desire to void, and strong desire to void during filling cystometry were compared between 55 female patients with OAB and 42 with non-OAB. CPT measurements from the bladder mucosa taken after neuroselective electrostimulation at frequencies of 2000, 250, and 5 Hz were compared between the 2 groups. In OAB patients, the correlations between CPT values and voiding variables based on 3-day bladder diaries were investigated.

RESULTS

OAB patients showed significantly more detrusor overactivity than non-OAB patients (P <.05). Bladder volumes at first sensation of bladder filling, first desire to void, and strong desire to void were significantly lower in OAB patients than in non-OAB patients (P <.05). CPT values at all 3 frequencies were also significantly lower in OAB patients (P <.05). The total number of urgency episodes correlated with CPT values at 250 (r = -0.274, P = .045) and 5 Hz (r = -0.293, P = .032). The total number of urge incontinence episodes also correlated with CPT values at 250 (r = -0.279, P = .041) and 5 Hz (r = -0.272, P = .046).

CONCLUSIONS

Bladder sensory profiles displayed a more sensitive bladder in OAB patients compared with non-OAB subjects. OAB patients may have bladders that are not only overactive, but also hypersensitive.

Changes in afferent activity after spinal cord injury

AIMS

To summarize the changes that occur in the properties of bladder afferent neurons following spinal cord injury.

METHODS

Literature review of anatomical, immunohistochemical, and pharmacologic studies of normal and dysfunctional bladder afferent pathways.

RESULTS

Studies in animals indicate that the micturition reflex is mediated by a spinobulbospinal pathway passing through coordination centers (periaqueductal gray and pontine micturition center) located in the rostral brain stem. This reflex pathway, which is activated by small myelinated (Adelta) bladder afferent nerves, is in turn modulated by higher centers in the cerebral cortex involved in the voluntary control of micturition. Spinal cord injury at cervical or thoracic levels disrupts voluntary voiding, as well as the normal reflex pathways that coordinate bladder and sphincter function. Following spinal cord injury, the bladder is initially areflexic but then becomes hyperreflexic due to the emergence of a spinal micturition reflex pathway. The recovery of bladder function after spinal cord injury is dependent in part on the plasticity of bladder afferent pathways and the unmasking of reflexes triggered by unmyelinated, capsaicin-sensitive, C-fiber bladder afferent neurons. Plasticity is associated with morphologic, chemical, and electrical changes in bladder afferent neurons and appears to be mediated in part by neurotrophic factors released in the spinal cord and the peripheral target organs.

CONCLUSIONS

Spinal cord injury at sites remote from the lumbosacral spinal cord can indirectly influence properties of bladder afferent neurons by altering the function and chemical environment in the bladder or the spinal cord.

Visceral pain: the neurophysiological mechanism

The mechanism of visceral pain is still less understood compared with that of somatic pain. This is primarily due to the diverse nature of visceral pain compounded by multiple factors such as sexual dimorphism, psychological stress, genetic trait, and the nature of predisposed disease. Due to multiple contributing factors there is an enormous challenge to develop animal models that ideally mimic the exact disease condition. In spite of that, it is well recognized that visceral hypersensitivity can occur due to (1) sensitization of primary sensory afferents innervating the viscera, (2) hyperexcitability of spinal ascending neurons (central sensitization) receiving synaptic input from the viscera, and (3) dysregulation of descending pathways that modulate spinal nociceptive transmission. Depending on the type of stimulus condition, different neural pathways are involved in chronic pain. In early-life psychological stress such as maternal separation, chronic pain occurs later in life due to dysregulation of the hypothalamic-pituitary-adrenal axis and significant increase in corticotrophin releasing factor (CRF) secretion. In contrast, in early-life inflammatory conditions such as colitis and cystitis, there is dysregulation of the descending opioidergic system that results excessive pain perception (i.e., visceral hyperalgesia). Functional bowel disorders and chronic pelvic pain represent unexplained pain that is not associated with identifiable organic diseases. Often pain overlaps between two organs and approximately 35% of patients with chronic pelvic pain showed significant improvement when treated for functional bowel disorders. Animal studies have documented that two main components such as (1) dichotomy of primary afferent fibers innervating two pelvic organs and (2) common convergence of two afferent fibers onto a spinal dorsal horn are contributing factors for organ-to-organ pain overlap. With reports emerging about the varieties of peptide molecules involved in the pathological conditions of visceral pain, it is expected that better therapy will be achieved relatively soon to manage chronic visceral pain.

Afferent nerve regulation of bladder function in health and disease

The afferent innervation of the urinary bladder consists primarily of small myelinated (Adelta) and unmyelinated (C-fiber) axons that respond to chemical and mechanical stimuli. Immunochemical studies indicate that bladder afferent neurons synthesize several putative neurotransmitters, including neuropeptides, glutamic acid, aspartic acid, and nitric oxide. The afferent neurons also express various types of receptors and ion channels, including transient receptor potential channels, purinergic, muscarinic, endothelin, neurotrophic factor, and estrogen receptors. Patch-clamp recordings in dissociated bladder afferent neurons and recordings of bladder afferent nerve activity have revealed that activation of many of these receptors enhances neuronal excitability. Afferent nerves can respond to chemicals present in urine as well as chemicals released in the bladder wall from nerves, smooth muscle, inflammatory cells, and epithelial cells lining the bladder lumen. Pathological conditions alter the chemical and electrical properties of bladder afferent pathways, leading to urinary urgency, increased voiding frequency, nocturia, urinary incontinence, and pain. Neurotrophic factors have been implicated in the pathophysiological mechanisms underlying the sensitization of bladder afferent nerves. Neurotoxins such as capsaicin, resiniferatoxin, and botulinum neurotoxin that target sensory nerves are useful in treating disorders of the lower urinary tract.

Emerging drugs for treatment of overactive bladder and detrusor overactivity

BACKGROUND

Overactive bladder (OAB) signifies the presence of urinary urgency and can have major effects on quality of life and social functioning. Standard antimuscarinic drugs have good initial response rates but substantial adverse effects and long-term compliance problems.

OBJECTIVES

To review the complexities of the mechanisms underlying OAB and the current drugs available for treating its symptoms.

METHODS

The literature was reviewed to define current therapies and drugs in clinical trials. Articles were identified by means of a computerised PubMed and Cochrane Library search (using the following keywords: overactive bladder, detrusor overactivity, urgency and bladder), supported by a search of the PharmaProjects database.

CONCLUSIONS

New drug classes, such as beta-3 adrenergic agonists, may work by reducing contractility or excitability of bladder muscle. Moderation of afferent activity may allow improved OAB symptoms, with lower risk of affecting voiding function. Agents acting on the CNS could influence OAB favourably, but target selection and adverse effects are an issue. The recognition of the functional contribution of the urothelium and the diversity of nerve transmitters has sparked interest in both peripheral and central modulation of OAB pathophysiology.

The neural control of micturition

Micturition, or urination, occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. The neural circuitry that controls this process is complex and highly distributed: it involves pathways at many levels of the brain, the spinal cord and the peripheral nervous system and is mediated by multiple neurotransmitters. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary or reflex micturition, leading to urinary incontinence. This is a major health problem, especially in those with neurological impairment. Here we review the neural control of micturition and how disruption of this control leads to abnormal storage and release of urine.

Urethral and Bladder Current Perception Thresholds: Normative Data in Women

PURPOSE

Given increased evidence of sensory dysfunction in lower urinary tract pathology, we determined normative current perception threshold values in the lower urinary tract of asymptomatic women.

MATERIALS AND METHODS

After receiving institutional review board approval women without lower urinary tract symptoms underwent current perception threshold testing of the urethra and bladder using a Neurometer constant current stimulator. Current perception threshold values were determined at 3 frequencies, including 2,000 Hz (corresponding to A-beta fibers), 250 Hz (corresponding to A-delta fibers) and 5 Hz (corresponding to C fibers).

RESULTS

A total of 48 women with a mean age of 38 years (range 23 to 67) underwent current perception threshold testing. Normative values were established for the urethra and bladder at 2,000, 250 and 5 Hz. Median urethral current perception thresholds at 2,000, 250 and 5 Hz were 1.2 (IQR 0.76-1.5), 0.45 (IQR 0.33-0.56) and 0.11 mA (IQR 0.07-0.24), respectively. Median bladder current perception thresholds at 2,000, 250 and 5 Hz were 4.1 (IQR 2.0-6.3), 2.3 (IQR 0.87-5.5) and 1.4 mA (IQR 0.22-2.9), respectively. Urethral and bladder current perception thresholds increased significantly with subject age at all 3 frequencies (p<0.0005). Prior pelvic surgery was associated with an increased bladder current perception threshold at all 3 frequencies (p<0.005) but not with the urethral current perception threshold.

CONCLUSIONS

We report urethral and bladder current perception thresholds for a large sample of asymptomatic women. These reference values may help elucidate changes in afferent nerve function in women with lower urinary tract dysfunction.

Electrophysiological characterization of vagal afferents relevant to mucosal nociception in the rat upper oesophagus

Emerging evidence indicates a nociceptive role of vagal afferents. A distinct oesophageal innervation in the rat, with muscular and mucosal afferents travelling predominantly in the recurrent (RLN) and superior laryngeal nerve (SLN), respectively, enabled characterization of mucosal afferents with nociceptive properties, using novel isolated oesophagus-nerve preparations. SLN and RLN single-fibre recordings identified 55 and 14 units, respectively, with none conducting faster than 8.7 m s(-1). Mucosal response characteristics in the SLN distinguished mechanosensors (n = 13), mechanosensors with heat sensitivity (18) from those with cold sensitivity (19) and a mechanoinsensitive group (5). The mechanosensitive fibres, all slowly adapting, showed a unimodal distribution of mechanical thresholds (1.4-128 mN, peak approximately 5.7 mN). No difference in response characteristics of C and Adelta fibres was encountered. Mucosal proton stimulation (pH 5.4 for 3 min), mimicking gastro-oesophageal reflux disease (GORD), revealed in 31% of units a desensitizing response that peaked around 20 s and faded within 60 s. Cold stimulation (15 degrees C) was proportionally encoded but the response showed slow adaptation. In contrast, the noxious heat (48 degrees C) response showed no obvious adaptation with discharge rates reflecting the temperature's time course. Polymodal (69%) mucosal units, > 30% proton sensitive, were found in each fibre category and were considered nociceptors; they are tentatively attributed to vagal nerve endings type I, IV and V, previously morphologically described. All receptive fields were mapped and the distribution indicates that the posterior upper oesophagus may serve as a 'cutbank', detecting noxious matters, ingested or regurgitated, and triggering nocifensive reflexes such as bronchoconstriction in GORD.

Sensory and biomechanical properties of the esophagus in non-erosive reflux disease

OBJECTIVES

To investigate possible differences between patients with non-erosive gastroesophageal reflux disease (NERD) and controls in a) sensitivity of the distal esophagus after mechanical and thermal stimuli and b) the referred pain areas.

MATERIAL AND METHODS

Fifteen healthy subjects (mean age 39+/-19.4 years) and 13 NERD patients (mean age 44.4+/-21 years) were enrolled in the study. Pain evoked by mechanical and thermal stimuli was assessed using a newly designed multimodal stimulation probe.

RESULTS

The patients were less sensitive to mechanical stimulation as assessed by the cross-sectional area (p<0.001) and volume (p=0.007). After thermal stimulation, the patients were hypersensitive to heat stimuli (p=0.04), whereas no significant difference was seen to cold stimuli. The referred pain areas were larger in patients compared with the pain areas in controls after mechanical (p=0.03) and heat stimuli (p=0.01), but not after cold stimuli. Balloon distension resulted in a significant higher number of reactive esophageal contractions in patients as compared with controls (p=0.001).

CONCLUSIONS

The present study showed that NERD patients were hypersensitive to heat stimuli of the esophagus, with an increase in referred pain to the evoked visceral pain. The data indicate that peripheral sensitization of heat-sensitive pathways together with facilitation of central pain mechanisms are important in the pathogenesis of NERD.

A bladder-cooling reflex in the anaesthetised guinea-pig: A model of the positive clinical ice-water test

INTRODUCTION

In patients with detrusor hyperreflexia, intravesical instillation of ice-cold water results in the development of involuntary bladder contractions at volumes less than normal cystometric capacity. This is referred to as a positive ice-water test (+IWT) and can be reversed by vanilloid receptor agonists and potentiated by menthol. The present study was designed to investigate the existence of an analogous cooling reflex in the guinea-pig bladder that could be used as a small animal model in order to test the effects of drugs on the reflex.

METHODS

Bladder pressure and external urethral sphincter electromyogram (EUS EMG) were recorded in alpha-chloralose/urethane anaesthetised guinea-pigs during rapid infusion of cold or warm saline into the bladder with or without prior intravesical exposure to menthol or resiniferatoxin (RTX).

RESULTS

The mean control micturition threshold volume (TV) of 2.58 ml at 38 degrees C was reduced to 1.52 ml in response to saline infusion at 3 degrees C (P=0.001). The cold-induced reduction in TV was reproducible during several subsequent repeat infusions at 38 degrees C and 3 degrees C and was accompanied by decreases in bladder voiding pressure. The duration of the micturition reflex was markedly increased following cold compared with warm saline infusion (mean 24.5 s at 3 degrees C, 10.2 s at 38 degrees C, P=0.001) and was associated with oscillations in bladder pressure and concomitant bursting activity in the EUS EMG. During step-wise decreases in infusate temperature from 38 degrees C to 23 degrees C, 15 degrees C, 7 degrees C and 3 degrees C, the threshold infusate temperature to elicit a significant reduction in TV was 15 degrees C. The reduction in TV at 3 degrees C was potentiated by intravesical infusion of 0.6 mM menthol whilst intravesical infusion of 500 nM RTX reversed the reduction in TV at 3 degrees C.

DISCUSSION

These data suggest that a bladder-cooling reflex is present in the anaesthetised guinea-pig and represents a useful small animal model of the clinical +IWT.

Influence of temperature on urethra to bladder micturition reflex in the awake ewe

AIMS

The flow of fluid along the urethra is known to facilitate detrusor contraction during micturition. This reflex, previously described in awake ewes, helps to achieve complete bladder emptying. In anesthetized cats, another urethra to bladder reflex involving urethral cold receptors has been described. The aim of this study was to investigate whether the urethral reflex first described in awake ewes could also be temperature-dependent.

METHODS

Experiments were performed on 10 healthy ewes. Urethral flows were performed by injecting 10 ml saline (ranging from 17 to 43 degrees C) at the level of the proximal urethra. Catheterization of the bladder was performed so that detrusor pressure was continually recorded during the experiments.

RESULTS

Urethral flows using body temperature saline (37-39 degrees C) consistently evoked detrusor contraction. Urethral flows using saline at temperatures between 40 and 43 degrees C induced detrusor contractions that were not significantly different from those observed at 37-39 degrees C. Urethral flows using saline at temperatures below 37-39 degrees C (17-36 degrees C) resulted in a weaker or absent detrusor contraction.

CONCLUSIONS

In ewes, we have shown that urethral to bladder micturition reflex involving mechanoreceptors is decreased at temperatures below the physiological range. It is suggested that transient receptor potential vanilloid cation channels (e.g., TRPV4 which is activated by sheer/stress flows at near-body temperature) could be involved in this urethra to bladder reflex. In humans, this reflex has hardly been described and is still a matter of debate. Our results reinforce that its full investigation may require systematic use of a range of saline flows at different temperatures.

Effect of cold-induced stress on rat bladder tissue contractility and histomorphology

AIMS

To investigate the effects of cold-induced stress on bladder tissue histomorphology and contractility in a rat model.

METHODS

Eighteen male Sprague-Dawley rats were divided into three groups: Control group (Group 1), acute cold-stress group (Group 2, kept at +4 degrees C for 8 hr), and chronic cold-stress group (Group 3, kept at +4 degrees C for 4 hr/day for 21 days). At the end of protocols, histological examination of general bladder tissue morphology and determination of mast cells was performed. Organ bath studies were conducted at basal tone where contractile responses to 120 mM potassium, electrical field stimulation (EFS), and carbachol (10(-9)-10(-4) M) were assessed. Relaxation responses to EFS, isoproterenol (10(-9)-10(-4) M), papaverine plus sodium nitroprusside (10(-4) M each) were recorded in carbachol pre-contracted strips. All data were compared by one-way ANOVA test.

RESULTS

Group 1 revealed regular bladder mucosa with intact urothelium. Groups 2 and 3 showed degeneration of urothelium with accumulation of neutrophils and significantly increased number of mast cells in both mucosa and muscularis. Mast cell counts were significantly higher in Group 3 compared to Group 2. Contractile responses to 120 mM potassium and EFS were significantly greater in the control group compared to other groups. Carbachol caused dose-dependent contractions that were significantly higher in the control group (at 10(-5), 3 x 10(-5), and 10(-4) M doses). There was no statistical difference between the groups in terms of relaxation responses.

CONCLUSIONS

In vivo cold exposure induces significant bladder injury and decreased tissue contractility. Mechanistic pathways involved in the response of the urinary bladder to cold-induced stress need further investigation.

Effect of the intravesical resiniferatoxin instillation evaluated by the ice provocative urodynamic study

STUDY DESIGN

Prospective urodynamic investigation before and after intravesical resiniferatoxin instillation treatment.

OBJECTIVE

To evaluate the effectiveness of intravesical resiniferatoxin instillation for the treatment of neurogenic detrusor overactivity (NDO), using conventional and ice provocative urodynamic studies to monitor the activity of the unmyelinated C-fiber.

SETTING

Spinal Cord Injury Unit, Yonsei Rehabilitation Hospital, Seoul, Korea.

METHODS

A measure of 100 ml of resiniferatoxin solution, at a concentration of 100 nM diluted in 10% ethanol, was intravesically instilled into the bladder of 15 spinal cord injury patients with NDO. Conventional and ice provocative urodynamic studies were performed to evaluate the change in the involuntary detrusor activity, reflex volume, maximal bladder capacity, compliance, maximal detrusor pressure and reflex volume ratio 7 days before and 30 days after the instillation.

RESULTS

Before the intravesical resiniferatoxin instillation, all patients exhibited NDO in both the conventional and ice provocative urodynamic studies, with a mean reflex volume ratio of 0.45+/-0.22. There was no significant change in the maximal bladder capacity, compliance and maximal detrusor pressure at the follow-up urodynamic study, but the reflex volume ratio was significantly increased (P<0.05) after the intravesical resiniferatoxin instillation. Among the 15 patients, three (20%) showed complete and nine (60%) partial suppression of the unmyelinated C-fiber activities.

CONCLUSION

Intravesical resiniferatoxin instillation was partially controlled by the unmyelinated C-fiber activities, which were estimated by an ice provocative urodynamic study. Therefore, further studies on the optimal dosage and accurate indications for resiniferatoxin instillation are required.

Multimodal pain stimulations in patients with grade B oesophagitis

AIM

To obtain a better understanding of nociceptive processing in patients with oesophagitis.

PATIENTS AND METHODS

Eleven patients with grade B oesophagitis were compared with an age and sex matched group of 16 healthy subjects. A probe was positioned in the lower part of the oesophagus. After preconditioning of the tissue, painful mechanical stimuli were applied as distensions with a bag using an impedance planimetric method. Distensions were done before and after pharmacological impairment of distension induced smooth muscle contractions. Thermal stimulation was performed by recirculating water at 1 and 60 degrees C in the bag. The area under the temperature curve (AUC) represented caloric load. The referred pain area (being a proxy for the central pain mechanisms) to the mechanical stimuli was drawn at maximum pain intensities.

RESULTS

Patients were hyposensitive to mechanical stimuli, as assessed by the distending volume (F=8.1, p=0.005). After relaxation of smooth muscle with butylscopolamine, the difference between the two groups was more evident (F=27.4, p<0.001). AUC for cold stimulation was 1048.6 (242.7) degrees Cxs in controls and 889.8 (202.6) degrees Cxs in patients (p=0.5). For heat stimuli, AUC values were 323.3 (104.1) and 81.3 (32.3) degrees Cxs in controls and patients, respectively (p=0.04). The referred pain area to the mechanical stimulations was larger and more widespread in patients (49.3 (6.2) cm2 compared with controls 23.9 (7) cm2; p=0.02).

CONCLUSIONS

The data indicate that peripheral sensitisation of heat sensitive receptors and pathways combined with facilitation of central pain mechanisms may explain the symptoms in patients with oesophagitis.

Recurrent inhibition of the bladder C fibre reflex in the cat and its response to naloxone

Recurrent inhibition of the bladder C fibre reflex was studied in adult female cats anaesthetized with alpha-chloralose. Test reflexes were evoked by electrical stimulation of bladder Adelta and C afferents in the right pelvic nerve and were recorded from the proximal end of a small ipsilateral pelvic nerve branch, transected close to the bladder. Such test reflexes were consistently depressed by repetitive electrical stimulation of the contralateral bladder pelvic nerve (20 Hz, 20 s) at intensities sufficient to recruit axons of bladder preganglionic neurones. The inhibition could be evoked after transection of the left dorsal roots S1-S4 and the sympathetic supply to the bladder but was abolished by transection of the pelvic nerve central to the site of stimulation. Hence, it most likely involved central recurrent collaterals of antidromically activated bladder preganglionic neurones. The reflex suppression was quite considerable - maximal C fibre reflexes were reduced to a group mean of 25% (+/- 9% confidence interval) of their control size. The effect had a slow onset, requiring a few seconds of conditioning stimulation to be revealed, and was very long lasting (minutes). Naloxone (0.01-0.5 mg kg(-1) i.v.) abolished the recurrent inhibition of both the C fibre and Adelta bladder reflexes, while inhibition from afferents in the dorsal clitoris nerve remained unchanged. It is concluded that the segmental bladder C fibre reflex and the spino-ponto-spinal Adelta micturition reflex are both targets of recurrent inhibition from bladder parasympathetic preganglionic neurones and that the effect involves an enkephalinergic mechanism.

Cool and menthol receptor TRPM8 in human urinary bladder disorders and clinical correlations

BACKGROUND

The recent identification of the cold-menthol sensory receptor (TRPM8; CMR1), provides us with an opportunity to advance our understanding of its role in the pathophysiology of bladder dysfunction, and its potential mediation of the bladder cooling reflex. In this study, we report the distribution of the cool and menthol receptor TRPM8 in the urinary bladder in patients with overactive and painful bladder syndromes, and its relationship with clinical symptoms.

METHODS

Bladder specimens obtained from patients with painful bladder syndrome (PBS, n = 16), idiopathic detrusor overactivity (IDO, n = 14), and asymptomatic microscopic hematuria (controls, n = 17), were immunostained using specific antibodies to TRPM8; nerve fibre and urothelial immunostaining were analysed using fibre counts and computerized image analysis respectively. The results of immunohistochemistry were compared between the groups and correlated with the Pain, Frequency and Urgency scores.

RESULTS

TRPM8-immunoreactive staining was observed in the urothelium and nerve fibres scattered in the suburothelium. The nerve fibre staining was seen in fine-calibre axons and thick (myelinated) fibres. There was marked increase of TRPM8-immunoreactive nerve fibres in IDO (P = 0.0249) and PBS (P < 0.0001) specimens, compared with controls. A significantly higher number of TRPM8-immunoreactive axons were also seen in the IDO (P = 0.0246) and PBS (P < 0.0001) groups. Urothelial TRPM8 and TRPM8-immunoreactive thick myelinated fibres appeared unchanged in IDO and PBS. The relative density of TRPM8-immunoreactive nerve fibres significantly correlated with the Frequency (r = 0.5487, P = 0.0004) and Pain (r = 0.6582, P < 0.0001) scores, but not Urgency score.

CONCLUSION

This study demonstrates increased TRPM8 in nerve fibres of overactive and painful bladders, and its relationship with clinical symptoms. TRPM8 may play a role in the symptomatology and pathophysiology of these disorders, and may provide an additional target for future overactive and painful bladder pharmacotherapy.

Oxybutynin and its new transdermal application for the treatment of overactive bladder

It has long been accepted that antimuscarinic agents are the backbone of the pharmacological treatment of overactive bladder. Oxybutynin has been the gold standard of these medications for years due to its efficacy, but suffers from a lack of selectivity for the bladder, and extensive metabolism and lipophilicity result in significant side-effect issues. The transdermal delivery of oxybutynin turns this disadvantage of lipophilicity into an advantage. This, in turn, bypasses gastrointestinal absorption and metabolism by the cytochrome P450 system and reduces the breakdown into metabolites responsible for many of the side effects, while providing equivalent efficacy to the immediate-release oral formulation.

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.