Mechanical irritation induces neurogenic inflammation in the rat urethra

Best practices for cystometric evaluation of lower urinary tract function in muriform rodents

AIMS

Rodent cystometry has provided valuable insights into the impact of the disease, injury, and aging on the cellular and molecular pathways, neurologic processes, and biomechanics of lower urinary tract function. The purpose of this white paper is to highlight the benefits and shortcomings of different experimental methods and strategies and to provide guidance on the proper interpretation of results.

METHODS

Literature search, selection of articles, and conclusions based on discussions among a panel of workers in the field.

RESULTS

A range of cystometric tests and techniques used to explore biological phenomena relevant to the lower urinary tract are described, the advantages and disadvantages of various experimental conditions are discussed, and guidance on the practical aspects of experimental execution and proper interpretation of results are provided.

CONCLUSIONS

Cystometric evaluation of rodents comprises an extensive collection of functional tests that can be performed under a variety of experimental conditions. Decisions regarding which approaches to choose should be determined by the specific questions to be addressed and implementation of the test should follow standardized procedures.

Role of neurogenic inflammation in local communication in the visceral mucosa

Intense research has focused on the involvement of the nervous system in regard to cellular mechanisms underlying neurogenic inflammation in the pelvic viscera. Evidence supports the neural release of inflammatory factors, trophic factors, and neuropeptides in the initiation of inflammation. However, more recently, non-neuronal cells including epithelia, endothelial, mast cells, and paraneurons are likely important participants in nervous system functions. For example, the urinary bladder urothelial cells are emerging as key elements in the detection and transmission of both physiological and nociceptive stimuli in the lower urinary tract. There is mounting evidence that these cells are involved in sensory mechanisms and can release mediators. Further, localization of afferent nerves next to the urothelium suggests these cells may be targets for transmitters released from bladder nerves and that chemicals released by urothelial cells may alter afferent excitability. Modifications of this type of communication in a number of pathological conditions can result in altered release of epithelial-derived mediators, which can activate local sensory nerves. Taken together, these and other findings highlighted in this review suggest that neurogenic inflammation involves complex anatomical and physiological interactions among a number of cell types in the bladder wall. The specific factors and pathways that mediate inflammatory responses in both acute and chronic conditions are not well understood and need to be further examined. Elucidation of mechanisms impacting on these pathways may provide insights into the pathology of various types of disorders involving the pelvic viscera.

Serotonergic paraneurones in the female mouse urethral epithelium and their potential role in peripheral sensory information processing

AIM

The mechanisms underlying detection and transmission of sensory signals arising from visceral organs, such as the urethra, are poorly understood. Recently, specialized ACh-expressing cells embedded in the urethral epithelium have been proposed as chemosensory sentinels for detection of bacterial infection. Here, we examined the morphology and potential role in sensory signalling of a different class of specialized cells that express serotonin (5-HT), termed paraneurones.

METHODS

Urethrae, dorsal root ganglia neurones and spinal cords were isolated from adult female mice and used for immunohistochemistry and calcium imaging. Visceromotor reflexes (VMRs) were recorded in vivo.

RESULTS

We identified two morphologically distinct groups of 5-HT+ cells with distinct regional locations: bipolar-like cells predominant in the mid-urethra and multipolar-like cells predominant in the proximal and distal urethra. Sensory nerve fibres positive for calcitonin gene-related peptide, substance P, and TRPV1 were found in close proximity to 5-HT+ paraneurones. In vitro 5-HT (1 μm) stimulation of urethral primary afferent neurones, mimicking 5-HT release from paraneurones, elicited changes in the intracellular calcium concentration ([Ca2+ ]i ) mediated by 5-HT2 and 5-HT3 receptors. Approximately 50% of 5-HT responding cells also responded to capsaicin with changes in the [Ca2+ ]i . In vivo intra-urethral 5-HT application increased VMRs induced by urethral distention and activated pERK in lumbosacral spinal cord neurones.

CONCLUSION

These morphological and functional findings provide insights into a putative paraneurone-neural network within the urethra that utilizes 5-HT signalling, presumably from paraneurones, to modulate primary sensory pathways carrying nociceptive and non-nociceptive (mechano-sensitive) information to the central nervous system.

Evidence of a functional effect of transient transurethral catheterization on micturition in women

INTRODUCTION AND HYPOTHESIS

The objective of this study is to evaluate the effect of transient catheterization on uroflow parameters.

METHODS

Consenting women (ages 18-90) provided an uninstrumented uroflow pre- and post-indicated in urodynamic procedures. Voided volume, Qmax, and Qave were recorded for both uninstrumented uroflows. Uroflow curves were classified as "normal" or "abnormal." Pre- and post-urodynamic uroflow data were compared.

RESULTS

Thirty-five patients were included in the study. There was a statistically significant decrease in Qave from the pre- to the post-urodynamic uroflows from 14.71 to 10.55 ml/s (p = 0.012). Additionally, 28.6% of uroflow tracing patterns changed from "normal" to "abnormal," whereas only one (2.9%) changed from "abnormal" to "normal" (p = 0.031).

CONCLUSIONS

This study showed a degradative effect of transient catheterization on uroflow parameters, suggesting that catheterization may cause more than simply a passive obstructive effect. Urethral stimulation due to catheterization may perturb detrusor urethral function, altering voiding and possibly filling performance.

The pathogenesis of catheter-associated urinary tract infection

Catheter-associated urinary tract infection (CAUTI) remains one of the most common types of hospital-acquired infections. Further progress in the prevention of CAUTI requires a better understanding of its pathogenesis. Bacteria may enter the bladder through contamination of the tip during insertion with the flora of the distal urethra or from bacteria ascending the outside or the inside of the catheter. Residual urine in the bladder of catheterised patients increases the risk of bacteriuria. During the process of infection, bacteria need first to adhere to the epithelial cells of the urinary tract and/or the surface of the catheter. They will then develop into biofilms on the catheter surface and are resistant to the immune system and antibiotics. Catheters by themselves may cause immediate physical damage to the bladder epithelium; they may be toxic and also cause inflammation. Bacteria can also damage the epithelium and cause inflammation and the combination of both may be synergistic in producing symptoms in the patient. Most episodes of catheter-associated bacteriuria are asymptomatic but it is not known why some patients are symptomatic and others are not. Further research into the pathogenesis of CAUTI needs to be carried out. A suggestion for the prevention of CAUTI is the use of catheters with an additional eye-hole beneath the balloon to prevent residual urine in the bladder or to remove the tip and balloon altogether, with the additional benefit of having no tip to cause damage or inflammation to the bladder epithelium.

Comparison of cystometric methods in female rats

AIMS

Rat cystometry is a common model used to investigate urinary storage and voiding function. The effect of cystometric instrumentation in rat studies might be a source of deviation from normal physiologic responses. We hypothesized that transurethral catheterization would produce obstruction-related changes, and that suprapubic catheterization would limit volume-related functions as well as disrupt normal urothelial sensory function. We investigated the influence of transurethral and suprapubic catheterization on storage and voiding in the rat model.

METHODS

Three groups of female SD rats 250-300 g under urethane anesthesia were studied. Cystometric and pseudoaffective responses to physiologic voiding with and without suprapubic catheter placement, and cystometry via suprapubic and transurethral catheterization were studied.

RESULTS

In free-voiding animals, per-void volume was 1.8 +/- 0.2 ml with an average flow rate of 0.18 ml/sec, and intercontraction interval (ICI) 60 min. Suprapubic catheterization decreased the ICI and per-void volume consistent with capacity reduction. Suprapubic cystometry did not significantly alter parameters compared to voiding except for a shortened ICI. Bladder pressures and somatic responses were increased, and urine flow impaired by transurethral cystometry. Terazosin did not significantly improve voiding parameters.

CONCLUSIONS

Other than volume-related parameter changes probably related to surgical compromise of bladder capacity, suprapubic catheterization does not alter the cystometric and physiologic responses to voiding when compared to normal, uninstrumented voiding. Transurethral cystometry appears to be obstructive and may activate nociceptive reflexes. For this reason, whenever possible, urodynamic testing using the rat model should employ suprapubic catheterization.

Tachykinins and tachykinin receptors: effects in the genitourinary tract

Tachykinins (TKs) are a family of peptides involved in the central and peripheral regulation of urogenital functions through the stimulation of TK NK1, NK2 and NK3 receptors. At the urinary system level, TKs locally stimulate smooth muscle tone, ureteric peristalsis and bladder contractions, initiate neurogenic inflammation and trigger local and spinal reflexes aimed to maintain organ functions in emergency conditions. At the genital level, TKs are involved in smooth muscle contraction, in inflammation and in the modulation of steroid secretion by the testes and ovaries. TKs produce vasodilatation of maternal and fetal placental vascular beds and appear to be involved in reproductive function, stress-induced abortion, and pre-eclampsia. The current data suggest that the genitourinary tract is a primary site of action of the tachykininergic system.

Tachykinins as modulators of the micturition reflex in the central and peripheral nervous system

In the normal urinary bladder, tachykinins (TKs) are expressed in a population of bladder nociceptors that is sensitive to the excitatory and desensitizing effects of capsaicin (i.e., capsaicin-sensitive primary afferent neurons (CSPANs)). Several endobiotics or xenobiotics excite CSPANs and release TKs and other mediators at both the peripheral and spinal cord level. The peripheral release of TKs determines a set of responses (known as neurogenic inflammation) that includes vasodilatation, plasma protein extravasation, smooth muscle contraction and stimulation of afferent nerves. Following chronic inflammation, both immune cells and capsaicin-resistant sensory neurons can de novo express TKs: whether these pools of TKs are releasable and contribute to inflammatory processes is presently unsettled. At the spinal cord level, the release of TKs contributes in determining an altered pattern of vesicourethral reflexes in response to nociceptive stimulation of the bladder by conveying: (a) the afferent transmission to supraspinal sites, and (b) descending or sensory inputs to the sacral parasympathetic nucleus (SPN). Recent evidence also attribute a synergetic role of TKs in the supraspinal modulation of the sensory arm of the micturition reflex. The overall available information suggests that TK receptor antagonists may affect bladder motility/reflexes which occur during different pathological states, while having little influence on the normal motor bladder function.

Irritant contact stomatitis: a review of the condition

Several different types of interactions are possible between a chemical, a mixture of chemicals, and associated extrinsic factors (i.e., mechanical irritation) in the oral mucosa. These interactions can be broadly classified as irritative or allergenic in nature. In each case, the pathology usually includes mucosal inflammation. The information compiled and reviewed in this article suggests that, given the broad definition of surface lesions/mucosal abnormalities, there may be a continuum of irritation that can be termed "irritant contact stomatitis." This may be due to the fact that the mouth is lined with highly vascular mucosa that turns over rapidly compared to the skin, and may or may not be covered by keratin. Some regions in the mouth are uniquely sensitive to irritants because they can penetrate through the tissue easily. Key factors involved in the potential development of irritation are: inherent irritation potential of the agent, amount of exposure (concentration, duration, and frequency), ability to penetrate the tissue, and inherent reactivity of the subject as well as other extrinsic factors. Irritation leading to oral mucosal alterations is a common occurrence caused by a wide variety of exposures and insults to the oral cavity. Various irritants such as foods, chemicals, friction, thermal/mechanical injury, metals, spices, and oral care products have been documented to cause irritant reactions in susceptible individuals, particularly if used under exaggerated exposure conditions. It is important to note that most irritation in the oral cavity tends to reverse quickly when the causative agent is removed. Oral irritation is a commonly occurring phenomenon. Thus, it is important that the clinician be aware of the clinical manifestations and etiology of the condition.

The tachykinin NK1 receptor. Part II: Distribution and pathophysiological roles

The tachykinin NK1 receptor is widely distributed in both the central and peripheral nervous system. In the CNS, NK1 receptors have been implicated in various behavioural responses and in regulating neuronal survival and degeneration. Moreover, central NK1 receptors regulate cardiovascular and respiratory function and are involved in activating the emetic reflex. At the spinal cord level, NK1 receptors are activated during the synaptic transmission, especially in response to noxious stimuli applied at the receptive field of primary afferent neurons. Both neurophysiological and behavioural evidences support a role of spinal NK1 receptors in pain transmission. Spinal NK1 receptors also modulate autonomic reflexes, including the micturition reflex. In the peripheral nervous system, tachykinin NK1 receptors are widely expressed in the respiratory, genitourinary and gastrointestinal tracts and are also expressed by several types of inflammatory and immune cells. In the cardiovascular system, NK1 receptors mediate endothelium-dependent vasodilation and plasma protein extravasation. At respiratory level, NK1 receptors mediate neurogenic inflammation which is especially evident upon exposure of the airways to irritants. In the carotid body, NK1 receptors mediate the ventilatory response to hypoxia. In the gastrointestinal system, NK1 receptors mediate smooth muscle contraction, regulate water and ion secretion and mediate neuro-neuronal communication. In the genitourinary tract, NK1 receptors are widely distributed in the renal pelvis, ureter, urinary bladder and urethra and mediate smooth muscle contraction and inflammation in response to noxious stimuli. Based on the knowledge of distribution and pathophysiological roles of NK1 receptors, it has been anticipated that NK1 receptor antagonists may have several therapeutic applications at central and peripheral level. At central level, it is speculated that NK1 receptor antagonists could be used to produce analgesia, as antiemetics and for treatment of certain forms of urinary incontinence due to detrusor hyperreflexia. In the peripheral nervous system, tachykinin NK1 receptor antagonists could be used in several inflammatory diseases including arthritis, inflammatory bowel diseases and cystitis. Several potent tachykinin NK1 receptor antagonists are now under evaluation in the clinical setting, and more information on their usefulness in treatment of human diseases will be available in the next few years.

Capsaicin-induced nitric-oxide-dependent relaxation in isolated dog urethra

Capsaicin (5 x 10[-8] to 5 x 10[-5] M) produced a non-adrenergic and non-cholinergic phasic relaxation in a concentration-dependent manner in isolated dog urethral preparations precontracted by noradrenaline. The mode of action of capsaicin was investigated with special reference to the possible involvement of endogenous nitric oxide (NO). A marked tachyphylaxis was observed in the responses to capsaicin. Pretreatment with NG-nitro-L-arginine-methyl-ester (L-NAME) prevented or markedly reduced the inhibitory effect of L-NAME. Methylene blue inhibited the capsaicin-induced relaxation. In preparations stored at 4 degrees C for 72 h, the reduction in the capsaicin-induced relaxation was significantly greater than that in the relaxation induced by either electrical field stimulation or by sodium nitroprusside. We conclude that capsaicin produces an endogenous-NO-dependent relaxation in the isolated dog urethra via mechanisms that deteriorate during cold storage of the preparations.

Effects of opioids on mechanosensitive pelvic nerve afferent fibers innervating the urinary bladder of the rat

A total of 443 pelvic nerve afferent fibers in the L6 dorsal root of the rat were identified by electrical stimulation of the pelvic nerve; 319 (72%) were myelinated A delta fibers with a mean conduction velocity (CV) of 11.8 m/s and 124 (28%) were unmyelinated C fibers with mean CV of 1.9 m/s. Two hundred fifty-two fibers (57%) responded to noxious urinary bladder distension (UBD; 80 mmHg); 108 were C fibers (mean CV; 1.9 m/s) and 144 were A delta fibers (mean CV; 8.2 m/s). Forty-nine UBD-sensitive fibers were further characterized; all gave monotonic increases in firing to increasing distending pressures. Thirty-six fibers (73%) had a low-threshold (LT) for response (mean: 6 mmHg) and 13 fibers (27%) had high-thresholds (HT) for response (mean: 32 mmHg). Responses of 15 fibers to graded UBD (11 LT and 4 HT) were tested before and after instillation of 0.5 ml of 30% xylenes (n = 11) or 5% mustard oil (n = 4) into the bladder. The mean resting activity of 13 fibers significantly increased, and 7 fibers exhibited sensitization of responses to graded UBD 30 min after xylenes or mustard oil instillation. All 4 HT fibers were sensitized; 3 of the 11 LT fibers were sensitized (i.e., gave increased responses to UBD). The effects of opioid receptor agonists were tested on responses to noxious UBD (80 mmHg). Cumulative intraarterial doses of mu-opioid receptor agonists (morphine, 8 mg/kg, and fentanyl, 300 micrograms/kg) and of delta-opioid receptor agonists (DPDPE, 300 micrograms/kg, and SNC-80, 300 micrograms/kg) did not affect responses to noxious UBD. In contrast, cumulative 16 mg/kg intraarterial doses of the kappa-opioid receptor agonists U50,488H, U69,593 and U62,066 dose-dependently attenuated responses to noxious UBD. There were no differences in the dose-response relationships of these drugs on afferent fibers from untreated and xylenes- or mustard oil-treated urinary bladder. These results reveal that there is a greater proportion of UBD-sensitive fibers in the L6 dorsal root (57%) than in the S1 dorsal root of the rat (38%; a previous study). The attenuation of responses to UBD by kappa, but not mu or delta opioid receptor agonists suggests a potential use for peripherally acting kappa opioid receptor agonists in the control of urinary bladder pain.

Capsaicin-induced relaxation in the rat isolated external urethral sphincter: characterization of the vanilloid receptor and mediation by CGRP

1. The potential role of capsaicin-sensitive nerves in the relaxation of the rat external urethral sphincter (REUS) was evaluated by demonstrating the existence of specific vanilloid (capsaicin) receptors and by investigating the sensory neurotransmitter(s) putatively involved in this relaxation. 2. Capsaicin (1 microM) relaxed REUS strips precontracted with noradrenaline (NA) (0.1 mM). This effect underwent desensitization and it was absent in preparations taken from adult capsaicin-pretreated rats. 3. Capsaicin-induced relaxation of NA-precontracted REUS was mimicked by calcitonin gene-related peptide (CGRP, 0.3-10 microM), but not by substance P (1 microM), vasoactive intestinal polypeptide (VIP, 1 microM), alpha-beta methylene ATP (10 microM), gamma-aminobutyric acid (GABA, 3 mM) or galanin (1 microM). A cross-tachyphylaxis between capsaicin (1 microM) and CGRP (1 microM) was observed. Both capsaicin and CGRP-induced relaxation were partially antagonized by the proposed CGRP antagonist, CGRP (8-37) (10 microM). 4. Electrical field stimulation (EFS, 2.5 Hz, 60 V, 1 ms, trains of 5 s every 5 min) of REUS evoked a contraction characterized by a largely adrenergic slowly developing tonic contraction with superimposed fast twitches due to the striated component of the strips. Both capsaicin (1 microM) and CGRP (0.01-1 microM) produced an almost complete inhibition of EFS-induced tonic contraction. A cross-tachyphylaxis between capsaicin and CGRP was observed. Furthermore, these inhibitory actions were unaffected by CGRP (8-37) (10 microM). 5. [3H]-resiniferatoxin displayed specific, saturable binding to rat urethral membranes. Data were consistent with a single site with a Kd of 105 pM and a Bmax of 40 fmol mg-1 protein. This binding was inhibited by capsaicin with a Ki of 0.6 microM and it was reduced by approximately 80% in preparations taken from rats that had undergone surgical ablation of the major pelvic ganglion 4 days earlier.6. In conclusion we have demonstrated the existence of vanilloid receptors on capsaicin-sensitive nerves innervating the rat urethra mainly through the major pelvic ganglion. The activation of this set of nerves could lead to a local release of CGRP that in turn elicits a remarkable urethral relaxation. Such a mechanism could be of relevance in physiological conditions to facilitate urine expulsion during micturition and in pathological conditions to help removal of noxious stimuli following mechanical/chemical irritation of the lower urinary tract.

Effect of bradykinin and tachykinin receptor antagonist on xylene-induced cystitis in rats

The effects of the bradykinin receptor selective antagonist, Hoe 140, and of the tachykinin NK-1 receptor antagonist (+/-)CP 96,345 were investigated in a rat model of chemically-induced cystitis (intravesical instillation of xylene in female rats). Intravenous injection of bradykinin (1 mumol./kg.) or substance P (3 nmol./kg.) produced plasma protein extravasation (PPE) in the rat urinary bladder. Bradykinin response was prevented by Hoe 140 (100 nmol./kg. intravenously) and unaffected by (+/-)CP 96,345 (10 mumol./kg. intravenously). Plasma protein extravasation produced by substance P was inhibited by (+/-)CP 96,345 but unchanged by Hoe 140. Catheterization required for intravesical xylene instillation into the female rat bladder produced per se an inflammatory response which was abolished by either Hoe 140 or (+/-)CP 96,345. Intravesical instillation of xylene produced a large PPE response which was reduced by about 65% by Hoe 140 or (+/-)CP 96,345. Combined administration of the two antagonists produced an additive effect on the PPE response to xylene. We conclude that both bradykinin and tachykinins are involved in the inflammatory reaction of the rat urinary bladder to catheterization and xylene irritation.