Crucial role of TRPC1 and TRPC4 in cystitis-induced neuronal sprouting and bladder overactivity.

PURPOSE: During cystitis, increased innervation of the bladder by sensory nerves may contribute to bladder overactivity and pain. The mechanisms whereby cystitis leads to hyperinnervation of the bladder are, however, poorly understood. Since TRP channels have been implicated in the guidance of growth cones and survival of neurons, we investigated their involvement in the increases in bladder innervation and bladder activity in rodent models of cystitis. MATERIALS AND METHODS: To induce bladder hyperactivity, we chronically injected cyclophosphamide in rats and mice. All experiments were performed a week later. We used quantitative transcriptional analysis and immunohistochemistry to determine TRP channel expression on retrolabelled bladder sensory neurons. To assess bladder function and referred hyperalgesia, urodynamic analysis, detrusor strip contractility and Von Frey filament experiments were done in wild type and knock-out mice. RESULTS: Repeated cyclophosphamide injections induce a specific increase in the expression of TRPC1 and TRPC4 in bladder-innervating sensory neurons and the sprouting of sensory fibers in the bladder mucosa. Interestingly, cyclophosphamide-treated Trpc1/c4(-/-) mice no longer exhibited increased bladder innervations, and, concomitantly, the development of bladder overactivity was diminished in these mice. We did not observe a difference neither in bladder contraction features of double knock-out animals nor in cyclophosphamide-induced referred pain behavior. CONCLUSIONS: Collectively, our data suggest that TRPC1 and TRPC4 are involved in the sprouting of sensory neurons following bladder cystitis, which leads to overactive bladder disease.

Chronic administration of anticholinergics in rats induces a shift from muscarinic to purinergic transmission in the bladder wall.

BACKGROUND: First-line pharmacotherapy for overactive bladder consists of anticholinergics. However, patient compliance is exceptionally low, which may be due to progressive loss of effectiveness. OBJECTIVE: To decipher the involved molecular mechanisms and to evaluate the effects of chronic systemic administration of anticholinergics on bladder function and on muscarinic and purinergic receptors expression in rats. DESIGN, SETTING, AND PARTICIPANTS: Female Wistar rats were implanted with an osmotic pump that chronically administered vehicle (Vehc), 0.36 mg/kg per day oxybutynin (Oxyc), or 0.19 mg/kg per day fesoterodine (Fesoc) for 28 d. INTERVENTIONS: For cystometry experiments, a small catheter was implanted in the bladder. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Urologic phenotype was evaluated by the analysis of the micturition pattern and urodynamics. Expression of muscarinic and purinergic receptors was assessed by Western blot analysis of detrusor membrane protein. Functional responses to carbachol and adenosine triphosphate (ATP) were evaluated using muscle-strip contractility experiments. RESULTS AND LIMITATIONS: The number of voided spots was transiently decreased in Oxyc rats. In Oxyc rats, the effect of an acute high dose of oxybutynin (1mg/kg intraperitoneally [IP]) on the intermicturition interval was abolished. Expression experiments revealed a decrease of muscarinic acetylcholine receptors M2 (mAChR2) and M3 (mAChR3), whereas the purinergic receptor P2X, ligand-gated ion channel, 1 (P2X1) was enhanced in Oxyc and Fesoc rats compared to Vehc rats. In concordance with the modification of the expression pattern in Oxyc rats, the force generated by carbachol and ATP in muscle-strip contractility experiments was, respectively, lower and higher. Urodynamics revealed that the effects of systemic administration of the purinergic blocker pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (50mg/kg IP) were enhanced in Oxyc rats. As rat bladder physiology is different from that of humans, it is difficult to directly extrapolate our findings to human patients. CONCLUSIONS: Chronic administration of anticholinergics in rats induces receptor loss of efficiency and a shift from muscarinic to purinergic transmission.

The use of cystometry in small rodents: a study of bladder chemosensation.

The lower urinary tract (LUT) functions as a dynamic reservoir that is able to store urine and to efficiently expel it at a convenient time. While storing urine, however, the bladder is exposed for prolonged periods to waste products. By acting as a tight barrier, the epithelial lining of the LUT, the urothelium, avoids re-absorption of harmful substances. Moreover, noxious chemicals stimulate the bladder's nociceptive innervation and initiate voiding contractions that expel the bladder's contents. Interestingly, the bladder's sensitivity to noxious chemicals has been used successfully in clinical practice, by intravesically infusing the TRPV1 agonist capsaicin to treat neurogenic bladder overactivity. This underscores the advantage of viewing the bladder as a chemosensory organ and prompts for further clinical research. However, ethical issues severely limit the possibilities to perform, in human subjects, the invasive measurements that are necessary to unravel the molecular bases of LUT clinical pharmacology. A way to overcome this limitation is the use of several animal models. Here we describe the implementation of cystometry in mice and rats, a technique that allows measuring the intravesical pressure in conditions of controlled bladder perfusion. After laparotomy, a catheter is implanted in the bladder dome and tunneled subcutaneously to the interscapular region. Then the bladder can be filled at a controlled rate, while the urethra is left free for micturition. During the repetitive cycles of filling and voiding, intravesical pressure can be measured via the implanted catheter. As such, the pressure changes can be quantified and analyzed. Moreover, simultaneous measurement of the voided volume allows distinguishing voiding contractions from non-voiding contractions. Importantly, due to the differences in micturition control between rodents and humans, cystometric measurements in these animals have only limited translational value. Nevertheless, they are quite instrumental in the study of bladder pathophysiology and pharmacology in experimental pre-clinical settings. Recent research using this technique has revealed the key role of novel molecular players in the mechano- and chemo-sensory properties of the bladder.

An autocrine neuronal interleukin-6 loop mediates chloride accumulation and NKCC1 phosphorylation in axotomized sensory neurons.

The cation-chloride cotransporter NKCC1 plays a fundamental role in the central and peripheral nervous systems by setting the value of intracellular chloride concentration. Following peripheral nerve injury, NKCC1 phosphorylation-induced chloride accumulation contributes to neurite regrowth of sensory neurons. However, the molecules and signaling pathways that regulate NKCC1 activity remain to be identified. Functional analysis of cotransporter activity revealed that inhibition of endogenously produced cytokine interleukin-6 (IL-6), with anti-mouse IL-6 antibody or in IL-6⁻/⁻ mice, prevented chloride accumulation in a subset of axotomized neurons. Nerve injury upregulated the transcript and protein levels of IL-6 receptor in myelinated, TrkB-positive sensory neurons of murine lumbar dorsal root ganglia. Expression of phospho-NKCC1 was observed mainly in sensory neurons expressing IL-6 receptor and was absent from IL-6⁻/⁻ dorsal root ganglia. The use of IL-6 receptor blocking-function antibody or soluble IL-6 receptor, together with pharmacological inhibition of Janus kinase, confirmed the role of neuronal IL-6 signaling in chloride accumulation and neurite growth of a subset of axotomized sensory neurons. Cell-specific expression of interleukin-6 receptor under pathophysiological conditions is therefore a cellular response by which IL-6 contributes to nerve regeneration through neuronal NKCC1 phosphorylation and chloride accumulation.

Functional characterization of a chronic cyclophosphamide-induced overactive bladder model in mice.

AIMS: To describe a new mouse model of overactive bladder (OAB) at the histological level, pain, voiding behavior, and urodynamics, while assessing the physiological state of mice. METHODS: This paper compares the pathophysiological features of mice that received intraperitoneal injections of cyclophosphamide (CYP) (40 and 80 mg/kg - body weight) every 2 days for 7 days. Specifically, the heart rate, the body temperature, and the general activity were assessed by telemetry. The abdominal sensitivity was determined with Von Frey filaments. Voiding behavior and detrusor activity were respectively quantified by urine spotting experiments and cystometry. Hematoxylin & Eosin staining was performed to detect inflammation in tissue and NGF concentration in urine was quantified. RESULTS: Affected mice exhibit clearly an OAB characterized by an increase in the number of voiding events and an urodynamically-demonstrated detrusor overactivity associated with referred hyperalgesia. The injected mice displayed inflamed bladder, urothelial hyperplasia, and increased NGF concentration in urine in dose dependant manner. However, the physiological features of mice with CYP-induced cystitis are not changed. CONCLUSIONS: We can show that this model of chronic OAB with pain in mice fits more closely to the clinical signs of patients with OAB than the available animal models (acute and chronic) and will therefore be useful to highlight potential drug targets in genetically modified mice in the future.