Lidocaine prevents referred hyperalgesia associated with cystitis

Anesthetic protocols for urodynamic studies of the lower urinary tract in small rodents-A systematic review

Urodynamic studies in rats and mice are broadly used to examine pathomechnisms of disease and identify and test therapeutic targets. This review aims to highlight the effects of the anesthetics on the lower urinary tract function and seeks to identify protocols that allow recovery from anesthesia and repeated measurements while preserving the function which is being studied. All studies published in English language, which compared the data obtained under various types of anesthesia and the urodynamics performed in awake animals were included. It appears that urethane, an anesthetic recommended extensively for the investigation of lower urinary tract function, is appropriate for acute urodynamic studies only. Major advantages of urethane are its stability and ability to preserve the micturition reflex. Due to its toxicity and carcinogenicity, urethane anesthesia should not be used for recovery procedures. This review evaluated available alternatives including propofol, isoflurane and combinations of urethane, ketamine/xylazine, ketamine/medetomidine, and/or fentanyl/fluanisone/midazolam. Different effects have been demonstrated among these drugs on the urinary bladder, the urethral sphincter, as well as on their neuroregulation. The lowest incidence of adverse effects was observed with the use of a combination of ketamine and xylazine. Although the variations in the reviewed study protocols represent a limitation, we believe that this summary will help in standardizing and optimizing future experiments.

Intrathecal cannabinoid-1 receptor agonist prevents referred hyperalgesia in acute acrolein-induced cystitis in rats

We investigated the capacity of intrathecal arachidonyl-2'-chloroethylamide (ACEA), a cannabinoid-1 receptor (CB1R) agonist, to inhibit referred hyperalgesia and increased bladder contractility resulting from acute acrolein-induced cystitis in rats. 24 female rats were divided into 4 groups: 1) intrathecal vehicle/intravesical saline; 2) intrathecal vehicle/intravesical acrolein; 3) intrathecal ACEA/intravesical saline; and 4) intrathecal ACEA/intravesical acrolein. Bladder catheters were placed 4-6 days prior to the experiment. On the day of the experiment, rats were briefly anesthetized with isoflurane to recover the external end of the cystostomy catheter. After recovery from anesthesia, pre-treatment cystometry was performed, and mechanical sensitivity of the hindpaws was determined. Rats were again briefly anesthetized with isoflurane to inject ACEA or vehicle into the intrathecal space between L5-L6. Beginning 10 minutes after intrathecal injection, saline or acrolein was infused into the bladder for 30 minutes. Post-treatment cystometry and mechanical sensitivity testing were performed. Rats were euthanized, and bladders were collected, weighed, and fixed for histology. The intrathecal vehicle/intravesical acrolein group developed mechanical hyperalgesia with post-treatment mechanical sensitivity of 6 ± 0.3 g compared to pretreatment of 14 ± 0.4 g (p < 0.01). Pre- and post-treatment hind paw mechanical sensitivity was statistically similar in rats that received intrathecal ACEA prior to intravesical infusion of acrolein (15 ± 0.2 g and 14 ± 0.4 g, respectively). Acrolein treatment increased basal bladder pressure and maximal voiding pressure and decreased intercontraction interval and voided volume. However, intrathecal ACEA was ineffective in improving acrolein-related urodynamic changes. In addition, bladder histology demonstrated submucosal and muscularis edema that was similar for all acrolein-treated groups, irrespective of ACEA treatment. Intravesical saline had no effect on results of cystometry or mechanical sensitivity of the hind paws, regardless of intrathecal treatment. Intrathecal ACEA prevented referred hyperalgesia associated with acute acrolein-induced cystitis. However, in this experimental model, ACEA did not ameliorate the associated urodynamic changes. These findings suggest that pain arising from cystitis may be inhibited by activation of spinal CB1R but the acute local response of the bladder appeared to be unaffected by stimulation of spinal CB1R.

Mechanisms of pain from urinary tract infection

The pain response to urinary tract infection is largely uncharacterized, but the symptomatic response to urinary tract infection contrasts with the lack of pain response among individuals with asymptomatic bacteriuria. Quantifying pelvic pain in a murine urinary tract infection model, uropathogenic Escerichia coli induces transient pelvic pain, whereas an asymptomatic bacteriuria E. coli isolate causes no pain, thus recapitulating the spectrum of clinical responses to intravesical E. coli. These differential pain responses are not correlated with bladder colonization or inflammation, but instead are intrinsic to E. coli lipopolysaccharide and dependent on the lipopolysaccharide receptor, TLR4. Epidemiological data suggest a link between interstitial cystitis and a history of urinary tract infection, so it was evaluated whether repetitive uropathogenic E. coli instillation would result in chronic pain through central sensitization. Although repeated infection with wild type uropathogenic E. coli results in only transient episodes of acute pain, a uropathogenic E. coli mutant lacking O-antigen causes chronic, post-urinary tract infection pelvic pain. Similarly, a K-12 E. coli strain lacking O-antigen induces chronic pain that persisted long after bacterial clearance, and expressing O-antigen nullified the pain phenotype. Spinal cords isolated from mice with post-urinary tract infection chronic pain showed deficits in short-term depression consistent with central sensitization. Deleting O-antigen gene complex from a uropathogenic E. coli strain and subsequent heterologous expression of O-antigen gene clusters shows that a single bacterial isolate can exhibit pain phenotypes ranging from a null phenotype, an acute pain phenotype, to a chronic pain phenotype. Post-urinary tract infection chronic pain is also associated with voiding dysfunction and anxious/depressive behavior. These effects are also mediated by TRPV1 at the level of pain establishment and CCR2 at the level of pain maintenance. Together, these findings show that transient infection with E. coli might result in chronic visceral pain with the hallmarks of neuropathic pain. This pattern of behaviors mimics the spectrum of interstitial cystitis symptoms, thus supporting the possibility of an infectious etiology of interstitial cystitis.

A novel method for assessing bladder-related pain reveals the involvement of nerve growth factor in pain associated with cyclophosphamide-induced chronic cystitis in mice

BACKGROUND

Pain is a prominent feature of interstitial cystitis/painful bladder syndrome (IC/PBS), but the underlying mechanisms are not fully understood. There is a lack of well-characterized research tools, such as pain evaluation methods and experimental animal models, for investigating non-ulcerative cystitis. We developed a novel method for evaluating bladder pain in mice with cyclophosphamide (CYP)-induced cystitis.

METHODS

Cystitis was produced by a single intraperitoneal injection of CYP (300 mg/kg) or repeated injections of CYP (150 mg/kg once daily for 4 days). Blunt stimulation with a cotton probe was applied to the abdominal region, and the thresholds for withdrawal responses were measured quantitatively using an anaesthesiometer.

RESULTS

The single injection of CYP provoked acute cystitis with severe bladder inflammation in mice. In these mice, we could detect an increased sensitivity to blunt stimulation, which was abolished by intravesical lidocaine. The stimulation induced phosphorylation of extracellular signal-regulated kinases in bladder-projecting sensory neurons. Chronic treatment with CYP produced persistent pain responses to the blunt stimulus. Although there were few signs of bladder inflammation in these mice, the concentration of nerve growth factor (NGF) was elevated in bladder tissue, and NGF antiserum inhibited the hypersensitivity.

CONCLUSIONS

The blunt probe method is useful for evaluating bladder pain signalling in mice, and revealed the involvement of an NGF-sensitive pain pathway in chronic cystitis pain. This assessment method may be useful for studying the pathophysiology of bladder pain and for developing therapeutic strategies for non-ulcerative IC/PBS in patients.

Time-dependent changes in bladder function and plantar sensitivity in a rat model of fibromyalgia syndrome induced by hydrochloric acid injection into the gluteus

OBJECTIVE

To examine the correlation between muscular pain and bladder hypersensitivity in order to clarify the pathogenesis of comorbidity of bladder pain syndrome/interstitial cystitis with other chronic pain conditions such as fibromyalgia syndrome (FMS).

MATERIALS AND METHODS

Under isoflurane anaesthesia, 0.2 mL of hydrochloric acid (HCl) solution (pH 4.0) was injected into the bilateral gluteus muscles of female Sprague-Dawley rats to produce an FMS model, as the gluteus is one of the specific tender points in patients with FMS. Control rats received saline injection (0.2 mL). The mechanical sensitivity of the plantar was evaluated using the mean number of bilateral hindlimb withdrawals in response to tactile stimulation with a 2.0-g von Frey filament at 1, 2 and 3 weeks after the HCl injection. In a separate rat group, cystometry was performed with the rats awake during saline infusion (0.06 mL/min) into the bladder before and after 1% lidocaine injection (0.2 mL) into the bilateral gluteus 1, 2 and 3 weeks after the HCl injection.

RESULTS

The mean number of hindlimb withdrawals was significantly higher in FMS rats than in controls at 1 and 2 weeks. Using cystometry, we found that the intercontraction interval (ICI) and voided volume (VV) were significantly lower in FMS rats than in controls at 1 and 2 weeks. In addition, the voiding threshold pressure, ICI and VV were significantly higher after lidocaine injection in FMS rats, but not in controls, at 1 and 2 weeks.

CONCLUSIONS

HCl injection (pH 4.0) into the gluteus can induce plantar hypersensitivity and urinary frequency for up to 2 weeks after the injection, suggesting that somatic (gluteus)-to-visceral (bladder) cross-sensitization might underlie bladder hypersensitivity in patients with FMS. Moreover, intervention at specific tender points outside the bladder could be effective in treating urinary frequency because lidocaine injection into the gluteus normalized bladder function in FMS rats for up to 2 weeks.

Perioperative nerve blockade: clues from the bench

Peripheral and neuraxial nerve blockades are widely used in the perioperative period. Their values to diminish acute postoperative pain are established but other important outcomes such as chronic postoperative pain, or newly, cancer recurrence, or infections could also be influenced. The long-term effects of perioperative nerve blockade are still controversial. We will review current knowledge of the effects of blocking peripheral electrical activity in different animal models of pain. We will first go over the mechanisms of pain development and evaluate which types of fibers are activated after an injury. In the light of experimental results, we will propose some hypotheses explaining the mitigated results obtained in clinical studies on chronic postoperative pain. Finally, we will discuss three major disadvantages of the current blockade: the absence of blockade of myelinated fibers, the inappropriate duration of blockade, and the existence of activity-independent mechanisms.