Visceral pain in humans: lessons from animals

Prevalence, Risk Factors, Pathophysiology, Potential Biomarkers and Management of Feline Idiopathic Cystitis: An Update Review

Feline idiopathic cystitis is a widespread disease in small animal clinics, which mainly presents with urinary signs like dysuria, stranguria, hematuria, pollakiuria, and periuria. The etiopathogenesis of the disease may involve interactions between the environmental stressors, neuroendocrine system and bladder of affected cats. Diagnostic biomarkers have not been tested in clinical studies though they are theoretically feasible, and since the clinical signs of the disease assemble those of other feline lower urinary diseases, its diagnosis is a procedure of exclusion. The primary treatment of the disease is long-term multimodal environmental modification (or enrichment) while anti-anxiety drugs and nutritional supplements are recommended for chronic recurrent cases. Still, many medicines need to be evaluated for their efficacy and safety. This review aims to provide readers with a comprehensive understanding of feline idiopathic cystitis by summarizing and updating studies concerning the prevalence, risk factors, etiological hypotheses, diagnostic procedures, possible treatments, and prognosis of the disease.

Translational pain assessment: could natural animal models be the missing link?

Failure of analgesic drugs in clinical development is common. Along with the current "reproducibility crisis" in pain research, this has led some to question the use of animal models. Experimental models tend to comprise genetically homogeneous groups of young, male rodents in restricted and unvarying environments, and pain-producing assays that may not closely mimic the natural condition of interest. In addition, typical experimental outcome measures using thresholds or latencies for withdrawal may not adequately reflect clinical pain phenomena pertinent to human patients. It has been suggested that naturally occurring disease in veterinary patients may provide more valid models for the study of painful disease. Many painful conditions in animals resemble those in people. Like humans, veterinary patients are genetically diverse, often live to old age, and enjoy a complex environment, often the same as their owners. There is increasing interest in the development and validation of outcome measures for detecting pain in veterinary patients; these include objective (eg, locomotor activity monitoring, kinetic evaluation, quantitative sensory testing, and bioimaging) and subjective (eg, pain scales and quality of life scales) measures. Veterinary subject diversity, pathophysiological similarities to humans, and diverse outcome measures could yield better generalizability of findings and improved translation potential, potentially benefiting both humans and animals. The Comparative Oncology Trial Consortium in dogs has pawed the way for translational research, surmounting the challenges inherent in veterinary clinical trials. This review describes numerous conditions similarly applicable to pain research, with potential mutual benefits for human and veterinary clinicians, and their respective patients.

Role of the urothelium in bladder function

Historically, the urinary bladder urothelium has been viewed as a passive barrier; however, recent evidence has demonstrated that the urothelium is a responsive structure, which exhibits both "sensor" (i.e. ability to respond to thermal, mechanical and chemical stimuli) and "transducer" (i.e. ability to release chemicals) functions. Studies have also revealed that afferent nerves and urothelial cells in the bladder exhibit a number of common properties, including the expression of certain receptors and ion channels (i.e. vanilloid receptor-1). In addition, localization of afferent nerves adjacent to the urothelium suggests that these cells may be targets for transmitter release from bladder nerves or that chemicals released by urothelial cells may alter afferent excitability. Taken together, these and other findings suggest that alterations in afferents or epithelial cells in pelvic viscera may contribute to the sensory abnormalities in a number of pelvic disorders.

Experimental oesophagitis in the rat is associated with decreased voluntary movement

Growing interest has arisen regarding the mechanism of dyspeptic symptom generation. However, no evaluation system of these symptoms in animals has been developed. In this study, we examined whether voluntary movement of rats could be a measure to assess visceral symptoms of reflux oesophagitis. A chronic acid reflux oesophagitis model was made using rats, and the size of erosions was measured. Omeprazole was administered to the oesophagitis rats for 10 days. The amount of voluntary movement was measured by an infrared sensor. Intracellular spaces in oesophageal epithelium were also measured using a emission electron microscope. NP-40 soluble and insoluble fractions of claudins were examined by Western blot. Voluntary movement was significantly lower in the oesophagitis model rats than in the sham-operated rats (P < 0.01). Although omeprazole reduced the size of erosions, it did not significantly affect the total amount of voluntary movement (r = -0.033, P = 0.916). Intracellular spaces were significantly dilated in the oesophagitis model rats and claudin-3 showed a significantly lower relative quantity in the NP-40 insoluble fraction. Omeprazole significantly increased voluntary movement of oesophagitis model rats and the relative quantity of claudin-3 in the insoluble fraction (P < 0.05). Dilated intercellular spaces and the lower level of claudin-3 may relate to the voluntary movement of oesophagitis model rats. Decreases in voluntary movement of oesophagitis model rats may reflect visceral symptoms and be able to serve as an index of chronic abdominal symptoms.

Neuropathic pain in dogs and cats: if only they could tell us if they hurt

Neuropathic pain is difficult to diagnose in veterinary patients because they are unable to verbalize their pain. By assuming that neuropathic pain may exist based on the history of events that each patient has experienced, a focused client history and neurologic examination may identify a lesion resulting in persistent or spontaneous pain. Once neuropathic pain is diagnosed, a trial analgesic or acupuncture session(s) should be prescribed with instructions for owners to observe behavior. Dosing of the analgesic can be titrated to the patient's needs while avoiding adverse effects. When a particular analgesic may be ineffectual, an alternate class should be tried. As research into the neurobiologic mechanisms of neuropathic pain continues, specific therapies for its management should eventually appear in the human clinical setting and subsequently be investigated for veterinary clinical use.

Urinary bladder urothelium: Molecular sensors of chemical/thermal/mechanical stimuli

The identification of functional receptors/ion channels in bladder urothelial cells and the involvement of these sensor molecules in the release of chemical mediators (nitric oxide, NO; ATP) suggest that urothelial cells exhibit specialized sensory and signaling properties. Such mechanisms could allow these cells to respond to their chemical and physical environments and to engage in reciprocal communication with neighboring urothelial cells as well as nerves in the bladder wall. These and other findings highlight the functional importance of the urinary bladder urothelium and suggest that perturbations in urothelial targets and/or cell-cell interactions may lead to a number of urinary tract abnormalities.

Evaluation of the effects of stress in cats with idiopathic cystitis

OBJECTIVE

To determine the effects of stress in cats with feline idiopathic cystitis (FIC) by evaluating bladder permeability, sympathetic nervous system function, and urine cortisol:creatinine (C:Cr) ratios during periods of stress and after environmental enrichment.

DESIGN

Prospective study.

ANIMALS

13 cats with FIC and 12 healthy cats.

PROCEDURE

Cats subjected to an acute-onset moderate stressor for 8 days received IV injections of fluorescein. Serum fluorescein concentrations were determined and compared with those of controls to evaluate bladder permeability, and urine C:Cr ratios were compared to evaluate function of the hypothalamic-pituitary-adrenal (HPA) axis. Plasma catecholamine concentrations were analyzed in a subset of cats. After 8 days of moderate stress, cats were moved to an enriched environment, and tests were repeated after 21 days.

RESULTS

Serum fluorescein concentrations were significantly higher in cats with FIC at all time points. In the cats in which plasma catecholamine concentrations were determined, concentrations of dihydroxyphenylalanine, norepinephrine, and dihyroxyphenylglycol were significantly higher in cats with FIC at all time points, whereas no differences in urine C:Cr ratio between groups were observed.

CONCLUSION AND CLINICAL RELEVANCE

Cats with FIC appeared to have altered bladder permeability, most notably during the period of initial stress. The increase in plasma dihydroxyphenylalanine concentration suggests that there may be stress-induced increase in the activity of tyrosine hydroxylase, which catalyzes the rate-limiting step in catecholamine synthesis. In contrast, no effects of stress on C:Cr ratios were observed, which suggests there was dissociation between the sympathetic nervous system and HPA-axis responses to stress.

More than just a barrier: urothelium as a drug target for urinary bladder pain

Although the urinary bladder urothelium has classically been thought of as a passive barrier to ions/solutes, a number of novel properties have been recently attributed to these cells. Studies have revealed that the urothelium is involved in sensory mechanisms (i.e., ability to express a number of sensor molecules or respond to thermal, mechanical, and chemical stimuli) and can release chemical mediators. Localization of afferent nerves next to the urothelium suggests these cells may be targets for transmitters released from bladder nerves or that chemicals released by urothelial cells may alter afferent excitability. Taken together, these and other findings highlighted in this review suggest a sensory function for the urothelium. Elucidation of mechanisms impacting on urothelial function may provide insights into the pathology of bladder dysfunction.

In vivo models of interstitial cystitis

PURPOSE

We systematically identified and evaluated various animal models that have been studied to help identify the underlying mechanisms of and possible treatment options for interstitial cystitis.

MATERIALS AND METHODS

Models of interstitial cystitis published between 1983 and 2001 were obtained by searching MEDLINE and other Internet databases using cystitis and model as the primary key words. Models with characteristics of interstitial cystitis similar to those defined by National Institutes of Arthritis, Diabetes, Digestive and Kidney Diseases criteria were reviewed. Some articles describing animal models with similar pathological conditions in other organs were also included to enlarge the base of potentially relevant material.

RESULTS

We identified and evaluated some 16 animal models of interstitial cystitis, which we categorized as bladder inflammation induced by intravesical administration of an irritant or immune stimulant, systemic and environmentally induced inflammation, and a naturally occurring model of interstitial cystitis that occurs in cats. Some abnormalities identified in humans and cats with interstitial cystitis can be reproduced in healthy animals using luminal, systemic or environmental stimuli. At the level of the bladder the source of stimulation cannot be discriminated. Variability in the extent of bladder distention complicated the interpretation of some studies. In addition, the noxious stimuli used can affect many epithelial surfaces as well as the urothelium, suggesting they are nonspecific responses to injury rather than specific to interstitial cystitis.

CONCLUSIONS

No model in bladder injury in healthy animals currently reproduces as many features of interstitial cystitis as the naturally occurring disease in cats. While induced models of relative injury may help to provide insight into the bladder response to injury, feline interstitial cystitis follows a similar chronic waxing and waning time course as does interstitial cystitis in humans, which may be more suitable for studying the effects of stressors on the severity of clinical signs as well as newly proposed therapies.