Neuroplasticity of Micturition Reflex Pathways with Cyclophosphamide-Induced Cystitis

摘要

Micturition requires the precise reciprocal function of the urinary bladder and urethral outlet. Perhaps due to this degree of precision, micturition is prone to dysfunction with injury or disease. One such disease, interstitial cystitis (IC)/painful bladder syndrome (PBS), is characterized by urinary urgency, frequency and pelvic pain. Inflammation has been implicated as a factor in IC/PBS. The overall hypothesis of this project is that urinary bladder inflammation induces expression of inflammatory mediators and changes neurotrophin receptor expression that contribute to functional changes in the urinary bladder. Using a well-characterized rat model of cyclophosphamide (CYP)-induced urinary bladder inflammation, the expression and function of cyclooxygenase-2 (COX-2), a known inflammatory enzyme, and the p75 neurotrophin receptor (p75NTR), involved in neurotrophin signaling, were examined in micturition reflex pathways using neuroanatomical, biochemical, molecular and physiological techniques. Although COX-2 expression is increased in urinary bladder and involved in bladder hyperreflexia after CYP-induced cystitis, the localization and time course of upregulation was not known. We hypothesized increased COX-2 expression in specific tissue compartments (urothelium or smooth muscle) of the urinary bladder with CYPinduced inflammation. Western blotting for COX-2 showed a significant increase in COX-2 expression in both detrusor and urothelium/suburothelium, with the greatest increase in the urothelium/suburothelium. Immunostaining showed increased COX-2 staining in suburothelium with cystitis, co-localized with CD86, a marker for dendritic cells and macrophages. Nerve growth factor (NGF) has been implicated in inflammation, increased voiding frequency and altered sensation in urinary bladder. The specific NGF tyrosine kinase receptor, TrkA, is increased in bladder afferent cells with CYP. NGF also binds p75NTR. The second goals were to examine the expression and functional role of p75NTR in urinary bladder pathways in control and CYP-treated rats. We hypothesized that p75NTR is constitutively expressed in micturition pathways and upregulated with cystitis. With cystitis, p75NTR expression was increased in lumbosacral spinal cord and in bladder afferent cells in dorsal root ganglia. Western blotting for p75NTR showed increased expression in whole urinary bladder with cystitis. Based on bladder function effects of TrkA blockade with cystitis, we hypothesized that p75NTR blockade in the urinary bladder would also decrease bladder hyperreflexia with cystitis. The functional role of p75NTR was studied by intravesical blockade by immunoneutralization with a monoclonal antibody to p75NTR and by PD90780, known to block NGF-p75NTR binding. Both forms of p75NTR blockade significantly decreased bladder capacity in control and CYP-treated rats. Changes in micturition and threshold pressure, and non-voiding contractions were also demonstrated. In conclusion, these dissertation studies demonstrate that CYP-induced bladder inflammation alters expression of inflammatory mediators and neurotrophin receptors in micturition pathways. This altered expression can affect overall urinary bladder function.