| Visceral pain is one of the most difficult symptoms of bladder disease to control. Bladder inflammation induces secretion of intercellular signaling molecules that sensitize afferent nerve fibers, leading to hyperalgesia. The fundamental hypothesis that guided this work is that the endocannabinoid anandamide inhibits nociceptive responses in the bladder during inflammation. First, we characterized expression of cannabinoid receptors in normal and inflamed bladders and their associated innervation. We confirmed the presence of CB1 and CB2 in normal bladders, L6/S 1 spinal cord, and root dorsal ganglia (DRG). Acute and chronic inflammation induced CB2 up-regulation in the bladder, but no changes in CB1 or CB2 were detected in the spinal cord or DRG. Second, we demonstrated that fatty acid ethanolamides, including the endogenous cannabinoid anandamide (AEA), are present in the bladder and are increased after bladder inflammation. Inhibition of fatty acid amide hydrolase (FAAH), the enzyme that degrades AEA, suppressed referred hyperalgesia of the hind paws associated with bladder inflammation. These results suggest that endogenous fatty acid ethanolamides, mainly AEA, inhibit sensitization of afferent nerve fibers in the inflamed bladder. Third, we verified the expression of cannabinoid receptors in human bladder urothelial cells (HBUCs) and investigated the downstream consequences of AEA treatment in these cells. Both CB1 and CB2 are expressed in HBUCs. Treatment with AEA induced phosphorylation of ERK1 and ERK2, and increased COX2 expression in a time- and concentration-dependent manner. Finally, we measured the effects of AEA on potassium currents in HBUCs. We found that AEA inhibits potassium currents at relatively high concentrations (10 muM), but AEA had no significant effect at lower concentrations (0.1-0.01 muM). In this body of work we have established the presence of multiple components of the endocannabinoid system in the bladder and demonstrated that inhibition of FAAH can suppress referred pain associated with bladder inflammation. We have also identified several biochemical and electrophysiological effects of endocannabinoid signaling that occur at the cellular level in isolated bladder urothelial cells. Future studies will investigate whether or not FAAH inhibitors can be used to treat bladder pain in patients with bladder disorders. |
