Cannabinoid CB1 receptors are expressed in the mouse urinary bladder and their activation modulates afferent bladder activity

Pharmacological studies have indirectly shown the possible presence of cannabinoid receptors in the urinary bladder and their potential role in reducing bladder inflammatory pain. However, the localization of cannabinoid receptors in the urinary bladder remains unknown and there are no published data on the effects of cannabinoids on the sensory system of the bladder. The present study was performed to evaluate the expression of the cannabinoid CB1 receptors in the mouse urinary bladder and to assess their co-localization with the purinergic P2X3 receptor, a major player in the transduction of sensory events in the bladder. Also, the effect of intravesical administration of a cannabinoid agonist on the electrical activity of bladder afferent fibers was studied. The expression of mRNA coding for CB1 receptor was assessed by reverse transcriptase–polymerase chain reaction (RT-PCR). Immunofluorescence experiments were performed to study CB1 and P2X3 protein expression in the bladder. The electrical activity of bladder afferent fibers was recorded using an ex vivo bladder-nerve preparation. Mechanical stimulation of the bladder was performed by a controlled slow inflation with an external pump. A bolus of a cannabinoid agonist (AZ12646915) was administered intravesically prior to a second inflation. Afferent activity was measured before and after administration of the cannabinoid compound or its vehicle. The effects of CB1 receptor antagonist (AM251) on the AZ12646915 response were also analyzed. Cannabinoid receptor CB1 mRNA was detected in the urinary bladder of the mouse. The protein was found in the urothelium, as well as in nerve fibers. CB1 and P2X3 receptors were found to be co-expressed in urothelial cells and in some nerve fibers. In addition, intravesical administration of a cannabinoid receptor agonist reduced the mechanically-evoked activity of bladder afferents in the pelvic nerve. This effect was abolished by the previous administration of the CB1 antagonist AM251. These data demonstrate the presence of cannabinoid CB1 receptor mRNA and the protein in the mouse urinary bladder. CB1 and P2X3 protein co-localization supports the hypothesis of an interaction between the cannabinoid and the purinergic systems in the transduction of sensory information in the urinary bladder. Finally, the reduction of nerve activity induced by cannabinoid-receptor activation implicates CB1 receptors in the peripheral modulation of bladder afferent information.