Cannabinoid receptor 2 is increased in acutely and chronically inflamed bladder of rats

Increased cannabinoid receptor 1-immunoreactive nerve fibers in overactive and painful bladder disorders and their correlation with symptoms

OBJECTIVE

To study the expression of cannabinoid receptor 1 (CB1) in human urinary bladder hypersensitivity and overactivity disorders, and correlate changes with symptoms. Cannabinoid receptor agonists have been shown to modulate urinary bladder contractility and reduce pain after bladder inflammation; their clinical efficacy on lower urinary tract symptoms was demonstrated in the Cannabinoids in Multiple Sclerosis study.

METHODS

Bladder tissue specimens were obtained from patients with painful bladder syndrome (PBS, n=13), idiopathic detrusor overactivity (IDO, n=14), and from controls with asymptomatic microscopic hematuria (n=16). The severity of symptoms was assessed using the Pelvic Pain and Urgency/Frequency Questionnaire. Pain score was also recorded on a visual analogue scale. Specimens were immunostained using specific antibodies to CB1 and to neurofilaments as a structural maker. Detrusor and suburothelial nerve fiber density was quantified with a visual grading scale. The immunohistochemistry results were correlated with "Pain, Frequency, and Urgency" scores.

RESULTS

CB1-immunoreative nerve fibers were significantly increased in the suburothelium of PBS (P=.0123) and IDO (P=.0013) specimens, and in detrusor layer in IDO (P=.0003), as compared with controls. CB1-immunoreactive suburothelial nerve fiber density correlated significantly with pain scores (Visual Analogue Scale) in PBS (r=.6878, P=.0347) and urgency scores in IDO (r=.6623, P=.0027). Neurofilaments-immunoreactive suburothelial nerve fibers were significantly increased in PBS (P=.019) and IDO (P=.05).

CONCLUSIONS

The results of this study suggest that increased nerve fibers, which express CB1, may be related to bladder pain in PBS and urgency in IDO. Our findings support clinical trials of CB1 agonists in bladder disorders.

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 CB(1) receptors in the mouse urinary bladder and to assess their co-localization with the purinergic P2X(3) 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 CB(1) receptor was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). Immunofluorescence experiments were performed to study CB(1) and P2X(3) 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 CB(1) receptor antagonist (AM251) on the AZ12646915 response were also analyzed. Cannabinoid receptor CB(1) mRNA was detected in the urinary bladder of the mouse. The protein was found in the urothelium, as well as in nerve fibers. CB(1) and P2X(3) 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 CB(1) antagonist AM251. These data demonstrate the presence of cannabinoid CB(1) receptor mRNA and the protein in the mouse urinary bladder. CB(1) and P2X(3) 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 CB(1) receptors in the peripheral modulation of bladder afferent information.