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

Abstract

Cannabinoid receptors 1 and 2 (CB1 and CB2) are G-protein coupled receptors that are expressed throughout the body. Cannabinoid receptors are expressed in the urinary bladder and may affect bladder function. The purpose of this study was twofold: to confirm the presence of cannabinoid receptors in the bladder, the L6/S1 spinal cord, and dorsal root ganglia (DRG), and to determine the effects of acute and chronic bladder inflammation on expression of cannabinoid receptors. Acute or chronic bladder inflammation was induced in rats by intravesical administration of acrolein. Abundance of CB1 and CB2 protein and their respective mRNA was determined using immunoblotting and quantitative real-time PCR, respectively. We confirmed the presence of CB1 and CB2 receptor protein and mRNA in bladder, L6-S spinal cord, and DRG. Acute bladder inflammation induced increased expression of CB2, but not CB1, protein in the bladder detrusor. Chronic bladder inflammation increased expression of bladder CB2 protein and mRNA but not CB1 protein or mRNA. Expression of CB1 or CB2 in spinal cord or DRG was unaffected by acute or chronic bladder inflammation. CB1 and CB2 receptors are present in the bladder and its associated innervation, and CB2 receptors are up-regulated in bladder after acute or chronic inflammation. CB2 receptors may be a viable target for pharmacological treatment of bladder inflammation and associated pain.

Figure 1

Immunoblotting for CB1 receptor in rats with acute cystitis. Intensity of bands for CB1 was normalized to that of beta-actin in the same sample. Average intensity of bands for control tissues was arbitrarily set at 1, and samples from treated animals were compared to controls. (A) There were no significant changes in CB1 expression. (B) Representative blots of CB1 expression. (C) Bar graph summarizing data. Data presented as mean of optical density ± S.E.M. DRG, dorsal root ganglia; SC, spinal cord; C, control; T, treated.

Figure 2

Immunoblotting for CB2 receptor in rats with acute cystitis. Intensity of bands for CB2 was normalized to that of beta-actin in the same sample. Average intensity of bands for control tissues was arbitrarily set at 1, and samples from treated animals were compared to controls. (A) CB2 expression was significantly increased in bladder detrusor. (B) Representative blots of CB2 expression. Data presented as mean of optical density ± S.E.M. DRG, dorsal root ganglia; SC, spinal cord; C, control; T, treated.

Figure 3

Immunoblotting for CB1 receptor in rats with chronic cystitis. Intensity of bands for CB1 was normalized to that of beta-actin in the same sample. Average intensity of bands for control tissues was arbitrarily set at 1, and samples from treated animals were compared to controls. (A) There were no significant changes in CB1 expression. (B) Representative blots of CB1 expression. (C) Bar graph summarizing data. Data presented as mean of optical density ± S.E.M. DRG, dorsal root ganglia; SC, spinal cord; C, control; T, treated.

Figure 4

Immunoblotting for CB2 receptor in rats with chronic cystitis. Intensity of bands for CB2 was normalized to that of beta-actin in the same sample. Average intensity of bands for control tissues was arbitrarily set at 1, and samples from treated animals were compared to controls. (A) CB2 expression was significantly increased in bladder mucosa and detrusor. (B) Representative blots of CB2 expression. (C) Bar graph summarizing data. Data presented as mean of optical density ± S.E.M. DRG, dorsal root ganglia; SC, spinal cord; C, control; T, treated.

Figure 5

CB1 and CB2 mRNA in rats with acute cystitis. Gene expression was normalized to abundance of mRNA for GAPDH in the same sample. Average abundance of mRNA from control tissues was arbitrarily set at 1. Relative changes in CB1 and CB2 mRNA in treated animals were compared to control. (A) There were no significant changes in abundance of CB1 and CB2 mRNA. (B) Bar graph summarizing data. Data presented as mean ± S.E.M. DRG, dorsal root ganglia; SC, spinal cord; C, control; T, treated.

Figure 6

CB1 and CB2 mRNA in rats with chronic cystitis. Gene expression was normalized to abundance of mRNA for GAPDH in the same sample. Average abundance of mRNA from control tissues was arbitrarily set at 1. Relative changes in CB1 and CB2 mRNA in treated animals were compared to control. (A) There was a significant increase in abundance of CB2 mRNA in bladder. (B) Bar graph summarizing data. Data presented as mean ± S.E.M. DRG, dorsal root ganglia; SC, spinal cord; C, control; T, treated.