Cellular Distribution and Expression of Cannabinoid Receptors Type 1 and 2 in the Urinary Bladder of Cats (Felis catus)

This study aimed to qualitatively and quantitatively characterize the gene and protein expression of cannabinoid receptors type 1 (CB1) and 2 (CB2), and to describe their cellular distribution in the urinary bladder of cats. Samples were collected post-mortem from 11 cats with no history of lower urinary tract disease and were analyzed using reverse-transcription quantitative PCR (RT-qPCR), Western blot, and immunofluorescence. Mean fluorescence intensity was analyzed in the urothelium and detrusor muscle using a paired t-test (p < 0.05). CNR2 transcripts were detected in both compartments, whereas CNR1 transcripts were not detectable. Western blot detected both CB1 and CB2 bands. CB1R immunoreactivity (CB1R-IR) was sparse within the urothelium, with occasional umbrella and basal cells, and was detected in endothelial cells, intramural neurons, nerve fibers, and detrusor smooth muscle cells. CB1R-IR was significantly higher in the detrusor muscle (p = 0.0006). CB2R-IR showed marked staining in umbrella cells and faint staining in basal cells; it was also observed in bundles of nerve fibers, intramural neurons, detrusor smooth muscle cells, and vascular structures. CB2R-IR was significantly higher in the urothelium (p < 0.0001). These findings provide a molecular basis for studies investigating the endocannabinoid system as a potential therapeutic target in feline lower urinary tract disorders.