Beta-3 adrenergic receptor is expressed in acetylcholine-containing nerve fibers of the human urinary bladder: An immunohistochemical study

AIMSTo identify in the human bladder the structures which express the Beta-3 adrenoceptor (3AR). METHODSHuman bladders from cadaveric organ donors (equally balanced in sex and age) were collected. Bladders were immediately fixed in paraformaldehyde and further processed for cryostat sectioning. Single and double immunohistochemistry was performed using antibodies against 3AR C-terminal, 3AR N-terminal, a pan-neuronal marker (3-Tubulin) and markers of cholinergic (Vesicular Acetylcholine Transporter), adrenergic (Tyrosine Hidroxylase), and peptidergic (Calcitonin Gene-Related Peptide) nerve fibers. RESULTSNerve fibers expressing immunoreactivity for 3AR were abundantly found in the mucosa and muscular layers of the human bladder. No 3AR-IR was detected on urothelial or smooth muscle cells. The presence of 3AR-IR in nerve fibers was confirmed by co-expression with 3-Tubulin. Nerve fibers expressing 3AR-IR were cholinergic, VAChT(+), and abundantly observed in the suburothelium. The cholinergic fibers were in close proximity and intermingled with adrenergic TH+ and peptidergic CGRP(+) fibers. CONCLUSIONSWe demonstrated that 3AR is abundantly located in acetylcholine-containing nerve fibers. These findings have important consequences to understand the mechanism of action of 3AR agonists currently used for the treatment of OAB.