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

AIMS To identify in the human bladder the structures which express the Beta-3 adrenoceptor (β3AR). METHODS Human 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 β3AR C-terminal, β3AR N-terminal, a pan-neuronal marker (β3-Tubulin) and markers of cholinergic (Vesicular Acetylcholine Transporter), adrenergic (Tyrosine Hidroxylase), and peptidergic (Calcitonin Gene-Related Peptide) nerve fibers. RESULTS Nerve fibers expressing immunoreactivity for β3AR were abundantly found in the mucosa and muscular layers of the human bladder. No β3AR-IR was detected on urothelial or smooth muscle cells. The presence of β3AR-IR in nerve fibers was confirmed by co-expression with β3-Tubulin. Nerve fibers expressing β3AR-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. CONCLUSIONS We demonstrated that β3AR is abundantly located in acetylcholine-containing nerve fibers. These findings have important consequences to understand the mechanism of action of β3AR agonists currently used for the treatment of OAB.