Sensory afferent innervation of the bladder wall is critical for regulating lower urinary tract function. Calcitonin gene–related peptide (CGRP) is a neuropeptide expressed predominantly in unmyelinated C-fibers and serves as a marker of sensory afferent fibers. While previous studies suggested regional differences in bladder innervation, quantitative evidence across the rostro–caudal axis is lacking. Here, we systematically quantified regional differences in CGRP-positive afferent innervation across the mouse bladder. Bladder tissue from nine mice was processed and stained for CGRP immunofluorescence. Images were segmented into seven equal rostro–caudal regions from bladder dome to bladder neck, and CGRP-positive area was quantified and normalized to total tissue area. A permutation testing approach was applied to determine whether CGRP increased along the rostro–caudal axis. CGRP-positive fibers were detected throughout the bladder wall and showed a gradual increase in CGRP-positive area from dome to bladder neck. Linear regression analysis across segment means yielded a positive slope (β = 0.0095). Exact permutation testing across all 5,040 possible segment arrangements showed that only 1.7% of permuted datasets produced slopes equal to or greater than the observed value (p = 0.0171). These results confirm that CGRP-positive afferent innervation of the mouse bladder wall is not evenly distributed but follows an exponential-like gradient along the rostro–caudal axis, with higher density toward the bladder neck. These findings establish a quantitative baseline for regional sensory organization and may inform studies of pathological remodeling and new region-targeted therapies.
Chadily et al. (Sun,) studied this question.