Bladder sensory signalling is traditionally attributed to stretch-sensitive sensory nerves (afferents) within the detrusor muscle. However, a substantial population of stretch-insensitive afferents resides within the bladder mucosa, and their role in bladder sensation and function remains unknown. We hypothesised that these mucosal afferents act as specialised detectors of pathological stimuli, rather than physiological bladder filling, and are critical for driving sensory and behavioural responses during urinary tract infection (UTI). This study aimed to (i) define the functional role of mucosal afferents in healthy bladder function, and (ii) determine their contribution to sensory signalling, behaviour, and host defence during UTI.

We developed a novel mouse model of selective bladder mucosal afferent denervation using intravesical instillation of resiniferatoxin (RTX) in female mice for 3 days. Assessment of bladder innervation using CGRP immunohistochemistry and Nav1.8tdTomato reporter mice, afferent function (ex vivo single-unit and whole-nerve recordings), and bladder physiology (voiding assays) were conducted 7 days after the final RTX infusion. To investigate disease-specific roles, female mice were challenged with uropathogenic E. coli (UPEC – strain CFT073 - 5 x 106 CFU/mouse) to induce acute UTI. Sensory neuron responses (ex-vivo single unit recordings, pelvic pain (Electronic von Frey testing), urinary behaviour (voiding spot assays), bacterial burden (urine, bladder, kidney), and immune responses (flow cytometry) were assessed in control and mucosal-denervated mice (7 days after RTX treatment) 24hrs post infection.

Intravesical RTX selectively ablated mucosal afferents, markedly reducing CGRP⁺ and NaV1.8tdTomato⁺ fibre density in the mucosa (P<0.001) while preserving detrusor innervation (P>0.05). Functionally, RTX significantly reduced mucosal afferent responses (P<0.001) without affecting stretch-sensitive muscular afferents (P>0.05). In healthy mice, mucosal denervation had no impact on afferent responses to bladder distension ex vivo (P>0.05), bladder compliance (P>0.05), or voiding behaviour (P>0.05), indicating these afferents are not required for normal mechanosensation or bladder function. During UTI, mucosal afferents developed significant hypersensitivity (P<0.001), with increased spontaneous firing and enhanced responses to mucosal stimulation whilst muscular afferent responses to stretch were unchanged (P>0.05). Selective mucosal denervation with RTX prevented infection-induced sensitisation. At the behavioural level, UTI induced significant pelvic hyperalgesia (P<0.01) and urinary frequency (P<0.01), both of which were abolished by mucosal denervation by RTX. Importantly, loss of these responses following RTX pretreatment resulted in significantly increased bacterial burden in the bladder, urine, and kidneys (P<0.01), with greater infection dissemination and increased neutrophil infiltration, consistent with heightened infection severity.

These findings demonstrate a fundamental division of labour within bladder sensory pathways: muscular afferents regulate physiological bladder function, while mucosal afferents act as sensors of infection. During UTI, mucosal afferents become selectively sensitised and drive pain and urinary frequency, responses that are not merely symptoms, but functional components of host defence that facilitate bacterial clearance.
The absence of effects in healthy conditions highlights the context-dependent role of mucosal afferents and suggests that targeting these pathways could modulate pathological sensations without disrupting normal bladder function.

Bladder mucosal afferents are key detectors of infection that drive protective sensory and behavioural responses during UTI. These findings redefine the neural basis of bladder sensation and identify mucosal sensory pathways as promising therapeutic targets for treating bladder pain and urgency while preserving normal function. Whether mucosal nerves represent a ubiquitous sensor for non-infectious cystitis remains to be determined.