Cold- and menthol-sensitive C afferents of cat urinary bladder

Cold-sensitive C afferents of the urinary bladder were studied in adult cats anaesthetised with a-chloralose. The bladder was catheterised for fluid instillations and bladder pressure recordings. Pelvic nerve branches were stimulated electrically close to the bladder. Evoked afferent activity was recorded from dissected filaments of the ipsilateral S1-S2 dorsal roots. Responsive afferents were identified using the 'marking technique', based on activity-dependent decrease in C fibre conduction velocity. Of 108 examined bladder C afferents, 14 were activated by innocuous cooling of the bladder wall. Their conduction velocities ranged from 0.6 to 1.7 ms(-1) and their activity dependent decrease in conduction velocity was <10%. All nine cold-sensitive afferents tested responded to menthol exposure. Cold-sensitive C afferents failed to respond to bladder filling with body-warm saline and to active bladder contractions. These characteristics indicate that the cold-sensitive C afferents of the bladder resemble cutaneous cold receptors rather than cold-sensitive mechanoreceptors or nociceptors. It is concluded that the bladder wall is endowed with cold receptors with unmyelinated C afferents in the pelvic nerves and that these afferents are responsible for the bladder cooling reflex.