The C fibre reflex of the cat urinary bladder

1. Reflexes evoked in bladder parasympathetic neurones by electrical stimul ation of bladder C afferent fibres were studied in cats anaesthetized with alpha-chloralose. The responses were compared with the ordinary micturition reflex evoked by low-threshold A delta afferents from bladder mechanorecep tors and mediated by a spino-ponto-spinal reflex pathway. 2. The bladder was catheterized for fluid instillations and pressure record ings. Efferent reflex discharges were recorded from the cut central end of a small distal bladder branch of the pelvic nerve. The remaining bladder pe lvic nerve branches were stimulated electrically close to the bladder. 3. Stimulation at C afferent intensity evoked a late reflex discharge in bl adder pelvic efferents in all animals. The response was centrally mediated, had a latency of 150-250 ms, and was much weaker after stimulation on the contralateral nerve. 4. The bladder C fibre reflex differed in several functional aspects from t he ordinary A delta micturition reflex. It could be evoked at a low rate of stimulation, with an empty bladder and no background activity from bladder mechanoreceptors. In this situation, the normal A delta micturition reflex is not elicited. The C fibre reflex also survived an acute spinalization a t a low thoracic level. 5. The C fibre reflex was strongly inhibited by dorsal clitoris or dorsal p enis nerve stimulation, an effect that was maintained after spinalization. It was facilitated by bladder or urethra exposure to cold and menthol, stim uli that activate specific cold-sensitive receptors associated with unmyeli nated C afferents. 6. It is concluded that the central pathway of the C fibre reflex is spinal and partly separate from that of the ordinary micturition reflex. These ob servations are in keeping with the clinical finding that a bladder cooling reflex can be elicited in patients with disturbed descending control of the bladder.