Mechanisms of continence

Abstract

While disorders of urine storage are of considerable clinical significance, little is known about autonomic nervous system dysfunction and the neural control of continence. The paucity of studies on the sympathetic reflex to the bladder may be partly related to doubts about the involvement of the nervous system in the continence process, particularly at filling rates within the naturally occurring range. In the present study, the characteristics of the postganglionic sympathetic outflow to the feline bladder were examined at filling rates within the naturally occurring range. The sympathetic outflow was observed to have a net inhibitory effect on bladder wall tension for a significant portion of the continence process, although both tonic sympathoinhibitory and phasic sympatho-excitatory influences were detected. The sympathetic reflex to the bladder was characterised as a simple rate independent reflex, the tonic increases in activity being augmented by prolonged after-discharges, possibly arising at the ganglion level. Both the level of sympathetic reflex activation and the degree of sympatho-inhibitory control over the bladder appeared to be dependent on the level of bladder wall tension, as transduced by the pelvic and possibly hypogastric afferent mechanoreceptors. Bladder distension dependent activity from the whole hypogastric nerve was similar to activity in hypogastric filaments near the bladder wall. However, a large vasomotor component in the hypogastric nerves of female animals was probably destined for the female genital organs. The present observations were made while deliberately using pentobarbitone anaesthesia. The continence control system appeared functionally similar under other anaesthetics. The sympatho-inhibitory reflex reduced bladder wall tension, promoting urine storage by reducing the level of afferent discharge impinging upon the nervous system. The sympatho-excitatory reflex appears to be involved in the production of non-micturating contractions in the anaesthetised cat, by providing a synchronous excitation of the bladder detrusor