Supraspinal control of external anal sphincter motility: effects of vesical distension in humans and cats

A pontine centre located near the micturition centre controlling external anal sphincter (EAS) motility via noradrenergic neurones has been described in cats. The aim of this study was to determine (i) whether a similar centre controls EAS motility in humans and (ii) whether this centre is involved in vesico-sphincteric reflexes in cats and humans. The effects of an alpha-1-adrenoceptor antagonist (nicergoline) and those of vesical distension on the electrical activity of the EAS were studied in paraplegic and non-paraplegic volunteers. The effects of vesical distension by injecting saline at physiological levels on the responses of the EAS to pudendal nerve stimulation were investigated in intact cats and cats with nerve sections. In non-paraplegic subjects, nicergoline and vesical distension abolished the activity of the EAS. These effects were no longer observed in paraplegic patients. In cats, vesical distension inhibited the reflex response of the EAS to pudendal nerve stimulation. This vesico-sphincteric reflex, which was no longer observed in spinal animals, persisted after nicergoline injection. These findings indicate that in humans, there exists a supra-spinal centre facilitating the tonic activity of the EAS via noradrenergic neurones not involved in the inhibitory vesico-sphincteric reflex.