Neuronally mediated interactions between urinary bladder and internal anal sphincter motility in the cat

The effects of stimulation of vesical afferents on the electrical activity of the internal anal sphincter were studied in anaesthetized cats. Excitation of vesical afferents, either by electrical stimulation of nerves running at the vesico-ureteral junction or by bladder distension, produced (1) an increase in the electrical activity of the internal anal sphincter which was abolished by the alpha-blocker phentolamine (1.5 mg/kg, I.V.); (2) an inhibition of the excitatory response evoked in the internal anal sphincter by stimulation of one hypogastric nerve. This effect was blocked by naloxone (2 mg/kg, I.V.). These reflexes were abolished by hexamethonium (1 mg/kg, I.V.). Both reflexes were unaffected by section of sacral spinal roots (S1-S3) or by administration of atropine (0.1 mg/kg, I.V.). This excludes any participation of the parasympathetic nervous system. The excitatory and inhibitory reflexes were only slightly affected by section of the lumbar dorsal spinal roots (L1-L7) whereas they were strongly decreased after section of the corresponding ventral roots. The reflexes were abolished after section of the remaining hypogastric nerve. These results provide evidence for crossed reflexes between urinary bladder and internal anal sphincter which are achieved partly in the lumbar spinal cord and partly within the inferior mesenteric ganglion. Some of the vesical afferent nerve fibres responsible for these interactions presumably reach the spinal cord via the lumbar ventral spinal roots.