Reflex firing in the lumbar sympathetic outflow to activation of vesical afferent fibres.

1. Activation of vesical afferent fibres in the Agammadelta range by electrical stimulation of the pelvic nerve or by bladder distension elicited reflex firing in hypogastric nerves and in preganglionic nerves to the inferior mesenteric ganglion.2. The multisynaptic reflex was present in cats with an intact spinal cord and in acute and chronic spinal animals (transections at T10-T12). The reflex pathway was partially crossed in the sacral cord, and in the periphery at the level of the inferior mesenteric ganglia. In contrast, an inhibitory response to raised intravesical pressure was mediated by a supraspinal inhibitory mechanism which was activated in parallel with the micturition reflex.3. Since enhancement as well as depression of sympathetic firing accompanied reflex micturition, it is concluded that at least two distinct populations of lumbar preganglionic neurones are responsive to vesical afferent activity: one population being excited, the other depressed, during micturition. The latter population may be involved in an inhibitory feed-back mechanism on to the bladder.