Recurrent inhibition in sacral parasympathetic pathways to the bladder.

1. The effects produced by stimulation of the central end of transected ventral roots were observed on spontaneous and evoked vesical contractions and on the firing of sacral parasympathetic neurones.2. Recurrent inhibition of sacral parasympathetic neurones was demonstrated at frequencies of stimulation above 10/sec and at intensities above threshold for the parasympathetic axons.3. Recurrent inhibition was present in chloralose cats, as well as in decerebrate animals and was unaffected by chronic spinal transection.4. Interneurones were located which are presumed to be the autonomic equivalents of the somatic Renshaw cells. They were synaptically activated by antidromic stimulation of preganglionic fibres in sacral ventral roots.5. The inhibition of vesical contractions and the firing of the interneurones was reduced when the intravesical pressure was raised.6. The recurrent inhibition was unaffected by the intravenous injection of dihydro-beta-erythroidine.7. Strychnine reduced the recurrent inhibition in some experiments but the results were inconsistent. The effects of picrotoxin were inconclusive.8. The possible role of recurrent inhibition in micturition is discussed.