Functional role of lumbar sympathetic nerves and supraspinal mechanism in the defecation reflex of the cat

The role of the lumbar sympathetic nerves and supraspinal mechanism in the defecation reflex was investigated in 30 adult cats and 6 kittens. One or two propulsive contractions, whose mean pressure evoked was more than about 90 cmH2O (adult cats) and 50 cmH2O (kittens), were induced in the rectum of all animals by rectal distension. These propulsive contractions could be generated at the descending and the transverse colons. The removal of the supraspinal influence by spinal transection at T13 or removal of pelvic afferents to the supraspinal center by spinal transection at L abolished the propulsive contractions. Successive lumbar sympathectomy restored the contractions. Lumbar sympathectomy and the successive removal of the supraspinal influence did not affect the propulsive contractions. In both cases, the final exclusion of the sacral segments by pithing of the spinal cord abolished the propulsive contractions. These results suggest that the sacral excitatory reflex mediated via pelvic nerves and the lumbar inhibitory reflex mediated via lumbar sympathetic nerves can function during rectal distension in spinal cats and that the lumbar inhibitory reflex is suppressed by the supraspinal sympathetic inhibitory reflex activated by pelvic afferents in intact cats, as in guinea pigs, resulting in propulsive contractions.