The sacral parasympathetic reflex pathway regulating colonic motility and defaecation in the cat.

Abstract

SUMMARY1. The sacral parasympathetic outflow to the large intestine of the cat was studied by monitoring simultaneously intestinal motility and the efferent firing in postganglionic fibres on the serosal surface of the mid-distal colon.2. Increases in efferent firing were noted during the occurrence of spontaneous propulsive activity (tonic pressure waves) or segmental contractions (slow rhythmic pressure waves). The neural discharge was not altered by transaction of the lumbar sympathetic innervation to the colon but was blocked by interruption of the sacral parasympathetic outflow.3. Electrical stimulation of pelvic nerve afferents arising in the colon or distension of the colon or rectum evoked reflex increases in efferent firing and sustained propulsive contractions that were associated with defaecation. Both responses were abolished by transaction of the pelvic nerves or sacral dorsal roots.4. Electrical stimulation of colonic afferent fibres also evoked synchronous reflex discharges in colonic efferents at latencies ranging from 180 to 300 msec. The discharges were enhanced during propulsive contractions, abolished by transaction of the pelvic nerves but not altered by transaction of the lumbar sympathetic nerves.5. Sacral reflexes were present in cats with intact spinal cord and in chronic spinal animals transactionn at T10-T12). The reflexes recovered within minutes to several hours after acute transaction of the spinal cord.6. Electrophysiological measurements indicated that the sacral reflexes to the large intestine were mediated by non-myelinated afferent and preganglionic efferent fibres. The central delay for the reflex was estimated to be 45-60 msec.7. It is concluded that the sacral parasympathetic reflexes to the large intestine are mediated via a spinal pathway and have an essential role in the initiation of propulsive activity during defaecation.

Spinal cord stimulation modulates intraspinal colorectal visceroreceptive transmission in rats

“…This observation supports our statement that the inhibitory responses were the result of SCS modulating spinal neuronal activity and did not result from a change in colonic compliance. It has been shown that directly stimulating pelvic nerve afferent nerves from the colon with a high intensity and low frequency (12 V with trains of stimuli at 1.5 c/s, 4 shocks at 100 c/s and 0.05 msec duration) produce strong propulsive contractions of the colon (De Groat and Krier 1978). In the present studies, the stimulus intensity was much lower.…”

Extrinsic primary afferent signalling in the gut

“…18 Similarly, pelvic and/or sacral afferent fibres run in parallel to sacral parasympathetic outflow and are intimately connected by synapses in the spinal cord. 19 The anatomical sharing of peripheral nerve trunks by efferents and primary afferents is not just parsimonious-it reflects important functional connectivity.…”

“…Low levels of distension of the rectum activate rectal contractions and anal relaxations; 48 largely via sacral parasympathetic pathways. 19 Rectal distension in humans evokes sensations of urge at low pressures, unpleasantness at high pressures and pain at still higher pressures. 149 Pain and unpleasantness co-vary more closely than either sensation with urge.…”

Bowel dysfunction following spinal cord injury

“…17 It is able to organise defecation even after upper spinal cord section. 19 However the sacral parasympathetic centre is also in¯uenced by supraspinal nervous structures. In the dog, the ®ring of sacral parasympathetic neurons is modulated by the pontine reticular formation.…”