A sympathetic projection from sacral paravertebral ganglia to the pelvic nerve and to postganglionic nerves on the surface of the urinary bladder and large intestine of the cat.

Anatomical and electrophysiological experiments have demonstrated a prominent projection from the sacral sympathetic chain via the pelvic nerve to postganglionic nerves on the surface of the urinary bladder and the large intestine of the cat. Retrograde labeling studies revealed that the pelvic nerve, which is generally believed to carry primarily parasympathetic axons, has a considerable population of sympathetic fibers originating mainly from the S1-S3 paravertebral ganglia. The number of sympathetic neurons projecting to the pelvic nerve (2,100) was about 75% of that projecting to the pudendal nerve (2,900), a somatic nerve which would be expected to carry a large sympathetic fiber constituent. Sympathetic neurons projecting to the pudendal nerve were located primarily in the L6-S2 ganglia. Electrophysiological studies confirmed the presence of a sympathetic pathway from the paravertebral ganglia to the pelvic viscera. Electrical stimulation (thresholds 1.5-3 V) of the lumbar sympathetic chain evoked firing in the pelvic nerve and in postganglionic nerves on the surface of the colon and bladder at latencies of 60-150 msec. The responses were unaffected by cutting the chain one segment rostral to the site of stimulation, but were abolished by the administration of a ganglionic-blocking agent (tetraethylammonium). The responses on the colon and bladder postganglionic nerves were also abolished by transection of the pelvic nerve. The conduction velocity in the sympathetic postganglionic axons was approximately 1 m/second. In summary, these studies indicate that the pelvic nerve, like somatic nerves, receives a prominent projection from the sympathetic chain ganglia. The function of this sympathetic paravertebral pathway and its relationship with prevertebral innervation of the pelvic organs remains to be established.