The identification and characteristics of sacral parasympathetic preganglionic neurones

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Abstract
Sacral parasympathetic preganglionic neurons were identified by intracellular and extracellular micro-electrode recording of antidromic potentials in response to stimulation of the pelvic nerve or the 2nd or 3rd sacral ventral roots. The segmental distribution of autonomic neurons varied in different cats. In some cats they were mainly in S2 segment, in others in S3 and in the remainder, in both S2 and S3. The antidromic potentials showed initial segment-somadendritic (IS-SD) inflexions and delayed depolarizations and were slightly less prolonged than those of sympathetic neurons but more prolonged than those of spinal motoneurons. After hyperpolarization was observed after the antidromic spike potential. The conduction velocities for sacral parasympathetic preganglionic fibers were less than 12.5 m/sec. and thus were similar to those of sympathetic preganglionic fibers. Parasympathetic neurons were not excited by micro-electrophoretically applied 5-hydroxytryptamine, noradrenaline or acetylcholine.