The distribution and morphology of parasympathetic preganglionic neurons in the cat sacral spinal cord as revealed by horseradish peroxidase applied to the sacral ventral roots.

Parasympathetic preganglionic neurons in the sacral parasympathetic nucleus (SPN) of the cat were studied by applying horseradish peroxidase (HRP) to the sacral ventral roots. The results were compared to data from earlier experiments in which these same neurons were labelled by HRP applied to the pelvic nerve at a point much further from the spinal cord. The present experiments have shown. The total number of neurons in the SPN determined by ventral root labelling is equal to the number obtained by pelvic nerve labelling. This indicates that virtually all SPN neurons send their axons into the pelvic nerve. More extensive dendritic projections from SPN neurons were revealed than in the pelvic nerve experiments. In particular, a strong dendritic projection extended within the lateral marginal zone of the dorsal horn close to Lissauer's tract and horizontal dendrites projected well into the contralateral gray matter, some reaching the contralateral sacral parasympathetic nucleus. The neurons labelled via any one ventral root were all contained within a region equal in length to one spinal segment but shifted rostrally by a small amount. Thus, no evidence was obtained for a long intraspinal pathway in which axons of spinal cord neurons entered ventral roots many segments away from their somata.