Preganglionic neurons of the sacral parasympathetic nucleus (SPN) were located almost exclusively (98%) within the L6-S1 spinal cord segments. The SPN contained approximately 550 neurons of medium size (10 X 20 micron). These were mainly located in the intermediolateral gray matter and had dendrites that extended into the dorsolateral funiculus, along the lateral marginal zone of the dorsal horn, and medially into the dorsal gray commissure. Labeled dorsal root ganglion cells were almost all located (95%) in the L6 and S1 ganglia. An average of approximately 1,500 sensory neurons were found. These were small cells (17 X 25 micron) whose central processes entered Lissauer's tract from which two groups of collaterals emerged: 1) a prominent lateral pathway along the lateral margin of the dorsal horn that extended into the region of the SPN and also into the dorsal gray commissure, 2) a less prominent medial pathway extending around the dorsal margin of the dorsal horn to terminate in the dorsal gray commissure. These two collateral groups formed fiber bundles that were spaced by approximately 100 micron between centers when observed in the horizontal plane. A third afferent bundle, composed of rostrocaudally oriented fibers, was located in the sagittal plane immediately ventral to the central canal. Comparisons are made between the results in rats and the results of similar experiments performed in cats and monkeys.

No abstract

No abstract

In male rats a large number of the postganglionic neurons which innervate the pelvic organs are located in the major pelvic ganglion. In the present study we have identified the location within this ganglion of neurons which project to either of three pelvic organs, the penis, colon or urinary bladder. Two fluorescent retrogradely-transported dyes, Fast Blue and Fluoro-Gold, were used. For most animals one dye was injected into the cavernous space of the penis, the wall of the distal colon or the wall of the urinary bladder. In a small number of animals two organs were injected, each with a different dye. One to six weeks after injection the major pelvic ganglia were fixed in buffered formaldehyde. The distribution of fluorescent dye-labelled cells was observed in whole mounts of complete ganglia and, in most cases, also in small accessory ganglia located between the ureter and the prostate. The studies showed a unique pattern of distribution for each organ-specific group of neurons. Most of the colon neurons are located in the major pelvic ganglion near the entrance of the pelvic nerve, whereas almost all of the penis neurons are near or within the penile nerve. Bladder neurons are relatively evenly distributed throughout the ganglion. These results demonstrate a distinct topographical organization of organ-specific neurons of the major pelvic ganglion of the male rat, a phenomenon which has also been observed in other peripheral ganglia.

No abstract