Involvement of the sacral parasympathetic nucleus in the innervation of the descending colon and rectum in cats.

Studies in anesthetized (urethane, 1.5 g/kg, i.p.) cats using retrograde transport of horseradish peroxidase addressed the locations and morphometric characteristics of neurons in the sacral parasympathetic nucleus of the spinal cord innervating the descending colon and rectum. Marker solution was injected beneath the serous membrane of the study areas of the large intestine. Transcardiac perfusion with fixative solution was performed 48 h later and frontal sections of the sacral segments of the spinal cord were prepared; these were processed by the Mesulam method (1978). The results showed that these areas of the large intestine receive innervation from neurons in the sacral parasympathetic nucleus located in spinal cord segments SI, SII, and SIII. The largest number of labeled cells was seen in segment SII. The neurons of this nucleus innervating the study areas of the large intestine formed two longitudinally distributed group (a lateral and a dorsal), the cells of which differed in terms of size and the orientation of the long axis. The largest number of labeled cells was seen in the lateral group.