Gray commissure

Abstract: The central distribution of visceral primary afferent fibers from the pelvic nerve of the cast and the relationship of these fibers to preganglionic neurons of the sacral parasympathetic neurons (SPN) have been studied. Horseradish peroxidase (HRP) applied to the cut pelvic nerve was detected ipsilaterally in preganglionic neurons and dorsal root ganglion cells (segments S1-S3), and in central afferent projections to Lissauer's tract (LT), the dorsal columns, the dorsolateral funiculus, and spinal gray matter. The afferent projections were strongest in the region of the SPN (S1-S3) but extended far beyond its limits (e.g., LT was labeled from L4 to Cx7). In the transverse plane, collateral fiber bundles formed a thin shell around the dorsal horn predominantly within lamina I and expanded into terminal fields in the gray matter. The more prominent lateral collateral projection (LCP) extended into laminae V and VI, whereas the medial one (MCP) ended in the dorsal commissure. In longitudinal planes these projections exhibited a periodicity with an interval of approximately 200 micrometer. The distribution of afferent collateral projections overlaps the regions where many preganglionic neurons and their dendritic extensions are located, and also areas known to contain interneurons involved in visceral pathways. A differential distribution of afferents within the SPN was noted where a higher intensity was observed in proximity to those neurons located in laminae V and VI, which innervate the colon, and a lower intensity near neurons located in Lamina VII which innervate the bladder. This is consistent with the known spinal control of colon reflexes and the supraspinal control of bladder reflexes. The widespread rostrocaudal extent of the pelvic primary afferent projection is consistent with the necessity for the integration of somatic and autonomic elements from various levels of the lumbo-sacral-coccygeal spinal cord in the performance of pelvic visceral functions.

Abstract: 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.

Abstract: Application of horseradish peroxidase to the pudendal nerve in the female cat labelled lumbosacral afferent and efferent neurons and their processes. Afferent axons entered the spinal cord primarily at the S1 and S2 segments and traveled rostrocaudally in Lissauer's tract and the dorsal columns. A distinctive component of the dorsal column projection was located at the lamina I-dorsal column border as a densely labelled, compact bundle that distributed fibers to the dorsal horn at spinal levels near the segments of entry of the afferent axons. Afferent terminal labelling was located in the marginal zone, the intermediate gray matter, and the dorsal gray commissure in the lumbosacral and coccygeal spinal cord. A well-defined terminal field restricted to the S1 and rostral S2 segments was present in the medial third of the nucleus proprius and substantia gelatinosa. Labelled motoneurons in Onuf's nucleus (S1 and S2) exhibited longitudinal dendrites that extended rostrocaudally within the nucleus and three groups of transverse dendrites that emanated periodically from the nucleus and passed to the ventrolateral funiculus, the intermediate gray, and the dorsal gray commissure. Components of the pudendal nerve that innervate the anal and urethral sphincters were also labelled by injecting HRP into the respective sphincter muscles. Motoneurons innervating the anal and urethral sphincters were located in the dorsomedial and ventrolateral divisions, respectively, of Onuf's nucleus. Afferent projections from the two sphincters were similar; the most prominent terminations were present in the marginal zone, intermediate gray, and dorsal gray commissure. These results are discussed with respect to the physiological function of the pudendal nerve and its relationship with sacral autonomic pathways.

Abstract: The distribution in the spinal cord of the rat of preganglionic neurons sending fibers into the hypogastric nerve was determined with the retrograde transport of horseradish peroxidase (HRP). Labeled cells were present in the intermediate gray matter of spinal segments L1-L2. The majority (81%) of HRP-filled cells formed a continuous column along the midline in the dorsal gray commissure. This cell column was termed the dorsal commissural nucleus (DCN). The remainder of HRP-labeled cells were present bilaterally in the middle and lateral regions of the intermediate gray; the majority of the latter cells were located along the lateral border of the intermediate gray. The present finding of a midline preganglionic autonomic cell column in the spinal cord of a mammal is contrary to previous reports, in which sympathetic preganglionic neurons have been localized primarily in the lateral intermediate gray. The DCN may be species-specific and related to the system of short adrenergic neurons present in the pelvis.

Abstract: Comparison of the immunocytochemical localizations revealed distinct patterns of differential distribution and overlapping of calbindin-D28K (CB-D28K), calretinin (CR), calmodulin (CM) and parvalbumin (PV) in the rat spinal cord. In some areas, one of the four calcium-binding proteins (CBPs) appears to be predominant, for example, CB-D28K in lamina I and ependymal cells, PV at the inner part of laminae II, CR in laminae V and VI and CM in motoneurons of lamina IX. In other regions of the spinal cord, more than one CBPs was abundant. CB-D28K and CR were similarly distributed in lamina II and the lateral spinal and cervical nucleus; CM and PV were similarly abundant in the ventromedial dorsal horn, internal basilar and central cervical nucleus; CR and PV were similarly heterogeneous in the gracile fasciculus from caudal to rostral spinal cord. In the sacral dorsal gray commissure, the distribution patterns of CR and PV were clearly complementary. The unilateral ganglionectomies resulted