ReviewPropriospinal pathways in the dorsal horn (laminae I-IV) of the rat lumbar spinal cord

The spinal dorsal horn is regarded as a unit that executes the function of sensory information processing without any significant communication with other regions of the spinal gray matter. Within the spinal dorsal horn, however, the different rostro-caudal and medio-lateral subdivisions intensively communicate with each other through propriospinal pathways. This review gives an overview about these propriospinal systems, and emphasizes that the medial and lateral parts of the spinal dorsal horn show the following distinct features in their propriospinal interconnectivities: (a) A 100-300 μm long section of the medial aspects of laminae I-IV projects to and receives afferent fibers from a three segment long compartment of the spinal dorsal gray matter, whereas the same length of the lateral aspects of laminae I-IV projects to and receives afferent fibers from the entire rostro-caudal extent of the lumbar spinal cord. (b) The medial aspects of laminae I-IV project extensively to the lateral areas of the dorsal horn. In contrast to this, the lateral areas of laminae I-IV, with the exception of a few fibers at the segmental level, do not project back to the medial territories. (c) There is a substantial direct commissural connection between the lateral aspects of laminae I-IV on the two sides of the lumbar spinal cord. The medial part of laminae I-IV, however, establishes only a minor commissural propriospinal connection with the gray matter on the opposite side.

► An overview about the propriospinal interconnectivities of the dorsal horn. ► A short rostro-caudal propriospinal pathway exists in the medial part of the dorsal horn. ► A long rostro-caudal propriospinal pathway exists in the lateral part of the dorsal horn. ► There is a unidirectional medio-lateral propriospinal pathway in the dorsal horn. ► A commissural propriospinal pathway interconnects the lateral parts of the dorsal horn.