Histological distribution and ultrastructural features of immunoreactive terminals against RT97, a monoclonal antibody to a 200 kD neurofilament, in the spinal dorsal horn of a rat.

Localization and ultrastructural features of immunoreactive fibers and terminals against RT-97, a mouse monoclonal antibody that recognizes subunit of a 200-kD neurofilament, were examined in the spinal dorsal horn of adult rats. Under a light-microscope, many RT-97 immunoreactive fibers were detected in the dorsal root, collaterals of the dorsal root in the dorsal funiculus, and laminae III and IV in the dorsal horn. Few immunoreactive fibers were found in laminae I and II. Electron microscopic observation demonstrated that almost all RT-97 immunoreactive fibers in the dorsal root were myelinated, and unmyelinated fibers immunonegative. The immunoreactive fibers entered into the dorsal horn passing through the collaterals of the dorsal root along the superficial gray lamina. In the dorsal horn, these fibers ascended into and then terminated in lamina II. RT-97 immunoreactive central terminals were semicircular or ellipsoid in appearance and contained many flat-type presynaptic vesicles. Some terminals made synaptic contact with dendritic profiles in lamina II. Our present results indicate that RT-97 is a useful marker for ultrastructural examination of terminals served by non-nociceptive A-fibers.