Segmental somatotopic organization of cutaneous afferent fibers in the lumbar spinal cord dorsal horn in rats.

In the present study, we investigated the central representation of segmental cutaneous afferent fiber projection fields in the horizontal plane of the spinal cord dorsal horn in adult rats. The neurotracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil) was applied to spinal nerves T12-S2 and cutaneous ventrodorsal axial lines T13-S1. The Dil fluorescent zones in transverse sections of the dorsal horn were observed microscopically. Mediolateral locations of Dil fluorescent zones were measured, followed by reorganization on the horizontal plane through lamina I-I111. Rostral and caudal boundary lines of the central projection fields of spinal nerves T12-S2 formed 'waves' in the horizontal plane of the dorsal horn, pitching rostrocaudally about one spinal cord segment. The rostral and caudal apexes of the waves could be linked with those of adjacent segments, suggesting that the wave pattern is continuous rostrocaudally in the dorsal horn. The waves were markedly transformed in the central projection fields of the hindlimb and genital regions, in the L5 and L6 spinal cord segments.