Organization of cutaneous ventrodorsal and rostrocaudal axial lines in the rat hindlimb and trunk in the dorsal horn of the spinal cord.

The somatotopic organization of cutaneous primary afferents projecting to the dorsal horn of the rat spinal cord was investigated. The fluorescent neurotracer, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was applied to cutaneous incisions made along ventrodorsal axial lines (VDALs) or rostrocaudal axial lines (RCALs) of the trunk and hindlimb. DiI-induced fluorescent zones appeared in laminae I-III of the dorsal horn in the transverse section. Several fluorescent zones appeared at different mediolateral portions after tracer application to VDALs. After tracer was applied to RCALs, a single zone of fluorescence was observed. Serial transverse sections were used to reconstruct fluorescent zones in lamina II and to illustrate the rostrocaudally elongated band-like projection fields in a horizontal plane. In the horizontal plane, the fluorescent zones of VDALs were reconstructed to band-like projection fields. These fields were arranged mediolaterally and extended rostrocaudally for approximately the length of one spinal cord segment or less. The fluorescent zones of RCALs were reconstructed to one band-like projection field. This field extended rostrocaudally over several spinal cord segments. Cutaneous afferents from the ventral median line of the trunk, tail, hindlimb, sole, and ventral side of the digits projected to the medial margin of the dorsal horn. Cutaneous afferents from the dorsal median lines projected to the lateral margin of the dorsal horn. By analyzing the pattern of the body surface regions and the VDALs and RCALs, the central projection fields of body surface regions could be hypothesized, based on the central projection fields of the individual VDAL and RCAL afferents. Thus, we established a detailed dorsal view map of the central projection fields of cutaneous primary afferents. Copyright 2002 Wiley-Liss, Inc.