The Journal of comparative neurology
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The tract of Lissauer receives small caliber dorsal root fibers in addition to axons arising from dorsal horn neurons. The termination of Lissauer's tract and dorsal root fibers was examined in the C7 segment of the rhesus monkey spinal cord. The distribution of normal dorsal root afferents was mapped by labelling the C7 dorsal root ganglion with tritiated amino acids, and then compared with the degeneration of C7 dorsal root fibers following an intradural dorsal rhizotomy. ⋯ The tract of Lissauer consists of two populations, each containing small afferents. One population degenerates at three to five days and distributes mainly to laminae II and III (substantia gelatinosa); the other degenerates around 12 days and distributes mainly to lamina I and the outer zone of II. It is suggested that the exclusive termination of the small afferents to laminae I, II and III may be correlated with certain unique histochemical properties (e.g., high substance P and high opiate receptor binding levels) of these same dorsal horn areas...