Exp Neurobiol 2:33-41, 1993

Distribution of calcitonin gene-related peptide (CGRP) immunoreactive first sacral primary afferent terminals in the dorsal horn of the rat.

Won Taek Lee, *Eun Sook Park, Jong Eun Lee, Ho Jung Kim and Kyung Ah Park

Department of Anatomy and *Rehabilitation Medicine,
Yonsei University College of Medicine, Seoul 120-749, Korea

Despite many investigations on the spinal distribution of pain-conducting unmyelinated and small myelinated primary afferent fibers, the fundamental questions of the extent of the projection of the primary afferent neurons to the spinal cord.

In order to determine the extent of primary afferent fiber distribution in the spinal dorsal horn, the new technique using neuropeptide calcitonin gene-related peptide(CGRP) as a marker substance of primary afferent fibers was tried. Bilateral surgical transection of dorsal roots from L1 to S4 were done except S1 dorsal root, hence the only S1 primary afferent fibers remained. Immunohistochemistry of CGRP at both light and electron microscopic level were done and results were analyzed by computer-assisted area densitometry.

From S1 dorsal root, ipsilateral ascending fibers of CGRP-immunolabelled small diameter were limited to 3 segments, descending fibers limited to 1 segment. Contralateral ascending of CGRP-immunolabelled fibers were limited to 2 segment. Crossed fibers of the S1 spinal level were extensive, the average area occupied by crossed fibers were about 63% of the ipsilateral S1 immunoreactive area.

Based on our light microscopic observation, at least in the rat S1 dorsal horn, the majority of the fibers were confined in the two segments above and one segment below the route of entry.

Key Words: spinal cord, dorsal rhizotomy, area densitometry

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