ORGANIZATION OF HINDLIMB NERVE PROJECTIONS TO THE RAT SPINAL-CORD - ACHOLERAGENOID HORSERADISH-PEROXIDASE STUDY

The aim of the present study has been to investigate the projections o f hindlimb muscle afferent fibers to the spinal cord with particular e mphasis on the ventral horn and the column of Clarke. Following transe ctions of the appropriate ventral roots, injections of the B-subunit o f cholera toxin conjugated to horseradish peroxidase were made into th e tibial, peroneal, hamstring, superior gluteal, femoral, and obturato r nerves in one group of adult rats. In another group of rats, similar experiments were done with intact ventral roots in order to map the l ocation in the ventral horn of the motoneuron cell columns supplying e ach investigated nerve. An extensive overlap was found for the differe nt nerve projections to Rexed's laminae V-VII. A somatotopic organizat ion of the nerve projections was seen in the lamina IX cell groups of the ventral horn as well as in the column of Clarke, even though an ov erlap existed. The densest primary afferent projection from each injec ted nerve was to its homonymous motoneurons. Only a small to moderate overlap between the projections of the tributary branches of the sciat ic nerve was found in the ventral horn, whereas the obturator and femo ral nerve projections showed more profound overlap. In the column of C larke, hindlimb nerves innervating distal muscles projected medially, and nerves innervating proximal muscles projected laterally. (C) 1996 Wiley-Liss, Inc.