This study was undertaken to determine the origins of dorsal root ganglion (DRG) cells containing calcitonin gene-related peptide (CGRP) which innervate the quadriceps femoris tendon in the rat.

DRG cells containing CGRP, which innervate the quadriceps femoris tendon, from 25 rats (Sprague-Dawley, 200-250 g) were examined using the retrograde tracing technique (neural tracers: horseradish peroxidase and fluorogold) combined with immunohistochemistry.

Injection of horseradish peroxidase (HRP) or fluoro-gold (FG) into the quadriceps femoris tendon resulted in the ipsilaterally labelling of cells between L1 and L6 DRGs. However, a large number of the labelled cells innervating the quadriceps femoris tendon were found in the L3 and L4 DRGs. Many DRG cells were immunostained with CGRP antibody in the L1-6 DRGs. The number of CGRP immunoreactive cells in the lumbar DRGs was larger than in the sacral DRG. FG labelled cells containing CGRP immunoreactivity (FG+CGRP cells) were found in the lumbosacral DRGs. Many FG+CGRP cells innervating the quadriceps femoris tendon were located in the L3 and L4 DRGs.

These results show that the main DRG origin for the sensory innervation of the quadriceps femoris tendon is L3 or L4. The neurogenic pain of the quadriceps femoris tendon may originate from this region, and suggests that this may be important for the release of neurogenic pain.