Abstract
Low back muscle pain is problematic because the pathway and mechanisms still remain to be solved. The neuroanatomical pathway of nociception originating in low back muscles (erector spinae, ES) was examined in this study. The neurotracer true blue (2%, 10µl) injected into ES muscles just beside the spinous process L5 was retrogradely transported to dorsal root ganglia (DRG) cells mainly at L3, not at L5. Intramuscular injection of 5% formalin into ES muscles beside the spinous processes L4 and L5 induced c-Fos protein expression with wide craniocaudal distribution from L1-L5 of the spinal dorsal horn. The labeling with c-Fos was particularly marked in the most lateral part of the superficial dorsal horn. The supraspinal projection of the spinal nociceptive input was also examined. The neuronal tracer fluorogold (2%, 0.3µl) was injected into the lateral thalamus 6 days prior to the formalin injection. Fluorogold-positive neurons with c-Fos immunoreactive nuclei were rare in the spinal dorsal horn from L1-L5. These results indicate that 1) the input from ES muscles at L5 level mainly goes to DRG L3, 2) the craniocaudal distribution of nociceptive input from ES muscles is very wide with a well organized somatotopy in the spinal dorsal horn, and 3) the lateral thalamus is probably not a main target region for nociceptive information from ES muscles. [J Physiol Sci. 2007;57 Suppl:S98]
