An immunohistochemical investigation of the opioid cell column in lamina X of the male rat lumbosacral spinal cord.

Tri-color immunohistochemistry was employed to examine enkephalin-like immunoreactive neurons in lamina X of the rat lumbosacral spinal cord. Serial coronal sections from levels L1 to S3 were examined. A rostral group of large (40-50 microm diameter), pyramidal-shaped enkephalin-like immunoreactive neurons were shown from levels L1 to L4-5. Essentially all of these neurons were also immunoreactive for galanin and cholecystokinin. A second enkephalin-like immunoreactive cell group, extending from L5 to approximately the S2-3 level, contained smaller (20-30 microm diameter), ovoid-shaped perikaryia. Approximately 75% of these enkephalin-like immunoreactive neurons were also immunoreactive for neuropeptide Y. Neurotensin-immunoreactivity was also present in this area, having varying amounts of co-localization with these other two peptides. These results demonstrate that the lumbosacral opioid cell column in lamina X is not a neurochemically homogenous structure.