Double-immunolabeling studies of glucocorticoid receptors in enkephalinergic neurons of the rat spinal cord

Using double-immunolabeling, we attempted to localize the glucocorticoid receptor (GR) and methionine-enkephalin-octapeptide (ENK-8) in the rat spinal cord. The 2nd to 8th cervical segments were analyzed in intact and in colchicine-injected animals. GR immunoreactivity was detected in the nuclei of neurons in all segments, and was most intense in small neurons in the superficial layers (laminae 1-3) of the dorsal horn. Medium-sized neurons in laminae 4-6 and the reticular formation, as well as the large ventral horn neurons, all showed moderate immunoreactivity. Double-immunolabeling revealed that, in all regions examined except the ventral horn, some of the GR-positive neurons were also ENK-8-positive. These findings suggest that enkephalinergic neurons in the spinal cord may be regulated by glucocorticoids, each of which is presumably related to the neuronal antinociceptive mechanism in the dorsal horn.