Distribution of enkephalin in human fetus and infant spinal cord: an immunofluorescence study

The distribution of enkephalin-like immunoreactivity in the human fetus and infant spinal cord have been studied by indirect immunofluorescence. Enkephalin-like immunoreactive fibers were detectable in the lateral funiculus of fetal spinal cord as early as 10 weeks. At the other fetal ages examined, ranging from 12 to 28 weeks, and in infant, enkephalinlike immunoreactivity was found widely distributed throughout the whole spinal cord. In fetus spinal cord several enkephalin-like immunoreactive cells were sometimes seen scattered in the intermediate gray region. Most of the labeling was, however, represented by thin, varicose, immunofluorescent fibers mainly localized in the intermediate gray regions, in the ventral horn and in the superficial dorsal horn layers where they progressively increased in number. Further, the white matter exhibited enkephalin-like immunoreactive fibers particularly in the lateral funiculus where a dense punctiform immunofluorescence could be seen. On the whole, similar patterns were also visible in infant spinal cord. Thus, the superficial layers of the dorsal horn and the intermediolateral and reticular nuclei areas displayed dense plexuses of immunoreactive fibers. In contrast, the white matter showed only little labeling. In addition, no immunoreactivity was found in fetus and infant dorsal root ganglia. Our results emphasize the wide distribution of the enkephalin-like immunoreactivity in the fetus as in the infant spinal cord and further suggest its first appearance early in fetal life, possibly at the embryonic stage.