Ontogeny of somatostatin-like immunoreactivity in the human fetus and infant spinal cord

The localization and distribution of somatostatin like-immunoreactivity (SSLI) in postmortem human fetus and infant spinal cord and dorsal root ganglia were studied by using the indirect immunofluorescence technique. SSLI, which was mostly located within varicose fibers and terminal-like structures, occasionally within cell bodies, was detected during early fetal life (on gestational week 9 and beyond). The changes occurring from the early to the late fetal and infant stages mainly resulted in a progressive increase in the number of somatostatin-like immunoreactive fibers within most of the gray areas. On the whole the majority of immunolabelled fibers and terminal-like structures were observed over the superficial layers of the dorsal gray including the marginal zone and the substantia gelatinosa. Other regions displaying a moderate number of somatostatin-like immunoreactive fibers were the intermediate gray and the gray commissure area around the central canal. A few scattered immunofluorescent fibers were unevenly distributed over the white matter especially in the lateral and ventral funiculus areas and near the ventral motor nuclei. A few somatostatin-like immunoreactive cell bodies were occasionally found in the superficial layers of the dorsal gray and in the intermediolateral gray. Immunolabelled cells were further usually vizualized in dorsal root ganglia. Although the distribution patterns of somatostatin-like immunoreactive structures were similar throughout the entire spinal cord, the highest density of immunolabeled fibers, however, was seen at the lumbosacral level. Our results indicate that in the human spinal cord SSLI is already widespread before birth. It is further suggested that somatostatin ontogenesis in human spinal cord and dorsal root ganglia begins early in fetal life.