Immunocytochemical study of the ontogenesis of the hypothalamic somatostatin-containing neurons in the human fetus.

Abstract

Immunocytochemical techniques have enabled us to characterize the hypothalamic somatostatin system in the human fetus and to study its ontogenesis. Somatostatin-containing neurons appear as early as the 16th week of fetal life. Their perikarya belong to two distinct cell populations: some of them, of large size, form clusters in the magno-cellular nuclei (S.O.N.-P.V.N.); they seem to be neurophysin-positive. The others, parvo-cellular, lie scattered in ventral periventricular areas; they are neurophysin-negative. Most of the immunoreactive fibers pass through the M.E. and terminate in two distinct territories: on the one hand close to the vessels of the primary portal plexus (these territories being neurophysin-negative) and on the other hand, in the peripheral regions of the neural lobe (these territories being neurophysin-positive). The staining reactions obtained with the anti-somatostatin and anti-neurophysin I.S. suggest the existence of 2 hypothalamic somatostatin systems. The former (neurophysin-negative) which appears to originate from the parvocellular perikarya and which terminates in the M.E., controlling adenohypophyseal cells, the latter (neurophysin-positive) originating from one of the S.O.N. and P.V.N. cell populations appears to terminate in the neural lobe. The existence of the latter system suggested by the results of the present and the preceding studies on other species has yet to be fully established.