Development of interlaminar astroglial processes in the cerebral cortex of control and Down's syndrome human cases.

Glial cytoarchitecture in human cerebral cortex is constituted by two overlapping layouts: the (general mammalian) "glial syncytium" and the (primate-specific) "interlaminar glial palisade" (IGP) composed by astroglial cells, with long, radial processes that traverse several supragranular layers. In this study, the emergence and early organization of the IGP was analyzed using immunocytochemical procedures in postmortem infantile human control and age matched, Down's syndrome (DS) cases. In control cases, first signs of a radial array of unbranched astroglial processes were apparent at the end of the period of "physiological astrocytosis" (20-40 days of postnatal life), and its general profile (except perhaps the density of cell processes) reached the adult-like configuration by the second month of life. The initial organization of the IGP was similar in control and DS cases, although a breakdown in DS became manifest by the first year of age, or earlier, albeit with individual variations. These changes tended to evolve in a "mosaic" fashion and included partial disruption of the palisade, or persistence of the "physiological astrocytosis". These observations were compared against samples from elder DS cases with an Alzheimer's type of dementia (AtD). Collectively, results suggest that DS also involves astroglial alterations during early stages of brain development, and that those changes progress with age, until an AtD ensues during adult life.