GOLGI-STUDY OF RADIAL GLIAL-CELLS IN DEVELOPING MONKEY TELENCEPHALON - MORPHOGENESIS AND TRANSFORMATION INTO ASTROCYTES

Radial glial cells (epithelial cells of Ramón y Cajal) impregnated by a modified del Rio Hortega rapid Golgi method were studied in the occipital lobes of 38 rhesus monkeys from embryonic day 48 (E48) to birth which occurs at E165 and in 27 postnatal animals to day 365 (P365). Some radial glial cells are already recognized at E48 by their bipolar shape and elongated radial fiber, which terminates with characteristic endfeet on the walls of blood vessels or at the pial surface. At slightly older ages-between E60 and E70-all cells spanning the cerebral wall develop lamellate expansions along their radial fiber and their endfeet become PAS positive. After E60, some radial glia detach from the ventricular surface and their somas become displaced outwards in the cerebral wall. After this age, radial glial cells are easily distinguished from migrating neurons by their larger oval nucleus located in the ventricular or subventricular zone, radial fiber extending outwards to the pial surface where it terminates in one or more endfeet, and the delicate lamellate expansions on both radial fiber and soma. Displaced radial glial cells have more closely packed lamellate expansions and display a range of transitional shapes leading to either fibrous or protoplasmic astrocytes. Between E95 and E140, when neuron migration to the visual cortex tapers off, perikarya of displaced radial glial cells form a conspicuous band at the outer border of the subventricular zone. Numerous transitional forms are present in the cortical plate at this age. After birth, fewer radial glial fibers are present in occipital lobe and their length is difficult to determine in the convoluted lateral cerebral wall expanded up to 10-20 mm. However, at P7 and P20, many radial fibers still span the medial cerebral wall in the depth of the calcarine fissure where it remains less than 2 mm thick. Even here, no fibers spanning the cerebral wall were seen in 17 animals from P50 to P200 despite the presence of well-impregnated transitional forms situated near the lateral ventricle and myriad astrocytes dispersed throughout the hemisphere. By P365, end of the first year, the few short remaining radial fibers belong to ependymal cells or mature astrocytes while all immature transitional forms have disappeared. © 1979 Springer-Verlag.