Extended Data Figure 4: TEM analysis of cell types in the DG of human brains obtained from a 13-year-old individual and an adult; absence of SGZ precursor cells or immature neurons.

a, Reconstruction of 5 ultrathin sections (separated by 1.5 μm) from the GCL of the 13-year-old individual with outlines of cell membranes. Colours corresponding to the different cell types defined by their ultrastructural characteristics are indicated in the key. No clusters or isolated cells with a young neuronal ultrastructure were found. Cells associated in small groups were identified as astrocytes, oligodendrocytes or microglia. b, c, Reconstructions of astroglial cells next to the GCL, searching for possible examples of radial astrocytes in the DG of an adult human. b, Example of an astrocyte with radial morphology in the adult GCL. Five serial semi-thin sections of this astrocyte (black arrows) next to the GCL of the DG of a 48-year-old individual are shown; alternating semi-thin sections show that this cell is GFAP⁺. This cell extends a thin radial fibre through the GCL, but has multiple processes (stellate morphology) in the hilus. Boxed area shows the ultrastructure from the indicated semi-thin section of this astrocyte (pseudocoloured in blue) and the bundles of intermediate filaments present in the expansion (arrows). c, Another example of a serially reconstructed astrocyte in the DG of a 30-year-old individual with epilepsy (separated by 1.4 μm), showing a short radial expansion and processes into the hilus. Scale bars, 10 μm (a, b, semi-thin sections and TEM micrographs), 5 μm (c), 2 μm (b, soma) and 500 nm (b, intermediate filaments).