Interlaminar astroglial processes in the cerebral cortex of great apes.

The present study was designed to document the architecture of neocortical astroglia in great apes, following glial fibrillary acidic protein immunohistochemistry. These anthropoid species were missing from previous phylogenetic descriptions of astroglia with interlaminar processes, a characteristic event of the cerebral cortex within the Primate Order. Pongo pygmaeus (orangutan), Gorilla gorilla (gorilla) and Pan troglodytes (chimpanzee) brain samples showed the typical "palisade" of interlaminar processes. Yet, those from Pan troglodytes were less uniform, showing extended cortical segments with astrocytic ("syncytial-type") appearance, intermingled with segments expressing the interlaminar "palisade". Present observations contribute to fill in missing data on the phylogenetic emergence of the cerebral cortex astroglial interlaminar processes. Considering the extreme consistency of the expression of astroglial interlaminar "palisades" among anthropoid species, this apparent variability among Pan individuals could be due to various possibilities, which are considered in this report.