"Rodent-like" and "primate-like" types of astroglial architecture in the adult cerebral cortex of mammals: a comparative study

Previous observations disclosed that astroglia with interlaminar processes were present in the cerebral cortex of adult New and Old World monkeys, but not in the rat, and scarcely in the prosimian Microcebus murinus. The pres ent report is a more systematic and comprehensive comparative analysis of t he occurrence of such processes in the cerebral cortex of several mammalian species. Brain samples were obtained from adult individuals from the follo wing orders: Cavnivora (canine), Rodentia (rat and mouse), Marsupialia (Mac ropus eugenii), Artiodactyl (bovine and ovine), Scandentia (Tupaia glis), C hiroptera (Cynopteris horsfieldii and C. brachyotis), and Primate: Prosimia n (Eulemur fulvus), non-h;man primate species (Cebus apella, Saimiri bolivi ensis, Callithrix, Macaca mulatta, Papio hamadryas, Macaca fascicularis, Ce rcopithecus campbelli and C. ascanius) and from a human autopsy. Tissues we re processed for immunocytochemistry using several antibodies directed agai nst glial fibrillary acidic protein (GFAP), with or without additional proc edures aimed at the retrieval of antigens and enhancement of their immunocy tochemical expression. The cerebral cortex of non-primate species had an al most exclusive layout of stellate astrocytes, with only the occasional pres ence of long GFAP-IR processes in the dog that barely crossed the extent of lamina I, which in this species had comparatively increased thickness. Spe cies of Insectivora and Chiroptera showed presence of astrocytes with long processes limited to the ventral basal cortex. Interlaminar GFAP-IR process es were absent in Eulemur fulvus, at variance with their limited presence a nd large within- and inter-individual variability as reported previously in Microcebus murinus. In New World monkeys such processes were absent in Cal lithrix samples, at variance with Cebus apella and Saimiri boliviensis. Ove rall, the expression of GFAP-IR interlaminar processes followed a progressi ve pattern: bulk of non-primate species (lack of interlaminar processes)- C hiroptera and Insectivora (processes restricted to allocortex) <sterpsirhin i <haplorhini (platirrhini<cartarrhini). This trend is suggestive of the em ergence of new evolutionary traits in the organization of the cerebral cort ex, namely, the emergence of GFAP-IR long, interlaminar processes in the pr imate brain. Interlaminar processes may participate in a spatially restrict ed astroglial role, as compared to the one provided by the astroglial syncy tium. It is proposed that the widely accepted concept of an exclusively ast roglial syncytium is probably linked with a specific laboratory animal spec ies ("rodent-type" or, rather, "general mammalian-type" model) that misrepr esents the astroglial architecture present in the cerebral cortex of most a nthropoid adult primates ("primate-type" model), including man.