Interlaminar Glia and Other Glial Themes Revisited: Pending Answers Following Three Decades of Glial Research

Abstract

This review aims to highlight the various significant matters in glial research stemming from personal work by the author and associates at the Unit of Applied Neurobiology (UNA, CEMIC-CONICET), and some of the pending questions. A reassessment and further comments on interlaminar astrocytes-an astroglial cell type that is specific to humans and other non-human primates, and is not found in rodents, is presented. Tentative hypothesis regarding their function and future possible research lines that could contribute to further the analysis of their development and possible role(s), are suggested. The possibility that they function as a separate entity from the "territorial" astrocytes, is also considered. In addition, the potential significance of our observations on interspecies differences in in vitro glial cell dye coupling, on glial diffusible factors affecting the induction of this glial phenotype, and on their interference with the cellular toxic effects of cerebrospinal fluid obtained from L-DOPA treated patients with Parkinson´s disease, is also considered. The major differences oberved in the cerebral cortex glial layout between human and rodents-the main model for studying glial function and pathology-calls for a careful assessment of known and potential species differences in all aspects of glial cell biology. This is essential to provide a better understanding of the organization and function of human and non-human primate brain, and of the neurobiological basis of their behavior.

Sublaminar organization of the human subplate: developmental changes in the distribution of neurons, glia, growing axons and extracellular matrix

“…Our results do not provide a definitive answer as to when SP astroglia complete maturation and achieve a full‐size phenotype as previously described (Oberheim et al. , ; Colombo, ), or as to when human astrocytes reach their full maturational state. Namely, even in the oldest specimen examined (near term age), when fibrous astrocytes seem to be relatively mature, transient forms of astroglia are still present in the SP remnant.…”

“…Regarding the functional integrative role of astrocytes in fetal SP, it is important to determine whether these cells form functional domains, as has been proposed for the adult cortex. Some of the characteristically human glia, such as interlaminar glia, develop postnatally (Colombo & Reisin, ; Colombo, ), which is also in line with the prolonged process of postnatal synaptogenesis (Bourgeois et al. ; Huttenlocher & Dabholkar, ; Petanjek et al.…”

The Special Case of Human Astrocytes

“…The first type of uniquely human astrocyte that came under scrutiny was the class of interlaminar astrocytes, so-named by Jorge Colombo [55], whose historic and personal perspective is published in Neuroglia [56]. Notably, these cells were also seen by early neuroanatomists (Figure 2).…”

Modeling human‐specific interlaminar astrocytes in the mouse cerebral cortex

“…Similar to primates (Colombo, Lipina, et al, 1997), interlaminar astrocytes in the chimeric mouse cortex projected tortuous processes in a radial pattern with some ending with a bulbous structure, suggesting that these two features are either intrinsic properties or, if extrinsic, are not altered by the mouse cerebral cortex environment. The previously reported presence of mitochondria in the terminals suggests a special energy requirement associated with the ionic and molecular exchange and homeostasis (Colombo, 2018).…”