Distribution of GFAP in Squamata: Extended Immunonegative Areas, Astrocytes, High Diversity, and Their Bearing on Evolution

Abstract

Squamata is one of the richest and most diverse extant groups. The present study investigates the glial fibrillary acidic protein (GFAP)-immunopositive elements of five lizard and three snake species; each represents a different family. The study continues our former studies on bird, turtle, and caiman brains. Although several studies have been published on lizards, they usually only investigated one species. Almost no data are available on snakes. The animals were transcardially perfused. Immunoperoxidase reactions were performed with a mouse monoclonal anti-GFAP (Novocastra). The original radial ependymoglia is enmeshed by secondary, non-radial processes almost beyond recognition in several brain areas like in other reptiles. Astrocytes occur but only as complementary elements like in caiman but unlike in turtles, where astrocytes are absent. In most species, extended areas are free of GFAP-a meaningful difference from other reptiles. The predominance of astrocytes and the presence of areas free of GFAP immunopositivity are characteristic of birds and mammals; therefore, they must be apomorphic features of Squamata, which appeared independently from the evolution of avian glia. However, these features show a high diversity; in some lizards, they are even absent. There was no principal difference between the glial structures of snakes and lizards. In conclusion, the glial structure of Squamata seems to be the most apomorphic one among reptiles. The high diversity suggests that its evolution is still intense. The comparison of identical brain areas with different GFAP contents in different species may promote understanding the role of GFAP in neuronal networks. Our findings are in accordance with the supposal based on our previous studies that the GFAP-free areas expand during evolution.

Evolutionary Modifications Are Moderate in the Astroglial System of Actinopterygii as Revealed by GFAP Immunohistochemistry

“…Avian homologs of some GFAP-rich turtle or Caiman brain areas were frequently almost free of GFAP (e.g., most of DVR, the superficial layers of the tectum, the molecular layer of the cerebellum, Kálmán, 2002 , 2009 ). The results on Squamata species, another florescent and diversive group were in accordance with these tendencies ( Lőrincz and Kálmán, 2020 ).…”

“…In general, the diversity of astroglial architecture reflexes only moderately the evolutionary diversity of Actinopterygii brains demonstrated, e.g., by Nieuwenhuys and Meek (1997) . No variability similar to that of Squamata ( Lőrincz and Kálmán, 2020 ) or Chondrichthyes ( Ari and Kálmán, 2008 ) was found. The predominant GFAP-immunopositive elements were tanycytes, long, tiny fiber-like cells, whereas true astrocytes (stellate-shape cells) were nowhere found.…”

“…f Similarly in chondrichthyans (Ari and Kálmán, 2008); and amniotes (Kálmán et al, 1994;Kálmán and Pritz, 2001;Lőrincz and Kálmán, 2020) except for birds (Roeling and Feirabend, 1988;Kálmán et al, 1993). Similar data, in several cases in different species and by different methods (see also Appendix 1).…”

“…The question is, how the astroglial architecture reflexes the evolutionary diversity of Actinopterygii. In Chondrichthyes and Amniotes our former studies found considerable diversity in the astroglial architecture, and a relative withdraw of GFAP immunopositivity during evolution ( Kálmán, 2002 , 2009 ; Ari and Kálmán, 2008 ; Lőrincz and Kálmán, 2020 ). The present study completes the former ones extending our investigations over the Actinopterygii, and therefore helps to understand the role of GFAP in brain evolution.…”

“…b Characteristic of sharks and reptiles (Horstmann, 1954;Kálmán, 2002;Lőrincz and Kálmán, 2020). c Similarly in reptiles and birds (Kálmán et al, 1993(Kálmán et al, , 1994Kálmán and Pritz, 2001;Lőrincz and Kálmán, 2020). d Similar glial structures in sharks, reptiles and birds, but not in batoids and mammals (Kálmán et al, 1993(Kálmán et al, , 1994Kálmán and Pritz, 2001;Ari and Kálmán, 2008;Lőrincz and Kálmán, 2020).…”