Abstract
The present paper is the first comparative study on the astroglia of several actinopterygian species at different phylogenetical positions, teleosts (16 species), and non-teleosts (3 species), based on the immunohistochemical staining of GFAP (glial fibrillary acidic protein), the characteristic cytoskeletal intermediary filament protein, and immunohistochemical marker of astroglia. The question was, how the astroglial architecture reflexes the high diversity of this largest vertebrate group. The actinopterygian telencephalon has a so-called ‘eversive’ development in contrast to the ‘evagination’ found in sarcopterygii (including tetrapods). Several brain parts either have no equivalents in tetrapod vertebrates (e.g., torus longitudinalis, lobus inferior, lobus nervi vagi), or have rather different shapes (e.g., the cerebellum). GFAP was visualized applying DAKO polyclonal anti-GFAP serum. The study was focused mainly on the telencephalon (eversion), tectum (visual orientation), and cerebellum (motor coordination) where the evolutionary changes were most expected, but the other areas were also investigated. The predominant astroglial elements were tanycytes (long, thin, fiber-like cells). In the teleost telencephala a ‘fan-shape’ re-arrangement of radial glia reflects the eversion. In bichir, starlet, and gar, in which the eversion is less pronounced, the ‘fan-shape’ re-arrangement did not form. In the tectum the radial glial processes were immunostained, but in Ostariophysi and Euteleostei it did not extend into their deep segments. In the cerebellum Bergmann-like glia was found in each group, including non-teleosts, except for Cyprinidae. The vagal lobe was uniquely enlarged and layered in Cyprininae, and had a corresponding layered astroglial system, which left almost free of GFAP the zones of sensory and motor neurons. In conclusion, despite the diversity and evolutionary alterations of Actinopterygii brains, the diversity of the astroglial architecture is moderate. In contrast to Chondrichthyes and Amniotes; in Actinopterygii true astrocytes (stellate-shaped extraependymal cells) did not appear during evolution, and the expansion of GFAP-free areas was limited.
Highlights
The present paper is the first comparative study on the astroglia of several actinopterygian species at different phylogenetical positions (Figure 1) based on the immunohistochemical staining of GFAP, the characteristic cytoskeletal intermediate filament protein, and immunohistochemical marker of astroglia (Bignami et al, 1980).Teleostei, the largest group of Actinopterygii, and even Chordata, is a relatively new and efflorescent group of high diversity
The question is, how the astroglial architecture reflexes the evolutionary diversity of Actinopterygii
In gar (Figures 3F,G) the eversion is moderate, a mild sulcus is only found on the outer, lateral surface of telencephalon
Summary
The largest group of Actinopterygii, and even Chordata, is a relatively new and efflorescent group of high diversity (for the diversity of their brains see, e.g., Nieuwenhuys and Meek, 1997). Until now GFAP studies usually focused only single species, mainly cyprinids, and the results were extended to all the Teleostei, or even Actinopterygii, disregarding the possible interfamily differences. 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; Lorincz and Kálmán, 2020). The present study completes the former ones extending our investigations over the Actinopterygii, and helps to understand the role of GFAP in brain evolution
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