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Distribution of PSA-NCAM in brains of two venomous species: Vipera ammodytes and Vipera berus bosniensis

Adult neurogenesis is well preserved throughout evolution and production of new neurons continues throughout life in most invertebrates and vertebrates. Fish and amphibians with high adult neurogenesis can significantly repair neural structures such as brain, spinal cord, retina and olfactory system while reptiles, birds and mammals have some regenerative abilities but they are much reduced. Neural cell adhesion molecule (NCAM), a member of the immunoglobulin superfamily of cell adhesion molecules involved in cell surface recognition, has a crucial role in neurogenesis and neuron migration. The addition of the polysialic acid (PSA) moiety to NCAM is essential to neural remodeling and synaptic plasticity. The aim of this study was to detect and compare expression of PSA-NCAM positive migratory zones in brains of two venomous viper species: Bosnian adder (Vipera berus bosniensis) and horned viper (Vipera ammodytes). These two species differ by environment they inhabit - Bosnian adder lives in variety of habitats and is endemic to the Balkan Peninsula while horned viper inhabits dry, rocky hillsides with sparse vegetation and has a reputation of being the most dangerous of the European vipers due to its high venom toxicity. For easier orientation on sections we used two markers - NeuN antibody to detect neurons and SMI 312 as marker of myelinized fibers. NeuN and SMI 312 were positive in rostral tectum mesencephali, cerebellum, rhombencephalon, and spinal cord but not in telencephalon (Figure 1 and 2). When compared with these two markers, distribution of PSA-NCAM positive zones correlates with NeuN and SMI 312 antibody but is also highly expressed in telencephalon where these two markers were distributed in more restricted areas. The strongest expression of PSA-NCAM was detected in periventricular zones of telencephalon suggesting that those are areas where new neurons are born while other areas with lower expression are probably migratory zones. It is considered that reptiles have lower regeneration potential what makes them more similar to birds and mammals. However, investigated species of reptiles show expression and distribution of PSA-NCAM migrating zones more similar to fishes and amphibians than to mammals (Figure 3 and 4). PSA-NCAM as one of the markers indicating potential for regeneration is widely expressed in brains of both snakes showing that reptiles could be models for studying relationships between maintenance of adult neurogenesis and regenerative capability and also a good model for brain evo- devo research.

neural cell adhesion molecule; polysialic acid; migratory zones; regeneration; immunohistochemistry; brain; Vipera

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