| Abstract |
The existence of sexually differentiated areas characterizes the brain of fish as well as other invertebrates. Many of the brain differences between the two sexes are genetically determined. There are however dimorphisms that result from external stimuli on the brain. This ability of the brain to respond and adapt to a changing environment is called plasticity. Sexual plasticity of the fish brain specifically represents alterations of its sexual phenotype influenced by social and environmental factors. Cell genesis, migration, differentiation to neural or glial cells and apoptosis, are all mechanisms contributing to brain organization and reorganization, according to external stimuli and internal needs. The participation of cell genesis, migration, differentiation and apoptosis were studied in order to identify sexual differentiations in the adult brain of a model organism, the zebrafish (Danio rerio). The immunohistochemical method of BrdU was applied on short term (24 hours) and long term (21 days) surviving individuals, to study cell genesis. After BrdU administration, long term surviving individuals, were used for the study of cell differentiation, where the glial phenotype was detected with the use of antibodies against GFAP, a structural protein of astoglia cells. Marking of neural cells was achieved with the use of antibodies against parvalbumin, a protein binding Ca++ and characterizing GABAergic neural cells. The study of apoptosis was based on the TUNEL method. The mapping of mitotic activity in adult brain suggests that all the main brain structures are mitotically active, with the areas of the cerebellum producing the greatest number of cells. The post mitotic cells in the adult brain of zebrafish did not show any expression of GFAP, and are not therefore differentiated to glial cells. However BrdU labelled cells seem to be using astroglia fibres, in the cerebellum in order to migrate from the molecular layer, where they are born, to the adjoining granular cell layer. Contrary to GFAP, parvalbumin is expressed by a percentage of newly born cells in areas of the telencephalon, diencephalon and mesencephalon after 21 days. The apoptotic activity in the zebrafish adult brain is retained in high levels as opposed to mammals. The mapping of areas characterized by apoptotic activity revealed the correlation between areas of apoptotic and mitotic activity or to the final positions of newly born cells. The number of newly born cells was estimated in short and long term surviving individuals. The quantitative and statistical analysis showed statistically significant differences between the two sexes in the middle zone of the dorsal telencephalon, an area homologous to the mammal amygdale. This difference is preserved in long term surviving individuals. In the diencephalon significant sexual differentiations in the short term surviving individuals appear in the pretectal nucleus PPv, the periventricular nucleus of posterior tuberculum TPp, and the dorsal zone of periventricular hypothalamus Hd, Finally in the cerebellum statistically significant difference in the number of newly born cells between male and female individuals was observed in areas of the molecular layer of corpus cerebelli (CCe mol), as well as in the granular layer of the caudal lobe of cerebellum (LCa gr). These areas present a higher number of BrdU labeled cells for male individuals. Only the LCa gr retained this difference after 21 days. The sexualdifferentiations observed are probably related to sexually specific behaviors and activities observed in populations of adult zebrafish.
|
Φυλετικός διμορφισμός στη γέννηση νευρικών κυττάρων στον ενήλικο εγκέφαλο: μελέτη στον οργανισμό μοντέλο zebrafish (Danio rerio)
