Structural Organization of Astrocytes in the Subgranular Zone of the Rabbit Hippocampal Dentate Fascia

Resumo

Neurogenesis in the subgranular zone (SGZ) of the mammalian hippocampus is well known to occur throughout the life span. Astrocytes in this specialized proliferative zone are supposed to have properties of progenitor cells. Structural features of these cells and their interspecies differences remain understudied, while data on the structural organization of the SGZ in the rabbit (order Lagomorpha, superorder Glires), which is widely used in medical and biological studies, are lacking at all. The present work was focused on the structural and cytochemical organization of astrocytes in the SGZ of the rabbit hippocampal dentate fascia as studied by laser confocal microscopy. The study was carried out on the brain of adult Chinchilla rabbits compared to that of adult Wistar rats. Two morphological astrocyte types were identified in the rabbit SGZ: radial gliocyte-like (type I) and atypical fibrous astrocyte-like (type II) cells. By contrast, the rat SGZ exhibited a predominance of type II astrocytes which lacked long unramified processes penetrating through the granular layer and reaching the molecular layer. SGZ astrocytes, both in the rabbit and rat, were characterized by intense immunoreactivity for glutamine synthetase, most pronounced in the processes that formed the perivascular glia limitans. Importantly, the peculiarities of the astrocyte organization in the dentate fascia of the rabbit hippocampus allowed SGZ delimitation, whereas astrocytes in the rat SGZ exhibited no local morphological distinctions. The latter finding indicates a more complex organization of the neurogenic zone in the hippocampus of lagomorphs in contrast to the same zone in rodents.