Characterization Of Adult Neurogenesis In Phrynocephalus Vlangalii

Adult neurogenesis, a process of giving rise to neurons and glia continually from progenitors residing in restricted regions of the adult central nervous system (CNS) throughout life, varies considerably across species. Although remarkable progress has been made over the past decade in unraveling the regulation and function of adult neurogenesis, the role of adult neurogenesis in reptiles, the amniotic vertebrates that possess spontaneous regenerative capacity is less known. In the present study, we used Phrynocephalus vlangalii--typical reptile in Qinghai-Tibetan Plateau of China to investigate the general pattern and characteristics of adult neurogenesis.Lizards were intraperitoneally injected with Bromodeoxyuridine (BrdU) in order to label dividing cells. Distinct immunocytochemistry were performed:DAB-immunostaining and fluorescence-immunostaining, combined with microscope imaging to observe the location and proliferation of newborn cells. Golgi staining technology was used in order to describe the morphology structure of principal neurons in medial cortex of the lizard. DCX-immunostaining and GFAP-immunostaining were carried out to display the general pattern of immature neurons and glial lineage. Our results showed that:1. Compared with mammals, the brains of P. vlangalii own simpler cytoarchitectonical patterns, but still characteristic of three-laminated fashion:most somata are packed into a cell layer sandwiched between the inner and outer plexiform layers. The cells both in MOB and in AOB of P. vlangalii are irregularly distributed, instead of having laminar organization.2. Three days after BrdU injection, BrdU-labeled cells were mostly distributed in the ventricular zone of lateral ventricle with cell proliferation highest in region referred to anterior olfactory nucleus (AON).3. The majority of neurons populating the medial cortex were projection neurons, displaying various soma morphologies. Their projecting processes either reached adjacent dorsal cortical areas and/or the bilateral septum.4. Immunostaining against DCX showed immature neurons were not only widely distributed in telencephalon, but also had migrated into inner plexiform layer. Some immature neurons orderly arrayed in a line in cell layer of MC and displayed typical migrating newborn neurons.5. GFAP-immunostaining in telencephalon, diencephalon and mesencephalon were fundamentally represented by radial glial structures, including tanycytes and radial glial cells. Radial GFAP-positive fibers spreaded throughout the entire cortex and terminated with swollen endfeet anchoring the submeningeal surface. The thicker sinuous fibers in OB appeared to interweave together forming a mesh network. An intriguing finding was the emergence of GFAP-positive, star-shaped cells in the mesencephalon.In conclusion, the adult neurogenesis in lizard is possessed of its own characteristics, which are closely related with phylogenetic differences dependent on the coordinated interaction between different environmental cues and growth of sensory systems. Lizard brain provides us an excellent access to investigate the neuronal regeneration and neurotrophic signals, and cell fate specification, since reptiles represent the first vertebrate group presenting astrocytes proper. Therefore, these findings may not only have implications for understanding the effect of distinctive seasons and ecological environment on the adult neurogenesis of reptiles, but also could favor the elucidation of potential mechanism regulating the endogenous neurogenetic capacity and compatibility in mammalian adult brain.