Newly formed (daily formed) brain cells - Research Paper Example

Even though there were a few studies in which the presence of [3H] thymidine labeled newly formed neurons was described in hippocampus of rodent at postnatal stages (Altman and Das, 337), but these studies were not given significance in absence of functional evidences (Gage et al., 210). It was only in the 1990s, that the technologies such as [3H] thymidine replacement and immunophenotyping of newborn cells using bromodeoxyuridine (BrdU) along with other neuronal markers were developed. During this period twin evidences gradually took shape breaking the dogma of neurogenesis being restricted to prenatal stages.

The first evidence came in the success of Reynolds and Weiss (1707) in culturing mutipotent neural progenitors derived from adult mouse brain. The second line of evidences was provided by Kuhn and colleagues (5820) immunophenotyping newly formed cells of rodent brain using BrdU and other neuronal markers. With further advances in technology the presence of neuronal stem cells were found to occur in many areas of the brain. On October 15, 1999, two biologists at Princeton University; Dr. Elizabeth Gould and Dr.

Charles G. Gross, reported that neurogenesis occurs regularly in primate (monkey) adding neurons continuously to cerebral cortex (Gross and Gould, 619). Thus the firmly established belief that adult brain is incapable of forming new cells was shattered, more so in light of recent similar evidence provided for birds (Bailey & Kandel, 397). B. Neurogenesis: The mammalian brain comprises of four main types of cells: neurons, astrocytes, oligodendrocytes and ependymal cells. These cells originate from early neural epithelium which forms a neural plate in the developing embryo, neurogenesis being preceded by gliogenesis.

The differentiation of neuroepithelial cells is determined by inductive cellular interactions and the concentration of expression of patterning gene in the surrounding cells. The patterning genes are determining factors in type and stage of neurogenesis. Neurogenesis occurs first, the newly formed neurons having moved beyond the germinal ventricular zone by midgestation with help of newly formed glial cells, forming the subventricular Zone (SVZ). This is followed by formation of glioblasts from rest of the neuroepthellial cells in VZ, which then move to adjacent subventricular zone and form astrocytes and oligodendrocytes (Clarke, S13).

After birth, glioblast formation stops, germinal VZ vanishes and the remaining neuroepithillial cells form ependymal cells which remain in adult brain as well. SVZ too decreases in size, present next to ependymal cell layer in brain. With further development of the new brain, these neural stem cells become restricted to six major zones of brain, namely olfactory bulb, VZ and SVZ of forebrain, hippocampus, cerebral cortex and cerebellum, each of which is distinct and develop into cells with unique characteristics depending on the region they occupy (Gage, 1433). C. Neurogenesis in adult brain: New cells in adult brain are established to be formed by: Neural Progenitor cell (NPC) population in olfactory bulb (OB) and dentate gyrus (DG) of hippocampus, the brain area responsible for learning and memory.

2 mutipotential neural stem cell populations (NPC) namely SVZ astrocytes and ventricular ependymal cells from cerebral cortex. Besides these NSCs from non neurogenic periventricular cells have also been isolated and grown in vitro,