Features Of Neurogenesis Research Articles

Cellular composition and organization of the subventricular zone and rostral migratory stream in the adult and neonatal common marmoset brain

The adult subventricular zone (SVZ) of the lateral ventricle contains neural stem cells. In rodents, these cells generate neuroblasts that migrate as chains toward the olfactory bulb along the rostral migratory stream (RMS). The neural-stem-cell niche at the ventricular wall is conserved in various animal species, including primates. However, it is unclear how the SVZ and RMS organization in nonhuman primates relates to that of rodents and humans. Here we studied the SVZ and RMS of the adult and neonatal common marmoset (Callithrix jacchus), a New World primate used widely in neuroscience, by electron microscopy, and immunohistochemical detection of cell-type-specific markers. The marmoset SVZ contained cells similar to type B, C, and A cells of the rodent SVZ in their marker expression and morphology. The adult marmoset SVZ had a three-layer organization, as in the human brain, with ependymal, hypocellular, and astrocyte-ribbon layers. However, the hypocellular layer was very thin or absent in the adult-anterior and neonatal SVZ. Anti-PSA-NCAM staining of the anterior SVZ in whole-mount ventricular wall preparations of adult marmosets revealed an extensive network of elongated cell aggregates similar to the neuroblast chains in rodents. Time-lapse recordings of marmoset SVZ explants cultured in Matrigel showed the neuroblasts migrating in chains, like rodent type A cells. These results suggest that some features of neurogenesis and neuronal migration in the SVZ are common to marmosets, humans, and rodents. This basic description of the adult and neonatal marmoset SVZ will be useful for future studies on adult neurogenesis in primates.

Cell lineage tree models of neurogenesis

The production of neurons to form the mammalian cortex, known as embryonic cortical neurogenesis, is a complex developmental process. Insight into the process of cell division during neurogenesis is provided by murine cortical cell lineage trees, recorded through experimental observation. Recurring patterns within cell lineage trees may be indicative of predetermined cell behaviour. The application of mathematical modelling to this process requires careful consideration and identification of the key features to be incorporated into the model. A biologically plausible stochastic model of evolution of cell lineage trees is developed, based on the most important known features of neurogenesis. Tractable means of measuring lineage tree shape are discussed. Symmetry is identified as a significant feature of shape and is measured using Colless's Index of Imbalance. Distributions of tree size and imbalance for large tree sizes are computed and results compared to experimental data. Several refinements to the model are investigated, when the cell division probabilities are weighted according to cell generation. Two models involving generation-dependent cell division probabilities produce imbalance distributions which are the most consistent with the available experimental results. The results indicate that a stochastic cell division mechanism is a plausible basis of mammalian neurogenesis.

Immunohistochemical study of the development of serotonergic neurons in the rat CNS

In this study the development of serotonergic (5-HT) neurons is followed from their initiation of transmitter synthesis until the establishment of an essentially mature morphology. We have used the new and sensitive technique of 5-HT immunocytochemistry to visualize the precise features of this process. The great stability of this method, and the feasibility of counter-staining tissue sections permits the visualization of dendritic processes and axon terminals, as well as perikarya, and facilitates the localization of these structures with respect to non-5-HT components of the neuropil. Serial transverse and sagittal sections of rat fetuses on embryonic days (ED) 13, 14, 15, 17, 19 and 21, and postnatal rats on days 1,3,4 and 10 were examined. A detailed photomicrographic map showing the locations of 5-HT neurons at all prenatal stages is provided. The development of 5-HT neurons is evaluated in terms of their cellular morphology, particularly dendritic architecture, the relationship of these cells to the development of the surrounding brainstem, and the morphology and packing density of the 5-HT nuclei. From these considerations a model is proposed of the pattern of cell migration within the nuclei that give rise to the ascending 5-HT projections. At E14 a relatively simple configuration of bilateral superior (rostral) and inferior (caudal) 5-HT cell groups is present. In the period extending from E14 to E19 several subgroupings of these cells develop, presumably as the result of differential cell migration. Based on the predominant dendritic orientation of these cells it is possible to reconstruct their probable migratory paths. At E19 the 5-HT neurons are distributed in groups that are similar to those seen in the adult. In the time from E19 until the end of the first postnatal week there is rapid growth of 5-HT dendrites and a marked decrease in cellular packing density. These alterations shape the nuclear aggregates into the form seen in the adult. The development of the 5-HT cell groups is discussed in the context of known features of neurogenesis, migration, and axonal projections of the raphe and medial reticular nuclei of the brainstem. The possibility is raised that the decrease in cellular packing density in the 5-HT nuclei may reflect the appearance of the non-5-HT components of the raphe nuclei.