Neurogenesis is the process underlying the development of the highly evolved central nervous system (CNS) in vertebrates. Neurogenesis takes place by differentiation of specific Neural Precursor ...Cells in the neurogenic niche. The main objective of this review is to highlight the specific relationship between the brain cavities, and neurogenesis from neural precursors. Brain cavities and their content, Cerebrospinal Fluid (CSF), establish a key relation with the neurogenic “niche” because of the presence in this fluid of neurogenic signals able to control neural precursor cell behaviour, inducing precursor proliferation and neuronal differentiation. This influence seems to be ontogenically preserved, despite the temporal and spatial variations that occur throughout life. In order to better understand this concept, we consider three main life periods in the CSF-Neurogenesis interaction: The “Embryonic” period, which take place at the Neural Tube stage and extends from the isolation of the neural tube at the end of “neurulation” to the beginning of Choroid Plexus activity; the “Fetal” period, which includes the remaining developmental and the early postnatal stages; and the “Adult” period, which continues for the rest of adult life.
Each period has specific characteristics in respect of CSF synthesis and composition, and the location, extension and neurogenic activity of the neurogenic niche. However, CSF interaction with the neurogenic niche is a common factor, which should be taken into account to better understand the ontogeny of neuron formation and replacement, as well as its potential role in the success or failure of therapies for the ageing, injured or diseased brain.
Background
At the earliest stages of brain development, the neuroepithelium works as an interdependent functional entity together with cerebrospinal fluid, which plays a key regulatory role in ...neuroepithelial cell survival, replication and neurogenesis; however, the underlying mechanism remains unknown in mammals.
Results
We show the presence of fibroblast growth factor 2 (FGF2) and epidermal growth factor (EGF), in 13.5‐day rat embryo cerebrospinal fluid (eCSF). Immunohistochemical detection of FGF2 expression localized this factor inside neuroepithelial precursors close to the neuroepithelial‐CSF interface, suggesting that FGF2 from eCSF could originate in the neuroepithelium by apical secretion. The colocalization of FGFR1 and FGF2 in some neuroepithelial cells close to the ventricular surface suggests they are target cells for eCSF FGF2. Brain neuroepithelium EGF expression was negative. By using a neuroepithelial organotypic culture, we demonstrate that FGF2 and EGF from eCSF plays a specific role in triggering the self‐renewal and are involved in neurogenetic induction of mesencephalic neuroepithelial precursor cells during rat development.
Conclusions
We propose eCSF as an intercommunication medium for neuroepithelial precursor behavior control during early rat brain development, and the neuroepithelial regulation of FGF2 and EGF presence in eCSF, as a regulative mechanism controlling precursor proliferation and neurogenesis.
Key Findings
We show the presence of Fibroblast Growth Factor (FGF2 and EGF) in 13.5‐day rat embryos cerebro‐spinal fluid (eCSF).
FGF2 expression localized this factor at the apical end of the neuroepithelial precursors in contact with eCSF.
We demonstrate that FGF2/EGF from eCSF plays a specific role in triggering replication and in neurogenesis induction of neuropeithelial cells.
We propose eCSF as a common phylogenetical factor in neuroepithelial precursor behavior during rat brain development.
The adult mouse hippocampal neurogenic niche is a complex structure which is not completely understood. It has mainly been related to the Subgranular layer of the dentate gyrus; however, as a result ...of differential neural stem cell populations reported in the subventricular zone of the lateral ventricle and associated with the hippocampus, the possibility remains of a multifocal niche reproducing developmental stages. Here, using a set of molecular markers for neural precursors, we describe in the adult mouse brain hippocampus the existence of a disperse population of neural precursors in the Subependymal Zone, the Dentate Migratory Stream and the hilus; these display dynamic behaviour compatible with neurogenesis. This supports the idea that the adult hippocampal niche cannot be restricted to the dentate gyrus subgranular layer. In other neurogenic niches such as the Subventricular Zone, a functional periventricular dependence has been shown due to the ability to respond to embryonic cerebro-spinal fluid. In this study, we demonstrate that neural precursors from the three areas studied (Sub-ependymal Zone, Dentate Migratory Stream and hilus) are able to modify their behaviour by increasing neurogenesis in a locally differential manner. Our results are compatible with the persistence in the adult mouse hippocampus of a neurogenic niche with the same spatial structure as that seen during development and early postnatal stages.
•CSF activate neural precursors neurogenesis.•Adult subependymal zone remains active and connected with the hippocampus.•Adult hippocampal niche includes periventricular neural precursors
Integration of several geologic lines of evidence reveals the prevalence of a lowland trans-Andean portal communicating western Amazonia and the westernmost Andes from at least middle Miocene until ...Pliocene times. Volcanism and crustal shortening built up relief in the southernmost Central and Eastern Cordilleras of Colombia, closing this lowland gap. Independent lines of evidence consist first, of field mapping in the Tatacoa Desert with a coverage area of ∼381 km
2
, 1,165 km of geological contact traces, 164 structural data points, and 3D aerial digital mapping models. This map documents the beginning of southward propagation of the southernmost tip of the Eastern Cordillera’s west-verging, fold-and-thrust belt between ∼12.2 and 13.7 Ma. Second, a compilation of new and published detrital zircon geochronology in middle Miocene strata of the Tatacoa Desert shows three distinctive age populations: middle Miocene, middle Eocene, and Jurassic; the first two sourced west of the Central Cordillera, the latter in the Magdalena Valley. Similar populations with the three distinctive peaks have now been recovered in western Amazonian middle Miocene strata. These observations, along with published molecular and fossil fish data, suggest that by Serravallian times (∼13 Ma), the Northern Andes were separated from the Central Andes at ∼3°N by a fluvial system that flowed into the Amazon Basin through the Tatacoa Desert. This paleogeographic configuration would be similar to a Western Andean, or Marañon Portal. Late Miocene flattening of the subducting Nazca slab caused the eastward migration of the Miocene volcanic arc, so that starting at ∼4 Ma, large composite volcanoes were built up along the axis of today's Central Cordillera, closing this lowland Andean portal and altering the drainage patterns to resemble a modern configuration.
There is a nondeveloped neurogenic potential in the adult mammalian brain, which could be the basis for neuroregenerative strategies. Many research efforts have been made to understand the control ...mechanisms which regulate the transition from a neural precursor to a neuron in the adult brain. Embryonic cerebrospinal fluid (CSF) is a complex fluid which has been shown to play a key role in neural precursor behavior during development, working as a powerful neurogenic inductor. We tested if the neurogenic properties of embryonic CSF are able to increase the neurogenic activity of neuronal precursors from the subventricular zone (SVZ) in the brains of adult mice.
Our results show that mouse embryonic CSF significantly increases the neurogenic activity in precursor cells from adult brain SVZ. This intense neurogenic effect was specific for embryonic CSF and was not induced by adult CSF.
Embryonic CSF is a powerful neurogenesis inductor in homologous neuronal precursors in the adult brain. This property of embryonic CSF could be a useful tool in neuroregeneration strategies.
Guadua angustifolia has been used in Colombia as construction material for centuries. The different earthquakes in Colombian history have demonstrated the good seismic performance of structures and ...pointed the errors of inadequate use. So, normalized parameters are necessary for seismic resistant design of G. angustifolia structures; these parameters must include allowable stresses values and demand a material quality control during the construction process. This paper presents the results obtained from the project “Validation of G. angustifolia as a structural material for allowable stresses method design”, financed by the Ministry of Agriculture and Rural Development of Colombia and carried out by the National University of Colombia. The project aims to establish values of allowable stresses, to design methods for structures and to establish a protocol of the material quality control during construction. Samples of G. angustifolia from three different areas of Colombia have been tested in compression, tension and shear parallel to the fiber, bending, torsion and perpendicular compression, in order to determine allowable stresses for different loads. The samples were taken from the bottom, middle and top parts of the culm. The design methods by allowable stresses and the protocol of quality control are based on structural mechanics and different research projects made at National University of Colombia.
Signo de la copa del mundo World Cup Sign La Mura, J.; Holguín Díaz, A.; Trujillo, M. ...
Revista argentina de radiología,
03/2015, Letnik:
79, Številka:
1
Journal Article
Signo de la copa del mundo La Mura, J.; Holguín Díaz, A.; Trujillo, M. ...
Revista argentina de radiología,
January-March 2015, 2015-01-00, Letnik:
79, Številka:
1
Journal Article
Signo de la copa del mundo J. La Mura; A. Holguín Díaz; M. Trujillo ...
Revista argentina de radiología,
01/2015, Letnik:
79, Številka:
1
Journal Article
The purpose of the study was to compare the segmental measurement tool from the Shick Technologies CDR digital system with the conventional film radiography measurement technique to determine ...preoperative working length. Natural extracted human teeth with varying degrees of root curvature were used. All teeth were imaged using the Shick Technologies CDR direct digital system and conventional E-speed film. Measurements from digital radiography and conventional film were compared with measurements made directly from the endodontic files. The Wilks' Lambda multivariate test was used. The mean measurement of each modality was compared with the other and with the gold standard. The test showed statistically significant differences between the two modalities at p<0.05. The mean measurements for both modalities were not significantly different from the gold standard. The modality most closely approaching the gold standard was the conventional film.
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