Abstract
In vertebrates, early brain development takes place at the expanded anterior end of the neural tube, which is filled with embryonic cerebrospinal fluid (E-CSF). We have recently identified a transient blood–CSF barrier that forms between embryonic days E3 and E4 in chick embryos and that is responsible for the transport of proteins and control of E-CSF homeostasis, including osmolarity. Here we examined the presence of glucose transporter GLUT-1 as well the presence of caveolae-structural protein Caveolin1 (CAV-1) in the embryonic blood-CSF barrier which may be involved in the transport of glucose and of proteins, water and ions respectively across the neuroectoderm. In this paper we demonstrate the presence of GLUT-1 and CAV-1 in endothelial cells of blood vessels as well as in adjacent neuroectodermal cells, located in the embryonic blood–CSF barrier. In blood vessels, these proteins were detected as early as E4 in chick embryos and E12.7 in rat embryos, i.e. the point at which the embryonic blood–CSF barrier acquires this function. In the neuroectoderm of the embryonic blood-CSF barrier, GLUT-1 was also detected at E4 and E12.7 respectively, and CAV-1 was detected shortly thereafter in both experimental models. These experiments contribute to delineating the extent to which the blood–CSF embryonic barrier controls E-CSF composition and homeostasis during early stages of brain development in avians and mammals. Our results suggest the regulation of glucose transport to the E-CSF by means of GLUT-1 and also suggest a mechanism by which proteins are transported via transcellular routes across the neuroectoderm, thus reinforcing the crucial role of E-CSF in brain development.
Highlights
The microenvironment of the Central Nervous System (CNS) is decisive for neuronal development and function
Our results suggest the regulation of glucose transport to the embryonic cerebrospinal fluid (E-CSF) by means of GLUT-1 and suggest a mechanism by which proteins are transported via transcellular routes across the neuroectoderm, reinforcing the crucial role of E-CSF in brain development
To extrapolate the avian data to a mammalian system, we examined the localisation of CAV-1 and GLUT-1 in rat embryos from E12.7 to E13.7, as these developmental stages are equivalent to those examined in chick embryos with respect to brain development
Summary
The microenvironment of the Central Nervous System (CNS) is decisive for neuronal development and function. We identified a transient blood–CSF barrier located in the brain stem lateral to the ventral midline, at the mesencephalon and prosencephalon level, between embryonic days E3 and E5 in chick embryos and 12.7–13.7 days post-coitum in rats [15,16]. This embryonic blood–CSF barrier transports proteins in a selective manner via transcellular routes [15] as well as water and ions via specific transporters, identified by the presence of aquaporins 1 and 4 (AQP1 and AQP4) and the inwardly rectifying K+ channel (Kir4.1) [16]. AQP1, Published Online October 2010 in SciRes. http://www.scirp.org/journal/abb
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