The role of glutamate and its receptors in the proliferation, migration, differentiation and survival of neural progenitor cells

The mammalian central nervous system derives from multipotent neural progenitor cells (NPCs) of the developing brain. During development the progenitor cells have enormous potential. They proliferate actively and differentiate into all the three main cell types, i.e., neurons, astrocytes and oligodendrocytes, of the adult brain through a tightly regulated process that coordinates cell proliferation, survival, migration, differentiation and apoptosis. This process is regulated by multiple extracellular signals including neurotrophic factors, chemoattractants and neurotransmitters in a coordinated manner. The main excitatory neurotransmitter glutamate is involved in promoting and/or inhibiting the proliferation, survival, migration and differentiation of NPCs acting via ionotropic or metabotropic receptors. The role of glutamate in the regulation of cortical NPCs has been most extensively studied. Glutamate appears to have a similar role in hippocampal, striatal as well as adult neural progenitors. Ionotropic alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate (KA) receptors and metabotropic glutamate receptor 5 (mGluR5) are expressed early during embryonic development as well as in the neurogenic zones of the adult brain. Ca2+-permeable AMPA/KA receptors are initially of importance for cell proliferation and neuronal motility. At later stages of development N-methyl-D-aspartate (NMDA) receptors have a more prominent role. MGluR5, which is the main metabotropic glutamate receptor during early development, is expressed in early progenitors and radial glial cells. Activation of this receptor promotes the proliferation and survival of NPCs. MGluR5 is involved in the extension of radial glial processes and in regulation of the migration of early cortical neurons.