Activation of NMDA receptors increases proliferation and differentiation of hippocampal neural progenitor cells

The prolonged effects of N-methyl-D-aspartate (NMDA) receptor activation on the proliferation and differentiation of hippocampal neural progenitor cells (NPCs) were studied. Under conditions of mitogen-mediated proliferation, a single NMDA pulse (5 µM) increased the fraction of 5-bromo-2-deoxyuridine (BrdU)-positive (BrdU⁺) cells after a delay of 72 hours. Similarly, a single systemic injection of NMDA (100 mg/kg) increased the number of BrdU⁺ cells in the dentate gyrus (DG) after 28 days, but not after 3 days. NMDA receptor activation induced an immediate influx of Ca²⁺ into the NPCs and the NPCs expressed and released vascular endothelial growth factor (VEGF) in an NMDA receptor-dependent manner within 72 hours. With repetitive stimulation at the same dose, NMDA stimulated the acquisition of a neuronal phenotype accompanied by an increase in the expression of proneural basic helix-loop-helix (bHLH) factors. Together these findings suggest that neurogenesis in the developing brain is likely to be both directly and indirectly regulated by complex interactions between Ca²⁺ influx and excitation-releasable cytokines, even at mild levels of excitation. In addition, our results are the first to show that stimulation of NPCs may lead to either proliferation or neuronal differentiation, depending on the level of NMDA receptor activation.