Glutamate stimulates neurogranin phosphorylation in cultured rat hippocampal neurons

Neurogranin is a calmodulin-binding and a protein kinase C substrate, that is expressed in telencephalic regions of the rat brain and has been associated with signal transduction and long-term potentiation (LTP). We here report that neurogranin is present in cultured hippocampal neurones, although in amounts lower than those present in the adult hippocampus, and that is also phosphorylated 'in vivo'. Glutamate receptor activation rapidly and significantly increases neurogranin phosphorylation, which achieves maximal phosphate labeling after ionotropic receptor stimulation (kainate and N-methyl-D-aspartate) and more moderate one after metabotropic receptor activation. It is proposed that neurogranin phosphorylation responds to changes in intracellular free Ca2+ and, also, that an increase in neurogranin phosphorylation contributes to enhance and extend calmodulin action, and therefore participate in post-synaptic signal transduction and LTP. (C) 1997 Elsevier Science Ireland Ltd.