Glutamate-induced increases in intracellular Ca2+ in cultured rat neocortical neurons

In neurons, changes in intracellular Ca2+ concentration ([Ca2+]i) trigger neurotransmitter release, regulate membrane excitability, affect gene expression, and govern short- and long-term forms of synaptic plasticity. Rises in cytoplasmic Ca2+ are thought to underlie the various effects of glutamatergic neurotransmitters within the central nervous system. In the present study, we applied a calcium imaging technique using a confocal laser scanning microscope to investigate the effects of excitatory amino acids on glutamate induced calcium influx in primary cultured neocortical neurons. Glutamate (5 microM) induced increases in [Ca2+]i in both the soma and dendritic processes of the cells. The increase was partially blocked by 10 microM DL-2-amino-5-phosphovaleric acid (APV), a NMDA antagonist. The reduction was higher in the dendritic process than in the cell body: the reduction was 58% in the cell body and 67% in the dendritic processes. In contrast, 5 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA antagonist, had less effect on the response. We observed an 11% reduction in the dendritic processes, but no change in the cell bodies. The results demonstrated the heterogeneous distribution of APV- and CNQX-sensitive channels in primary cultured neocortical neurons. In both the cell body and dendritic processes, [Ca2+]i increase induced by low concentrations of glutamate was mainly due to the activation of NMDA receptors.