Acidic amino acids evoke a smaller [Ca2+]i rise in GABAergic than non-GABAergic hippocampal neurons

Changes in intracellular calcium concentration ([Ca2+]i) in response to topical application of the glutamate agonists N-methyl-D-aspartate (NMDA), or amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were measured in cultured rat hippocampal neurons loaded with Fluo-3 and visualized in a confocal laser scanning microscope. These neurons were subsequently stained for the presence of the enzyme marker for gamma-amino butyric acid (GABA), glutamate decarboxylase (GAD). GAD-positive, putative interneurons were less responsive to NMDA and AMPA than GAD-negative neurons. The time course of the rise and decay of [Ca2+]i was similar in the two groups of neurons. Also, there was no clear difference in the shape and size of these two neuron groups indicating that the difference between them is not due to diffusion distances. These data indicate that interneurons are probably more able to handle a calcium load than other neurons, a difference that may underly their resistance to treatments which cause degeneration of other neurons in the hippocampus.