Development and regulation of excitatory amino acid receptors involved in the release of arachidonic acid in cultured hippocampal neural cells

Abstract

Release of [ 3H]arachidonic acid mediated by excitatory amino acid (EAA) receptors was investigated from prelabelled primary cultures of hippocampal neurons and astroglial cells. Treatment with N- methyl- d-aspartate (NMDA), quisqualate (QA) and kainate resulted in age- and dose-dependent stimulation of [ 3H]arachidonic acid release. During development, the maximum response for NMDA was observed relatively earlier (at 7 days) than those for QA and kainate (at 14 days) in the hippocampal neuronal cultures. The half maximal effects were obtained at about 15 μM NMDA at all ages studied and about 0.5 μM QA at 14 and 20 days. At optimum concentrations NMDA- and QA-induced releases were additive. Unlike with neurons, treatment with all the 3 EAA receptor agonists, NMDA, QA and kainate, had no significant effect on [ 3H]arachidonate release in hippocampal astroglial cells. In cultured 14-day-old neurons, the increases in NMDA- and QA-mediated [ 3H]arachidonic acid release were completely blocked by the NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid, and the ionotropic QA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, respectively. But the ionotropic QA receptor agonist α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) had no significant effect on [ 3H]arachidonate release, indicating that interaction between ionotropic QA and metabolotropic QA receptors may be essential for optimal QA-mediated arachidonic acid release. At physiological concentrations of Mg 2+ (1.2 mM), AMPA was found to potentiate NMDA-induced release of [ 3H]arachidonic acid; the effect appeared to be related to a removal of Mg 2+ blockade mediated by mild depolarisation. Our findings would suggest a role for associative stimulation of different types of EAA receptors in the effector mechanisms responsible for signal transduction and synaptic plasticity in the hippocampus.