DNQX-induced toxicity in cultured rat hippocampal neurons: an apparent AMPA receptor-independent effect?

To evaluate the involvement of AMPA receptor activation in neuronal cell death and survival, rat hippocampal neurons in culture were treated with AMPA receptor antagonists. A 46 h treatment with 6,7-dinitroquinoxaline-2,3-dione (DNQX), added 2 h after cell plating, induces a dose-dependent neurotoxicity. Similar effects are also observed in more mature hippocampal neurons (treatment at 14 days in vitro). DNQX toxic effect is neuron-specific since cultured hippocampal glial cells are unaffected. Attempts to characterise the site of action of DNQX suggest that ionotropic glutamate receptors would not be implicated. Indeed, (i) other AMPA receptor antagonists are either ineffective or only moderately efficient in mimicking DNQX effects; (ii) AMPA alone or in the presence of cyclothiazide, as well as, other AMPA receptor agonists, do not reverse DNQX action; (iii) DNQX neurotoxicity is not likely to involve blockade of NMDA receptor glycine site, since this effect is neither mimicked by 7-chlorokynurenate nor reversed by D-serine. Thus, DNQX toxicity in cultured hippocampal neurons is apparently mediated through an ionotropic glutamate receptor-independent way.