The central neurotoxicity of the excitatory amino acid neurotransmitter glutamate has been postulated to participate in the pathogenesis of the neuronal cell loss associated with several neurological disease states, but the complexity of the intact nervous system has impeded detailed analysis of the phenomenon. In the present study, glutamate neurotoxicity was studied with novel precision in dissociated cell cultures prepared from the fetal mouse neocortex.Brief exposure to glutamate was found to produce morphological changes in mature cortical neurons beginning as quickly as 90 set after exposure, followed by widespread neuronal degeneration over the next hours. Quantitative dose-toxicity study suggested an ED, of 50-l 00 MM for a 5 min exposure to glutamate. Immature cortical neurons and glia were not injured by such exposures to glutamate. Uptake processes probably do not limit GNT in culture, as the uptake inhibitor dihydrokainate did not potentiate GNT. Possibly reflecting the lack of uptake limitation, glutamate was found to be actually more potent than kainate as a neurotoxin in these cultures, a dramatic reversal of the in vivo potency rank order. Some neurons regularly survived brief glutamate exposure; these possibly glutamate-resistant neurons had electrophysiologic properties, including chemosensitivity to glutamate, that were grossly similar to those of the original population.The amino acid glutamate is present at several millimolar concentration in mammalian central gray matter (Waelsch, 195 1) and has a ubiquitous excitatory effect on central neurons (Curtis et al., 1960;Crawford and Curtis, 1964; Krnjevic, 1974), properties that support the current belief that glutamate is likely a major mammalian central excitatory neurotransmitter (DiChiara and Gessa, 198 1). It is therefore somewhat surprising that glutamate is also a neurotoxin (Lucas and Newhouse, 1957;Olney, 1969; Coyle et al., 198 1). Under normal circumstances, protective mechanisms presumably limit neuronal glutamate exposure and prevent toxicity, but a potential for pathogenesis is surely ever present. Glutamate neurotoxicity (GNT) has now been proposed to participate specifically in the neuronal cell loss associated with a number of neurologic diseases, including Huntington's disease (Coyle and Schwartz, 1976;McGeer and McGeer, 1976), olivopontocerebellar atrophy (Plaitakis et al., Received Feb. 25, 1986; revised June 12, 1986; accepted July 23, 1986. We thank M. (Nadler et al., 1978; Sloviter, 1983), stroke (Rothman, 1984;Simon et al., 1984), and hypoglycemic encephalopathy (Wieloch, 1985). Despite this potential clinical importance, little is presently known about the phenomenon of GNT at the cellular level. The major obstacle to the study of GNT has been the complexity of the intact nervous system; indeed, it is somewhat problematic to demonstrate the phenomenon at all in viva Systemic administration of glutamate to rodents generally produces brain lesions only in immature animals without a fully developed blood-brain barrie...

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