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Glaucoma is a neurological disorder leading to blindness initially through the loss of retinal ganglion cells, followed by loss of neurons higher in the visual system. Some work has been undertaken to develop prostheses for glaucoma patients targeting tissues along the visual pathway, including the lateral geniculate nucleus (LGN) of the thalamus, but especially the visual cortex. This review makes the case for a visual prosthesis that targets the LGN. The compact nature and orderly structure of this nucleus make it a potentially better target to restore vision than the visual cortex. Existing research for the development of a thalamic visual prosthesis will be discussed along with the gaps that need to be addressed before such a technology could be applied clinically, as well as the challenge posed by the loss of LGN neurons as glaucoma progresses. 1964-2012 IEEE. Scopus

Alzheimer's disease (AD) is characterized by the accumulation and deposition of amyloid-beta (Aβ) peptides in the brain. Neuroinflammation occurs in the AD brain and plays a critical role in the neurodegenerative pathology. Particularly, Aβ evokes an inflammatory response that leads to synaptic dysfunction, neuronal death, and neurodegeneration. Apolipoprotein E (ApoE) proteins are involved in cholesterol transport, Aβ binding and clearance, and synaptic functions in the brain. The ApoE4 isoform is a key risk factor for AD, while the ApoE2 isoform has a neuroprotective effect. However, studies have reached different conclusions about the roles of the isoforms; some show that both ApoE3 and ApoE4 have anti-inflammatory effects, while others show that ApoE4 causes a predisposition to inflammation or promotes an inflammatory response following lipopolysaccharide treatment. These discrepancies may result from the differences in models, cell types, experimental conditions, and inflammatory stimuli used. Further, little was known about the role of ApoE isoforms in the Aβ-induced inflammatory response and in the neuroinflammation of AD. Our recent work showed that ApoE isoforms differentially regulate and modify the Aβ-induced inflammatory response in neural cells, with ApoE2 suppressing and ApoE4 promoting the response. In this article, we review the roles, mechanisms, and interrelations among Aβ, ApoE, and neuroinflammation in AD. © 2014 Shanghai Institutes for Biological Sciences, CAS and Springer-Verlag.

In ischemic and traumatic brain injury, hyperactivated glutamate (N-methyl-D-aspartic acid, NMDA) and sodium (Nav) channels trigger excitotoxic neuron death. Na(+), Ca(++) and H2O influx into affected neurons elicits swelling (increased cell volume) and pathological blebbing (disassociation of the plasma membrane's bilayer from its spectrin-actomyosin matrix). Though usually conflated in injured tissue, cell swelling and blebbing are distinct processes. Around an injury core, salvageable neurons could be mildly swollen without yet having suffered the bleb-type membrane damage that, by rendering channels leaky and pumps dysfunctional, exacerbates the excitotoxic positive feedback spiral. Recognizing when neuronal inflation signifies non-lethal osmotic swelling versus blebbing should further efforts to salvage injury-penumbra neurons. To assess whether the mechanical properties of osmotically-swollen versus excitotoxically-blebbing neurons might be cytomechanically distinguishable, we measured cortical neuron elasticity (gauged via atomic force microscopy (AFM)-based force spectroscopy) upon brief exposure to hypotonicity or to excitotoxic agonists (glutamate and Nav channel activators, NMDA and veratridine). Though unperturbed by solution exchange per se, elasticity increased abruptly with hypotonicity, with NMDA and with veratridine. Neurons then invariably softened towards or below the pre-treatment level, sometimes starting before the washout. The initial channel-mediated stiffening bespeaks an abrupt elevation of hydrostatic pressure linked to NMDA or Nav channel-mediated ion/H2O fluxes, together with increased [Ca(++)]int-mediated submembrane actomyosin contractility. The subsequent softening to below-control levels is consistent with the onset of a lethal level of bleb damage. These findings indicate that dissection/identification of molecular events during the excitotoxic transition from stiff/swollen to soft/blebbing is warranted and should be feasible.

The pathophysiological mechanisms underlying the onset and inexorable progression of the late‑onset form of Alzheimer's disease (AD) are still the object of controversy. This review takes stock of some most recent advancements of this field concerning the complex roles played by the amyloid‑β (Aβ)‑binding p75 neurotrophin receptor (p75NTR) and calcium‑sensing receptor (CaSR) and by the primary cilia in AD. Apart from their physiological roles, p75NTR is more intensely expressed in the hippocampus of human AD brains and Aβ‑bound p75NTR triggers cell death, whereas Aβ‑bound CaSR signalling induces the de novo synthesis and release of nitric oxide (NO), vascular endothelial growth factor (VEGF)‑A and Aβ peptides (Aβs), particularly on the part of normal adult human astrocytes. The latter effect could significantly increase the pool of Aβ‑ and NO‑producing nerve cells favouring the progressive spread of a self‑sustaining and self‑reinforcing 'infectious' mechanism of neural and vascular (i.e. blood-brain barrier) cell damage. Interestingly, primary cilia concentrate p75NTR receptors in their membranes and are abnormally structured/damaged in transgenic (Tg) AD‑model mice, which could impact on the adult neurogenesis occurring in the dentate gyrus's subgranular zone (SGZ) that is necessary for new memory encoding, thereby favouring typical AD cognitive decline. Altogether, these findings may pave the way to novel therapeutic approaches to AD, particularly in its mild cognitive impairment (MCI) and pre‑MCI stages of development.

Evidence has implicated apoptosis as a mechanism underlying cell demise in diverse neurodegenerative diseases including Parkinson's disease (PD). Endogenous toxins and other stress signals activate the sphingomyelin pathway increasing the levels of ceramide, an important regulator of cell death.In the present paper we have analysed the contribution of PI3K/AKT-GSK3? and MAPK (ERK and JNK) pathways to cell death in a catecholaminergic cell line following exposure to C2-ceramide. We also explored the potential neuroprotective action of insulin-like growth factor-1 (IGF-1) and neurotrophin-3 (NT3).We demonstrated that C2-ceramide-induced cell death is associated to an early decrease in phosphorylation (inhibition) of PI3K/AKT and ERK, followed by phosphorylation (activation) of JNK and de-phosphorylation (activation) of glycogen synthase kinase-3 beta (GSK3?). NT3 and IGF-1 increased survival at early time points, but only IGF-1 is capable to attenuate C2-ceramide-mediated neuronal death, and this neuroprotection is associated to strong and permanent activation of AKT and inhibition of GSK3?. In conclusion, C2-ceramide initiates a series of events including an early inactivation of PI3K/AKT and ERK pathways followed by activation of JNK and activation of GSK3? and neuronal death, changes that are counteracted by IGF-1. © 2010 Elsevier Inc.

Vertebrate α-bungarotoxin-like molecules of the Ly-6 superfamily have been implicated as balancers of activity and survival in the adult nervous system. To determine whether a member of this family could be involved in the development of the avian ciliary ganglion, we identified 6 Gallus genes by their homology in structure to mouselynx1andlynx2. One of these genes, an ortholog of prostate stem cell antigen (psca), is barely detectable at embryonic day (E) 8, before neuronal cell loss in the ciliary ganglion, but increases >100-fold as the number of neurons begins to decline between E9 and E14. PSCA is highly expressed in chicken and mouse telencephalon and peripheral ganglia and correlates with expression of α7-containing nicotinic acetylcholine receptors (α7-nAChRs). Misexpressing PSCA before cell death in the ciliary ganglion blocks α7-nAChR activation by nicotine and rescues the choroid subpopulation from dying. Thus, PSCA, a molecule previously identified as a marker of prostate cancer, is a member of the Ly-6 neurotoxin-like family in the nervous system, and is likely to play a role as a modulator of α7 signaling-induced cell death during development.

Brain-derived neurotrophic factor (BDNF) is a member of the nerve growth factor family, and is widely expressed in the adult mammalian brain. Besides its well known neuroprotective activity after traumatic brain injury the evidences regarding its activity dependent release by the pathophysiology of major depression are rapidly replicating. Considering the data that stress plays an important role by the development of depression which is characterized with prominent hippocampal cell death, as well as the well known neuroprotective effects of BDNF, we aimed to investigate the link between the BDNF, stress and depression. Thus we prepared a minireview in order to evaluate the neuroprotective role of BDNF by psychiatric disorders which are characterized with prominent neuronal cell death.

Aging is a risk factor for the development of adult-onset neurodegenerative diseases. Although some of the molecular pathways regulating longevity and stress resistance in lower organisms are defined (i.e., those activating the transcriptional regulators DAF-16 and HSF-1 in Caenorhabditis elegans), their relevance to mammals and disease susceptibility are unknown. We studied the signaling controlled by the mammalian homolog of DAF-16, FOXO3a, in model systems of motor neuron disease. Neuron death elicited in vitro by excitotoxic insult or the expression of mutant SOD1, mutant p150glued, or polyQ-expanded androgen receptor was abrogated by expression of nuclear-targeted FOXO3a. We identify a compound [Psammaplysene A (PA)] that increases nuclear localization of FOXO3a in vitro and in vivo and show that PA also protects against these insults in vitro. Administration of PA to invertebrate model systems of neurodegeneration similarly blocked neuron death in a DAF-16/FOXO3a-dependent manner. These results indicate that activation of the DAF-16/FOXO3a pathway, genetically or pharmacologically, confers protection against the known causes of motor neuron diseases. Copyright © 2009 Society for Neuroscience. 29 25 8236 8247 Cited By :52

Different VGF peptides derived from Vgf, originally identified as a nerve growth factor responsive gene, have been detected in neurons within the central and peripheral nervous system and in various endocrine cells. In the current study, we have evaluated the ability of TLQP-21, a VGF-derived peptide, to protect, in a dose- and time-dependent manner, primary cultures of rat cerebellar granule cells (CGCs) from serum and potassium deprivation-induced cell death. We demonstrated that TLQP-21 increased survival of CGCs by decreasing the degree of apoptosis as assessed by cell viability and DNA fragmentation. Moreover, TLQP-21 significantly activated extracellular signal-regulated kinase 1/2, serine/threonine protein kinase, and c-jun N-terminal kinase phosphorylation, while decreased the extent of protein kinase C phosphorylation, as demonstrated by western blot analysis. In addition, TLQP-21 induced significant increase in intracellular calcium (as measured by fura-2AM) in about 60% of the recorded neurons. Taken together, the present results demonstrate that TLQP-21 promotes the survival of CGCs via pathways involving, within few minutes, modulation of kinases associated with CGCs survival, and by increasing intracellular calcium which can contribute to the neuroprotective effect of the peptide.

Amyotrophic lateral sclerosis is a neurodegenerative disease characterized by the selective degeneration of motor neurons in the spinal cord, brainstem and cerebral cortex. In this study we have analysed the electrophysiological properties of GABA(A) receptors and GABA(A) alpha1 and alpha2 subunits expression in spinal motor neurons in culture obtained from a genetic model of ALS (G93A) and compared with transgenic wild type SOD1 (SOD1) and their corresponding non transgenic litter mates (Control). Although excitotoxic motor neuron death has been extensively studied in relation to Ca(2+)-dependent processes, strong evidence indicates that excitotoxic cell death is also remarkably dependent on Cl(-) ions and on GABA(A) receptor activation. In this study we have analysed the electrophysiological properties of GABA(A) receptors and the expression of GABA(A)alpha(1) and alpha(2) subunits in cultured motor neurons obtained from a genetic model of amyotrophic lateral sclerosis (G93A) and compared them with transgenic wild-type Cu,Zn superoxide dismutase and their corresponding non-transgenic littermates (Control). In all tested motor neurons, the application of gamma-aminobutyric acid (GABA) (0.5-100 mum) evoked an inward current that was reversibly blocked by bicuculline (100 mum), thus indicating that it was mediated by the activation of GABA(A) receptors. Our results indicate that the current density at high GABA concentrations is similar in control, Cu,Zn superoxide dismutase and G93A motor neurons. However, the dose-response curve significantly shifted toward lower concentration values in G93A motor neurons and the extent of desensitization also increased in these neurons. Finally, multiplex single-cell real-time polymerase chain reaction and immunofluorescence revealed that the amount of GABA(A)alpha(1) subunit was significantly increased in G93A motor neurons, whereas the levels of alpha(2) subunit were unchanged. These data show that the functionality and expression of GABA(A) receptors are altered in G93A motor neurons inducing a higher Cl(-) influx into the cell with a possible consequent neuronal excitotoxicity acceleration.

The H2 allele of APOC1, giving rise to increased gene expression of apolipoprotein C-I (apoC-I), is in genetic disequilibrium with the APOE4 allele and may provide a major risk factor for Alzheimer's disease (AD). We found that apoC-I protein is present in astrocytes and endothelial cells within hippocampal regions in both human control and AD brains. Interestingly, apoC-I colocalized with β-amyloid (Aβ) in plaques in AD brains, and in vitro experiments revealed that aggregation of Aβ was delayed in the presence of apoC-I. Moreover, apoC-I was found to exacerbate the soluble Ab oligomer-induced neuronal death. To establish a potential role for apoC-I in cognitive functions, we used human (h) APOC1+/0 transgenic mice that express APOC1 mRNA throughout their brains and apoC-I protein in astrocytes and endothelial cells. The hAPOC1+/0 mice displayed impaired hippocampal-dependent learning and memory functions compared with their wild-type litter- mates, as judged from their performance in the object recognition task (P = 0.012) and in the Morris water maze task (P = 0.010). ApoC-I may affect learning as a result of its inhibitory properties toward apoE-dependent lipid metabolism. However, no differences in brain mRNA or protein levels of endogenous apoE were detected between transgenie and wild-type mice. Copyright © 2008 by the American Society for Biochemistry and Molecular Biology, Inc.

The H2 allele of APOC I, giving rise to increased gene expression of apolipoprotein C-I (apoC-I), is in genetic disequilibrium with the APOE4 allele and may provide a major risk factor for Alzheimer's disease (AD). We found that apoC-I protein is present in astrocytes and endothelial cells within hippocampal regions in both human control and AD brains. Interestingly, apoC-I colocalized with R-amyloid (A beta) in plaques in AD brains, and in vitro experiments revealed that aggregation of A beta was delayed in the presence of apoC-I. Moreover, apoC-I was found to exacerbate the soluble A beta oligomer-induced neuronal death. To establish a potential role for apoC-I in cognitive functions, we used human (h) APOC1(+/0) transgenic mice that express APOC1 mRNA throughout their brains and apoC-I protein in astrocytes and endothelial cells. The hAPOC1(+/0) mice displayed impaired hippocampal-dependent learning and memory functions compared with their wild-type litter-mates, as judged from their performance in the object recognition task (P = 0.012) and in the Morris water maze task (P = 0.010). ApoC-I may affect learning as a result of its inhibitory properties toward apoE-dependent lipid metabolism. However, no differences in brain mRNA or protein levels of endogenous apoE were detected between transgenic and wild-type mice. In conclusion, human apoC-I expression impairs cognitive functions in mice independent of apoE expression, which supports the potential of a modulatory role for apoC-I during the development of AD.

Glucocorticoids are potent regulators of the innate immune response, and alteration in this inhibitory feedback has detrimental consequences for the neural tissue. This study profiled and investigated functionally candidate genes mediating this switch between cell survival and death during an acute inflammatory reaction subsequent to the absence of glucocorticoid signaling. Oligonucleotide microarray analysis revealed that following lipopolysaccharide (LPS) intracerebral administration at striatum level, more modulated genes presented transcription impairment than exacerbation upon glucocorticoid receptor blockage. Among impaired genes we identified ceruloplasmin (Cp), which plays a key role in iron metabolism and is implicated in a neurodegenative disease. Microglial and endothelial induction of Cp is a natural neuroprotective mechanism during inflammation, because Cp-deficient mice exhibited increased iron accumulation and demyelination when exposed to LPS and neurovascular reactivity to pneumococcal meningitis. This study has identified genes that can play a critical role in programming the innate immune response, helping to clarify the mechanisms leading to protection or damage during inflammatory conditions in the CNS. © 2007 Glezer et al. Fil: Glezer, Isaias. Centre Hospitalier de L'université Laval (chul); Canadá Fil: Chernomoretz, Ariel. Universidad de Buenos Aires; Argentina. Centre Hospitalier de L'université Laval (chul); Canadá. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: David, Samuel. Centre Universitaire de Santé Mcgill, Institut de Recherche; Canadá Fil: Plante, Marie-Michèlle. Centre Hospitalier de L'université Laval (chul); Canadá Fil: Rivest, Serge. Centre Hospitalier de L'université Laval (chul); Canadá

In the present study, we examined the effects of nilvadipine and amlodipine, both dihydropyridine-derivative calcium antagonists, on the impairment of spatial memory induced by a combination of ischemia and β-amyloid (Aβ). Nilvadipine (3.2 mg/kg, i.p.) significantly prevented the impairment of spatial memory and neuronal apoptosis in this model. By contrast, amlodipine had no effect on this impairment of spatial memory. These findings suggest that nilvadipine may prevent impairment of spatial memory by inhibiting neuronal apoptosis; this drug might therefore be useful for the prevention of the progression to dementia in Alzheimer's disease (AD). © 2007 Pharmaceutical Society of Japan.

Previously we have reported that Toki-shakuyaku-san (TSS) ameliorated the impairment of spatial memory induced by single cerebral ischemia (1 × 10 minutes) and scopolamine, a muscarinic receptor antagonist. In this experiment, we studied the effect of TSS on repeated cerebral ischemia (2 × 10 minutes, 1-hour interval) induced impairment of spatial memory and neuronal injury in rats. The 8-day post-ischemic treatment with TSS (30-300 mg/kg) was administered p.o. once per day. TSS dose-dependently prevented the impairment of spatial memory, neuronal death and TUNEL positive cells induced by repeated cerebral ischemia. In order to determine the mechanism of TSS, we also studied the effect of TSS on GluR2 mRNA, one of the glutamate ?-amino-3- hydroxy-5-methyl-4-isoxazole (AMPA) receptor subunits. Repeated cerebral ischemia significantly decreased GluR2 flop mRNA at 1 and 3 days after the occlusion. TSS (300 mg/kg) significantly suppressed the decrease in GluR2 flop at 3 days after repeated cerebral ischemia. These results suggested that the TSS has neuroprotective action which may be indirectly mediated by the AMPA receptor, and TSS may be beneficial for the treatment of cerebrovascular dementia. © 2005 World Scientific Publishing Company. Institute for Advanced Research in Asian Science and Medicine.

The spatial memory impairment and expression of apoptotic cells in hippocampal CA1 cells were investigated in rats using single and repeated ischemia models. The neuroprotective and memory-improving effect of YM-90K, an ?-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptor antagonist, was compared to MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist. Twice-repeated ischemia, but not single ischemia, impaired the spatial memory and increased expression of apoptotic cells. YM-90K, given before and 6 h after the second reperfusion, significantly improved the memory and reduced the apoptotic cells 7 days after the second reperfusion in repeated ischemia. MK-801 neither improved the spatial memory nor reduced apoptotic cells. The present study showed that delayed expression of apoptotic cells is mediated by mechanisms involving AMPA receptors, but not by NMDA receptor, during the late phase after reperfusion. YM-90K could provide neuroprotective activity and improve the spatial memory impaired by repeated ischemia. © 2003 Elsevier B.V. All rights reserved.

The spatial memory impairment and expression of apoptotic cells in hippocampal CA1 cells were investigated in rats using single and repeated ischemia models. The neuroprotective and memory-improving effect of YM-90K, an α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptor antagonist, was compared to MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist. Twice-repeated ischemia, but not single ischemia, impaired the spatial memory and increased expression of apoptotic cells. YM-90K, given before and 6 h after the second reperfusion, significantly improved the memory and reduced the apoptotic cells 7 days after the second reperfusion in repeated ischemia. MK-801 neither improved the spatial memory nor reduced apoptotic cells. The present study showed that delayed expression of apoptotic cells is mediated by mechanisms involving AMPA receptors, but not by NMDA receptor, during the late phase after reperfusion. YM-90K could provide neuroprotective activity and improve the spatial memory impaired by repeated ischemia. © 2003 Elsevier B.V. All rights reserved.

Although the role of the microtubule-binding domain of the tau protein in the modulation of microtubule assembly is widely established, other possible functions of this protein have been poorly investigated. We have analyzed the effect of adenovirally mediated expression of two fragments of the N-terminal portion - free of microtubule-binding domain - of the tau protein in cerebellar granule neurons (CGNs). We found that while the expression of the tau (1-230) fragment, as well as of full-length tau, inhibits the onset of apoptosis, the tau (1-44) fragment exerts a powerful toxic action on the same neurons. The antiapoptotic action of tau (1-230) is exerted at the level of Akt-mediated activation of the caspase cascade. On the other hand, the toxic action of the (1-44) fragment is not prevented by inhibitors of CGN apoptosis, but is fully inhibited by NMDA receptor antagonists. These findings point to a novel, physiological role of the N-terminal domain of tau, but also underlay that its possible proteolytic truncation mediated by apoptotic proteases may generate a highly toxic fragment that could contribute to neuronal death.

Copper is an essential trace element which forms an integral component of many enzymes. While trace amounts of copper are needed to sustain life, excess copper is extremely toxic in the brain. Also, ethanol intake causes morphological changes in the brain. The present study aims to investigate effects of copper overload with ethanol intake in hippocampal neuron numbers of rat brain. Control and experimental group of rats (n=6 for each group) were fed ad libitum. Experimental group were given ethanol with copper in drinking water each day for ten days. Control group animals were given only drinking water during this period. Afterwards, animals were decapitated and their brains were removed by craniotomy. Frozen brains were cut by a cryostat. Sections collected via systematic random sampling were stained with hematoxylin and eosin. On microscopic images obtained from pyramidal cell layers in hippocampus, total neuron numbers were estimated using the optical fractionator method. We observed that pyramidal neuron numbers in the subdivisions of hippocampus were significantly lower in the experimental group than in the control group. These results suggest that copper overdose with ethanol intake can cause neuronal loss in hippocampus of rat brain. © 2003 Tohoku University Medical Press.

Using primary cultures of mouse cerebellar granule cells as an in vitro model system, it has been demonstrated that different profiles of temporal expression of the c-fos proto-oncogene are observed under non-excitotoxic and excitotoxic conditions. A ratio has been derived previously for the steady- state level of c-fos mRNA after 30 min and 240 min which suggests that a 240 min/30 min ratio of greater than 1 correlates with excitotoxicity, whereas a ratio of less than 1 correlates with a non-excitotoxic outcome. Moreover, a positive correlation is seen with abrogation of excitotoxicity in response to selective excitatory amino acid receptor antagonists. This test, proposed as a specific biomarker for excitotoxicity is undergoing prevalidation. Excitotoxicity is defined as neuronal cell death mediated by hyperactivation of glutamate receptor subtypes and therefore might be expected to be prevented by selective glutamate receptor antagonists. In preliminary evaluation studies, we have conducted work under the direction of the European Center for Validation of Alternate Methods (ECVAM) using compounds specified by ECVAM that have been subdivided into four groups based on known or presumed actions. These groups comprise: Group 1 - endogenous/synthetic excitotoxins; Group 2 - environmental, putative excitotoxins; Group 3 - neurotoxic but non-excitotoxic compounds, and Group 4 - non-toxic compounds. The results of this study support the proposal that the c-fos mRNA time-ratio test is a specific biomarker of excitotoxicity. Just as importantly, this test has the potential for application in screening newly-designed EAA receptor antagonists in the search for clinically relevant drugs to treat a variety of neuropathologies. (C) 2000 Elsevier Science Ltd. Chemicals/CAS: Excitatory Amino Acid Antagonists; Glutamic Acid, 56-86-0; Proto-Oncogene Proteins c-fos; RNA, Messenger

Using primary cultures of mouse cerebellar granule cells as an in vitro model system, it has been demonstrated that different profiles of temporal expression of the c-fos proto-oncogene are observed under non-excitotoxic and excitotoxic conditions. A ratio has been derived previously for the steady- state level of c-fos mRNA after 30 min and 240 min which suggests that a 240 min/30 min ratio of greater than 1 correlates with excitotoxicity, whereas a ratio of less than 1 correlates with a non-excitotoxic outcome. Moreover, a positive correlation is seen with abrogation of excitotoxicity in response to selective excitatory amino acid receptor antagonists. This test, proposed as a specific biomarker for excitotoxicity is undergoing prevalidation. Excitotoxicity is defined as neuronal cell death mediated by hyperactivation of glutamate receptor subtypes and therefore might be expected to be prevented by selective glutamate receptor antagonists. In preliminary evaluation studies, we have conducted work under the direction of the European Center for Validation of Alternate Methods (ECVAM) using compounds specified by ECVAM that have been subdivided into four groups based on known or presumed actions. These groups comprise: Group 1 - endogenous/synthetic excitotoxins; Group 2 - environmental, putative excitotoxins; Group 3 - neurotoxic but non-excitotoxic compounds, and Group 4 - non-toxic compounds. The results of this study support the proposal that the c-fos mRNA time-ratio test is a specific biomarker of excitotoxicity. Just as importantly, this test has the potential for application in screening newly-designed EAA receptor antagonists in the search for clinically relevant drugs to treat a variety of neuropathologies. (C) 2000 Elsevier Science Ltd. Chemicals/CAS: Excitatory Amino Acid Antagonists; Glutamic Acid, 56-86-0; Proto-Oncogene Proteins c-fos; RNA, Messenger