Activation of Parabrachial Nucleus Glutamatergic Neurons Accelerates Reanimation from Sevoflurane Anesthesia in Mice.

BACKGROUND: The parabrachial nucleus (PBN), which is a brainstem region containing glutamatergic neurons, is a key arousal nucleus. Injuries to the area often prevent patient reanimation. Some studies suggest that brain regions that control arousal and reanimation are a key part of the anesthesia recovery. Therefore, we hypothesize that the PBN may be involved in regulating emergence from anesthesia. METHODS: We investigated the effects of specific activation or inhibition of PBN glutamatergic neurons on sevoflurane general anesthesia using the chemogenetic "designer receptors exclusively activated by designer drugs" approach. Optogenetic methods combined with polysomnographic recordings were used to explore the effects of transient activation of PBN glutamatergic neuron on sevoflurane anesthesia. Immunohistochemical techniques are employed to reveal the mechanism by which PBN regulated sevoflurane anesthesia. RESULTS: Chemogenetic activation of PBN glutamatergic neurons by intraperitoneal injections of clozapine-N-oxide decreased emergence time (mean ± SD, control vs. clozapine-N-oxide, 55 ± 24 vs. 15 ± 9 s, P = 0.0002) caused by sevoflurane inhalation and prolonged induction time (70 ± 15 vs. 109 ± 38 s, n = 9, P = 0.012) as well as the ED50 of sevoflurane (1.48 vs. 1.60%, P = 0.0002), which was characterized by a rightward shift of the loss of righting reflex cumulative curve. In contrast, chemogenetic inhibition of PBN glutamatergic neurons slightly increased emergence time (56 ± 26 vs. 87 ± 26 s, n = 8, P = 0.034). Moreover, instantaneous activation of PBN glutamatergic neurons expressing channelrhodopsin-2 during steady-state general anesthesia with sevoflurane produced electroencephalogram evidence of cortical arousal. Immunohistochemical experiments showed that activation of PBN induced excitation of cortical and subcortical arousal nuclei during sevoflurane anesthesia. CONCLUSIONS: Activation of PBN glutamatergic neurons is helpful to accelerate the transition from general anesthesia to an arousal state, which may provide a new strategy in shortening the recovery time after sevoflurane anesthesia.

Modafinil attenuates reinstatement of cocaine seeking: role for cystine-glutamate exchange and metabotropic glutamate receptors.

Modafinil may be useful for treating stimulant abuse, but the mechanisms by which it acts to do so are unknown. Indeed, a primary effect of modafinil is to inhibit dopamine transport, which typically promotes rather than inhibits motivated behavior. Therefore, we examined the role of nucleus accumbens extracellular glutamate and the group II metabotropic glutamate receptor (mGluR2/3) in modafinil effects. One group of rats was trained to self-administer cocaine for 10 days and extinguished, then given priming injections of cocaine to elicit reinstatement. Modafinil (300 mg/kg, intraperitoneal) inhibited reinstated cocaine seeking (but did not alter extinction responding by itself), and this effect was prevented by pre-treatment with bilateral microinjections of the mGluR2/3 antagonist LY-341495 (LY) into nucleus accumbens core. No reversal of modafinil effects was seen after unilateral accumbens core LY, or bilateral LY in the rostral pole of accumbens. Next, we sought to explore effects of modafinil on extracellular glutamate levels in accumbens after chronic cocaine. Separate rats were administered non-contingent cocaine, and after 3 weeks of withdrawal underwent accumbens microdialysis. Modafinil increased extracellular accumbens glutamate in chronic cocaine, but not chronic saline-pre-treated animals. This increase was prevented by reverse dialysis of cystine-glutamate exchange or voltage-dependent calcium channel antagonists. Voltage-dependent sodium channel blockade partly attenuated the increase in glutamate, but mGluR1 blockade did not. We conclude that modafinil increases extracellular glutamate in nucleus accumbens from glial and neuronal sources in cocaine-exposed rats, which may be important for its mGluR2/3-mediated antirelapse properties.

The "blue" side of glutamatergic neurotransmission: NMDA receptor antagonists as possible novel therapeutics for major depression.

In spite of the wide-ranging, continuously expanding arsenal of antidepressants and intensive research on depression, the treatment of severe, recurrent mood disorders as well as antidepressant-resistant refractory mood disturbances has not yet entirely been solved. In this article we attempt to review some data from the growing body of evidence that underlie the presumed implication of the glutamatergic neurotransmission in severe mood disorders and thereby some strategies allowing reinstatement of the normal functioning of the glutamatergic system, particularly through N-methyl-d-aspartate (NMDA) receptors. Thus, here we focus on one of the most promising ones, the NMDA receptor-modulating agents including competitive NMDA antagonists, glycine site partial antagonists and channel site antagonists: high- and low-affinity non-competitive NMDA receptor blockers. The glutamate-modulating therapies that specifically affect this system, above all low-affinity non-competitive NMDA receptor antagonists such as amantadine and its derivative memantine which are clinically well tolerated and currently used in other indications hold considerable promise for the development of new, improved antidepressants to treat severe, recurrent and refractory mood disorders.

Regulation of glutamate signaling in the extended amygdala by adolescent alcohol exposure.

Adolescence is a critical period for brain development and behavioral maturation, marked by increased risk-taking behavior and the initiation of drug use. There are significant changes in gray matter volume and pruning of synapses along with a shift in excitatory to inhibitory balance which marks the maturation of cognition and decision-making. Because of ongoing brain development, adolescents are particularly sensitive to the detrimental effects of drugs, including alcohol, which can cause long-lasting consequences into adulthood. The extended amygdala is a region critically implicated in withdrawal and negative affect such as anxiety and depression. As negative affective disorders develop during adolescence, the effects of adolescent alcohol exposure on extended amygdala circuitry needs further inquiry. Here we aim to provide a framework to discuss the existing literature on the extended amygdala, the neuroadaptations which result from alcohol use, and the intersection of factors which contribute to the long-lasting effects of this exposure.

An overview of ongoing clinical trials assessing pharmacological therapeutic strategies to manage chemotherapy-induced peripheral neuropathy, based on preclinical studies in rodent models.

Chemotherapy-induced peripheral neuropathy (CIPN) is a major dose-limiting side effect induced by a variety of chemotherapeutic agents. Symptoms are mainly sensory: pain, tingling, numbness, and temperature sensitivity. They may require the tapering of chemotherapy regimens or even their cessation; thus, the prevention/treatment of CIPN is critical to increase effectiveness of cancer treatment. However, CIPN management is mainly based on conventional neuropathic pain treatments, with poor clinical efficacy. Therefore, significant effort is made to identify new pharmacological targets to prevent/treat CIPN. Animal modeling is a key component in predicting human response to drugs and in understanding the pathophysiological mechanisms underlying CIPN. In fact, studies performed in rodents highlighted several pharmacological targets to treat/prevent CIPN. This review provides updated information about ongoing clinical trials testing drugs for the management of CIPN and presents some of their proof-of-concept studies conducted in rodent models. The presented drugs target oxidative stress, renin-angiotensin system, glutamatergic neurotransmission, sphingolipid metabolism, neuronal uptake transporters, nicotinamide adenine dinucleotide metabolism, endocannabinoid system, transient receptor potential channels, and serotoninergic receptors. As some clinical trials focus on the effect of the drugs on pain, others evaluate their efficacy by assessing general neuropathy. Moreover, based on studies conducted in rodent models, it remains unclear if some of the tested drugs act in an antinociceptive fashion or have neuroprotective properties. Thus, further investigations are needed to understand their mechanism of action, as well as a global standardization of the methods used to assess efficacy of new therapeutic strategies in the treatment of CIPN.

Stress-Reducing Function of Matcha Green Tea in Animal Experiments and Clinical Trials.

Theanine, a major amino acid in green tea, exhibits a stress-reducing effect in mice and humans. Matcha, which is essentially theanine-rich powdered green tea, is abundant in caffeine. Caffeine has a strong antagonistic effect against theanine. The stress-reducing effect of matcha was examined with an animal experiment and a clinical trial. The stress-reducing effect of matcha marketed in Japan and abroad was assessed based on its composition. The stress-reducing effect of matcha in mice was evaluated as suppressed adrenal hypertrophy using territorially-based loaded stress. High contents of theanine and arginine in matcha exhibited a high stress-reducing effect. However, an effective stress-reducing outcome was only possible when the molar ratio of caffeine and epigallocatechin gallate (EGCG) to theanine and arginine was less than two. Participants (n = 39) consumed test-matcha, which was expected to have a stress-reducing effect, or placebo-matcha, where no effect was expected. Anxiety, a reaction to stress, was significantly lower in the test-matcha group than in the placebo group. To predict mental function of each matcha, both the quantity of theanine and the ratios of caffeine, EGCG, and arginine against theanine need to be verified.

N-acetyl cysteine, a glutamate-modulating agent, in the treatment of pathological gambling: a pilot study.

BACKGROUND: Although pathological gambling (PG) is relatively common, pharmacotherapy research for PG is limited. N-acetyl cysteine (NAC), an amino acid, seems to restore extracellular glutamate concentration in the nucleus accumbens and therefore offers promise in reducing addictive behavior. METHODS: Twenty-seven subjects (12 women) with DSM-IV PG were treated in an 8-week open-label trial of NAC with responders (defined as a > or = 30% reduction in Yale Brown Obsessive Compulsive Scale Modified for Pathological Gambling [PG-YBOCS] total score at end point) randomized to 6 weeks of double-blind NAC or placebo. RESULTS: The PG-YBOCS scores decreased from a mean of 20.3 +/- 4.1 at baseline to 11.8 +/- 9.8 at the end of the open-label phase (p < .001). Sixteen of 27 subjects (59.3%) met responder criteria. The mean effective dose of NAC was 1476.9 +/- 311.3 mg/day. Of 16 responders, 13 entered the double-blind phase. Of those assigned to NAC, 83.3% still met responder criteria at the end of the double-blind phase, compared with only 28.6% of those assigned to placebo. CONCLUSIONS: The efficacy of NAC lends support to the hypothesis that pharmacological manipulation of the glutamate system might target core symptoms of reward-seeking addictive behaviors such as gambling. Larger, longer, placebo-controlled double-blind studies are warranted.

Decreased levels of plasma glutamate in patients with first-episode schizophrenia and bipolar disorder.

A variety of studies have suggested that glutamatergic neurotransmission is altered in schizophrenia and bipolar disorder. Here, we tested if plasma glutamate levels are altered in 56 patients diagnosed with schizophrenia, bipolar disorder or non-specified psychosis at the first psychotic episode and at various stages during one-year follow-up. A decrease in the levels of plasma glutamate was observed in all groups of patients at the first psychotic episode. Furthermore, plasma glutamate levels were restored after treatment in all instances. Decreased plasma glutamate levels at first psychotic episodes may reflect impaired glutamate signaling during the initial stages of schizophrenia and bipolar disorder.

The tipsy terminal: presynaptic effects of ethanol.

Considerable evidence suggests that the synapse is the most sensitive CNS element for ethanol effects. Although most alcohol research has focussed on the postsynaptic sites of ethanol action, especially regarding interactions with the glutamatergic and GABAergic receptors, few such studies have directly addressed the possible presynaptic loci of ethanol action, and even fewer describe effects on synaptic terminals. Nonetheless, there is burgeoning evidence that presynaptic terminals play a major role in ethanol effects. The methods used to verify such ethanol actions range from electrophysiological analysis of paired-pulse facilitation (PPF) and spontaneous and miniature synaptic potentials to direct recording of ion channel activity and transmitter/messenger release from acutely isolated synaptic terminals, and microscopic observation of vesicular release, with a focus predominantly on GABAergic, glutamatergic, and peptidergic synapses. The combined data suggest that acute ethanol administration can both increase and decrease the release of these transmitters from synaptic terminals, and more recent results suggest that prolonged or chronic ethanol treatment (CET) can also alter the function of presynaptic terminals. These new findings suggest that future analyses of synaptic effects of ethanol should attempt to ascertain the role of presynaptic terminals and their involvement in alcohol's behavioral actions. Other future directions should include an assessment of ethanol's effects on presynaptic signal transduction linkages and on the molecular machinery of transmitter release and exocytosis in general. Such studies could lead to the formulation of new treatment strategies for alcohol intoxication, alcohol abuse, and alcoholism.

Unsuccessful rechallenge with pemetrexed after a previous radiation recall dermatitis.

Radiation recall dermatitis is characterized by an inflammatory reaction within a previously irradiated volume after administration of a drug. Antineoplastic drugs have mainly been involved in radiation recall reactions. This phenomenon is well known but poorly understood. Many hypotheses as stem-cell depletion in the radiotherapy field, heritable mutations within surviving stem cells, local vascular changes as well as a drug hypersensitivity reaction have been proposed to explain these reactions. In this report, we describe a non-small cell lung cancer patient treated with a carboplatin plus gemcitabine combination chemotherapy as first line followed by pemetrexed as second line therapy. Twenty-five years ago, she completed radiation therapy for breast cancer. Three days after the first cycle of pemetrexed, she presented with a radiation recall dermatitis. As EGFR-staining was negative, we rechallenged the patient with pemetrexed. Unfortunately, although less intense, we faced a recurrence of the skin reaction and pemetrexed was no longer continued.

Glutamine affects glutamate metabolism in isolated rat kidney cortex mitochondria.

The active state respiration of isolated rat kidney cortex mitochondria with 10 mM glutamate as single substrate is substantially increased by the addition of 10 mM glutamine. This increase in respiration was accompanied by a higher transamination rate and was found to be insensitive to the selective inhibition of either the transamination or the desamination pathway of glutamate oxidation. These data can be explained by an approximately 2-fold elevated intramitochondrial glutamate concentration observed in the additional presence of glutamine.

Effects of ketamine on anterior cingulate glutamate metabolism in healthy humans: a 4-T proton MRS study.

OBJECTIVE: The authors' goal was to test in humans the hypothesis that N-methyl-d-aspartate receptor (NMDAR) antagonism results in increased cortical glutamate activity, as proposed by the NMDAR hypofunction model of schizophrenia. METHOD: 4-T 1H proton magnetic resonance spectroscopy (1H-MRS) was used to acquire in vivo spectra from the bilateral anterior cingulate of 10 healthy subjects while they received a subanesthetic dose of either placebo or ketamine, an NMDAR antagonist. Assessments given before and after ketamine or placebo administration included the Brief Rating Psychiatric Rating Scale, the Scale for the Assessment of Negative Symptoms, the Clinician-Administered Dissociative States Scale, and the Stroop task. RESULTS: As predicted, there was a significant increase in anterior cingulate glutamine, a putative marker of glutamate neurotransmitter release, with ketamine administration. This increase was not related to schizophrenia-like positive or negative symptoms but was marginally related to Stroop performance. CONCLUSIONS: In humans as in animals, an acute hypofunctional NMDAR state is associated with increased glutamatergic activity in the anterior cingulate.

The glutamatergic basis of human alcoholism.

OBJECTIVE: Although alcoholism is one of the most common psychiatric diagnoses, understanding of its pathophysiology remains poor. Accumulating evidence suggests that neurophysiological and pathological effects of ethanol are mediated to a considerable extent through the glutamatergic system. This article reviews the evidence of ethanol's effects on glutamatergic transmission and proposes a glutamatergic basis for alcoholism. METHOD: The information was derived from original research. The authors located more than 100 articles from psychiatry and neuroscience journals that related ethanol to glutamatergic transmission. They critically reviewed the neurobiology of the glutamatergic system in alcoholism and synthesized a unifying glutamatergic theory. RESULTS: Acute effects of ethanol disrupt glutamatergic neurotransmission by inhibiting the response of the N-methyl-D-aspartate (NMDA) receptor. Prolonged inhibition of the NMDA receptor by ethanol results in development of supersensitivity; acute removal of ethanol causes marked augmentation of activity of postsynaptic neurons, such as those in the noradrenergic system, and, in the extreme, glutamate-induced excitotoxicity. Neurobiological effects of alcoholism, such as intoxication, withdrawal seizures, delirium tremens, Wernicke-Korsakoff syndrome, and fetal alcohol syndrome, can be understood as a spectrum of consequences of ethanol's effect on the glutamatergic system. CONCLUSIONS: A host of findings support the hypothesis that the unifying mechanism of action of ethanol in interference with glutamatergic neurotransmission, especially through the NMDA receptor. Alcoholism may be considered another member of the expanding family of glutamate-related neuropsychiatric disorders. These insights should increase understanding of the biologic vulnerabilities leading to ethanol abuse and dependence and aid development of more effective pharmacologic interventions.

The emerging role of glutamate in the pathophysiology and treatment of schizophrenia.

OBJECTIVE: Research has implicated dysfunction of glutamatergic neurotransmission in the pathophysiology of schizophrenia. This review evaluates evidence from preclinical and clinical studies that brain glutamatergic neurotransmission is altered in schizophrenia, may affect symptom expression, and is modulated by antipsychotic drugs. METHOD: A comprehensive review of scientific articles published over the last decade that address the role of glutamate in the pathophysiology of schizophrenia was carried out. RESULTS: Glutamatergic neurons are the major excitatory pathways linking the cortex, limbic system, and thalamus, regions that have been implicated in schizophrenia. Postmortem studies have revealed alterations in pre- and postsynaptic markers for glutamatergic neurons in several brain regions in schizophrenia. The N-methyl-D-aspartic acid (NMDA) subtype of glutamate receptor may be particularly important as blockade of this receptor by the dissociative anesthetics reproduces in normal subjects the symptomatic manifestations of schizophrenia, including negative symptoms and cognitive impairments, and increases dopamine release in the mesolimbic system. Agents that indirectly enhance NMDA receptor function via the glycine modulatory site reduce negative symptoms and variably improve cognitive functioning in schizophrenic subjects receiving typical antipsychotics. CONCLUSIONS: Dysfunction of glutamatergic neurotransmission may play an important role in the pathophysiology of schizophrenia, especially of the negative symptoms and cognitive impairments associated with the disorder, and is a promising target for drug development.

Inhibition of neuronal Ca(2+) influx by gabapentin and subsequent reduction of neurotransmitter release from rat neocortical slices.

Cytosolic calcium ion concentrations ([Ca(2+)](i)) were measured in rat neocortical synaptosomes using fura-2, and depolarization of synaptosomal membranes was induced by K(+) (30 mM). The release of the endogenous excitatory amino acids glutamate and aspartate was evoked by K(+) (50 mM) and determined by HPLC. The release of [(3)H]-noradrenaline from rat neocortical synaptosomes or slices was evoked by K(+) (15 and 25 mM) and measured by liquid scintillation counting. Gabapentin produced a concentration-dependent inhibition of the K(+)-induced [Ca(2+)](i) increase in synaptosomes (IC(50)=14 microM; maximal inhibition by 36%). The inhibitory effect of gabapentin was abolished in the presence of the P/Q-type Ca(2+) channel blocker omega-agatoxin IVA, but not by the N-type Ca(2+) channel antagonist omega-conotoxin GVIA. Gabapentin (100 microM) decreased the K(+)-evoked release of endogenous aspartate and glutamate in neocortical slices by 16 and 18%, respectively. Gabapentin reduced the K(+)-evoked [(3)H]-noradrenaline release in neocortical slices (IC(50)=48 microM; maximal inhibition of 46%) but not from synaptosomes. In the presence of the AMPA receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2, 3-dioxo-6-nitro-1,2,3,4-tetrahydro[f]quinoxaline-7-sulphonamide (NBQX), gabapentin did not reduce [(3)H]-noradrenaline release. Gabapentin did, however, cause inhibition in the presence of the NMDA receptor antagonist DL-(E)-2-amino-4-methyl-5-phosphono-3-pentanoic acid (CGP 37849). Gabapentin is concluded to reduce the depolarization-induced [Ca(2+)](i) increase in excitatory amino acid nerve terminals by inhibiting P/Q-type Ca(2+) channels; this decreased Ca(2+) influx subsequently attenuates K(+)-evoked excitatory amino acid release. The latter effect leads to a reduced activation of AMPA receptors which contribute to K(+)-evoked noradrenaline release from noradrenergic varicosities, resulting in an indirect inhibition of noradrenaline release.

Evaluating glutamatergic transmission in schizophrenia.

Our findings with schizophrenia and the glutamate system have relied on the characterization of the clinical response of patients to ketamine and their functional brain imaging response (rCBF) to the drug. Prior to the human studies reported here, we had evaluated the region activation characteristics and pharmacology of PCP and its congener MK 801 in animals. What I will report in this paper has been individually reported elsewhere but brought together here in a new synthesis.

Metyrapone alleviates ischemic neuronal damage in the gerbil hippocampus.

Transient forebrain ischemia was induced in gerbils, and the effect of a pre-ischemic treatment with metyrapone (100 mg/kg) on delayed neuronal death in hippocampal CA1 neurons was evaluated. The effect of metyrapone on the ischemic release of amino acids in the CA1 region was also examined by microdialysis. Hippocampal slices were used for the evaluation of the hypoxia-induced intracellular Ca2+ increase by microfluorometry. The metyrapone treatment morphologically improved the damage provoked by 3 min of ischemia, although it did not alleviate the damage by 5 min. Ischemia for 3 min produced a 306% increase in the glutamate concentration in perfusates, and metyrapone suppressed the peak value to 42% of that in the control group. The extent of the increase in fluorescence intensity by intracellular Ca2+ was lower by 16% in slices from metyrapone-treated animals than in controls 600 s after induction of hypoxia. The removal of Ca2+ from the perfusion medium suppressed the hypoxic Ca2+ increase, and the increase was further reduced in slices pretreated with metyrapone. The increase in the level of endogenous glucocorticoids, which occurs in cerebral ischemia, may aggravate ischemic neuronal damage.

Effects of diazepam on extracellular brain neurotransmitters in pilocarpine-induced seizures in rats.

The present study was undertaken to gain insights into the mechanism of action of diazepam in focally-evoked pilocarpine-induced seizures by concomitantly assessing the changes produced in the extracellular levels of glutamate, GABA (gamma-aminobutyric acid) and dopamine. In vivo microdialysis, coupled to continuous monitoring of electrocorticographic (ECoG) recordings, was performed in freely moving rats. Intrahippocampal perfusion with 10 mM pilocarpine (40 min, 2 microl/min) produced limbic seizures. A single dose of intraperitoneal diazepam (5 mg/kg) was administered 2 h after pilocarpine perfusion was started. Dialysates were sampled both from hippocampus and cerebellum and analysed by microbore liquid chromatography. Diazepam produced instant inhibition of behavioural and ECoG seizure activity. Pilocarpine-induced increases in the extracellular levels of glutamate and dopamine in hippocampus were promptly reduced by diazepam. No concurrent alterations in pilocarpine-induced increases in the extracellular levels of GABA in either hippocampus or cerebellum were seen. Pilocarpine enhanced cerebellar glutamate levels only transiently and levels returned to baseline before diazepam administration. No further changes in cerebellar glutamate levels were observed with diazepam. Our findings suggest that the anti-convulsant action of diazepam against pilocarpine-induced seizures is associated with a prompt attenuation of extracellular hippocampal glutamate overflow without concurrent alteration of pilocarpine-induced increases in endogenous GABA levels. Diazepam also significantly decreased pilocarpine-induced increases in extracellular dopamine levels within the hippocampus. No immediate alterations of the basal levels of the neurotransmitters monitored were observed with diazepam.

Opposing effects of cyclooxygenase-2 selective inhibitors on oxygen-glucose deprivation-induced neurotoxicity.

Cyclooxygenase-2 inhibitors protect against excitotoxicity in vitro yet provide conflicting results in in vivo models of ischemia. To bridge the gap in understanding the discrepancies among these studies, the effects of different cyclooxygenase-2 inhibitors were studied in an in vitro model of ischemia. Oxygen-glucose deprivation (OGD) induced cyclooxygenase-2 protein expression in neuronal cortical cultures. Cyclooxygenase-2 inhibitors exhibited opposing effects on neuronal death induced by OGD. The acidic sulfonamides, N-(2-cyclohexyloxy-4-nitrophenyl) methanesulfonamide (NS-398) and N-(4-nitro-2-phenoxyphenyl)-methanesulfonamide (nimesulide), aggravated neuronal death by enhancing OGD-induced increases in extracellular glutamate and intracellular Ca2+ levels. In contrast, 1-[(4-methylsulfonyl)phenyl]-3-tri-fluoromethyl-5-(4-fluorophenyl)pyrazole (SC-58125) dose-dependently protected cultures against OGD by suppressing increases in extracellular glutamate and intracellular Ca2+ levels. The NS-398-induced aggravation of neuronal death was lost if the inhibitor was added only following the OGD. The timing of inhibitor application also determined its effects on N-methyl-D-aspartate (NMDA)-induced excitoxicity. NS-398 was protective when added both during and post-NMDA exposure, but not if NS-398 was also applied for 60 min prior to the insult. In contrast, SC-58125 afforded protection against NMDA in the presence or absence of a pre-incubation period. This study demonstrates that certain cyclooxygenase-2 inhibitors have opposing effects on neuronal survival depending on the timing of application and the nature of the insult. These results may account for the discrepancies among previous studies which used different inhibitors and different models of neurotoxicity.