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A Frandsen

Publications and source records attributed to A Frandsen.

At least 19 recordsLinked to original sources
PubMed1997

Association of c-fos mRNA expression and excitotoxicity in primary cultures of mouse neocortical and cerebellar neurons.

The effect of excitatory amino acids (EAAs) on c-fos mRNA expression was studied in primary cultures of mouse cerebellar granule cells and in neocortical neurons after 2 and 7 days in vitro (div). In cultured granule cells at 2 and 7 div, and in cortical neurons at 2 div, exposure to low levels (< or = 10 microM) of a variety of EAAs (viz. glutamate [Glu], S-sulpho-L-cysteine [SC], N-methyl-D-aspartate [NMDA], alpha-amino-3-hydroxy-5-methyl-4-isoxazole [AMPA], and kainate [KA]) resulted in a transient increase in the level of c-fos mRNA which peaked at 30 min but returned to a basal level by 120 min. However, exposure of granule cells (7 div) to high levels (250 microM) of Glu, NMDA, KA, SC and of cortical neurons (7 div) to high levels (250 microM) of Glu, NMDA, KA, SC, or AMPA and to low levels (< or = 10 microM) of Glu and AMPA resulted in a delay in c-fos mRNA induction but a subsequent, progressive increase that was sustained for at least 240 min. Furthermore, this effect was accompanied by a dose-related increase in the release of the cytosolic enzyme, lactate dehydrogenase, used as an indicator of excitotoxicity. A ratio (Q240/30) for the steady-state levels of c-fos mRNA after 30 min and 240 min of exposure to EAAs was determined which showed that Q240/30 >2 correlated reproducibly with excitotoxic cell death, whereas a ratio of < or = 1 correlated with a nonexcitotoxic event. In both cell types at 7 div, coadministration of the selective NMDA receptor antagonist, DL(+/-)-2-amino-5-phosphonopentanoic acid (APV) with cytotoxic levels of Glu 1) protected against EAA-induced neurotoxicity and 2) exhibited a transient c-fos mRNA expression (Q240/30 values approximately 1). In contrast, the AMPA/KA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), provided no protection against excitotoxicity and had no significant effect on the Glu-induced delay in c-fos mRNA expression. These results suggest that the Q240/30 c-fos mRNA ratio may 1) be used as a predictive index for excitotoxic neuronal death, 2) provide information on the identity of the receptor subtype mediating excitotoxicity in different brain cell types, and 3) aid in establishing the role of excitotoxicity during the development of neurons in vitro.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1997

Properties of ryanodine receptors in cultured cerebellar granule neurons: effects of hexachlorocyclohexane isomers and calcium.

The binding of [3H]ryanodine was determined in microsomal membrane preparations obtained from cultured cerebellar granule cells. A KD of 1 nM and a Bmax of 64 fmol/mg protein were calculated from saturation experiments. This binding was calcium dependent and maximum values were obtained at 100-300 microM Ca+2. Caffeine increased [3H]ryanodine binding only at Ca+2 concentrations lower than optimum. The binding of [3H]ryanodine was inhibited by ruthenium red, procaine and the delta-isomer of hexachlorocyclohexane (delta-HCH). Dantrolene, a ryanodine receptor antagonist in skeletal sarcoplasmic reticulum, and the pesticide gamma-HCH (lindane) had no effect on [3H]ryanodine binding. The obtained binding parameters, the Ca+2 dependence and the effects of the agents tested agree with previous reports using brain microsomal membranes, further indicating a neuronal localization of [3H]ryanodine binding sites. When the interaction between dantrolene and gamma- and delta-HCH was tested, no changes were detected on the effects of HCH isomers on [3H]ryanodine binding. Dantrolene, which inhibits Ca+2 release from sarcoplasmic reticulum and from unidentified internal Ca+2 stores in neurons, also inhibits the intracellular Ca+2 mobilization induced by gamma-HCH but only marginally that induced by delta-HCH in the same preparation of cerebellar granule cells (Rosa et al.; Toxicol Appl Pharmacol, in press). Thus, the results obtained in this work verify the presence of different intracellular sites of action for the two HCH isomers: the ryanodine Ca+2 channel for delta-HCH and an unidentified dantrolene-sensitive Ca+2 channel for the gamma-HCH isomer.

Anesthetics, Local↗
PubMed1997

The mechanism for hexachlorocyclohexane-induced cytotoxicity and changes in intracellular Ca2+ homeostasis in cultured cerebellar granule neurons is different for the gamma- and delta-isomers.

The cytotoxic action of the delta- and gamma-isomers of hexachlorocyclohexane (HCH) as well as their ability to induce changes in intracellular Ca2+ homeostasis was studied in cultured rat cerebellar granule neurons. Changes in the free intracellular Ca2+ concentration ([Ca2+]i) related to Ca2+ influx and release from intracellular stores were investigated using, in addition to the physiological incubation medium, media without added Ca2+ (nominally Ca2+ free) or containing verapamil or dantrolene, drugs which block influx through voltage-gated Ca2+ channels and release from intracellular stores, respectively. Cytotoxicity was monitored using leakage of lactate dehydrogenase (LDH) and staining of damaged cells with either trypan blue or propidium iodide. In the latter case, when fluorescence microscopy was employed, undamaged cells were visualized using the vital stain calcein acetoxymethyl ester (calcein-AM). The delta-isomer of HCH was found to be more potent and active as a cytotoxic agent than the gamma-isomer (lindane) and it was demonstrated that the moderate cytotoxic action of lindane could be ameliorated by dantrolene which on the other hand had no effect on cytotoxicity induced by delta-HCH. It was noticed that pronounced (50% increase in fluorescence) staining with propidium iodide was associated with only a marginal (20%) LDH leakage and staining of only a few (<25%) cells with trypan blue. Both delta- and gamma-HCH induced an increase in [Ca2+]i which was most pronounced in case of delta-HCH. Analysis of the different mechanisms governing the increase in [Ca2+li using dantrolene, verapamil, and Ca2+-free medium revealed distinct differences between the two isomers with regard to the Ca2+ pools affected. Both isomers stimulated Ca2+ influx through voltage-gated Ca2+ channels but only the gamma-isomer affected a Ca2+-dependent, dantrolene-sensitive pool. On the other hand, delta-HCH affected mainly a Ca2+-independent dantrolene-insensitive pool. The finding that delta-HCH was more toxic than lindane may be correlated to the differences between the isomers with regard to the action on the different Ca2+ pools. Thus, delta-HCH affected primarily the dantrolene-insensitive Ca2+ pools which partly reflect influx. On the contrary, lindane had little effect on these Ca2+ pools but affected primarily dantrolene-sensitive intracellular Ca2+ stores. This may suggest that delta-HCH may exert its cytotoxic action by stimulating a large influx of Ca2+ possibly leading to release of Ca2+ from dantrolene-insensitive stores. In contrast, the toxic action of lindane may be primarily related to release of Ca2+ from the dantrolene-sensitive stores.

Animals↗
PubMed1997

Characterization of glutamate-induced formation of N-acylphosphatidylethanolamine and N-acylethanolamine in cultured neocortical neurons.

Glutamate-induced formation of N-acylethanolamine (NAE) and N-acylphosphatidylethanolamine (NAPE) was studied in primary cultures of mouse neocortical neurons prelabeled with [14C] ethanolamine. The formation of these two lipids was dependent on the maturity of the cell culture; i.e., no glutamate-induced formation was seen in 2-day-old cultures, whereas glutamate induced a pronounced formation in 6-day-old cultures. The calcium ionophore A23187 (2 microM) stimulated, within 2 h, formation of NAPE in 2-day-old cultures (fourfold) as well as in 6-day-old cultures (eightfold). Glutamate exerted its effect via NMDA receptors as seen by the inhibitory action of the NMDA-selective receptor antagonists D-(-)-2-amino-5-phosphonovalerate and N-(1-(2-thienyl)cyclohexyl)piperidine and the lack of effect of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate-receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In 6-day-old cultures, exposure to NMDA (100 microM for 24 h) induced a linear increase in the formation of NAPE and NAE as well as a 40-50% neuronal death, as measured by a decrease in cellular formazan formation [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay]. The increase in NAPE and NAE could be detected earlier than the neuronal death. Neither cyclic AMP, cyclic GMP, nitric oxide, protein kinase C, nor peroxidation appears to be involved in the formation of NAPE and NAE, as assessed by the use of different pharmacological agents. Exposure to 5 mM NaN3 for 8 h resulted in a >80% decrease in the cellular MTT staining and a pronounced linear increase in the formation of NAE and NAPE (reaching 25-30% of total labeling). [14C]Anandamide was also formed in [14C]arachidonic acid-labeled neurons exposed to NaN3. No NAPE formation was detected in A23187-stimulated mouse astrocytes, rat Leydig cells and cardiomyocytes, and several other cells. These results suggest that the glutamate-induced formation of NAPE and NAE was mediated by the NMDA receptor and the formation of these lipids may be associated with neuronal death.

2-Amino-5-phosphonovalerate↗
PubMed1997

Role of Ca+2 and other second messengers in excitatory amino acid receptor mediated neurodegeneration: clinical perspectives.

Neurodegeneration associated with neurological disorders such as epilepsy, Huntington's Chorea, Alzheimer's disease, and olivoponto cerebellar atrophy or with energy failure such as ischemia, hypoxia, and hypoglycemia proceeds subsequent to overexposure of neurons to excitatory amino acids of which glutamate and aspartate may be quantitatively the most important. The toxic action of glutamate and aspartate is mediated through activation of glutamate receptors of the N-methyl-D-aspartate (NMDA) and non-NMDA subtypes. Antagonists for these receptors can act as neuroprotectants both in in vitro model systems (e.g., cultured neurons) and in vivo. Activation of receptors leads to an increase in the intracellular Ca++ concentration and also to an increase in other second messengers such as cGMP. Thus, Ca++ channel antagonists may have neuroprotective action under certain conditions.

Animals↗
PubMed1996

Characterization of a chemical anoxia model in cerebellar granule neurons using sodium azide: protection by nifedipine and MK-801.

Induction of chemical anoxia, using sodium azide in cerebellar granule cells maintained in primary culture, was evaluated as an in vitro assay for screening of potential neuroprotective compounds. The purpose of this study was to evaluate sodium azide as an alternative to cyanide salts, compounds which, despite their unfavorable characteristics, are often used in assays for chemical anoxia. The viability of neuronal cultures after treatment with azide, with or without preincubation with calcium channel blockers, tetrodotoxin (TTX), or glutamate receptor antagonists, was monitored by subsequent incubation with the tetrazolium dye MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), followed by isopropanol extraction and spectrophotometric quantification of cellularly reduced MTT. The azide-induced degeneration of neurons was shown to be dependent on the concentration as well as on the duration of incubation with submaximal concentrations of azide. Incubation of the neurons with nifedipine, a blocker of L-type voltage-sensitive calcium channels (L-VSCC), or with the noncompetitive N-methyl-D-aspartate (NMDA) subtype glutamate receptor antagonist MK-801, prior to addition of submaximal concentrations of azide, significantly attenuated azide-induced neuronal death. Blockers of N-type and Q-type VSCC (omega-conotoxin MVIIA and MVIIC, respectively) and the P-type VSCC blocker omega-agatoxin IVA had no effect in this assay. The sodium channel blocker TTX was without effect when added to neurons under depolarizing conditions, but potently and effectively protected cells when experiments were performed in a nondepolarizing buffer. The results show that chemical anoxia induced by incubation of cultured neurons with azide leads to detrimental effects, which may be quantitatively monitored by the capability of the cells to reduce MTT. This procedure is a suitable method for screening of compounds for possible protective effects against neuronal death induced by energy depletion. In addition, the results suggest involvement of L-type VSCC as well as of glutamate receptors in the pathways leading to neuronal degradation induced by energy depletion in cerebellar granule neurons. This would further support the notion that these pathways might be important in neurodegeneration induced by cerebral ischemia or anoxia.

Animals↗
PubMed1996

Temporal and spatial differences in intracellular Ca++ changes elicited by K+ and glutamate in single cultured neocortical neurons.

Changes as a function of time in the intracellular Ca++ concentration ([Ca++]i) in cultured cerebral cortical neurons were monitored after exposure of the cells to either 55 mM KCl or 100 microM glutamate using the fluorescent Ca++ chelator fura-2. The changes in [Ca++]i were followed in both cell bodies and neurites. Depolarization with K+ led to an immediate increase in [Ca++]i in neurites followed by a slower rise in the cell bodies. In contrast, glutamate elicited a slow increase in [Ca++]i in both neurites and cell bodies, and this increase showed a plateau rather than a peak as that seen after exposure to K+. The Ca++ channel blockers verapamil and nifedipine affecting N- and L-type channels, respectively had differential effects on K+ stimulated increases in [Ca++]i. Nifedipine only affected the increase marginally whereas verapamil inhibited the response by 50-60% both in cell bodies and neurites. The glutamate-induced increase in [Ca++]i was inhibited by nifedipine by 60% in neurites whereas no effect was observed in cell bodies. The results show that depolarization elicited by K+ and glutamate has different effects in different parts of the neurons and that the pharmacological characteristics of voltage gated Ca++ channels are dramatically different in cell bodies and neurites. Moreover, the distribution of L-type channels activated by glutamate differs in cell bodies and neurites. Such differences in the spatial distribution of Ca++ channels are likely to be of major importance for the functional consequences of depolarization coupled increases in [Ca++]i such as transmitter release and neurotoxicity.

Animals↗
PubMed1995

Glutamate stimulates the formation of N-acylphosphatidylethanolamine and N-acylethanolamine in cortical neurons in culture.

The formation of anandamide (N-arachidonoylethanolamine), N-acylethanolamine, and N-acylphosphatidylethanolamine was studied in primary cultures of rat cortical neurons. The cells were incubated for 22 h with [14C]ethanolamine, [U-14C]arachidonic acid, [3H]arachidonic acid, [32P]phosphate, [14C]stearic acid, or [3H]myristic acid. The lipids from the cells and media were separated by thin layer chromatography. [14C]Ethanolamine labelling revealed two compounds (I and II), which on different thin layer chromatography systems migrated as N-acylethanolamine (0.06-0.55% of total radioactivity) and N-acylphosphatidylethanolamine (0.66-6.49% of total radioactivity), respectively. Compound II was also labelled with [32P]phosphate, and radioactive fatty acids. Treatment of compound II with phospholipase D (Streptomyces chromofuscus) resulted in two compounds, one comigrating as phosphatidic acid and the other as N-acylethanolamine. Compound I could be labelled with [14C]stearic acid and [3H]myristic acid, but not with [3H]- or [14C]arachidonic acid. Exogenous [3H]anandamide was metabolised with a t1/2 of 2.6 h. The labelling of the two compounds identified as N-acylethanolamine and N-acylphosphatidylethanolamine were more pronounced the older the culture. The neurotoxic amino acid, glutamate, stimulated within 2 h dose-dependently (ED50 = 40 microM) the formation of both compounds. It is suggested that N-acylethanolamine and N-acylphosphatidylethanolamine are formed in relation to the cytotoxicity induced by glutamate, and that these compounds may be markers of neurotoxicity. We could not detect any formation of anandamide using radioactive arachidonic acid.

Animals↗
PubMed1995

Kainic acid-induced seizures and brain damage in the rat: role of calcium homeostasis.

Seizure activity induced by kainic acid (KA) and subsequent neuronal death are thought to be associated with an increase in cytoplasmic free calcium ([Ca2+]i) and can be prevented by N-methyl-D-aspartate (NMDA) antagonists. In addition to influx through receptor operated Ca2+ channels the increase in [Ca2+]i may be the result of an increased influx through voltage-operated calcium channels and/or release from intracellular deposits. It was therefore investigated whether compounds other than NMDA antagonists with known actions on the intracellular Ca2+ homeostasis had any protective effect against KA-induced neuronal death. Voltage-operated calcium channels in the cell membrane were blocked with the L-type ion channel antagonist, Nimodipine (1.0 mg/kg), and release of Ca2+ from internal stores was prevented with Dantrolene (10 mg/kg). Animals from two control groups injected with kainate (8 mg/kg) exhibited a survival rate of 67 and 53%, respectively. Countings of neurons in dorsal hippocampus showed subtotal or total loss in the CA1 and CA3 subregions. There were no significant differences concerning seizure and survival rates in the groups injected with kainate and treated with Dantrolene or Nimodipine and the control groups. The group treated with Dantrolene showed no neuropathological changes in the hippocampal CA3 region and only slight changes in the Ca1 region, while the neuron loss in the Nimodipine group did not differ from that of its control group. The results emphasize the importance of Dantrolene-sensitive Ca2+ release from intracellular stores for the development of seizure-induced neuronal death.

Animals↗
PubMed1995

Blockade by polyamine NMDA antagonists related to ifenprodil of NMDA-induced synthesis of cyclic GMP, increases in calcium and cytotoxicity in cultured neurones.

1. Antagonists acting at the polyamine site of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor, including a number of heterocyclic aminoalcohols related to ifenprodil, were investigated to establish their functional interaction at the NMDA receptor and their neuroprotective profile. 2. In murine cultured neocortical neurones, NMDA (100 microM)-stimulated production of guanosine 3':5'-cyclic monophosphate (cyclic GMP) was blocked by N-1([thienyl]-cyclohexyl)-piperidine (1 microM) and by the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (100 microM). Ifenprodil and structurally related heterocyclic aminoalcohols inhibited in a concentration-dependent manner the NMDA-stimulated, NO-dependent production of cyclic GMP; rank potency order was: ifenprodil > 2309 BT > tibalosine > threo-tibalosine > 840S. 3. All of the polyamine NMDA antagonists blocked NMDA (300 microM)-stimulated increases in intracellular calcium concentrations as measured by changes in the fluorescence of pre-loaded fluo-3-acetoxy methyl ester. Rank potency order was: ifenprodil > 2309 BT > 840S > tibalosine > threo-tibalosine. 4. In a series of experiments to evaluate the effectiveness of the polyamine NMDA antagonists as blockers of NMDA-induced cytotoxicity, all of the drugs were found to inhibit the leakage of lactate dehydrogenase after the exposure of the murine neocortical cultures to NMDA (100 microM, 5 h). Rank potency order was: 2309 BT > ifenprodil > tibalosine > threo-tibalosine > 840S. 5. These results provide direct evidence that polyamine NMDA antagonists produce a functional blockade of the NMDA receptor complex. The heterocyclic amino alcohols described herein, likeifenprodil, block NMDA-mediated elevation of intracellular NO and calcium, two key events in the excitotoxic cascade, and are cytoprotective.

Animals↗
PubMed1994

Lindane cytotoxicity in cultured neocortical neurons is ameliorated by GABA and flunitrazepam.

The effect of lindane (gamma-hexachlorocyclohexane) on [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding and GABA-stimulated 36Cl- influx was investigated in cultured cerebral cortical neurons. In addition, the cytotoxic action of lindane as well as a protection by GABA and flunitrazepam were studied together with the ability of lindane to increase the intracellular concentration of free Ca2+. Lindane was found to be toxic to the neurons, an effect that could be completely prevented by the simultaneous presence of GABA (0.1 microM) and flunitrazepam (100 microM) and reduced by GABA alone. An interaction with the GABA receptor-gated chloride channel was demonstrated by an inhibitory action of lindane on [35S]TBPS binding (IC50 188 +/- 51 nM) and on GABA-stimulated 36Cl- influx in the neurons. Lindane only marginally increased the intracellular Ca2+ concentration in the neurons. It is concluded that the cytotoxic action of lindane is mediated through interaction with GABA receptors in a manner essentially independent of changes in intracellular Ca2+ homeostasis.

Animals↗
PubMed1994

Complex correlation between excitatory amino acid-induced increase in the intracellular Ca2+ concentration and subsequent loss of neuronal function in individual neocortical neurons in culture.

Primary cultures of cerebral cortical neurons and single-cell imaging of intracellular free Ca2+ concentration ([Ca2+]i) with the ratiometric dye fura-2 were used to assess excitatory amino acid (EAA)-induced neurotoxicity; the loss of neuronal function as defined by the ability of the cells to respond to K(+)-induced depolarization by a transient increase in Ca2+ influx was measured. The responsiveness of individual neurons was measured quantitatively as the [Ca2+]i values of the second KCl (2.KCl) stimulation divided by those of the first KCl (1.KCl) stimulation, giving the value of the ratio (2.KCl/1.KCl). Exposure to EAAs led to an increase in [Ca2+]i, but no simple correlation between the increase in [Ca2+]i and neuronal responsiveness could be demonstrated. Rather, below a threshold level of [Ca2+]i (ca. 1 microM), the neuronal responsiveness was largely independent of the glutamate receptor-agonist-induced increase in [Ca2+]i. However, when [Ca2+]i increased above this threshold level, the neurons almost invariably lost the ability to respond to a K(+)-induced depolarization, particularly after exposure to glutamate. Therefore, the cortical neurons were found to be exceptionally vulnerable to the glutamate-induced loss of function when compared with the effect induced by the glutamate receptor subtype-specific agonists, N-methyl-D-aspartate, quisqualate, and 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionate. The findings suggest that the loss of neuronal membrane polarization precedes plasma membrane disruption and is a sensitive marker of EAA-induced neurodegeneration observed at the single-cell level.

Animals↗
PubMed1994

Mixed actions of TMB-8 as a Ca2+ antagonist in cultured mouse cortical neurones.

The action of TMB-8 [8-N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate] on glutamate (Glu)- and 55 mM KCl (K+)-induced increases in intracellular free calcium levels ([Ca2+]i) was studied in cultured mouse cerebral cortical neurones. Glu-induced responses were mediated by two mechanisms, one independent of and the other dependent on extracellular Ca2+, both being inhibited by TMB-8 in a dose-dependent manner. TMB-8 had no effect on [3H]dizocilpine binding kinetics in cortical membrane preparations. The transient and sustained phases of K(+)-induced increases in [Ca2+]i were also inhibited by TMB-8 in a dose-dependent manner. The Ca2+ channel antagonist, verapamil, blocked K(+)-induced responses but had no effect on Glu-induced responses. Although TMB-8 displays multiple effects, its action at voltage-gated Ca2+ channels does not appear to contribute significantly to its inhibition of the Glu-induced increase in [Ca2+]i.

Animals↗
PubMed1994

Effect of magnesium on NMDA mediated toxicity and increases in [Ca2+]i and cGMP in cultured neocortical neurons: evidence for distinct regulation of different responses.

The effect of varying external concentrations of Mg2+ has been studied on NMDA induced toxicity, increases in the intracellular calcium concentration, [Ca2+]i, and cGMP production in cultured neocortical neurons. The neurotoxic potency of NMDA during a 5 h exposure period in 7-day-old cultures was examined in three different exposure media: phosphate buffered saline, PBS (137 mM NaCl, 2.7 mM KCl, 7.3 mM Na2HPO4, 1.5 mM KH2PO4, 0.9 mM CaCl2, 0.6 mM MgCl2; pH 7.4); PBS without addition of Mg2+; and Neuronal Dulbecco's Minimal Essential Medium (NDMEM = DMEM with a final concentration of KCl of 25.5 mM KCl; cf. Experimental Procedures). In the presence of Mg2+, no toxicity of NMDA was observed in PBS (ED50 > 1000 microM) whereas omission of Mg2+ in PBS resulted in an ED50 value for NMDA of 9 +/- 3 microM. Using NDMEM as the exposure medium, an intermediate neurotoxic potency of NMDA (ED50 = 40 +/- 5 microM) was observed. This intermediate value is probably due to partial attenuation of the Mg2+ block of the NMDA associated cation channel by the depolarizing conditions in NDMEM (with 25.5 mM KCl). Diminishing the external Mg2+ concentration also potentiated the increase in [Ca2+]i after stimulation with NMDA. This potentiation was maximally 3-fold (obtained at 300 microM NMDA), and the IC50 was 15 +/- 2 microM. Surprisingly, the NMDA induced production of cGMP was not sensitive to variations in the external Mg2+ concentration. These findings of distinct regulatory mechanisms of different NMDA receptor coupled responses may indicate the existence of several types of NMDA receptors.

Animals↗
PubMed1994

Neurotoxicity and excitatory amino acid antagonists.

The cytotoxic action of excitatory amino acids (glutamate, aspartate, NMDA, AMPA, and kainate) was studied in cultured neocortical neurons. It was demonstrated that all amino acids triggered an increase in the intracellular Ca2+ concentration which appeared to be prerequisite for their cytotoxic action. However, while glutamate and NMDA affected both Ca2+ influx and release from intracellular stores, AMPA and kainate preferentially stimulated influx with little (kainate) or no (AMPA) effect on the intracellular store. Using NMDA and non-NMDA receptor selective antagonists it was shown that glutamate cytotoxicity in these neurons is mediated by both receptor subtypes. using the AMPA/kainate selective antagonists AMOA and AMNH it was demonstrated that excitation and neurotoxicity may not be correlated in a simple manner. antagonist and an agonist at AMPA receptors depending on the AMPA concentration.

Animals↗
PubMed1993

Effects of t-ACPD on neural survival and second messengers in cultured cerebral cortical neurones.

The cytotoxic potential of (1S,3R)-1-amino-cyclopentane-1,3-dicarboxylic acid (t-ACPD) in cultured murine cerebral cortical neurones was examined. Exposure to t-ACPD (1 mM, 16 h) did not induce cytotoxicity per se or affect N-methyl-D-aspartate-induced toxicity. Phosphoinositide hydrolysis was weakly stimulated by t-ACPD (1 mM), while no alteration of intracellular calcium levels was observed after exposure to 1 mM t-ACPD. However, forskolin-stimulated cAMP formation was inhibited by t-ACPD (IC50 = 8 +/- 2 microM) with a maximal inhibition of 36 +/- 4% of control levels. These data suggest that the lack of neurotoxic effects of t-ACPD may be related to the negligible efficacy of t-ACPD to activate mGluRs coupled to the IP3/Ca(2+)-cascade and/or putative counteracting effects of t-ACPD mediated by mGluRs negatively coupled to the cAMP-cascade.

Animals↗
PubMed1993

Cytotoxic actions and effects on intracellular Ca2+ and cGMP concentrations of sulphur-containing excitatory amino acids in cultured cerebral cortical neurons.

Effects of the sulphur-containing acidic amino acids (SAAs) cysteic acid (CA), homocysteic acid (HCA), cysteine sulphinic acid (CSA), homocysteine sulphinic acid (HCSA), and S-sulphocysteine (SC) on intracellular concentrations of Ca2+ ([Ca2+]i) and cGMP ([cGMP]i) as well as their cytotoxic actions were investigated in cultured cerebral cortical neurons. The glutamate receptor subtype selective antagonists APV (D-(-)-2-amino-5-phosphonopentanoate) acting on N-methyl-D-aspartate (NMDA) receptors and DNQX (6,7-dinitroquinoxaline-2,3-dione) acting on non-NMDA receptors were employed to obtain information about the involvement of glutamate receptor subtypes in these actions of the SAAs. It was found that all SAAs exerted a cytotoxic action on the neurons. The ED50 values for CSA, CA, HCSA, and HCA were around 30 to 50 microM and that for SC was about 150 microM. The glutamate transport blocker L-aspartate-beta-hydroxamate increased the efficacy of CSA and CA but had no effect on the cytotoxic actions of the remaining SAAs. In case of CA, HCA, and SC the cytotoxicity could be prevented by APV alone and for HCSA, DNQX could block the toxic action. DNQX reduced the toxicity of HCA somewhat but the presence of APV was required for complete protection. CSA toxicity could only be blocked by the combination of APV and DNQX. All SAAs induced an increase in [cGMP]i and [Ca2+]i and with regard to [Ca2+]i SC was the most potent and CA the least potent SAA. The effect of all SAAs on [cGMP]i could be blocked by APV alone whereas DNQX had no effect except in the case of HCSA where the response was blocked completely and HCA where the response was inhibited by 75%.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗