Examination of the role of calcium in neuronal death

Failed Neuroprotection of Combined Inhibition of L-Type and ASIC1a Calcium Channels with Nimodipine and Amiloride

Effective pharmacological neuroprotection is one of the most desired aims in modern medicine. We postulated that a combination of two clinically used drugs-nimodipine (L-Type voltage-gated calcium channel blocker) and amiloride (acid-sensing ion channel inhibitor)-might act synergistically in an experimental model of ischaemia, targeting the intracellular rise in calcium as a pathway in neuronal cell death. We used organotypic hippocampal slices of mice pups and a well-established regimen of oxygen-glucose deprivation (OGD) to assess a possible neuroprotective effect. Neither nimodipine (at 10 or 20 µM) alone or in combination with amiloride (at 100 µM) showed any amelioration. Dissolved at 2.0 Vol.% dimethyl-sulfoxide (DMSO), the combination of both components even increased cell damage (p = 0.0001), an effect not observed with amiloride alone. We conclude that neither amiloride nor nimodipine do offer neuroprotection in an in vitro ischaemia model. On a technical note, the use of DMSO should be carefully evaluated in neuroprotective experiments, since it possibly alters cell damage.

Calcium-mediated Gene Expression: Mechanism for Neuronal Plasticity and Survival

Calcium plays a central role in many proposed mechanisms of neuronal plasticity as well as neuronal death and degeneration. The observation that certain calcium channel antag onists dramatically protect neurons in a variety of neurological disease models has led to a general strategy for neuroprotection: broadly block calcium entry. However, emerging evidence suggests that calcium can promote neuronal survival and plasticity or death and degeneration, depending on the route of entry. Calcium may partly promote neuronal survival through the autocrine action of neurotrophins such as brain-derived neurotrophic factor. Calcium-mediated neurotrophin secretion may also promote synapse formation during development and in conditions of chronic abnormal neuronal activity such as ep ilepsy. A full understanding of these signal transduction pathways could lead to refined pharmacological strategies that minimize calcium's deadly effects and optimize its growth- and survival-promoting properties. The Neuroscientist 1:317-320,1995

Improving the inhibitory activity of arylidenaminoguanidine compounds at the N-methyl-D-aspartate receptor complex from a recursive computational-experimental structure-activity relationship study

Using a combination of both the partial least squares (PLS) and back-propagation artificial neural network (ANN) pattern recognition methods, several models have been developed to predict the activity of a series of arylidenaminoguanidine analogs as inhibitory modulators of the N-methyl-D-aspartate receptor complex. This was done by correlating structural and physicochemical descriptors obtained from computation software with the experimentally observed [(3)H]MK-801 displacement ability of a small library of synthesized and in vitro screened arylidenaminoguanidines. Results for the generated PLS model were r(2)=0.814, rmsd=0.208, rCV(2)=0.714, loormsd=0.261. The ANN model was created utilizing the eleven descriptors from the PLS model for comparison. The quality of the ANN model (r(2)=0.828, rmsd=0.200, rCV(2)=0.721, loormsd=0.257) is similar to the PLS model, and indicates that the feature between the inputs and the output is majorly linear. These computational models were able to predict inhibition of the NMDA receptor complex by this series of compounds in silico, affording a predictive structure-based 'pre-screening' paradigm for the arylideneaminoguanidine analogs.

Responses in the brain proteome of Atlantic cod (Gadus morhua) exposed to methylmercury

The molecular mechanisms underlying the neurotoxicity of methylmercury (MeHg), a ubiquitous environmental contaminant, are not yet fully understood. Furthermore, there is a lack of biomarkers of MeHg neurotoxicity for use in environmental monitoring. We have undertaken a proteomic analysis of brains from Atlantic cod (Gadus morhua) exposed to 0, 0.5 and 2 mg/kg MeHg administered by intraperitoneal injection. The doses were given in two injections, half of the dose on the first day and the second half after 1 week, and the total exposure period lasted 2 weeks. Using 2-DE coupled with MALDI-TOF MS and MS/MS, we observed the level of 71 protein spots to be 20% or more significantly altered following MeHg exposure, and successfully identified 40 of these protein spots. Many of these proteins are associated with main known molecular targets and mechanisms of MeHg-induced neurotoxicity in mammals, such as mitochondrial dysfunction, oxidative stress, altered calcium homeostasis and tubulin/disruption of microtubules. More interestingly, several of the affected proteins, with well-established or recently demonstrated critical functions in nervous system-specific processes, have not previously been associated with MeHg exposure in any species. These proteins include the strongest up-regulated protein, pyridoxal kinase (essential for synthesis of several neurotransmitters), G protein (coupled to neurotransmitter receptors), nicotinamide phosphoribosyl-transferase (protection against axonal degeneration), dihydropyrimidinase-like 5 (or collapsin response mediator protein 5, CRMP-5) (axon guidance and regeneration), septin (dendrite development), phosphatidylethanolamine binding protein (precursor for hippocampal cholinergic neurostimulating peptide) and protein phosphatase 1 (control of brain recovery by synaptic plasticity). The results of the present study aid our understanding of molecular mechanisms underlying MeHg neurotoxicity and defense responses, and provide a large panel of protein biomarker candidates for aquatic environmental monitoring.

Comparative effects of sodium pyrithione evoked intracellular calcium elevation in rodent and primate ventral horn motor neurons

Oral administration of sodium pyrithione (NaP) causes hindlimb weakness in rodents, but not in primates. Previous work using Aplysia neurons has demonstrated that NaP produces a persistent influx of Ca(2+) ions across the plasma membrane. To determine whether this also occurs in mammalian neurons and whether this could underlie the inter-species difference between rodents and primates, we have tested the effects of NaP on intracellular Ca(2+) levels ([Ca(2+)](i)) in rat and monkey motor neurons in vitro. Motor neurons present in spinal cord slices from rhesus monkey embryos (E37 and 56) and from rat E16 were dissected and cultured on glass coverslips. Following 2 weeks (rhesus) or 2-3 days (rat) in culture, neurons were loaded with fura-PE3/AM, and examined for [Ca(2+)](i) changes in response to NaP. Rhesus motor neurons were identified by immunostaining for Islet-1 (MN specific antigen) and neuron specific enolase (NSE). Motor neurons from both species exhibited dose-dependent NaP-evoked increases in [Ca(2+)](i) However, the dose-response curve for the Rhesus motor neurons was significantly shifted to the right of the rat dose-response curve, whereas the overall amplitude of the Ca(2+) rise was similar in both species. As shown previously for the Aplysia neurons, the action of NaP is attenuated by SKF 96365, an inhibitor of store-operated calcium entry. In contrast the action of NaP is unaffected by nifedipine and tetrodotoxin, blockers of voltage-dependent Ca(2+) and Na(+) channels, respectively, or by ouabain, an inhibitor of the plasma membrane Na(+)/K(+) ATPase. Our results indicate that the NaP-induced increase in [Ca(2+)](i) is conserved across species and suggest that the toxicological sensitivity of rodent over primate to pyrithione could be due to the enhanced sensitivity of rodent motor neurons to NaP-evoked intracellular Ca(2+) elevation.

Comparative sensitivity of rat cerebellar neurons to dysregulation of divalent cation homeostasis and cytotoxicity caused by methylmercury

The objective of the present study was to determine the relative effectiveness of methylmercury (MeHg) to alter divalent cation homeostasis and cause cell death in MeHg-resistant cerebellar Purkinje and MeHg-sensitive granule neurons. Application of 0.5-5 microM MeHg to Purkinje and granule cells grown in culture caused a concentration- and time-dependent biphasic increase in fura-2 fluorescence. At 0.5 and 1 microM MeHg, the elevations of fura-2 fluorescence induced by MeHg were biphasic in both cell types, but significantly delayed in Purkinje as compared to granule cells. Application of the heavy-metal chelator, TPEN, to Purkinje cells caused a precipitous decline in a proportion of the fura-2 fluorescence signal, indicating that MeHg causes release of Ca(2+) and non-Ca(2+) divalent cations. Purkinje cells were also more resistant than granule cells to the neurotoxic effects of MeHg. At 24.5 h after-application of 5 microM MeHg, 97.7% of Purkinje cells were viable. At 3 microM MeHg there was no detectable loss of Purkinje cell viability. In contrast, only 40.6% of cerebellar granule cells were alive 24.5 h after application of 3 microM MeHg. In conclusion, Purkinje neurons in primary cultures appear to be more resistant to MeHg-induced dysregulation of divalent cation homeostasis and subsequent cell death when compared to cerebellar granule cells. There is a significant component of non-Ca(2+) divalent cation released by MeHg in Purkinje neurons.

Early and delayed glutamate effects in rat primary cortical neurons

Glutamate-induced changes in the subcellular distribution of protein kinase C isoforms and in the intracellular calcium concentration were investigated in rat primary cortical neurons. Western blot analysis of protein kinase C isoforms (alpha, beta1, beta2, gamma, delta, epsilon, zeta and theta), performed 30 min after a 10 min treatment with 30 microM glutamate, revealed a decrease in the total beta1 (-24%) and beta2 (-40%) isoform levels, without any significant change in any of the other isozymes. All conventional isoforms translocated to the membrane compartment, while delta, epsilon, zeta and theta; maintained their initial subcellular distribution. Twenty-four hours after glutamate treatment, the total protein kinase C labelling had increased, particularly the epsilon isoform, which accounted for 34% of the total densitometric signal. At this time, protein kinase C beta1, delta, epsilon and zeta isoforms were mainly detected in the membrane compartment, while gamma and theta; signals were displayed almost solely in the cytosol. Basal intracellular calcium concentration (FURA 2 assay) was concentration-dependently increased (maximum effect +77%) 30 min, but not 24h after a 10 min glutamate (10-100 microM) treatment, while the net increase induced by electrical stimulation (10 Hz, 10s) was consistently reduced (maximum effect -64%). The N-methyl-d-aspartate receptor antagonist, MK-801, 1 microM, prevented glutamate action both 30 min and 24 h after treatment, while non-selective protein kinase C inhibitors, ineffective at 30 min, potentiated it at 24 h. These findings show that protein kinase C isoforms are differently activated and involved in the early and delayed glutamate actions, and that the prevailing effect of their activation is neuroprotective.

57Co SPECT, 99mTc-ECD SPECT, MRI and neuropsychological testing in senile dementia of the Alzheimer type

Inflammatory mechanisms contribute to the pathophysiology of senile dementia of the Alzheimer type (sDAT). Previous studies have shown that 57Co single photon emission computed tomography (SPECT) is able to visualize inflammatory lesions, probably by means of the final common pathway of Ca2+ homeostasis disturbance in both neuronal degeneration and inflammation. The aims of this study were: (1) to detect 57Co SPECT changes in sDAT patients; (2) to correlate these findings with those of conventional neuroimaging techniques and neuropsychological testing (NPT); and (3) to compare 57Co SPECT findings in sDAT patients with those in other types of dementia. Six patients suffering from probable sDAT were included and compared with four patients suffering from other types of dementia. All patients had a magnetic resonance imaging (MRI) scan, NPT, 57Co and 99mTc-ethyl cysteinate dimer (ECD) SPECT scan. Perfusion SPECT images were semiquantitatively evaluated by comparison with an age-matched normal database, while 57Co SPECT scans were assessed qualitatively. MRI and 99mTc-ECD SPECT scans yielded conclusive results with regard to the exclusion of other pathologies and the confirmation of the diagnosis. Using visual analysis, 57Co SPECT scans were unable to show any regional raised uptake, irrespective of the disorder, depth or extent of the perfusion defects, presence of atrophy on MRI or the results of NPT.

Modification of ion channels and calcium homeostasis of basal forebrain neurons during aging

In this paper we review the last several years of work from our lab with attention to changes in the properties of basal forebrain neurons during aging. These neurons play a central role in behavioral functions, such as: attention, arousal, cognition and autonomic activity, and these functions can be adversely affected during aging. Therefore, it is fundamental to define the cellular mechanisms of aging in order to understand the basal forebrain and to correct deficits associated with aging. We have examined changes in the physiological properties of basal forebrain neurons during aging with whole-cell and single-channel patch-clamp, as well as, microfluorimetric measurements of intracellular calcium concentrations. These studies contribute to the understanding of integration within the basal forebrain and to the identification of age-related changes within central mammalian neurons. Although extensive functional/behavioral decline is often assumed to occur during aging, our data support an interpretation of compensatory increases in function for excitatory amino acid receptors, GABA(A) receptors, voltage-gated calcium currents and calcium homeostatic mechanisms. We believe that these changes occur to compensate for decrements accruing with age, such as decreased synaptic contacts, ion imbalances or neuronal loss. The basal forebrain must retain functionality into late aging if senescence is to be productive. Thus, it is critical to recognize the potential cellular and subcellular targets for therapeutic interventions intended to correct age-related behavioral deficits.

AR-R15896AR reduces cerebral infarction volumes after focal ischemia in cats

OBJECTIVE

The use of competitive and noncompetitive N-methyl-D-aspartate receptor antagonists to prevent neuronal death during ischemia has been comprehensively studied. This study was performed to examine the neuroprotective effects and pharmacokinetics of the noncompetitive N-methyl-D-aspartate receptor channel blocker (S)-alpha-phenylpyridine-ethanamine dihydrochloride, AR-R15896AR (formerly designated ARL 15896AR), using a gyrencephalic cat middle cerebral artery occlusion model.

METHODS

In a separate experiment, three cats were used for pharmacokinetic analysis, thus establishing the optimal dose of AR-R15896AR. Focal cerebral ischemia was induced in 21 cats. After 30 minutes of a 90-min ischemic insult, the cats received an intravenous infusion (total volume, 3 ml), in a 15-minute period, of either AR-R15896AR or normal saline solution (control). Physiological data were obtained after 40 and 80 minutes of ischemia and at 2, 4, and 6 hours after ischemia. At 6 hours after ischemia, each cat was positioned for both T2- and diffusion-weighted scans (eight slices, 5-mm thick). At 8 hours after ischemia, the animals were perfusion-fixed for histopathological analysis.

RESULTS

Pharmacokinetic studies indicated that AR-R15896AR remained in the blood at elevated levels for the 6 hours studied, with a calculated half-life of approximately 6 hours. AR-R15896AR rapidly entered the brain and exhibited a brain/plasma ratio of approximately 8:1. The infarction volumes for the AR-R15896AR-treated group were 1138.5+/-363.1, 651.3+/-428.9, and 118.6+/-50.1 mm3, as calculated using diffusion- and T2-weighted MRI and histopathological data, respectively. The infarction volumes for the control group were 3866.3+/-921, 3536+/-995.7, and 359.9+/-80.2 mm3, as calculated using diffusion- and T2-weighted MRI and histopathological data, respectively. No significant changes were observed in the physiological parameters measured (mean arterial blood pressure, pH, arterial carbon dioxide pressure, arterial oxygen pressure, sodium, potassium, chloride, and glucose levels, hematocrit, and temperature) for either the control or AR-R15896AR-treated group. Postischemic calcium levels returned to normal in the AR-R15896AR-treated cats, whereas they decreased in the control cats.

CONCLUSION

When administered after ischemia, AR-R15896AR was effective in significantly reducing infarction volumes, as measured using diffusion- or T2-weighted magnetic resonance imaging data or quantitative histopathological data. This study also demonstrated that infarction volumes were greater in the diffusion- and T2-weighted magnetic resonance imaging scans than in the qualitative histopathological analyses, with the diffusion-weighted scans exibiting the largest infarction volumes.

Zinc deficiency exacerbates loss in blood-brain barrier integrity induced by hyperoxia measured by dynamic MRI

Using dynamic Magnetic Resonance Imaging (dMRI), blood-brain barrier (BBB) permeability (k(PSrho)) and tissue interstitial leakage space (v(e)) were evaluated in zinc-deficient (ZnDF) male weanling Wistar rats following 3 days exposure to hyperoxia (85% O2). Temporal monitoring of T1-weighted MR image changes, following a bolus intravenous injection of gadolinium-DTPA, allowed estimation of BBB integrity. Three-day exposure of hyperoxia caused a marginal loss of BBB integrity, reflected in a slight increase in kPSrho and v(e), observed in both the animals fed adequate zinc (ZnAL) and pair-fed controls (ZnPF). However, zinc deficiency resulted in a significant increase in both kPSrho and v(e), indicating a severely disturbed BBB. In addition MR-visible free water was elevated in ZnDF brains following hyperoxia treatment indicating that a loss of BBB integrity may be associated with neuronal edema. The diminished BBB integrity may be free-radical mediated as the ratio of oxidized to reduced glutathione (GSSG:GSH) was significantly elevated.

Reduced voltage-dependent Ca2+ signaling in CA1 neurons after brief ischemia in gerbils

An initial overload of intracellular Ca2+ plays a critical role in the delayed death of hippocampal CA1 neurons that die a few days after transient ischemia. Without direct evidence, the prevailing hypothesis has been that Ca2+ overload may recur until cell death. Here, we report the first measurements of intracellular Ca2+ in living CA1 neurons within brain slices prepared 1, 2, and 3 days after transient (5 min) ischemia. With no sign of ongoing Ca2+ overload, voltage-dependent Ca2+ transients were actually reduced after 2-3 days of reperfusion. Resting Ca2+ levels and recovery rate after loading were similar to neurons receiving no ischemic insult. The tetrodotoxin-insensitive Ca spike, normally generated by these neurons, was absent at 2 days postischemia, as was a large fraction of Ca2+-dependent spike train adaptation. These surprising findings may lead to a new perspective on delayed neuronal death and intervention.

Developmental regulation of the recovery process following glutamate-induced calcium rise in rodent primary neuronal cultures

CNS neurons exhibit a profound, maturation-dependent increase in the vulnerability to injury. Little is, however, known about the cellular mechanisms involved. This study investigated the developmental influence on the ability to recover the resting concentration of free cytoplasmic Ca2+ ([Ca2+]i) following stimulation with 100 microM glutamate in hippocampal and cerebellar granule cells in culture. Primary neurons were exposed to glutamate for either 1 min or 10 min. Hippocampal neurons were evaluated at 7, 12-14, and 17-19 days in vitro (DIV), and cerebellar granule cells were tested at 8-9 or 15-16 DIV. In hippocampal neurons, either an increased age in culture or longer drug exposure were both associated with less efficient [Ca2+]i recovery. Additionally, for both 1-min and 10-min drug exposure, increased age in culture was the primary determinant of the development of secondary [Ca2+]i destabilization followed by a very variable recovery patterns. Similar to hippocampal neurons, older cerebellar granule cells also recovered less efficiently from glutamate-mediated [Ca2+]i rise. The difference in the extent of recovery was not directly influenced by the magnitude of the [Ca2+]i rise, since cerebellar granule cells recovered from both high or low [Ca2+]i rise with similar kinetic profiles. Overall, the results presented in this study implicate the age in culture as an important influencing factor of both the less efficient recovery from glutamate-induced Ca2+ load and the development of secondary [Ca2+]i destabilizations. The progressive, maturation-dependent, decrease in the ability to recover from Ca2+ load might represent a potentially important mechanism contributing to the increased vulnerability of fully developed neurons to injury.

Elevations of intracellular Ca2+ as a probable contributor to decreased viability in cerebellar granule cells following acute exposure to methylmercury

In these experiments we examined whether the elevations in intracellular Ca2+ concentration ([Ca2+]i) induced by methylmercury (MeHg)(described in our previous study) might contribute to cerebellar granule cell mortality following exposure to MeHg in vitro. Cells were exposed to 0.5 microM MeHg for 45 min or 1 microM MeHg for 38 min, conditions previously shown to induce elevations in [Ca2+]i in these cells. Control cells were exposed to buffer alone for 60 min. Viability was assessed using the Live/Dead viability/cytotoxicity kit. At 30 min post-MeHg exposure, there was no immediate increase in cell mortality; however, by 3.5 h after the onset of MeHg exposure, cell viability decreased to 74 and 54% of control values for 0.5 and 1.0 microM MeHg, respectively. At 24.5 h after MeHg exposure, cell viability declined to approximately 27%. Losses in cell viability at 3.5 h were prevented by pretreating the granule cells for 65 min with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl)ester (BAPTA; 10 microM), then exposing the cells to MeHg in the continued presence of BAPTA; however, at 24.5 h, BAPTA no longer prevented MeHg-induced cell death. Exposure to the Ca2+ channel blockers omega-conotoxin MVIIC (1 microM) or nifedipine (1 microM), previously shown to delay elevations in [Ca2+]i with MeHg exposure in vitro, protected granule cells from MeHg-induced mortality at 3.5 h postexposure. These data suggest that at early time points, MeHg-induced increases in [Ca2+]i may contribute to granule cell mortality; however, the role of Ca2+ at later time points is unclear.

Reactive oxygen production by glutamate agonists in dissociated cerebellar cells: a flow cytometric study

1. The effect of glutamate, N-methyl-D-aspartate (NMDA) and kainate on radical oxygen species (ROS) production and calcium influx was studied in dissociated cerebellar granule cells with the use of flow cytometry. 2. Glutamate and NMDA induced an intracellular ROS increase by an activation of NMDA receptors. 3. (+)MK-801 inhibited the effect on ROS production of both agonists (IC50 values of 1.52 +/- 0.05 and 0.71 +/- 0.02 microM, respectively). 4. (+)MK-801 inhibited the intracellular calcium increase induced by glutamate and NMDA, whereas 6-cyano-7-nitroquinoxaline-2,3-dione inhibited that induced by kainate. 5. NG-Nitro-L-arginine, but not nitrendipine, inhibited the ROS production induced by glutamate agonists. Consequently, nitric oxide synthase might play an important role in the neurotoxic process induced by excitatory amino acids.

Effects of intrastriatal injection of quinolinic acid on electrical activity and extracellular ion concentrations in rat striatum in vivo

Changes in neuronal activity and extracellular concentrations of ions were measured in rat striatum for 60-90 min after intrastriatal injection of quinolinic acid, an agonist of the N-methyl-D-aspartate receptor. The excitotoxin induced bursts of synchronous electrical activity which were accompanied by rises in [K+]e (to approximately 6 mM) and decreases in [Ca2+]e (by less than 0.1 mM); [H+]e usually increased (0.1-0.3 pH unit) after a short and small (< 0.1 pH unit) alkaline shift. The magnitude and frequency of these periodic changes decreased with time; after 90 min the amplitudes fell to 10-20% of the early values and the frequency to about one every 8 min as compared to one every 2-3 min immediately after quinolinate injection. By 90 min there was an increase in [K+]e from 3.3 mM to 4.2 mM and a decrease in [Ca2+]e from 1.34 mM to 1.30 mM. It is postulated that activation of the N-methyl-D-aspartate receptor causes disturbances in neuronal activity and ion gradients; restoration of the original ionic balances raises utilization of ATP and places an additional demand on energy-producing pathways. Increased influx of calcium into neurons may lead to an enhanced accumulation and subsequent overload of mitochondria with the cation. This, in turn, could result in dysfunction of the organelles and account for the decrease in respiration and [ATP]/[ADP] that have been observed previously in this model. The results of the present study lead to the conclusion that quinolinic acid produces early changes in activity of striatal neurons and movements of several cations which may contribute to subsequent abnormalities in energy metabolism and ultimately, cell death.

Calpain I activation in rat hippocampal neurons in culture is NMDA receptor selective and not essential for excitotoxic cell death

Administration of glutamate (100 microM) to primary cultures of rat hippocampal neurons for 1 h led to calpain I activation as determined by monitoring the extent of spectrin breakdown with the antibodies designed to specifically recognize the calpain I-mediated spectrin breakdown products. Based on the studies with subtype selective antagonists of glutamate receptors, glutamate caused calpain I activation specifically through the activation of the NMDA receptor. In parallel experiments, the magnitude and the temporal profiles of Ca2+ rise were determined by Fura-2 microfluorimetry. Ca2+ influx through voltage-sensitive Ca2+ channels, even though leading to substantial Ca2+ rise, did not by itself activate calpain I. These results indicate that for calpain I activation, the source of Ca1+ influx is more important than the magnitude of Ca2+ rise. Glutamate-mediated calpain I activation was fully blocked by preincubation (30 min) of the cultures with calpain inhibitor I, calpain inhibitor II, or calpeptin (all 10 microM). The presence of calpain inhibitors did not, however, in any way ameliorate the massive excitotoxicity resulting from 16 h exposure to glutamate, indicating that calpain I activation and excitotoxicity are not causally related events. Similarly, preincubation with any of the tested calpain inhibitors was detrimental to the clearance of neuritic from a 10-min exposure to glutamate. Additionally, the presence of calpain inhibitors was detrimental to the clearance of neuritic varicosities resulting from a short-term sublethal exposure to glutamate, suggesting that a physiological level of calpain I activation might actually play an important homeostatic role in the restoration of normal cytoskeletal organization.

The role of calcium in apoptosis

One general signalling mechanism used to transfer the information delivered by agonists into appropriate intracellular compartments involves the rapid redistribution of ionised calcium throughout the cell, which results in transient elevations of the cytosolic free Ca2+ concentration. Various physiological stimuli increase [Ca2+]i transiently and, thereby, induce cellular responses. However, under pathological conditions, changes of [Ca2+]i are generally more pronounced and sustained. Marked elevations of [Ca2+]i activate hydrolytic enzymes, lead to exaggerated energy expenditure, impair energy production, initiate cytoskeletal degradation, and ultimately result in cell death. Such Ca(2+)-induced cytotoxicity may play a major role in several diseases, including neuropathological conditions such as chronic neurodegenerative diseases and acute neuronal losses (e.g. in stroke).

Modulation of neuronal mitochondrial membrane potential by the NMDA receptor: role of arachidonic acid

Activation of NMDA receptors in dissociated cerebellar granule cells reduced mitochondrial membrane potential (MMP), as measured by rhodamine 123 fluorescence in a flow cytometer. This effect was inhibited by several NMDA-receptor antagonists with the following rank order of potency: MK-801 > PCP > TCP > dextrorphan > dichlorokynurenic acid > D-AP5 > dextromethorphan. Neither spermine nor arcaine modified the NMDA-induced reduction in MMP, whereas ifenprodil and eliprodil inhibited this response in the micromolar range. The mechanism responsible for the alteration of MMP mediated by NMDA was studied. Mepacrine and dibucaine prevented the MMP reduction induced by NMDA, as did W13 (calmodulin antagonist). In contrast, this effect was not blocked by cyclooxygenase or lipooxygenase inhibitors, H7 (a protein kinase C inhibitor) or nitroarginine (nitric oxide synthase inhibitor). These data suggest a direct interaction between NMDA-receptor activation and arachidonic acid formation, and indicate that NMDA receptor-mediated effect on MMP could involve arachidonic acid.

Ionized intracellular calcium concentration predicts excitotoxic neuronal death: observations with low-affinity fluorescent calcium indicators

Cytosolic calcium ([Ca2+]i) is an important mediator of neuronal signal transduction, participating in diverse biochemical reactions that elicit changes in synaptic efficacy, metabolic rate, and gene transcription. Excessive [Ca2+]i also has been implicated as a cause of acute neuronal injury, although measurement of [Ca2+]i in living neurons by fluorescent calcium indicators has not consistently demonstrated a correlation between [Ca2+]i and the likelihood of neuronal death after a variety of potentially lethal insults. Using fluorescence videomicroscopy and microinjected calcium indicators, we measured [Ca2+]i in cultured cortical neurons during intense activation with either NMDA (300 microM) or AMPA (450 microM). At these concentrations NMDA killed >80% of the cultured neurons by the next day, whereas neuronal death from AMPA was <20%. Using the conventional calcium indicator, fura-2/AM, we estimated [Ca2+]i elevations to be approximately 300-400 nM during exposure to either glutamate agonist. In contrast, indicators with lower affinity for calcium, benzothiazole coumarin (BTC), and fura-2/dextran reported [Ca2+]i levels >5 microM during lethal NMDA exposure, but [Ca2+]i levels were <1.5 microM during nonlethal activation of AMPA receptors or voltage-gated calcium channels. Fura-2 reported [Ca2+]i responses during brief exposure to glutamate, NMDA, AMPA, kainate, and elevated extracellular K+ between 0.5 and 1 microM. With the use of BTC, only NMDA and glutamate exposures resulted in micromolar [Ca2+]i levels. Neurotoxic glutamate receptor activation is associated with sustained, micromolar [Ca2+]i elevation. The widely used calcium indicator fura-2 selectively underestimates [Ca2+]i, depending on the route of entry, even at levels that appear to be within its range of detection.

Age-related loss of calbindin from human basal forebrain cholinergic neurons

Loss of basal forebrain cholinergic neurons (BFCN) occurs in many age-related neurological diseases. Although age is the common risk factor in these disorders, no consistent age-related changes have been reported in the human BFCN. We investigated age-related alterations in choline acetyltransferase (ChAT), low-affinity nerve growth factor receptor (p75LNGFR) and calbindin-D28k (CalBP) immunoreactivity in the human BFCN. No significant age-related changes were observed in ChAT or p75LNGFR immunoreactivity. By contrast, normal aging was accompanied by a selective, substantial and significant loss of CalBP immunoreactivity from the BFCN. Other CalBP-positive neurons were unchanged. Loss of the calcium buffering capacity conferred by CalBP may leave the BFCN vulnerable to damage in neurodegenerative disorders.

Activation of protein kinase C by intracellular free calcium in the motoneuron cell line NSC-19

The relationship between intracellular free calcium ([Ca2+]i) and the activation of protein kinase C (PKC) and Ca2+/calmodulin-dependent protein kinase II (CaMKII) was investigated in the NSC-19 motoneuron cell line. Increased extracellular calcium ([Ca2+]o) up to 10 mM resulted in sustained elevations of [Ca2+]i. Control cell cultures (1.3 mM [Ca2+]o, [Ca2+]i = 83 +/- 17 nM) contained Ca2+- and PS/DO lipid-dependent PKC activity predominantly in the cytosol. However, elevation of [Ca2+]o up to 5 mM ([Ca2+]i = 232 +/- 24 nM) resulted in almost complete loss of cytosolic PKC activity. Cells incubated in 10 mM [Ca2+]o ([Ca2+]i = 365 +/- 13 nM) showed increased levels of both cytosolic and membrane PKC activity compared to control. These alterations in PKC activity appeared to be translocation-independent, since PKC protein levels were unchanged as demonstrated by Western blotting analysis. When cells were exposed to 25 or 50 mM [Ca2+]o, [Ca2+]i rose transiently to over 600 and 900 nM, respectively, and then returned to near basal values. Under these conditions, total PKC activity decreased, and increased amounts of the catalytic fragment of PKC, protein kinase M, were generated. Extracts from cells exposed to [Ca2+]o between 1.3 and 25 mM did not differ significantly in the levels of measurable CaMKII activity 10 min following the change in [Ca2+]o.

Nimodipine at a dose that slows ABR latencies does not protect the ear against noise

We tested the hypothesis that nimodipine, a dihydropyridine reported to increase blood flow, block calcium and potassium channels, and reduce ischemic damage, would alleviate noise-induced hearing loss. Young C57B1/6J mice were exposed to wide-band noise (2 min, 120 dB SPL), with ABR thresholds (4-50 kHz) determined before noise exposure, and from 1 h to 2 weeks afterwards. One group (n = 7) received nimodipine (30 mg/kg/day) in daily peanut butter food supplements beginning 24 h before exposure; the other group (n = 6) received peanut butter alone. In the pretest nimodipine significantly increased the latency of Wave P1 of the ABR (mean difference: 0.16 ms; P < 0.02), showing that calcium blockade depressed sensorineural efficiency, but ABR thresholds were not affected. Noise exposure produced a severe threshold loss that partially recovered in the first week after exposure, and then suffered a slight but significant loss in the second week. These effects were seen equally in both groups: nimodipine did not reduce the severity of the immediate hearing loss following noise exposure, nor did it benefit recovery.

Cobalt-55 positron emission tomography in ischemic stroke

After acute cerebral stroke, the (peri-) infarct tissue is characterized by calcium (Ca)-mediated neuronal damage and inflammatory processes. Monitoring Ca-mediated damage using the isotope cobalt-55 (Co) as a Ca-tracer may enable PET-imaging of this tissue. Since the fate of (peri-) infarct tissue determines clinical outcome, Co-PET may have prognostic value in stroke. Six stroke patients were examined with Co-PET, MRI and a middle cerebral artery (mca) stroke scale (Orgogozo). In every patient, specific Co-accumulation in the appropriate brain region was seen, irrespective of the integrity of the blood-brain barrier. This pilot study suggests Co-PET as a diagnostic tool in stroke, which may provide additional information on the clinical outcome. Validation of method in larger patient series is necessary.

Effect of glutamate receptor ligands on mitochondrial membrane potential in rat dissociated cerebellar cells

The effect of three different glutamate receptor ligands on mitochondrial membrane potential has been studied in rat pup dissociated cerebellar cells by measuring rhodamine 123 fluorescence. L-glutamate, NMDA (N-methyl-D-aspartate) and kainate (from 10(-8) to 10(-3) M) decreased in a concentration-dependent manner the mitochondrial membrane potential with EC50 values of 6.7 +/- 1.7, 3.8 +/- 0.5, and 37.4 +/- 14 microM, respectively. Dizocilpine ((+)MK 801) was able to inhibit the NMDA- and L-glutamate-induced decrease in rhodamine 123 fluorescence, while kainate-induced fluorescence-decreases were unaffected. However, 6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX) totally prevented the effect of kainate on mitochondrial membrane potential, but failed to block the L-glutamate effect. It is concluded that, in our cell preparation, L-glutamate exerts its action mainly through NMDA-subtype receptors, and that Ca2+ and Na+ entry through ionotropic glutamate receptors could be responsible for an impairment of mitochondrial membrane potential.

Cytotoxic action of tri-n-butyltin on dissociated rat cerebellar neurones: a flow-cytometric study

The effects of tri-n-butyltin on cell viability and intracellular Ca2+ concentration ([CA2+]i) were examined by a flow cytometer in rat cerebellar neurones to reveal the contribution of tri-n-butyltin-induced increased in the [Ca2+]i to its cytotoxicity. Tri-n-Butyltin decreased the cell viability in association with increased [Ca2+]i at concentrations of 0.3 microM or more. Decrease or increase of the extracellular Ca2+ concentration ([Ca2+]o) respectively decreased or increased the cell viability. However, cell viability in the presence of ionomycin which increased [Ca2+]i more significantly than tri-n-butyltin was higher than that in the presence of tri-n-butyltin. Tri-n-butyltin also decreased cell viability under nominally [Ca2+]o-free conditions although the [Ca2+]i increase by tri-n-butyltin was still lower than the control [Ca2+]i under normal [Ca2+]o (2 mM). Therefore, it is unlikely that neuronal death induced by tri-n-butyltin is entirely dependent on the tri-n-butyltin-induced increase in [Ca2+]i.

Androgen modulates N-methyl-D-aspartate-mediated depolarization in CA1 hippocampal pyramidal cells

Previously, research elucidating steroid hormone actions in the central nervous system has focused on their role in sexual reproduction and maintaining homeostasis. The hippocampus is a target of steroid modulation and is involved in the development of emotional behavior and memory storage. Area CA1 of the hippocampus contains a high density of androgen receptor (AR) and N-methyl-D-aspartate (NMDA) receptors. NMDA receptors underlie excitatory synaptic transmission and excitotoxicity in CA1 neurons. The effects of AR activation on the neurophysiology of hippocampal pyramidal neurons is unknown. Standard intracellular recording techniques in hippocampal slices were used to investigate the effects of the non-aromatizable androgen, 5-alpha-dihydrotestos-terone-proprionate (DHTP), on CA1 pyramidal cell characteristics and NMDA receptor-mediated responses. Male Sprague-Dawley rats were unoperated, sham-operated (SHAM), gonadectomized (GDX), or gonadectomized with DHTP replacement therapy (GDX + DHTP). Neuronal AR was saturated by DHTP treatment as determined by binding studies and immunocytochemistry. Chronic DHTP treatment increased the action potential duration and decreased the fast afterhyperpolarization (fAHP) amplitude. To test the effect of DHTP on glutamate receptor-mediated responses, hippocampal slices were exposed to increasing concentrations of NMDA. In pyramidal cells from SHAM and GDX-treated animals, 30 microM NMDA induced an irreversible depolarization; the membrane potential of pyramidal cells from GDX + DHTP-treated animals recovered to baseline. The effect of DHTP was time dependent, implicating protein synthetic mechanisms. Our findings demonstrate that androgens can influence pyramidal cell characteristics and neurotransmitter-evoked actions in hippocampal CA1 pyramidal cells.

The effects of perinatal hypoxia on the behavioral, neurochemical, and neurohistological toxicity of the metabolic inhibitor 3-nitropropionic acid

3-nitropropionic acid (3-NPA) neurotoxicity and long-term effects of perinatal hypoxia were evaluated in 18 adult rats. Hypoxia-insulted (I) and noninsulted (NI) rats were delivered by cesarean section. Hypoxic insult was effected by submerging dissected uterine horns in warmed saline for 15 min. NI rats were delivered from the adjacent nonsubmerged horns. At postnatal day 90, I and NI rats were trained to perform tasks thought to measure behaviors dependent upon aspects of time estimation (TE), motivation, and learning. At 12 months of age, rats were injected i.p. with escalating doses of 3-NPA (5 mg/kg/day to a maximum of 30 mg/kg/day) immediately after each test session and sacrificed at the end of treatment. Additional male rats were used as untreated controls. Although 3-NPA produced a dose-dependent impairment of performance in each task, the effects were qualitatively similar for each group. A significant difference between I and NI rats was, however, observed in the TE task where NI rats completed less of the task at high doses of 3-NPA compared to I rats. Compared to untreated controls, dopamine concentrations were decreased in caudate nucleus of both I and NI rats after 3-NPA. Specific areas most frequently damaged included cerebral cortex, hippocampal subfield CA1, thalamus, caudate nucleus, and the cerebellum. Lesions usually were less extensive in the I rather than NI members of a littermate pair, suggesting a possible protective effect of perinatal hypoxia against subsequent 3-NPA neurotoxicity.

Motor alterations and neuronal damage induced by intracerebral administration of Ruthenium red: effect of NMDA receptor antagonists and other anticonvulsant drugs

The effects of the intracerebroventricular (icv) and the intrahippocampal (ih) microinjection of the inorganic dye Ruthenium red (RuR) on motor activity, and the protective action of excitatory amino acid receptor antagonists and of GABAergic drugs, were studied in the rat. When administered icv, RuR produced intense tonic-clonic convulsions which were refractory to N-methyl-D-aspartate (NMDA) receptor antagonists and to diphenylhydantoin, whereas aminooxyacetic acid (AOA) and valproate only partially protected against seizure activity. The most notable motor effect of the ih RuR administration was the appearance of intense wet-dog shakes (WDS) behavior, which was remarkably attenuated by the icv or intraperitoneal (ip) administration of the NMDA receptor antagonists (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), CGP-37849, and MK-801, but not by their ih coinjection with RuR. Systemic AOA and valproate were also effective in reducing the number of WDS, whereas the non-NMDA receptor antagonist CNQX was ineffective. Light and electron microscopic observations of the RuR-injected brains revealed that the dye was highly concentrated in neuronal somas located in or near the injected areas. In the case of the CA1 region, remarkable damage of the pyramidal neurons was manifested by vacuolization, and 5-9 d after the injection notable cell loss and disruption of the CA1 cell layer organization was apparent. The results indicate that RuR penetrates selectively neuronal bodies and damage them, and suggest that the resulting motor alterations involve hyperactivity of glutamatergic neurotransmission.

N-acetylaspartate complexes with calcium and lanthanide ions

N-acetylaspartate (NAA) is the one of the most prominent resonances observed in the solvent-suppressed NMR spectrum of the human brain. Although it is present in the brain at about 10 mM, its precise metabolic function is still unclear, We have examined the NAA as a potential chelator for divalent metal ions such as Ca2+. We have employed the perturbations induced by Ln3+ ions in the 1H and 13C NMR spectrum of NAA to monitor formation of NAA complexes. 1H NMR measurements showed that the dissociation constants for the formation of Eu(3+)-NAA, Yb(3+)-NAA, and Ca(2+)-NAA complexes were 0.07, 0.13, and 0.86 mM, respectively. Scatchard analysis of the results indicates the formation of a 1:1 metal-ligand complex. We also inferred the structure of the NAA-metal ion complex from an analysis of paramagnetic perturbations induced in the 1H NMR and 13C NMR spectra of NAA. The structural analysis of the NAA-metal ion complex indicates that the two carboxylic groups participate in chelating the metal ion, forming the binding site for the metal ion.

Inability to restore resting intracellular calcium levels as an early indicator of delayed neuronal cell death

The hippocampus is especially vulnerable to excitotoxicity and delayed neuronal cell death. Chronic elevations in free intracellular calcium concentration ([Ca2+]i) following glutamate-induced excitotoxicity have been implicated in contributing to delayed neuronal cell death. However, no direct correlation between delayed cell death and prolonged increases in [Ca2+]i has been determined in mature hippocampal neurons in culture. This investigation was initiated to determine the statistical relationship between delayed neuronal cell death and prolonged increases in [Ca2+]i in mature hippocampal neurons in culture. Using indo-1 confocal fluorescence microscopy, we observed that glutamate induced a rapid increase in [Ca2+]i that persisted after the removal of glutamate. Following excitotoxic glutamate exposure, neurons exhibited prolonged increases in [Ca2+]i, and significant delayed neuronal cell death was observed. The N-methyl-D-aspartate (NMDA) channel antagonist MK-801 blocked the prolonged increases in [Ca2+]i and cell death. Depolarization of neurons with potassium chloride (KCl) resulted in increases in [Ca2+]i, but these increases were buffered immediately upon removal of the KCl, and no cell death occurred. Linear regression analysis revealed a strong correlation (R = 0.973) between glutamate-induced prolonged increases in [Ca2+]i and delayed cell death. These data suggest that excitotoxic glutamate exposure results in an NMDA-induced inability to restore resting [Ca2+]i (IRRC) that is a statistically significant indicator of delayed neuronal cell death.

Selective neurotoxicity of ruthenium red in primary cultures

The inorganic dye ruthenium red (RuR) has been shown to be neurotoxic in vivo when injected intracerebrally. In this work the toxicity of RuR was compared in primary cultures of rat cortical neurons, cerebellar granule neurons and cerebellar astroglia. Microscopic examination of the cultures revealed that RuR penetrates the somata of both types of neurons used and produces vacuolization and loss and fragmentation of neurites. In contrast, no RuR was seen inside cultured astrocytes and no morphological signs of damage were observed in these cells. RuR toxicity was also assessed by immunocytochemistry of alpha-tubulin and by biochemical measurement of the reduction of (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) by the cultured cells. The morphological alterations in the neurons were closely correlated with loss of tubulin immunoreactivity and particularly with a notable decrement in the ability to reduce MTT. Using the latter parameter, it was found that neuronal damage was independent of the age of the cultures, augmented progressively with time of incubation with RuR, from 8 to 24 h, and showed a clear dose-response curve from 20 to 100 microM RuR. Astrocytes showed only a slight decrease in MTT reduction after 24 h of incubation with 100 microM RuR. It is concluded that RuR seems to be toxic for neurons but not for astroglia, and that this selectivity is probably related to the ability of the neurons to internalize the dye. The possible mechanisms of RuR penetration and neuronal damage are discussed.

Regional and temporal profiles of calcium accumulation and glial fibrillary acidic protein levels in rat brain after systemic injection of kainic acid

Cerebral calcium accumulation and increases in the astroglial intermediate filament protein, glial fibrillary acidic protein (GFAP), have been used as markers of neurotoxic and ischemic brain damage. The present study was aimed at quantitatively investigating the regional and temporal relationship of those indices following a neurotoxic insult. For this purpose, regional changes in 45Ca uptake and GFAP levels, using ELISA, were evaluated in rat brains at both early (several hours) and late time points (up to 6 months) after a single systemic injection of kainic acid (12 mg/kg). After 4 h, limbic brain areas were already heavily labelled by 45Ca. In most investigated brain areas 45Ca accumulation peaked at day 4 (maximum 5 fold increase in amygdala) and returned to normal levels within 1 week (cerebellum, pons/medulla, occipital cortex), 2 weeks (striatum, frontal cortex), 2 or 4 months (limbic brain areas), or remained significantly elevated until 6 months (thalamus). In contrast, in all investigated brain areas, except cerebellum and pons/medulla, GFAP was increased from day 2, reaching maximum levels at day 28 in most limbic structures and remained significantly elevated at the same high level (15 fold increase) in amygdala, or somewhat lower levels in other affected regions (2-7 fold), but not in the thalamus. In all brain areas with 45Ca accumulation, GFAP was increased and the peak responses were highly correlated. Thus, both indices are useful quantitative biochemical markers of acute or subchronic neurotoxicity.

The effects of reduced perfusion and reperfusion on c-fos and HSP-72 protein immunohistochemistry in gestational day 21 rat brains

Metabolic stressors such as hyperthermia, seizures and ischemic hypoxia result in the induction of c-fos and heat-shock proteins (HSP) in affected brain cells of the adult rodent, especially within the hippocampal region, which normally has high metabolic demands. Here we ligated the uterine vessels of gestational day (GD) 21 rat pups to produce ischemic hypoxia. We confirmed that HSP-72 protein, as previously reported, was activated in the perinatal rat pup, especially in the hippocampal CA3 region. However, the capability of hippocampal cells to produce c-fos protein following drug-induced seizures has been reported to develop only after postnatal day 13. Here, ischemic hypoxia caused CA1 hippocampal cells to produce immunohistochemically detectable c-fos protein in GD-21 rats. These results seem to contradict the previous reports of no c-fos induction in rats this young by demonstrating a functional c-fos translational mechanism by GD-21. However, seizure vs ischemic hypoxia-induced c-fos expression may involve several different pre-translational pathways. A delayed development of a receptor, second messenger, or genomic element for regulating c-fos transcription remain as possible explanations for the late maturity of responsivity to seizures.