Increased release of excitatory amino acids in rat locus coeruleus in κ-opioid agonist dependent rats precipitated by nor-binaltorphimine

Extracellular fluid levels of glutamate and aspartate in the locus coeruleus (LC) during nor-binaltorphimine (nor-BNI)-precipitated withdrawal from butorphanol, (5α,7α,8β)-(+)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro [4,5] dec-8-yl]-benzeneacetamide (U-69,593), or morphine were measured in rats. When the microdialysis probe was located in the core of the LC, increases in glutamate and aspartate were noted after nor-BNI (48 nmol/50 μl, LC)-precipitated withdrawal in rats that had been intracerebroventricularly infused with butorphanol (26 nmol/l μl/h) or U-69,593 (26 nmol/10 μl/h) for 3 days. The glutamate and aspartate levels in the LC markedly increased in the butorphanol- or U-69,593-dependent rats within 60 min following administration of nor-BNI. However, there was no significant increase in levels of glutamate, and only a slight increase in levels of aspartate, after nor-BNI treatment of the morphine (26 nmol/1 μl/h)-infused rats. Behavioral signs of withdrawal (teeth-chattering, wet-dog shakes, etc.) were observed following nor-BNI challenge in the butorphanol- or U-69,593-infused rats, with only minimal signs in the morphine-infused rats, and none in the saline-infused controls. These results directly suggest that κ-opioid receptors and excitatory amino acids within the LC mediate withdrawal in animals dependent on butorphanol or U-69,593, but not on morphine. © 1997 Elsevier Science B.V. All rights reserved.     

Electrophysiological changes accompanying DSP-4 lesions of rat locus coeruleus neurons

The electrophysiological characteristics of intracellularly recorded locus coeruleus (LC) neurons in brain stem slices from DSP-4 treated animals have been compared to those from untreated controls. LC neurons from DSP-4 treated animals had action potentials and Ca²⁺ spikes (elicited in the presence of TTX) of significantly reduced duration compared to controls. These observations suggest that chemical axotomy with DSP-4 reduces Ca²⁺ conductance in neurons of the locus coeruleus.     

High potassium-induced glutamate release in the cochlea: in vivo microdialysis study combined with on-line enzyme fluorometric detection of glutamate

The time course of changes in perilymphatic glutamate release and their Ca²⁺-dependency were studied in the guinea pig cochlea during high K⁺-evoked depolarization. The glutamate concentration was analyzed continuously by an enzyme-linked fluorometric assay combined with microdialysis. Two peaks of glutamate increase were found in response to perfusion for 10 min. In the absence of Ca²⁺, the first peak was diminished, whereas the inhibition of the second peak was minimal.     

A new type of Ca channel blocker, NC-1100, inhibits the low- and high-threshold Ca currents in the rat CNS neurons

The effect of a new type of organic Ca²⁺ channel blocker, NC-1100 [(±)-1-(3,4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl)ethanol dihydrochloride], on both low- and high-threshold Ca²⁺ currents was studied in the whole-cell mode of the pyramidal neurons freshly dissociated from rat hippocampal CA1 region under voltage-clamp condition. The NC-1100 reversibly reduced the high-threshold Ca²⁺ current (HVAI_Ca) in a concentration-dependent manner without affecting the current-voltage relationship. The values of half-inhibition (IC₅₀) were 1.3 × 10⁻⁵ and 9.1 × 10⁻⁶M in external solution containing 10 and 2.5 mM Ca²⁺, respectively. The NC-1100 also decreased the low-threshold Ca²⁺ current (LVAI_Ca) in a concentration-dependent manner. The inhibitory potency was augmented by increasing the stimulation frequency and / or decreasing the extracellular Ca²⁺ concentration to a physiological range (2.5 mM). The IC₅₀ value decreased to 7.7 × 10⁻⁷M in external solution containing 2.5 mM Ca²⁺ at a stimulation frequency of 1 Hz. The NC-1100 delayed the reactivation of LVA Ca²⁺ channel and enhanced voltage-dependently the steady-state inactivation, suggesting that this drug bound not only the resting LVA Ca²⁺ channel but also the inactivated one.     

Measured increase in intracellular Ca during stimulated release of endogenous glutamate from human cerebrocortical synaptosomes

Presynaptic terminals (synaptosomes) prepared from guinea pig and rat cerebral cortex release endogenous glutamate in a Ca²⁺-dependent manner in response to membrane depolarisation. In the present study, synaptosomes were prepared from human cerebral cortex removed in association with temporal lobe resections in epileptic patients. The cytosolic free Ca²⁺ concentration increased from 474±66 before to 649±89 nM after 2 min depolarisation. The basal level of free cytosolic Ca²⁺ is higher and the increase in response to depolarisation is more pronounced in human synaptosomes than observed in animal experiments. The Ca²⁺-dependent glutamate release, estimated as the difference between total — and the Ca²⁺-independent glutamate release, increased from 0 to 5.4±1.9 nmol/mg protein. The released amount of glutamate is larger than reported in animal models. These results demonstrate that membrane depolarisation of synaptosomes from human brain evokes a rapid rise in cytosolic free Ca²⁺ and a more prolonged rise in synaptic, Ca²⁺-dependent glutamate release.     

Potentiating effects of L-type Ca2+ channel blockers on pentobarbital-induced hypnosis are influenced by serotonergic system

Summary. In order to elucidate the mechanism(s) behind the interactions between barbiturates and Ca²⁺ antagonists, the effects of three structurally diverse types of Ca²⁺ antagonists combined or not with 5-HT on pentobarbital-induced hypnosis in mice were investigated. The results showed that dihydropyridine derivative nifedipine (10.0 and 20.0 mg/kg, p.o.) and other types of Ca²⁺ antagonist, verapamil (5.0 and 10.0 mg/kg, p.o.) and diltiazem (2.5, 5.0 and 10.0 mg/kg, p.o.) increased both the sleeping time in hypnotic dosage of pentobarbital (45 mg/kg, i.p.) treated mice and the rate of sleep onset in the sub-hypnotic dosage of pentobarbital (28 mg/kg, i.p.) treated mice in a dose-dependent manner, respectively, and these effects were significantly augmented by 5-hydroxytryptophan (5-HTP), the immediate precursor of 5-hydroxytryptamine (5-HT). Pretreatment with p-chlorophenylalanine (PCPA, 300 mg/kg, s.c.), an inhibitor of tryptophan hydroxylase, significantly decreased pentobarbital-induced sleeping time and nifedipine (10.0 mg/kg, p.o.), verapamil (5.0 mg/kg, p.o.) and diltiazem (2.5 mg/kg, p.o.) abolished this effect. From these results, it should be presumed that the augmentative effect of L-type Ca²⁺ channel blockers on pentobarbital-induced sleep may be influenced by serotonergic system.     

Block of P-type Ca channels in freshly dissociated rat cerebellar Purkinje neurons by diltiazem and verapamil

We investigated the effects of organic Ca²⁺ channel blockers, diltiazem and verapamil, on the high voltage-activated P-type Ca²⁺ channels in freshly isolated rat Purkinje neurons. Both diltiazem and verapamil blocked P-type Ca²⁺ channel current without any change in the current-voltage relation. The block was concentration-dependent. In the presence of these agents, the inactivation curve was shifted to hyperpolarizing potentials. The characteristics of block of P-type Ca²⁺ channels by diltiazem and verapamil are similar to that of L-type Ca²⁺ channels. These results indicate that both benzothiazepine and phenylalkylamine react with P-type Ca²⁺ channels and suggest that some structural features common to which operate in both L-type and P-type Ca²⁺ channels may be involved in drug binding to these channels.     

The contribution of voltage-gated Ca currents to K channel activation during ovine adrenal chromaffin cell development

Prior to the development of adrenal innervation, the adrenal medulla is capable of responding to low blood oxygen directly. However, this response is lost once adrenal innervation is established. Previous work by our group has outlined mechanisms involved in this direct hypoxic response and the means by which innervation causes the loss of the direct hypoxic response in the ovine adrenal. The current study further investigates mechanisms which may underlie the developmental loss of the direct hypoxic response by concentrating on two aspects of cell function which regulate catecholamine secretion: the contribution of different types of Ca²⁺ channels to the total Ca²⁺ current and the contribution of each Ca²⁺ channel type to K⁺ channel activation. We identified that Ca²⁺ current size at −40 to −10 mV is increased in amplitude in fetal chromaffin cells. This is not due to the increased prevalence or size of T-type Ca²⁺ currents present at these voltages. The relative contribution of L-, N- or P/Q-type Ca²⁺ channels to total Ca²⁺ current and to activation of the K⁺ current is unchanged during chromaffin cell development, however K⁺ current density increases with age. Our results indicate that there is a developmental shift in relative expression of T-type, but not L-, N- or P/Q-type, Ca²⁺ channels in ovine chromaffin cells. The increased K⁺ current density in adult cells may result in an altered response to an equal stimulus, while larger Ca²⁺ current at negative voltages in fetal cells may facilitate Ca²⁺ entry and catecholamine secretion in response to small depolarisations such as those induced by hypoxia.     

Neuroprotective effect of NS-7, a novel Na+ and Ca2+ channel blocker,in a focal ischemic model in the rat

NS-7 is a novel, voltage-dependent Na(+) and Ca(2+) channel blocker. This study evaluated the in vivo neuroprotective effect of NS-7 in a rat transient focal ischemic model when administered during occlusion. Left middle cerebral artery occlusion was induced in adult male Sprague-Dawley rats for 120 min using an intraluminal thread method. The rats received a single intravenous injection of NS-7 or saline (control group) just after the onset of ischemia, and at 30, 60 and 120 min after ischemia. Their brains were removed after 48 h reperfusion, sectioned, and stained with hematoxylin and eosin. Animals were evaluated by neurological examination at 120 min ischemia and 48 h reperfusion. Infarcted cortex and striatum were measured quantitatively and infarction volumes were calculated. Cortical infarction volumes were 128+/-74 (NS-7) and 214+/-64 mm(3) (control) immediately after the ischemia group, 155+/-48 (NS-7) and 225+/-12 mm(3) (control) after the 30 min group, 160+/-54 (NS-7) and 225+/-48 mm(3) (control) after the 60 min group, and 176+/-43 (NS-7) and 223+/-38 mm(3) (control) after the 120 min group. Cortices in NS-7-treated groups were significantly less infarcted than in control groups at all treatment times. There was no significant difference in the striatal infarction volume between the treatment and control groups. Neurological examination showed that hemiparesis and abnormal posture of the NS-7 groups were significantly more improved at 48 h reperfusion than those of the control groups without posture examination in the 120 min group. These observations suggest that NS-7 may be a new potential therapeutic agent for the acute phase of cerebral infarction.     

Homeostatic compensation maintains Ca2+ signaling functions in Purkinje neurons in the leaner mutant mouse

Several human neurological disorders have been associated with mutations in the gene coding for the alpha1 subunit of the P/Q type voltage-gated calcium channel (alpha1A/Ca(v)2.1). Mutations in this gene also occur in a number of neurologically affected mouse strains, including leaner (tg(la)/tg(la)). Because the P-type calcium current is very prominent in cerebellar Purkinje neurons, these cells from mice with alpha1 subunit mutations make excellent models for the investigation of the functional consequences of native mutations in a voltage-gated calcium channel of mammalian central nervous system. In this review, we describe the impact of altered channel function on cellular calcium homeostasis and signaling. Remarkably, calcium buffering functions of the endoplasmic reticulum and calcium-binding proteins appear to be regulated in order to compensate for altered calcium influx through the mutant channels. Although this compensation may serve to maintain calcium signaling functions, such as calcium-induced calcium release, it remains uncertain whether such compensation alleviates or contributes to the behavioral phenotype.     

Glutamate selectively increases the high-threshold Ca channel current in sensory and hippocampal neurons

Previous studies resulted in conflicting conclusions that glutamate application either decreases or increases the activity of Ca²⁺ channels in hippocampal neurons. We studied whole-cell Ca²⁺ currents (I_Ca) in chick dorsal root ganglion neurons and rat hippocampal cells. For both cell types glutamate (1–30 μM) increased high-threshold Ca²⁺ current. It was independent of the charge carriers, Ca²⁺ or Ba²⁺. Low-threshold Ca²⁺ channel current and the fast sodium current were not changed with glutamate application. The effect developed within 1–2 min and then further facilitated after washout of the agonist. A second application of glutamate produced no additional increase in _ICa. No changes in the time-course of whole-cell currents were observed, suggesting that glutamate recruits ‘sleepy’ Ca²⁺ channels. Whatever its mechanism, overlasting increase of I_Ca by glutamate may be important in neuronal plasticity.     

Involvement of the glutamate transporter and the sodium–calcium exchanger in the hypoxia-induced increase in intracellular Ca in rat hippocampal slices

Hippocampal slices prepared from adult rats were loaded with fura-2 and the intracellular free Ca²⁺ concentration ([Ca²⁺]_i) in the CA1 pyramidal cell layer was measured. Hypoxia (oxygen–glucose deprivation) elicited a gradual increase in [Ca²⁺]_i in normal Krebs solution. At high extracellular sodium concentrations ([Na⁺]_o), the hypoxia-induced response was attenuated. In contrast, hypoxia in low [Na⁺]_o elicited a significantly enhanced response. This exaggerated response to hypoxia at a low [Na⁺]_o was reversed by pre-incubation of the slice at a low [Na⁺]_o prior to the hypoxic insult. The attenuation of the response to hypoxia by high [Na⁺]_o was no longer observed in the presence of antagonist to glutamate transporter. However, antagonist to Na⁺–Ca²⁺ exchanger only slightly influenced the effects of high [Na⁺]_o. These observations suggest that disturbance of the transmembrane gradient of Na⁺ concentrations is an important factor in hypoxia-induced neuronal damage and corroborates the participation of the glutamate transporter in hypoxia-induced neuronal injury. In addition, the excess release of glutamate during hypoxia is due to a reversal of Na⁺-dependent glutamate transporter rather than an exocytotic process.     

Effect of nicardipine, a Ca channel blocker, on pyruvate dehydrogenase activity and energy metabolites during cerebral ischemia and reperfusion in gerbil brain

The purpose of this study was to determine if nicardipine, a calcium ion channel blocker, affects pyruvate dehydrogenase (PDH) activity and improves energy metabolism during cerebral ischemia and reperfusion. Cerebral ischemia was induced, using the bilateral carotid artery occlusion method, for 60 min followed by reperfusion up to 120 min in gerbils. Nicardipine (1 mg/kg) or saline (vehicle-treated) was given to gerbils 30 min prior to the occlusion of the common carotid arteries. PDH activity and metabolites (ATP, PCr, and lactate) were measured in cortex prior to ischemia, immediately following ischemia, and after each reperfusion period. After 60 min ischemia, PDH activity increased in both groups, and was significantly higher in the nicardipine-treated group. After 20 min reperfusion, PDH activity in the nicardipine-treated group recovered to control levels, whereas, the PDH activity in the vehicle-treated group remained elevated, and was higher than the nicardipine-treated animals. At 60 and 120 min reperfusion, the activities in the vehicle-treated group were significantly below control levels, there were no differences, however, between the two groups. ATP and PCr concentrations were markedly depleted immediately after ischemia in both groups. ATP levels at 20 min reperfusion and PCr levels at 60 min reperfusion were significantly higher in the nicardipine-treated group. Lactate concentrations in both groups increased 7–8 fold, similarly, immediately after ischemia. During reperfusion, the lactate remained elevated in both groups, though the levels in the nicardipine-treated group were lower than those in the vehicle-treated group, but not significantly. Nicardipine treatment normalized PDH activity quickly and improved energy metabolism after reperfusion.     

Prostaglandins block a Ca-dependent slow spike afterhyperpolarization independent of effects on Ca influx in visceral afferent neurons

The blockade of a slow Ca2+-activated K+-dependent afterhyperpolarization (AHPs) in rabbit visceral sensory neurons by the prostaglandins, PGE1 and PGD2, was investigated to determine whether the blockade was indirectly due to a reduction in Ca2+ influx. The prostaglandins (PGs) could block the AHPs in the absence of any change in Ca2+-dependent spikes elicited in the presence of tetrodotoxin and tetraethylammonium bromide. A PG-induced decrease in Ca2+-dependent spike width observed in some neurons was temporally dissociated from the PG-induced block of the AHPs. In addition, a slow afterhyperpolarization produced by the application of the Ca2+ ionophore, A23187, was blocked by the PGs. It is concluded that a reduction in Ca2+ influx is not responsible for the PG-induced blockade of the AHPs.     

Effect of the removal of extracellular Ca on the response of cytosolic concentrations of Ca to ouabain in carotid body glomus cells of adult rabbits

Effect of the removal of extracellular Ca²⁺ on the response of cytosolic concentrations of Ca²⁺ ([Ca²⁺]_i) to ouabain, an Na⁺/K⁺ exchanger antagonist, was examined in clusters of cultured carotid body glomus cells of adult rabbits using fura-2AM and microfluorometry. Application of ouabain (10 mM) induced a sustained increase in [Ca²⁺]_i (mean±S.E.M.; 38±5% increase, n=16) in 55% of tested cells (n=29). The ouabain-induced [Ca²⁺]_i increase was abolished by the removal of extracellular Na⁺. D600 (50 μM), an L-type voltage-gated Ca²⁺ channel antagonist, inhibited the [Ca²⁺]_i increase by 57±7% (n=4). Removal of extracellular Ca²⁺ eliminated the [Ca²⁺]_i increase, but subsequent washing out of ouabain in Ca²⁺-free solution produced a rise in [Ca²⁺]_i (62±8% increase, n=6, P<0.05), referred to as a [Ca²⁺]_i rise after Ca²⁺-free/ouabain. The magnitude of the [Ca²⁺]_i rise was larger than that of ouabain-induced [Ca²⁺]_i increase. D600 (5 μM) inhibited the [Ca²⁺]_i rise after Ca²⁺-free/ouabain by 83±10% (n=4). These results suggest that ouabain-induced [Ca²⁺]_i increase was due to Ca²⁺ entry involving L-type Ca²⁺ channels which could be activated by cytosolic Na⁺ accumulation. Ca²⁺ removal might modify the [Ca²⁺]_i response, resulting in the occurrence of a rise in [Ca²⁺]_i after Ca²⁺-free/ouabain which mostly involved L-type Ca²⁺ channels.     

Apamin, a blocker of the calcium-activated potassium channel, induces neurodegeneration of Purkinje cells exclusively

Following acute intracerebroventricular injections of 1 ng of apamin and chronic apamin infusion (0.4 ng/μl, 0.5 μl/h, 14 days), the rat brains exhibited bilateral damage only in the cerebellum. The argyrophilic cells were Purkinje cells in copula pyramis, flocculus, paraflocculus, and paramedian lobules. These data demonstrate that the inactivation of small conductance Ca²⁺-activated K⁺ channels by apamin induces a non-limbic neurodegeneration.     

Cerebroprotective action of a Na/Ca channel blocker NS-7: I. Effect on the cerebral infarction and edema at the acute stage of permanent middle cerebral artery occlusion in rats

The effect of a novel Na⁺/Ca²⁺ channel blocker NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride] on the cerebral infarction, edema and brain energy metabolism was investigated in rats after permanent middle cerebral artery occlusion (MCAO). The infarction and brain water content were evaluated at 48 h and 24 h after MCAO, respectively. A single bolus injection of NS-7 (0.03125–0.25 mg/kg) immediately after MCAO produced a dose-dependent reduction in the infarct volume as well as edema both in the cerebral cortex and striatum. Glycerol (4 g/kg) also decreased water content both in the occluded and non-occluded brain, but it did not reduce the size of cerebral infarction. Unlike glycerol, NS-7 did not change the water content in non-occluded brain. Moreover, a significant protective action was still observed even when NS-7 was injected once at 12 h after occlusion. In addition, NS-7 significantly reversed the decrease in tissue ATP content observed at 3 h but not at 0.5 h after MCAO. These findings suggest that a Na⁺/Ca²⁺ channel blocker NS-7 protects cerebral tissues against ischemic insults by improving the disturbance of cerebral energy metabolism and suppressing the cerebral edema.     

Cerebroprotective action of a Na/Ca channel blocker NS-7: II. Effect on the cerebral infarction, behavioral and cognitive impairments at the chronic stage of permanent middle cerebral artery occlusion in rats

We have previously shown that NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride] reduces the size of cerebral infarction measured by 2,3,5-triphenyltetrazolium chloride staining at 48 h after permanent middle cerebral artery occlusion (MCAO) in rats. To determine whether NS-7 improves the pathological and behavioral changes at the chronic stage of MCAO, the effect of this compound on the cerebral infarction as well as the neurological and cognitive impairments was investigated 7 days after MCAO. Single or five daily injections of NS-7 (0.125–0.5 mg/kg, i.v.) significantly reduced the infarct volume and improved the neuronal dysfunction including the hind leg paralysis, walking disability and motor incoordination, and the deficit of passive avoidance task, although the neuroprotective efficacy was not different among these dosing regimens. On the other hand, the effects of single versus repeated injections of NS-7 at 0.1 or 0.2 mg/kg on the neurological symptoms were compared at 4 weeks after MCAO. At a lower dose, repeated but not single injection of NS-7 significantly improved the neurological symptoms, although the single injection was effective at a higher dose. From these findings, it is suggested that NS-7 reverses the behavioral and cognitive dysfunction observed at the chronic stage of cerebral ischemia by suppressing the cerebral infarction.     

Effects of Hg and CH3Hg on Ca fluxes in rat brain microsomes

A permanent increase in cytosolic Ca²⁺ levels seems to be associated with various pathological situations which may result in cell death. Hg²⁺ and CH₃Hg⁺ are potent neurotoxic agents, but the precise molecular mechanism(s) underlying their effects are not sufficiently understood. In the present study we investigated the potential role of Ca²⁺-ATPase located in the endoplasmic reticulum as a molecular target for mercury. Hg²⁺ and CH₃Hg⁺ inhibited Ca²⁺-ATPase and Ca²⁺ uptake by brain microsomes with similar potencies. However, the inhibitory potency of Hg²⁺ was higher than that of CH3Hg+, probably reflecting differences in the affinity for the sulfhydryl groups of these compounds. Passive or unidirectional Ca²⁺ efflux (measured in the absences of Ca²⁺-ATPase ligands) was increased significantly by CH₃Hg⁺ and Hg²⁺. Again, the potency of Hg²⁺ was higher than that of CH₃Hg⁺. Blockers of Ca²⁺ channels (ruthenium red, procaine, heparin) did not affect the increase in passive Ca t+ efflux induced by mercury compounds, possibly indicating that Ca²⁺ release occurs through Ca²⁺-ATPase. Addition of physiological concentrations of glutathione (GSH) simultaneously with mercury abolished the inhibitory effects of both forms of Hg on Ca Z+-transport. However, if the enzyme was first inhibited with Hg²⁺ or CH₃Hg⁺ and subsequently treated with GSH, the reversal of inhibition was about 50%, suggesting that part of the cysteinyl residues involved in the inhibitory actions of mercury in Ca t+-transport bind to mercury with an extremely high affinity.     

Effect of dantrolene on KCl- or NMDA-induced intracellular Ca2+ changes and spontaneous Ca2+ oscillation in cultured rat frontal cortical neurons

Summary Dantrolene has been known to affect intracellular Ca²⁺ concentration ([Ca²⁺]_i) by inhibiting Ca²⁺ release from intracellular stores in cultured neurons. We were interested in examining this property of dantrolene in influencing the [Ca²⁺]_i affected by the NMDA receptor ligands, KCl, L-type Ca²⁺ channel blocker nifedipine, and two other intracellular Ca²⁺-mobilizing agents caffeine and bradykinin. Effect of dantrolene on the spontaneous oscillation of [Ca²⁺]_i was also examined. Dantrolene in M concentrations dose-dependently inhibited the increase in [Ca²⁺]_i elicited by NMDA and KCl. AP-5, MK-801 (NMDA antagonists), and nifedipine respectively reduced the NMDA and KCl-induced increase in [Ca²⁺]_i. Dantrolene, added to the buffer solution together with the antagonists or nifedipine, caused a further reduction in [Ca²⁺]_i to a degree similar to that seen with dantrolene alone inhibiting the increase in [Ca₂₊]_i caused by NMDA or KCl. At 30 M, dantrolene partially inhibited caffeine-induced increase in [Ca²⁺]_i whereas it has no effect on the bradykinin-induced change in [Ca²⁺]_i. The spontaneous oscillation of [Ca²⁺]_i in frontal cortical neurons was reduced both in amplitude and in base line concentration in the presence of 10 M dantrolene. Our results indicate that dantrolene's mobilizing effects on intracellular Ca²⁺ stores operate independently from the influxed Ca²⁺ and that a component of the apparent increase in [Ca²⁺]_i elicited by NMDA or KCl represents a dantrolene-sensitive Ca₂₊ release from intracellular stores. Results also suggest that dantrolene does not affect the IP₃-gated release of intracellular Ca²⁺ and that the spontaneous Ca²⁺ oscillation is, at least partially, under the control of Ca²⁺ mobilization from internal stores.Abbreviations AP-5 (±)-2-amino-5-phosphonopentanoic acid - AMPA amino-3-hydroxy-5-methyl-isoxazole-4-propionate - BSS balanced salt solution - CNS central nervous system - CICR Ca²⁺-induced Ca²⁺ release - DCKA 5,7-dichlorokynurenate - DNasel deoxyribonuclease I - DMEM Dulbecco's Modified Eagle's Medium - EGTA ethylene glycol-bis(-aminoethyl ether)N,N,N,N,-tetraacetic acid - FCS fetal calf serum - fura-2-AM 1-(2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy-2-ethane-N,N,N,N-te-traacetic acid, pentaacetoxymethyl ester - HEPES N-[2-hydroxyethyl] piperazine-N-[2-ethanesulfonic acid] - [Ca ²⁺] _i intracellular free Ca²⁺ concentration - LTP long-term potantiation - MK-801 (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,b]-cyclohepten-5,10-imine hydrogen maleate - NMDA N-methyl-D-aspartate