Modulation of epileptiform activity by metabotropic glutamate receptors in immature rat neocortex

1995 ◽  
Vol 73 (1) ◽  
pp. 205-217 ◽  
Author(s):  
J. P. Burke ◽  
J. J. Hablitz
Keyword(s):  
Metabotropic Glutamate Receptors ◽  
Epileptiform Activity ◽  
Brain Slices ◽  
Small Population ◽  
Cortical Layers ◽  
Metabotropic Glutamate ◽  
Epileptiform Discharges ◽  
Bath Application ◽  
Rat Neocortex

1. Intracellular and extracellular recordings were obtained from neocortical brain slices of immature rats (postnatal days 9-16) maintained in vitro. Spontaneous and evoked epileptiform discharges (termed paroxysmal depolarizing shifts or PDSs) were recorded from upper cortical laminae (layers II-III) after exposure to the gamma-aminobuturic acid-A receptor antagonist, bicuculline methiodide. The effects of mGluR activation on PDS duration, spontaneous frequency, and threshold for evoking a PDS were determined. Putative mGluR agonists and antagonists also were tested. 2. Bath application of the mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (ACPD, 50-200 mM) elicited biphasic, time-dependent effects on evoked and spontaneous epileptiform discharges. At times early in drug wash-in, ACPD increased PDS duration and spontaneous PDS frequency. In > 60% of the slices, the spontaneous PDSs became regular. Subsequently, ACPD reduced PDS duration and increased the stimulus threshold for evoking a PDS, suggesting that the actions of ACPD were dose dependent. 3. Investigation of the concentration-dependence revealed that sustained low ACPD concentrations (5 microM) elicited only facilitatory actions, whereas higher concentrations were suppressive. These observations suggest the activation of different mGluR subtypes, which may be localized differentially at pre- and postsynaptic sites. 4. Bath application of the mGluR agonists, L-2-amino-4-phosphonobutyrate or (2S,3S,4S)-alpha-(carboxycyclopropyl) glycine, produced only suppressive effects on epileptiform activity in the immature neocortex. L-2-amino-3-phosphonopropionate was an ineffective antagonist of ACPD-mediated modulation of epileptiform activity. Application of the putative antagonist, alpha-methyl-4-carboxyphenylglycine (MCPG), failed to antagonize the biphasic actions of ACPD. MCPG had suppressive effects of epileptiform activity, suggesting activation of mGluRs by endogenous agonists. 5. Simultaneous recordings from deeper and upper cortical layers indicated that the initial negativity of both evoked and spontaneous PDSs began in deeper cortical layers under control conditions and in the presence of ACPD. Intracellular records from neurons in deeper layers displayed two distinct patterns of activity during mGluR activation. Most deep layer neurons received a barrage of excitatory postsynaptic potentials before a spontaneous PDS during ACPD application. A small population of neurons depolarized and entered a tonically firing mode, which was interrupted by spontaneous PDSs. Different neuronal populations, possible expressing different mGluR subtypes or coupling mechanisms, may play integral roles in the induction and generation of epileptiform activities. 6. Thapsigargin or dantrolene, agents thought to block release of Ca2+ from intracellular stores, were both applied for periods < or = min.(ABSTRACT TRUNCATED AT 400 WORDS)

Excitatory synaptic involvement in epileptiform bursting in the immature rat neocortex

1991 ◽  
Vol 66 (6) ◽  
pp. 1894-1901 ◽  
Author(s):  
W. L. Lee ◽  
J. J. Hablitz
Keyword(s):  
Voltage Clamp ◽  
Excitatory Amino Acid ◽  
Epileptiform Activity ◽  
Brain Slices ◽  
Synaptic Activity ◽  
Epileptiform Discharges ◽  
Bath Application ◽  
Gabaa Receptor Antagonist ◽  
Rat Neocortex

1. Neocortical brain slices were prepared from animals 8-15 days of age and maintained in vitro. Intracellular recordings were obtained from neurons in cortical layers 2-3. The role of synaptic activity and excitatory amino acid receptors in generation of picrotoxin-induced ictal-like epileptiform activity in the immature neocortex was investigated. D-2-amino-5-phosphonovaleric acid (D-APV) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were used as selective antagonists of N-methyl-D-aspartate (NMDA) and non-NMDA receptors, respectively. 2. Ictal-like epileptiform discharges were induced by bath application of the GABAA-receptor antagonist picrotoxin. Paroxysmal discharges, 7-25 s in duration, occurred spontaneously or could be evoked by electrical stimulation. These events consisted of an initial paroxysmal depolarizing shift (PDS) followed by a long-duration depolarization (LLD) with superimposed late PDSs. 3. The amplitudes of the initial PDS, LLD, and late PDSs were linearly dependent on membrane potential, increasing with hyperpolarization and diminishing on depolarization. All responses reversed polarity near 0 mV. Under voltage-clamp conditions, both transient and sustained currents were observed, coincident with PDSs and the LLD, respectively. The duration of the ictal-like events was similar under current- and voltage-clamp conditions, suggesting activation of intrinsic membrane currents did not significantly prolong epileptiform discharges. 4. Bath application of D-APV (20 microM) decreased the amplitude and duration of both the initial PDS and LLD without affecting the time-to-onset of epileptiform activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of metabotropic glutamate receptors induces long-term depression of GABAergic inhibition in hippocampus

1993 ◽  
Vol 69 (3) ◽  
pp. 1000-1004 ◽  
Author(s):  
Y. B. Liu ◽  
J. F. Disterhoft ◽  
N. T. Slater
Keyword(s):  
Glutamate Receptors ◽  
Metabotropic Glutamate Receptors ◽  
Hippocampal Slices ◽  
Input Resistance ◽  
Nmda Receptor Antagonist ◽  
Metabotropic Glutamate ◽  
Epileptiform Discharges ◽  
Bath Application

1. The long-term enhancement of synaptic excitability in CA1 hippocampal pyramidal neurons produced by activation of metabotropic glutamate receptors (mGluRs) was studied in rabbit hippocampal slices in vitro. 2. Bath application of the mGluR agonist (1S,3R)-1-aminocyclopentane-1,3- dicarboxylic acid (1S,3R-ACPD) (5-20 microM) for 20 min produced a reversible depolarization of membrane potentiatil, blockade of spike accommodation, and increase in input resistance of CA1 neurons. However, a long-lasting increase in synaptic excitability was observed: single stimuli applied to the Schaffer collateral commisural fiber pathway evoked epileptiform discharges in the presence of 1S,3R-ACPD and after the washout of 1S,3R-ACPD, persistent paroxysmal depolarization shifts (PDSs) were evoked by afferent stimulation. A long-lasting enhancement of synaptic excitability was also observed in the presence of the NMDA receptor antagonist D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5), which blocked the stimulation-evoked PDS and associated afterdischarges. 3. When biphasic, monosynaptically evoked inhibitory post-synaptic potentials (IPSPs) were recorded in the presence of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10–15 microM) and D-AP5 (20 microM), the bath application of 1S,3R-ACPD produced a significant reduction (approximately 50%) of both components of the IPSP, which persisted after the washout of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of Synaptic Metabotropic Glutamate Receptors in Epileptiform Discharges in Hippocampal Slices

2002 ◽  
Vol 88 (4) ◽  
pp. 1625-1633 ◽  
Author(s):  
Angela C. Lee ◽  
Robert K. S. Wong ◽  
Shih-Chieh Chuang ◽  
Hee-Sup Shin ◽  
Riccardo Bianchi
Keyword(s):  
Metabotropic Glutamate Receptors ◽  
Metabotropic Glutamate Receptor ◽  
Hippocampal Slices ◽  
Brain Slices ◽  
Wild Type ◽  
Metabotropic Glutamate ◽  
Epileptiform Discharges ◽  
Group I ◽  
Group I Mglurs

Application of group I metabotropic glutamate receptor (mGluR) agonists elicits seizure discharges in vivo and prolonged ictal-like activity in in vitro brain slices. In this study we examined 1) if group I mGluRs are activated by synaptically released glutamate during epileptiform discharges induced by convulsants in hippocampal slices and, if so, 2) whether the synaptically activated mGluRs contribute to the pattern of the epileptiform discharges. The GABAAreceptor antagonist bicuculline (50 μM) was applied to induce short synchronized bursts of ∼250 ms in mouse hippocampal slices. Addition of 4-aminopyridine (4-AP; 100 μM) prolonged these bursts to 0.7–2 s. The mGluR1 antagonist ( S)-(+)-α-amino-4-carboxy-2-methylbenzeneacetic acid (LY 367385; 25–100 μM) and the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP; 10–50 μM), applied separately, significantly reduced the duration of the synchronized discharges. The effects of these antagonists were additive when applied together, suggesting that mGluR1 and mGluR5 exert independent actions on the epileptiform bursts. In phospholipase C β1 (PLCβ1) knockout mice, bicuculline and 4-AP elicited prolonged synchronized discharges of comparable duration as those observed in slices from wild-type littermates. Furthermore, mGluR1 and mGluR5 antagonists reduced the duration of the epileptiform discharges to the same extent as they did in the wild-type preparations. The results suggest that mGluR1 and mGluR5 are activated synaptically during prolonged epileptiform discharges induced by bicuculline and 4-AP. Synaptic activation of these receptors extended the duration of synchronized discharges. In addition, the data indicate that the synaptic effects of the group I mGluRs on the duration of epileptiform discharges were mediated by a PLCβ1-independent mechanism.

scholarly journals Epileptiform Discharges With In-Vivo-Like Features in Slices of Rat Piriform Cortex With Longitudinal Association Fibers

2001 ◽  
Vol 86 (5) ◽  
pp. 2445-2460 ◽  
Author(s):  
Rezan Demir ◽  
Lewis B. Haberly ◽  
Meyer B. Jackson
Keyword(s):  
Seizure Activity ◽  
Epileptiform Activity ◽  
Piriform Cortex ◽  
Brain Slices ◽  
Epileptiform Discharges ◽  
Local Circuitry ◽  
Association Fibers ◽  
Discharge Propagation

Brain slices serve as useful models for the investigation of epilepsy. However, the preparation of brain slices disrupts circuitry and severs axons, thus complicating efforts to relate epileptiform activity in vitro to seizure activity in vivo. This issue is relevant to studies in transverse slices of the piriform cortex (PC), the preparation of which disrupts extensive rostrocaudal fiber systems. In these slices, epileptiform discharges propagate slowly and in a wavelike manner, whereas such discharges in vivo propagate more rapidly and jump abruptly between layers. The objective of the present study was to identify fiber systems responsible for these differences. PC slices were prepared by cutting along three different nearly orthogonal planes (transverse, parasagittal, and longitudinal), and epileptiform discharges were imaged with a voltage-sensitive fluorescent dye. Interictal-like epileptiform activity was enabled by either a kindling-like induction process or disinhibition with bicuculline. The pattern of discharge onset was very similar in slices cut in different planes. As described previously in transverse PC slices, discharges were initiated in the endopiriform nucleus (En) and adjoining regions in a two-stage process, starting with low-amplitude “plateau activity” at one site and leading to an accelerating depolarization and discharge onset at another nearby site. The similar pattern of onset in slices of various orientations indicates that the local circuitry and neuronal properties in and around the En, rather than long-range fibers, assume dominant roles in the initiation of epileptiform activity. Subtle variations in the onset site indicate that interneurons can fine tune the site of discharge onset. In contrast to the mode of onset, discharge propagation showed striking variations. In longitudinal slices, where rostrocaudal association fibers are best preserved, discharge propagation resembled in vivo seizure activity in the following respects: propagation was as rapid as in vivo and about two to three times faster than in other slices; discharges jumped abruptly between the En and PC; and discharges had large amplitudes in superficial layers of the PC. Cuts in longitudinal slices that partially separated the PC from the En eliminated these unique features. These results help clarify why epileptiform activity differs between in vitro and in vivo experiments and suggest that rostrocaudal pyramidal cell association fibers play a major role in the propagation of discharges in the intact brain. The longitudinal PC slice, which best preserves these fibers, is ideally suited for the study their role.

Pattern-Specific Synaptic Mechanisms in a Multifunctional Network. II. Intrinsic Modulation by Metabotropic Glutamate Receptors

2006 ◽  
Vol 95 (3) ◽  
pp. 1334-1344 ◽  
Author(s):  
Steven P. Lieske ◽  
Jan-Marino Ramirez
Keyword(s):  
Glutamate Receptors ◽  
Metabotropic Glutamate Receptors ◽  
Activity Patterns ◽  
Nmda Receptor Antagonist ◽  
Group Iii ◽  
Metabotropic Glutamate ◽  
Respiratory Network ◽  
Bath Application ◽  
A Minor

The in vitro respiratory network contained in the transverse brain stem slice of mice simultaneously generates fast (∼15 min-1) and slow (∼0.5 min-1) rhythmic activities corresponding to fictive eupnea (“normal” breathing) and fictive sighs. We show that these two activity patterns are differentially controlled through the modulatory actions of metabotropic glutamate receptors (mGluRs). Sighs were selectively inhibited by agonists of the group III mGluRs according to a pharmacological profile most consistent with activation of mGluR8. Sighs were also blocked by the supposedly inactive L-isomer of the widely used N-methyl-d-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanoic acid (L-AP5, 5 μM), an effect that was abolished in the presence of group III mGluR antagonists. Excitatory postsynaptic potentials (EPSPs) were recorded in pre-Bötzinger Complex neurons after stimulation of the contralateral ventral respiratory group (VRG); evoked EPSP amplitude was variably reduced after bath application of the group III agonist l-serine- O-phospate (L-SOP), with an average reduction of 15%. Therefore although group III mGluRs do play a role in regulating synapse strength, this seems to be only a minor factor in the regulation of synapses made by midline-crossing axons. Intrinsic modulation of the respiratory central pattern generator by mGluRs appears to be an essential component of the multifunctionality that characterizes this network.

GABAA-mediated inhibition and in vitro epileptogenesis in the human neocortex

1995 ◽  
Vol 73 (2) ◽  
pp. 468-484 ◽  
Author(s):  
M. Avoli ◽  
J. Louvel ◽  
C. Drapeau ◽  
R. Pumain ◽  
I. Kurcewicz
Keyword(s):  
Epileptiform Activity ◽  
Field Potential ◽  
High Strength ◽  
Epileptiform Discharge ◽  
Gamma Aminobutyric Acid ◽  
Epileptiform Discharges ◽  
Bath Application ◽  
Gabaa Receptor Antagonist ◽  
K Concentration

1. We made intracellular and extracellular field potential recordings and ion-selective measurements of extracellular Ca2+ concentration ([Ca2+]o) and extracellular K+ concentration ([K+]o) in human neocortical slices that were obtained in the course of epilepsy surgery. Slices were maintained in vitro at 34-35 degrees C and were perfused with Mg(2+)-free artificial cerebrospinal fluid (ACSF). 2. Spontaneous field potential epileptiform discharges (duration = 2.5-80 s) occurred in most of the slices studied (approximately 60%) after 1.5-2 h of perfusion with Mg(2+)-free ACSF. Intracellular recordings from regular-spiking neocortical neurons showed that epileptiform events consisted of large-amplitude (15-30 mV) depolarizing shifts that were capped by bursts of fast action potentials. A decrease in [Ca2+]o (change in [Ca2+]o = 0.02-0.17 mM, 0.07 +/- 0.046 mM, mean +/- SD, from a baseline of 1.8 mM, n = 10 slices) and an increase in [K+]o (change in [K+]o = 0.5-3.8 mM, 1.6 +/- 1.24 mM, from a baseline of 3.25 mM, n = 10) were associated with each epileptiform discharge. 3. The epileptiform activity induced by Mg(2+)-free ACSF was abolished by bath application of antagonists of the N-methyl-D-aspartate (NMDA) receptor. This procedure also blocked the appearance of spreading depression-like episodes. By contrast, the rate of occurrence of epileptiform discharges was not significantly modified by antagonizing non-NMDA receptors. 4. We also observed spontaneous, rhythmic potentials of positive polarity during perfusion of Mg(2+)-free ACSF; the potentials became hyperpolarizing when the neuron membrane was made less negative than -75 mV with intracellular injection of depolarizing current, and they were decreased or abolished during application of the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline methiodide (BMI). The rate of occurrence and/or the amplitude of these presumably GABAA-mediated events decreased approximately 2 s before the onset of each epileptiform discharge. 5. Application of BMI prolonged the epileptiform discharges while decreasing their rate of occurrence. These changes were also accompanied by an increase in the amplitude of the epileptiform field potential DC shift, whereas the concomitant decreases in [Ca2+]o and increases in [K+]o became more pronounced than in control Mg(2+)-free medium (31.2% and 42.8%, respectively, n = 10 slices). 6. Intracellular analysis of regular-spiking neurons in slices that did not generate spontaneous epileptiform discharges after > 2 h of perfusion with Mg2+-free ACSF showed all-or none, variable-latency epileptiform bursts that were induced by high-strength focal extracellular stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Group III Metabotropic Glutamate Receptors (mGluRs) Modulate Transmission of Gustatory Inputs in the Brain Stem

2009 ◽  
Vol 102 (1) ◽  
pp. 192-202 ◽  
Author(s):  
Robert M. Hallock ◽  
Christopher J. Martyniuk ◽  
Thomas E. Finger
Keyword(s):  
Glutamate Receptors ◽  
Metabotropic Glutamate Receptors ◽  
Field Potential ◽  
Taste System ◽  
Group Iii ◽  
Metabotropic Glutamate ◽  
Group I ◽  
Bath Application ◽  
Afferent Synapse

Glutamate is the principal neurotransmitter at the primary sensory afferent synapse in the medulla for the taste system. At this synapse, glutamate activates N-methyl-d-aspartate (NMDA) and non-NMDA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA] and kainate) ionotropic receptors to effect a response in the second-order neurons. The current experiment is the first to examine the role of metabotropic glutamate receptors (mGluRs) in the transmission of taste information. In an in vitro slice preparation of the primary vagal gustatory nucleus in goldfish, primary gustatory afferent fibers were stimulated electrically, whereas evoked dendritic field potentials were recorded in the sensory layers. Recordings were made before, during, and after bath application of mGluR agonists for various mGluR groups and subtypes. Whereas l-AP4, a group III agonist, reduced the field potential, group I and group II agonists had no effect. Furthermore, the selective mGluR4 agonist ACPT-III and mGluR8 agonist PPG were effective at reducing the field potential, whereas agonists selective for mGluR6 and 7 were not. MAP4, a group III mGluR antagonist, attenuated frequency-dependent depression, indicating that endogenous glutamate binds to presynaptic mGluRs under normal conditions. Furthermore, polymerase chain reaction showed that mRNA for mGluR4 and 8 is expressed in the vagal ganglia, a prerequisite if those receptors are expressed presynaptically in the vagal lobe. Collectively, these experiments indicate that mGluR4 and 8 are presynaptic at the primary gustatory afferent synapse and that their activation inhibits glutamatergic release.

scholarly journals Epileptiform activity in mouse hippocampal slices induced by moderate changes in extracellular Mg2+, Ca2+, and K+

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Haiyu Liu ◽  
Sai Zhang ◽  
Liang Zhang
Keyword(s):  
Prolonged Exposure ◽  
Epileptiform Activity ◽  
Hippocampal Slices ◽  
Brain Slices ◽  
Experimental Investigations ◽  
High Frequency Stimulation ◽  
Field Potentials ◽  
Epileptiform Discharges ◽  
Frequency Stimulation

Abstract Background Rodent brain slices—particularly hippocampal slices—are widely used in experimental investigations of epileptiform activity. Oxygenated artificial cerebrospinal fluid (ACSF) is used to maintain slices in vitro. Physiological or standard ACSF containing 3–3.5 mM K+, 1–2 mM Mg2+, and 1–3 mM Ca2+ generally does not induce population epileptiform activity, which can be induced by ACSF with high K+ (8–10 mM), low Mg2+, or low Ca2+ alone or in combination. While low-Mg2+ ACSF without intentionally added Mg salt but with contaminating Mg2+ (≤ 50–80 µM) from other salts can induce robust epileptiform activity in slices, it is unclear whether such epileptiform activity can be achieved using ACSF with moderately decreased Mg2+. To explore this issue, we examined the effects of moderately modified (m)ACSF with 0.8 mM Mg2+, 1.3 mM Ca2+, and 5.7 mM K+ on induction of epileptiform discharges in mouse hippocampal slices. Results Hippocampal slices were prepared from young (21–28 days old), middle-aged (13–14 months old), and aged (24–26 months old) C57/BL6 mice. Conventional thin (0.4 mm) and thick (0.6 mm) slices were obtained using a vibratome and pretreated with mACSF at 35–36 °C for 1 h prior to recordings. During perfusion with mACSF at 35–36 °C, spontaneous or self-sustained epileptiform field potentials following high-frequency stimulation were frequently recorded in slices pretreated with mACSF but not in those without the pretreatment. Seizure-like ictal discharges were more common in thick slices than in thin slices. Conclusions Prolonged exposure to mACSF by pretreatment and subsequent perfusion can induce epileptiform field potentials in mouse hippocampal slices.

Physiology, Pharmacology, and Topography of Cholinergic Neocortical Oscillations In Vitro

1997 ◽  
Vol 77 (5) ◽  
pp. 2427-2445 ◽  
Author(s):  
Heath S. Lukatch ◽  
M. Bruce Maciver
Keyword(s):  
Current Source ◽  
Brain Slices ◽  
Receptor Activation ◽  
Brain Regions ◽  
Oscillatory Activity ◽  
Cortical Layers ◽  
Eeg Activity ◽  
Layer 2

Lukatch, Heath S. and M. Bruce MacIver. Physiology, pharmacology, and topography of cholinergic neocortical oscillations in vitro. J. Neurophysiol. 77: 2427–2445, 1997. Rat neocortical brain slices generated rhythmic extracellular field [microelectroencephalogram (micro-EEG)] oscillations at theta frequencies (3–12 Hz) when exposed to pharmacological conditions that mimicked endogenous ascending cholinergic and GABAergic inputs. Use of the specific receptor agonist and antagonist carbachol and bicuculline revealed that simultaneous muscarinic receptor activation and γ-aminobutyric acid-A (GABAA)-mediated disinhibition werenecessary to elicit neocortical oscillations. Rhythmic activity was independent of GABAB receptor activation, but required intact glutamatergic transmission, evidenced by blockade or disruption of oscillations by 6-cyano-7-nitroquinoxaline-2,3-dione and (±)-2-amino-5-phosphonovaleric acid, respectively. Multisite mapping studies showed that oscillations were localized to areas 29d and 18b (Oc2MM) and parts of areas 18a and 17. Peak oscillation amplitudes occurred in layer 2/3, and phase reversals were observed in layers 1 and 5. Current source density analysis revealed large-amplitude current sinks and sources in layers 2/3 and 5, respectively. An initial shift in peak inward current density from layer 1 to layer 2/3 indicated that two processes underlie an initial depolarization followed by oscillatory activity. Laminar transections localized oscillation-generating circuitry to superficial cortical layers and sharp-spike-generating circuitry to deep cortical layers. Whole cell recordings identified three distinct cell types based on response properties during rhythmic micro-EEG activity: oscillation-on (theta-on) and -off (theta-off) neurons, and transiently depolarizing glial cells. Theta-on neurons displayed membrane potential oscillations that increased in amplitude with hyperpolarization (from −30 to −90 mV). This, taken together with a glutamate antagonist-induced depression of rhythmic micro-EEG activity, indicated that cholinergically driven neocortical oscillations require excitatory synaptic transmission. We conclude that under the appropriate pharmacological conditions, neocortical brain slices were capable of producing localized theta frequency oscillations. Experiments examining oscillation physiology, pharmacology, and topography demonstrated that neocortical brain slice oscillations share many similarities with the in vivo and in vitro theta EEG activity recorded in other brain regions.

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