Abstract TP281: Increased Susceptibility to Excitotoxic Injury in Rat Hippocampal Slices Exposed to Intermittent Hypoxia

Stroke ◽  
2016 ◽  
Vol 47 (suppl_1) ◽  
Author(s):  
Rekha Jagadapillai ◽  
Nicholas Mellen ◽  
Leroy R Sachleben ◽  
Evelyne Gozal
Keyword(s):  
Intermittent Hypoxia ◽  
Glutamate Release ◽  
Hippocampal Slices ◽  
Optical Recording ◽  
Network Activity ◽  
Viable Cells ◽  
High K ◽  
Obstructive Sleep ◽  
Increased Risk ◽  
Glutamate Homeostasis

Introduction: The effect of sustained hypoxia (SH) on brain metabolism has been well studied. However less is known about intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), associated with increased risk for stroke, outcome severity and functional consequences. Hypothesis: Impaired glutamate homeostasis after IH may underlie increased brain vulnerability to stroke-induced excitotoxicity. Methods: P4 organotypic rat hippocampal slices cultured for 7 days, were exposed for 7 additional days to IH (alternating 2 min 5% O2 - 15 min 21% O2), SH (5% O2) or normoxia (RA; 21% O2), followed by 3 glutamate challenges (first and last 200 μM, 15 min, emulating a physiological stimulus; second, 10 mM, 10 min, emulating stroke-induced excitotoxicity). Viability was assessed by propidium iodide (PI) uptake at baseline then after each glutamate challenge to assess whether hypoxia impairs the response to physiological or excitotoxic glutamate release. Glial GFAP, neuronal MAP2, EAAT1 and EAAT2 glutamate transporters expression was assessed by immunohistochemistry. Spontaneous and evoked Ca2+ transient activity was assessed in Fluo-8LTM AM loaded slices, by optical recording of Ca2+ spikes proximal to a bipolar stimulating electrode, before and after each of 3 single 2 ms stimuli (0.6 mA). Ca2+ transients after high K+ were used to determine the total number of viable cells. Results: Viability, GFAP, MAP2, EAAT1 and EAAT2 expression and basal Ca2+ spikes activity significantly decreased in IH. The number of neurons with spikes evoked within 500 ms of stimuli was not significantly different, but RA evoked responses were more tightly clustered. Residual network activity, assessed by number of neurons with spikes 500 ms post stimulus, was significantly different RA>SH>IH. Overall number of spiking cells after high K+, representing total viable cells, confirmed the viability data obtained with PI staining. Conclusions: IH is more detrimental to cell survival and glutamate homeostasis than SH, suggesting that in addition to vascular changes, impaired glutamate homeostasis may increase OSA patients’ susceptibility to ischemic events.

Presynaptic Modulation of Synaptic Transmission by Pregnenolone Sulfate as Studied by Optical Recordings

2005 ◽  
Vol 94 (6) ◽  
pp. 4131-4144 ◽  
Author(s):  
Ling Chen ◽  
Masahiro Sokabe
Keyword(s):  
Synaptic Transmission ◽  
Glutamate Release ◽  
Hippocampal Slices ◽  
Receptor Activation ◽  
Optical Recording ◽  
Perforant Path ◽  
Dependent Manner ◽  
Pregnenolone Sulfate ◽  
Voltage Sensitive Dyes ◽  
Dose Dependent

The effects of pregnenolone sulfate (PREGS), a putative neurosteroid, on the transmission of perforant path–granule cell synapses were investigated with an optical recording technique in rat hippocampal slices stained with voltage-sensitive dyes. Application of PREGS to the bath solution resulted in an acute augmentation of EPSP in a dose-dependent manner. The PREGS effect was dependent on the extracellular Ca2+ concentration ([Ca2+]o), but independent of NMDA receptor activation. PREGS caused a decrease in paired-pulse facilitation, which implies that PREGS positively modulates presynaptic neurotransmitter releases. Firmer support for this mechanism was that PREGS augmented the synaptically induced glial depolarization (SIGD) that reflects the activity of electrogenic glutamate transporters in glial cells during the uptake of released glutamate. The selective α7nAChR antagonist α-BGT or MLA prevented the SIGD increase by PREGS. Furthermore DMXB, a selective α7nAChR agonist, mimicked the PREGS effect on SIGD and antagonized the effect of PREGS. The presynaptic effect of PREGS was partially attenuated by the L-type Ca2+ channel (VGCC) blocker nifedipine. Based on these findings, we proposed a novel mechanism underlying the facilitated synaptic transmission by PREGS: this neurosteroid sensitizes presynaptic α7nAChR that is followed by an activation of L-type VGCC to increase the presynaptic glutamate release.

Spontaneous interictal-like activity originates in multiple areas of the CA2-CA3 region of hippocampal slices

1994 ◽  
Vol 71 (4) ◽  
pp. 1574-1585 ◽  
Author(s):  
L. V. Colom ◽  
P. Saggau
Keyword(s):  
Guinea Pig ◽  
Epileptiform Activity ◽  
Hippocampal Slices ◽  
Optical Recording ◽  
Objective Lens ◽  
Gamma Aminobutyric Acid ◽  
Subsequent Increase ◽  
Epileptiform Discharges ◽  
High K ◽  
Ca3 Region

1. The sites of origin of spontaneous interictal-like epileptiform activity in hippocampal slices from guinea pig, mouse, and rat were determined. A multisite fast optical recording technique using voltage-sensitive dyes and an array of 100 photodiodes was employed. The use of a low-magnification objective lens allowed the visualization of almost the entire transverse hippocampal slice. Three in vitro models of epilepsy were employed, utilizing different manipulations of the bath perfusion medium to induce epileptiform activity: 1) raising the external potassium (K+) concentration, 2) adding the potassium channel blocker 4-aminopyridine (4-AP), and 3) adding antagonists of gamma-aminobutyric acid-A (GABAA) receptors (bicuculline and picrotoxin, BIC-PTX). 2. Spontaneous epileptiform discharges were detected in each subfield of cornu ammonis (CA) but not in the dentate gyrus (DG) of each studied species. Preliminary experiments confirmed that interictal-like epileptiform activity originated in the CA2-CA3 region. Ictal-like activity was never observed in our experiments. 3. In the guinea pig, when GABAA antagonists were employed, the site of origin of spontaneous epileptiform discharges was consistently located in the CA2-CA3a region. When high K+ or 4-AP was used, this region was the most frequent site of origin. Subsequent epileptiform discharges with similar sites of origin occasionally invaded different areas of the CA2-CA3 region, revealing a variable area of occupance of epileptiform discharges. 4. In the mouse and rat, the site of origin of spontaneous discharges was invariably located in the CA3b-CA3c region independent of the epilepsy model. 5. In both the guinea pig and rat, when the CA2-CA3a region was surgically separated from the CA3b-CA3c region, independent discharges were observed in both regions. Areas that could generate discharges only under certain epileptogenic conditions were found in these species (potential sites of origin). Two independent sites of origin with different propagation patterns and area of occupance were occasionally observed within the CA2-CA3a region. 6. In the guinea pig, such lesions demonstrated that both regions can independently generate epileptiform discharges at different frequencies. When high K+ or 4-AP was employed, epileptiform activity was observed in both regions. Although BIC-PTX only generated discharges in the CA2-CA3a region, a subsequent increase in K+ induced additional discharges in the CA3b-CA3c region, revealing a potential site of origin. 7. In rat hippocampal slices with such lesions, spontaneous epileptiform discharges were observed in both CA2-CA3a and CA3b-CA3c region when 4-AP was employed.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals The Association of Sleep Disorders, Obesity and Sleep-Related Hypoxia with Cancer

2020 ◽  
Vol 21 (6) ◽  
pp. 444-453
Author(s):  
Anna Brzecka ◽  
Karolina Sarul ◽  
Tomasz Dyła ◽  
Marco Avila-Rodriguez ◽  
Ricardo Cabezas-Perez ◽  
...  
Keyword(s):  
Risk Factors ◽  
Obstructive Sleep Apnea ◽  
Sleep Apnea ◽  
Sleep Disorders ◽  
Intermittent Hypoxia ◽  
Clock Genes ◽  
Cell Cancer ◽  
Cancer Risk Factors ◽  
Obstructive Sleep ◽  
Increased Risk

Background: Sleep disorders have emerged as potential cancer risk factors. Objective: This review discusses the relationships between sleep, obesity, and breathing disorders with concomitant risks of developing cancer. Results: Sleep disorders result in abnormal expression of clock genes, decreased immunity, and melatonin release disruption. Therefore, these disorders may contribute to cancer development. Moreover, in sleep breathing disorder, which is frequently experienced by obese persons, the sufferer experiences intermittent hypoxia that may stimulate cancer cell proliferation. Discussion: During short- or long- duration sleep, sleep-wake rhythm disruption may occur. Insomnia and obstructive sleep apnea increase cancer risks. In short sleepers, an increased risk of stomach cancer, esophageal squamous cell cancer, and breast cancer was observed. Among long sleepers (>9 hours), the risk of some hematologic malignancies is elevated. Conclusion: Several factors including insomnia, circadian disruption, obesity, and intermittent hypoxia in obstructive sleep apnea are contributing risk factors for increased risk of several types of cancers. However, further studies are needed to determine the more significant of these risk factors and their interactions.

Effects of intermittent hypoxia on oxidative stress-induced myocardial damage in mice

2007 ◽  
Vol 102 (5) ◽  
pp. 1806-1814 ◽  
Author(s):  
Ah-Mee Park ◽  
Yuichiro J. Suzuki
Keyword(s):  
Oxidative Stress ◽  
Obstructive Sleep Apnea ◽  
Sleep Apnea ◽  
Intermittent Hypoxia ◽  
Myocardial Injury ◽  
Ischemia Reperfusion Injury ◽  
Ischemia Reperfusion ◽  
Cardiac Damage ◽  
Obstructive Sleep ◽  
Increased Risk

Obstructive sleep apnea is associated with increased risk for cardiovascular diseases. As obstructive sleep apnea is characterized by episodic cycles of hypoxia and normoxia during sleep, we investigated effects of intermittent hypoxia (IH) on ischemia-reperfusion-induced myocardial injury. C57BL/6 mice were subjected to IH (2 min 6% O2 and 2 min 21% O2) for 8 h/day for 1, 2, or 4 wk; isolated hearts were then subjected to ischemia-reperfusion. IH for 1 or 2 wk significantly enhanced ischemia-reperfusion-induced myocardial injury. However, enhanced cardiac damage was not seen in mice treated with 4 wk of IH, suggesting that the heart has adapted to chronic IH. Ischemia-reperfusion-induced lipid peroxidation and protein carbonylation were enhanced with 2 wk of IH, while, with 4 wk, oxidative stress was normalized to levels in animals without IH. H2O2 scavenging activity in adapted hearts was higher after ischemia-reperfusion, suggesting the increased antioxidant capacity. This might be due to the involvement of thioredoxin, as the expression level of this protein was increased, while levels of other antioxidant enzymes were unchanged. In the heart from mice treated with 2 wk of IH, ischemia-reperfusion was found to decrease thioredoxin. Ischemia-reperfusion injury can also be enhanced when thioredoxin reductase was inhibited in control hearts. These results demonstrate that IH changes the susceptibility of the heart to oxidative stress in part via alteration of thioredoxin.

scholarly journals Coincident Glutamatergic and Cholinergic Inputs Transiently Depress Glutamate Release at Rat Schaffer Collateral Synapses

2007 ◽  
Vol 97 (6) ◽  
pp. 4108-4119 ◽  
Author(s):  
Keith E. Gipson ◽  
Mark F. Yeckel
Keyword(s):  
Acetylcholine Receptors ◽  
Glutamate Release ◽  
Acetylcholinesterase Inhibitor ◽  
Hippocampal Slices ◽  
Medial Septum ◽  
Network Activity ◽  
Stratum Radiatum ◽  
Hippocampal Function ◽  
Schaffer Collateral ◽  
Single Receptor

The mammalian hippocampus, together with subcortical and cortical areas, is responsible for some forms of learning and memory. Proper hippocampal function depends on the highly dynamic nature of its circuitry, including the ability of synapses to change their strength for brief to long periods of time. In this study, we focused on a transient depression of glutamatergic synaptic transmission at Schaffer collateral synapses in acute hippocampal slices. The depression of evoked excitatory postsynaptic current (EPSC) amplitudes, herein called transient depression, follows brief trains of synaptic stimulation in stratum radiatum of CA1 and lasts for 2–3 min. Depression results from a decrease in presynaptic glutamate release, as NMDA-receptor–mediated EPSCs and composite EPSCs are depressed similarly and depression is accompanied by an increase in the paired-pulse ratio. Transient depression is prevented by blockade of metabotropic glutamate and acetylcholine receptors, presumably located presynaptically. These two receptor types—acting together—cause depression. Blockade of a single receptor type necessitates significantly stronger conditioning trains for triggering depression. Addition of an acetylcholinesterase inhibitor enables depression from previously insufficient conditioning trains. Furthermore, a strong coincident, but not causal, relationship existed between presynaptic depression and postsynaptic internal Ca2+ release, emphasizing the potential importance of functional interactions between presynaptic and postsynaptic effects of convergent cholinergic and glutamatergic inputs to CA1. These convergent afferents, one intrinsic to the hippocampus and the other likely originating in the medial septum, may regulate CA1 network activity, the induction of long-term synaptic plasticity, and ultimately hippocampal function.

Glutamine enhances glutamate release in preference to γ-aminobutyrate release in hippocampal slices

1984 ◽  
Vol 62 (8) ◽  
pp. 919-923 ◽  
Author(s):  
John C. Szerb ◽  
Patrick A. O'Regan
Keyword(s):  
High Performance Liquid Chromatography ◽  
High Performance ◽  
Glutamate Release ◽  
Hippocampal Slices ◽  
Gaba Release ◽  
Reversed Phase ◽  
Precolumn Derivatization ◽  
Spontaneous Release ◽  
High K ◽  
Spontaneous Conversion

To see the effect of physiological concentrations of glutamine on glutamate and γ-aminobutyrate (GABA) release, rat hippocampal slices were incubated and (or) superfused without or with 0.25 mM glutamine in the presence or absence of Ca2+. The spontaneous and high K+-evoked release of glutamine, glutamate, and GABA was measured by precolumn derivatization and reversed phase high performance liquid chromatography. The spontaneous release of glutamate was increased by super-fusion with glutamine and this increase was three times greater in the absence than in the presence of Ca2+. Spontaneous GABA release was not increased by glutamine. While in the absence of glutamine, the release of glutamate and GABA evoked by 50 mM K+ was about equal, in the presence of glutamine the evoked release of glutamate was nearly three times greater than that of GABA. The large evoked release of glutamate in the presence of glutamine was Ca2+ dependent nearly to the same extent as the smaller evoked release in the absence of glutamine. Results suggest that the availability of extracellular glutamine regulates the release of glutamate but not of GABA. Extracellular Ca2+ controls the spontaneous conversion of glutamine to glutamate but the site and mechanism of this control is uncertain.

scholarly journals Release probability increases towards distal dendrites boosting high-frequency signal transfer in the rodent hippocampus

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Thomas P Jensen ◽  
Olga Kopach ◽  
James P Reynolds ◽  
Leonid P Savtchenko ◽  
Dmitri A Rusakov
Keyword(s):  
High Frequency ◽  
Glutamate Release ◽  
Hippocampal Slices ◽  
Network Activity ◽  
Signal Transfer ◽  
High Frequency Signal ◽  
Release Probability ◽  
Acute Hippocampal Slices ◽  
Rats And Mice ◽  
Trace Formation

Dendritic integration of synaptic inputs involves their increased electrotonic attenuation at distal dendrites, which can be counterbalanced by the increased synaptic receptor density. However, during network activity, the influence of individual synapses depends on their release fidelity, the dendritic distribution of which remains poorly understood. Here, we employed classical optical quantal analyses and a genetically encoded optical glutamate sensor in acute hippocampal slices of rats and mice to monitor glutamate release at CA3-CA1 synapses. We find that their release probability increases with greater distances from the soma. Similar-fidelity synapses tend to group together, whereas release probability shows no trends regarding the branch ends. Simulations with a realistic CA1 pyramidal cell hosting stochastic synapses suggest that the observed trends boost signal transfer fidelity, particularly at higher input frequencies. Because high-frequency bursting has been associated with learning, the release probability pattern we have found may play a key role in memory trace formation.

scholarly journals Chronic Intermittent Hypoxia Participates in the Pathogenesis of Atherosclerosis and Perturbs the Formation of Intestinal Microbiota

2021 ◽  
Vol 11 ◽  
Author(s):  
Chaowei Hu ◽  
Pan Wang ◽  
Yunyun Yang ◽  
Juan Li ◽  
Xiaolu Jiao ◽  
...  
Keyword(s):  
Intestinal Microbiota ◽  
Intermittent Hypoxia ◽  
Causal Effect ◽  
Atherosclerotic Lesion ◽  
Chronic Intermittent Hypoxia ◽  
Physiological Status ◽  
Microbial Composition ◽  
Obstructive Sleep ◽  
Increased Risk ◽  
Rdna Sequencing

Chronic intermittent hypoxia (CIH) is the prominent signature of highly prevalent obstructive sleep apnea (OSA) pathophysiology, which leads to increased risk and aggravation of atherosclerotic cardiovascular diseases. However, whether intestinal microbiota is implicated in the mechanisms linking CIH to arteriosclerosis (AS) pathogenesis remains unclear. The association of CIH with the development of altered gut microbiota (GM) may provide the opportunity to develop preventive strategies for atherosclerotic cardiovascular risk reduction. Animal models of apolipoprotein E-deficient (apoE-/-) mice treated with high-fat diet (HFD) and subjected to CIH conditions was applied to mimic the AS observed in patients with OSA. The physiological status and atherosclerotic lesion formation were confirmed by histological analysis. 16S rDNA sequencing of fecal samples was conducted to determine the changes in gut microbial composition. Morphometric analysis demonstrated that CIH caused aggravated atherosclerotic lesions and facilitated AS in apoE-/- mice treated with HFD. The gut bacteria was significantly varied in AS and AS+CIH mice compared with that in the control mice. Significantly perturbed GM profiles were detected in AS mice with and without CIH, with altered microbial α- and β- diversity and shifts in bacterial compositions at phylum and genus levels. While the difference between AS and AS+CIH was observed at different bacteria taxa levels. Aggravation of reduced Sutterella and increased Halomonas, Halomonadaceae and Oceanospirillales was noted in CIH-treated AS mice. The correlation of intestinal bacterial parameters with pathological changes in artery indicated complicated interactions under CIH-induced GM dysbiosis. Furthermore, the gut microbial functions in the potential ability of replication recombination and repair proteins, glycan biosynthesis and metabolism, as well as metabolism of cofactors and vitamins were identified to be further suppressed by CIH. Our findings demonstrated a causal effect of CIH on GM alterations in AS mice and suggested that the disordered GM features in AS development were deteriorated by CIH, which may be associated with AS aggravation. Preventative strategies targeting gut microbiome are highly recommended for intervention of OSA-related AS.

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