Anesthetic protection of neurons injured by hypothermia and rewarming: roles of intracellular Ca2+ and excitotoxicity

The Effect of Propofol on the Hippocampus in Chronic Cerebral Hypoxia in a Rat Model Through Klotho Regulation

BACKGROUND/AIM

Chronic cerebral hypoxia often leads to brain damage and inflammation. Propofol is suggested to have neuroprotective effects under anaesthesia.

MATERIALS AND METHODS

This study used rat models with carotid artery coarctation or closure. Four groups of rats were compared: a control group, a propofol-treated group, a group with bilateral common carotid artery blockage (BCAO), and a BCAO group treated with propofol post-surgery.

RESULTS

The Morris water maze test indicated cognitive impairment in BCAO rats, which also showed hippocampal structure changes, oxidative stress markers alteration, and reduced Klotho expression. Propofol treatment post-BCAO surgery improved these outcomes, suggesting its potential in mitigating chronic cerebral hypoxia effects.

CONCLUSION

Propofol may increase klotho levels and reduce apoptosis and inflammation linked to oxidative stress in cognitively impaired mice.

Activation of immune signals during organ transplantation

The activation of host's innate and adaptive immune systems can lead to acute and chronic graft rejection, which seriously impacts graft survival. Thus, it is particularly significant to clarify the immune signals, which are critical to the initiation and maintenance of rejection generated after transplantation. The initiation of response to graft is dependent on sensing of danger and stranger molecules. The ischemia and reperfusion of grafts lead to cell stress or death, followed by releasing a variety of damage-associated molecular patterns (DAMPs), which are recognized by pattern recognition receptors (PRRs) of host immune cells to activate intracellular immune signals and induce sterile inflammation. In addition to DAMPs, the graft exposed to 'non-self' antigens (stranger molecules) are recognized by the host immune system, stimulating a more intense immune response and further aggravating the graft damage. The polymorphism of MHC genes between different individuals is the key for host or donor immune cells to identify heterologous 'non-self' components in allogeneic and xenogeneic organ transplantation. The recognition of 'non-self' antigen by immune cells mediates the activation of immune signals between donor and host, resulting in adaptive memory immunity and innate trained immunity to the graft, which poses a challenge to the long-term survival of the graft. This review focuses on innate and adaptive immune cells receptor recognition of damage-associated molecular patterns, alloantigens and xenoantigens, which is described as danger model and stranger model. In this review, we also discuss the innate trained immunity in organ transplantation.

Neuroprotective effect of miR-204-5p downregulation against isoflurane-induced learning and memory impairment via targeting EphB2 and inhibiting neuroinflammation

BACKGROUND

Isoflurane, one of the most commonly used inhalational anesthetics, is usually used in surgery patients and often causes long-term learning and memory impairment. The aim of this study was to explore the role of microRNA-204-5p (miR-204-5p) in isoflurane-induced learning and memory impairment in rats.

METHODS

The Morris Water Maze (MWM) test was used to estimate the spatial learning and memory abilities of laboratory rats. Enzyme-linked immunosorbent assay (ELISA) was used to determine interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) concentrations in the hippocampal tissues. The expression level of miR-204-5p was determined by using quantitative reverse transcription polymerase chain reaction (qRT-PCR). The potential target genes of miR-204-5p were predicted and verified by the TargetScan and dual-luciferase reporter assay, respectively.

RESULTS

Isoflurane-induced rats showed significantly higher neurological function scores, higher escape latency and shorter time spent in the original quadrant. Isoflurane could significantly induce neuroinflammation, and the expression of miR-204-5p was increased in the hippocampal tissue of rats exposed to isoflurane. Moreover, downregulation of miR-204-5p attenuated the effect of isoflurane treatment on the escape latency and the time in the original quadrant, and inflammatory cytokines level was downregulated by inhibiting the expression of miR-204-5p. EphB2 was verified as a direct target gene of miR-204-5p.

CONCLUSION

Downregulated miR-204-5p exerts protective effects against isoflurane-induced learning and memory impairment via targeting EphB2 and inhibiting neuroinflammation. MiR-204-5p could serve as a potential therapeutic target for the lightening of cognitive dysfunction induced by isoflurane.

Extracellular Zn2+-Dependent Amyloid-β1-42 Neurotoxicity in Alzheimer's Disease Pathogenesis

The basal level of extracellular Zn²⁺ is in the range of low nanomolar (~ 10 nM) in the hippocampus. However, extracellular Zn²⁺ dynamics plays a key role for not only cognitive activity but also cognitive decline. Extracellular Zn²⁺ dynamics is modified by glutamatergic synapse excitation and the presence of amyloid-β_1-42 (Aβ_1-42), a causative peptide in Alzheimer's disease (AD). When human Aβ_1-42 reaches high picomolar (> 100 pM) in the extracellular compartment of the rat dentate gyrus, Zn-Aβ_1-42 complexes are readily formed and taken up into dentate granule cells, followed by Aβ_1-42-induced cognitive decline that is linked with Zn²⁺ released from intracellular Zn-Aβ_1-42 complexes. Aβ_1-42-induced intracellular Zn²⁺ toxicity is accelerated with aging because of age-related increase in extracellular Zn²⁺. The recent findings suggest that Aβ_1-42 secreted continuously from neuron terminals causes age-related cognitive decline and neurodegeneration via intracellular Zn²⁺ dysregulation. On the other hand, metallothioneins (MTs), zinc-binding proteins, quickly serve for intracellular Zn²⁺-buffering under acute intracellular Zn²⁺ dysregulation. On the basis of the idea that the defense strategy against Aβ_1-42-induced pathogenesis leads to preventing the AD development, this review deals with extracellular Zn²⁺-dependent Aβ_1-42 neurotoxicity, which is accelerated with aging.

New insight into Parkinson's disease pathogenesis from reactive oxygen species-mediated extracellular Zn2+ influx

BACKGROUND

Parkinson's disease (PD) is the common neurodegenerative disorder in the elderly characterized by motor symptoms such as tremors, which is caused by selective loss of nigral dopaminergic neurons. Oxidative stress induced by the auto-oxidation of dopamine has been implicated as a key cause of the selective loss of dopaminergic neurons.

METHODS

To understand the selective loss of nigral dopaminergic neurons, the PD pathogenesis is reviewed focused on paraquat (PQ) and 6-hydroxydopamine (6-OHDA)-induced PD in rats.

RESULTS

Reactive oxygen species (ROS), which are produced by PQ and 6-OHDA, are retrogradely transported to presynaptic glutamatergic neuron terminals. ROS activate presynaptic transient receptor potential melastatin 2 (TRPM2) cation channels and induce extracellular glutamate accumulation in the substantia nigra pars compacta (SNpc), followed by age-related intracellular Zn2+ dysregulation. Loss of nigral dopaminergic neurons is accelerated by age-related intracellular Zn2+ dysregulation in the SNpc of rat PD models. The intracellular Zn2+ dysregulation in nigral dopaminergic neurons is linked with the rapid influx of extracellular Zn2+ via postsynaptic AMPA receptor activation, suggesting that PQ- and 6-OHDA-induced pathogenesis is linked with age-related intracellular Zn2+ dysregulation in the SNpc. Postsynaptic TRPM2 channels may be also involved in intracellular Zn2+ dysregulation in the SNpc.

CONCLUSION

A novel mechanism of nigral dopaminergic degeneration, in which ROS induce rapid intracellular Zn2+ dysregulation, figures out the PD pathogenesis induced by PQ and 6-OHDA in rats. This review deals with new insight into PD pathogenesis from ROS-mediated extracellular Zn2+ influx and its proposed defense strategy.

The Impact of Synaptic Zn2+ Dynamics on Cognition and Its Decline

The basal levels of extracellular Zn²⁺ are in the range of low nanomolar concentrations and less attention has been paid to Zn²⁺, compared to Ca²⁺, for synaptic activity. However, extracellular Zn²⁺ is necessary for synaptic activity. The basal levels of extracellular zinc are age-dependently increased in the rat hippocampus, implying that the basal levels of extracellular Zn²⁺ are also increased age-dependently and that extracellular Zn²⁺ dynamics are linked with age-related cognitive function and dysfunction. In the hippocampus, the influx of extracellular Zn²⁺ into postsynaptic neurons, which is often linked with Zn²⁺ release from neuron terminals, is critical for cognitive activity via long-term potentiation (LTP). In contrast, the excess influx of extracellular Zn²⁺ into postsynaptic neurons induces cognitive decline. Interestingly, the excess influx of extracellular Zn²⁺ more readily occurs in aged dentate granule cells and intracellular Zn²⁺-buffering, which is assessed with ZnAF-2DA, is weakened in the aged dentate granule cells. Characteristics (easiness) of extracellular Zn²⁺ influx seem to be linked with the weakened intracellular Zn²⁺-buffering in the aged dentate gyrus. This paper deals with the impact of synaptic Zn²⁺ signaling on cognition and its decline in comparison with synaptic Ca²⁺ signaling.

General anesthetics protects against cardiac arrest-induced brain injury by inhibiting calcium wave propagation in zebrafish

Cardiac arrest is a leading cause of death and disability worldwide. Although many victims are initially resuscitated, they often suffer from serious brain injury, even leading to a “persistent vegetative state”. Therefore, it is need to explore therapies which restore and protect brain function after cardiac arrest. In the present study, using Tg (HuC:GCaMP5) zebrafish as a model, we found the zebrafish brain generated a burst of Ca²⁺ wave after cardiac arrest by in vivo time-lapse confocal imaging. The Ca²⁺ wave was firstly initiated at hindbrain and then sequentially propagated to midbrain and telencephalon, the neuron displayed Ca²⁺ overload after Ca²⁺ wave propagation. Consistent with this, our study further demonstrated neuronal apoptosis was increased in cardiac arrest zebrafish by TUNEL staining. The cardiac arrest-induced Ca²⁺ wave propagation can be prevented by general anesthetics such as midazolam or ketamine pretreatment. Moreover, midazolam or ketamine pretreatment dramatically decreased the neuronal apoptosis and improved the survival rate in CA zebrafish. Taken together, these findings provide the first in vivo evidence that general anesthetics pretreatment protects against cardiac arrest-induced brain injury by inhibiting calcium wave propagation in zebrafish.

Long-Term Deficits in Cortical Circuit Function after Asphyxial Cardiac Arrest and Resuscitation in Developing Rats

Cardiac arrest is a common cause of global hypoxic-ischemic brain injury. Poor neurologic outcome among cardiac arrest survivors results not only from direct cellular injury but also from subsequent long-term dysfunction of neuronal circuits. Here, we investigated the long-term impact of cardiac arrest during development on the function of cortical layer IV (L4) barrel circuits in the rat primary somatosensory cortex. We used multielectrode single-neuron recordings to examine responses of presumed excitatory L4 barrel neurons to controlled whisker stimuli in adult (8 ± 2-mo-old) rats that had undergone 9 min of asphyxial cardiac arrest and resuscitation during the third postnatal week. Results indicate that responses to deflections of the topographically appropriate principal whisker (PW) are smaller in magnitude in cardiac arrest survivors than in control rats. Responses to adjacent whisker (AW) deflections are similar in magnitude between the two groups. Because of a disproportionate decrease in PW-evoked responses, receptive fields of L4 barrel neurons are less spatially focused in cardiac arrest survivors than in control rats. In addition, spiking activity among L4 barrel neurons is more correlated in cardiac arrest survivors than in controls. Computational modeling demonstrates that experimentally observed disruptions in barrel circuit function after cardiac arrest can emerge from a balanced increase in background excitatory and inhibitory conductances in L4 neurons. Experimental and modeling data together suggest that after a hypoxic-ischemic insult, cortical sensory circuits are less responsive and less spatially tuned. Modulation of these deficits may represent a therapeutic approach to improving neurologic outcome after cardiac arrest.

In vitro and in vivo physiology of low nanomolar concentrations of Zn2+ in artificial cerebrospinal fluid

Artificial cerebrospinal fluid (ACSF), i.e., brain extracellular medium, which includes Ca²⁺ and Mg²⁺, but not other divalent cations such as Zn²⁺, has been used for in vitro and in vivo experiments. The present study deals with the physiological significance of extracellular Zn²⁺ in ACSF. Spontaneous presynaptic activity is suppressed in the stratum lucidum of brain slices from young rats bathed in ACSF containing 10 nM ZnCl₂, indicating that extracellular Zn²⁺ modifies hippocampal presynaptic activity. To examine the in vivo action of 10 nM ZnCl₂ on long-term potentiation (LTP), the recording region was perfused using a recording electrode attached to a microdialysis probe. The magnitude of LTP was not modified in young rats by perfusion with ACSF containing 10 nM ZnCl₂, compared to perfusion with ACSF without Zn²⁺, but attenuated by perfusion with ACSF containing 100 nM ZnCl₂. Interestingly, the magnitude of LTP was not modified in aged rats even by perfusion with ACSF containing 100 nM ZnCl₂, but enhanced by perfusion with ACSF containing 10 mM CaEDTA, an extracellular Zn²⁺ chelator. The present study indicates that the basal levels of extracellular Zn²⁺, which are in the range of low nanomolar concentrations, are critical for synaptic activity and perhaps increased age-dependently.

Protective effect of propofol on noise-induced hearing loss

PURPOSE

Iatrogenic noise produced by mastoid or craniotomy drills may cause hearing damage, which is induced by the generation of reactive oxygen species (ROS) and the reduction of cochlear blood flow (CoBF). This study investigated whether propofol could reduce noise-induced hearing loss (NIHL) in a guinea pig model.

METHODS

Sixty-four male pigmented guinea pigs were randomly and equally divided into 4 groups: control, noise, propofol and propofol+noise. Propofol was infused intravenously for 20min prior to noise exposure with a loading dose of 5mg·kg^-1 for 5min and a maintenance infusion of 20mg·kg^-1·h^-1 for 135min. For noise exposure, an octave band noise at a 124dB sound pressure level (SPL) was administered to animals for 2h. The mean arterial pressure (MAP) and CoBF were monitored continuously. Auditory function was measured by the level of distortion product otoacoustic emission (DPOAE) before and at 1h, 72h and 240h after noise exposure. Cochlear levels of 8-iso-Prostaglandin F_2alpha (8-iso-PGF2α) were measured immediately after the termination of noise exposure. Cochlear silver nitrate staining and outer hair cell (OHC) counting were performed after the final functional test.

RESULTS

Noise exposure caused decreases in the CoBF and DPOAE amplitudes, over-generation of 8-iso-PGF2α and the loss of OHCs. Pre-treatment with propofol significantly increased the CoBF and DPOAE amplitudes, decreased 8-iso-PGF2α and the loss of OHCs.

CONCLUSIONS

Propofol exerted protective effects against NIHL in this animal model by suppressing a lipid peroxidation reaction and improving CoBF.

Neuroprotective effects of vitexin against isoflurane-induced neurotoxicity by targeting the TRPV1 and NR2B signaling pathways

Vitexin is a bioactive compound extracted from hawthorn leaves, which reduces blood pressure and has anti‑inflammatory and potential anticancer effects. However, the mechanisms underlying the protective effects of vitexin against isoflurane‑induced neurotoxicity remain elusive. Therefore, the aim of the present study was to investigate these mechanisms further. Sprague Dawley rats received 1.4% isoflurane in a 100% oxygen environment for 2 h. Human PC12 pheochromocytoma neurosecretory cells were exposed to 2% isoflurane for 12 h before they were treated with 1, 10 or 100 µM vitexin for a further 24 h. Vitexin inhibited the isoflurane-induced cell cytotoxicity and weakened isoflurane-induced neuroinflammation and oxidative stress pathways in PC12 cells. In addition, treatment with vitexin suppressed isoflurane‑induced caspase‑3 activation and increased β-secretase 1 levels in PC12 cells. Furthermore, vitexin treatment decreased the levels of isoflurane‑induced cytosolic calcium and reactive oxygen species, and downregulated the expression of transient receptor potential cation channel subfamily V member 1 (TRPV1) and glutamate ionotropic receptor NMDA type subunit 2B (NR2B) protein expression in isoflurane-treated PC12 cells. These results suggest that vitexin mediates its protective effects against isoflurane-induced neurotoxicity by targeting the TRPV1 and NR2B signaling pathways.

Neuroprotective effects of deep hypothermia in refractory status epilepticus

Objective

Pharmacoresistance develops quickly during repetitive seizures, and refractory status epilepticus (RSE) remains a therapeutic challenge. The outcome of RSE is poor, with high mortality and morbidity. New treatments are needed. Deep hypothermia (20°C) is used clinically during reconstructive cardiac surgery and neurosurgery, and has proved safe and effective in those indications. We tested the hypothesis that deep hypothermia reduces RSE and its long‐term consequences.

Methods

We used a model of SE induced by lithium and pilocarpine and refractory to midazolam. Several EEG measures were recorded in both hypothermic (n = 17) and normothermic (n = 20) animals. Neuronal injury (by Fluoro‐Jade B), cell‐mediated inflammation, and breakdown of the blood–brain barrier (BBB) (by immunohistochemistry) were studied 48 h following SE onset.

Results

Normothermic rats in RSE seized for 4.1 ± 1.1 h, and at 48 h they displayed extensive neuronal injury in many brain regions, including hippocampus, dentate gyrus, amygdala, entorhinal and pyriform cortices, thalamus, caudate/putamen, and the frontoparietal neocortex. Deep hypothermia (20°C) of 30 min duration terminated RSE within 12 min of initiation of hypothermia, reduced EEG power and seizure activity upon rewarming, and eliminated SE‐induced neuronal injury in most animals. Normothermic rats showed widespread breakdown of the BBB, and extensive macrophage infiltration in areas of neuronal injury, which were completely absent in animals treated with hypothermia.

Interpretation

These results suggest that deep hypothermia may open a new therapeutic avenue for the treatment of RSE and for the prevention of its long‐term consequences.

Deep hypothermia for the treatment of refractory status epilepticus

In a rat model of status epilepticus (SE) induced by lithium and pilocarpine and refractory to midazolam, deep hypothermia (20 °C for 30 min) reduced EEG power over 50-fold, stopped SE within 12 min, and reduced EEG spikes by 87%. Hypothermia deserves further investigation as a treatment of last resort for refractory SE. This article is part of a Special Issue entitled "Status Epilepticus".

Xenon improves neurologic outcome and reduces secondary injury following trauma in an in vivo model of traumatic brain injury

OBJECTIVES

To determine the neuroprotective efficacy of the inert gas xenon following traumatic brain injury and to determine whether application of xenon has a clinically relevant therapeutic time window.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male C57BL/6N mice (n = 196).

INTERVENTIONS

Seventy-five percent xenon, 50% xenon, or 30% xenon, with 25% oxygen (balance nitrogen) treatment following mechanical brain lesion by controlled cortical impact.

MEASUREMENTS AND MAIN RESULTS

Outcome following trauma was measured using 1) functional neurologic outcome score, 2) histological measurement of contusion volume, and 3) analysis of locomotor function and gait. Our study shows that xenon treatment improves outcome following traumatic brain injury. Neurologic outcome scores were significantly (p < 0.05) better in xenon-treated groups in the early phase (24 hr) and up to 4 days after injury. Contusion volume was significantly (p < 0.05) reduced in the xenon-treated groups. Xenon treatment significantly (p < 0.05) reduced contusion volume when xenon was given 15 minutes after injury or when treatment was delayed 1 or 3 hours after injury. Neurologic outcome was significantly (p < 0.05) improved when xenon treatment was given 15 minutes or 1 hour after injury. Improvements in locomotor function (p < 0.05) were observed in the xenon-treated group, 1 month after trauma.

CONCLUSIONS

These results show for the first time that xenon improves neurologic outcome and reduces contusion volume following traumatic brain injury in mice. In this model, xenon application has a therapeutic time window of up to at least 3 hours. These findings support the idea that xenon may be of benefit as a neuroprotective treatment in patients with brain trauma.

Influence of cooling rate on activity of ionotropic glutamate receptors in brain slices at hypothermia

Hypothermia is a known approach in the treatment of neurological pathologies. Mild hypothermia enhances the therapeutic window for application of medicines, while deep hypothermia is often accompanied by complications, including problems in the recovery of brain functions. The purpose of present study was to investigate the functioning of glutamate ionotropic receptors in brain slices cooled with different rates during mild, moderate and deep hypothermia. Using a system of gradual cooling combined with electrophysiological recordings in slices, we have shown that synaptic activity mediated by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate receptors in rat olfactory cortex was strongly dependent on the rate of lowering the temperature. High cooling rate caused a progressive decrease in glutamate receptor activity in brain slices during gradual cooling from mild to deep hypothermia. On the contrary, low cooling rate slightly changed the synaptic responses in deep hypothermia. The short-term potentiation may be induced in slices by electric tetanization at 16 °C in this case. Hence, low cooling rate promoted preservation of neuronal activity and plasticity in the brain tissue.

Limitations of Mild, Moderate, and Profound Hypothermia in Protecting Developing Hippocampal Neurons After Simulated Ischemia

Mild hypothermia (33°C-34°C) after cerebral ischemia in intact animals or ischemia-like conditions in vitro reduces neuron death. However, it is now clear that more profound hypothermia or delayed hypothermia may not provide significant protection. To further define the limitations of hypothermia after cerebral ischemia, we used hippocampal slice cultures to examine the effects of various degrees, durations, and delays of hypothermia on neuron death after an ischemia-like insult. Organotypic cultures of the hippocampus from 7- to 8 day-old rat pups were cooled to 32°C, 23°C, 17°C, or 4°C immediately or after a 2-4 hour delay from an injurious insult of oxygen and glucose deprivation (OGD). Cell death in CA1, CA3 and dentate regions of the cultures was assessed 24 hours later with SYTOX® or propidium iodide, both of which are fluorescent markers labeling damaged cells. OGD caused extensive cell death in CA1, CA3, and dentate regions of the hippocampal cultures. Hypothermia (32°C, 23°C and 17°C) for 4-6 hours immediately after OGD was protective at 24 hours, but when hypothermia was applied for longer periods or delayed after OGD, no protection or increased death was seen. Ultra-profound hypothermia (4°C) increased cell death in all cell areas of the hippocampus even when after a milder insult of only hypoxia. In an in vitro model of recovery after an ischemia-like insult, mild to profound hypothermia is protective only when applied without delay and for limited periods of time (6-8 hours). Longer durations of hypothermia, or delayed application of the hypothermia can increase neuron death. These findings may have implications for clinical uses of therapeutic hypothermia after hypoxic or ischemic insults, and suggest that further work is needed to elucidate the limitations of hypothermia as a protective treatment after ischemic stress.

Neuroprotection against Traumatic Brain Injury by Xenon, but Not Argon, Is Mediated by Inhibition at the N-Methyl-d-Aspartate Receptor Glycine Site

Background:

Xenon, the inert anesthetic gas, is neuroprotective in models of brain injury. The authors investigate the neuroprotective mechanisms of the inert gases such as xenon, argon, krypton, neon, and helium in an in vitro model of traumatic brain injury.

Methods:

The authors use an in vitro model using mouse organotypic hippocampal brain slices, subjected to a focal mechanical trauma, with injury quantified by propidium iodide fluorescence. Patch clamp electrophysiology is used to investigate the effect of the inert gases on N-methyl-d-aspartate receptors and TREK-1 channels, two molecular targets likely to play a role in neuroprotection.

Results:

Xenon (50%) and, to a lesser extent, argon (50%) are neuroprotective against traumatic injury when applied after injury (xenon 43 ± 1% protection at 72 h after injury [N = 104]; argon 30 ± 6% protection [N = 44]; mean ± SEM). Helium, neon, and krypton are devoid of neuroprotective effect. Xenon (50%) prevents development of secondary injury up to 48 h after trauma. Argon (50%) attenuates secondary injury, but is less effective than xenon (xenon 50 ± 5% reduction in secondary injury at 72 h after injury [N = 104]; argon 34 ± 8% reduction [N = 44]; mean ± SEM). Glycine reverses the neuroprotective effect of xenon, but not argon, consistent with competitive inhibition at the N-methyl-d-aspartate receptor glycine site mediating xenon neuroprotection against traumatic brain injury. Xenon inhibits N-methyl-d-aspartate receptors and activates TREK-1 channels, whereas argon, krypton, neon, and helium have no effect on these ion channels.

Conclusions:

Xenon neuroprotection against traumatic brain injury can be reversed by increasing the glycine concentration, consistent with inhibition at the N-methyl-d-aspartate receptor glycine site playing a significant role in xenon neuroprotection. Argon and xenon do not act via the same mechanism.

Sevoflurane preconditioning attenuates the fall in adenosine triphosphate levels, but does not alter the changes in sodium and potassium levels during hypoxia in rat hippocampal slices

BACKGROUND

Sevoflurane preconditioning improves recovery after hypoxia. Sevoflurane administered before and during hypoxia improved recovery and attenuated the changes in intracellular sodium, potassium, and adenosine triphosphate (ATP) levels during hypoxia. In this study, the authors examine the effects of sevoflurane applied only before hypoxia on sodium, potassium, and ATP.

METHODS

Hippocampal slices from adult male Sprague-Dawley rats were pretreated with 4% sevoflurane, washed, and then subjected to hypoxia (n≥8 animals/group). The cornus ammonis 1 regions of the hippocampal slices were micro-dissected and sodium, potassium, and ATP concentrations measured.

RESULTS

Pretreatment with sevoflurane for 15 or 60 min did not attenuate the increase in intracellular sodium or the decrease in intracellular potassium during hypoxia. After 60 min of preconditioning and 5 min of hypoxia, sodium increased 57% (vs. nonpreconditioned hypoxia 54% increase) and potassium decreased 31% (vs. 26%). These changes were not statistically significant versus untreated hypoxia. The 60-min sevoflurane preconditioning group had statistically significant higher ATP levels at 5 min of hypoxia (3.8 nmol/mg dry wt.) when compared to untreated hypoxic tissue (2.1 nmol/mg). There was no significant difference in ATP levels between the sevoflurane preconditioned and the untreated tissue before hypoxia (8.9 vs. 8.5 nmoles/mg, respectively).

CONCLUSION

Preconditioning with sevoflurane for 60 min before hypoxia does not alter changes in intracellular sodium and potassium during hypoxia but does attenuate the fall in intracellular ATP levels during hypoxia. Thus, there are differences between anesthetic preconditioning and when anesthetics are present before and during hypoxia.

Xenon Neurotoxicity in Rat Hippocampal Slice Cultures Is Similar to Isoflurane and Sevoflurane

Background:

Anesthetic neurotoxicity in the developing brain of rodents and primates has raised concern. Xenon may be a nonneurotoxic alternative to halogenated anesthetics, but its toxicity has only been studied at low concentrations, where neuroprotective effects predominate in animal models. An equipotent comparison of xenon and halogenated anesthetics with respect to neurotoxicity in developing neurons has not been made.

Methods:

Organotypic hippocampal cultures from 7-day-old rats were exposed to 0.75, 1, and 2 minimum alveolar concentrations (MAC) partial pressures (60% xenon at 1.2, 2.67, and 3.67 atm; isoflurane at 1.4, 1.9, and 3.8%; and sevoflurane at 3.4 and 6.8%) for 6 h, at atmospheric pressure or in a pressure chamber. Cell death was assessed 24 h later with fluorojade and fluorescent dye exclusion techniques.

Results:

Xenon caused death of hippocampal neurons in CA1, CA3, and dentate regions after 1 and 2 MAC exposures, but not at 0.75 MAC. At 1 MAC, xenon increased cell death 40% above baseline (P &lt; 0.01; ANOVA with Dunnett test). Both isoflurane and sevoflurane increased neuron death at 1 but not 2 MAC. At 1 MAC, the increase in cell death compared with controls was 63% with isoflurane and 90% with sevoflurane (both P &lt; 0.001). Pretreatment of cultures with isoflurane (0.75 MAC) reduced neuron death after 1 MAC xenon, isoflurane, and sevoflurane.

Conclusion:

Xenon causes neuronal cell death in an in vitro model of the developing rodent brain at 1 MAC, as does isoflurane and sevoflurane at similarly potent concentrations. Preconditioning with a subtoxic dose of isoflurane eliminates this toxicity.

Antiapoptotic activity of argon and xenon

Although chemically non-reactive, inert noble gases may influence multiple physiological and pathological processes via hitherto uncharacterized physical effects. Here we report a cell-based detection system for assessing the effects of pre-defined gas mixtures on the induction of apoptotic cell death. In this setting, the conventional atmosphere for cell culture was substituted with gas combinations, including the same amount of oxygen (20%) and carbon dioxide (5%) but 75% helium, neon, argon, krypton, or xenon instead of nitrogen. The replacement of nitrogen with noble gases per se had no effects on the viability of cultured human osteosarcoma cells in vitro. Conversely, argon and xenon (but not helium, neon, and krypton) significantly limited cell loss induced by the broad-spectrum tyrosine kinase inhibitor staurosporine, the DNA-damaging agent mitoxantrone and several mitochondrial toxins. Such cytoprotective effects were coupled to the maintenance of mitochondrial integrity, as demonstrated by means of a mitochondrial transmembrane potential-sensitive dye and by assessing the release of cytochrome c into the cytosol. In line with this notion, argon and xenon inhibited the apoptotic activation of caspase-3, as determined by immunofluorescence microscopy coupled to automated image analysis. The antiapoptotic activity of argon and xenon may explain their clinically relevant cytoprotective effects.