The effects of l-carnitine on the combination of, inhalation anesthetic-induced developmental, neuronal apoptosis in the rat frontal cortex

The effects of general anesthetics on mitochondrial structure and function in the developing brain

The use of general anesthetics in modern clinical practice is commonly regarded as safe for healthy individuals, but exposures at the extreme ends of the age spectrum have been linked to chronic cognitive impairments and persistent functional and structural alterations to the nervous system. The accumulation of evidence at both the epidemiological and experimental level prompted the addition of a warning label to inhaled anesthetics by the Food and Drug Administration cautioning their use in children under 3  years of age. Though the mechanism by which anesthetics may induce these detrimental changes remains to be fully elucidated, increasing evidence implicates mitochondria as a potential primary target of anesthetic damage, meditating many of the associated neurotoxic effects. Along with their commonly cited role in energy production via oxidative phosphorylation, mitochondria also play a central role in other critical cellular processes including calcium buffering, cell death pathways, and metabolite synthesis. In addition to meeting their immense energy demands, neurons are particularly dependent on the proper function and spatial organization of mitochondria to mediate specialized functions including neurotransmitter trafficking and release. Mitochondrial dependence is further highlighted in the developing brain, requiring spatiotemporally complex and metabolically expensive processes such as neurogenesis, synaptogenesis, and synaptic pruning, making the consequence of functional alterations potentially impactful. To this end, we explore and summarize the current mechanistic understanding of the effects of anesthetic exposure on mitochondria in the developing nervous system. We will specifically focus on the impact of anesthetic agents on mitochondrial dynamics, apoptosis, bioenergetics, stress pathways, and redox homeostasis. In addition, we will highlight critical knowledge gaps, pertinent challenges, and potential therapeutic targets warranting future exploration to guide mechanistic and outcomes research.

Neonatal Isoflurane Exposure in Rats Impairs Short-Term Memory, Cell Viability, and Glutamate Uptake in Slices of the Frontal Cerebral Cortex, But Not the Hippocampus, in Adulthood

Neonatal exposure to general anesthetics has been associated with neurotoxicity and morphologic changes in the developing brain. Isoflurane is a volatile anesthetic widely used in pediatric patients to induce general anesthesia, analgesia, and perioperative sedation. In the present study, we investigated the effects of a single neonatal isoflurane (3% in oxygen, 2 h) exposure in rats at postnatal day (PND) 7, in short-term (24 h - PND8) and long-term (adulthood) protocols. In PND8, ex vivo analysis of hippocampal and frontal cortex slices evaluated cell viability and susceptibility to in vitro glutamate challenge. In adult rats, behavioral parameters related to anxiety-like behavior, short-term memory, and locomotor activity (PND60-62) and ex vivo analysis of cell viability, membrane permeability, glutamate uptake, and susceptibility to in vitro glutamate challenge in hippocampal and cortical slices from PND65. A single isoflurane (3%, 2 h) exposure at PND7 did not acutely alter cell viability in cortical and hippocampal slices of infant rats (PND8) per se and did not alter slice susceptibility to in vitro glutamate challenge. In rat's adulthood, behavioral analysis revealed that the neonatal isoflurane exposure did not alter anxiety-like behavior and locomotor activity (open field and rotarod tests). However, isoflurane exposure impaired short-term memory evaluated in the novel object recognition task. Ex vivo analysis of brain slices showed isoflurane neonatal exposure selectively decreased cell viability and glutamate uptake in cortical slices, but it did not alter hippocampal slice viability or glutamate uptake (PND65). Isoflurane exposure did not alter in vitro glutamate-induced neurotoxicity to slices, and isoflurane exposure caused no significant long-term damage to cell membranes in hippocampal or cortical slices. These findings indicate that a single neonatal isoflurane exposure did not promote acute damage; however, it reduced cortical, but not hippocampal, slice viability and glutamate uptake in the adulthood. Additionally, behavioral analysis showed neonatal isoflurane exposure induces short-term recognition memory impairment, consolidating that neonatal exposure to volatile anesthetics may lead to behavioral impairment in the adulthood, although it may damage brain regions differentially.

Do We Have Viable Protective Strategies against Anesthesia-Induced Developmental Neurotoxicity?

Since its invention, general anesthesia has been an indispensable component of modern surgery. While traditionally considered safe and beneficial in many pathological settings, hundreds of preclinical studies in various animal species have raised concerns about the detrimental and long-lasting consequences that general anesthetics may cause to the developing brain. Clinical evidence of anesthetic neurotoxicity in humans continues to mount as we continue to contemplate how to move forward. Notwithstanding the alarming evidence, millions of children are being anesthetized each year, setting the stage for substantial healthcare burdens in the future. Hence, furthering our knowledge of the molecular underpinnings of anesthesia-induced developmental neurotoxicity is crucially important and should enable us to develop protective strategies so that currently available general anesthetics could be safely used during critical stages of brain development. In this mini-review, we provide a summary of select strategies with primary focus on the mechanisms of neuroprotection and potential for clinical applicability. First, we summarize a diverse group of chemicals with the emphasis on intracellular targets and signal-transduction pathways. We then discuss epigenetic and transgenerational effects of general anesthetics and potential remedies, and also anesthesia-sparing or anesthesia-delaying approaches. Finally, we present evidence of a novel class of anesthetics with a distinct mechanism of action and a promising safety profile.

Tetraethylammonium chloride reduces anaesthetic-induced neurotoxicity in Caenorhabditis elegans and mice

BACKGROUND

If anaesthetics cause permanent cognitive deficits in some children, the implications are enormous, but the molecular causes of anaesthetic-induced neurotoxicity, and consequently possible therapies, are still debated. Anaesthetic exposure early in development can be neurotoxic in the invertebrate Caenorhabditis elegans causing endoplasmic reticulum (ER) stress and defects in chemotaxis during adulthood. We screened this model organism for compounds that alleviated neurotoxicity, and then tested these candidates for efficacy in mice.

METHODS

We screened compounds for alleviation of ER stress induction by isoflurane in C. elegans assayed by induction of a green fluorescent protein (GFP) reporter. Drugs that inhibited ER stress were screened for reduction of the anaesthetic-induced chemotaxis defect. Compounds that alleviated both aspects of neurotoxicity were then blindly tested for the ability to inhibit induction of caspase-3 by isoflurane in P7 mice.

RESULTS

Isoflurane increased ER stress indicated by increased GFP reporter fluorescence (240% increase, P<0.001). Nine compounds reduced induction of ER stress by isoflurane by 90-95% (P<0.001 in all cases). Of these compounds, tetraethylammonium chloride and trehalose also alleviated the isoflurane-induced defect in chemotaxis (trehalose by 44%, P=0.001; tetraethylammonium chloride by 23%, P<0.001). In mouse brain, tetraethylammonium chloride reduced isoflurane-induced caspase staining in the anterior cortical (-54%, P=0.007) and hippocampal regions (-46%, P=0.002).

DISCUSSION

Tetraethylammonium chloride alleviated isoflurane-induced neurotoxicity in two widely divergent species, raising the likelihood that it may have therapeutic value. In C. elegans, ER stress predicts isoflurane-induced neurotoxicity, but is not its cause.

Neuroprotective Effects of Carnitine and Its Potential Application to Ameliorate Neurotoxicity

Carnitine is an essential metabolite that is absorbed from the diet and synthesized in the kidney, liver, and brain. It ferries fatty acids across the mitochondrial membrane to undergo β-oxidation. Carnitine has been studied as a therapy or protective agent for many neurological diseases and neurotoxicity (e.g., prolonged anesthetic exposure-induced developmental neurotoxicity in preclinical models). Preclinical and clinical data support the notion that carnitine or acetyl carnitine may improve a patient's quality of life through increased mitochondrial respiration, release of neurotransmitters, and global gene expression changes, showing the potential of carnitine beyond its approved use to treat primary and secondary carnitine deficiency. In this review, we summarize the beneficial effects of carnitine or acetyl carnitine on the central nervous system, highlighting protective effects against neurotoxicity-induced damage caused by various chemicals and encouraging a thorough evaluation of carnitine use as a therapy for patients suffering from neurotoxicant exposure.

Protective Effects of Xenon on Propofol-Induced Neurotoxicity in Human Neural Stem Cell-Derived Models

Early life exposure to general anesthetics can have neurotoxic consequences. Evidence indicates that xenon, a rare noble gas with anesthetic properties, may lessen neuronal damage under certain conditions. However, its potential neuroprotective properties, when used alone or in combination with other anesthetics, remain largely unknown. While it is difficult to verify the adverse effects of long duration anesthetic exposure in infants and children, the utilization of relevant non-clinical models (i.e., human-derived neural stem cells) may serve as a "bridging" model for evaluating the vulnerability of the nervous system. Neural stem cells, purchased from PhoenixSongs Biologicals, Inc., were guided to differentiate into neurons, astrocytes, and oligodendrocytes, which were then exposed to propofol (50 μM) for 16 h in the presence or absence of xenon (33%). Differentiation into cells of the neural lineage was confirmed by labelling with cell-specific markers, β-tubulin for neurons, glial fibrillary acidic protein (GFAP) for astrocytes, and galactocerebroside (GALC) for oligodendrocytes after 5 days of differentiation. The presence and severity of neural damage induced by anesthetic exposures were assessed by several methods, including the TUNEL assay, and immuno-histochemical measurements. Our data demonstrate that prolonged exposure to propofol results in a significant increase in the number of TUNEL-positive cells, indicating increased neural apoptosis. No significant changes were detected in the number of GFAP-positive astrocytes or GALC-positive oligodendrocytes. However, the number of β-tubulin-positive neurons was substantially reduced in the propofol-exposed cultures. Co-administration of xenon effectively blocked the propofol-induced neuronal damage/loss. No significant effects were observed when xenon was administered alone. The data indicate that prolonged exposure to propofol during development produces elevated levels of neuronal apoptosis in a human neural stem cell-derived model. However, sub-clinical, non-anesthetic concentrations of xenon, when used in combination with propofol, can prevent or ameliorate the toxic effects associated with prolonged anesthetic exposure. This is important as a more complete understanding of the neurotoxic mechanisms associated with a variety of clinically relevant anesthetic combinations becomes available. Protective approaches are critical for developing sound guidance on best practices for the use of these agents in the pediatric setting.

Research progress and treatment strategies for anesthetic neurotoxicity

Every year, a large number of infants and young children worldwide are administered general anesthesia. Whether general anesthesia adversely affects the intellectual development and cognitive function of children at a later date remains controversial. Many animal experiments have shown that general anesthetics can cause nerve damage during development, affect synaptic plasticity, and induce apoptosis, and finally affect learning and memory function in adulthood. The neurotoxicity of pediatric anesthetics (PAN) has received extensive attention in the field of anesthesia, which has been listed as a potential problem affecting public health by NFDA of the United States. Previous studies on rodents and non-human primates indicate that inhalation of anesthetics early after birth can induce long-term and sustained impairment of learning and memory function, as well as changes in brain function. Many anti-oxidant drugs, dexmedetomidine, as well as a rich living environment and exercise have been proven to reduce the neurotoxicity of anesthetics. In this paper, we summarize the research progress, molecular mechanisms and current intervention measures of anesthetic neurotoxicity.

Maternal chlormequat chloride exposure disrupts embryonic growth and produces postnatal adverse effects

We showed previously that chlormequat chloride, a widely used plant growth regulator, could affect embryonic growth and growth hormone (GH)-insulin-like growth factor 1 (IGF-1) axis of rats. However, the potential effects of low dose chlormequat chloride exposure during pregnancy on embryonic and postnatal growth and development remain unclear. To further assess the risk of chlormequat chloride to human embryonic growth and postnatal health, we exposed maternal rats orally to the chemical during pregnancy at 5 mg/kg bw, a dose corresponding to the human acceptable daily intake (ADI) level set by World Health Organization (WHO), and determined the effects of chlormequat on embryo growth and postnatal health. We found that chlormequat chloride increased embryonic growth parameters, GH, and GH-releasing hormone (GHRH) levels, but did not affect somatostatin and IGF-1 on gestational day (GD) 11. In the pups of postnatal day (PD) 7, we observed increased head length, decreased body fat percentage, hypoglycemia, hyperlipidemia and hyperproteinemia. In conclusion, maternal exposure to chlormequat chloride during pregnancy disrupts the embryonic growth probably through its effects on growth regulators and even has adverse effects on postnatal health.

Acetyl-l-carnitine does not prevent neurodegeneration in a rodent model of prolonged neonatal anesthesia

Many studies have shown that prolonged or repeated use of general anesthesia early in life can cause an increase in neurodegeneration and lasting changes in behavior. While short periods of general anesthesia appear to be safe, there is a concern about the neurotoxic potential of prolonged or repeated general anesthesia in young children. Unfortunately, the use of general anesthesia in children cannot be avoided. It would be a great benefit to develop a strategy to reduce or reverse anesthesia mitigated neurotoxicity. The mechanisms behind anesthesia related neurotoxicity are unknown, but evidence suggests that mitochondrial dysfunction and abnormal energy utilization are involved. Recent research suggests that a class of compounds known as carnitines may be effective at preventing anesthesia related neurotoxicity by influencing fatty acid metabolism in the mitochondria. However, it is unknown if carnitines can provide protection against changes in behavior associated with early life exposure to anesthesia. Accordingly, we evaluated the neuroprotective potential of acetyl-l-carnitine in 7-day old rats. Rat pups were exposed to 6 h of general anesthesia with sevoflurane or a control condition, with and without acetyl-l-carnitine. The oxygenation level of animals was continuously monitored during sevoflurane exposure, and any animal showing signs of hypoxia was removed from the study. Animals exposed to sevoflurane showed clear signs of neurodegeneration 2 h after sevoflurane exposure. The hippocampus, cortex, thalamus, and caudate putamen all had elevated levels of Fluoro-Jade C staining. Despite the elevated levels of Fluoro-Jade C, few behavioral changes were observed in an independent cohort of animals treated with sevoflurane. Furthermore, acetyl-l-carnitine had little impact on levels of Fluoro-Jade C staining in animals treated with sevoflurane. These data suggest that acetyl-l-carnitine may offer little protection again anesthesia related neurotoxicity in fully oxygenated animals.

Neuroactive steroids alphaxalone and CDNC24 are effective hypnotics and potentiators of GABAA currents, but are not neurotoxic to the developing rat brain

BACKGROUND

The most currently used general anaesthetics are potent potentiators of γ-aminobutyric acid A (GABA_A) receptors and are invariably neurotoxic during the early stages of brain development in preclinical animal models. As causality between GABA_A potentiation and anaesthetic-induced developmental neurotoxicity has not been established, the question remains whether GABAergic activity is crucial for promoting/enhancing neurotoxicity. Using the neurosteroid analogue, (3α,5α)-3-hydroxy-13,24-cyclo-18,21-dinorchol-22-en-24-ol (CDNC24), which potentiates recombinant GABA_A receptors, we examined whether this potentiation is the driving force in inducing neurotoxicity during development.

METHODS

The neurotoxic potential of CDNC24 was examined vis-à-vis propofol (2,6-diisopropylphenol) and alphaxalone (5α-pregnan-3α-ol-11,20-dione) at the peak of rat synaptogenesis. In addition to the morphological neurotoxicity studies of the subiculum and medial prefrontal cortex (mPFC), we assessed the extra-, pre-, and postsynaptic effects of these agents on GABAergic neurotransmission in acute subicular slices from rat pups.

RESULTS

CDNC24, like alphaxalone and propofol, caused dose-dependent hypnosis in vivo, with a higher therapeutic index. CDNC24 and alphaxalone, unlike propofol, did not cause developmental neuroapoptosis in the subiculum and mPFC. Propofol potentiated post- and extrasynaptic GABA_A currents as evidenced by increased spontaneous inhibitory postsynaptic current (sIPSC) decay time and prominent tonic currents, respectively. CDNC24 and alphaxalone had a similar postsynaptic effect, but also displayed a strong presynaptic effect as evidenced by decreased frequency of sIPSCs and induced moderate tonic currents.

CONCLUSIONS

The lack of neurotoxicity of CDNC24 and alphaxalone may be at least partly related to suppression of presynaptic GABA release in the developing brain.

Acetyl-L-Carnitine Attenuates Arsenic-Induced Oxidative Stress and Hippocampal Mitochondrial Dysfunction

Augmentation of mitochondrial oxidative stress through activating a series of deadly events has implicated as the main culprit of arsenic toxicity and therapeutic approaches based on improving mitochondrial function hold a great promise for attenuating the arsenic-induced toxicity. Acetyl-L-carnitine (ALC) through balancing the coenzyme A (CoA)/acyl-CoA ratio plays an important role in mitochondrial metabolism and thereby can help protect hippocampal neurons from oxidative damage. In the present study, we aimed to explore the effect of arsenic interactions on the mitochondrial function in the hippocampus of rats. Rats were randomly divided into five groups of control (distilled water), sodium arsenite (NaAsO₂, 20 mg/kg), and co-treatment of NaAsO₂ with various doses of ALC in three groups (100, 200, 300 mg/kg) and were treated orally for 21 consecutive days. Our results point out that arsenic exposure caused oxidative stress in rats' hippocampus, which led to the reactive oxygen species (ROS) generation, mitochondrial swelling, the collapse of the mitochondrial membrane potential, and release of cytochrome c. It also altered Bcl-2/Bax expression ratio and increased caspase-3 and caspase-9 activities. Furthermore, arsenic exposure via activation of NF-κB and microglia increased inflammation. ALC could concentration-dependently counteract the arsenic-induced oxidative stress, modulate the antioxidant defense capacity, and improve mitochondrial functions. In addition, ALC decreased the expression of both death-associated proteins and of inflammatory markers. These findings indicate that ALC improved the arsenic-induced hippocampal mitochondrial dysfunction which underlines the importance of ALC in providing a possible therapeutic strategy for the prevention of arsenic-induced neurodegeneration.

Collapsin Response Mediator Protein-2 Ameliorates Sevoflurane-Mediated Neurocyte Injury by Targeting PI3K-mTOR-S6K Pathway

Background

Collapsin response mediator protein-2 (CRMP-2) is the first member of the CRMP family that has been identified in primary neuronal cells; it was originally found and identified in the regulation of microtubule dimerization into microtubules.

Material/Methods

In the present study, we aimed to investigate the roles and mechanisms of CRMP-2 in sevoflurane-induced neurocyte injury. Cell viability, proliferation, and apoptosis were measured by Cell Counting Kit-8 (CCK-8) assay and flow cytometry. Colorimetry was performed to measure the activity of caspase-3. Western blot and quantitative real-time reverse transcription assays were used to evaluate the related mRNAs and proteins expression.

Results

We found that CRMP-2 reversed the inhibitory effect of sevoflurane on the viability of nerve cells. Moreover, CRMP-2 accelerated the proliferation and suppressed the apoptosis of sevoflurane-induced nerve cells. CRMP-2 modulated the expression levels of apoptosis-associated protein in sevoflurane-induced nerve cells. Furthermore, it was demonstrated that CRMP-2 impacted the PI3K-mTOR-S6K pathway.

Conclusions

CRMP2 ameliorated sevoflurane-mediated neurocyte injury by targeting the PI3K-mTOR-S6K pathway. Thus, CRMP2 might be an effective target for sevoflurane-induced neurocyte injury therapies.

Ionizing radiation from computed tomography versus anesthesia for magnetic resonance imaging in infants and children: patient safety considerations

In the context of health care, risk assessment is the identification, evaluation and estimation of risk related to a particular clinical situation or intervention compared to accepted medical practice standards. The goal of risk assessment is to determine an acceptable level of risk for a given clinical treatment or intervention in association with the provided clinical circumstances for a patient or group of patients. In spite of the inherent challenges related to risk assessment in pediatric cross-sectional imaging, the potential risks of ionizing radiation and sedation/anesthesia in the pediatric population are thought to be quite small. Nevertheless both issues continue to be topics of discussion concerning risk and generate significant anxiety and concern for patients, parents and practicing pediatricians. Recent advances in CT technology allow for more rapid imaging with substantially lower radiation exposures, obviating the need for anesthesia for many indications and potentially mitigating concerns related to radiation exposure. In this review, we compare and contrast the potential risks of CT without anesthesia against the potential risks of MRI with anesthesia, and discuss the implications of this analysis on exam selection, providing specific examples related to neuroblastoma surveillance imaging.

Mechanistic studies on ketamine-induced mitochondrial toxicity in zebrafish embryos

Ketamine, a phencyclidine derivative, is an antagonist of the Ca²⁺-permeable N-methyl-d-aspartate (NMDA)-type glutamate receptors. It is a pediatric anesthetic and has been implicated in developmental neurotoxicity. Ketamine has also been shown to deplete ATP in mammalian cells. Our previous studies showed that acetyl l-carnitine (ALCAR) prevented ketamine-induced cardiotoxicity and neurotoxicity in zebrafish embryos. Based on our finding that ALCAR's protective effect was blunted by oligomycin A, an inhibitor of ATP synthase, we further investigated the effects of ketamine and ALCAR on ATP levels, mitochondria and ATP synthase in zebrafish embryos. The results demonstrated that ketamine reduced ATP levels in the embryos but not in the presence of ALCAR. Ketamine reduced total mitochondrial protein levels and mitochondrial potential, which were prevented with ALCAR co-treatment. To determine the cause of ketamine-induced ATP deficiency, we explored the status of ATP synthase. The results showed that a subunit of ATP synthase, atp5α1, was transcriptionally down-regulated by ketamine, but not in the presence of ALCAR, although ketamine caused a significant upregulation in another ATP synthase subunit, atp5β and total ATP synthase protein levels. Most of the ATP generated by heart mitochondria are utilized for its contraction and relaxation. Ketamine-treated embryos showed abnormal heart structure, which was abolished with ALCAR co-treatment. This study offers evidence for a potential mechanism by which ketamine could cause ATP deficiency mediated by mitochondrial dysfunction.

Cyclosporine exacerbates ketamine toxicity in zebrafish: Mechanistic studies on drug-drug interaction

Cyclosporine A (CsA) is an immunosuppressive drug commonly used in organ transplant patients to prevent allograft rejections. Ketamine is a pediatric anesthetic that noncompetitively inhibits the calcium-permeable N-methyl-d-aspartic acid receptors. Adverse drug-drug interaction effects between ketamine and CsA have been reported in mammals and humans. However, the mechanism of such drug-drug interaction is unclear. We have previously reported adverse effects of combination drugs, such as verapamil/ketamine and shown the mechanism through intervention by other drugs in zebrafish embryos. Here, we show that ketamine and CsA in combination produce developmental toxicity even leading to lethality in zebrafish larvae when exposure began at 24 h post-fertilization (hpf), whereas CsA did not cause any toxicity on its own. We also demonstrate that acetyl l-carnitine (ALCAR) completely reversed the adverse effects. Both ketamine and CsA are CYP3A4 substrates. Although ketamine and CsA independently altered the expression of the hepatic marker CYP3A65, a zebrafish ortholog of human CYP3A4, both drugs together induced further increase in CYP3A65 expression. In the presence of ALCAR, however, CYP3A65 expression was normalized. ALCAR has been shown to prevent ketamine toxicity in mammal and zebrafish. In conclusion, CsA exacerbated ketamine toxicity and ALCAR reversed the effects. These results, providing evidence for the first time on the reversal of the adverse effects of CsA/ketamine interaction by ALCAR, would prove useful in addressing potential occurrences of such toxicities in humans. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

L-Carnitine and Acetyl-L-carnitine Roles and Neuroprotection in Developing Brain

L-Carnitine functions to transport long chain fatty acyl-CoAs into the mitochondria for degradation by β-oxidation. Treatment with L-carnitine can ameliorate metabolic imbalances in many inborn errors of metabolism. In recent years there has been considerable interest in the therapeutic potential of L-carnitine and its acetylated derivative acetyl-L-carnitine (ALCAR) for neuroprotection in a number of disorders including hypoxia-ischemia, traumatic brain injury, Alzheimer's disease and in conditions leading to central or peripheral nervous system injury. There is compelling evidence from preclinical studies that L-carnitine and ALCAR can improve energy status, decrease oxidative stress and prevent subsequent cell death in models of adult, neonatal and pediatric brain injury. ALCAR can provide an acetyl moiety that can be oxidized for energy, used as a precursor for acetylcholine, or incorporated into glutamate, glutamine and GABA, or into lipids for myelination and cell growth. Administration of ALCAR after brain injury in rat pups improved long-term functional outcomes, including memory. Additional studies are needed to better explore the potential of L-carnitine and ALCAR for protection of developing brain as there is an urgent need for therapies that can improve outcome after neonatal and pediatric brain injury.

Do anesthetics harm the developing human brain? An integrative analysis of animal and human studies

Anesthetics that permit surgical procedures and stressful interventions have been found to cause structural brain abnormalities and functional impairment in immature animals, generating extensive concerns among clinicians, parents, and government regulators regarding the safe use of these drugs in young children. Critically important questions remain, such as the exact age at which the developing brain is most vulnerable to the effects of anesthetic exposure, whether a particular age exists beyond which anesthetics are devoid of long-term effects on the brain, and whether any specific exposure duration exists that does not lead to deleterious effects. Accordingly, the present analysis attempts to put the growing body of animal studies, which we identified to include >440 laboratory studies to date, into a translational context, by integrating the preclinical data on brain structure and function with clinical results attained from human neurocognitive studies, which currently exceed 30 studies. Our analysis demonstrated no clear exposure duration threshold below which no structural injury or subsequent cognitive abnormalities occurred. Animal data did not clearly identify a specific age beyond which anesthetic exposure did not cause any structural or functional abnormalities. Several potential mitigating strategies were found, however, no general anesthetic was identified that consistently lacked neurodegenerative properties and could be recommended over other anesthetics. It therefore is imperative, to expand efforts to devise safer anesthetic techniques and mitigating strategies, even before long-term alterations in brain development are unequivocally confirmed to occur in millions of young children undergoing anesthesia every year.

Minimally invasive biomarkers of general anesthetic-induced developmental neurotoxicity

The association of general anesthesia with developmental neurotoxicity, while nearly impossible to study in pediatric populations, is clearly demonstrable in a variety of animal models from rodents to nonhuman primates. Nearly all general anesthetics tested have been shown to cause abnormal brain cell death in animals when administered during periods of rapid brain growth. The ability to repeatedly assess in the same subjects adverse effects induced by general anesthetics provides significant power to address the time course of important events associated with exposures. Minimally-invasive procedures provide the opportunity to bridge the preclinical/clinical gap by providing the means to more easily translate findings from the animal laboratory to the human clinic. Positron Emission Tomography or PET is a tool with great promise for realizing this goal. PET for small animals (microPET) is providing valuable data on the life cycle of general anesthetic induced neurotoxicity. PET radioligands (annexin V and DFNSH) targeting apoptotic processes have demonstrated that a single bout of general anesthesia effected during a vulnerable period of CNS development can result in prolonged apoptotic signals lasting for several weeks in the rat. A marker of cellular proliferation (FLT) has demonstrated in rodents that general anesthesia-induced inhibition of neural progenitor cell proliferation is evident when assessed a full 2weeks after exposure. Activated glia express Translocator Protein (TSPO) which can be used as a marker of presumed neuroinflammatory processes and a PET ligand for the TSPO (FEPPA) has been used to track this process in both rat and nonhuman primate models. It has been shown that single bouts of general anesthesia can result in elevated TSPO expression lasting for over a week. These examples demonstrate the utility of specific PET tracers to inform, in a minimally-invasive fashion, processes associated with general anesthesia-induced developmental neurotoxicity. The fact that PET procedures are also used clinically suggests an opportunity to confirm in humans what has been repeatedly observed in animals.

In Vivo Monitoring of Sevoflurane-induced Adverse Effects in Neonatal Nonhuman Primates Using Small-animal Positron Emission Tomography

Background

Animals exposed to sevoflurane during development sustain neuronal cell death in their developing brains. In vivo micro-positron emission tomography (PET)/computed tomography imaging has been utilized as a minimally invasive method to detect anesthetic-induced neuronal adverse effects in animal studies.

Methods

Neonatal rhesus monkeys (postnatal day 5 or 6, 3 to 6 per group) were exposed for 8 h to 2.5% sevoflurane with or without acetyl-l-carnitine (ALC). Control monkeys were exposed to room air with or without ALC. Physiologic status was monitored throughout exposures. Depth of anesthesia was monitored using quantitative electroencephalography. After the exposure, microPET/computed tomography scans using 18F-labeled fluoroethoxybenzyl-N-(4-phenoxypyridin-3-yl) acetamide (FEPPA) were performed repeatedly on day 1, 1 and 3 weeks, and 2 and 6 months after exposure.

Results

Critical physiologic metrics in neonatal monkeys remained within the normal range during anesthetic exposures. The uptake of [18F]-FEPPA in the frontal and temporal lobes was increased significantly 1 day or 1 week after exposure, respectively. Analyses of microPET images recorded 1 day after exposure showed that sevoflurane exposure increased [18F]-FEPPA uptake in the frontal lobe from 0.927 ± 0.04 to 1.146 ± 0.04, and in the temporal lobe from 0.859 ± 0.05 to 1.046 ± 0.04 (mean ± SE, P &lt; 0.05). Coadministration of ALC effectively blocked the increase in FEPPA uptake. Sevoflurane-induced adverse effects were confirmed by histopathologic evidence as well.

Conclusions

Sevoflurane-induced general anesthesia during development increases glial activation, which may serve as a surrogate for neurotoxicity in the nonhuman primate brain. ALC is a potential protective agent against some of the adverse effects associated with such exposures.

Cognitive Dysfunction in Children with Heart Disease: The Role of Anesthesia and Sedation

As physicians and caregivers of children with congenital heart disease, we are aware of the increasing need for procedures requiring anesthesia. While these procedures may be ideal for medical and cardiac surgical management, the risks and benefits must be assessed carefully. There are well known risks of cardiovascular and respiratory complications from anesthesia and sedation and a potentially under-appreciated risk of neurocognitive dysfunction. Both animal and human studies support the detrimental effects of repeated anesthetic exposure on the developing brain. Although the studies in humans are less convincing of this risk, the Society of Pediatric Anesthesia jointly with SmartTots provided a consensus statement on the use of anesthetic and sedative drugs in infants and toddlers when speaking to families. (www.pedsanesthesia.org; http://smarttots.org/wp-content/uploads/2015/10/ConsensusStatementV910.5.2015.pdf). An excerpt of the statement is "Concerns regarding the unknown risk of anesthetic exposure to your child's brain development must be weighed against the potential harm associated with cancelling or delaying a needed procedure. Each child's care must be evaluated individually based on age, type, and urgency of the procedure and other health factors. This review provides a summary of the current evidence regarding anesthesia-induced neurotoxicity and the developing brain and its implications for children with congenital heart disease.

Acetyl L-carnitine targets adenosine triphosphate synthase in protecting zebrafish embryos from toxicities induced by verapamil and ketamine: An in vivo assessment

Verapamil is a Ca²⁺ channel blocker and is highly prescribed as an anti-anginal, antiarrhythmic and antihypertensive drug. Ketamine, an antagonist of the Ca²⁺ -permeable N-methyl-d-aspartate-type glutamate receptors, is a pediatric anesthetic. Previously we have shown that acetyl l-carnitine (ALCAR) reverses ketamine-induced attenuation of heart rate and neurotoxicity in zebrafish embryos. Here, we used 48 h post-fertilization zebrafish embryos that were exposed to relevant drugs for 2 or 4 h. Heart beat and overall development were monitored in vivo. In 48 h post-fertilization embryos, 2 mm ketamine reduced heart rate in a 2 or 4 h exposure and 0.5 mm ALCAR neutralized this effect. ALCAR could reverse ketamine's effect, possibly through a compensatory mechanism involving extracellular Ca²⁺ entry through L-type Ca²⁺ channels that ALCAR is known to activate. Hence, we used verapamil to block the L-type Ca²⁺ channels. Verapamil was more potent in attenuating heart rate and inducing morphological defects in the embryos compared to ketamine at specific times of exposure. ALCAR reversed cardiotoxicity and developmental toxicity in the embryos exposed to verapamil or verapamil plus ketamine, even in the presence of 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester, an inhibitor of intracellular Ca²⁺ release suggesting that ALCAR acts via effectors downstream of Ca²⁺ . In fact, ALCAR's protective effect was blunted by oligomycin A, an inhibitor of adenosine triphosphate synthase that acts downstream of Ca²⁺ during adenosine triphosphate generation. We have identified, for the first time, using in vivo studies, a downstream effector of ALCAR that is critical in abrogating ketamine- and verapamil-induced developmental toxicities. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Erythropoietin diminishes isoflurane-induced apoptosis in rat frontal cortex

BACKGROUND

During the brain growth spurt, anesthetic drugs can cause cellular and behavioral changes in the developing brain. The aim of this study was to determine the neuroprotective effect of erythropoietin after isoflurane anesthesia in rat pups.

METHODS

A total of 42, 7-day-old Wistar rats were divided into three groups. Control group (GC; n = 14): Rats breathed 100% oxygen for 6 h; Isoflurane group (GI; n = 14): Rats were exposed to 1.5% isoflurane in 100% oxygen for 6 h; Isoflurane + erythropoietin group (GIE; n = 14): 1000 IU·kg(-1) (intraperitoneal; IP) Erythropoietin was administered after isoflurane anesthesia. Each group was divided into two groups for pathology and learning and memory tests. Silver, caspase-3, and fluoro-jade C staining were used for detecting apoptotic cells in frontal cortex, striatum, hippocampus, thalamus, and amygdala. Morris water maze was used to evaluate learning and memory.

RESULTS

There was a significant increase in apoptotic cell count after isoflurane anesthesia in the frontal cortex when compared with control group (29.0 ± 9.27 vs 3.28 ± 0.75 [P = 0.002], 20.85 ± 10.94 vs 2.0 ± 0.81 [P = 0.002] and 24.57 ± 10.4 vs 5.14 ± 0.69 [P = 0.024] with silver, caspase-3, and fluoro-jade C staining, respectively). The apoptotic cell count in the frontal cortex was significantly higher in GIE than GC with caspase-3 staining (9.14 ± 3.13 vs 2.0 ± 0.81, P = 0.002). The apoptotic cell count in GIE was significantly reduced in the frontal cortex when compared with GI (4.0 ± 0.81 vs 29.0 ± 9.27 [P = 0.002], 9.14 ± 3.13 vs 20.85 ± 10.94 [P = 0.04] and 4.0 ± 1.63 vs 24.57 ± 10.4 [P = 0.012] with silver, caspase-3, and fluoro-jade C staining, respectively).

CONCLUSIONS

A total of 1000 IU·kg(-1) IP erythropoietin diminished isoflurane-induced neuroapoptosis. Further experimental studies have to be planned to reveal the optimal dose and timing of erythropoietin before adaptation to clinical practice.

Anaesthesia in early childhood - is the development of the immature brain in danger?

Experimental studies performed on immature animal brains had demonstrated a neurotoxic effect following sedation and general anaesthetics administration. The same magnitude of neurotoxicity has been suggested but not been proven to neonates, infants and small children who have undergone anaesthesia. There is a justified and increasing inquiry regarding the administration of general anaesthesia to paediatric patients.

Lithium Protects Against Anaesthesia Neurotoxicity In The Infant Primate Brain

Exposure of infant animals, including non-human primates (NHPs), to anaesthetic drugs causes apoptotic death of neurons and oligodendrocytes (oligos) and results in long-term neurodevelopmental impairment (NDI). Moreover, retrospective clinical studies document an association between anaesthesia exposure of human infants and significant increase in NDI. These findings pose a potentially serious dilemma because millions of human infants are exposed to anaesthetic drugs every year as part of routine medical care. Lithium (Li) at clinically established doses is neuroprotective in various cerebral injury models. We therefore investigated whether Li also protects against anaesthesia neurotoxicity in infant NHPs. On postnatal day 6 NHPs were anaesthetized with the widely used anaesthetic isoflurane (ISO) for 5 h employing the same standards as in a human pediatric surgery setting. Co-administration of Li completely prevented the acute ISO-induced neuroapoptosis and significantly reduced ISO-induced apoptosis of oligodendroglia. Our findings are highly encouraging as they suggest that a relatively simple pharmacological manipulation might protect the developing primate brain against the neurotoxic action of anaesthetic drugs while not interfering with the beneficial actions of these drugs. Further research is needed to determine Li’s potential to prevent long-term NDI resulting from ISO anaesthesia, and to establish its safety in human infants.

Distinct effects of ketamine and acetyl L-carnitine on the dopamine system in zebrafish

Ketamine, a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist is commonly used as a pediatric anesthetic. We have previously shown that acetyl L-carnitine (ALCAR) prevents ketamine toxicity in zebrafish embryos. In mammals, ketamine is known to modulate the dopaminergic system. NMDA receptor antagonists are considered as promising anti-depressants, but the exact mechanism of their function is unclear. Here, we measured the levels of dopamine (DA) and its metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the zebrafish embryos exposed to ketamine in the presence and absence of 0.5 mM ALCAR. Ketamine, at lower doses (0.1-0.3 mM), did not produce significant changes in DA, DOPAC or HVA levels in 52 h post-fertilization embryos treated for 24 h. In these embryos, tyrosine hydroxylase (TH) mRNA expression remained unchanged. However, 2 mM ketamine (internal embryo exposure levels equivalent to human anesthetic plasma concentration) significantly reduced DA level and TH mRNA indicating that DA synthesis was adversely affected. In the presence or absence of 2 mM ketamine, ALCAR showed similar effects on DA level and TH mRNA, but increased DOPAC level compared to control. ALCAR reversed 2 mM ketamine-induced reduction in HVA levels. With ALCAR alone, the expression of genes encoding the DA metabolizing enzymes, MAO (monoamine oxidase) and catechol-O-methyltransferase (COMT), was not affected. However, ketamine altered MAO mRNA expression, except at the 0.1 mM dose. COMT transcripts were reduced in the 2 mM ketamine-treated group. These distinct effects of ketamine and ALCAR on the DA system may shed some light on the mechanism on how ketamine can work as an anti-depressant, especially at sub-anesthetic doses that do not affect DA metabolism and suppress MAO gene expression.

Opposing effects of ketamine and acetyl L-carnitine on the serotonergic system of zebrafish

Ketamine, a pediatric anesthetic, is a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist. Studies show that ketamine is neurotoxic in developing mammals and zebrafish. In both mammals and zebrafish, acetyl L-carnitine (ALCAR) has been shown to be protective against ketamine toxicity. Ketamine is known to modulate the serotonergic system in mammals. Here, we measured the levels of serotonin (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the embryos exposed to ketamine in the presence and absence of ALCAR. Ketamine, at lower doses, did not produce significant changes in the 5-HT or 5-HIAA levels in 3 dpf (day post-fertilization) embryos. However, 2 mM ketamine (internal embryo exposure levels comparable to human anesthetic plasma concentration) significantly reduced 5-HT level, and 5-HIAA was not detectable indicating that 5-HT metabolism was abolished. In the presence or absence of 2 mM ketamine, ALCAR by itself did not significantly alter 5-HT or 5-HIAA levels compared to the control. Ratios of metabolite/5-HT indicated that 2 mM ketamine inhibited 5-HT metabolism to 5-HIAA whereas lower doses (0.1-0.3 mM) of ketamine did not have any effect. ALCAR reversed the effects of 2 mM ketamine not only by restoring 5-HT and 5-HIAA levels but also 5-HT turnover rate to control levels. Whole mount immunohistochemical studies showed that 2 mM ketamine reduced the serotonergic area in the brain whereas ALCAR expanded it with increased axonal sprouting and branching. These results indicate that ketamine and ALCAR have opposing effects on the zebrafish serotonergic system.

Perils of paediatric anaesthesia and novel molecular approaches: An evidence-based review

Evolution of anaesthesia has been largely helped by progress of evidence-based medicine. In spite of many advancements in anaesthesia techniques and availability of newer and safer drugs, much more needs to be explored scientifically for the development of anaesthesia. Over the last few years, the notion that the actions of the anaesthesiologist have only immediate or short-term consequences has largely been challenged. Evidences accumulated in the recent years have shown that anaesthesia exposure may have long-term consequences particularly in the extremes of ages. However, most of the studies conducted so far are in vitro or animal studies, the results of which have been extrapolated to humans. There have been confounding evidences linking anaesthesia exposure in the developing brain with poor neurocognitive outcome. The results of animal studies and human retrospective studies have raised concern over the potential detrimental effects of general anaesthetics on the developing brain. The purpose of this review is to highlight the long-term perils of anaesthesia in the very young and the potential of improving anaesthesia delivery with the novel molecular approaches.

Effects of silver nanoparticles on human and rat embryonic neural stem cells

Silver nano-particles (Ag-NPs) are becoming increasingly prevalent in consumer products as antibacterial agents. The increased use of Ag NP-enhanced products will almost certainly increase environmental silver levels, resulting in increased exposures and the potential for increased adverse reactions including neurotoxic effects. In the present study, embryonic neural stem cells (NSCs) from human and rat fetuses (gestational day-16) were used to determine whether Ag-NPs are capable of causing developmental neurotoxicity. The NSCs were cultured in serum free medium supplemented with appropriate growth factors. On the eighth day in vitro (DIV 8), the cells were exposed to Ag-NPs at concentrations of 1, 5, 10, and 20 μg/ml for 24 h. The cultured cells then were characterized by NSC markers including nestin and SOX2 and a variety of assays were utilized to determine the effects of Ag-NPs on NSC proliferation and viability and the underlying mechanisms associated with these effects. The results indicate that mitochondrial viability (MTT metabolism) was substantially attenuated and LDH release was increased significantly in a dose-dependent manner. Ag-NPs-induced neurotoxicity was further confirmed by up-regulated Bax protein expression, an increased number of TUNEL-positively stained cells, and elevated reactive oxygen species (ROS). NSC proliferation was also significantly decreased by Ag-NPs. Co-administration of acetyl-L-carnitine, an antioxidant agent, effectively blocked the adverse effects associated with Ag-NP exposure.

Positron Emission Tomography with [(18)F]FLT Revealed Sevoflurane-Induced Inhibition of Neural Progenitor Cell Expansion in vivo

Neural progenitor cell expansion is critical for normal brain development and an appropriate response to injury. During the brain growth spurt, exposures to general anesthetics, which either block the N-methyl-d-aspartate receptor or enhance the γ-aminobutyric acid receptor type A can disturb neuronal transduction. This effect can be detrimental to brain development. Until now, the effects of anesthetic exposure on neural progenitor cell expansion in vivo had seldom been reported. Here, minimally invasive micro positron emission tomography (microPET) coupled with 3'-deoxy-3' [(18)F] fluoro-l-thymidine ([(18)F]FLT) was utilized to assess the effects of sevoflurane exposure on neural progenitor cell proliferation. FLT, a thymidine analog, is taken up by proliferating cells and phosphorylated in the cytoplasm, leading to its intracellular trapping. Intracellular retention of [(18)F]FLT, thus, represents an observable in vivo marker of cell proliferation. Here, postnatal day 7 rats (n = 11/group) were exposed to 2.5% sevoflurane or room air for 9 h. For up to 2 weeks following the exposure, standard uptake values (SUVs) for [(18)F]-FLT in the hippocampal formation were significantly attenuated in the sevoflurane-exposed rats (p < 0.0001), suggesting decreased uptake and retention of [(18)F]FLT (decreased proliferation) in these regions. Four weeks following exposure, SUVs for [(18)F]FLT were comparable in the sevoflurane-exposed rats and in controls. Co-administration of 7-nitroindazole (30 mg/kg, n = 5), a selective inhibitor of neuronal nitric oxide synthase, significantly attenuated the SUVs for [(18)F]FLT in both the air-exposed (p = 0.00006) and sevoflurane-exposed rats (p = 0.0427) in the first week following the exposure. These findings suggested that microPET in couple with [(18)F]FLT as cell proliferation marker could be used as a non-invasive modality to monitor the sevoflurane-induced inhibition of neural progenitor cell proliferation in vivo.

Anesthesia for the young child undergoing ambulatory procedures: current concerns regarding harm to the developing brain

PURPOSE OF REVIEW

Sedation and anesthesia are often necessary for children at any age, and are frequently provided in ambulatory settings. Concerns have mounted, based on both laboratory studies including various mammalian species and retrospective human clinical studies, that the very drugs that induce sedation and anesthesia may trigger an injury in the developing brain, resulting in long-lasting neurobehavioral consequences.

RECENT FINDINGS

New retrospective studies further augment these concerns. Specifically, recent studies support that a single anesthesia exposure before age 3 may increase the risk for long-term disabilities in language acquisition and abstract reasoning, and that exposure to two or more anesthetics before age 2 nearly doubles the risk for an attention-deficit hyperactivity disorder diagnosis by age 19. However, methodological limitations preclude final conclusions or change in practice based on these reports, as retrospective studies cannot prove causation. Ongoing prospective clinical studies such as 'General Anesthesia and Apoptosis Study', 'Pediatric Anesthesia NeuroDevelopment Assessment', and 'Mayo Safety in Kids' trials will offer more answers in the future. Meanwhile, laboratory experiments continue to describe differential morphologic injury to individual structures in the neuropil, and have identified mitochondrial dysfunction and neuroinflammation as potential links in the injury process. Additionally, concepts for protection against anesthesia-induced neurotoxicity continue to be tested in the laboratory.

SUMMARY

Results from ongoing prospective clinical trials and translational research will help clarify whether anesthesia-associated neurotoxicity affects the developing human brain, including whether it causes long-term disability, and may further identify the injury mechanisms and potential strategies for protection. Currently, the available evidence does not support a change in practice.

Comparison of neurodegeneration and cognitive impairment in neonatal mice exposed to propofol or isoflurane

Background

While previous studies have demonstrated neuronal apoptosis and associated cognitive impairment after isoflurane or propofol exposure in neonatal rodents, the effects of these two anesthetics have not been directly compared. Here, we compare and contrast the effectiveness of isoflurane and propofol to cause neurodegeneration in the developing brain and associated cognitive dysfunction.

Methods

Seven-day-old mice were used. Mice in the isoflurane treatment group received 6 h of 1.5% isoflurane, while mice in propofol treatment group received one peritoneal injection (150 mg/kg), which produced persistent anesthesia with loss of righting for at least 6 h. Mice in control groups received carrying gas or a peritoneal injection of vehicle (intralipid). At 6 h after anesthetic treatment, a subset of each group was sacrificed and examined for evidence of neurodegeneration, using plasma levels of S100β, and apoptosis using caspase-3 immunohistochemistry in the cerebral cortex and hippocampus and Western blot assays of the cortex. In addition, biomarkers for inflammation (interleukin-1, interleukin-6, and tumor necrosis factor alpha) were examined with Western blot analyses of the cortex. In another subset of mice, learning and memory were assessed 32 days after the anesthetic exposures using the Morris water maze.

Results

Isoflurane significantly increased plasma S100β levels compared to controls and propofol. Both isoflurane and propofol significantly increased caspase-3 levels in the cortex and hippocampus, though isoflurane was significantly more potent than propofol. However, there were no significant differences in the inflammatory biomarkers in the cortex or in subsequent learning and memory between the experimental groups.

Conclusion

Both isoflurane and propofol caused significant apoptosis in the mouse developing brain, with isoflurane being more potent. Isoflurane significantly increased levels of the plasma neurodegenerative biomarker, S100β. However, these neurodegenerative effects of isoflurane and propofol in the developing brain were not associated with effects on inflammation or with cognitive dysfunction in later life.

Anaesthetics-induced neurotoxicity in developing brain: an update on preclinical evidence

Every year millions of young people are treated with anaesthetic agents for surgery and sedation in a seemingly safe manner. However, growing and convincing preclinical evidence in rodents and nonhuman primates, together with recent epidemiological observations, suggest that exposure to anaesthetics in common clinical use can be neurotoxic to the developing brain and lead to long-term neurological sequelae. These findings have seriously questioned the safe use of general anaesthetics in obstetric and paediatric patients. The mechanisms and human applicability of anaesthetic neurotoxicity and neuroprotection have remained under intense investigation over the past decade. Ongoing pre-clinical investigation may have significant impact on clinical practice in the near future. This review represents recent developments in this rapidly emerging field. The aim is to summarise recently available laboratory data, especially those being published after 2010, in the field of anaesthetics-induced neurotoxicity and its impact on cognitive function. In addition, we will discuss recent findings in mechanisms of early-life anaesthetics-induced neurotoxicity, the role of human stem cell-derived models in detecting such toxicity, and new potential alleviating strategies.

Antioxidants L-carnitine and D-methionine modulate neuronal activity through GABAergic inhibition

Antioxidants are well known for their neuroprotective properties against reactive oxygen species in cortical neurons and auditory cells. We recently identified L-carnitine and D-methionine to be among agents that provide such protection. Here, we investigated their neuronal modulatory actions. We used cultured neuronal networks grown on microelectrode arrays to assess the effects of L-carnitine and D-methionine on network function. Spike production and burst properties of neuronal networks were used as parameters to monitor pharmacological responses. L-Carnitine and D-methionine reduced spike activity with 100% efficacy with EC50 values of 0.22 (± 0.01) mM and 1.06 (± 0.05) mM, respectively. In the presence of 1.0-40 μM of the GABAA antagonist bicuculline, the sigmoidal concentration-response curves of both compounds exhibited stepwise shifts, without a change in efficacy. Under a maximal bicuculline concentration of 40 μM, the EC50 increased to 3.57 (± 0.26) mM for L-carnitine and to 10.52 (± 0.97) mM for D-methionine, more than a tenfold increase. The agonist-antagonist interactions with bicuculline were estimated by Lineweaver-Burk plot analyses to be competitive, corroborated by the computed dissociation constants of bicuculline. For both compounds, the effects on the network burst pattern, activity reversibility, and bicuculline antagonism resembled that elicited by the GABAA agonist muscimol. We showed that the antioxidants L-carnitine and D-methionine modulate cortical electrical spike activity primarily through GABAA receptor activation. Our findings suggest the involvement of GABAergic mechanisms that perhaps contribute to the protective actions of these compounds.

Adverse effect of inhalational anesthetics on the developing brain

We did a PubMed search and summarized studies on the potential adverse effect of anesthetics especially neurotoxicity in the developing brain, so named anesthesia-induced developmental neurotoxicity. Even though many experimental studies using animal models indicated some adverse effect of anesthetics, more evidence is needed before a recommendation can be made to change the way those anesthetics are used in the pediatric population. Two large clinical trials are underway and may provide insight to the potential human neurotoxic effect of anesthetics.

Acetyl L-carnitine protects motor neurons and Rohon-Beard sensory neurons against ketamine-induced neurotoxicity in zebrafish embryos

Ketamine, a non-competitive antagonist of N-methyl-D-aspartate (NMDA) type glutamate receptors is commonly used as a pediatric anesthetic. Multiple studies have shown ketamine to be neurotoxic, particularly when administered during the brain growth spurt. Previously, we have shown that ketamine is detrimental to motor neuron development in the zebrafish embryos. Here, using both wild type (WT) and transgenic (hb9:GFP) zebrafish embryos, we demonstrate that ketamine is neurotoxic to both motor and sensory neurons. Drug absorption studies showed that in the WT embryos, ketamine accumulation was approximately 0.4% of the original dose added to the exposure medium. The transgenic embryos express green fluorescent protein (GFP) localized in the motor neurons making them ideal for evaluating motor neuron development and toxicities in vivo. The hb9:GFP zebrafish embryos (28 h post fertilization) treated with 2 mM ketamine for 20 h demonstrated significant reductions in spinal motor neuron numbers, while co-treatment with acetyl L-carnitine proved to be neuroprotective. In whole mount immunohistochemical studies using WT embryos, a similar effect was observed for the primary sensory neurons. In the ketamine-treated WT embryos, the number of primary sensory Rohon-Beard (RB) neurons was significantly reduced compared to that in controls. However, acetyl L-carnitine co-treatment prevented ketamine-induced adverse effects on the RB neurons. These results suggest that acetyl L-carnitine protects both motor and sensory neurons from ketamine-induced neurotoxicity.

Functional implications of an early exposure to general anesthesia: are we changing the behavior of our children?

There is a rapidly growing body of animal and clinical evidence suggesting that the exposure to anesthetics and sedatives during the critical stages of brain development results in long-lasting (perhaps permanent) impairment in cognitive development in a variety of mammalian species. With improved understanding of the mechanisms responsible for behavioral outcomes of anesthesia-induced developmental neurotoxicity, there is hope for development of protective strategies that will enable safe use of anesthesia in the youngest members of our society. Here, I review presently available evidence regarding anesthesia-induced neurocognitive and social behavioral impairments and possible strategies for preventing them. I also review limited and somewhat controversial evidence that examines the effects of nociception and surgical stimulation on anesthesia--induced developmental neurotoxicity.

Anaesthetic neurotoxicity and neuroplasticity: an expert group report and statement based on the BJA Salzburg Seminar

Although previously considered entirely reversible, general anaesthesia is now being viewed as a potentially significant risk to cognitive performance at both extremes of age. A large body of preclinical as well as some retrospective clinical evidence suggest that exposure to general anaesthesia could be detrimental to cognitive development in young subjects, and might also contribute to accelerated cognitive decline in the elderly. A group of experts in anaesthetic neuropharmacology and neurotoxicity convened in Salzburg, Austria for the BJA Salzburg Seminar on Anaesthetic Neurotoxicity and Neuroplasticity. This focused workshop was sponsored by the British Journal of Anaesthesia to review and critically assess currently available evidence from animal and human studies, and to consider the direction of future research. It was concluded that mounting evidence from preclinical studies reveals general anaesthetics to be powerful modulators of neuronal development and function, which could contribute to detrimental behavioural outcomes. However, definitive clinical data remain elusive. Since general anaesthesia often cannot be avoided regardless of patient age, it is important to understand the complex mechanisms and effects involved in anaesthesia-induced neurotoxicity, and to develop strategies for avoiding or limiting potential brain injury through evidence-based approaches.

Impact of anaesthetics and surgery on neurodevelopment: an update

Accumulating preclinical and clinical evidence suggests the possibility of neurotoxicity from neonatal exposure to general anaesthetics. Here, we review the weight of the evidence from both human and animal studies and discuss the putative mechanisms of injury and options for protective strategies. Our review identified 55 rodent studies, seven primate studies, and nine clinical studies of interest. While the preclinical data consistently demonstrate robust apoptosis in the nervous system after anaesthetic exposure, only a few studies have performed cognitive follow-up. Nonetheless, the emerging evidence that the primate brain is vulnerable to anaesthetic-induced apoptosis is of concern. The impact of surgery on anaesthetic-induced brain injury has not been adequately addressed yet. The clinical data, comprising largely retrospective cohort database analyses, are inconclusive, in part due to confounding variables inherent in these observational epidemiological approaches. This places even greater emphasis on prospective approaches to this problem, such as the ongoing GAS trial and PANDA study.