Brain regional vulnerability to anaesthesia-induced neuroapoptosis shifts with age at exposure and extends into adulthood for some regions

Early childhood general anesthesia and risk of Attention Deficit Hyperactivity Disorder

BACKGROUND

The relationship between early childhood exposure to general anesthesia (GA) and the risk of developing Attention Deficit Hyperactivity Disorder (ADHD) is still uncertain and previous studies have presented conflicting results. This population-based cohort study aimed to investigate the potential relationship between GA exposure and ADHD risk using propensity score matching (PSM) in a large sample size.

METHODS

The study included 15,072 children aged 0-3 years who received GA and were hospitalized for more than 1 day in Taiwan from 2004 to 2014. The nonexposed group was randomly selected through 1:1 PSM from the Taiwan Maternal and Child Health Database (TMCHD). The primary objectives of this study were to determine the incidence rates (IR) and incidence rate ratios (IRR) of ADHD in the two cohorts, employing Poisson regression models.

RESULTS

The GA group and non-GA group each comprised 7,536 patients. The IR of ADHD was higher in the GA group (122.45 per 10,000 person-years) than in the non-GA group (64.15 per 10,000 person-years), and the IRR of ADHD in the GA group was 1.39 (95% CI: 1.26, 1.55). The study found that the number of times of exposure to GA, duration of exposure, male gender, and central nervous system surgery were significant risk factors for ADHD in the future.

CONCLUSIONS

This study's findings suggest that there is a significant correlation between early childhood exposure to GA and the risk of developing ADHD, and GA may be an important risk factor for ADHD in children undergoing surgery. The study also identified several risk factors for ADHD, including the number of times of exposure to GA, duration of exposure, male gender, and central nervous system surgery.

Brief isoflurane administration as an adjunct treatment to control organophosphate-induced convulsions and neuropathology

Organophosphate-based chemical agents (OP), including nerve agents and certain pesticides such as paraoxon, are potent acetylcholinesterase inhibitors that cause severe convulsions and seizures, leading to permanent central nervous system (CNS) damage if not treated promptly. The current treatment regimen for OP poisoning is intramuscular injection of atropine sulfate with an oxime such as pralidoxime (2-PAM) to mitigate cholinergic over-activation of the somatic musculature and autonomic nervous system. This treatment does not provide protection against CNS cholinergic overactivation and therefore convulsions require additional medication. Benzodiazepines are the currently accepted treatment for OP-induced convulsions, but the convulsions become refractory to these GABAA agonists and repeated dosing has diminishing effectiveness. As such, adjunct anticonvulsant treatments are needed to provide improved protection against recurrent and prolonged convulsions and the associated excitotoxic CNS damage that results from them. Previously we have shown that brief, 4-min administration of 3%-5% isoflurane in 100% oxygen has profound anticonvulsant and CNS protective effects when administered 30 min after a lethal dose of paraoxon. In this report we provide an extended time course of the effectiveness of 5% isoflurane delivered for 5 min, ranging from 60 to 180 min after a lethal dose of paraoxon in rats. We observed substantial effectiveness in preventing neuronal loss as shown by Fluoro-Jade B staining when isoflurane was administered 1 h after paraoxon, with diminishing effectiveness at 90, 120 and 180 min. In vivo magnetic resonance imaging (MRI) derived T2 and mean diffusivity (MD) values showed that 5-min isoflurane administration at a concentration of 5% prevents brain edema and tissue damage when administered 1 h after a lethal dose of paraoxon. We also observed reduced astrogliosis as shown by GFAP immunohistochemistry. Studies with continuous EEG monitoring are ongoing to demonstrate effectiveness in animal models of soman poisoning.

Whole-brain characterization of apoptosis after sevoflurane anesthesia reveals neuronal cell death patterns in the mouse neonatal neocortex

In the last two decades, safety concerns about general anesthesia (GA) arose from studies documenting brain cell death in various pharmacological conditions and animal models. Nowadays, a thorough characterization of sevoflurane-induced apoptosis in the entire neonatal mouse brain would help identify and further focus on underlying mechanisms. We performed whole-brain mapping of sevoflurane-induced apoptosis in post-natal day (P) 7 mice using tissue clearing and immunohistochemistry. We found an anatomically heterogenous increase in cleaved-caspase-3 staining. The use of a novel P7 brain atlas showed that the neocortex was the most affected area, followed by the striatum and the metencephalon. Histological characterization in cortical slices determined that post-mitotic neurons were the most affected cell type and followed inter- and intracortical gradients with maximal apoptosis in the superficial layers of the posterodorsal cortex. The unbiased anatomical mapping used here allowed us to confirm sevoflurane-induced apoptosis in the perinatal period, neocortical involvement, and indicated striatal and metencephalic damage while suggesting moderate hippocampal one. The identification of neocortical gradients is consistent with a maturity-dependent mechanism. Further research could then focus on the interference of sevoflurane with neuronal migration and survival during development.

Ketamine impairs growth cone and synaptogenesis in human GABAergic projection neurons via GSK-3β and HDAC6 signaling

The growth cone guides the axon or dendrite of striatal GABAergic projection neurons that protrude into the midbrain and cortex and form complex neuronal circuits and synaptic networks in a developing brain, aberrant projections and synaptic connections in the striatum related to multiple brain disorders. Previously, we showed that ketamine, an anesthetic, reduced dendritic growth, dendritic branches, and spine density in human striatal GABAergic neurons. However, whether ketamine affects the growth cone, the synaptic connection of growing striatal GABAergic neurons has not been tested. Using human GABAergic projection neurons derived from human inducible pluripotent stem cells (hiPSCs) and embryonic stem cells (ES) in vitro, we tested ketamine effects on the growth cones and synapses in developing GABAergic neurons by assessing the morphometry and the glycogen synthase kinase-3 (GSK-3) and histone deacetylase 6 (HDAC6) pathway. Ketamine exposure impairs growth cone formation, synaptogenesis, dendritic development, and maturation via ketamine-mediated activation of GSK-3 pathways and inhibiting HDAC6, an essential stabilizing protein for dendritic morphogenesis and synapse maturation. Our findings identified a novel ketamine neurotoxic pathway that depends on GSK-3β and HDAC6 signaling, suggesting that microtubule acetylation is a potential target for reducing ketamine's toxic effect on GABAergic projection neuronal development.

Bumetanide attenuates sevoflurane-induced neuroapoptosis in the developing dentate gyrus and impaired behavior in the contextual fear discrimination learning test

INTRODUCTION

Sevoflurane acts as a gamma-aminobutyric acid subtype A receptor agonist and can induce widespread apoptosis of immature dentate granule cells in postnatal day 21 mice. The dentate granule cells of postnatal day 21 mice undergo a developmental stage when gamma-aminobutyric acid (GABA) shifts from inducing the depolarization of neurons to causing hyperpolarization. However, it is unclear whether sevoflurane induces apoptosis of immature granule cells by facilitating the depolarization or hyperpolarization of neurons.

METHODS

We utilized bumetanide, an Na⁺ -K⁺ -2Cl^- cotransporter isoform 1 (NKCC1) antagonist, to determine whether the NKCC1-mediated GABA depolarization of neurons plays a role in sevoflurane-induced neuroapoptosis. We also investigated whether sevoflurane exposure is related to long-term cognitive dysfunction in postnatal day 21 mice and explored the possible protective effects of bumetanide.

RESULTS

Bumetanide attenuated the sevoflurane-induced apoptosis of dentate granule cells in postnatal day 21 mice. Exposure to sevoflurane at postnatal day 21 mice did not affect their motor ability or anxiety level, and it had no effect on spatial learning or memory functions. However, sevoflurane exposure at postnatal day 21 impaired the pattern separation ability in the contextual fear discrimination test; bumetanide mitigated this effect of sevoflurane as well.

CONCLUSION

Bumetanide attenuates sevoflurane-induced apoptosis and is a promising prospect for protecting against anesthesia-induced neurotoxicity in the developing brain.

RIPK1/RIPK3-Mediated Necroptosis is Involved in Sevoflurane-Induced Neonatal Neurotoxicity in the Rat Hippocampus

Recent studies have shown that exposure to sevoflurane in developing brains causes neuronal apoptosis and cognitive dysfunction. "Necroptosis" is a novel pathway of necrosis. We introduced the caspase-specific inhibitor Z-VAD in addition to the receptor-interacting protein kinase 1 (RIPK1) inhibitor Nec-1, to ascertain the existence and importance of necroptosis. Sprague-Dawley rat pups postnatal day 7 were randomly assigned into one of five groups: control, sevoflurane + Z-VAD, sevoflurane + Nec-1, sevoflurane + Z-VAD + Nec-1 and 3% sevoflurane group. Neuronal apoptosis was evaluated by hematoxylin and eosin staining. The MTT assay was performed to evaluate cell viability. Immunofluorescence was employed to measure expression of RIPK1 and RIPK3. Western blots showing expression of RIPK1, RIPK3 and phosphorylation of mixed lineage kinase domain-like (p-MLKL) were used to explore the role of necroptosis. Binding of RIPK1/RIPK3 was detected via co-immunoprecipitation. Finally, the Morris water maze test was used to determine cognitive function. Exposure to 3% sevoflurane for 6 h induced neurotoxicity and inhibited cell viability. Neuron viability was low in the SEV, SEV + Z-VAD and SEV + Nec-1 groups. The study revealed that RIPK1 and RIPK3 protein expression increased significantly, but there was no significant differences between the SEV and SEV + Z-VAD groups. The expression of p-MLKL significantly increased in the SEV and SEV + Z-VAD groups, but not in the SEV + Nec-1 group or SEV + Z-VAD + Nec-1 group compared to the control group. Co-immunoprecipitation results showed that sevoflurane exposure enhanced binding of RIPK1/RIPK3 protein significantly. Blockade of apoptosis and necroptosis alleviated sevoflurane-induced cognitive impairment. Sevoflurane exposure elicited neurotoxicity within neonatal hippocampal neurons and tissues. Blockade of apoptosis or necroptosis alone did not attenuate sevoflurane-induced neurotoxicity (SIN). RIPK1/RIPK3-mediated necroptosis was involved in SIN in hippocampal neurons. SIN could be attenuated only by inhibiting both apoptosis and necroptosis.

General anesthesia in children and long-term neurodevelopmental deficits: A systematic review

Background

Millions of children experienced surgery procedures requiring general anesthesia (GA). Any potential neurodevelopmental risks of pediatric anesthesia can be a serious public health issue. Various animal studies have provided evidence that commonly used GA induced a variety of morphofunctional alterations in the developing brain of juvenile animals.

Methods

We conducted a systematic review to provide a brief overview of preclinical studies and summarize the existing clinical studies. Comprehensive literature searches of PubMed, EMBASE, CINAHL, OVID Medline, Web of Science, and the Cochrane Library were conducted using the relevant search terms “general anesthesia,” “neurocognitive outcome,” and “children.” We included studies investigating children who were exposed to single or multiple GA before 18, with long-term neurodevelopment outcomes evaluated after the exposure(s).

Results

Seventy-two clinical studies originating from 18 different countries published from 2000 to 2022 are included in this review, most of which are retrospective studies (n = 58). Two-thirds of studies (n = 48) provide evidence of negative neurocognitive effects after GA exposure in children. Neurodevelopmental outcomes are categorized into six domains: academics/achievement, cognition, development/behavior, diagnosis, brain studies, and others. Most studies focusing on children <7 years detected adverse neurocognitive effects following GA exposure, but not all studies consistently supported the prevailing view that younger children were at greater risk than senior ones. More times and longer duration of exposures to GA, and major surgeries may indicate a higher risk of negative outcomes.

Conclusion

Based on current studies, it is necessary to endeavor to limit the duration and numbers of anesthesia and the dose of anesthetic agents. For future studies, we require cohort studies with rich sources of data and appropriate outcome measures, and carefully designed and adequately powered clinical trials testing plausible interventions in relevant patient populations.

The impact of early exposure to general anesthesia on visual and neurocognitive development

Every year millions of children are exposed to general anesthesia while undergoing surgical and diagnostic procedures. In the field of ophthalmology, 44,000 children are exposed to general anesthesia annually for strabismus surgery alone. While it is clear that general anesthesia is necessary for sedation and pain minimization during surgical procedures, the possibility of neurotoxic impairments from its exposure is of concern. In animals there is strong evidence linking early anesthesia exposure to abnormal neural development. but in humans the effects of anesthesia are debated. In humans many aspects of vision develop within the first year of life, making the visual system vulnerable to early adverse experiences and potentially vulnerable to early exposure to general anesthesia. We attempt to address whether the visual system is affected by early postnatal exposure to general anesthesia. We first summarize key mechanisms that could account for the neurotoxic effects of general anesthesia on the developing brain and review existing literature on the effects of early anesthesia exposure on the visual system in both animals and humans and on neurocognitive development in humans. Finally, we conclude by proposing future directions for research that could address unanswered questions regarding the impact of general anesthesia on visual development.

Early Development of the GABAergic System and the Associated Risks of Neonatal Anesthesia

Human and animal studies have elucidated the apparent neurodevelopmental effects resulting from neonatal anesthesia. Observations of learning and behavioral deficits in children, who were exposed to anesthesia early in development, have instigated a flurry of studies that have predominantly utilized animal models to further interrogate the mechanisms of neonatal anesthesia-induced neurotoxicity. Specifically, while neonatal anesthesia has demonstrated its propensity to affect multiple cell types in the brain, it has shown to have a particularly detrimental effect on the gamma aminobutyric acid (GABA)ergic system, which contributes to the observed learning and behavioral deficits. The damage to GABAergic neurons, resulting from neonatal anesthesia, seems to involve structure-specific changes in excitatory-inhibitory balance and neurovascular coupling, which manifest following a significant interval after neonatal anesthesia exposure. Thus, to better understand how neonatal anesthesia affects the GABAergic system, we first review the early development of the GABAergic system in various structures that have been the focus of neonatal anesthesia research. This is followed by an explanation that, due to the prolonged developmental curve of the GABAergic system, the entirety of the negative effects of neonatal anesthesia on learning and behavior in children are not immediately evident, but instead take a substantial amount of time (years) to fully develop. In order to address these concerns going forward, we subsequently offer a variety of in vivo methods which can be used to record these delayed effects.

Evaluation of neurotoxicity and long-term function and behavior following intrathecal 1 % 2-chloroprocaine in juvenile rats

Spinally-administered local anesthetics provide effective perioperative anesthesia and/or analgesia for children of all ages. New preparations and drugs require preclinical safety testing in developmental models. We evaluated age-dependent efficacy and safety following 1 % preservative-free 2-chloroprocaine (2-CP) in juvenile Sprague-Dawley rats. Percutaneous lumbar intrathecal 2-CP was administered at postnatal day (P)7, 14 or 21. Mechanical withdrawal threshold pre- and post-injection evaluated the degree and duration of sensory block, compared to intrathecal saline and naive controls. Tissue analyses one- or seven-days following injection included histopathology of spinal cord, cauda equina and brain sections, and quantification of neuronal apoptosis and glial reactivity in lumbar spinal cord. Following intrathecal 2-CP or saline at P7, outcomes assessed between P30 and P72 included: spinal reflex sensitivity (hindlimb thermal latency, mechanical threshold); social approach (novel rat versus object); locomotor activity and anxiety (open field with brightly-lit center); exploratory behavior (rearings, holepoking); sensorimotor gating (acoustic startle, prepulse inhibition); and learning (Morris Water Maze). Maximum tolerated doses of intrathecal 2-CP varied with age (1.0 μL/g at P7, 0.75 μL/g at P14, 0.5 μL/g at P21) and produced motor and sensory block for 10-15 min. Tissue analyses found no significant differences across intrathecal 2-CP, saline or naïve groups. Adult behavioral measures showed expected sex-dependent differences, that did not differ between 2-CP and saline groups. Single maximum tolerated in vivo doses of intrathecal 2-CP produced reversible spinal anesthesia in juvenile rodents without detectable evidence of developmental neurotoxicity. Current results cannot be extrapolated to repeated dosing or prolonged infusion.

Testosterone attenuates sevoflurane-induced tau phosphorylation and cognitive impairment in neonatal male mice

BACKGROUND

Sevoflurane anaesthesia induces phosphorylation of the microtubule-associated protein tau and cognitive impairment in neonatal, but not adult, mice. The underlying mechanisms remain largely to be determined. Sex hormones can be neuroprotective, but little is known about the influence of testosterone on age-dependent anaesthesia effects.

METHODS

Six- and 60-day-old male mice received anaesthesia with sevoflurane 3% for 2 h daily for 3 days. Morris water maze, immunoassay, immunoblotting, co-immunoprecipitation, nanobeam technology, and electrophysiology were used to assess cognition; testosterone concentrations; tau phosphorylation; glycogen synthase kinase-3β (GSK3β) activation; binding or interaction between tau and GSK3β; and neuronal activation in mice, cells, and neurones.

RESULTS

Compared with 60-day-old male mice, 6-day-old male mice had lower testosterone concentrations (3.03 [0.29] vs 0.44 [0.12] ng ml^-1; P<0.01), higher sevoflurane-induced tau phosphorylation in brain (133 [20]% vs 100 [6]% in 6-day-old mice, P<0.01; 103 [8]% vs 100 [13]% in 60-day-old mice, P=0.77), and sevoflurane-induced cognitive impairment. Testosterone treatment increased brain testosterone concentrations (1.76 [0.10] vs 0.39 [0.05] ng ml^-1; P<0.01) and attenuated the sevoflurane-induced tau phosphorylation and cognitive impairment in neonatal male mice. Testosterone inhibited the interaction between tau and GSK3β, and attenuated sevoflurane-induced inhibition of excitatory postsynaptic currents in hippocampal neurones.

CONCLUSIONS

Lower brain testosterone concentrations in neonatal compared with adult male mice contributed to age-dependent tau phosphorylation and cognitive impairment after sevoflurane anaesthesia. Testosterone might attenuate the sevoflurane-induced tau phosphorylation and cognitive impairment by inhibiting the interaction between tau and GSK3β.

Intranasal insulin rescues repeated anesthesia-induced deficits in synaptic plasticity and memory and prevents apoptosis in neonatal mice via mTORC1

Long-lasting cognitive impairment in juveniles undergoing repeated general anesthesia has been observed in numerous preclinical and clinical studies, yet, the underlying mechanisms remain unknown and no preventive treatment is available. We found that daily intranasal insulin administration to juvenile mice for 7 days prior to repeated isoflurane anesthesia rescues deficits in hippocampus-dependent memory and synaptic plasticity in adulthood. Moreover, intranasal insulin prevented anesthesia-induced apoptosis of hippocampal cells, which is thought to underlie cognitive impairment. Inhibition of the mechanistic target of rapamycin complex 1 (mTORC1), a major intracellular effector of insulin receptor, blocked the beneficial effects of intranasal insulin on anesthesia-induced apoptosis. Consistent with this finding, mice lacking mTORC1 downstream translational repressor 4E-BP2 showed no induction of repeated anesthesia-induced apoptosis. Our study demonstrates that intranasal insulin prevents general anesthesia-induced apoptosis of hippocampal cells, and deficits in synaptic plasticity and memory, and suggests that the rescue effect is mediated via mTORC1/4E-BP2 signaling.

Isoflurane impairs oogenesis through germ cell apoptosis in C. elegans

Anesthetic isoflurane has been reported to induce toxicity. However, the effects of isoflurane on fecundity remain largely unknown. We established a system in C. elegans to investigate the effects of isoflurane on oogenesis. Synchronized L4 stage C. elegans were treated with 7% isoflurane for 4 h. Dead cells, ROS, embryos, and unfertilized eggs laid by hermaphrodites were measured by fluorescence imaging and counting. The C. elegans with losses of ced-3, cep-1, abl-1, male C. elegans, and oxidative stress inhibitor N-acetyl-cysteine were used in the interaction studies. We found that isoflurane decreased the numbers of embryos and unfertilized eggs and increased the levels of dead cells and ROS in C. elegans. The isoflurane-induced impairment of oogenesis was associated with abl-1, ced-3, but not cep-1. N-acetyl-cysteine attenuated the isoflurane-induced impairment of oogenesis in C. elegans. Mating with male C. elegans did not attenuate the isoflurane-induced changes in oogenesis. These findings suggest that isoflurane may impair oogenesis through abl-1- and ced-3-associated, but not cep-1-associated, germ cell apoptosis and oxidative stress, pending further investigation. These studies will promote more research to determine the potential effects of anesthesia on fecundity.

HDAC6 is critical for ketamine-induced impairment of dendritic and spine growth in GABAergic projection neurons

Ketamine is widely used in infants and children for anesthesia; both anesthetic and sub-anesthetic doses of ketamine have been reported to preferentially inhibit the GABAergic neurons. Medium spiny neurons (MSNs), the GABAergic projection neurons in the striatum, are vulnerable to anesthetic exposure in the newborn brain. Growth of dendrites requires a deacetylase to remove acetyl from tubulin in the growth cone to destabilize the tubulin. Histone deacetylase 6 (HDAC6) affects microtubule dynamics, which are involved in neurite elongation. In this study we used a human induced pluripotent stem cells (iPSCs)-derived striatal GABA neuron system to investigate the effects of ketamine on HDAC6 and the morphological development of MSNs. We showed that exposure to ketamine (1-500 μM) decreased dendritic growth, dendrite branches, and dendritic spine density in MSNs in a time- and concentration-dependent manner. We revealed that ketamine treatment concentration-dependently inhibited the expression of HDAC6 or aberrantly translocated HDAC6 into the nucleus. Ketamine inhibition on HDAC6 resulted in α-tubulin hyperacetylation, consequently increasing the stability of microtubules and delaying the dendritic growth of MSNs. Finally, we showed that the effects of a single-dose exposure on MSNs were reversible and lasted for at least 10 days. This study reveals a novel role of HDAC6 as a regulator for ketamine-induced deficits in the morphological development of MSNs and provides an innovative method for prevention and treatment with respect to ketamine clinical applications.

Surgery requiring general anesthesia in preterm infants is associated with altered brain volumes at term equivalent age and neurodevelopmental impairment

BACKGROUND

The aim of the study was to describe and contrast the brain development and outcome among very preterm infants that were and were not exposed to surgery requiring general anesthesia prior to term equivalent age (TEA).

METHODS

Preterm infants born ≤30 weeks' gestation who did (n = 25) and did not (n = 59) have surgery requiring general anesthesia during the preterm period were studied. At TEA, infants had MRI scans performed with measures of brain tissue volumes, cortical surface area, Gyrification Index, and white matter microstructure. Neurodevelopmental follow-up with the Bayley Scales of Infant and Toddler Development, Third Edition was undertaken at 2 years of corrected age. Multivariate models, adjusted for clinical and social risk factors, were used to compare the groups.

RESULTS

After controlling for clinical and social variables, preterm infants exposed to surgical anesthesia demonstrated decreased relative white matter volumes at TEA and lower cognitive and motor composite scores at 2-year follow-up. Those with longer surgical exposure demonstrated the greatest decrease in white matter volumes and lower cognitive and motor outcomes at age 2 years.

CONCLUSIONS

Very preterm infants who required surgery during the preterm period had lower white mater volumes at TEA and worse neurodevelopmental outcome at age 2 years.

IMPACT

In very preterm infants, there is an association between surgery requiring general anesthesia during the preterm period and reduced white mater volume on MRI at TEA and lower cognitive and motor composite scores at age 2 years. It is known that the very preterm infant's brain undergoes rapid growth during the period corresponding to the third trimester. The current study suggests an association between surgery requiring general anesthesia during this period and worse outcomes.

Effect of dexmedetomidine on sevoflurane-induced neurodegeneration in neonatal rats

BACKGROUND

Structural brain abnormalities in newborn animals after prolonged exposure to all routinely used general anaesthetics have raised substantial concerns for similar effects occurring in millions of children undergoing surgeries annually. Combining a general anaesthetic with non-injurious sedatives may provide a safer anaesthetic technique. We tested dexmedetomidine as a mitigating therapy in a sevoflurane dose-sparing approach.

METHODS

Neonatal rats were randomised to 6 h of sevoflurane 2.5%, sevoflurane 1% with or without three injections of dexmedetomidine every 2 h (resulting in 2.5, 5, 10, 25, 37.5, or 50 μg kg^-1 h^-1), or fasting in room air. Heart rate, oxygen saturation, level of hypnosis, and response to pain were measured during exposure. Neuronal cell death was quantified histologically after exposure.

RESULTS

Sevoflurane at 2.5% was more injurious than at 1% in the hippocampal cornu ammonis (CA)1 and CA2/3 subfields; ventral posterior and lateral dorsal thalamic nuclei; prefrontal, retrosplenial, and somatosensory cortices; and subiculum. Although sevoflurane 1% did not provide complete anaesthesia, supplementation with dexmedetomidine dose dependently increased depth of anaesthesia and diminished responses to pain. The combination of sevoflurane 1% and dexmedetomidine did not reliably reduce neuronal apoptosis relative to an equianaesthetic dose of sevoflurane 2.5%.

CONCLUSIONS

A sub-anaesthetic dose of sevoflurane combined with dexmedetomidine achieved a level of anaesthesia comparable with that of sevoflurane 2.5%. Similar levels of anaesthesia caused comparable programmed cell death in several developing brain regions. Depth of anaesthesia may be an important factor when comparing the neurotoxic effects of different anaesthetic regimens.

[Effect of Long-time Postnatal Exposure to Sevoflurane on Causing Attention-deficit/Hyperactivity Disorder in Rats]

OBJECTIVE

To investigate whether long-term exposure to inhaled sevoflurane, a volatile anesthetic, causes abnormal activities and memory impairment related to attention-deficit/hyperactivity disorder (ADHD) in neonatal rats.

METHODS

On postnatal day 5 (P5), Sprague-Dawley rats were randomly assigned to two sevoflurane subgroups and two control subgroups and underwent experimental intervention. The two sevoflurane (SEVO) subgroups were exposed to 3% sevoflurane for 2 h and 4 h respectively, while the two control subgroups were given pure oxygen for the same amount and duration. Behavioral tests, including open-field test (OFT), five-choice serial reaction time task (5-CSRTT), fear-conditioning (FC) and Morris water maze (MWM), were applied to evaluate changes in cognition, memory, anxiety and ADHD-related behavioral changes in the rats in adolescence (-P25) and in adulthood (-P65).

RESULTS

In OFT, the SEVO 2 h and SEVO 4 h subgroups displayed activity level and exploratory behaviors similar to those of the control subgroups on P21 and P61, with no statistically significant difference identified in the data. 5-CSRTT results on P25 and P65 indicated no statistically significant difference between the SEVO subgroups and the control subgroups in regard to ADHD-related abnormal behaviors, including number of immature reaction, rate of correct response and omission rate. In the FC experiment, SEVO 4 h group had a shorter freezing period and longer period of freezing latency ( P=0.029) in comparison to the control groups. The results of the MWM test showed that the escape latency period of rats in the SEVO 4 h group was significantly prolonged on the second day and the third day, compared to the control groups ( P<0.05). The average swimming speed of SEVO groups did no exhibit any statistically significant difference on P69 or P76. The time the SEVO 4 h group spent in the target quadrant was significantly shorter than that of the control group ( P=0.039) and percentage of distance traveled in the target quadrant was significantly reduced compared to that the control group ( P=0.048).

CONCLUSION

The findings suggest that four hours of inhaled sevoflurane exposure in neonate rats may cause memory impairment, but does no increase risks for ADHD-related abnormal activities.

Integrin-dependent microgliosis mediates ketamine-induced neuronal apoptosis during postnatal rat retinal development

PURPOSE

Remodeling of the extracellular matrix (ECM) by matrix metalloproteinases (MMPs) plays a pivotal role for microglia in developing retina. We tested whether integrin-dependent microgliosis mediates ketamine-induced neuronal apoptosis in the developing rat retina.

METHODS

We performed immunofluorescence assays to investigate the role of integrin receptors expressed in the microglia in ketamine-induced neuronal apoptosis. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) were used to investigate the protein and mRNA levels of cytokines (TNF-α, IL-1β) and/or chemokines (CCL2, CXCL6, CXCL10, and CXCL12). Experiments were performed using whole-mount retinas dissected from P7 Sprague-Dawley rats.

RESULTS

Integrin receptors expressed in microglia were upregulated in ketamine-induced neuronal apoptosis in the early developing rat retina. Downregulating integrin receptors with RGD peptide ameliorated ketamine-induced microgliosis through: 1) ameliorating the change in microglia morphology from immature ramified microglia to an amoeboid state; 2) decreasing the number of microglia and intensity of activated microglia in the retinal ganglion cell layer (GCL); and 3) decreasing cytokine (TNF-α and IL-1β) and chemokine (CCL2, CXCL10) levels in the retinal tissue. Inhibition of activated microglia with minocycline or the blockade of cytokines (TNF-α and IL-1β) with a receptor antagonist (RA) attenuated neuronal apoptosis after exposure to ketamine.

CONCLUSIONS

The upregulation of integrin β1 receptors in the microglia acts as a signaling molecule, triggering microgliosis to aggravate ketamine-induced neuronal apoptosis via the release of TNF-α and IL-1β in the early developing rat retina.

Sevoflurane-Induced Neuroapoptosis in Rat Dentate Gyrus Is Activated by Autophagy Through NF-κB Signaling on the Late-Stage Progenitor Granule Cells

Objective

The mechanisms by which exposure of the late-stage progenitor cells to the anesthesia sevoflurane alters their differentiation are not known. We seek to query whether the effects of sevoflurane on late-stage progenitor cells might be regulated by apoptosis and/or autophagy.

Methods

To address the short-term impact of sevoflurane exposure on granule cell differentiation, we used 5-bromo-2-deoxyuridine (BrdU) to identify the labeled late-stage progenitor granule cells. Male or female rats were exposed to 3% sevoflurane for 4 h when the labeled granule cells were 2 weeks old. Differentiation of the BrdU-labeled granule cells was quantified 4 and 7 days after exposure by double immunofluorescence. The expression of apoptosis and autophagy in hippocampal dentate gyrus (DG) was determined by western blot and immunofluorescence. Western blot for the expression of NF-κB was used to evaluate the mechanism. Morris water maze (MWM) test was performed to detect cognitive function in the rats on postnatal 28–33 days.

Results

Exposure to sevoflurane decreased the differentiation of the BrdU-labeled late-stage progenitor granule cells, but increased the expression of caspase-3, autophagy, and phosphorylated-P65 in the hippocampus of juvenile rats and resulted in cognitive deficiency. These damaging effects of sevoflurane could be mitigated by inhibitors of autophagy, apoptosis, and NF-κB. The increased apoptosis could be alleviated by pretreatment with the autophagy inhibitor 3-MA, and the increased autophagy and apoptosis could be reduced by pretreatment with NF-κB inhibitor BAY 11-7085.

Conclusion

These findings suggest that a single, prolonged sevoflurane exposure could impair the differentiation of late-stage progenitor granule cells in hippocampal DG and cause cognitive deficits possibly via apoptosis activated by autophagy through NF-κB signaling. Our results do not preclude the possibility that the affected differentiation and functional deficits may be caused by depletion of the progenitors pool.

General anesthesia activates the mitochondrial unfolded protein response and induces age-dependent, long-lasting changes in mitochondrial function in the developing brain

General anesthesia induces changes in dendritic spine number and synaptic transmission in developing mice. These changes are rather disturbing, as similar changes are seen in animal models of neurodevelopmental disorders. We previously suggested that mTor-dependent upregulation of mitochondrial function may be involved in such changes. To further understand the significance of mitochondrial changes after general anesthesia during neurodevelopment, we exposed young mice to 2.5 % sevoflurane for 2 h followed by injection of rotenone, a mitochondrial complex I inhibitor. In postnatal day 17 (PND17) mice, intraperitoneal injection of rotenone not only blocked sevoflurane-induced increases in mitochondrial function, it also prevented sevoflurane-induced changes in excitatory synaptic transmission. Interestingly, similar changes were not observed in younger, neonatal mice (PND7). We next assessed whether the mitochondrial unfolded protein response (UPR^mt) acted as a link between anesthetic exposure and mitochondrial function. Expression of UPR^mt proteins, which help maintain protein-folding homeostasis and increase mitochondrial function, was increased 6 h after sevoflurane exposure. Our results show that a single, brief sevoflurane exposure induces age-dependent changes in mitochondrial function that constitute an important mechanism for the increase in excitatory synaptic transmission in late postnatal mice, and also suggest mitochondria and UPR^mt as potential targets for preventing anesthesia toxicity.

The Effects of Anesthesia on Adult Hippocampal Neurogenesis

In animal studies, prolonged sedation with general anesthetics has resulted in cognitive impairments that can last for days to weeks after exposure. One mechanism by which anesthesia may impair cognition is by decreasing adult hippocampal neurogenesis. Several studies have seen a reduction in cell survival after anesthesia in rodents with most studies focusing on two particularly vulnerable age windows: the neonatal period and old age. However, the extent to which sedation affects neurogenesis in young adults remains unclear. Adult neurogenesis in the dentate gyrus (DG) was analyzed in male and female rats 24 h after a 4-h period of sedation with isoflurane, propofol, midazolam, or dexmedetomidine. Three different cell populations were quantified: cells that were 1 week or 1 month old, labeled with the permanent birthdate markers EdU or BrdU, respectively, and precursor cells, identified by their expression of the endogenous dividing cell marker proliferating cell nuclear antigen (PCNA) at the time of sacrifice. Midazolam and dexmedetomidine reduced cell proliferation in the adult DG in both sexes but had no effect on postmitotic cells. Propofol reduced the number of relatively mature, 28-day old, neurons specifically in female rats and had no effects on younger cells. Isoflurane had no detectable effects on any of the cell populations examined. These findings show no general effect of sedation on adult-born neurons but demonstrate that certain sedatives do have drug-specific and sex-specific effects. The impacts observed on different cell populations predict that any cognitive effects of these sedatives would likely occur at different times, with propofol producing a rapid but short-lived impairment and midazolam and dexmedetomidine altering cognition after a several week delay. Taken together, these studies lend support to the hypothesis that decreased neurogenesis in the young adult DG may mediate the effects of sedation on cognitive function.

Early childhood general anesthesia exposure associated with later developmental delay: A national population-based cohort study

Exposure to general anesthesia has been reported to induce neurotoxicity, impair learning, memory, attention, motor functions, as well as affect behavior in adult rodents and nonhuman primates. Though many have speculated similar effects in humans, previous literature has shown conflicting findings. To investigate the differences in risk of developmental delay among young children exposed to general anesthesia compared to matched unexposed individuals, a population-based cohort study was conducted with a longitudinal dataset spanning 2000 to 2013 from the Taiwan National Health Insurance Research Database (NHIRD). Procedure codes were used to identify children who received anesthesia. For each exposed child, two unexposed children matched by gender and age were enrolled into the comparison cohort. Neurocognitive outcome was measured by the presence of ICD-9-CM codes related to developmental delay (DD). Cox regression models were used to obtain hazard ratios of developing DD after varying levels of anesthesia exposure. After excluding 4,802 individuals who met the exclusion criteria, a total of 11,457 children who received general anesthesia before two years of age was compared to 22,914 children (matched by gender and age) unexposed to anesthesia. Increased risk of DD was observed in the exposure group with a hazard ratio (HR) of 1.320 (95% CI 1.143-1.522, P < 0.001). Subgroup analysis demonstrated further elevated risks of DD with multiple anesthesia exposures (1 anesthesia event: HR 1.145, 95% CI 1.010-1.246, P = 0.04; 2 anesthesia events: HR 1.476, 95% CI 1.155-1.887, P = 0.005; ≥3 anesthesia events: HR 2.222, 95% CI 1.810-2.621, P < 0.001) and longer total anesthesia durations (Total anesthesia <2 hours: HR 1.124, 95% CI 1.003-1.499, P = 0.047; Total anesthesia 2-4 hours: HR 1.450, 95% CI 1.157-1.800, P = 0.004; Total anesthesia > 4 hours: HR 1.598, 95% CI 1.343-1.982, P < 0.001) compared with children unexposed to anesthesia. These results suggest that children exposed to general anesthesia before two years of age have an increased risk of DD. This risk is further elevated with increased frequency of anesthesia, and longer total anesthesia duration. The findings of this study should prompt clinical practitioners to proceed with caution when assessing young patients and planning managements involving procedures requiring general anesthesia.

Is Anesthesia Bad for the Brain? Current Knowledge on the Impact of Anesthetics on the Developing Brain

There are compelling preclinical data that common general anesthetics cause increased neuroapoptosis in juvenile animals. Retrospective studies demonstrate that young children exposed to anesthesia have school difficulties, which could be caused by anesthetic neurotoxicity, perioperative hemodynamic and homeostatic instability, underlying morbidity, or the neuroinflammatory effects of surgical trauma. Unnecessary procedures should be avoided. Baseline measures of blood pressure are important in determining perioperative blood pressure goals. Inadvertent hypocapnia or moderate hypercapnia and hyperoxia or hypoxia should be avoided. Pediatric patients should be maintained in a normothermic, euglycemic state with neutral positioning. Improving outcomes of infants and children requires the collaboration of anesthesiologists, surgeons, pediatricians and neonatologists.

Regions of the basal ganglia and primary olfactory system are most sensitive to neurodegeneration after extended sevoflurane anesthesia in the perinatal rat

Extended general anesthesia early in life is neurotoxic in multiple species. However, little is known about the temporal progression of neurodegeneration after general anesthesia. It is also unknown if a reduction in natural cell death, or an increase in cell creation, occurs as a form of compensation after perinatal anesthesia exposure. The goal of this study was to evaluate markers of neurodegeneration and cellular division at 2, 24, or 72 h after sevoflurane (Sevo) exposure (6 h) in fully oxygenated postnatal day (PND) 7 rats. Neurodegeneration was observed in areas throughout the forebrain, while the largest changes (fold increase above vehicle) were observed in areas associated with either the primary olfactory learning pathways or the basal ganglia. These regions included the indusium griseum (IG, 25-fold), the posterior dorso medial hippocampal CA1 (17-fold), bed nucleus of the stria terminalis (Bed Nuclei STM, 5-fold), the shell of the nucleus accumbens (Acb, 5-fold), caudate/putamen (CPu, 5-fold), globus pallidus (GP, 9-fold) and associated thalamic (11-fold) and cortical regions (5-fold). Sevo neurodegeneration was minimal or undetectable in the ventral tegmentum, substantia nigra, and most of the hypothalamus and frontal cortex. In most brain regions where neurodegeneration was increased 2 h post Sevo exposure, the levels returned to <4-fold above control levels by 24 h. However, in the IG, CA1, GP, anterior thalamus, medial preoptic nucleus of the hypothalamus (MPO), anterior hypothalamic area (AHP), and the amygdaloid nuclei, neurodegeneration at 24 h was double or more than that at 2 h post exposure. Anesthesia exposure causes either a prolonged period of neurodegeneration in certain brain regions, or a distinct secondary degenerative event occurs after the initial insult. Moreover, regions most sensitive to Sevo neurodegeneration did not necessarily coincide with areas of new cell birth, and new cell birth was not consistently affected by Sevo. The profile of anesthesia related neurotoxicity changes with time, and multiple mechanisms of toxicity may exist in a time-dependent fashion.

Impact of anesthesia exposure in early development on learning and sensory functions

Each year, millions of children undergo anesthesia, and both human and animal studies have indicated that exposure to anesthesia at an early age can lead to neuronal damage and learning deficiency. However, disorders of sensory functions were not reported in children or animals exposed to anesthesia during infancy, which is surprising, given the significant amount of damage to brain tissue reported in many animal studies. In this review, we discuss the relationship between the systems in the brain that mediate sensory input, spatial learning, and classical conditioning, and how these systems could be affected during anesthesia exposure. Based on previous reports, we conclude that anesthesia can induce structural, functional, and compensatory changes in both sensory and learning systems. Changes in myelination following anesthesia exposure were observed as well as the neurodegeneration in the gray matter across variety of brain regions. Disproportionate cell death between excitatory and inhibitory cells induced by anesthesia exposure can lead to a long-term shift in the excitatory/inhibitory balance, which affects both learning-specific networks and sensory systems. Anesthesia may directly affect synaptic plasticity which is especially critical to learning acquisition. However, sensory systems appear to have better ability to compensate for damage than learning-specific networks.

Sevoflurane Induces Learning and Memory Impairment in Young Mice Through a Reduction in Neuronal Glucose Transporter 3

Sevoflurane, which is widely used in paediatric anaesthesia, induces neural apoptosis in the developing brain and cognitive impairment in young mammals. Glucose hypometabolism is the key pathophysiological modulator of cognitive dysfunction. However, the effects and mechanism of sevoflurane on cerebral glucose metabolism after its use as an anaesthetic and its complete elimination are still unknown. We therefore investigated the influence of sevoflurane on neuronal glucose transporter isoform 3 (GLUT3) expression, glucose metabolism and apoptosis in vivo and in vitro and on neurocognitive function in young mice 24 h after the third exposure to sevoflurane. Postnatal day 14 (P14) mice and neural cells were exposed to 3% sevoflurane 2 h daily for three days. We found that sevoflurane anaesthesia decreased GLUT3 gene and protein expression in the hippocampus and temporal lobe, consistent with a decrease in glucose metabolism in the hippocampus and temporal lobe observed by [18F] fluorodeoxyglucose positron emission tomography (18F-FDG PET). Moreover, sevoflurane anaesthesia increased the number of TUNEL-positive cells and the levels of Bax, cleaved caspase 3 and cleaved PARP and reduced Bcl-2 levels in the hippocampus and temporal lobe. Young mice exposed to sevoflurane multiple times also showed learning and memory impairment. In addition, sevoflurane inhibited GLUT3 expression in primary hippocampal neurons and PC12 cells. GLUT3 overexpression in cultured neurons ameliorated the sevoflurane-induced decrease in glucose utilization and increase in the apoptosis rate. These data indicate that GLUT3 deficiency may contribute to sevoflurane-induced learning and memory deficits in young mice.

TRPM2 channel regulates cytokines production in astrocytes and aggravates brain disorder during lipopolysaccharide-induced endotoxin sepsis

Sepsis is one of the most significant challenges in intensive care units, which is associated with increased morbidity and mortality. Sepsis-associated encephalopathy (SAE) is a severe complication which can cause death and serious disabilities. Calcium signaling in astrocyte is essential for cellular activation and the potential resolution of infection or inflammation in SAE patients. The transient receptor potential melastatin 2 (TRPM2) channel has been identified as a unique fusion of a Ca2+-permeable nonselective cation channel, which plays an important role in inflammation and immune response. Because of its role as an oxidative stress sensor in astrocytes, we investigated the function of TRPM2 in inflammation mediators (interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α) release, Bcl-2/E1B-19 K-interacting protein 3 (BNIP3), apoptosis inducing factor (AIF) and Endonuclease G (Endo G) expression. We showed that TRPM2-KO mice, when intraperitoneally (i.p) injected with LPS, exhibited better neurologic assessment scores and decreased inflammatory injury in hippocampal neurons compared with wild-type (WT) mice. The absence of TRPM2 triggered less production of inflammatory mediators (IL-1β, IL-6, TNF-α) and decreased apoptosis related proteins (BNIP3, AIF, Endo G) expressions in response to LPS induced sepsis. Furthermore, TRPM2-deficient astrocytes (transfected with TRPM2 siRNA) upon LPS stimulation also induced decreased IL-1β, IL-6 and TNF-α level. Our data suggested that decreased production of inflammatory cytokines and apoptosis related proteins with TRPM2 deletion could regulate inflammatory stress and decrease inflammatory injury in hippocampal neurons, and consequently, ameliorate brain disorder.

Defining the Vulnerability Window of Anesthesia-Induced Neuroapoptosis in Developing Dentate Gyrus Granule Cells - A Transgenic Approach Utilizing POMC-EGFP Mice

Exposure to commonly used anesthetics is associated with widespread neuroapoptosis in neonatal animals. Vulnerability of developing hippocampal dentate gyrus granule cells to anesthetic neurotoxicity peaks approximately 2 weeks after cell birth, as measured by bromodeoxyuridine birth dating, regardless of the age of the animal. The present study examined whether the vulnerable window can be further characterized by utilizing a transgenic approach. Proopiomelanocortin enhanced green fluorescent protein (POMC-EGFP) mice (postnatal day 21) were exposed to 3% sevoflurane for 6 h. Following exposure, cleaved caspase 3, expression of EGFP and differential maturational markers were quantified and compared with unanesthetized littermates. Electrophysiological properties of EGFP⁺ and EGFP^- cells in the subgranular zone and the inner half of the granule cell layer were recorded by whole-cell patch-clamp. We found that sevoflurane significantly increased apoptosis of POMC-EGFP⁺ granule cells that accounted for approximate 1/3 of all apoptotic cells in dentate gyrus. Apoptotic EGFP^- granule cells more frequently expressed the immature neuronal marker calretinin (75.4% vs 45.0%, P < 0.001) and less frequently the late progenitor marker NeuroD1 (21.9% vs 87.9%, P < 0.001) than EGFP⁺ granule cells. Although EGFP^- granule cells were more mature in immunostaining than EGFP⁺ granule cells, their electrophysiological properties partially overlapped in terms of input resistance, resting membrane potential and action potential amplitude. Our results revealed the POMC stage, when GABA acts as an excitatory neurotransmitter, only partly captures susceptibility to anesthetic neurotoxicity, suggesting the vulnerable window of anesthesia-induced neuroapoptosis extends from the end of POMC⁺ stage to the post-POMC⁺ stage when depolarizing glutamatergic inputs emerge.

Neonatal exposure to propofol affects interneuron development in the piriform cortex and causes neurobehavioral deficits in adult mice

RATIONALE

Animal studies have shown that early postnatal propofol administration is involved in neurobehavioral alterations in adults. However, the underlying mechanism is not clear.

METHODS

We used c-Fos immunohistochemistry to identify activated neurons in brain regions of neonatal mice under propofol exposure and performed behavioral tests to observe the long-term consequences.

RESULTS

Exposure to propofol (30g or 60 mg/kg) on P7 produced significant c-Fos expression in the deep layers of the piriform cortex on P8. Double immunofluorescence of c-Fos with interneuron markers in the piriform cortex revealed that c-Fos was specifically induced in calbindin (CB)-positive interneurons. Repeated propofol exposure from P7 to P9 induced behavioral deficits in adult mice, such as olfactory function deficit in a buried food test, decreased sociability in a three-chambered choice task, and impaired recognitive ability of learning and memory in novel object recognition tests. However, locomotor activity in the open-field test was not generally affected. Propofol treatment also significantly decreased the number of CB-positive interneurons in the piriform cortex of mice on P21 and adulthood.

CONCLUSIONS

These results suggest that CB-positive interneurons in the piriform cortex are vulnerable to propofol exposure during the neonatal period, and these neurons are involved in the damage effects of propofol on behavior changes. These data provide a new target of propofol neurotoxicity and may elucidate the mechanism of neurobehavioral deficits in adulthood.

Impact of Traumatic Brain Injury on Neurogenesis

New neurons are generated in the hippocampal dentate gyrus from early development through adulthood. Progenitor cells and immature granule cells in the subgranular zone are responsive to changes in their environment; and indeed, a large body of research indicates that neuronal interactions and the dentate gyrus milieu regulates granule cell proliferation, maturation, and integration. Following traumatic brain injury (TBI), these interactions are dramatically altered. In addition to cell losses from injury and neurotransmitter dysfunction, patients often show electroencephalographic evidence of cortical spreading depolarizations and seizure activity after TBI. Furthermore, treatment for TBI often involves interventions that alter hippocampal function such as sedative medications, neuromodulating agents, and anti-epileptic drugs. Here, we review hippocampal changes after TBI and how they impact the coordinated process of granule cell adult neurogenesis. We also discuss clinical TBI treatments that have the potential to alter neurogenesis. A thorough understanding of the impact that TBI has on neurogenesis will ultimately be needed to begin to design novel therapeutics to promote recovery.

What do recent human studies tell us about the association between anaesthesia in young children and neurodevelopmental outcomes?

Anaesthetic and sedative drugs transiently disrupt normal neural activity to facilitate healthcare procedures in children, but they can also cause long-term brain injury in experimental animal models. The US Food and Drug Administration (FDA) has recently advised that repeated or lengthy exposures to anaesthetic and sedative drugs prior to 3 yr of age have the potential to harm the development of children's brains and added warnings to these drug labels. Paediatric anaesthesia toxicity could represent a significant public health issue, and concern about this potential injury in children has become an important issue for families, paediatric clinicians and healthcare regulators. Since late 2015, important new data from five major clinical studies have been published. This narrative review aims to provide a brief overview of the preclinical and clinical literature, including a comprehensive review of these recent additions to the human literature. We integrate these new data with prior studies to provide further insights into how these clinical findings can be applied to children.

Alternative technique or mitigating strategy for sevoflurane-induced neurodegeneration: a randomized controlled dose-escalation study of dexmedetomidine in neonatal rats

Background

Brain injury in newborn animals from prolonged anaesthetic exposure has raised concerns for millions of children undergoing anaesthesia every yr. Alternative anaesthetic techniques or mitigating strategies are urgently needed to ameliorate potentially harmful effects. We tested dexmedetomidine, both as a single agent alternative technique and as a mitigating adjuvant for sevoflurane anaesthesia.

Methods

Neonatal rats were randomized to three injections of dexmedetomidine (5, 25, 50, or 100 µg kg -1 every 2 h), or 6 h of 2.5% sevoflurane as a single agent without or with dexmedetomidine (1, 5, 10, or 20 µg kg -1 every 2 h). Heart rate, oxygen saturation, level of consciousness, and response to pain were assessed. Cell death was quantified in several brain regions.

Results

Dexmedetomidine provided lower levels of sedation and pain control than sevoflurane. Exposure to either sevoflurane or dexmedetomidine alone did not cause mortality, but the combination of 2.5% sevoflurane and dexmedetomidine in doses exceeding 1 µg kg -1 did. Sevoflurane increased apoptosis in all brain regions; supplementation with dexmedetomidine exacerbated neuronal injury, potentially as a result of ventilatory or haemodynamic compromise. Dexmedetomidine by itself increased apoptosis only in CA2/3 and the ventral posterior nucleus, but not in prefrontal cortex, retrosplenial cortex, somatosensory cortex, subiculum, lateral dorsal thalamic nucleaus, or hippocampal CA1.

Conclusions

We confirm previous findings of sevoflurane-induced neuronal injury. Dexmedetomidine, even in the highest dose, did not cause similar injury, but provided lesser degrees of anaesthesia and pain control. No mitigation of sevoflurane-induced injury was observed with dexmedetomidine supplementation, suggesting that future studies should focus on anaesthetic-sparing effects of dexmedetomidine, rather than injury-preventing effects.

Effects of compound 21, a non‑peptide angiotensin II type 2 receptor agonist, on general anesthesia‑induced cerebral injury in neonatal rats

General anesthesia has a great impact on neurodevelopment. However, the mechanisms underlying this effect and therapeutic methods to address it remain limited. The present study aimed to investigate the effects of compound (C)21, a non-peptide angiotensin II type 2 receptor agonist, on general anesthesia-induced cerebral injury in neonatal rats. Neonatal Sprague Dawley rats (postnatal day 7) were randomly divided into three groups (n=6 per group): The control, isoflurane and C21+ isoflurane (C21) group. General anesthesia was induced through inhalation of 1.3% isoflurane. Apoptosis and synaptic structure were analyzed. The levels of peroxisome proliferator-activated receptor (PPAR)-α were detected using an enzyme-linked immunosorbent assay. BCL2, apoptosis regulator (Bcl-2) expression was also measured. Compared with the control group, the cerebral cortex, hippocampus, amygdala and hypothalamus in the isoflurane group had significantly more apoptotic cells (P<0.05). The nuclei of the control group were round and transparent, while shrunken nuclei and condensed chromatin were visible in the isoflurane group. A reduction in synapse number was observed in the isoflurane group compared with the control. By contrast, nuclei shrinkage and the decrease in synaptic number was improved in the C21 group. PPAR-α and Bcl-2 expression, at the mRNA and protein levels, was significantly reduced in the isoflurane group compared with the control (P<0.05). C21 treatment reduced the decrease in PPAR-α and Bcl-2 in the cerebral cortex, hippocampus, amygdala and hypothalamus (P<0.05). Collectively, it was demonstrated that C21 prevented apoptosis and synaptic loss induced by general anesthesia in neonatal rats by enhancing the expression of PPAR-α and Bcl-2.

Intravenous anesthetic-induced calcium dysregulation and neurotoxic shift with age during development in primary cultured neurons

Anesthetic-induced neurotoxicity in the developing brain is a concern. This neurotoxicity is closely related to anesthetic exposure time, dose, and developmental stages. Using calcium imaging and morphological examinations in vitro, we sought to determine whether intravenous anesthetic-induced direct neurotoxicity varies according to different stages of the days in vitro (DIV) of neurons in primary culture. Cortical neurons from E17 Wistar rats were prepared. On DIV 3, 7, and 13, cells were exposed to the intravenous anesthetics thiopental sodium (TPS), midazolam (MDZ), or propofol (PPF), to investigate direct neurotoxicity using morphological experiments. Furthermore, using calcium imaging, the anesthetic-induced intracellular calcium concentration ([Ca²⁺]i) elevation was monitored in cells on DIV 4, 8, and 13. All anesthetics elicited significant [Ca²⁺]i increases on DIV 4. While TPS (100 μM) and MDZ (10 μM) did not alter neuronal death, PPF (10 μM and 100 μM) decreased the survival ratio (SR) significantly. On DIV 8, TPS and MDZ did not elicit [Ca²⁺]i elevation or SR decrease, while PPF still induced [Ca²⁺]i elevation (both at 10 μM and 100 μM) and significant SR decrease at 100 μM (0.76 ± 0.03; P < 0.05), but not at 10 μM (0.91 ± 0.03). Such anesthetic-induced [Ca²⁺]i elevation and SR decrease were not observed on DIV 13-14 for any of the anesthetic drugs. Our study indicates that more caution may be exercised when using PPF compared to TPS or MDZ during development.

Does pediatric anesthesia cause brain damage? - Addressing parental and provider concerns in light of compelling animal studies and seemingly ambivalent human data

Anesthesia facilitates surgery in millions of young children every year. Structural brain abnormalities and functional impairment observed in animals have created substantial concerns among clinicians, parents, and government regulators. Clinical studies seemed ambivalent; it remains unclear whether differential species effects exist towards anesthetic exposure. The current literature search and analysis attempts to unify the available clinical and animal studies, which currently comprise of > 530 in vivo animal studies and > 30 clinical studies. The prevalence of abnormalities was lowest for exposures < 1 hour, in both animals and humans, while studies with injurious findings increased in frequency with exposure time. Importantly, no exposure time, anesthetic technique, or age during exposure was clearly identifiable to be entirely devoid of any adverse outcomes. Moreover, the age dependence of maximum injury clearly identified in animal studies, combined with the heterogeneity in age in most human studies, may impede the discovery of a specific human neurological phenotype. In summary, animal and human research studies identify a growing prevalence of injurious findings with increasing exposure times. However, the existing lack of definitive data regarding safe exposure durations, unaffected ages, and non-injurious anesthetic techniques precludes any evidence-based recommendations for drastically changing current clinical anesthesia management. Animal studies focusing on brain maturational states more applicable to clinical practice, as well as clinical studies focusing on prolonged exposures during distinct developmental windows of vulnerability, are urgently needed to improve the safety of perioperative care for thousands of young children requiring life-saving and quality of life-improving procedures daily.

Brain changes due to hypoxia during light anaesthesia can be prevented by deepening anaesthesia; a study in rats

In anaesthetic practice the risk of cerebral ischemic/hypoxic damage is thought to be attenuated by deep anaesthesia. The rationale is that deeper anaesthesia reduces cerebral oxygen demand more than light anaesthesia, thereby increasing the tolerance to ischemia or hypoxia. However, evidence to support this is scarce. We thus investigated the influence of light versus deep anaesthesia on the responses of rat brains to a period of hypoxia. In the first experiment we exposed adult male Wistar rats to deep or light propofol anaesthesia and then performed [18F]- Fludeoxyglucose (FDG) Positron Emission Tomography (PET) scans to verify the extent of cerebral metabolic suppression. In subsequent experiments, rats were subjected to light/deep propofol anaesthesia and then exposed to a period of hypoxia or ongoing normoxia (n = 9-11 per group). A further 5 rats, not exposed to anaesthesia or hypoxia, served as controls. Four days later a Novel Object Recognition (NOR) test was performed to assess mood and cognition. After another 4 days, the animals were sacrificed for later immunohistochemical analyses of neurogenesis/neuroplasticity (Doublecortin; DCX), Brain Derived Neurotrophic Factor (BDNF) expression and neuroinflammation (Ionized calcium-binding adaptor protein-1; Iba-1) in hippocampal and piriform cortex slices. The hippocampi of rats subjected to hypoxia during light anaesthesia showed lower DCX positivity, and therefore lower neurogenesis, but higher BDNF levels and microglia hyper-ramification. Exploration was reduced, but no significant effect on NOR was observed. In the piriform cortex, higher DCX positivity was observed, associated with neuroplasticity. All these effects were attenuated by deep anaesthesia. Deepening anaesthesia attenuated the brain changes associated with hypoxia. Hypoxia during light anaesthesia had a prolonged effect on the brain, but no impairment in cognitive function was observed. Although reduced hippocampal neurogenesis may be considered unfavourable, higher BDNF expression, associated with microglia hyper-ramification may suggest activation of repair mechanisms. Increased neuroplasticity observed in the piriform cortex supports this, and might reflect a prolonged state of alertness rather than damage.

Age at Exposure to Surgery and Anesthesia in Children and Association With Mental Disorder Diagnosis

BACKGROUND

Animals exposed to anesthetics during specific age periods of brain development experience neurotoxicity, with neurodevelopmental changes subsequently observed during adulthood. The corresponding vulnerable age in children, however, is unknown.

METHODS

An observational cohort study was performed using a longitudinal dataset constructed by linking individual-level Medicaid claims from Texas and New York from 1999 to 2010. This dataset was evaluated to determine whether the timing of exposure to anesthesia ≤5 years of age for a single common procedure (pyloromyotomy, inguinal hernia, circumcision outside the perinatal period, or tonsillectomy and/or adenoidectomy) is associated with increased subsequent risk of diagnoses for any mental disorder, or specifically developmental delay (DD) such as reading and language disorders, and attention deficit hyperactivity disorder (ADHD). Exposure to anesthesia and surgery was evaluated in 11 separate age at exposure categories: ≤28 days old, >28 days and ≤6 months, >6 months and ≤1 year, and 6-month age intervals between >1 year old and ≤5 years old. For each exposed child, 5 children matched on propensity score calculated using sociodemographic and clinical covariates were selected for comparison. Cox proportional hazards models were used to measure the hazard ratio of a mental disorder diagnosis associated with exposure to surgery and anesthesia.

RESULTS

A total of 38,493 children with a single exposure and 192,465 propensity score-matched children unexposed before 5 years of age were included in the analysis. Increased risk of mental disorder diagnosis was observed at all ages at exposure with an overall hazard ratio of 1.26 (95% confidence interval [CI], 1.22-1.30), which did not vary significantly with the timing of exposure. Analysis of DD and ADHD showed similar results, with elevated hazard ratios distributed evenly across all ages, and overall hazard ratios of 1.26 (95% CI, 1.20-1.32) for DD and 1.31 (95% CI, 1.25-1.37) for ADHD.

CONCLUSIONS

Children who undergo minor surgery requiring anesthesia under age 5 have a small but statistically significant increased risk of mental disorder diagnoses and DD and ADHD diagnoses, but the timing of the surgical procedure does not alter the elevated risks. Based on these findings, there is little support for the concept of delaying a minor procedure to reduce long-term neurodevelopmental risks of anesthesia in children. In evaluating the influence of age at exposure, the types of procedures included may need to be considered, as some procedures are associated with specific comorbid conditions and are only performed at certain ages.

Sevoflurane exposure in postnatal rats induced long-term cognitive impairment through upregulating caspase-3/cleaved-poly (ADP-ribose) polymerase pathway

The association of anesthetic exposure in infants or young children with the long-term impairment of neurologic functions has been reported previously; however, the underlying mechanisms remain largely unknown. In order to identify dysregulated gene expression underlying long-term cognitive impairment caused by sevoflurane exposure at the postnatal stage, the present study initially performed behavioral tests on adult Wistar rats, which received 3% sevoflurane at postnatal day 7 (P7) for different time course. Subsequently, transcriptome profiling of hippocampal tissues from experimental and control rats was performed. Significant impairment of the working memory was observed in adult rats with sevoflurane exposure for 4-6 h, when compared with the control rats. The results indicated that a total of 264 genes were aberrantly expressed (51 downregulated and 213 upregulated; fold change >2.0; P<0.05; false discovery rate <0.05) in the hippocampus of experimental adult rats compared with those from control rats. Particularly, the expression of caspase-3 gene (CASP3), encoding caspase-3 protein, presented the most significant upregulation, which was further validated by quantitative polymerase chain reaction and immunohistochemical analysis. Further analysis revealed that CASP3 expression level was negatively correlated with the rats' spatial working memory performance, as indicated by the Y-maze test. The level of cleaved-poly (ADP-ribose) polymerase (PARP), a substrate of caspase-3, was also increased in the hippocampus of experimental adult rats. Thus, the present study revealed that upregulation of caspase-3/cleaved-PARP may be involved in long-term cognitive impairment caused by sevoflurane exposure in infants, which may be useful for the clinical prevention of cognitive impairment.

Anesthetic Neurotoxicity in Congenital Hand Surgery: An Overview of the Evidence and Advice for Counseling Parents

Millions of children undergo general anesthesia for surgical procedures each year, the implications of which are not fully understood. Animal models demonstrate neurotoxicity and long-term cognitive impairment following exposure to common general anesthetic agents. However, it is unclear if human brains are affected in a similar fashion and what-if any-the implications on cognitive development may be. Furthermore, it is not known if these effects are additive and if they can be avoided by delaying reconstruction. Here, we explore reconstructive surgical timelines for common congenital hand differences in light of the available anesthetic neurotoxicity evidence, with an emphasis on preoperative counseling.

Long-term Fate Mapping to Assess the Impact of Postnatal Isoflurane Exposure on Hippocampal Progenitor Cell Productivity

BACKGROUND

Exposure to isoflurane increases apoptosis among postnatally generated hippocampal dentate granule cells. These neurons play important roles in cognition and behavior, so their permanent loss could explain deficits after surgical procedures.

METHODS

To determine whether developmental anesthesia exposure leads to persistent deficits in granule cell numbers, a genetic fate-mapping approach to label a cohort of postnatally generated granule cells in Gli1-CreER::GFP bitransgenic mice was utilized. Green fluorescent protein (GFP) expression was induced on postnatal day 7 (P7) to fate map progenitor cells, and mice were exposed to 6 h of 1.5% isoflurane or room air 2 weeks later (P21). Brain structure was assessed immediately after anesthesia exposure (n = 7 controls and 8 anesthesia-treated mice) or after a 60-day recovery (n = 8 controls and 8 anesthesia-treated mice). A final group of C57BL/6 mice was exposed to isoflurane at P21 and examined using neurogenesis and cell death markers after a 14-day recovery (n = 10 controls and 16 anesthesia-treated mice).

RESULTS

Isoflurane significantly increased apoptosis immediately after exposure, leading to cell death among 11% of GFP-labeled cells. Sixty days after isoflurane exposure, the number of GFP-expressing granule cells in treated animals was indistinguishable from control animals. Rates of neurogenesis were equivalent among groups at both 2 weeks and 2 months after treatment.

CONCLUSIONS

These findings suggest that the dentate gyrus can restore normal neuron numbers after a single, developmental exposure to isoflurane. The authors' results do not preclude the possibility that the affected population may exhibit more subtle structural or functional deficits. Nonetheless, the dentate appears to exhibit greater resiliency relative to nonneurogenic brain regions, which exhibit permanent neuron loss after isoflurane exposure.

MicroRNA-34c is regulated by p53 and is involved in sevoflurane-induced apoptosis in the developing rat brain potentially via the mitochondrial pathway

The commonly used inhalation anesthetic, sevoflurane, has been previously demonstrated to induce apoptosis in the developing brain; however, the underlying molecular mechanisms remain largely unknown. MicroRNAs (miRNAs) serve important roles in multiple physiological/pathological processes, such as cell death and survival. In the present study, the miRNA sequence that was most closely associated with sevoflurane‑induced apoptosis in the hippocampus of neonatal rat brains was identified. Seven‑day‑old Sprague Dawley rats were first exposed to 2.3% sevoflurane for 6 h. Hippocampal brain tissues were harvested at 6 h following sevoflurane exposure. Cleaved caspase‑3 levels were examined using an immunofluorescence assay. Alterations in miRNA expression were assessed by microarray analysis and reverse transcription-quantitative polymerase chain reaction. The protein levels of p53, phosphorylated (p)‑p53, B-cell lymphoma-2 (Bcl-2) and Bax were assessed by western blot analysis. Sevoflurane exposure significantly increased the levels of cleaved caspase‑3 in the hippocampus. In addition, among the 688 miRNAs that were observed to be expressed in the hippocampus, sevoflurane exposure altered the expression levels of 266 miRNAs. Among these differentially expressed miRNAs, eight were significantly upregulated and one (miRNA‑34c) was significantly downregulated following sevoflurane exposure. Bioinformatics analyses indicated the miRNA‑34c was a direct downstream target of p53. Sevoflurane exposure induced significant alterations in the level of p‑p53, Bcl‑2 and Bax in the hippocampus of neonatal rats. In conclusion, the results of the present study suggest that miRNA‑34c may be regulated by p53 and is involved in sevoflurane‑induced neural apoptosis in the hippocampus of developing rat brains, potentially via the mitochondrial pathway.