Visual recognition memory is impaired in rhesus monkeys repeatedly exposed to sevoflurane in infancy

A Scoping Review of the Mechanisms Underlying Developmental Anesthetic Neurotoxicity

Although anesthesia makes painful or uncomfortable diagnostic and interventional health care procedures tolerable, it may also disrupt key cellular processes in neurons and glia, harm the developing brain, and thereby impair cognition and behavior in children. Many years of studies using in vitro, animal behavioral, retrospective database studies in humans, and several prospective clinical trials in humans have been invaluable in discerning the potential toxicity of anesthetics. The objective of this scoping review was to synthetize the evidence from preclinical studies for various mechanisms of toxicity across diverse experimental designs and relate their findings to those of recent clinical trials in real-world settings.

Repeated sevoflurane exposure causes hypomyelination in the prefrontal cortex of adult male mice

As one of the most commonly used general anesthetics (GAs) in surgery, numerous studies have demonstrated the detrimental effects of sevoflurane exposure on myelination in the developing and elderly brain. However, the impact of sevoflurane exposure on intact myelin structure in the adult brain is barely discovered. Here, we show that repeated sevoflurane exposure, but not single exposure, causes hypomyelination and abnormal ultrastructure of myelin sheath in the prefrontal cortex (PFC) of adult male mice, which is considered as a critical brain region for general anesthesia mediated consciousness change. Furthermore, disrupted proliferation of oligodendrocyte precursor cells (OPCs) contributes to repeated sevoflurane exposure-induced myelin defect. This may be owing to an accumulated tuberous sclerosis complex 1 (TSC1) expression and inhibition of mammalian target of rapamycin (mTOR) signaling, leading to the unbalance of TSC1-mTORC1 activity after repeated sevoflurane exposure, which is critical for proper myelination of the central nervous system (CNS). Moreover, repeated sevoflurane exposure aggregates myelination defect in the cuprizone-induced demyelination model. Together, our present work establishes the role of sevoflurane exposure in myelin integrity in the PFC of the adult male mice and provides a new insight to elucidate the mechanism of GAs-induced brain dysfunctions.

Up-regulation of miR-490-3p improves learning/memory disability of sevoflurane exposure by relieving neuroinflammation

Our study focused on the potential mechanism of microRNA-490-3p (miR-490-3p) on learning/memory disability of rats resulting from sevoflurane (Sev). The rat model of cognitive dysfunction was established by infection with miR-490-3p mimic and Sev-exposure. Morris water maze and open field test assay were used for the assessment of cognitive deficits. Enzyme-linked immunosorbent assay and quantitative real-time polymerase chain reaction assays were used for the measurements of neuroinflammatory cytokines and inflammatory-related genes in respective order. Bioinformatics analysis was employed for the predictive miR-490-3p-related genes. The targeted interaction was verified via dual-luciferase reporter assay. A significant decline of miR-490-3p was discovered in rats with Sev treatment, while the levels were up-regulated in rats with infection miR-490-3p pretreatment (P < 0.001). For Sev-induced rats, the stay time in the target quadrant was shorten, while distance travelled lengthened significantly with the control group by comparison (P < 0.001). Notably, an increased time of the escape latency and a decreased number of platform crossings were found in the Sev group, which alleviated by infection with miR-490-3p mimic pretreatment (P < 0.001). Moreover, the neuroinflammatory cytokines were elevated in the Sev group, the effects of which were recovered via miR-490-3p pretreatment (P < 0.001). Bioinformatics analysis predicted the miR-490-3p-associated genes. CDK1 (Cyclin-dependent kinase 1) was a potential target gene of miR-490-3p, which confirmed by dual-luciferase reporter detection. MiR-490-3p alleviated the learning and memory deficits in Sev-treated rats via the modulation of CDK1.

New methods needed to investigate the potential adverse effects of anaesthesia on neurological development in childhood

The issue of potentially harmful effects of neurotoxicity or anaesthesia management on children undergoing general anaesthesia is still not resolved. Studies have so far been limited by methodological problems. In a retrospective cohort study, a new noninvasive method was used to demonstrate visual processing changes in children with a single previous exposure to anaesthesia. We need new noninvasive methods that can be used before and after exposure to anaesthesia and surgery to detemine possible effects on long-term neurodevelopment.

Repeated postnatal sevoflurane exposure impairs social recognition in mice by disrupting GABAergic neuronal activity and development in hippocampus

BACKGROUND

Repeated exposure to sevoflurane during early developmental stages is a risk factor for social behavioural disorders, but the underlying neuropathological mechanisms remain unclear. As the hippocampal cornu ammonis area 2 subregion (CA2) is a critical centre for social cognitive functions, we hypothesised that sevoflurane exposure can lead to social behavioural disorders by disrupting neuronal activity in the CA2.

METHODS

Neonatal mice were anaesthetised with sevoflurane 3 vol% for 2 h on postnatal day (PND) 6, 8, and 10. Bulk RNA sequencing of CA2 tissue was conducted on PND 12. Social cognitive function was assessed by behavioural experiments, and in vivo CA2 neuronal activity was recorded by multi-channel electrodes on PND 60-65.

RESULTS

Repeated postnatal exposure to sevoflurane impaired social novelty recognition in adulthood. It also caused a decrease in the synchronisation of neuronal spiking, gamma oscillation power, and spike phase-locking between GABAergic spiking and gamma oscillations in the CA2 during social interaction. After sevoflurane exposure, we observed a reduction in the density and dendritic complexity of CA2 GABAergic neurones, and decreased expression of transcription factors critical for GABAergic neuronal development after.

CONCLUSIONS

Repeated postnatal exposure to sevoflurane disturbed the development of CA2 GABAergic neurones through downregulation of essential transcription factors. This resulted in impaired electrophysiological function in adult GABAergic neurones, leading to social recognition deficits. These findings reveal a potential electrophysiological mechanism underlying the long-term social recognition deficits induced by sevoflurane and highlight the crucial role of CA2 GABAergic neurones in social interactions.

Effects of general anaesthesia in early childhood on local and global visual processing: a post hoc analysis of the APEX cohort study

BACKGROUND

Preclinical studies suggest that early exposure to anaesthesia alters the visual system in mice and non-human primates. We investigated whether exposure to general anaesthesia leads to visual attention processing changes in children, which could potentially impact essential life skills, including learning.

METHODS

This was a post hoc analysis of data from the APprentissages EXécutifs et cerveau chez les enfants d'âge scolaire (APEX) cohort study. A total of 24 healthy 9-10-yr-old children who were or were not exposed to general anaesthesia (for surgery) by a mean age of 3.8 (2.6) yr performed a visual attention task to evaluate ability to process either local details or general global visual information. Whether children were distracted by visual interference during global and local information processing was also assessed.

RESULTS

Participants included in the analyses (n=12 participants exposed to general anaesthesia and n=12 controls) successfully completed (>90% of correct answers) the trial tasks. Children from both groups were equally distracted by visual interference. However, children who had been exposed to general anaesthesia were more attracted to global visual information than were control children (P=0.03).

CONCLUSIONS

These findings suggest lasting effects of early-life exposure to general anaesthesia on visuospatial abilities. Further investigations of the mechanisms by which general anaesthesia could have delayed effects on how children perceive their visual environment are needed.

Identification of differential m6A RNA methylomes and ALKBH5 as a potential prevention target in the developmental neurotoxicity induced by multiple sevoflurane exposures

Sevoflurane, as a commonly used inhaled anesthetic for pediatric patients, has been reported that multiple sevoflurane exposures are associated with a greater risk of developing neurocognitive disorder. N6-Methyladenosine (m6A), as the most common mRNA modification in eukaryotes, has emerged as a crucial regulator of brain function in processes involving synaptic plasticity, learning and memory, and neurodevelopment. Nevertheless, the relevance of m6A RNA methylation in the multiple sevoflurane exposure-induced developmental neurotoxicity remains mostly elusive. Herein, we evaluated the genome-wide m6A RNA modification and gene expression in hippocampus of mice that received with multiple sevoflurane exposures using m6A-sequencing (m6A-seq) and RNA-sequencing (RNA-seq). We discovered 19 genes with differences in the m6A methylated modification and differential expression in the hippocampus. Among these genes, we determined that a total of nine differential expressed genes may be closely associated with the occurrence of developmental neurotoxicity induced by multiple sevoflurane exposures. We further found that the alkB homolog 5 (ALKBH5), but not methyltransferase-like 3 (METTL3) and Wilms tumor 1-associated protein (WTAP), were increased in the hippocampus of mice that received with multiple sevoflurane exposures. And the IOX1, as an inhibitor of ALKBH5, significantly improved the learning and memory defects and reduced neuronal damage in the hippocampus of mice induced by multiple sevoflurane exposures. The current study revealed the role of m6A methylated modification and m6A-related regulators in sevoflurane-induced cognitive impairment, which might provide a novel insight into identifying biomarkers and therapeutic strategies for inhaled anesthetic-induced developmental neurotoxicity.

The role of anesthesia in peri‑operative neurocognitive disorders: Molecular mechanisms and preventive strategies

Peri-operative neurocognitive disorders (PNDs) include postoperative delirium (POD) and postoperative cognitive dysfunction (POCD). Children and the elderly are the two populations most vulnerable to the development of POD and POCD, which results in both high morbidity and mortality. There are many factors, including neuroinflammation and oxidative stress, that are associated with POD and POCD. General anesthesia is a major risk factor of PNDs. However, the molecular mechanisms of PNDs are poorly understood. Dexmedetomidine (DEX) is a useful sedative agent with analgesic properties, which significantly improves POCD in elderly patients. In this review, the current understanding of anesthesia in PNDs and the protective effects of DEX are summarized, and the underlying mechanisms are further discussed.

Lessons learned from big data (APRICOT, NECTARINE, PeDI)

Big data in paediatric anaesthesia allows the evaluation of morbidity and mortality of anaesthesia in a large population, but also the identification of rare critical events and of their causes. This is a major step to focus education and design clinical guidelines. Moreover, they can help trying to determine normative data in a population with a wide range of ages and body weights. The example of blood pressure under anaesthesia will be detailed. Big data studies should encourage every department of anaesthesia to collect its own data and to benchmark its performance by comparison with published data. The data collection processes are also an opportunity to build collaborative research networks and help researchers to complete multicentric studies. Up to recently, big data studies were only performed in well developed countries. Fortunately, big data collections have started in some low and middle income countries and truly international studies are ongoing.

Translatome and transcriptome profiling of neonatal mice hippocampus exposed to sevoflurane anesthesia

Exposure to anesthesia in early life may cause severe damage to the brain and lead to cognitive impairment. The underlying mechanisms, which have only been investigated in a limited scale, remains largely elusive. We performed translatome and transcriptome sequencing together for the first time in hippocampus of neonatal mice that were exposed to sevoflurane. We treated a group of neonatal mice with 2.5 % sevoflurane for 2 h on day 6, 7, 8, 9 and treated another group on day 6, 7. We performed behavioral study after day 30 for both groups and the control to evaluate the cognitive impairment. On day 36, we collected translatome and transcriptome from the hippocampus in the two groups, compared the gene expression levels between the groups and the control, and validated the results with RT-qPCR. We identified 1750 differentially expressed genes (DEGs) from translatome comparison and 1109 DEGs from transcriptome comparison. As expected, translatome-based DEGs significantly overlapped with transcriptome-based DEGs, and functional enrichment analysis generated similar enriched cognition-related GO terms and KEGG pathways. However, for many genes like Hspa5, their alterations in translatome differed remarkably from those in transcriptome, and Western blot results were largely concordant with the former, suggesting that translational regulation plays a significant role in cellular response to sevoflurane. Our study revealed global alterations in translatome and transcriptome of mice hippocampus after neonatal exposure to sevoflurane anesthesia and highlighted the importance of translatome analysis in understanding the mechanisms responsible for anesthesia-induced cognitive impairment.

Siglec-E Ligand Downregulation on Hippocampus Neurons Induced Inflammation in Sevoflurane-Associated Perioperative Neurocognitive Disorders in Aged Mice

Activated microglia-induced inflammation in the hippocampus plays an important role in perioperative neurocognitive disorders. Previous studies have shown that sialic acid-binding immunoglobulin-like lectin 3 (hSiglec-3, ortholog of mouse Siglec-E) engagement in microglia and its glycan ligands on neurons contributes to inflammatory homeostasis through an endogenous negative regulation pathway. This study aimed to explore whether the glycan ligand alteration on neurons plays a role in sevoflurane-induced perioperative neurocognitive disorders. This study's data has shown that a slight Siglec-E ligands' expression decrease does not induce inflammation homeostasis disruption. We also demonstrated that the ligand level on neurons was decreased with age, and the reduced Siglec-E ligand expression on neurons caused via sevoflurane was induced by neuraminidase 1. Furthermore, this study has shown that the Siglec-E ligand expression decline caused by age and sevoflurane treatment could decrease the ligands' level, thus leading to inflammatory homeostasis disruption. This research provided a novel mechanism for perioperative neurocognitive disorder susceptibility in the elderly.

Effects of multiple anesthetic exposures on rhesus macaque brain development: a longitudinal structural MRI analysis

Concerns about the potential neurotoxic effects of anesthetics on developing brain exist. When making clinical decisions, the timing and dosage of anesthetic exposure are critical factors to consider due to their associated risks. In our study, we investigated the impact of repeated anesthetic exposures on the brain development trajectory of a cohort of rhesus monkeys (n = 26) over their first 2 yr of life, utilizing longitudinal magnetic resonance imaging data. We hypothesized that early or high-dose anesthesia exposure could negatively influence structural brain development. By employing the generalized additive mixed model, we traced the longitudinal trajectories of brain volume, cortical thickness, and white matter integrity. The interaction analysis revealed that age and cumulative anesthetic dose were variably linked to white matter integrity but not to morphometric measures. Early high-dose exposure was associated with increased mean, axial, and radial diffusivities across all white matter regions, compared to late-low-dose exposure. Our findings indicate that early or high-dose anesthesia exposure during infancy disrupts structural brain development in rhesus monkeys. Consequently, the timing of elective surgeries and procedures that require anesthesia for children and pregnant women should be strategically planned to account for the cumulative dose of volatile anesthetics, aiming to minimize the potential risks to brain development.

Needle in a haystack: localising the long-term neuronal changes from early-life exposure to general anaesthesia

Narrowing down the histopathological changes in the brain after early-life exposure to general anaesthesia has presented a consistent challenge for preclinical models of anaesthetic neurotoxicity. Using resting-state functional magnetic resonance imaging, in this issue of the journal Neudecker and colleagues demonstrated in vivo connectivity changes in the brain following a seed-based analysis that was derived from previously reported histopathology in the same animals. The combination of neurohistology and neuroimaging should help focus future preclinical studies investigating the developmental consequences of early exposure to general anaesthesia.

Proteomic analysis of gene expression in the prefrontal cortex in infant rhesus macaques after multiple sevoflurane exposures

PURPOSE

Repeated exposure of infant rhesus macaques to sevoflurane induces neurotoxicity and is associated with neurocognitive impairment in later life. We aimed to investigate the effect of repeated sevoflurane exposure on the expression of proteins in the prefrontal cortex of infant rhesus macaques by proteomics.

METHODS

Rhesus macaques were exposed to sevoflurane three times, on postnatal days 7, 21 and 35. Quantitative proteomics employing LC-MS with isobaric labeling (TMT10plex), western blotting, and transmission electron microscopy (TEM) were utilized in the studies.

RESULTS

The results of a proteomics investigation of the brain revealed that the proteins that were differentially expressed in rhesus macaques after sevoflurane exposures were associated mainly with mitochondrial respiration. Following multiple sevoflurane exposures, the prefrontal cortices of rhesus macaques exhibited increases in NDUFA8 and COX IV protein levels, while no alterations in mitochondrial morphology were observed through TEM.

CONCLUSION

Multiple exposures to sevoflurane increased the mitochondrial protein levels in rhesus macaques.

Melatonin-mediated mitophagy protects against long-term impairments after repeated neonatal sevoflurane exposures

BACKGROUND

Melatonin is known to have protective effects in aging, neurodegenerative disorders and mitochondria-related diseases, while there is a poor understanding of the effects of melatonin treatment on mitophagy in neonatal cognitive dysfunction after repeated sevoflurane exposures. This study explores the protective effects of melatonin on mitophagy and cognition in developing rats exposed to sevoflurane.

METHODS

Postnatal day six (P6) neonatal rats were exposed to 3 % sevoflurane for 2 h daily from P6 to P8. In the intervention groups, rats received 3-Methyladenine (3-MA) intracerebroventricularly from P6 to P8 and melatonin intraperitoneally from P6 to P8 following water drinking once daily from P21 to P41, respectively. Behavioral tests, including open field (OF), novel object recognition (NOR), and fear conditioning (FC) tests, were performed to assess cognitive function during young adulthood. In another experiment, rat brains were harvested for biochemical, histopathological, and electron microscopy studies.

RESULTS

Rats exposed to sevoflurane showed disordered mitophagy and mitochondrial dysfunction as revealed by increased mitophagy marker proteins (microtubule-associated protein 1 light chain 3 (LC3) II/I, and parkin), decreased autophagy marker protein (sequestosome 1 (P62/SQSTM1)), electron transport chain (ETC) proteins and ATP levels. Immunofluorescent staining of LC3 was co-localized mostly with a neuronal marker and microglial marker but was not co-localized with a marker for astrocytes in rats exposed to sevoflurane. These rats had poorer performance in the NOR and FC tests than control rats during young adulthood. Melatonin treatment reversed the abnormal expression of mitophagy proteins, mitochondrial energy metabolism, the activity of microglia, and impaired cognition. These ameliorations were blocked by an autophagy inhibitor, 3-MA, except for the activation of microglia.

CONCLUSION

We have demonstrated that melatonin inhibits microglial activation by enhancing mitophagy and finally significantly reduces sevoflurane-induced deficits in cognition in neonatal rats. These results suggest that melatonin might be beneficial if considered when the anesthesia must be administered at a very young age.

Inhibitory neuron map of sevoflurane induced neurotoxicity model in young primates

Introduction

Sevoflurane, one of the most commonly used anesthetic agents in children, may induce neuronal dysfunction and cognitive impairment. Exposure to sevoflurane might induce an imbalance between neural excitation and inhibition which could be a mechanism behind anesthesia-induced cognitive and affective dysfunctions. However, the underlying mechanisms remain unclear.

Methods

In this study, we used two rhesus macaques in the control group, and one rhesus macaques in the anesthesia group. We employed single-nucleus RNA sequencing (snRNA-seq) technology to explore alterations in distinct types of inhibitory neurons involved in the long-term cognitive impairment caused by sevoflurane in young macaques.

Results

Following sevoflurane treatment, an upregulation was observed in the SST+ inhibitory neuron in the LHX6+ neighborhood in the hippocampus of rhesus macaques. This alteration might impact brain development by influencing interneuron migration and maturation. Additionally, we proposed a novel classification of inhibitory neurons, defined by CNR1 and LHX6 applicable to both humans and macaques.

Discussion

Our study proposed a novel classification of inhibitory neurons defined by LHX6 and CNR1, relevant in macaques and humans. We also provide evidence that sevoflurane upregulated the SST+ inhibitory neuron in the LHX6+ neighborhood in the hippocampus of rhesus macaques, which may underlie the potential neurotoxic effects induced by general anesthetics. Our results also offer a more reliable approach for studying the structure and function of the human brain.

Neurobehavioral effects of general anesthesia and cochlear implantation on hearing-impaired infants: A prospective observational cohort study

INTRODUCTION

The potential adverse effects of prolonged exposure to anesthetics in pediatric patients with severe-to-profound sensorineural hearing loss remain unclear. This study aimed to examine whether early bilateral cochlear implantation involving long-duration anesthetic exposure caused greater developmental impairment than that with unilateral cochlear implantation.

METHODS

This prospective observational study included normally developing infants with bilateral severe-to-profound sensorineural hearing loss aged 6 months to 2 years who were candidates for unilateral/bilateral cochlear implantation surgery. Baseline (T0), 6-month (T1), and 1-year (T2) Gesell Scale scores were measured. The outcomes included fine motor, adaptability, gross motor, language, and social skills scale 6 and 12 months postoperatively.

RESULT

The 90 enrolled children with bilateral severe-to-profound sensorineural hearing loss (unilateral n = 43; bilateral n = 47) had a younger bilateral group (11.00 ± 3.66 vs. 15.63 ± 6.99 months, p < .001). Anesthesia duration was longer in the bilateral group (271.57 ± 36.09 vs. 148.81 ± 25.60 min, p < .001). Gross motor, fine motor, adaptability, and language scores improved in both groups, and no significant between-group differences occurred in the fine motor scale at T1 and T2. Language developmental quotients improved significantly in the bilateral group compared with the unilateral group at T1 (mean differences: 25.07 ± 4.37 vs. 10.88 ± 4.61, p < .001) and T2 (mean differences: 34.98 ± 5.94 vs. 15.28 ± 6.55, p < .001). Stepwise regression revealed that gross motor, adaptability, language, and social skill developmental quotients at T1 were positively correlated with those at T0. Gross motor, fine motor, and social skill developmental quotients at T2 were negatively correlated with age at operation. Language developmental quotients were positively correlated with T0 values (p < .001) and in the bilateral group (p < .001) at T1 and T2.

CONCLUSIONS

When evaluating young children with bilateral severe-to-profound sensorineural hearing loss, despite longer exposures to general anesthesia, bilateral cochlear implantations were associated with more improvement in language scores and no differences in other skills compared with those with only unilateral implantation.

Effects of Early Exposure to Isoflurane on Susceptibility to Chronic Pain Are Mediated by Increased Neural Activity Due to Actions of the Mammalian Target of the Rapamycin Pathway

Patients who have undergone surgery in early life may be at elevated risk for suffering neuropathic pain in later life. The risk factors for this susceptibility are not fully understood. Here, we used a mouse chronic pain model to test the hypothesis that early exposure to the general anesthetic (GA) Isoflurane causes cellular and molecular alterations in dorsal spinal cord (DSC) and dorsal root ganglion (DRG) that produces a predisposition to neuropathic pain via an upregulation of the mammalian target of the rapamycin (mTOR) signaling pathway. Mice were exposed to isoflurane at postnatal day 7 (P7) and underwent spared nerve injury at P28 which causes chronic pain. Selected groups were treated with rapamycin, an mTOR inhibitor, for eight weeks. Behavioral tests showed that early isoflurane exposure enhanced susceptibility to chronic pain, and rapamycin treatment improved outcomes. Immunohistochemistry, Western blotting, and q-PCR indicated that isoflurane upregulated mTOR expression and neural activity in DSC and DRG. Accompanying upregulation of mTOR and rapamycin-reversible changes in chronic pain-associated markers, including N-cadherin, cAMP response element-binding protein (CREB), purinergic P2Y12 receptor, glial fibrillary acidic protein (GFAP) in DSC; and connexin 43, phospho-extracellular signal-regulated kinase (p-ERK), GFAP, Iba1 in DRG, were observed. We concluded that early GA exposure, at least with isoflurane, alters the development of pain circuits such that mice are subsequently more vulnerable to chronic neuropathic pain states.

Lactate Improves Long-term Cognitive Impairment Induced By Repeated Neonatal Sevoflurane Exposures Through SIRT1-mediated Regulation of Adult Hippocampal Neurogenesis and Synaptic Plasticity in Male Mice

Repeated neonatal exposures to sevoflurane induce long-term cognitive impairment that has been reported to have sex-dependent differences. Exercise promotes learning and memory by releasing lactate from the muscle. The study tested the hypothesis that lactate may improve long-term cognitive impairment induced by repeated neonatal exposures to sevoflurane through SIRT1-mediated regulation of adult hippocampal neurogenesis and synaptic plasticity. C57BL/6 mice of both genders were exposed to 3% sevoflurane for 2 h daily from postnatal day 6 (P6) to P8. In the intervention experiments, mice received lactate at 1 g/kg intraperitoneally once daily from P21 to P41. Behavioral tests including open field (OF), object location (OL), novel object recognition (NOR), and fear conditioning (FC) tests were performed to assess cognitive function. The number of 5-Bromo-2'- deoxyuridine positive (BrdU+) cells and BrdU+/DCX+ (doublecortin) co-labeled cells, expressions of brain-derived neurotrophic factor (BDNF), activity-regulated cytoskeletal-associated protein (Arc), early growth response 1 (Egr-1), SIRT1, PGC-1α and FNDC5, and long-term potentiation (LTP) were evaluated in the hippocampus. Repeated exposures to sevoflurane induced deficits in OL, NOR and contextual FC tests in male but not female mice. Similarly, adult hippocampal neurogenesis, synaptic plasticity-related proteins and hippocampal LTP were impaired after repeated exposures to sevoflurane in male but not female mice, which could rescue by lactate treatment. Our study suggests that repeated neonatal exposures to sevoflurane inhibit adult hippocampal neurogenesis and induce defects of synaptic plasticity in male but not female mice, which may contribute to long-term cognitive impairment. Lactate treatment rescues these abnormalities through activation of SIRT1.

Effects of anesthesia exposure on postnatal maturation of white matter in rhesus monkeys

There is increasing concern about the potential effects of anesthesia exposure on the developing brain. The effects of relatively brief anesthesia exposures used repeatedly to acquire serial magnetic resonance imaging scans could be examined prospectively in rhesus macaques. We analyzed magnetic resonance diffusion tensor imaging (DTI) of 32 rhesus macaques (14 females, 18 males) aged 2 weeks to 36 months to assess postnatal white matter (WM) maturation. We investigated the longitudinal relationships between each DTI property and anesthesia exposure, taking age, sex, and weight of the monkeys into consideration. Quantification of anesthesia exposure was normalized to account for variation in exposures. Segmented linear regression with two knots provided the best model for quantifying WM DTI properties across brain development as well as the summative effect of anesthesia exposure. The resulting model revealed statistically significant age and anesthesia effects in most WM tracts. Our analysis indicated there were major effects on WM associated with low levels of anesthesia even when repeated as few as three times. Fractional anisotropy values were reduced across several WM tracts in the brain, indicating that anesthesia exposure may delay WM maturation, and highlight the potential clinical concerns with even a few exposures in young children.

Anesthesia, the developing brain, and dexmedetomidine for neuroprotection

Anesthesia-induced neurotoxicity is a set of unfavorable adverse effects on central or peripheral nervous systems associated with administration of anesthesia. Several animal model studies from the early 2000's, from rodents to non-human primates, have shown that general anesthetics cause neuroapoptosis and impairment in neurodevelopment. It has been difficult to translate this evidence to clinical practice. However, some studies suggest lasting behavioral effects in humans due to early anesthesia exposure. Dexmedetomidine is a sedative and analgesic with agonist activities on the alpha-2 (ɑ₂) adrenoceptors as well as imidazoline type 2 (I2) receptors, allowing it to affect intracellular signaling and modulate cellular processes. In addition to being easily delivered, distributed, and eliminated from the body, dexmedetomidine stands out for its ability to offer neuroprotection against apoptosis, ischemia, and inflammation while preserving neuroplasticity, as demonstrated through many animal studies. This property puts dexmedetomidine in the unique position as an anesthetic that may circumvent the neurotoxicity potentially associated with anesthesia.

Sevoflurane Exposure in Neonates Perturbs the Expression Patterns of Specific Genes That May Underly the Observed Learning and Memory Deficits

Exposure to commonly used anesthetics leads to neurotoxic effects in animal models-ranging from cell death to learning and memory deficits. These neurotoxic effects invoke a variety of molecular pathways, exerting either immediate or long-term effects at the cellular and behavioural levels. However, little is known about the gene expression changes following early neonatal exposure to these anesthetic agents. We report here on the effects of sevoflurane, a commonly used inhalational anesthetic, on learning and memory and identify a key set of genes that may likely be involved in the observed behavioural deficits. Specifically, we demonstrate that sevoflurane exposure in postnatal day 7 (P7) rat pups results in subtle, but distinct, memory deficits in the adult animals that have not been reported previously. Interestingly, when given intraperitoneally, pre-treatment with dexmedetomidine (DEX) could only prevent sevoflurane-induced anxiety in open field testing. To identify genes that may have been altered in the neonatal rats after sevoflurane and DEX exposure, specifically those impacting cellular viability, learning, and memory, we conducted an extensive Nanostring study examining over 770 genes. We found differential changes in the gene expression levels after exposure to both agents. A number of the perturbed genes found in this study have previously been implicated in synaptic transmission, plasticity, neurogenesis, apoptosis, myelination, and learning and memory. Our data thus demonstrate that subtle, albeit long-term, changes observed in an adult animal's learning and memory after neonatal anesthetic exposure may likely involve perturbation of specific gene expression patterns.

Alfaxalone Alleviates Neurotoxicity and Cognitive Impairment Induced by Isoflurane Anesthesia in Offspring Rats

BACKGROUND

The anesthetic isoflurane can cause neurotoxicity in fetuses and offspring of rats, affecting their neurodevelopment. However, the underlying mechanisms and therapeutic targets of isoflurane-induced neurotoxicity remain to be identified. Alfaxalone (ALF) is a steroid anesthetic. Steroids have been reported to have neuroprotective effects. This study aimed to investigate whether ALF could alleviate the isoflurane-induced neurotoxicity in fetuses and offspring of rats.

METHODS

On gestation day 15 (G15), the pregnant SD rats were randomly assigned to 4 groups: control 1 (CTL1) + control 2 (CTL2), isoflurane (ISO) + CTL2, CTL1 + ALF, and ISO + ALF. To analyze the changes in the expression levels of inflammatory cytokines, apoptotic factors, and synaptophysin, the brain tissues from the G15 fetuses and offspring at postnatal day 7 (P7), postnatal day 14 (P14), and postnatal day 31 (P31) were collected. The newborn neurons in the rats' offspring at P7, P14, and P31 were counted using immunofluorescence techniques. The Morris water maze (MWM) test was performed to assess the learning and memory abilities of P31 offspring rats.

RESULTS

ALF significantly alleviated the isoflurane-induced increase in the expression levels of inflammatory cytokines and apoptotic factors, such as interleukin (IL)-6 (ISO + CTL2 versus ISO + ALF: 5.133 ± 0.739 versus 1.093 ± 0.213, P < .001) and Caspase-3 (6.457 ± 0.6 versus 1.062 ± 0.1, P < .001) in the G15 fetuses. In P31 offspring rats, the expression levels of synaptophysin (0.719 ± 0.04 versus 1.068 ± 0.072, P < .001) and the number of newborn neurons in the dentate gyrus of the hippocampus were significantly lower in the ISO + CTL2 group as compared to those in the ISO + ALF group (118 ± 6 versus 140 ± 7, P < .001). These changes also occurred in the rat offspring at P7 and P14. In the MWM test, the escape latency of CTL1 + ALF group rats was significantly lower than that of ISO + ALF group rats (41 ± 6 versus 31 ± 7, P < .001) at P31.

CONCLUSIONS

Based on these findings, this study suggested that isoflurane exposure during pregnancy in rats could cause neuroinflammation and death of embryos as well as impairment of cognitive function in the offspring rats. ALF can be used to counteract the negative effects of isoflurane.

Multiple exposures to sevoflurane across postnatal development may cause cognitive deficits in older age

BACKGROUND

The aim of the study was to determine the effects of repeated anesthesia exposure across postnatal development.

METHODS

Seventy-two newborn Sprague-Dawley rats were randomly divided into Sev group and Con-aged group. Sev groups were exposed to 2.6% sevoflurane for 2 h on postnatal day (P) 7, P14, and P21; the Con groups only received carrier gas for 2 h. Learning and memory were evaluated using the MWM test at P31 (juvenile), P91 (adult), and 18 months postnatally (aged). The relative expression of APP and Mapt mRNA was detected by RT-PCR, while Aβ, tau, and P-tau protein levels were analyzed by immunohistochemistry.

RESULTS

After repeated inhalation of sevoflurane, MWM test performance was significantly decreased in the Sev-aged group compared to the Con-aged group (P > 0.05). The relative expression of APP and Mapt mRNA was not significantly different between groups in each growth period (P > 0.05). The tau expression in the juvenile hippocampal CA1, CA3, and dentate gyrus regions increased markedly in the Sev group, while P-tau only increased in the hippocampal CA3 region in the Sev-adult group. The expression of tau, P-tau, and Aβ in the hippocampal regions was upregulated in the Sev-aged group.

CONCLUSIONS

Multiple exposures to sevoflurane across postnatal development can induce or aggravate cognitive impairment in old age.

IMPACT

Whether multiple sevoflurane exposures across postnatal development cause cognitive impairment in childhood, adulthood, or old age, as well as the relationship between sevoflurane and the hippocampal Aβ, tau, and P-tau proteins, remains unknown. This study's results demonstrate that multiple exposures to sevoflurane across postnatal development do not appear to affect cognitive function in childhood and adulthood; however, multiple exposures may lead to a cognitive function deficit in old age. The underlying mechanism may involve overexpression of the tau, P-tau, and Aβ proteins in the hippocampus.

Neonatal exposures to sevoflurane in rhesus monkeys alter synaptic ultrastructure in later life

Repeated or prolonged early life exposure to anesthesia is neurotoxic in animals and associated with neurocognitive impairment in later life in humans. We used electron microscopy with unbiased stereological sampling to assess synaptic ultrastructure in dorsolateral prefrontal cortex (dlPFC) and hippocampal CA1 of female and male rhesus monkeys, four years after three 4-h exposures to sevoflurane during the first five postnatal weeks. This allowed us to ascertain long-term consequences of anesthesia exposure without confounding effects of surgery or illness. Synapse areas were reduced in the largest synapses in CA1 and dlPFC, predominantly in perforated spinous synapses in CA1 and nonperforated spinous synapses in dlPFC. Mitochondrial morphology and localization changed subtly in both areas. Synapse areas in CA1 correlated with response to a mild social stressor. Thus, exposure to anesthesia in infancy can cause long-term ultrastructural changes in primates, which may be substrates for long-term alterations in synaptic transmission and behavioral deficits.

Anesthesia and developing brain: What have we learned from recent studies

Anesthesia is unavoidable in surgical procedures. However, whether the general anesthetics are neurotoxic to immature brains remains undefined. Neurodevelopmental impairment induced by anesthesia has been a critical health issue and topic of concern. This review summarizes recent progress made in clinical and preclinical studies to provide useful suggestions and potential therapeutic targets for the protection of the immature brain. On the one hand, clinical researchers continue the debate about the effect of single and multiple exposures to anesthesia on developing brains. On the other hand, preclinical researchers focus on exploring the mechanisms of neurotoxic effects of general anesthesia on immature brains and seeking novel solutions. Rodent models have always been used in preclinical studies, but it is still unclear whether the mechanisms observed in rodent models have clinical relevance. Compared with these models, non-human primates (NHPs) are more genetically similar to humans. However, few research institutions in this area can afford to use NHP models in their studies. One way to address both problems is by combining single-cell sequencing technologies to screen differential gene expression in NHPs and perform in vivo validation in rodents. The mechanism of anesthesia-induced neurotoxicity still requires further elucidation in primates.

Egr2 contributes to age-dependent vulnerability to sevoflurane-induced cognitive deficits in mice

Sevoflurane inhalation is prone to initiate cognitive deficits in infants. The early growth response-2 (Egr-2) gene is DNA-binding transcription factor, involving in cognitive function. In this study we explored the molecular mechanisms underlying the vulnerability to cognitive deficits after sevoflurane administration. Six-day-old (young) and 6-week-old (early adult) mice received anesthesia with 3% sevoflurane for 2 h daily for 3 days. We showed that multiple exposures of sevoflurane induced significant learning ability impairment in young but not early adult mice, assessed in Morris water maze test on postnatal days 65. The integrated differential expression analysis revealed distinct transcription responses of Egr family members in the hippocampus of the young and early adult mice after sevoflurane administration. Particularly, Egr2 was significantly upregulated after sevoflurane exposure only in young mice. Microinjection of Egr2 shRNA recombinant adeno-associated virus into the dentate gyrus alleviated sevoflurane-induced cognitive deficits, and abolished sevoflurane-induced dendritic spins loss and BDNF downregulation in young mice. On the contrary, microinjection of the Egr2 overexpression virus in the dentate gyrus aggravated learning ability impairment induced by sevoflurane in young mice but not early adult mice. Furthermore, we revealed that sevoflurane markedly upregulated the nuclear factors of activated T-cells NFATC1 and NFATC2 in young mice, which were involved in Egr2 regulation. In conclusion, Egr2 serves as a critical factor for age-dependent vulnerability to sevoflurane-induced cognitive deficits.

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 &lt;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.

Prolonged sevoflurane exposure causes abnormal synapse development and dysregulates beta-neurexin and neuroligins in the hippocampus in neonatal rats

BACKGROUND

The underlying molecular mechanisms of the excitatory/inhibitory (E/I) imbalance induced by sevoflurane exposure to neonates remain poorly understood. This study aimed to investigate the long-term effects of prolonged sevoflurane exposure to neonatal rats during the peak period of synaptogenesis on the changes of trans-synaptic neurexin-neuroligin interactions, synaptic ultrastructure in the hippocampus and cognition.

METHODS

A total of 30 rat pups at postnatal day (P) 7 was randomly divided into two groups: the control group (exposed to 30 % oxygen balanced with nitrogen) and the sevoflurane group (exposed to 2.5 % sevoflurane plus 30 % oxygen balanced with nitrogen) for 6 h. Neurocognitive behaviors were assessed with the Open field test at P23-25 and the Morris water maze test at P26-30. The expression of β-neurexin (β-NRX), N-methyl-d-aspartate receptor 2 subunit (NR2A and NR2B), neuroligin-1 (NLG-1), neuroligin-2 (NLG-2), postsynaptic density protein-95 (PSD-95), α1-subunit of the γ-aminobutyric acid A receptor (GABAAα1) and gephyrin in the hippocampus at P30 were measured by Western blot. The ultrastructure of synapses was examined under electron microscope.

RESULTS

Prolonged sevoflurane exposure at P7 resulted in cognitive deficiency in adolescence, as well as the downregulation of β-NRX, NR2A, NR2B, NLG-1, and PSD-95, and the upregulation of GABAAα1, NLG-2, and gephyrin in the hippocampal CA3 region. Sevoflurane anesthesia also increased the number of symmetric synapses in the hippocampus.

CONCLUSIONS

Prolonged sevoflurane exposure during the brain development leads to cognitive deficiency and disproportion of excitatory/inhibitory synapses which may be caused by dysregulated expression of synaptic adhesion molecules of β-NRX and neuroligins.

Sevoflurane exposure during the second trimester induces neurotoxicity in offspring rats by hyperactivation of PARP-1

RATIONALE

Fetal exposure to general anesthesia may cause noteworthy neurocognitive impairment, but the mechanisms are unclear.

OBJECTIVES

Our study designed to explore the potential mechanism of neurotoxicity in offspring rats after sevoflurane exposure to the pregnant rats during the second trimester.

METHODS

Pregnant rats (G14 day) were administrated with or without 3.5% sevoflurane, 40 mg/kg 3-aminobenzamide (3-AB), inhibitor of poly ADP ribose polymerase 1 (PARP-1), or 10 mg/kg TC-2153, inhibitor of striatal-enriched phosphatase 61 (STEP61). Afterwards, the effects on expression of β-tubulin (TUJ1), neurite outgrowth inhibitor A (Nogo-A), parthanatos-related and STEP61/proline-rich tyrosine kinase 2 (Pyk2) pathway-associated proteins, and reactive oxygen species (ROS) levels were examined by immunofluorescence staining, Western blot, and dihydroethidium (DHE) staining, respectively. Moreover, morphological changes in the hippocampal CA3 region and neuronal cell death were tested by glycine silver staining and TUNEL and immunofluorescence double staining, respectively. Furthermore, spatial learning and memory functions of rats on postnatal 28-33 days (PND 28-33) were evaluated by morris water maze (MWM).

RESULTS

Mid-pregnancy exposure to sevoflurane led to excessive PARP-1 activation, poly (ADP-ribose) (PAR) polymer accumulation, apoptosis-inducing factor (AIF) nuclear translocation, and Nogo-A accumulation. Besides, sevoflurane significantly inhibited neurite growth and increased cell death in the fetal rat brain. Additionally, sevoflurane activated STEP61/Pyk2 pathway and increased ROS levels. However, 3-AB or TC-2153 significantly alleviated cell death, promoted neurites growth, and improved sevoflurane-induced spatial learning and memory impairment.

CONCLUSION

This study proposes that sevoflurane exposure during the second trimester incudes neurotoxicity in offspring rats by hyperactivation of PARP-1 via STEP61/Pyk2 pathway.

PP2A-associated tau hyperphosphorylation was involved in sevoflurane induced neonatal neurotoxicity

BACKGROUND

The effects of sevoflurane anesthesia on childhood neurodevelopment and adult brain function have attracted increasing scientific attentions. However, the exact mechanisms underlying hyperphosphorylation of tau protein in sevoflurane induced abnormalities in central nervous system (CNS) development, particularly in the hippocampus, have not been fully determined.

METHODS

We utilized molecular biological and behavioral approaches to compare the changes in cognitive function in mice exposed to repeated sevoflurane during the neonatal stage, and to assess whether PP2A-associated tau hyperphosphorylation is involved in sevoflurane induced neonatal neurotoxicity.

RESULTS

We reported that mice anesthetized with repeated sevoflurane during the neonatal period caused cognitive dysfunction during the adulthood. More importantly, we found that hyperphosphorylation of tau protein and decreased level of protein phosphatase 2A (PP2A) were detected in the hippocampus of mice after neonatal exposure of sevoflurane. Meanwhile, GSK-3β activity was found to be increased with repeated sevoflurane exposure, but not for more than 2 weeks.

CONCLUSION

Our results suggest that PP2A-associated hyperphosphorylation of tau protein might contribute to sevoflurane induced developmental neurotoxicity. These findings could provide a theoretical basis for the safely usage of sevoflurane in pediatric surgeries, and offer a valuable reference and potential therapeutic targets for the development of neuroprotective drugs.

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.

Multiple Sevoflurane Exposures During the Neonatal Period Cause Hearing Impairment and Loss of Hair Cell Ribbon Synapses in Adult Mice

Objectives

This study aims to investigate the effects of multiple sevoflurane exposures in neonatal mice on hearing function in the later life and explores the underlying mechanisms and protective strategies.

Materials and Methods

Neonatal Kunming mice were exposed to sevoflurane for 3 days. Auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) tests, immunofluorescence, patch-clamp recording, and quantitative real-time PCR were performed to observe hearing function, hair cells, ribbon synapses, nerve fibers, spiral ganglion neurons, and oxidative stress.

Results

Compared to control group, multiple sevoflurane exposures during the neonatal time significantly elevated ABR thresholds at 8 kHz (35.42 ± 1.57 vs. 41.76 ± 1.97 dB, P = 0.0256), 16 kHz (23.33 ± 1.28 vs. 33.53 ± 2.523 dB, P = 0.0012), 24 kHz (30.00 ± 2.04 vs. 46.76 ± 3.93 dB, P = 0.0024), and 32 kHz (41.25 ± 2.31 vs. 54.41 ± 2.94 dB, P = 0.0028) on P30, caused ribbon synapse loss on P15 (13.10 ± 0.43 vs. 10.78 ± 0.52, P = 0.0039) and P30 (11.24 ± 0.56 vs. 8.50 ± 0.84, P = 0.0141), and degenerated spiral ganglion neuron (SGN) nerve fibers on P30 (110.40 ± 16.23 vs. 55.04 ± 8.13, P = 0.0073). In addition, the V_half of calcium current become more negative (−21.99 ± 0.70 vs. −27.17 ± 0.60 mV, P < 0.0001), exocytosis was reduced (105.40 ± 19.97 vs. 59.79 ± 10.60 fF, P < 0.0001), and Lpo was upregulated (P = 0.0219) in sevoflurane group than those in control group. N-acetylcysteine (NAC) reversed hearing impairment induced by sevoflurane.

Conclusion

The findings suggest that multiple sevoflurane exposures during neonatal time may cause hearing impairment in adult mice. The study also demonstrated that elevated oxidative stress led to ribbon synapses impairment and SGN nerve fibers degeneration, and the interventions of antioxidants alleviated the sevoflurane-induced hearing impairment.

Safety of general anaesthetics on the developing brain: are we there yet?

Thirty years ago, neurotoxicity induced by general anaesthetics in the developing brain of rodents was observed. In both laboratory-based and clinical studies, many conflicting results have been published over the years, with initial data confirming both histopathological and neurodevelopmental deleterious effects after exposure to general anaesthetics. In more recent years, animal studies using non-human primates and new human cohorts have identified some specific deleterious effects on neurocognition. A clearer pattern of neurotoxicity seems connected to exposure to repeated general anaesthesia. The biochemistry involved in this neurotoxicity has been explored, showing differential effects of anaesthetic drugs between the developing and developed brains. In this narrative review, we start with a comprehensive description of the initial concerning results that led to recommend that any non-essential surgery should be postponed after the age of 3 yr and that research into this subject should be stepped up. We then focus on the neurophysiology of the developing brain under general anaesthesia, explore the biochemistry of the observed neurotoxicity, before summarising the main scientific and clinical reports investigating this issue. We finally discuss the GAS trial, the importance of its results, and some potential limitations that should not undermine their clinical relevance. We finally suggest some key points that could be shared with parents, and a potential research path to investigate the biochemical effects of general anaesthesia, opening up perspectives to understand the neurocognitive effects of repetitive exposures, especially in at-risk children.

Eye-tracking as a window into primate social cognition

Over the past decade, noninvasive, restraint-free eye-tracking research with primates has transformed our understanding of primate social cognition. The use of this technology with many primate species allows for the exploration and comparison of how these species attend to and understand social agents and interactions. The ability to compare and contrast the cognitive capacities of various primate species, including humans, provides insight into the evolutionary mechanisms and selective pressures that have likely shaped social cognition in similar and divergent ways across the primate order. In this review, we begin by discussing noninvasive behavioral methods used to measure primate gaze and attention before the introduction of noninvasive, restraint-free eye-tracking methodologies. Next, we focus on findings from recent eye-tracking research on primate social cognition, beginning with simple visual and search mechanisms. We then discuss the results that have built on this basic understanding of how primates view images and videos, exploring discrimination and knowledge of social agents, following social cues, tracking perspectives and predicting behavior, and the combination of eye-tracking and other behavioral and physiological methods. Finally, we discuss some future directions of noninvasive eye-tracking research on primate social cognition and current eye-tracking work-in-progress that builds on these previous studies, investigating underexplored socio-cognitive capacities and utilizing new methodologies.

Anesthesia and neurotoxicity study design, execution, and reporting in the nonhuman primate: A systematic review

BACKGROUND

Concern for a role of anesthesia in neurotoxicity in children originated from neonatal rodent and nonhuman primate (NHP) models, yet prospective clinical studies have largely not supported this concern. The goal of this study was to conduct an objective assessment of published NHP study rigor in design, execution, and reporting.

METHODS

A MEDLINE search from 2005 to December 2021 was performed. Inclusion criteria included full-length original studies published in English under peer-reviewed journals. We documented experimental parameters on anesthetic dosing, monitoring, vitals, and experimental outcomes.

RESULTS

Twenty-three manuscripts were included. Critical issues identified in study design included: lack of blinding in data acquisition (57%) and analysis (100%), supratherapeutic (4-12 fold) maintenance dosing in 22% of studies, lack of sample size justification (91%) resulting in a mean (SD) sample size of 6 (3) animals per group. Critical items identified in the conduct and reporting of studies included: documentation of anesthesia provider (0%), electrocardiogram monitoring (35%), arterial monitoring (4%), spontaneous ventilation employed (35%), failed intubations resulting in comingling ventilated and unventilated animals in data analysis, inaccurate reporting of failed intubation, and only 50% reporting on survival. Inconsistencies were noted in drug-related induction of neuroapoptosis and region of occurrence. Further, 67%-100% of behavior outcomes were not significantly different from controls.

CONCLUSIONS

Important deficits in study design, execution, and reporting were identified in neonatal NHP studies. These results raise concern for the validity and reliability of these studies and may explain in part the divergence from results obtained in human neonates.

General Anesthesia and the Young Brain: The Importance of Novel Strategies with Alternate Mechanisms of Action

Over the past three decades, we have been grappling with rapidly accumulating evidence that general anesthetics (GAs) may not be as innocuous for the young brain as we previously believed. The growing realization comes from hundreds of animal studies in numerous species, from nematodes to higher mammals. These studies argue that early exposure to commonly used GAs causes widespread apoptotic neurodegeneration in brain regions critical to cognition and socio-emotional development, kills a substantial number of neurons in the young brain, and, importantly, results in lasting disturbances in neuronal synaptic communication within the remaining neuronal networks. Notably, these outcomes are often associated with long-term impairments in multiple cognitive-affective domains. Not only do preclinical studies clearly demonstrate GA-induced neurotoxicity when the exposures occur in early life, but there is a growing body of clinical literature reporting similar cognitive-affective abnormalities in young children who require GAs. The need to consider alternative GAs led us to focus on synthetic neuroactive steroid analogues that have emerged as effective hypnotics, and analgesics that are apparently devoid of neurotoxic effects and long-term cognitive impairments. This would suggest that certain steroid analogues with different cellular targets and mechanisms of action may be safe alternatives to currently used GAs. Herein we summarize our current knowledge of neuroactive steroids as promising novel GAs.

Anesthesia and Developing Brains: Unanswered Questions and Proposed Paths Forward

Anesthetic agents disrupt neurodevelopment in animal models, but evidence in humans is mixed. The morphologic and behavioral changes observed across many species predicted that deficits should be seen in humans, but identifying a phenotype of injury in children has been challenging. It is increasingly clear that in children, a brief or single early anesthetic exposure is not associated with deficits in a range of neurodevelopmental outcomes including broad measures of intelligence. Deficits in other domains including behavior, however, are more consistently reported in humans and also reflect findings from nonhuman primates. The possibility that behavioral deficits are a phenotype, as well as the entire concept of anesthetic neurotoxicity in children, remains a source of intense debate. The purpose of this report is to describe consensus and disagreement among experts, summarize preclinical and clinical evidence, suggest pathways for future clinical research, and compare studies of anesthetic agents to other suspected neurotoxins.

Prophylactic progesterone prevents adverse behavioural and neurocognitive effects of neonatal anaesthesia exposure in rat

BACKGROUND

Evidence from animal models and human studies suggests an association between early general anaesthesia exposure and development of long-lasting neurocognitive problems including learning and memory impairments and an anxious phenotype. Because millions of children each year undergo procedures that require anaesthesia, it is important to investigate ways to protect the vulnerable developing brain. We evaluated whether progesterone treatment administered before general anaesthesia exposure could prevent long-term anaesthesia-induced neurocognitive and behavioural changes.

METHODS

Female and male Long-Evans rat pups were repeatedly exposed to 2 h of sevoflurane or control procedures at postnatal days 7, 10, and 13. Subcutaneous injections of progesterone or vehicle were administered immediately before general anaesthesia exposure or control procedures. Neurobehavioural and cognitive outcomes were evaluated using elevated plus maze and Morris water maze tests.

RESULTS

Prophylactic progesterone treatment attenuated the chemokine (C-X-C motif) ligand 1 (CXCL1) response to sevoflurane exposure. Rats given vehicle treatment with general anaesthesia exposure exhibited increased anxiety on the elevated plus maze and learning and memory impairments on the Morris water maze. However, rats treated with progesterone before general anaesthesia lacked these impairments and performed in a similar manner to controls on both tasks.

CONCLUSIONS

Progesterone attenuated the anaesthesia-induced, acute peripheral inflammatory response and prevented cognitive and behavioural alterations associated with early repeated general anaesthesia exposure. Importantly, our results suggest that progesterone treatments given before general anaesthesia may help to protect the developing brain.

Epitranscriptomic Analysis of N6-methyladenosine in Infant Rhesus Macaques after Multiple Sevoflurane Anesthesia

Clinical investigations to date have proposed the possibility that exposure to anesthetics is associated with neurodevelopmental deficits. Sevoflurane is the most commonly used general anesthetic in pediatric patients. Animal studies have demonstrated that multiple exposures to sevoflurane during the postnatal period resulted in neuropathological brain changes and long-term cognitive deficits. However, the underlying mechanisms remain to be clarified. In this study, methylated RNA immunoprecipitation sequencing (MeRIP-Seq) was performed to acquire genome-wide profiling of RNA N6-methyladenosine (m⁶A) in the prefrontal cortex of infant rhesus macaques. The macaques in the sevoflurane group had more m⁶A peaks than the macaques in the control group (p ≤ 0.05). After sevoflurane treatment, the mRNA levels of YT521-B homology domain family 1 (YTHDF1) and YT521-B homology domain family 3 (YTHDF3) were decreased, and sevoflurane anesthesia dynamically regulated RNA m⁶A methylation. Gene ontology (GO) analysis revealed that after sevoflurane exposure, genes with increased methylation of m⁶A sites were enriched in some physiological processes relevant to neurodevelopment, mainly focused on synaptic plasticity. The female macaques had 18 hypermethylated genes. The males had 35 hypermethylated genes, and some physiological processes related to the regulation of synaptic structure were enriched. Rhesus macaques are genetically closer to human beings. Our findings can help in the study of the mechanism of sevoflurane-relevant neurodevelopmental deficits at the posttranscriptional level and can provide new insights into potential clinical preventions and interventions for the neurotoxicity of neonatal anesthesia exposure.

Prolonged Volatile Anesthetic Exposure Exacerbates Cognitive Impairment and Neuropathology in the 5xFAD Mouse Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease which shows a set of symptoms involving cognitive changes and psychological changes. Given that AD is the most common form of dementia in aging population and the increasing demand for anesthesia/surgery with aging, there has been significant interest in the exact impact of volatile anesthetics on cognitive function and pathological alterations in AD population.

OBJECTIVE

This study aimed to investigate behavioral changes and neuropathology in the 5xFAD mouse model of Alzheimer's disease with short-term exposure or long-term exposure to desflurane, sevoflurane, or isoflurane.

METHODS

In this study, we exposed 5xFAD mouse model of AD to isoflurane, sevoflurane, or desflurane in two different time periods (30 min and 6 h), and the memory related behaviors as well as the pathological changes in 5xFAD mice were evaluated 7 days after the anesthetic exposure.

RESULTS

We found that short-term exposure to volatile anesthetics did not affect hippocampus dependent memory and the amyloid-β (Aβ) deposition in the brain. However, long-term exposure to sevoflurane or isoflurane significantly increased the Aβ deposition in CA1 and CA3 regions of hippocampus, as well as the glial cell activation in amygdala. Besides, the PSD-95 expression was decreased in 5xFAD mice with exposure to sevoflurane or isoflurane and the caspase-3 activation was enhanced in isoflurane, sevoflurane, and desflurane groups.

CONCLUSION

Our results demonstrate the time-dependent effects of common volatile anesthetics and implicate that desflurane has the potential benefits to prolonged anesthetic exposure in AD patients.

Lovastatin attenuates sevoflurane-induced cognitive disorder in aged rats via reducing Aβ accumulation

As a general anesthetic widely used in surgical, sevoflurane has been shown to cause cognitive and memory deficits in the elderly. It's important to find out agents that can counteract sevoflurane-induced cognitive dysfunction. This study is aimed to investigate the effect of lovastatin on sevoflurane-induced cognitive impairment in aged rats and reveal the potential mechanisms. BV-2 cells, rat hippocampal neurons or male aged rats were exposed to 2% sevoflurane for 5 h. The cells were pretreated with 10 μM lovastatin. The rats were intraperitoneally injected with 5 mg/kg/day lovastatin for three days. The results showed that lovastatin enhanced exosomal IDE secretion from sevoflurane-exposed BV-2 cells and promoted Aβ degradation. Lovastatin treatment also inhibited the increased expressions of β-secretase 1 (BACE1) and γ-secretase in hippocampal neurons under sevoflurane exposure in vitro. In animal experiments, the discrimination index in novel object recognition test and percentage of spontaneous alternation in Y-maze test were significantly elevated after lovastatin administration. In addition, Aβ plaque area and contents of soluble Aβ1-40 and Aβ1-42 in the hippocampal tissues were decreased upon lovastatin treatment. Furthermore, lovastatin reversed sevoflurane-induced Aβ accumulation via up-regulating IDE expression, and down-regulating amyloid precursor protein (APP)-related protein expression (β-C-terminal fragment (CTF), BACE1 and γ-secretase). In conclusion, lovastatin alleviates sevoflurane-induced cognitive deficient in aged rats via promoting Aβ degradation and reducing Aβ production. Lovastatin may be beneficial in preventing anesthetic-induced cognitive impairment.

Long-term evidence of neonatal anaesthesia neurotoxicity linked to behavioural phenotypes in monkeys: where do we go from here?

Whether anaesthesia exposure early in life leads to brain damage with long-lasting structural and behavioural consequences in primates has not been conclusively determined. A study in the British Journal of Anaesthesia by Neudecker and colleagues found that 2 yr after early anaesthesia exposure, monkeys exhibited signs of chronic astrogliosis which correlate with behavioural deficits. Given the increasing frequency of exposure to anaesthetics in infancy in humans, clinical trials are greatly needed to understand how sedative/anaesthetic agents may be impacting brain and behaviour development.

The application of noninvasive, restraint-free eye-tracking methods for use with nonhuman primates

Over the past 50 years there has been a strong interest in applying eye-tracking techniques to study a myriad of questions related to human and nonhuman primate psychological processes. Eye movements and fixations can provide qualitative and quantitative insights into cognitive processes of nonverbal populations such as nonhuman primates, clarifying the evolutionary, physiological, and representational underpinnings of human cognition. While early attempts at nonhuman primate eye tracking were relatively crude, later, more sophisticated and sensitive techniques required invasive protocols and the use of restraint. In the past decade, technology has advanced to a point where noninvasive eye-tracking techniques, developed for use with human participants, can be applied for use with nonhuman primates in a restraint-free manner. Here we review the corpus of recent studies (N=32) that take such an approach. Despite the growing interest in eye-tracking research, there is still little consensus on "best practices," both in terms of deploying test protocols or reporting methods and results. Therefore, we look to advances made in the field of developmental psychology, as well as our own collective experiences using eye trackers with nonhuman primates, to highlight key elements that researchers should consider when designing noninvasive restraint-free eye-tracking research protocols for use with nonhuman primates. Beyond promoting best practices for research protocols, we also outline an ideal approach for reporting such research and highlight future directions for the field.

Neonatal Anesthesia and dysregulation of the Epigenome

Each year, millions of infants and children are anesthetized for medical and surgical procedures. Yet, a substantial body of preclinical evidence suggests that anesthetics are neurotoxins that cause rapid and widespread apoptotic cell death in the brains of infant rodents and non-human primates. These animals have persistent impairments in cognition and behavior many weeks or months after anesthesia exposure, leading us to hypothesize that anesthetics do more than simply kill brain cells. Indeed, anesthetics cause chronic neuropathology in neurons that survive the insult, which then interferes with major aspects of brain development, synaptic plasticity, and neuronal function. Understanding the phenomenon of anesthesia-induced developmental neurotoxicity is of critical public health importance because clinical studies now report that anesthesia in human infancy is associated with cognitive and behavioral deficits. In our search for mechanistic explanations for why a young and pliable brain cannot fully recover from a relatively brief period of anesthesia, we have accumulated evidence that neonatal anesthesia can dysregulate epigenetic tags that influence gene transcription such as histone acetylation and DNA methylation. In this review, we briefly summarize the phenomenon of anesthesia-induced developmental neurotoxicity. We then discuss chronic neuropathology caused by neonatal anesthesia, including disturbances in cognition, socio-affective behavior, neuronal morphology, and synaptic plasticity. Finally, we present evidence of anesthesia-induced genetic and epigenetic dysregulation within the developing brain that may be transmitted intergenerationally to anesthesia-naïve offspring.

Astrogliosis in juvenile non-human primates 2 years after infant anaesthesia exposure

BACKGROUND

Infant anaesthesia causes acute brain cell apoptosis, and later in life cognitive deficits and behavioural alterations, in non-human primates (NHPs). Various brain injuries and neurodegenerative conditions are characterised by chronic astrocyte activation (astrogliosis). Glial fibrillary acidic protein (GFAP), an astrocyte-specific protein, increases during astrogliosis and remains elevated after an injury. Whether infant anaesthesia is associated with a sustained increase in GFAP is unknown. We hypothesised that GFAP is increased in specific brain areas of NHPs 2 yr after infant anaesthesia, consistent with prior injury.

METHODS

Eight 6-day-old NHPs per group were exposed to 5 h isoflurane once (1×) or three times (3×), or to room air as a control (Ctr). Two years after exposure, their brains were assessed for GFAP density changes in the primary visual cortex (V1), perirhinal cortex (PRC), hippocampal subiculum, amygdala, and orbitofrontal cortex (OFC). We also assessed concomitant microglia activation and hippocampal neurogenesis.

RESULTS

Compared with controls, GFAP densities in V1 were increased in exposed groups (Ctr: 0.208 [0.085-0.427], 1×: 0.313 [0.108-0.533], 3×: 0.389 [0.262-0.652]), whereas the density of activated microglia was unchanged. In addition, GFAP densities were increased in the 3× group in the PRC and the subiculum, and in both exposure groups in the amygdala, but there was no increase in the OFC. There were no differences in hippocampal neurogenesis among groups.

CONCLUSIONS

Two years after infant anaesthesia, NHPs show increased GFAP without concomitant microglia activation in specific brain areas. These long-lasting structural changes in the brain caused by infant anaesthesia exposure may be associated with functional alterations at this age.

Early Isoflurane Exposure Impairs Synaptic Development in Fmr1 KO Mice via the mTOR Pathway

General anesthetics (GAs) may cause disruptions in brain development, and the effect of GA exposure in the setting of pre-existing neurodevelopmental disease is unknown. We tested the hypothesis that synaptic development is more vulnerable to GA-induced deficits in a mouse model of fragile X syndrome than in WT mice and asked whether they were related to the mTOR pathway, a signaling system implicated in both anesthesia toxicity and fragile X syndrome. Early postnatal WT and Fmr1-KO mice were exposed to isoflurane and brain slices were collected in adulthood. Primary neuron cultures isolated from WT and Fmr1-KO mice were exposed to isoflurane during development, in some cases treated with rapamycin, and processed for immunohistochemistry at maturity. Quantitative immunofluorescence microscopy was conducted for synaptic markers and markers of mTOR pathway activity. Isoflurane exposure caused reduction in Synpasin-1, PSD-95, and Gephyrin puncta that was significantly lower in Fmr1-KO mice than in WT mice. Similar results were found in cell culture, where synapse loss was ameliorated with rapamycin treatment. Early developmental exposure to isoflurane causes more profound synapse loss in Fmr1- KO than WT mice, and this effect is mediated by a pathologic increase in mTOR pathway activity.