Repeated Neonatal Sevoflurane Exposure-Induced Developmental Delays of Parvalbumin Interneurons and Cognitive Impairments Are Reversed by Environmental Enrichment

Restricted Daily Exposure of Environmental Enrichment: Bridging the Practical Gap from Animal Studies to Human Application

Daily restricted environmental enrichment (REE) refers to limited, structured periods of enrichment aimed at improving both physical and cognitive well-being in animals and humans. This review explores the significance of REE, focusing on studies that investigate 2 and 3 h daily enrichment protocols. Through an analysis of 21 key studies, this paper highlights how even brief periods of REE can lead to substantial improvements in brain plasticity, cognitive function, and stress resilience. The review tracks the evolution of environmental enrichment from early research on enriched environments in animals to modern applications in human rehabilitation, particularly for stroke recovery and mental health treatment. While the traditional approach to environmental enrichment often involves continuous exposure, recent research suggests that restricted daily enrichment can yield comparable benefits, offering a practical, scalable solution for clinical settings. This review underscores the importance of adapting REE for individual needs and developing flexible, home-based programs for broader application.

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.

The Role of the SIRT1-mTOR Signaling Pathway in Regulating Autophagy in Sevoflurane-Induced Apoptosis of Fetal Rat Brain Neurons

BACKGROUND

Isoflurane is a commonly used general anesthetic widely employed in clinical surgeries. Recent studies have indicated that isoflurane might induce negative impacts on the nervous system, notably by triggering neuronal apoptosis. This process is pivotal to the development and emergence of neurological disorders; its misregulation could result in functional deficits and the initiation of diseases within nervous system. However, the potential molecular mechanism of isoflurane on the neuronal apoptosis remains fully unexplored. This study aims to investigate the regulatory role of the sirtuin 1-mechanistic target of rapamycin (SIRT1-mTOR) signaling pathway in autophagy during isoflurane-induced apoptosis of fetal rat brain neuronal cells.

METHODS

Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, real-time quantitative polymerase chain reaction (qPCR), and Western blot were utilized to evaluate the apoptotic status of hippocampal tissue cells in fetal mice after sevoflurane exposure. Our further investigation was commenced with flow cytometry, immunofluorescence, qPCR, and Western blot to determine the impact of autophagy on sevoflurane-induced apoptosis in these neurons. On the other hand, we conducted an additional set of analyses, including flow cytometric analysis, qPCR, and Western blot, to further elucidate the neuroprotective potential of autophagy in neural cells of fetal mice subjected to sevoflurane-induced apoptosis.

RESULTS

Our findings indicated that a 3% sevoflurane treatment led to a significant rise in apoptosis among fetal rat hippocampal tissue cells and neurons. Levels of apoptosis-associated proteins, cleaved-caspase-3 and Bcl-2 associated X protein (Bax), were found to be markedly higher, coinciding with an enhancement in autophagy as evidenced by increased microtubule-associated proteins 1A/1B-light chain 3 (LC3) and decreased p62 expression. Concurrently, there was a notable up-regulation of sirtuin 1 (SIRT1) and a down-regulation of mechanistic target of rapamycin (mTOR) expression. In conclusion, our research elucidated the pivotal function of cellular autophagy in an apoptosis induced by sevoflurane in fetal rat nerve cells. Through experimental manipulation, we observed that interference with SIRT1 resulted in a reduction of both cleaved-caspase-3 and Bax levels. This intervention also beget a diminished expression of the autophagy-associated factor LC3 and an up-regulation of p62. Furthermore, inhibition against mTOR reversed the effects induced by SIRT1 interference, suggesting a complex interplay amid these regulatory pathways.

CONCLUSIONS

SIRT1 possesses a capacity to modulate apoptosis in the hippocampal neurons of fetal rats triggered by sevoflurane, with mTOR functioning as an inhibitory factor within this signaling pathway.

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.

SynCAM1 deficiency in the hippocampal parvalbumin interneurons contributes to sevoflurane-induced cognitive impairment in neonatal rats

AIMS

Sevoflurane is widely used for general anesthesia in children. Previous studies reported that multiple neonatal exposures to sevoflurane can induce long-term cognitive impairment in adolescent rats, but the underlying mechanisms were not defined.

METHODS

Postnatal day 6 (P6) to P8 rat pups were exposed to 30% oxygen with or without 3% sevoflurane balanced with air. The Y maze test (YMT) and Morris water maze (MWM) tests were performed in some cohorts from age P35 to assess cognitive functions, and their brain samples were harvested at age P14, 21, 28, 35, and 42 for measurements of various molecular entities and in vivo electrophysiology experiments at age P35.

RESULTS

Sevoflurane exposure resulted in cognitive impairment that was associated with decreased synCAM1 expression in parvalbumin (PV) interneurons, a reduction of PV phenotype, disturbed gamma oscillations, and dendritic spine loss in the hippocampal CA3 region. Enriched environment (EE) increased synCAM1 expression in the PV interneurons and attenuated sevoflurane-induced cognitive impairment. The synCAM1 overexpression by the adeno-associated virus vector in the hippocampal CA3 region restored sevoflurane-induced cognitive impairment, PV phenotype loss, gamma oscillations decrease, and dendritic spine loss.

CONCLUSION

Our data suggested that neonatal sevoflurane exposure results in cognitive impairment through decreased synCAM1 expression in PV interneurons in the hippocampus.

Maternal sevoflurane exposure increases the epilepsy susceptibility of adolescent offspring by interrupting interneuron development

BACKGROUND

Exposure to general anesthesia influences neuronal functions during brain development. Recently, interneurons were found to be involved in developmental neurotoxicity by anesthetic exposure. But the underlying mechanism and long-term consequences remain elusive.

METHODS

Pregnant mice received 2.5% sevoflurane for 6-h on gestational day 14.5. Pentylenetetrazole (PTZ)-induced seizure, anxiety- and depression-like behavior tests were performed in 30- and 60-day-old male offspring. Cortical interneurons were labeled using Rosa26-EYFP/-; Nkx2.1-Cre mice. Immunofluorescence and electrophysiology were performed to determine the cortical interneuron properties. Q-PCR and in situ hybridization (ISH) were performed for the potential mechanism, and the finding was further validated by in utero electroporation (IUE).

RESULTS

In this study, we found that maternal sevoflurane exposure increased epilepsy susceptibility by using pentylenetetrazole (PTZ) induced-kindling models and enhanced anxiety- and depression-like behaviors in adolescent offspring. After sevoflurane exposure, the highly ordered cortical interneuron migration was disrupted in the fetal cortex. In addition, the resting membrane potentials of fast-spiking interneurons in the sevoflurane-treated group were more hyperpolarized in adolescence accompanied by an increase in inhibitory synapses. Both q-PCR and ISH indicated that CXCL12/CXCR4 signaling pathway downregulation might be a potential mechanism under sevoflurane developmental neurotoxicity which was further confirmed by IUE and behavioral tests. Although the above effects were obvious in adolescence, they did not persist into adulthood.

CONCLUSIONS

Our findings demonstrate that maternal anesthesia impairs interneuron migration through the CXCL12/CXCR4 signaling pathway, and influences the interneuron properties, leading to the increased epilepsy susceptibility in adolescent offspring. Our study provides a novel perspective on the developmental neurotoxicity of the mechanistic link between maternal use of general anesthesia and increased susceptibility to epilepsy.

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.

Melatonin attenuates sevoflurane-induced hippocampal damage and cognitive deficits in neonatal mice by suppressing CypD in parvalbumin neurons

BACKGROUND

Sevoflurane, a commonly administered inhaled anesthetic, is found to induce synaptic and mitochondrial damage in neonatal mice. Mitochondrial membrane potential (MMP) changes, mediated by Cyclophilin D (CypD), are implicated in mitochondrial function. Melatonin, known for its significant neuroprotective properties, was investigated in this study to elucidate its mechanisms in mitigating the cognitive impairment caused by sevoflurane.

METHODS

The mice were categorized into several groups, including the control, vehicle, sevoflurane, vehicle plus sevoflurane, and melatonin plus sevoflurane groups. From postnatal day 6 to day 8, the mice were administered inhaled sevoflurane or intraperitoneal melatonin. MMP and reactive oxygen species (ROS) were measured using appropriate detection kits. The protein expression levels of PSD95, Synapsin Ⅰ, and CypD in the hippocampus were analyzed through western blotting in acute and prolonged terms. Immunofluorescence staining was used to assess the co-localizations of PSD95 or CypD in parvalbumin (PV) neurons. Cognitive ability was evaluated through novel object recognition, social interaction experiment, and the Morris water maze.

RESULTS

The findings revealed that repeated exposure to sevoflurane in neonatal mice resulted in cognitive and synaptic impairment. Furthermore, melatonin administration suppressed the ROS and CypD protein expression, enhanced the MMP in mitochondria and synaptic protein expression in PV neurons, and ameliorated cognitive deficits.

CONCLUSION

Melatonin alleviated sevoflurane-induced cognitive deficits by suppressing CypD and promoting synaptic development in hippocampal PV neurons. These results provide valuable insights into a promising therapeutic approach for preventing neurotoxic injuries caused by general anesthetics.

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.

Sevoflurane induces microRNA-18a to delay rat neurodevelopment via suppression of the RUNX1/Wnt/β-catenin axis

Sevoflurane anesthesia is reported to repress neurogenesis of neural stem cells (NSCs), thereby affecting the brain development, but the underlying mechanism of sevoflurane on the proliferation of NSCs remains unclear. Thus, this study aims to discern the relationship between sevoflurane and NSC proliferation. Bioinformatics tools were employed to predict the expression of microRNA-18a (miR-18a) in 9-day-old neonatal rat hippocampal tissues after sevoflurane treatment and the downstream genes of miR-18a, followed by a series of assays to explore the relationship among miR-18a, runt related transcription factor 1 (RUNX1), and β-catenin in the hippocampal tissues. NSCs were isolated from the hippocampal tissues and subjected to gain-/loss-of-function assays to investigate the interactions among miR-18a, RUNX1, and β-catenin in NSCs and their roles in NSC development. Bioinformatics analysis and experimental results confirmed high expression of miR-18a in rat hippocampal tissues and NSCs after sevoflurane treatment. Next, we found that miR-18a downregulated RUNX1 expression, while RUNX1 promoted NSC proliferation by activating the Wnt/β-catenin signaling pathway. The behavioral experiments also showed that sevoflurane caused nerve injury in rats, whilst RUNX1 overexpression protected rat neurodevelopment. Our findings uncovered that sevoflurane attenuated NSC proliferation via the miR-18a-meidated RUNX1/Wnt/β-catenin pathway, thereby impairing rat neurodevelopment.

Testosterone is Sufficient to Impart Susceptibility to Isoflurane Neurotoxicity in Female Neonatal Rats

BACKGROUND

Volatile anesthetic exposure during development leads to long-term cognitive deficits in rats which are dependent on age and sex. Female rats are protected relative to male rats for the same exposure on postnatal day 7. Here we test our hypothesis that androgens can modulate chloride cotransporter expression to alter the susceptibility to neurotoxicity from GABAergic drugs using female rats with exogenous testosterone exposure.

METHODS

Female rats were injected with testosterone (100 μg/animal) or vehicle on postnatal days 1 to 6. On postnatal day 7, the animals were randomized to either isoflurane exposure or sham. Spatial memory was assessed with the Barnes maze starting on postnatal day 41. Western blots were run from testosterone treated postnatal day 7 animals to measure levels of chloride cotransporters sodium-potassium-chloride symporter (NKCC1) and chloride-potassium symporter 5 (KCC2).

RESULTS

Exogenous testosterone modulated isoflurane anesthetic neurotoxicity in female rats based on poor performance in the probe trial of the Barnes Maze. By contrast, females with vehicle and isoflurane exposure were able to differentiate the goal position. These behavioral differences corresponded to differences in the protein levels of NKCC1 and KCC2 after exogenous testosterone exposure, with NKCC1 increasing ( P <0.001) and KCC2 decreasing ( P =0.003) relative to female controls.

CONCLUSIONS

The expression of chloride cotransporters, NKCC1 and KCC2, is altered by testosterone in female rats and corresponds to a cognitive deficit after isoflurane exposure. This confirms the role of androgens in perinatal anesthetic neurotoxicity and supports our hypothesis that the developing GABAergic system plays a critical role in the underlying mechanism.

Repeated Sevoflurane Exposures in Neonatal Rats Increased the Brain Vulnerability to Future Stress Exposure and Resulted in Fear Extinction Deficit

Sevoflurane anesthesia during neonatal period was reported to sensitize the rodent animals to stress later in life. The authors tested the hypothesis that repeated sevoflurane exposures in neonatal rats increased the brain vulnerability to future stress exposure and resulted in fear extinction deficit and investigated whether the neonatal brain depolarizing γ-aminobutyric acid type A receptor (GABA_AR) is involved in mediating these abnormalities. Neonatal Sprague-Dawley male rats, pretreated with vehicle or the NKCC1 inhibitor, bumetanide, received sequential exposures to 3% sevoflurane for 2 h on postnatal days (P) 5, P6, and P7 and then were exposed to electric foot shock stress in fear conditioning training at P14. Juvenile rats at different developmental brain stage receiving identical sevoflurane exposures on P25, P26, and P27 were also studied. The results showed repeated sevoflurane exposures in neonatal rats and increased the cation-chloride cotransporters NKCC1/KCC2 ratio in the PFC at P14. Repeated exposures to sevoflurane in neonatal rather than juvenile rats enhanced the stress response and exacerbated neuroapoptosis in the PFC after exposed to electric foot shock in fear conditioning training. Neonatal rather than juvenile sevoflurane-exposed rats exhibited deficits in fear extinction training and recall. Pretreatment of neonatal rats prior to sevoflurane exposures with bumetanide reduced the NKCC1/KCC2 ratio at P14 and ameliorated most of the subsequent adverse effects. Our study indicates that repeated sevoflurane exposures in neonatal rats might increase the brain vulnerability to future stress exposure and resulted in fear extinction deficit, which might be associated with the neonatal enhanced brain depolarizing GABA_AR activity.

Environmental enrichment ameliorates high-fat diet induced olfactory deficit and decrease of parvalbumin neurons in the olfactory bulb in mice

Overweight induced by high-fat diet (HFD) represents one of the major health concerns in modern societies, which can cause lasting peripheral and central metabolic disorders in all age groups. Specifically, childhood obesity could lead to life-long impact on brain development and functioning. On the other hand, environmental enrichment (EE) has been demonstrated to be beneficial for learning and memory. Here, we explored the impact of high-fat diet on olfaction and organization of olfactory bulb cells in adolescent mice, and the effect of EE intervention thereon. Puberty mice (3-week-old) fed with HFD for 10 weeks exhibited poorer odor sensitivity and olfactory memory relative to controls consuming standard chows. The behavioral deficits were rescued in the HFD group with EE intervention. Neuroanatomically, parvalbumin (PV) interneurons in the olfactory bulb (OB) were reduced in the HFD-fed animals relative to control, while EE intervention also normalized this alteration. In contrast, cells expressing calbindin (CB), doublecortin (DCX) in the OB were not altered. Our findings suggest that PV interneurons may play a crucial role in mediating the HFD-induced olfactory deficit in adolescent mice, and can also serve a protective effect of EE against the functional deficit.

Timely N-Acetyl-Cysteine and Environmental Enrichment Rescue Oxidative Stress-Induced Parvalbumin Interneuron Impairments via MMP9/RAGE Pathway: A Translational Approach for Early Intervention in Psychosis

Research in schizophrenia (SZ) emphasizes the need for new therapeutic approaches based on antioxidant/anti-inflammatory compounds and psycho-social therapy. A hallmark of SZ is a dysfunction of parvalbumin-expressing fast-spiking interneurons (PVI), which are essential for neuronal synchrony during sensory/cognitive processing. Oxidative stress and inflammation during early brain development, as observed in SZ, affect PVI maturation. We compared the efficacy of N-acetyl-cysteine (NAC) and/or environmental enrichment (EE) provided during juvenile and/or adolescent periods in rescuing PVI impairments induced by an additional oxidative insult during childhood in a transgenic mouse model with gluthation deficit (Gclm KO), relevant for SZ. We tested whether this rescue was promoted by the inhibition of MMP9/RAGE mechanism, both in the mouse model and in early psychosis (EP) patients, enrolled in a double-blind, randomized, placebo-controlled clinical trial of NAC supplementation for 6 months. We show that a sequential combination of NAC+EE applied after an early-life oxidative insult recovers integrity and function of PVI network in adult Gclm KO, via the inhibition of MMP9/RAGE. Six-month NAC treatment in EP patients reduces plasma sRAGE in association with increased prefrontal GABA, improvement of cognition and clinical symptoms, suggesting similar neuroprotective mechanisms. The sequential combination of NAC+EE reverses long-lasting effects of an early oxidative insult on PVI/perineuronal net (PNN) through the inhibition of MMP9/RAGE mechanism. In analogy, patients vulnerable to early-life insults could benefit from a combined pharmacological and psycho-social therapy.

Gut microbiota mediates cognitive impairment in young mice after multiple neonatal exposures to sevoflurane

Multiple exposures to anesthesia may increase the risk of cognitive impairment in young children. However, the mechanisms underlying this neurodevelopmental disorder remain elusive. In this study, we investigated alteration of the gut microbiota after multiple neonatal exposures to the anesthetic sevoflurane and the potential role of microbiota alteration on cognitive impairment using a young mice model. Multiple neonatal sevoflurane exposures resulted in obvious cognitive impairment symptoms and altered gut microbiota composition. Fecal transplantation experiments confirmed that alteration of the microbiota was responsible for the cognitive disorders in young mice. Microbiota profiling analysis identified microbial taxa that showed consistent differential abundance before and after fecal microbiota transplantation. Several of the differentially abundant taxa are associated with memory and/or health of the host, such as species of Streptococcus, Lachnospiraceae, and Pseudoflavonifractor. The results reveal that abnormal composition of the gut microbiota is a risk factor for cognitive impairment in young mice after multiple neonatal exposures to sevoflurane and provide insight into a potential therapeutic strategy for sevoflurane-related neurotoxicity.

Sevoflurane impairs m6A-mediated mRNA translation and leads to fine motor and cognitive deficits

Clinical surgical practices have found that children who undergo multiple anesthesia may have an increased risk of deficiencies in cognition and fine motor control. Here, we report that YT521-B homology domain family 1 (YTHDF1), a critical reader protein for N6-methyladenosine-modified mRNA, was significantly downregulated in the prefrontal cortex of young mice after multiple sevoflurane anesthesia exposures. Importantly, sevoflurane led to a decrease in protein synthesis in mouse cortical neurons that was fully rescued by YTHDF1, suggesting that anesthesia may affect early brain development by affecting m6A-dependent mRNA translation. Transcriptome-wide experiments showed that numerous mRNA targets related to synaptic functions in the prefrontal mouse cortex were associated with m6A methylation and YTHDF1. In particular, we found that synaptophysin, a critical presynaptic protein, was specifically modified by m6A methylation and associated with YTHDF1, and m6A methylation of synaptophysin decreased with multiple sevoflurane exposures. Importantly, we showed that fine motor control skills and cognitive functions were impaired in mice with multiple anesthesia exposures, and these effects were fully reversed by reintroducing YTHDF1 through a blood-brain barrier (BBB)-crossing viral delivery system. Finally, we found that the fine motor skills in children who underwent prolonged anesthesia were compromised 6 months after surgery. Our findings indicated that impairment in the translational regulation of mRNA via N6-methyladenosine methylation is a potential mechanism underlying the effects of anesthesia on neural development in the young brain. 1. N6-methyladenosine (m6A) modifications were involved in anesthesia-induced neurotoxicity. 2. Sevoflurane impairs m6A-mediated mRNA translation and leads to fine motor deficits in young mice. 3. YTHDF1, a m6A reader protein, rescued sevoflurane-induced protein synthesis inhibition and fine motor deficits in young mice.

The relationship between exposure to general anesthetic agents and the risk of developing an impulse control disorder

Most studies examining the effect of extended exposure to general anesthetic agents (GAAs) have demonstrated that extended exposure induces both structural and functional changes in the central nervous system. These changes are frequently accompanied by neurobehavioral changes that include impulse control disorders that are generally characterized by deficits in behavioral inhibition and executive function. In this review, we will.

Role of the GABAA receptors in the long-term cognitive impairments caused by neonatal sevoflurane exposure

Sevoflurane is a widely used inhalational anesthetic in pediatric surgeries, which is considered reasonably safe and reversible upon withdrawal. However, recent preclinical studies suggested that peri-neonatal sevoflurane exposure may cause developmental abnormalities in the brain. The present review aimed to present and discuss the accumulating experimental data regarding the undesirable effects of sevoflurane on brain development as revealed by the laboratory studies. First, we summarized the long-lasting side effects of neonatal sevoflurane exposure on cognitive functions. Subsequently, we presented the structural changes, namely, neuroapoptosis, neurogenesis and synaptogenesis, following sevoflurane exposure in the immature brain. Finally, we also discussed the potential mechanisms underlying subsequent cognitive impairments later in life, which are induced by neonatal sevoflurane exposure and pointed out potential strategies for mitigating sevoflurane-induced long-term cognitive impairments. The type A gamma-amino butyric acid (GABAA) receptor, the main targets of sevoflurane, is excitatory rather than inhibitory in the immature neurons. The excitatory effects of the GABAA receptors have been linked to increased neuroapoptosis, elevated serum corticosterone levels and epigenetic modifications following neonatal sevoflurane exposure in rodents, which might contribute to sevoflurane-induced long-term cognitive abnormalities. We proposed that the excitatory GABAA receptor-mediated HPA axis activity might be a novel mechanism underlying sevoflurane-induced long-term cognitive impairments. More studies are needed to investigate the effectiveness and mechanisms by targeting the excitatory GABAA receptor as a prevention strategy to alleviate cognitive deficits induced by neonatal sevoflurane exposure in future.

Involvement of homodomain interacting protein kinase 2-c-Jun N-terminal kinase/c-Jun cascade in the long-term synaptic toxicity and cognition impairment induced by neonatal Sevoflurane exposure

Sevoflurane is one of the most widely used anesthetics with recent concerns rising about its pediatric application. The synaptic toxicity and mechanisms underlying its long‐term cognition impairment remain unclear. In this study, we investigated the expression and roles of homeodomain interacting protein kinase 2 (HIPK2), a stress activating kinase involved in neuronal survival and synaptic plasticity, and its downstream c‐Jun N‐terminal kinase (JNK)/c‐Jun signaling in the long‐term toxicity of neonatal Sevoflurane exposure. Our data showed that neonatal Sevoflurane exposure results in impairment of memory, enhancement of anxiety, less number of excitatory synapses and lower levels of synaptic proteins in the hippocampus of adult rats without significant changes of hippocampal neuron numbers. Up‐regulation of HIPK2 and JNK/c‐Jun was observed in hippocampal granular neurons shortly after Sevoflurane exposure and persisted to adult. 5‐((6‐Oxo‐5‐(6‐(piperazin‐1‐yl)pyridin‐3‐yl)‐1,6‐dihydropyridin‐3‐yl)methylene)thiazolidine‐2,4‐dione trifluoroacetate, antagonist of HIPK2, could significantly rescue the cognition impairment, decrease in long‐term potentiation, reduction in spine density and activation of JNK/c‐Jun induced by Sevoflurane. JNK antagonist SP600125 partially restored synapse development and cognitive function without affecting the expression of HIPK2. These data, in together, revealed a novel role of HIPK2‐JNK/c‐Jun signaling in the long‐term synaptic toxicity and cognition impairment of neonatal Sevoflurane exposure, indicating HIPK2‐JNK/c‐Jun cascade as a potential target for reducing the synaptic toxicity of Sevoflurane.

Cover Image for this issue: doi: 10.1111/jnc.14757.

Cognitive impairment and transcriptomic profile in hippocampus of young mice after multiple neonatal exposures to sevoflurane

Children with repeated inhalational anesthesia may develop cognitive disorders. This study aimed to investigate the transcriptome-wide response of hippocampus in young mice that had been exposed to multiple sevoflurane in the neonatal period. Mice received 3% sevoflurane for 2 h on postnatal day (PND) 6, 8, and 10, followed by arterial blood gas test on PND 10, behavioral experiments on PND 31–36, and RNA sequencing (RNA-seq) of hippocampus on PND 37. Functional annotation and protein-protein interaction analyses of differentially expressed genes (DEGs) and quantitative reverse transcription polymerase chain reaction (qPCR) were performed. Neonatal sevoflurane exposures induced cognitive and social behavior disorders in young mice. RNA-seq identified a total of 314 DEGs. Several enriched biological processes (ion channels, brain development, learning, and memory) and signaling pathways (oxytocin signaling pathway and glutamatergic, cholinergic, and GABAergic synapses) were highlighted. As hub-proteins, Pten was involved in nervous system development, synapse assembly, learning, memory, and behaviors, Nos3 and Pik3cd in oxytocin signaling pathway, and Cdk16 in exocytosis and phosphorylation. Some top DEGs were validated by qPCR. This study revealed a transcriptome-wide profile in mice hippocampus after multiple neonatal exposures to sevoflurane, promoting better understanding of underlying mechanisms and investigation of preventive strategies.

Developmental neurotoxicity in the context of multiple sevoflurane exposures: Potential role of histone deacetylase 6

Animal studies have demonstrated that multiple exposures to sevoflurane during the postnatal period lead to impaired synaptogenesis and cognitive deficits in adulthood. However, the underlying mechanisms remain unclear. Histone deacetylase 6 (HDAC6), a unique isoform of class II histone deacetylases (HDACs), mediates diverse cellular processes such as cell survival, inflammation, intracellular trafficking and protein degradation. Varieties of literature suggest the importance of HDAC6 in memory formation and abnormal neurodegenerative diseases. The aim of this study was to investigate potential roles of HDAC6 in sevoflurane-induced developmental neurotoxicity. Postnatal day 7 (P7) rat pups were randomly assigned to control group and sevoflurane group (n = 6 for each group). They were exposed to 60% oxygen and 40% nitrogen with or without 3% sevoflurane for 2 h daily for three consecutive days (P7, P8 and P9). Immediately after the last exposure, both hippocampi were harvested for detection of HDAC6 expression and activity. Next, P7 rat pups were divided into control group, sevoflurane group, sevoflurane + Tubastatin A, and Tubastatin A groups (n = 6 for each group in molecular experiments; n = 16 for each group in behavioral testing). A dose of 25 mg/kg body weight of Tubastatin A (a selective HDAC6 inhibitor) were administrated intraperitoneally 30 min prior to each sevoflurane exposure. After treatments, expression levels of synaptophysin and postsynaptic density 95 protein (PSD95) were quantified using Western blot, and synaptic ultrastructure was evaluated by transmission electron microscopy. Additional pups were raised until P49 to measure cognitive performance using the Morris water maze test. Our results demonstrated that multiple sevoflurane exposures enhanced HDAC6 expression and activity in hippocampi of the developing brain. Tubastatin A ameliorated sevoflurane-induced decreases in synaptophysin and PSD95 expression during development, as well as synaptic ultrastructural damage and cognitive deficits in adulthood. In conclusion, HDAC6 is involved in the developmental neurotoxicity caused by multiple sevoflurane exposures and its inhibition may prevent related damage.

Systemic Inflammation Impairs Mood Function by Disrupting the Resting-State Functional Network in a Rat Animal Model Induced by Lipopolysaccharide Challenge

Background

Systemic inflammation impairs cognitive performance, yet the brain networks mediating this process remain to be elucidated. The purpose of the current study was to use resting-state functional magnetic resonance imaging (fMRI) to explore changes in the functional connectivity in a lipopolysaccharide- (LPS-) induced systemic inflammation animal model.

Materials and Methods

We used the regional homogeneity (ReHo) method to examine abnormal brain regions between the control and LPS groups and then considered them as seeds of functional connectivity analysis.

Results

Compared with the control group, our study showed that (1) LPS impaired mood function, as reflected by a depression-like behavior in the forced swim test; (2) LPS induced significantly increased ReHo values in the anterior cingulate cortex (ACC) and caudate putamen (CPu); (3) the ACC seed showed increased functional connectivity with the retrosplenial cortex, superior colliculus, and inferior colliculus; and (4) the right CPu seed showed increased functional connectivity with the left CPu. Linear regression analysis showed a LPS-induced depression-like behavior which was associated with increased ReHo values in the ACC and right CPu. Moreover, the LPS-induced depression-like behavior was related to increased functional connectivity between the right CPu and left CPu.

Conclusion

This is the first study to show that systemic inflammation impairs mood function that is associated with an altered resting-state functional network based on ReHo analysis, providing evidence of the abnormal regional brain spontaneous activity which might be involved in inflammation-related neurobehavioral abnormalities.

Exercising New Neurons to Vanquish Alzheimer Disease

Alzheimer disease (AD) is the most common type of dementia in individuals over 65 years of age. The neuropathological hallmarks of the condition are Tau neurofibrillary tangles and Amyloid-β senile plaques. Moreover, certain susceptible regions of the brain experience a generalized lack of neural plasticity and marked synaptic alterations during the progression of this as yet incurable disease. One of these regions, the hippocampus, is characterized by the continuous addition of new neurons throughout life. This phenomenon, named adult hippocampal neurogenesis (AHN), provides a potentially endless source of new synaptic elements that increase the complexity and plasticity of the hippocampal circuitry. Numerous lines of evidence show that physical activity and environmental enrichment (EE) are among the most potent positive regulators of AHN. Given that neural plasticity is markedly decreased in many neurodegenerative diseases, the therapeutic potential of making certain lifestyle changes, such as increasing physical activity, is being recognised in several non-pharmacologic strategies seeking to slow down or prevent the progression of these diseases. This review article summarizes current evidence supporting the putative therapeutic potential of EE and physical exercise to increase AHN and hippocampal plasticity both under physiological and pathological circumstances, with a special emphasis on neurodegenerative diseases and AD.

Sevoflurane induces cognitive impairments via the MiR-27b/LIMK1-signaling pathway in developing rats

Exposure to sevoflurane in neonatal rats could induce learning deficits and abnormal social behaviors, but the specific molecular mechanism is unknown. Postnatal day-7 SD rats were treated with 3% sevoflurane plus 30% oxygen/air or 30% oxygen/air. As the rats grew, the Morris water maze (MWM) and fear conditioning tests were performed to evaluate cognitive function, while the expression of LIMK1 was analyzed by western blot. Luciferase reporter assay was performed to investigate the interaction between LIMK1 and miR-27b. The expression of miR-27b was measured by real-time polymerase chain reaction (PCR) after exposure to sevoflurane. Once the miR-27b inhibitor was transfected into the neurons, the expression of LIMK1 was analyzed by real-time PCR and western blot. Exposure to sevoflurane in neonatal rats induced memory and learning impairments according to the MWM and fear conditioning tests. Sevoflurane increased the expression of miR-27b and reduced the expression of LIMK1 in the brain tissues of rats compared to the control group. The results of the luciferase reporter assay showed that LIMK1 was a direct target of miR-27b. In the primary neurons, the inhibition of miR-27b could reverse the down-regulating effects of sevoflurane on LIMK1 expression. We suggest that sevoflurane-induced learning and memory impairments in rats might be mediated via the miR-27b-LIMK1-signaling pathway.

Neonatal alcohol exposure reduces number of parvalbumin-positive interneurons in the medial prefrontal cortex and impairs passive avoidance acquisition in mice deficits not rescued from exercise

Developmental alcohol exposure causes a host of cognitive and neuroanatomical abnormalities, one of which is impaired executive functioning resulting from medial prefrontal cortex (mPFC) damage. This study determined whether third-trimester equivalent alcohol exposure reduced the number of mPFC GABAergic parvalbumin-positive (PV+) interneurons, hypothesized to play an important role in local inhibition of the mPFC. The impact on passive avoidance learning and the therapeutic role of aerobic exercise in adulthood was also explored. Male C57BL/6J mice received either saline or 5g/kg ethanol (two doses, two hours apart) on PD 5, 7, and 9. On PD 35, animals received a running wheel or remained sedentary for 48days before behavioral testing and perfusion on PD 83. The number of PV+ interneurons was stereologically measured in three separate mPFC subregions: infralimbic, prelimbic and anterior cingulate cortices (ACC). Neonatal alcohol exposure decreased number of PV+ interneurons and volume of the ACC, but the other regions of the mPFC were spared. Alcohol impaired acquisition, but not retrieval of passive avoidance, and had no effect on motor performance on the rotarod. Exercise had no impact on PV+ cell number, mPFC volume, or acquisition of passive avoidance, but enhanced retrieval in both control and alcohol-exposed groups, and enhanced rotarod performance in the control mice. Results support the hypothesis that part of the behavioral deficits associated with developmental alcohol exposure are due to reduced PV+ interneurons in the ACC, but unfortunately exercise does not appear to be able to reverse any of these deficits.