Isoflurane exposure in newborn rats induces long-term cognitive dysfunction in males but not females

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

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

Sex Differences in Early Postnatal Microglial Colonization of the Developing Rat Hippocampus Following a Single-Day Alcohol Exposure

Microglia are involved in various homeostatic processes in the brain, including phagocytosis, apoptosis, and synaptic pruning. Sex differences in microglia colonization of the developing brain have been reported, but have not been established following alcohol insult. Developmental alcohol exposure represents a neuroimmune challenge that may contribute to cognitive dysfunction prevalent in humans with Fetal Alcohol Spectrum Disorders (FASD) and in rodent models of FASD. Most studies have investigated neuroimmune activation following adult alcohol exposure or following multiple exposures. The current study uses a single day binge alcohol exposure model (postnatal day [PD] 4) to examine sex differences in the neuroimmune response in the developing rat hippocampus on PD5 and 8. The neuroimmune response was evaluated through measurement of microglial number and cytokine gene expression at both time points. Male pups had higher microglial number compared to females in many hippocampal subregions on PD5, but this difference disappeared by PD8, unless exposed to alcohol. Expression of pro-inflammatory marker CD11b was higher on PD5 in alcohol-exposed (AE) females compared to AE males. After alcohol exposure, C-C motif chemokine ligand 4 (CCL4) was significantly increased in female AE pups on PD5 and PD8. Tumor necrosis factor-α (TNF-α) levels were also upregulated by AE in males on PD8. The results demonstrate a clear difference between the male and female neuroimmune response to an AE challenge, which also occurs in a time-dependent manner. These findings are significant as they add to our knowledge of specific sex-dependent effects of alcohol exposure on microglia within the developing brain.

Upregulation of Cdh1 Attenuates Isoflurane-Induced Neuronal Apoptosis and Long-Term Cognitive Impairments in Developing Rats

Neonatal exposure to isoflurane can result in neuroapoptosis and persistent cognitive impairments. However, the underlying mechanisms remain elusive. Anaphase-promoting complex/cyclosome (APC/C) and its co-activator Cdh1 are E3 ubiquitin ligases that play important roles in the central nervous system, including in the regulation of neuronal survival, synaptic development, and mammalian learning and memory. However, whether APC/C-Cdh1 is involved in isoflurane-induced neurotoxicity in developing rats remains unclear. In this study, postnatal day-7 (P7) rat pups and primary hippocampal neurons were exposed to 2% isoflurane for 6 h. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was used to detect neuronal apoptosis, and the expression of proteins involved in apoptosis (cleaved caspase-3, Bax and Bcl-2) was assessed by western blot. The level of Cdh1 in the hippocampus was downregulated during isoflurane-induced neuroapoptosis. Cdh1-encoding lentivirus was transfected before isoflurane-treatment to increase the level of Cdh1. Our results showed that Cdh1 overexpression by a recombinant Cdh1-encoding lentivirus reduced isoflurane-induced neuronal apoptosis. Moreover, bilateral intra-hippocampal injection with Cdh1-encoding lentivirus attenuated long-term cognitive deficits after exposure to isoflurane in developing rats. Our study indicates that Cdh1 is an important target to prevent isoflurane-induced developmental neurotoxicity.

Multiple exposures of sevoflurane during pregnancy induces memory impairment in young female offspring mice

Background

Earlier studies have reported conflicting results regarding long-term behavioral consequences after anesthesia during the fetal period. Previous studies also suggest several factors that may explain such conflicting data. Thus, we examined the influence of age and sex on long-term behavioral consequences after multiple sevoflurane exposures during the fetal period.

Methods

C57BL/6J pregnant mice received oxygen with or without sevoflurane for 2 hours at gestational day (GD) 14-16. Offspring mice were subjected to behavioral assays for general activity (open field test), learning, and memory (fear chamber test) at postnatal day 30–35.

Results

Multiple sevoflurane exposures at GD 14–16 caused significant changes during the fear chamber test in young female offspring mice. Such changes did not occur in young male offspring mice. However, general activity was not affected in both male and female mice.

Conclusions

Multiple sevoflurane exposures in the second trimester of pregnancy affects learning and memory only in young female mice. Further studies focusing on diverse cognitive functions in an age-, sex-dependent manner may provide valuable insights regarding anesthesia-induced neurotoxicity.

TREK-1 pathway mediates isoflurane-induced memory impairment in middle-aged mice

Post-operative cognitive dysfunction (POCD) has been widely reported, especially in elderly patients. An association between POCD and inhalational anesthetics, such as isoflurane, has been suggested. The TWIK-related K⁺ channel-1 (TREK-1) controls several major cellular responses involved in memory formation and is believed to participate in the development of depression, cerebral ischemia and blood-brain barrier dysfunction. However, the specific role of TREK-1 in mediating anesthesia-induced POCD remains unknown. In the current study, we determined that exposure to isoflurane affected memory in middle-aged mice and altered TREK-1 expression. In addition, TREK-1 over-expression exacerbated isoflurane-induced memory impairment, while TREK-1 silence attenuated the impairment. Taken together, our data demonstrate that inhibition of TREK-1 protects mice from cognitive impairment induced by anesthesia and TREK-1 is a potential therapeutic target against memory impairment induced by volatile anesthetics.

Inhibition of p75 neurotrophin receptor does not rescue cognitive impairment in adulthood after isoflurane exposure in neonatal mice

BACKGROUND

Isoflurane is widely used for anaesthesia in humans. Isoflurane exposure of rodents prior to post-natal day 7 (PND7) leads to widespread neurodegeneration in laboratory animals. Previous data from our laboratory suggest an attenuation of apoptosis with the p75 neurotrophin receptor (p75NTR) inhibitor TAT-Pep5. We hypothesized that isoflurane toxicity leads to behavioural and cognitive abnormalities and can be rescued with pre-anaesthesia administration of TAT-Pep5.

METHODS

Neonatal mouse pups were pretreated with either TAT-Pep5 (25 μl, 10 μM i.p.) or a scrambled control peptide (TAT-ctrl; 25 μl, 10 μM i.p.) prior to isoflurane exposure (1.4%; 4 h) or control ( n  = 15-26/group). Three to 5 months after exposure, behavioural testing and endpoint assays [brain volume (stereology) and immunoblotting] were performed.

RESULTS

No significant difference was observed in open field, T-maze, balance beam or wire-hanging testing. The Barnes maze revealed a significant effect of isoflurane ( P  = 0.019) in errors to find the escape tunnel during the day 5 probe trial, a finding indicative of impaired short-term spatial memory. No difference was found for brain volumes or protein expression. TAT-Pep5 treatment did not reverse the effects of isoflurane on neurocognitive behaviour.

CONCLUSION

A single isoflurane exposure to early post-natal mice caused a hippocampal-dependent memory deficit that was not prevented by pre-administration of TAT-Pep5, although TAT-Pep5, an inhibitor of p75NTR, has been shown to reduce isoflurane-induced apoptosis. These findings suggest that neuronal apoptosis is not requisite for the development of cognitive deficits in the adults attendant with neonatal anaesthetic exposure.

Downregulation of microRNA-448 improves isoflurane-induced learning and memory impairment in rats

The present study aimed to investigate the potential role of microRNA‑448 (miR‑448) in isoflurane-induced learning and memory impairment in rats. Sprague‑Dawley rats were used for the construction of isoflurane‑treated models. The Morris water maze test was used to evaluate the effects of isoflurane on rats regarding the following para-meters: Swimming speed, escape latency and time in original quadrant. Influences of isoflurane on neuron apoptosis and miR‑448 expression in rat hippocampus tissue were analyzed by flow cytometry and reverse transcription‑quantitative polymerase chain reaction, respectively. Furthermore, the effects of miR‑448 on the expression of cell apoptosis‑associated proteins were investigated by flow cytometry. The results demonstrated that isoflurane treatment induced higher escape latency and lower time spent in original quadrant compared with the control rats. In addition, isoflurane treatment induced neuron apoptosis and miR‑448 was highly expressed in the hippocampal tissue of isoflurane‑treated rats. Furthermore, Bcl‑x was significantly downregulated while caspase‑3 expression was upregulated by an miR‑448 inhibitor. Combined the results of the current study indicate that miR‑448 knockdown may have pivotal roles in improving isoflurane-induced learning and memory impairment via suppressing neuron apoptosis.

Lasting impact of general anaesthesia on the brain: mechanisms and relevance

General anaesthesia is usually considered to safely induce a reversible brain state allowing the performance of surgery under optimal conditions. An increasing number of clinical and experimental observations, however, suggest that anaesthetic drugs, especially when they are administered at the extremes of age, can trigger long-term morphological and functional alterations in the brain. Here, we review available mechanistic data linking general-anaesthesia exposure to impaired cognitive performance in both young and mature nervous systems. We also provide a critical appraisal of the translational value of animal models and highlight the important challenges that need to be addressed to strengthen the link between laboratory work and clinical investigations in the field of anaesthesia-neurotoxicity research.

Repeated brief isoflurane anesthesia during early postnatal development produces negligible changes on adult behavior in male mice

Brain development is a complex process regulated by genetic programs and activity-dependent neuronal connectivity. Anesthetics profoundly alter neuronal excitability, and anesthesia during early brain development has been consistently associated with neuroapoptosis, altered synaptogenesis, and persistent behavioral abnormalities in experimental animals. However, the depth, and even more the duration and developmental time point(s) of exposure to anesthesia determine the neuropathological and long-term behavioral consequences of anesthetics. Here, we have investigated adulthood phenotypic changes induced by repeated but brief (30 min) isoflurane anesthesia delivered during two distinct developmental periods in male mice. A set of animals were subjected to anesthesia treatments at postnatal days 7, 8 and 9 (P7-9) when the animals are susceptible to anesthesia-induced neuroapoptosis and reduced synaptogenesis. To control the potential influence of (handling) stress, a separate group of animals underwent repeated maternal separations of similar durations. Another set of animals were exposed to the same treatments at postnatal days 15, 16 and 17 (P15-17), a developmental time period when anesthetics have been shown to increase synaptogenesis. Starting from postnatal week 9 the mouse phenotype was evaluated using a battery of behavioral tests that assess general locomotor activity (home cage activity, open field), learning and memory (water maze) and depression- (saccharin preference, forced swim test), anxiety- (light-dark box, stress-induced hyperthermia) and schizophrenia- (nesting, prepulse inhibition) related endophenotypes. Apart from mild impairment in spatial navigation memory, exposure to anesthesia treatments during P7-9 did not bring obvious behavioral alterations in adult animals. Importantly, maternal separation during the same developmental period produced a very similar phenotype during the water maze. Mice exposed to anesthesia during P15-17 showed mild hyperactivity and risk-taking behavior in adulthood, but were otherwise normal. We conclude that significantly longer administration periods are needed in order for early-life repeated exposures to anesthetics to produce behavioral alterations in adult mice.

Surgery increases cell death and induces changes in gene expression compared with anesthesia alone in the developing piglet brain

In a range of animal species, exposure of the brain to general anaesthesia without surgery during early infancy may adversely affect its neural and cognitive development. The mechanisms mediating this are complex but include an increase in brain cell death. In humans, attempts to link adverse cognitive development to infantile anaesthesia exposure have yielded ambiguous results. One caveat that may influence the interpretation of human studies is that infants are not exposed to general anaesthesia without surgery, raising the possibility that surgery itself, may contribute to adverse cognitive development. Using piglets, we investigated whether a minor surgical procedure increases cell death and disrupts neuro-developmental and cognitively salient gene transcription in the neonatal brain. We randomly assigned neonatal male piglets to a group who received 6h of 2% isoflurane anaesthesia or a group who received an identical anaesthesia plus 15 mins of surgery designed to replicate an inguinal hernia repair. Compared to anesthesia alone, surgery-induced significant increases in cell death in eight areas of the brain. Using RNAseq data derived from all 12 piglets per group we also identified significant changes in the expression of 181 gene transcripts induced by surgery in the cingulate cortex, pathway analysis of these changes suggests that surgery influences the thrombin, aldosterone, axonal guidance, B cell, ERK-5, eNOS and GABA_A signalling pathways. This suggests a number of novel mechanisms by which surgery may influence neural and cognitive development independently or synergistically with the effects of anaesthesia.

Isoflurane Exposure Induces Cell Death, Microglial Activation and Modifies the Expression of Genes Supporting Neurodevelopment and Cognitive Function in the Male Newborn Piglet Brain

Exposure of the brain to general anesthesia during early infancy may adversely affect its neural and cognitive development. The mechanisms mediating this are complex, incompletely understood and may be sexually dimorphic, but include developmentally inappropriate apoptosis, inflammation and a disruption to cognitively salient gene expression. We investigated the effects of a 6h isoflurane exposure on cell death, microglial activation and gene expression in the male neonatal piglet brain. Piglets (n = 6) were randomised to: (i) naive controls or (ii) 6h isoflurane. Cell death (TUNEL and caspase-3) and microglial activation were recorded in 7 brain regions. Changes in gene expression (microarray and qPCR) were assessed in the cingulate cortex. Electroencephalography (EEG) was recorded throughout. Isoflurane anesthesia induced significant increases in cell death in the cingulate and insular cortices, caudate nucleus, thalamus, putamen, internal capsule, periventricular white matter and hippocampus. Dying cells included both neurons and oligodendrocytes. Significantly, microglial activation was observed in the insula, pyriform, hippocampus, internal capsule, caudate and thalamus. Isoflurane induced significant disruption to the expression of 79 gene transcripts, of these 26 are important for the control of transcription and 23 are important for the mediation of neural plasticity, memory formation and recall. Our observations confirm that isoflurane increases apoptosis and inflammatory responses in the neonatal piglet brain but also suggests novel additional mechanisms by which isoflurane may induce adverse neural and cognitive development by disrupting the expression of genes mediating activity dependent development of neural circuits, the predictive adaptive responses of the brain, memory formation and recall.

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

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

Etanercept, an inhibitor of TNF-a, prevents propofol-induced neurotoxicity in the developing brain

Propofol can induce acute neuronal apoptosis, neuronal loss or long-term cognitive impairment when exposed in neonatal rodents, but the mechanisms by which propofol induces developmental neurotoxicity are unclear. Recent studies have demonstrated that propofol can increase the TNF-α level in the developing brain, but there is a lack of direct evidence to show whether TNF-α is partially or fully involved in propofol-induced neurotoxicity. The present study shows that propofol exposure in neonatal rats induces an increase of TNF-α in the cerebral spinal fluid, hippocampus and prefrontal cortex (PFC). Etanercept, a TNF-α inhibitor, prevents propofol-induced short- or long-term neuronal apoptosis, neuronal loss, synaptic loss and long-term cognitive impairment. Furthermore, mTNF-α (precursor of TNF-α) expression in microglia cells is increased after propofol anaesthesia in either the hippocampus or PFC, but mTNF-α expression in neurons is only increased in the PFC. These findings suggest that TNF-α may mediate propofol-induced developmental neurotoxicity, and etanercept can provide neural protection. Microglia are the main cellular source of TNF-α after propofol exposure, while the synthesis of TNF-α in neurons is brain-region selective.

Is a short anesthetic exposure in children safe? Time will tell: a focused commentary of the GAS and PANDA trials

Early life exposure to general anesthesia in preclinical studies has consistently led to permanent cognitive deficits later in life. However, the extent to which this finding is translatable to humans is the subject of much debate as the results from clinical studies have been mixed. Recently two well-designed clinical trials have attempted to add clarity to our murky understanding. The General Anesthesia compared to Spinal anesthesia (GAS) trial, was an international, prospective, randomized, multicenter, equivalence trial comparing infants undergoing herniorrhaphy receiving general anesthesia vs. neuraxial anesthesia. The results released are from a pre-determined secondary outcome of a behavioral/developmental assessment of 2 years old that found equivalence between the two groups. The Pediatric Anesthesia NeuroDevelopment Assessment (PANDA) trial was an ambi-directional cohort trial, comparing patients receiving general anesthesia for hernia repair before 3 years old vs. sibling-matched controls. The neuropsychological battery performed showed no difference between siblings. Taken together, there is cautious optimism that short anesthesia exposure may not lead to significant cognitive decline in humans, but one should also consider that the GAS trial has yet to release the primary endpoint, IQ testing at age 5, and the PANDA trial may not represent the general population given the high socioeconomic status and high control IQ scores. Furthermore, as seen in preclinical studies, the cognitive deficit might not be significant until later in life, and longer exposures to anesthesia may have a more deleterious effect on cognitive function. While these new studies greatly increase our understanding in humans, there are many more questions that need to be addressed.

Effects of hypotension and/or hypocapnia during sevoflurane anesthesia on perfusion and metabolites in the developing brain of piglets-a blinded randomized study

BACKGROUND

Hypotension (HT) and/or hypocapnia (HC) are frequent complications occurring during pediatric anesthesia and may cause cerebral injury in the developing brain.

AIM

The aim of this study is to investigate the effects of HT and/or HC on perfusion and metabolism in the developing brain.

METHODS

Twenty-eight piglets were randomly allocated to four groups: control (C), HT, HC, and hypotension and hyocapnia (HTC). Anesthesia was induced and maintained using sevoflurane. Fentanyl was added for instrumentation. Piglets were fully monitored and their lungs were artificially ventilated. Before treatment, conventional magnetic resonance imaging (MRI), dynamic susceptibility-contrast-enhanced T2*-weighted MRI (DSC-MRI), and single voxel proton MR spectroscopy ((1) H MRS) were performed. Hypotension (mean arterial blood pressure: 30 ± 3 mmHg) was induced by blood withdrawal and nitroprusside infusion, and hyperventilation was used to induce HC (PaCO2 : 2.7-3.3 kPa). (1) H MRS and DSC-MRI were repeated immediately once treatment goals were achieved and 120 min later. Radiologists were blinded to the groups. DSCI-MRI and (1) H MRS analyses were performed in the thalamus, occipital and parietal lobe, hippocampus, and watershed areas.

RESULTS

In comparison to C, mean time to peak (TTP) increased with HTC in all brain areas as assessed with DSC-MRI (n = 26). Using (1) H MRS, a significant decrease in N-acetyl aspartate, choline, and myoinositol, as well as an increase in glutamine-glutamate complex (Glx) were detected independent of group. Compared to C, changes were more pronounced for Glx (due to an increase in glutamate) and myoinositol with HTC, for N-acetyl aspartate with HT, and for Glx with HC. No lactate signal was present.

CONCLUSIONS

The combination of HT and HC during sevoflurane anesthesia resulted in alteration of cerebral perfusion with signs of neuronal dysfunction and early neuronal ischemia. HT and HC alone also resulted in signs of metabolic disturbances despite the absence of detectable cerebral perfusion alterations.

Early-life single-episode sevoflurane exposure impairs social behavior and cognition later in life

BACKGROUND

Single-episode anesthetic exposure is the most prevalent surgery-related incidence among young children in the United States. Although numerous studies have used animals to model the effects of neonatal anesthetics on behavioral changes later on in life, our understanding of the functional consequences to the developing brain in a comprehensive and clinically relevant manner is unclear.

METHODS

The volatile anesthetic, sevoflurane (sevo) was administered to C57BL6 postnatal day 7 (P7) mice in a 40% oxygen and 60% nitrogen gas mixture. In order to examine the effects of sevo alone on the developing brain in a clinically relevant manner, mice were exposed to an average of 2.38 ± 0.11% sevo for 2 h. No sevo (control) mice were treated in an identical manner without sevo exposure. Mice were examined for cognition and neuropsychiatric-like behavioral changes at 1-5 months of age.

RESULTS

Using the active place avoidance (APA) test and the novel object recognition (NOR) test, we demonstrated that P7 sevo-treated mice showed a deficit in learning and memory both during periadolescence and adulthood. We then employed a battery of neuropsychiatric-like behavioral tests to examine social interaction, communication, and repetitive behavior. Interestingly, compared to the no-sevo-treated group, sevo-treated mice showed significant reductions in the time interacting with a novel mouse (push-crawl and following), time and interaction in a chamber with a novel mouse, and time sniffing a novel social odor.

CONCLUSIONS

Our study established that single-episode, 2-h sevo treatment during early life impairs cognition later on in life. With this approach, we also observed neuropsychiatric-like behavior changes such as social interaction deficits in the sevo-treated mice. This study elucidated the effects of a clinically relevant single-episode sevo application, given during the neonatal period, on neurodevelopmental behavioral changes later on in life.

Epigenetic Manipulation of Brain-derived Neurotrophic Factor Improves Memory Deficiency Induced by Neonatal Anesthesia in Rats

BACKGROUND

Although neonatal exposure to anesthetic drugs is associated with memory deficiency in rodent models and possibly in pediatric patients, the underlying mechanisms remain elusive. The authors tested their hypothesis that exposure of the developing brain to anesthesia triggers epigenetic modification, involving the enhanced interaction among transcription factors (histone deacetylase 2, methyl-cytosine-phosphate-guanine-binding protein 2, and DNA methyltransferase 1) in Bdnf promoter region(s) that inhibit brain-derived neurotrophic factor (BDNF) expression, resulting in insufficient drive for local translation of synaptic mRNAs. The authors further hypothesized that noninvasive environmental enrichment (EE) will attenuate anesthesia-induced epigenetic inhibition of BDNF signaling and memory loss in rodent models.

METHODS

Seven days after birth (P7), neonatal rats were randomly assigned to receive either isoflurane anesthesia for 6 h or sham anesthesia. On P21, pups were weaned, and animals were randomly assigned to EE or a standard cage environment (no EE). Behavioral, molecular, and electrophysiological studies were performed on rats on P65.

RESULTS

The authors found a substantial reduction of hippocampal BDNF (n = 6 to 7) resulting from the transcriptional factors-mediated epigenetic modification in the promoter region of Bdnf exon IV in rats exposed postnatally to anesthetic drugs. This BDNF reduction led to the insufficient drive for the synthesis of synaptic proteins (n = 6 to 8), thus contributing to the hippocampal synaptic (n = 8 to 11) and cognitive dysfunction (n = 10) induced by neonatal anesthesia. These effects were mitigated by the exposure to an enriched environment.

CONCLUSIONS

The findings of this study elucidated the epigenetic mechanism underlying memory deficiency induced by neonatal anesthesia and propose EE as a potential therapeutic approach.

Postnatal Isoflurane Exposure Induces Cognitive Impairment and Abnormal Histone Acetylation of Glutamatergic Systems in the Hippocampus of Adolescent Rats

Isoflurane can elicit cognitive impairment. However, the pathogenesis in the brain remains inconclusive. The present study investigated the mechanism of glutamate neurotoxicity in adolescent male rats that underwent postnatal isoflurane exposure and the role of sodium butyrate (NaB) in cognitive impairment induced by isoflurane exposure. Seven-day-old rats were exposed to 1.7 % isoflurane for 35 min every day for four consecutive days, and then glutamate neurotoxicity was examined in the hippocampus. Morris water maze analysis showed cognitive impairments in isoflurane-exposed rats. High-performance liquid chromatography found higher hippocampal glutamate concentrations following in vitro and in vivo isoflurane exposure. The percentage of early apoptotic hippocampal neurons was markedly increased after isoflurane exposure. Decreased acetylation and increased HDAC2 activity were observed in the hippocampus of isoflurane-exposed rats and hippocampal neurons. Furthermore, postnatal isoflurane exposure decreased histone acetylation of hippocampal neurons in the promoter regions of GLT-1 and mGLuR1/5, but not mGLuR2/3. Treatment with NaB not only restored the histone acetylation of the GLT-1 and mGLuR1/5 promoter regions and glutamate excitatory neurotoxicity in hippocampal neurons, but also improved cognitive impairment in vivo. Moreover, NaB may be a potential therapeutic drug for cognitive impairment caused by isoflurane exposure. These results suggest that postnatal isoflurane exposure contributes to cognitive impairment via decreasing histone acetylation of glutamatergic systems in the hippocampus of adolescent rats.

Role of histone acetylation in long-term neurobehavioral effects of neonatal Exposure to sevoflurane in rats

Human studies, and especially laboratory studies, provide evidence that early life exposure to general anesthesia may affect neurocognitive development via largely unknown mechanisms. We explored whether hippocampal histone acetylation had a role in neurodevelopmental effects of sevoflurane administered to neonatal rats. Male Sprague-Dawley rats were exposed to 3% sevoflurane or were subjected to maternal separation only for 2h daily at postnatal days 6, 7, and 8. The histone deacetylase inhibitor, sodium butyrate (250mg/kg, intraperitoneally), or saline was administered starting 2h prior to anesthesia or maternal separation and continued daily until the end of behavioral tests, which were performed between postnatal days 33 and 50. Upon completion of the behavioral tests, the brain tissues were harvested for further analysis. Rats neonatally exposed to sevoflurane exhibited decreased freezing time in the fear conditioning contextual test and increased escape latency, decreased time in target quadrant, and number of platform crossings in the Morris water maze test. The sevoflurane-exposed rats had lower hippocampal density of dendritic spines, reduced levels of the brain-derived neurotrophic factor, c-fos protein, microtubule-associated protein 2, synapsin1, postsynaptic density protein 95, pCREB/CREB, CREB binding protein, and acetylated histones H3 and H4, and increased levels of histone deacetylases 3 and 8. These neurobehavioral abnormalities were normalized in the sevoflurane-exposed rats treated with sodium butyrate. Our findings provide evidence that neonatal exposure to sevoflurane induces neurobehavioral abnormalities and long-lasting alterations in histone acetylation; normalization of histone acetylation may alleviate the neurodevelopmental side effects of the anesthetic.

Neurodevelopmental outcome at 2 years of age after general anaesthesia and awake-regional anaesthesia in infancy (GAS): an international multicentre, randomised controlled trial

BACKGROUND

Preclinical data suggest that general anaesthetics affect brain development. There is mixed evidence from cohort studies that young children exposed to anaesthesia can have an increased risk of poor neurodevelopmental outcome. We aimed to establish whether general anaesthesia in infancy has any effect on neurodevelopmental outcome. Here we report the secondary outcome of neurodevelopmental outcome at 2 years of age in the General Anaesthesia compared to Spinal anaesthesia (GAS) trial.

METHODS

In this international assessor-masked randomised controlled equivalence trial, we recruited infants younger than 60 weeks postmenstrual age, born at greater than 26 weeks' gestation, and who had inguinal herniorrhaphy, from 28 hospitals in Australia, Italy, the USA, the UK, Canada, the Netherlands, and New Zealand. Infants were randomly assigned (1:1) to receive either awake-regional anaesthesia or sevoflurane-based general anaesthesia. Web-based randomisation was done in blocks of two or four and stratified by site and gestational age at birth. Infants were excluded if they had existing risk factors for neurological injury. The primary outcome of the trial will be the Wechsler Preschool and Primary Scale of Intelligence Third Edition (WPPSI-III) Full Scale Intelligence Quotient score at age 5 years. The secondary outcome, reported here, is the composite cognitive score of the Bayley Scales of Infant and Toddler Development III, assessed at 2 years. The analysis was as per protocol adjusted for gestational age at birth. A difference in means of five points (1/3 SD) was predefined as the clinical equivalence margin. This trial is registered with ANZCTR, number ACTRN12606000441516 and ClinicalTrials.gov, number NCT00756600.

FINDINGS

Between Feb 9, 2007, and Jan 31, 2013, 363 infants were randomly assigned to receive awake-regional anaesthesia and 359 to general anaesthesia. Outcome data were available for 238 children in the awake-regional group and 294 in the general anaesthesia group. In the as-per-protocol analysis, the cognitive composite score (mean [SD]) was 98.6 (14.2) in the awake-regional group and 98.2 (14.7) in the general anaesthesia group. There was equivalence in mean between groups (awake-regional minus general anaesthesia 0.169, 95% CI -2.30 to 2.64). The median duration of anaesthesia in the general anaesthesia group was 54 min.

INTERPRETATION

For this secondary outcome, we found no evidence that just less than 1 h of sevoflurane anaesthesia in infancy increases the risk of adverse neurodevelopmental outcome at 2 years of age compared with awake-regional anaesthesia.

FUNDING

Australia National Health and Medical Research Council (NHMRC), Health Technologies Assessment-National Institute for Health Research UK, National Institutes of Health, Food and Drug Administration, Australian and New Zealand College of Anaesthetists, Murdoch Childrens Research Institute, Canadian Institute of Health Research, Canadian Anesthesiologists' Society, Pfizer Canada, Italian Ministry of Heath, Fonds NutsOhra, and UK Clinical Research Network (UKCRN).

Role of Steroids in Hyperexcitatory Adverse and Anesthetic Effects of Sevoflurane in Neonatal Rats

Recent studies have demonstrated that long-term developmental effects of neonatal anesthesia were more prominent in males. We tested whether steroids, in general, and sex steroids, in particular, are involved in the mediation of sevoflurane-caused paradoxical cortical seizures during the early postnatal period.

METHODS

Cortical electroencephalograms, hippocampal synaptic activity, serum levels of steroids and the loss of the righting reflex (LORR), a marker of anesthetic effect, were measured on postnatal days 4-6 in Sprague Dawley rats of both genders exposed to 2.1% sevoflurane.

RESULTS

Episodes of seizures, persistent spikes in electroencephalograms and increases in serum corticosterone were similar in both genders. In the order of increasing potency, the corticosteroid receptor antagonist RU 28318, the estradiol receptor antagonist ICI 182780 and the estradiol synthesis inhibitor formestane decreased sevoflurane-induced seizures. Exogenous estradiol increased sevoflurane-caused seizures, spikes and serum levels of corticosterone. These estradiol-enhanced seizures and spikes were depressed by ICI 182780 and the NKCC1 inhibitor, bumetanide, while RU 28318 decreased seizures only. In hippocampal CA1 neurons, estradiol increased the amplitude, rise time and area under the curve of gamma-aminobutyric acid type A receptor (GABAAR)-mediated miniature postsynaptic currents. Exogenous estradiol shortened, while ICI 182780 and formestane lengthened the time needed for sevoflurane to induce LORR.

CONCLUSION

These findings provide evidence for gender-independent acute electroencephalographic effects of sevoflurane at this age. Corticosterone and estradiol are involved in the mediation of sevoflurane-induced seizures. Estradiol, but not corticosterone, also contributes to sevoflurane-caused spikes, by enhancing GABAAR-mediated excitation in the cortex. By increasing GABAAR-mediated inhibition in more mature caudal regions of the brain, estradiol contributes to sevoflurane-induced LORR.

A systematic review of methodology applied during preclinical anesthetic neurotoxicity studies: important issues and lessons relevant to the design of future clinical research

Preclinical evidence suggests that anesthetic agents harm the developing brain thereby causing long-term neurocognitive impairments. It is not clear if these findings apply to humans, and retrospective epidemiological studies thus far have failed to show definitive evidence that anesthetic agents are harmful to the developing human brain.

AIM

The aim of this systematic review was to summarize the preclinical studies published over the past decade, with a focus on methodological issues, to facilitate the comparison between different preclinical studies and inform better design of future trials.

METHOD

The literature search identified 941 articles related to the topic of neurotoxicity. As the primary aim of this systematic review was to compare methodologies applied in animal studies to inform future trials, we excluded a priori all articles focused on putative mechanism of neurotoxicity and the neuroprotective agents. Forty-seven preclinical studies were finally included in this review.

RESULTS

Methods used in these studies were highly heterogeneous-animals were exposed to anesthetic agents at different developmental stages, in various doses and in various combinations with other drugs, and overall showed diverse toxicity profiles. Physiological monitoring and maintenance of physiological homeostasis was variable and the use of cognitive tests was generally limited to assessment of specific brain areas, with restricted translational relevance to humans.

CONCLUSION

Comparison between studies is thus complicated by this heterogeneous methodology and the relevance of the combined body of literature to humans remains uncertain. Future preclinical studies should use better standardized methodologies to facilitate transferability of findings from preclinical into clinical science.

Learning, memory and synaptic plasticity in hippocampus in rats exposed to sevoflurane

PURPOSE

Developmental exposure to volatile anesthetics has been associated with cognitive deficits at adulthood. Rodent studies have revealed impairments in performance in learning tasks involving the hippocampus. However, how the duration of anesthesia exposure impact on hippocampal synaptic plasticity, learning, and memory is as yet not fully elucidated.

METHODS

On postnatal day 7(P7), rat pups were divided into 3 groups: control group (n=30), 3% sevoflurane treatment for 1h (Sev 1h group, n=30) and 3% sevoflurane treatment for 6h (Sev 6h group, n=28). Following anesthesia, synaptic vesicle-associated proteins and dendrite spine density and synapse ultrastructure were measured using western blotting, Golgi staining, and transmission electron microscopy (TEM) on P21. In addition, the effects of sevoflurane treatment on long-term potentiation (LTP) and long-term depression (LTD), two molecular correlates of memory, were studied in CA1 subfields of the hippocampus, using electrophysiological recordings of field potentials in hippocampal slices on P35-42. Rats' neurocognitive performance was assessed at 2 months of age, using the Morris water maze and novel-object recognition tasks.

RESULTS

Our results showed that neonatal exposure to 3% sevoflurane for 6h results in reduced spine density of apical dendrites along with elevated expression of synaptic vesicle-associated proteins (SNAP-25 and syntaxin), and synaptic ultrastructure damage in the hippocampus. The electrophysiological evidence indicated that hippocampal LTP, but not LTD, was inhibited and that learning and memory performance were impaired in two behavioral tasks in the Sev 6h group. In contrast, lesser structural and functional damage in the hippocampus was observed in the Sev 1h group.

CONCLUSION

Our data showed that 6-h exposure of the developing brain to 3% sevoflurane could result in synaptic plasticity impairment in the hippocampus and spatial and nonspatial hippocampal-dependent learning and memory deficits. In contrast, shorter-duration exposure (1h) results in less damage. These results provide further evidences that duration of anesthesia exposure could have differential effects on neuronal plasticity and neurocognitive performance.

Pten Inhibitor-bpV Ameliorates Early Postnatal Propofol Exposure-Induced Memory Deficit and Impairment of Hippocampal LTP

Early postnatal propofol administration has potential detrimental effects on hippocampal synaptic development and memory. Therapeutic method is still lack due to unknown mechanisms. In this study, a 7-day propofol protocol was applied to model anesthesia in neonatal mice. Phosphatase and tensin homolog deleted on chromosome ten (Pten) inhibitor bisperoxovanadium (bpV) was pre-applied before propofol to study its potential protection. After propofol application, Pten level increased while phospho-AKT (p-AKT) (Ser473) decreased in dorsal hippocampus. Interestingly, i.p. injection of Pten inhibitor reversed the decrease of p-AKT. Two months after administration, basal synaptic transmission, hippocampal long-term potentiation (LTP) and long-term memory were reduced in propofol-administrated mice. By contrast, i.p. injection of Pten inhibitor at a dose of 0.2 mg/kg/day before propofol reversed the detrimental effects due to propofol application. Consistently, bpV injection also reversed propofol application-induced decrease of synaptic plasticity-related proteins, including p-CamKIIα, p-PKA and postsynaptic density protein 95. Taken together, our results demonstrate that bpV injection could reverse early propofol exposure-induced decrease of memory and hippocampal LTP. bpV might be a potential therapeutic for memory impairment after early propofol postnatal application.

Isoflurane impairs the capacity of astrocytes to support neuronal development in a mouse dissociated coculture model

BACKGROUND

There is growing concern that pediatric exposure to anesthetic agents may cause long-lasting deficits in learning by impairing brain development. Most studies to date on this topic have focused on the direct effects of anesthetics on developing neurons. Relatively little attention has been paid to possible effects of anesthetics on astrocytes, a glial cell type that plays an important supporting role in neuronal development.

METHODS

Astrocytes were exposed to isoflurane and then cocultured with unexposed neurons to test for astrocyte-specific toxic effects on neuronal growth. Axon length was measured in the cocultured neurons to assess neuronal growth.

RESULTS

We found that neurons cocultured with astrocytes exposed to isoflurane exhibited a 30% reduction in axon outgrowth. Further experimentation showed that this effect is likely due to reduced levels of brain-derived neurotrophic factor in the coculture media.

CONCLUSIONS

Isoflurane interferes with the ability of cultured astrocytes to support neuronal growth. This finding represents a potentially novel mechanism through which general anesthetics may interfere with brain development.

Review: effects of anesthetics on brain circuit formation

The results of several retrospective clinical studies suggest that exposure to anesthetic agents early in life is correlated with subsequent learning and behavioral disorders. Although ongoing prospective clinical trials may help to clarify this association, they remain confounded by numerous factors. Thus, some of the most compelling data supporting the hypothesis that a relatively short anesthetic exposure can lead to a long-lasting change in brain function are derived from animal models. The mechanism by which such changes could occur remains incompletely understood. Early studies identified anesthetic-induced neuronal apoptosis as a possible mechanism of injury, and more recent work suggests that anesthetics may interfere with several critical processes in brain development. The function of the mature brain requires the presence of circuits, established during development, which perform the computations underlying learning and cognition. In this review, we examine the mechanisms by which anesthetics could disrupt brain circuit formation, including effects on neuronal survival and neurogenesis, neurite growth and guidance, formation of synapses, and function of supporting cells. There is evidence that anesthetics can disrupt aspects of all of these processes, and further research is required to elucidate which are most relevant to pediatric anesthetic neurotoxicity.

Systemic physiology and neuroapoptotic profiles in young and adult rats exposed to surgery: A randomized controlled study comprising four different anaesthetic techniques

BACKGROUND

Experimental evidence indicates that general anaesthetics can induce apoptotic neurodegeneration in the developing brain. The majority of these studies have been performed in the absence of surgery and it currently remains unclear how the presence of surgical stimuli would influence neuroapoptosis as well as systemic homeostasis. Here we explored this possibility by performing dorsal skin flap surgery in young and adult rats under four distinct currently used anaesthesia regimens.

METHODS

Young (21-days) and adult (2 months) male Sprague-Dawley rats were randomized to 150 min exposure to one of four anaesthetics regimens: (i) sevoflurane/dexmedetomidine, (ii) sevoflurane/fentanyl; (iii) propofol/dexmedetomidine, and (iv) propofol/fentanyl. Animals underwent a dorsal skin flap procedure while physiologic, metabolic and biochemical parameters were closely monitored. Neuroapoptotic profiles were evaluated in the cortex, thalamus and hippocampus (CA1 and CA3) at the end of the procedure in each experimental group.

RESULTS

Significant perturbations of systemic homeostasis were found under all anaesthetic regimens. Hyperglycemia and decreased heart rate were particularly relevant in experimental groups receiving dexmedetomidine, while propofol administration was associated with increased systemic lactate levels and metabolic acidosis. A substantial difference in anaesthesia/surgery-induced neuroapoptosis was found between young and adult rats in several brain regions. Combination of sevoflurane and dexmedetomidine resulted in the highest number of caspase-3 positive cells, although the extent of cell death remained relatively low in all experimental groups.

CONCLUSION

Combination of anaesthesia and surgery induces significant perturbations of physiological parameters in both young and adult spontaneously breathing rats undergoing surgery. These observations further enlighten the need for detailed physiological monitoring under these experimental conditions. Although some statistically significant differences in activated caspase-3 profiles were detected between experimental groups, the overall extent of neuronal cell death remained very low under all conditions questioning, thereby, the physiological significance of apoptotic neurodegeneration in the context of anaesthesia and surgery.

Developmental stage-dependent impact of midazolam on calbindin, calretinin and parvalbumin expression in the immature rat medial prefrontal cortex during the brain growth spurt

BACKGROUND

Human epidemiological data suggest a link between anesthesia exposure in early postnatal life and subsequent lasting neurocognitive alterations. Understanding the underlying mechanisms of this potential association is of paramount importance in an attempt to develop protective strategies. While general anesthetics are powerful modulators of GABAergic neurotransmission, little is known about the impact of these drugs on developing GABAergic networks. Here we addressed this issue by evaluating the impact of a 6-h-long midazolam exposure on the development of calbindin-, calretinin- and parvalbumin-expressing GABAergic interneurons.

METHODS

Physiological expression patterns of calbindin-, calretinin-, and parvalbumin-positive neurons as well as the impact of a 6-h-long midazolam exposure on these cell populations were evaluated in the medial prefrontal cortex of Wistar rats at defined stages of the brain growth spurt using stereological analysis. Activated caspase-3 immunohistochemistry was used to quantify apoptotic death in controls and midazolam-treated subjects.

RESULTS

In control animals, the number of parvalbumin expressing cells significantly (p<0.01) increased while those of calbindin positive populations significantly (p<0.01) decreased between postnatal day 10 and 20. Expression of calretinin remained constant during this period. Immediately following exposure, midazolam induced neuroapoptosis at both early (postnatal day 5, p=0.016) and later (postnatal day 15, p=0.025) stages of brain development. While this did not diminish overall neuronal density in the medial prefrontal cortex, exposure at P5 led to a subsequent increase in the number of parvalbumin positive neurons in lower cortical layers, and midazolam administration at P15 increased the number of both parvalbumin and calretinin expressing neurons 5 days following exposure.

CONCLUSION

These observations demonstrate that midazolam exposure can impair the physiological differentiation patterns of GABAergic interneurons during the brain growth spurt. Considering the important role of GABAergic networks in neuronal physiology, these data provide us with one potential mechanism that could account for the lasting neurobehavioral and cognitive deficits observed in the context of anesthesia exposure in the early postnatal period.

Long-term Effects of Single or Multiple Neonatal Sevoflurane Exposures on Rat Hippocampal Ultrastructure

Background:

Neonatal exposure to general anesthetics may pose significant neurocognitive risk. Human epidemiological studies demonstrate higher rates of learning disability among children with multiple, but not single, exposures to anesthesia. The authors employ a rat model to provide a histological correlate for these population-based observations. The authors examined long-term differences in hippocampal synaptic density, mitochondrial density, and dendritic spine morphology.

Methods:

Twenty male rat pups (n = 5/condition) were exposed to 2.5% sevoflurane under one of four conditions: single 2-h exposure on postnatal day 7 (P7); single 6-h exposure on P7; repeated 2-h exposures on P7, P10, and P13 for a cumulative 6 h of general anesthetics; or control exposure to 30% oxygen on P7, P10, and P13.

Results:

Repeated exposure to general anesthetics resulted in greater synaptic loss relative to a single 2-h exposure (P &lt; 0.001). The magnitude of synaptic loss induced by three 2-h exposures (1.977 ± 0.040 μm3 [mean ± SEM]) was more profound than that of a single 6-h exposure (2.280 ± 0.045 μm3, P = 0.022). Repeated exposures did not alter the distribution of postsynaptic density length, indicating a uniform pattern of loss across spine types. In contrast, mitochondrial toxicity was best predicted by the cumulative duration of exposure. Relative to control (0.595 ± 0.017), both repeated 2-h exposures (0.479 ± 0.015) and a single 6-h exposure (0.488 ± 0.013) were associated with equivalent reductions in the fraction of presynaptic terminals containing mitochondria (P &lt; 0.001).

Conclusion:

This suggests a “threshold effect” for general anesthetic–induced neurotoxicity, whereby even brief exposures induce long-lasting alterations in neuronal circuitry and sensitize surviving synapses to subsequent loss.

Effect of general anesthesia in infancy on long-term recognition memory in humans and rats

Anesthesia in infancy impairs performance in recognition memory tasks in mammalian animals, but it is unknown if this occurs in humans. Successful recognition can be based on stimulus familiarity or recollection of event details. Several brain structures involved in recollection are affected by anesthesia-induced neurodegeneration in animals. Therefore, we hypothesized that anesthesia in infancy impairs recollection later in life in humans and rats. Twenty eight children ages 6-11 who had undergone a procedure requiring general anesthesia before age 1 were compared with 28 age- and gender-matched children who had not undergone anesthesia. Recollection and familiarity were assessed in an object recognition memory test using receiver operator characteristic analysis. In addition, IQ and Child Behavior Checklist scores were assessed. In parallel, thirty three 7-day-old rats were randomized to receive anesthesia or sham anesthesia. Over 10 months, recollection and familiarity were assessed using an odor recognition test. We found that anesthetized children had significantly lower recollection scores and were impaired at recollecting associative information compared with controls. Familiarity, IQ, and Child Behavior Checklist scores were not different between groups. In rats, anesthetized subjects had significantly lower recollection scores than controls while familiarity was unaffected. Rats that had undergone tissue injury during anesthesia had similar recollection indices as rats that had been anesthetized without tissue injury. These findings suggest that general anesthesia in infancy impairs recollection later in life in humans and rats. In rats, this effect is independent of underlying disease or tissue injury.