Selective anesthesia-induced neuroinflammation in developing mouse brain and cognitive impairment

Efficacy of rutin in inhibiting neuronal apoptosis and cognitive disturbances in sevoflurane or propofol exposed neonatal mice

Sevoflurane and propofol are widely used in pediatric anesthesia. Neurotoxicity of sevoflurane and propofol in developing brain has been reported and these effects raise concerns on the usage of the drugs. We investigated the influence of rutin, a flavonoid on the neurodegenerative effects of sevoflurane and propofol and on memory and cognition in neonatal rodent model. Separate groups of neonatal mice (C57BL/6) were administered with rutin at 25 or 50 mg/kg body weight (b.wt) from post natal day 2 (P1) to P21. P7 mice were exposed to 2.9% sevoflurane and/or propofol (150 mg/kg b.wt). Neuroapoptosis was assessed by measuring activated caspase-3 and by Fluoro-Jade C staining. Plasma S100β levels were detected by ELISA. Morris water maze test was performed to test learning and memory impairments in the animals. General behaviour of the mice was also assessed. Anesthesia exposure caused severe neuroapoptosis and also raised the levels of plasma S100β. Neuroapoptosis, memory and cognitive deficits observed following anesthetics were comparatively more profound in mice on exposure to combined drug (sevoflurane and propofol) than in those exposed to either of the anesthetics. Rutin at both the doses was effective in reducing the apoptotic cell counts and enhanced the memory and cognitive abilities. Rutin supplementation offered significant protection against anesthetic induced neurodegeneration and learning and memory disturbances.

Isoflurane inhibits embryonic stem cell self-renewal through retinoic acid receptor

The commonly used inhalation anesthetic isoflurane could permeate rapidly through the placental barrier and induce toxicity to the central nervous system of the developing fetus. However, the effects of isoflurane in utero during early gestation are unknown. We therefore treated pregnant mice with 1.4% isoflurane for 2h per day for three days at day3.5 (E3.5) to day6.5 (E6.5) to investigated the toxicity of isoflurane. Pregnant mice were executed and the fetal mice were weighed and observed. Mouse ESCs (E14) was exposed to 2% isoflurane for 6h. Twenty-four hours later, self-renewal was examined with AP staining. Effects of isoflurane on the expression of RAR-γ were examined using Western blot. As a result, anesthesia with 1.4% isoflurane for 2 hour per day for 3 days reduced fetal growth and development. Isoflurane decreased self-renewal and the expression stemness genes (Nanog, Oct4, Sox2, and Lin28) in mESCs. Vitamin A attenuated the effects of isoflurane inducing self-renewal inhibition. In summary, Anesthesia with 1.4% isoflurane for 2h per day for 3 days reduced fetal growth and development. Moreover, isoflurane inhibits mESCs self-renewal through retinoic acid receptor.

Environmental Enrichment Ameliorates Neonatal Sevoflurane Exposure-Induced Cognitive and Synaptic Plasticity Impairments

Early exposure to sevoflurane, an inhalation anesthetic, induces neurodegeneration in the developing brain and subsequent long-term neurobehavioral abnormalities. Here, we investigated whether an enriched environment could mitigate neonatal sevoflurane exposure-induced long-term cognitive and synaptic plasticity impairments. Male C57BL/6 mice were exposed to 3 % sevoflurane 2 h daily for 3 days from postnatal day 6 (P6) to P8. The exposed mice were randomly allocated to an enriched environment for 2 h daily between P8 and P42 or to a standard environment. Their behavior and cognition were assessed using open field (P35) and fear conditioning tests (P41-P42). Hematoxylin-eosin staining was used to study morphological changes in pyramidal neurons of hippocampal CA1 and CA3 regions. Synaptic plasticity alternations were assessed using western blotting, Golgi staining, and electrophysiological recording. We found that sevoflurane-exposed mice housed in a standard environment exhibited a reduced freezing response in the contextual test, decreased number of dendritic spines on pyramidal neurons and synaptic plasticity-related proteins in the hippocampus, and impaired long-term potentiation. However, in an enriched environment, some of these abnormities induced by repeated sevoflurane exposure. In conclusion, neonatal sevoflurane exposure-induced cognitive and synaptic plasticity impairments are ameliorated by an enriched environment.

Therapeutic effects of intravenous administration of bone marrow stromal cells on sevoflurane-induced neuronal apoptosis and neuroinflammation in neonatal rats

Background

Sevoflurane exposure during the early postnatal period causes neuroinflammation and neuronal apoptosis in rodents. Bone marrow stromal cells (BMSCs) have been shown to protect and repair the damaged central nervous system, for example in ischemic stroke models. In this study, we investigated whether intravenous administration of BMSCs ameliorated neurodegeneration, induced by sevoflurane exposure, in neonatal rats.

Methods

Sprague-Dawley rat pups (postnatal day 7) were exposed to 2% sevoflurane for 6 h (vehicle group, n = 7). BMSCs were administered 30 min after induction of sevoflurane anesthesia (BMSCs group, n = 7). The pups were exposed to carrier gas only, as a negative control (mock anesthesia group, n = 4). We assessed the therapeutic effects of BMSC treatment by measuring expression of the pro-inflammatory cytokine interleukin-6 (IL-6), and levels of cleaved caspase-3, in brain tissues immediately following sevoflurane anesthesia.

Results

Analysis of the cleaved caspase-3 bands revealed that levels of activated caspase-3 were elevated in the vehicle group compared with the mock anesthesia group, indicating that a single exposure to sevoflurane at subclinical concentrations can precipitate neuronal apoptosis. BMSC treatment did not suppress apoptosis induced by sevoflurane exposure (compared with the vehicle group). The vehicle group had higher proinflammatory cytokine IL-6 protein levels compared with the mock anesthesia group, indicating that sevoflurane exposure induces IL-6 expression. BMSC treatment suppressed sevoflurane-induced increases in IL-6 expression, indicating that these cells can inhibit the neuroinflammation induced by sevoflurane exposure (vehicle group vs. BMSC group).

Conclusions

Intravenous administration of BMSCs reduces neuroinflammation, but does not attenuate apoptosis induced by sevoflurane exposure.

Toxic and protective effects of inhaled anaesthetics on the developing animal brain: systematic review and update of recent experimental work

BACKGROUND

Accumulating preclinical data indicate that neonatal exposure to general anaesthetics is detrimental to the central nervous system. Some studies, however, display potential protective effects of exactly the same anaesthetic agents on the immature brain. The effects of inhaled anaesthetics on the developing brain have received close attention from researchers, clinicians and the public in recent decades.

OBJECTIVES

To summarise the preclinical evidence reported in the last 5 years on both the deleterious effects and the neuroprotective potential in special indications, of inhaled anaesthetics on the developing brain.

DESIGN

A systematic review.

DATA SOURCES

PubMed search performed in June 2013.

ELIGIBILITY CRITERIA

Search terms included brain, development, inhaled anaesthetic, toxicity and protection within the scope of the last 5 years with animals. The reference lists of relevant articles and recent reviews were also hand-searched for additional studies. The type, dose and exposure duration of anaesthetics, species and age of animals, histopathologic indicators, outcomes and affected brain areas, neuro developmental test modules and outcomes, as well as other outcomes and comments were summarised.

RESULTS

Two hundred and nineteen relevant titles were initially revealed. In total, 81 articles were identified, with 68 articles assessing the detrimental effects induced by inhaled anaesthetics in the immature brain along with possible treatments. The remaining 13 articles focused on the protective profile of inhaled anaesthetics on perinatal hypoxic-ischaemic brain injury. Administration of inhaled anaesthetic agents to the immature brain was shown to be deleterious in several preclinical studies. In perinatal hypoxic-ischaemic brain injury models, pre- and postconditioning of inhalational anaesthetics exerted neuroprotective effects.

CONCLUSION

The majority of studies have linked inhaled anaesthetics to toxic effects in the neonatal brain of rodents, piglets and primates. Only a few studies, however, could demonstrate long-lasting cognitive impairment. The results of inhalational anaesthetic-induced neuroprotection in perinatal hypoxic-ischaemic brain injury are a promising basis for more research in this field. In general, prospective clinical trials are needed to further differentiate the effects of inhaled anaesthetics on the immature brain.

Long-term action of propofol on cognitive function and hippocampal neuroapoptosis in neonatal rats

Propofol is a short-acting anesthetic and generally is utilized for the induction and maintenance of anesthesia in pediatrics and adults. However, whether repeated use of propofol affects long-term cognitive function remains unclear. This study investigated the effects of propofol on cognitive function and hippocampal neuroapoptosis in neonatal rat. A total of 112 male newborn 7-day old Sprague-Dawley rats were randomly divided into 8 groups (n=14 rats per group) and intraperitoneally injected either with saline or propofol at 50, 100, and 150 mg/kg/day for 5 consecutive days. Four non-surgical groups were assigned as Con1, P50, P100, and P150. Four surgical groups were received an appendicectomy under propofol anesthesia and assigned as Con2, SP50, SP100, SP150. After 2 months raising, cognitive function, hippocampal neuroapoptosis, and intracephalic inflammatory cytokines were evaluated. There was no obvious effect on the cognitive function and neuroapoptosis after repeated use of propofol at a low dose for 5 days, whereas repeated use of propofol at a middle/high dose significantly increase the expression of apoptotic factors (caspase-3 and Bax), pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), and impair the cognitive function. Thus, our data suggest that repeated use of propofol at a low dose may be safe during the period of brain growth spurt. Using propofol at a recommended or higher dose for anaesthesia may lead to the cognitive defects, attributed to hippocampal neuroapoptosis and the overexpression of pro-inflammatory cytokines in the brain.

Environmental Enrichment Attenuated Sevoflurane-Induced Neurotoxicity through the PPAR-γ Signaling Pathway

Sevoflurane is the most widely used inhaled anesthetic. Environmental enrichment (EE) can reverse sevoflurane-induced learning and memory impairment in young mice. However, the mechanism by which EE elicits this effect is unclear. The peroxisome proliferator-activated receptor (PPAR) regulatory pathway plays a critical role in the regulation of inflammation in central nervous system diseases. In this study, we investigated whether EE attenuates sevoflurane-induced learning and memory disability via the PPAR signaling pathway. Six-day-old mice were treated with 3% sevoflurane for 2 hours daily from postnatal day 6 (P6) to P8. Then, the mice were treated with EE. The effects of sevoflurane on learning and memory function, PPAR-γ expression in the brain, and the numbers of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells and 5-bromodeoxyuridine-positive cells in the hippocampus were determined. Sevoflurane induced neuronal apoptosis and neurogenesis inhibition, which may impair learning and memory in young mice. Furthermore, sevoflurane downregulated PPAR-γ expression. Both EE and the PPAR-γ agonist, rosiglitazone, attenuated sevoflurane-induced neuronal apoptosis, neurogenesis inhibition, and learning and memory impairment. Our findings suggest that EE ameliorated sevoflurane-induced neurotoxicity and learning and memory impairment through the PPAR-γ signaling pathway. PPAR-γ may be a potential therapeutic target for preventing or treating sevoflurane-induced neurotoxicity.

Repeated exposure to ketamine-xylazine during early development impairs motor learning-dependent dendritic spine plasticity in adulthood

BACKGROUND

Recent studies in rodents suggest that repeated and prolonged anesthetic exposure at early stages of development leads to cognitive and behavioral impairments later in life. However, the underlying mechanism remains unknown. In this study, we tested whether exposure to general anesthesia during early development will disrupt the maturation of synaptic circuits and compromise learning-related synaptic plasticity later in life.

METHODS

Mice received ketamine-xylazine (20/3 mg/kg) anesthesia for one or three times, starting at either early (postnatal day 14 [P14]) or late (P21) stages of development (n = 105). Control mice received saline injections (n = 34). At P30, mice were subjected to rotarod motor training and fear conditioning. Motor learning-induced synaptic remodeling was examined in vivo by repeatedly imaging fluorescently labeled postsynaptic dendritic spines in the primary motor cortex before and after training using two-photon microscopy.

RESULTS

Three exposures to ketamine-xylazine anesthesia between P14 and P18 impair the animals' motor learning and learning-dependent dendritic spine plasticity (new spine formation, 8.4 ± 1.3% [mean ± SD] vs. 13.4 ± 1.8%, P = 0.002) without affecting fear memory and cell apoptosis. One exposure at P14 or three exposures between P21 and P25 has no effects on the animals' motor learning or spine plasticity. Finally, enriched motor experience ameliorates anesthesia-induced motor learning impairment and synaptic deficits.

CONCLUSIONS

Our study demonstrates that repeated exposures to ketamine-xylazine during early development impair motor learning and learning-dependent dendritic spine plasticity later in life. The reduction in synaptic structural plasticity may underlie anesthesia-induced behavioral impairment.

Differential influence of propofol and isoflurane anesthesia in a non-human primate on the brain kinetics and binding of [(18)F]DPA-714, a positron emission tomography imaging marker of glial activation

Translocator protein 18 kDa (TSPO) expression at the mitochondrial membrane of glial cells is related to glial activation. TSPO radioligands such as [(18)F]DPA-714 are useful for the non-invasive study of neuroimmune processes using positron emission tomography (PET). Anesthetic agents were shown to impact mitochondrial function and may influence [(18)F]DPA-714 binding parameters and PET kinetics. [(18) F]DPA-714 PET imaging was performed in Papio anubis baboons anesthetized using either intravenous propofol (n = 3) or inhaled isoflurane (n = 3). Brain kinetics and metabolite-corrected input function were measured to estimate [(18) F]DPA-714 brain distribution (VT). Displacement experiments were performed using PK11195 (1.5 mg/kg). In vitro [(18)F]DPA-714 binding experiments were performed using baboon brain tissue in the absence and presence of tested anesthetics. Brain radioactivity peaked higher in isoflurane-anesthetized animals compared with propofol (SUVmax = 2.7 ± 0.5 vs. 1.3 ± 0.2, respectively) but was not different after 30 min. Brain VT was not different under propofol and isoflurane. Displacement resulted in a 35.8 ± 8.4% decrease of brain radioactivity under propofol but not under isoflurane (0.1 ± 7.0%). In vitro, the presence of propofol increased TSPO density and dramatically reduced its affinity for [(18)F]DPA-714 compared with control. This in vitro effect was not significant with isoflurane. Exposure to propofol and isoflurane differentially influences TSPO interaction with its specific radioligand [(18)F]DPA-714 with subsequent impact on its tissue kinetics and specific binding estimated in vivo using PET. Therefore, the choice of anesthetics and their potential influence on PET data should be considered for the design of imaging studies using TSPO radioligands, especially in a translational research context.

Neonatal exposure to sevoflurane may not cause learning and memory deficits and behavioral abnormality in the childhood of Cynomolgus monkeys

Results of animal studies have raised a significant concern that commonly used general anesthetics may induce neurotoxicity in children. It may be difficult to resolve this concern with human studies because randomizing children only for testing anesthetic toxicity may not be feasible. We randomized 6-day old male Cynomolgus monkeys to receive or not to receive sevoflurane anesthesia at surgical plane for 5 h. Sevoflurane is the most commonly used general anesthetic in children in the U.S.A. Here, we showed that sevoflurane anesthesia did not affect the behavior evaluated by holding cage method when the monkeys were 3 and 7 months old. However, there was an age-dependent decrease in the frequency of stress events and environmental exploration behavior during the test. Sevoflurane also did not affect the learning and memory of the monkeys when they were assessed from the age of 7 months. Finally, sevoflurane did not affect the expression of multiple neuron-specific proteins in the hippocampus and cerebral cortex of 10-month old monkeys after all behavioral and cognitive tests were completed. These results suggest that exposure of neonatal monkey to sevoflurane may not affect cognition, behavior and neuronal structures in childhood, indicating the safety of sevoflurane anesthesia in children.

Internalization of GluA2 and the underlying mechanisms of cognitive decline in aged rats following surgery and prolonged exposure to sevoflurane

BACKGROUND

We revealed that a high concentration of sevoflurane exacerbated cognitive impairment in aged rats, and the inhibition of GluA2 subunit internalization facilitated neuroprotection after a cerebral ischemic injury. However, the trafficking of GluA2 in POCD and its underlying mechanism are not clear. We thus detected the effects of sevoflurane for different inhalation durations on postoperative cognitive function and investigated the role of GluA2 subunit trafficking in this process.

METHODS

A rat model of orthopedic surgery was performed with different durations of 1.5 MAC sevoflurane inhalation. Cognitive function was evaluated by manipulating the Y maze and fear conditioning tests for 7 days after experiments. Western blot, ELISA and coimmunoprecipitation were applied to analyze GluA2 internalization, PI3K expression and its activity, as well as alterations to the MEF2-Arc pathway in the hippocampus. Neuron apoptosis and the spine morphology in the hippocampus were also observed.

RESULTS

We found that neuron apoptosis and GluA2 internalization increased following surgery and 1.5 MAC sevoflurane inhalation for 2h, possibly due to the decrease of the PI3K-GluA2 complex and PI3K activity in the hippocampus after prolonged 1.5 MAC sevoflurane inhalation. We also observed that the MEF2-Arc pathway contributed to long-term cognitive function, which also impaired the spinal morphology after 1.5 MAC sevoflurane inhalation for 2h.

CONCLUSION

The above results suggest that 1.5 MAC sevoflurane inhalation for 2h potentiated surgery-impaired cognitive function and that the inhibition of PI3K-AMPAR GluA2 as well as activation of the MEF2-Arc signal pathway contributes to different stages of POCD.

Neurodevelopmental implications of the general anesthesia in neonate and infants

Each year, about six million children, including 1.5 million infants, in the United States undergo surgery with general anesthesia, often requiring repeated exposures. However, a crucial question remains of whether neonatal anesthetics are safe for the developing central nervous system (CNS). General anesthesia encompasses the administration of agents that induce analgesic, sedative, and muscle relaxant effects. Although the mechanisms of action of general anesthetics are still not completely understood, recent data have suggested that anesthetics primarily modulate two major neurotransmitter receptor groups, either by inhibiting N-methyl-D-aspartate (NMDA) receptors, or conversely by activating γ-aminobutyric acid (GABA) receptors. Both of these mechanisms result in the same effect of inhibiting excitatory activity of neurons. In developing brains, which are more sensitive to disruptions in activity-dependent plasticity, this transient inhibition may have longterm neurodevelopmental consequences. Accumulating reports from preclinical studies show that anesthetics in neonates cause cellular toxicity including apoptosis and neurodegeneration in the developing brain. Importantly, animal and clinical studies indicate that exposure to general anesthetics may affect CNS development, resulting in long-lasting cognitive and behavioral deficiencies, such as learning and memory deficits, as well as abnormalities in social memory and social activity. While the casual relationship between cellular toxicity and neurological impairments is still not clear, recent reports in animal experiments showed that anesthetics in neonates can affect neurogenesis, which could be a possible mechanism underlying the chronic effect of anesthetics. Understanding the cellular and molecular mechanisms of anesthetic effects will help to define the scope of the problem in humans and may lead to preventive and therapeutic strategies. Therefore, in this review, we summarize the current evidence on neonatal anesthetic effects in the developmental CNS and discuss how factors influencing these processes can be translated into new therapeutic strategies.

Behavioral and emotional effects of repeated general anesthesia in young children

BACKGROUND

Preclinical and clinical data suggest the possibility of neurotoxicity following exposure of young children to general anesthetics with subsequent behavioral disturbances. The aim of the study was to determine the overall effect of repeated general anesthesia on behavior and emotions of young children aged 1½-5 years old, compared to healthy children.

MATERIALS AND METHODS

Thirty-five children underwent repeated anesthesia and surgery were matched with the same number of healthy children who attended vaccination clinic, as a control group. Both groups were administered the child behavior checklist (CBCL) 1½-5 years and Diagnostic and Statistical Manual of Mental Disorders (DSM) oriented scale. Behavior data were collected through a semi-structured questionnaire.

RESULTS

The CBCL score revealed that children with repeated anesthesia were at risk to become anxious or depressed (relative risk [RR]; 95% confidence interval [CI] = 11 [1.5-80.7]), to have sleep (RR; 95% CI = 4.5 [1.1-19.4]), and attention problems (RR; 95% CI = 8 [1.1-60.6]). There was no difference in the risk between the two groups regarding emotionally reactive, somatic complaints, withdrawn problems, aggressive behavior, internalizing or externalizing problems. On DSM scale, children with repeated anesthesia were at risk to develop anxiety problems (RR; 95% CI = 3.7 [1.1-12.0]), and attention deficit/hyperactivity problems (RR; 95% CI = 3 [1.1-8.4]). There was no difference in the risk between the two groups regarding affective, pervasive developmental and oppositional defiant problems.

CONCLUSION

Young children who undergone repeated surgical procedures under general anesthesia were at risk for subsequent behavioral and emotional disturbances. Proper perioperative pain management, social support, and avoidance of unpleasant surgical experiences could minimize these untoward consequences.

Inhibiting Rho kinase 2 reduces memory dysfunction in adult rats exposed to sevoflurane at postnatal days 7-9

The aim of the present study was to investigate the roles of Rho protein A (RhoA) and Rho kinases 2 (ROCK2) in the memory dysfunction of adult rats exposed to sevoflurane at postnatal days 7-9 (P7-9). One-week-old Sprague-Dawley rats were divided into four groups known as C, S1, S3 and F. Rats in the S1 (2 h at P7) and S3 groups (2 h/day at P7-9) were exposed to sevoflurane. The rats in the F group were treated with the ROCK2 inhibitor and subsequent sevoflurane exposure (2 h/day at P7-9). The rats in the C group received no sevoflurane. The protein levels of RhoA, ROCK2 and cleaved caspase-3 (Cl-Csp3) in the adult hippocampus were assessed by western blot analysis. Learning and memory of rats at postnatal 45-50 days (P45-50) were detected by the Morris water maze (MWM) test. During the training of MWM, the latency and distance of rats in the S3 group were significantly longer than that of the C group (P<0.05, respectively). In the probe test, the percentages of time and distance in the target quadrant for the S3 group were evidently less than that of the C group (P<0.05). There was no significant difference in the behaviors between the C and S1 groups (P>0.05, respectively). Corresponding to the behavioral changes, the levels of RhoA, ROCK2 and Cl-Csp3 in the hippocampus of the S3 group significantly increased, compared to that of the C and S1 groups (P<0.05). Additionally, the ROCK2 inhibitor clearly decreased ROCK2 and Cl-Csp3 expression and shortened the latency during the training (P<0.05, P46-49 respectively) and probe test (P<0.05) in the F group, compared to that of the S3 group. Compared to the C group, the expression of RhoA, ROCK2 and Cl-Csp3 in the hippocampus of the S1 group had no significant difference (P>0.05). Multiple inhalation of sevoflurane can induce neurotoxicity and memory dysfunction. RhoA and ROCK2 played important roles in the impairment of learning and memory of adults rats exposed to sevoflurane at the postnatal early stage.

Chronic treatment with anesthetic propofol improves cognitive function and attenuates caspase activation in both aged and Alzheimer's disease transgenic mice

There is a need to seek new treatment(s) for Alzheimer's disease (AD). A recent study showed that AD patients may have decreased levels of functional GABA receptors. Propofol, a commonly used anesthetic, is a GABA receptor agonist. We therefore set out to perform a proof of concept study to determine whether chronic treatment with propofol (50 mg/kg/week) can improve cognitive function in both aged wild-type (WT) and AD transgenic (Tg) mice. Propofol was administrated to the WT and AD Tg mice once a week for 8 or 12 weeks, respectively. Morris water maze was used to assess the cognitive function of the mice following the propofol treatment. Activation of caspase-3, caspase-9, and caspase-8 was investigated using western blot analysis at the end of the propofol treatment. In the mechanistic studies, effects of propofol, amyloid-β protein (Aβ), and GABA receptor antagonist flumazenil on caspase-3 activation and opening of the mitochondrial permeability transition pore were assessed in H4 human neuroglioma and mouse neuroblastoma cells by western blot analysis and flow cytometry. Here we showed that the propofol treatment improved cognitive function and attenuated brain caspase-3 and caspase-9 activation in both aged WT and AD Tg mice. Propofol attenuated Aβ-induced caspase-3 activation and opening of the mitochondrial permeability transition pore in the cells, and flumazenil inhibited the propofol's effects. These results suggested that propofol might improve cognitive function via attenuating the Aβ-induced mitochondria dysfunction and caspase activation, which explored the potential that anesthetic propofol could improve cognitive function in elderly and AD patients.

S6 inhibition contributes to isoflurane neurotoxicity in the developing brain

Postnatal isoflurane exposure leads to neurodegeneration and deficits of spatial learning and memory in the adulthood. However, the underlying mechanisms remain unclear. Ribosomal protein S6 is demonstrated to play a pivotal role in control of cell survival, protein synthesis and synaptogenesis for brain development. In this study, the possible role of S6 and its upstream signaling pathways in the developmental neurotoxicity of isoflurane was evaluated using models of primary cultured hippocampal neurons and postnatal day 7 rats. We found that isoflurane decreased IGF-1 level and suppressed activation of IGF-1 receptor, sequentially inhibiting S6 activity via IGF-1/MEK/ERK and IGF-1/PI3K/Akt signaling pathways. S6 inhibition enhanced isoflurane-induced decreased Bcl-xL and increased cleaved caspase-3 and Bad, also reduced PSD95 expression and aggravated deficits of spatial learning and memory. S6 activation could reverse the damages above. These results indicate that S6 inhibition, led by suppression of upstream IGF-1/MEK/ERK and IGF-1/PI3K/Akt signaling pathways, is involved in the neuroapoptosis, synaptogenesis impairment and spatial learning and memory decline caused by postnatal isoflurane exposure. S6 activation may exhibit protective potential against developmental neurotoxicity of isoflurane.

MicroRNAs: New Players in Anesthetic-Induced Developmental Neurotoxicity

Growing evidence demonstrates that prolonged exposure to general anesthetics during brain development induces widespread neuronal cell death followed by long-term memory and learning disabilities in animal models. These studies have raised serious concerns about the safety of anesthetic use in pregnant women and young children. However, the underlying mechanisms of anesthetic-induced neurotoxicity are complex and are not well understood. MicroRNAs are endogenous, small, non-coding RNAs that have been implicated to play important roles in many different disease processes by negatively regulating target gene expression. A possible role for microRNAs in anesthetic-induced developmental neurotoxicity has recently been identified, suggesting that microRNA-based signaling might be a novel target for preventing the neurotoxicity. Here we provide an overview of anesthetic-induced developmental neurotoxicity and focus on the role of microRNAs in the neurotoxicity observed in both human stem cell-derived neuron and animal models. Aberrant expression of some microRNAs has been shown to be involved in anesthetic-induced developmental neurotoxicity, revealing the potential of microRNAs as therapeutic or preventive targets against the toxicity.

Pre-administration of curcumin prevents neonatal sevoflurane exposure-induced neurobehavioral abnormalities in mice

Sevoflurane, a commonly used inhaled anesthetic, can induce neuronal apoptosis in the developing rodent brain and correlate with functional neurological impairment later in life. However, the mechanisms underlying these deleterious effects of sevoflurane remain unclear and no effective treatment is currently available. Herein, the authors investigated whether curcumin can prevent the sevoflurane anesthesia-induced cognitive impairment in mice. Six-day-old C57BL/6 mice were exposed to 3% sevoflurane 2h daily for 3 consecutive days and were treated with curcumin at the dose of 20 mg/kg or vehicle 30 min before the sevoflurane anesthesia from postnatal days 6 (P6) to P8. Cognitive functions were evaluated by open field, Morris water maze, and fear conditioning tests on P61, P63-69, and P77-78, respectively. In another separate experiment, mice were killed on day P8 or P78, and the brain tissues were harvested and then subjected to biochemistry studies. Our results showed that repeated neonatal sevoflurane exposure led to significant cognitive impairment later in life, which was associated with increased neuronal apoptosis, neuroinflammation, oxidative nitrosative stress, and decreased memory related proteins. By contrast, pre-administration of curcumin ameliorated early neuronal apoptosis, neuroinflammation, oxidative nitrosative stress, memory related proteins, and later cognitive dysfunction. In conclusion, our data suggested that curcumin pre-administration can prevent the sevoflurane exposure-induced cognitive impairment later in life, which may be partly attributed to its ability to attenuate the neural apoptosis, inflammation, and oxidative nitrosative stress in mouse brain.

Neuroanesthesiology update

We review topics pertinent to the perioperative care of patients with neurological disorders. Our review addresses topics not only in the anesthesiology literature, but also in basic neurosciences, critical care medicine, neurology, neurosurgery, radiology, and internal medicine literature. We include literature published or available online up through December 8, 2013. As our review is not able to include all manuscripts, we focus on recurring themes and unique and pivotal investigations. We address the broad topics of general neuroanesthesia, stroke, traumatic brain injury, anesthetic neurotoxicity, neuroprotection, pharmacology, physiology, and nervous system monitoring.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Inflammatory pain may induce cognitive impairment through an interlukin-6-dependent and postsynaptic density-95-associated mechanism

BACKGROUND

Pain might be associated with cognitive impairment in humans. However, the characterization of such effects in a preclinical model and the investigation of the underlying mechanisms remain largely to be determined. We therefore sought to establish a system to determine the effect of pain on cognitive function in mice.

METHODS

Complete Freund's adjuvant (CFA) was injected in the hindpaw of 5- to 8-month-old wild-type and interleukin-6 knockout mice. Learning and memory function, and the levels of interleukin-6 and postsynaptic density (PSD)-95 in the cortex and hippocampus of mice were assessed.

RESULTS

We found that the CFA injection-induced pain in the mice at 3 and 7 days after injection and decreased the freezing time (30.1 [16.5] vs 56.8 [28.1] seconds, P =0.023) in the tone test, which assesses the hippocampus-independent learning and memory function, but not in a context test of Fear Conditioning System (15.8 [6.7] vs 18.6 [8.8] seconds, P =0.622), which assesses the hippocampus-dependent learning and memory function, at 3 days after injection. Consistently, the CFA injection increased interleukin-6 (248% [11.6] vs 100% [7.9], P < 0.0001) and decreased the PSD-95 (40% [10.0] vs 100% [20.3], P < 0.0001) level in the cortex, but not hippocampus (95% [8.6] vs 100% [9.3], P =0.634), in the mice. The CFA injection induced neither reduction in the cortex PSD-95 levels nor cognitive impairment in the interleukin-6 knockout mice.

CONCLUSIONS

These results suggest that pain induced by CFA injection might increase interleukin-6 levels and decrease PSD-95 levels in the cortex, but not hippocampus of mice, leading to hippocampus-independent cognitive impairment in mice. These findings call for further investigation to determine the role of pain in cognitive function.

Sevoflurane induces tau phosphorylation and glycogen synthase kinase 3β activation in young mice

BACKGROUND

Children with multiple exposures to anesthesia and surgery may have an increased risk of developing cognitive impairment. Sevoflurane is a commonly used anesthetic in children. Tau phosphorylation contributes to cognitive dysfunction. The authors therefore assessed the effects of sevoflurane on Tau phosphorylation and the underlying mechanisms in young mice.

METHODS

Six-day-old wild-type and Tau knockout mice were exposed to sevoflurane. The authors determined the effects of sevoflurane anesthesia on Tau phosphorylation, levels of the kinases and phosphatase related to Tau phosphorylation, interleukin-6 and postsynaptic density protein-95 in hippocampus, and cognitive function in both young wild-type and Tau knockout mice.

RESULTS

Anesthesia with 3% sevoflurane 2 h daily for 3 days induced Tau phosphorylation (257 vs. 100%, P = 0.0025, n = 6) and enhanced activation of glycogen synthase kinase 3β, which is the kinase related to Tau phosphorylation in the hippocampus of postnatal day-8 wild-type mice. The sevoflurane anesthesia decreased hippocampus postsynaptic density protein-95 levels and induced cognitive impairment in the postnatal day-31 mice. Glycogen synthase kinase 3β inhibitor lithium inhibited the sevoflurane-induced glycogen synthase kinase 3β activation, Tau phosphorylation, increased levels of interleukin-6, and cognitive impairment in the wild-type young mice. Finally, the sevoflurane anesthesia did not induce an increase in interleukin-6 levels, reduction in postsynaptic density protein-95 levels in hippocampus, or cognitive impairment in Tau knockout young mice.

CONCLUSIONS

These data suggested that sevoflurane induced Tau phosphorylation, glycogen synthase kinase 3β activation, increase in interleukin-6 and reduction in postsynaptic density protein-95 levels in hippocampus of young mice, and cognitive impairment in the mice. Future studies will dissect the cascade relation of these effects.

Early exposure to volatile anesthetics impairs long-term associative learning and recognition memory

BACKGROUND

Anesthetic exposure early in life affects neural development and long-term cognitive function, but our understanding of the types of memory that are altered is incomplete. Specific cognitive tests in rodents that isolate different memory processes provide a useful approach for gaining insight into this issue.

METHODS

Postnatal day 7 (P7) rats were exposed to either desflurane or isoflurane at 1 Minimum Alveolar Concentration for 4 h. Acute neuronal death was assessed 12 h later in the thalamus, CA1-3 regions of hippocampus, and dentate gyrus. In separate behavioral experiments, beginning at P48, subjects were evaluated in a series of object recognition tests relying on associative learning, as well as social recognition.

RESULTS

Exposure to either anesthetic led to a significant increase in neuroapoptosis in each brain region. The extent of neuronal death did not differ between groups. Subjects were unaffected in simple tasks of novel object and object-location recognition. However, anesthetized animals from both groups were impaired in allocentric object-location memory and a more complex task requiring subjects to associate an object with its location and contextual setting. Isoflurane exposure led to additional impairment in object-context association and social memory.

CONCLUSION

Isoflurane and desflurane exposure during development result in deficits in tasks relying on associative learning and recognition memory. Isoflurane may potentially cause worse impairment than desflurane.

Disruption of hippocampal neuregulin 1-ErbB4 signaling contributes to the hippocampus-dependent cognitive impairment induced by isoflurane in aged mice

BACKGROUND

A prolonged isoflurane exposure may lead to cognitive decline in rodents. Neuregulin 1 (NRG1)-ErbB4 signaling plays a key role in the modulation of hippocampal synaptic plasticity through regulating the neurotransmission. The authors hypothesized that hippocampal NRG1-ErbB4 signaling is involved in isoflurane-induced cognitive impairments in aged mice.

METHODS

Fourteen-month-old C57BL/6 mice were randomized to receive 100% O2 exposure, vehicle injection after 100% O2 exposure, vehicle injection after exposure to isoflurane carried by 100% O2, NRG1-β1 injection after exposure to isoflurane carried by 100% O2, and NRG1-β1 and an ErbB4 inhibitor AG1478 injection after exposure to isoflurane carried by 100% O2. Fear conditioning test was used to assess the cognitive function of mice 48-h postexposure. The brain tissues were harvested 48-h postexposure to determine the levels of NRG1, ErbB4, p-ErbB4, parvalbumin, and glutamic acid decarboxylase 67 in the hippocampus using Western blotting, enzyme-linked immunosorbent assay, and immunofluorescence.

RESULTS

The percentage of freezing time to context was decreased from 50.28 ± 11.53% to 30.82 ± 10.00%, and the hippocampal levels of NRG1, p-ErbB4/ErbB4, parvalbumin, and glutamic acid decarboxylase 67 were decreased from 172.79 ± 20.85 ng/g, 69.15 ± 12.20%, 101.68 ± 11.21%, and 104.71 ± 6.85% to 112.92 ± 16.65 ng/g, 42.26 ± 9.71%, 75.89 ± 10.26%, and 73.87 ± 16.89%, respectively, after isoflurane exposure. NRG1-β1 attenuated the isoflurane-induced hippocampus-dependent cognitive impairment and the declines in the hippocampal NRG1, p-ErbB4/ErbB4, parvalbumin, and glutamic acid decarboxylase 67. AG1478 inhibited the rescuing effects of NRG1-β1.

CONCLUSION

Disruption of NRG1-ErbB4 signaling in the parvalbumin-positive interneurons might, at least partially, contribute to the isoflurane-induced hippocampus-dependent cognitive impairment after exposure to isoflurane carried by 100% O2 in aged mice.

Both JNK and P38 MAPK pathways participate in the protection by dexmedetomidine against isoflurane-induced neuroapoptosis in the hippocampus of neonatal rats

Dexmedetomidine, a highly selective α2-adrenergic agonist, has been reported to attenuate isoflurane-induced cognitive impairment and neuroapoptosis. However, the underlying molecular mechanisms remain poorly understood. The aim of this study was to investigate whether mitogen-activated protein kinase (MAPK) pathway was involved in dexmedetomidine-induced neuroprotection against isoflurane effects. Seven-day-old (P7) neonatal Sprague-Dawley rats were pretreated with various concentrations of dexmedetomidine, and then exposed to 0.75% isoflurane or air for 6h. Terminal deoxyribonucleotide transferase-mediated dUTP nick end labeling (TUNEL) was used to detect neuronal apoptosis in their hippocampus. Activated caspase-3, extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH2-terminal kinases (JNK), p38, phospho-ERK1/2, phospho-JNK and phospho-p38 proteins were detected by Western blotting in the hippocampus at the end of exposure. Also, P7 rats were pretreated with 75 μg/kg dexmedetomidine alone, or given the ERK inhibitor U0126 before dexmedetomidine pretreatment, or pretreated with the p38 MAPK inhibitor SB203580 or JNK inhibitor SP600125 alone, and then exposed to 0.75% isoflurane for 6h. Isoflurane induced significant neuroapoptosis, increased the protein expression of phospho-JNK, phospho-c-Jun, phospho-p38 and phospho-nuclear factor-κB (NF-κB), decreased the level of phospho-ERK1/2 protein and reduced the ratio of Bcl-2/Bax in the hippocampus. Dexmedetomidine pretreatment inhibited isoflurane-induced neuroapoptosis and restored proteins expression of MAPK pathways and the Bcl-2/Bax ratio after isoflurane exposure. Moreover, SB203580 and SP600125 also partly attenuated the isoflurane-induced protein changes. However, U0126 did not reverse dexmedetomidine-induced neuroprotection. Our results indicate that the JNK and p38 pathways, not the ERK pathway are involved in dexmedetomidine-induced neuroprotection against isoflurane effects.

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

Background

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

Methods

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

Results

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

Conclusion

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

2-Deoxy-d-glucose attenuates sevoflurane-induced neuroinflammation through nuclear factor-kappa B pathway in vitro

OBJECT

Sevoflurane, one of the most commonly used anesthetics in clinic, induced neuroinflammation and caused cognitive impairment. 2-deoxy-d-glucose (2-DG) is a synthetic analogue of glucose and is clinically used in medical imaging safely.

METHODS

We examined the effect of 2-DG on sevoflurane-induced neuroinflammation in the mouse primary microglia cells. Mouse microglia cells were treated with 4.1% sevoflurane for 6h to examine the expression of interleukin (IL)-6 and tumor necrosis factor (TNF-α) and activation of nuclear factor-kappa B (NF-κB). Pyrrolidine dithiocarbamate (PDTC) or 2-DG was used 1h before sevoflurane treatment.

RESULTS

In the present study, we found that sevoflurane increased level of IL-6 and TNF-α through activating NF-κB signaling, and that 2-DG reduced sevoflurane-induced increase in IL-6 and TNF-α and nuclear NF-κB in microglia cells.

CONCLUSION

Our data suggests that NF-κB signaling pathway could be a target for sevoflurane-induced neuroinflammation and 2-DG might be a potential therapy to prevent or treat sevoflurane-induced neuroinflammation.

Intranasal insulin prevents anesthesia-induced hyperphosphorylation of tau in 3xTg-AD mice

Background: It is well documented that elderly individuals are at increased risk of cognitive decline after anesthesia. General anesthesia is believed to be a risk factor for Alzheimer’s disease (AD). Recent studies suggest that anesthesia may increase the risk for cognitive decline and AD through promoting abnormal hyperphosphorylation of tau, which is crucial to neurodegeneration seen in AD.

Methods: We treated 3xTg-AD mice, a commonly used transgenic mouse model of AD, with daily intranasal administration of insulin (1.75 U/day) for one week. The insulin- and control-treated mice were then anesthetized with single intraperitoneal injection of propofol (250 mg/kg body weight). Tau phosphorylation and tau protein kinases and phosphatases in the brains of mice 30 min and 2 h after propofol injection were then investigated by using Western blots and immunohistochemistry.

Results: Propofol strongly promoted hyperphosphorylation of tau at several AD-related phosphorylation sites. Intranasal administration of insulin attenuated propofol-induced hyperphosphorylation of tau, promoted brain insulin signaling, and led to up-regulation of protein phosphatase 2A, a major tau phosphatase in the brain. Intranasal insulin also resulted in down-regulation of several tau protein kinases, including cyclin-dependent protein kinase 5, calcium/calmodulin-dependent protein kinase II, and c-Jun N-terminal kinase.

Conclusion: Our results demonstrate that pretreatment with intranasal insulin prevents AD-like tau hyperphosphorylation. These findings provide the first evidence supporting that intranasal insulin administration might be used for the prevention of anesthesia-induced cognitive decline and increased risk for AD and dementia.

Anesthetic sevoflurane reduces levels of hippocalcin and postsynaptic density protein 95

Sevoflurane, the commonly used inhalation anesthetic in children, has been shown to enhance cytosolic calcium levels and induce cognitive impairment in young mice. However, the downstream consequences of the sevoflurane-induced elevation in cytosolic calcium levels and the upstream mechanisms of the sevoflurane-induced cognitive impairment remain largely to be determined. Hippocalcin is one of the neuronal calcium sensor proteins, and also binds to postsynaptic density protein 95 (PSD-95). We therefore set out to determine the effects of sevoflurane on the levels of hippocalcin and PSD-95 in vitro and in vivo. Hippocampus neurons from mice and 6-day-old mice were treated with 4.1% sevoflurane for 6 h or 3% sevoflurane 2 h daily for 3 days, respectively. We then measured the levels of hippocalcin and PSD-95, and assessed whether BAPTA, an intracellular calcium chelator, and memantine, a partial antagonist of the NMDA receptor, could inhibit the sevoflurane's effects. We found that sevoflurane decreased the levels of hippocalcin and PSD-95 in the neurons; and decreased the levels of hippocalcin and PSD-95 in the hippocampus of mice immediately after the anesthesia, but only the PSD-95 levels three weeks after the anesthesia. BAPTA inhibited the sevoflurane's effects in the neurons. Memantine attenuated the sevoflurane-induced reductions in the levels of hippocalcin and PSD-95, as well as the sevoflurane-induced cognitive impairment in mice. These data suggested that sevoflurane decreased the levels of hippocalcin and PSD-95, which could serve as one of bridge mechanisms between the sevoflurane-induced elevation of cytosolic calcium levels and the sevoflurane-induced cognitive impairment.

Critical role of inflammatory cytokines in impairing biochemical processes for learning and memory after surgery in rats

Background

Patients with postoperative cognitive dysfunction have poor outcomes. Neuroinflammation may be the underlying pathophysiology for this dysfunction. We determined whether proinflammatory cytokines affect the trafficking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors to the plasma membrane, a fundamental biochemical process for learning and memory.

Methods

Four-month-old male Fischer 344 rats were subjected to right carotid exposure under isoflurane anesthesia. Some rats received intravenous lidocaine infusion during anesthesia. Rats were tested two weeks later by Barnes maze. The hippocampus was harvested six hours after the surgery for western blotting of interleukin (IL)-1β or IL-6. Hippocampal slices were prepared from control rats or rats subjected to surgery two weeks previously. They were incubated with tetraethylammonium, an agent that can induce long term potentiation, for determining the trafficking of GluR1, an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit.

Results

Surgery or anesthesia increased the time to identify the target box during the Barnes maze test training sessions and one day after the training sessions. Surgery also prolonged the time to identify the target box eight days after the training sessions. Surgery increased IL-1β and IL-6 in the hippocampus. The tetraethylammonium–induced GluR1 phosphorylation and trafficking were abolished in the hippocampal slices of rats after surgery. These surgical effects were partly inhibited by lidocaine. The incubation of control hippocampal slices with IL-1β and IL-6 abolished tetraethylammonium–induced GluR1 trafficking and phosphorylation. Lidocaine minimally affected the effects of IL-1β on GluR1 trafficking.

Conclusions

Our results suggest that surgery increases proinflammatory cytokines that then inhibit GluR1 trafficking, leading to learning and memory impairment.

Peripheral surgical wounding and age-dependent neuroinflammation in mice

Post-operative cognitive dysfunction is associated with morbidity and mortality. However, its neuropathogenesis remains largely to be determined. Neuroinflammation and accumulation of β-amyloid (Aβ) have been reported to contribute to cognitive dysfunction in humans and cognitive impairment in animals. Our recent studies have established a pre-clinical model in mice, and have found that the peripheral surgical wounding without the influence of general anesthesia induces an age-dependent Aβ accumulation and cognitive impairment in mice. We therefore set out to assess the effects of peripheral surgical wounding, in the absence of general anesthesia, on neuroinflammation in mice with different ages. Abdominal surgery under local anesthesia was established in 9 and 18 month-old mice. The levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), Iba1 positive cells (the marker of microglia activation), CD33, and cognitive function in mice were determined. The peripheral surgical wounding increased the levels of TNF-α, IL-6, and Iba1 positive cells in the hippocampus of both 9 and 18 month-old mice, and age potentiated these effects. The peripheral surgical wounding increased the levels of CD33 in the hippocampus of 18, but not 9, month-old mice. Finally, anti-inflammatory drug ibuprofen ameliorated the peripheral surgical wounding-induced cognitive impairment in 18 month-old mice. These data suggested that the peripheral surgical wounding could induce an age-dependent neuroinflammation and elevation of CD33 levels in the hippocampus of mice, which could lead to cognitive impairment in aged mice. Pending further studies, anti-inflammatory therapies may reduce the risk of postoperative cognitive dysfunction in elderly patients.

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

Volatile anesthetics are used widely for achieving a state of unconsciousness, yet these agents are incompletely understood in their mechanisms of action and effects on neural development. There is mounting evidence that children exposed to anesthetic agents sustain lasting effects on learning and memory. The explanation for these behavioral changes remains elusive, although acute neuronal death after anesthesia is commonly believed to be a principal cause. Rodent models have shown that isoflurane exposure in newborns induces acute neuroapoptosis and long-term cognitive impairment. However, the assessment of predisposing factors is lacking. We investigated the role of sex by delivering isoflurane to postnatal day (P)7 male and female Sprague Dawley rats for 4 h. Brain cell death was assessed 12 h later using FluoroJade C staining in the thalamus, CA1-3 regions of hippocampus, and dentate gyrus. Behavior was assessed separately using a series of object recognition tasks and a test of social memory beginning at P38. We found that isoflurane exposure significantly increased neuronal death in each brain region with no difference between sexes. Behavioral outcome was also equivalent in simple novel object recognition. However, only males were impaired in the recognition of objects in different locations and contexts. Males also exhibited deficient social memory while females were intact. The profound behavioral impairment in males relative to females, in spite of comparable cell death, suggests that males are more susceptible to long-term cognitive effects and this outcome may not be exclusively attributed to neuronal death.

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

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

The potential dual effects of sevoflurane on AKT/GSK3β signaling pathway

Background

Anesthesia with multiple exposures of commonly used inhalation anesthetic sevoflurane induces neuroinflammation and cognitive impairment in young mice, but anesthesia with a single exposure to sevoflurane does not. AKT/glycogen synthase kinase 3β (GSK3β) signaling pathway is involved in neurotoxicity and neurobehavioral deficits. However, whether sevoflurane can induce a dual effect (increase versus decrease) on the activation of AKT/GSK3β signaling pathway remains to be determined. We therefore set out to assess the effects of sevoflurane on AKT/GSK3β signaling pathway in vivo and in vitro.

Methods

Six day-old wild-type mice were exposed to 3% sevoflurane two hours daily for one or three days. In the in vitro studies, H4 human neuroglioma cells were treated with 4% sevoflurane for two or six hours. We then determined the effects of different sevoflurane treatments on the levels of phosphorylated (P)-GSK3β(ser9) and P-AKT(ser473) by using Western blot analysis.

Results

Here we show that anesthesia with 3% sevoflurane two hours daily for one day increased the levels of P-GSK3β(ser9) and P-AKT(ser473), but the anesthesia with 3% sevoflurane daily for three days decreased them in the mice. The treatment with 4% sevoflurane for two hours increased, but the treatment with 4% sevoflurane for six hours decreased, the levels of P-GSK3β(ser9) and P-AKT(ser473) in the H4 human neuroglioma cells.

Conclusions

Anesthetic sevoflurane might induce a dual effect (increase versus decrease) on the activation of the AKT/GSK3β signaling pathway. These studies have established a system to perform further studies to determine the effects of sevoflurane on brain function.

Early exposure to sevoflurane inhibits Ca(2+) channels activity in hippocampal CA1 pyramidal neurons of developing rats

Sevoflurane is one of inhalation anesthetics and has been commonly used in obstetric and pediatric anesthesia. The widespread use of sevoflurane in newborns and infants has made its safety a health issue of concern. Voltage-gated Ca(2+) channels (VGCCs) play an important role in neuronal excitability and are essential for normal brain development. However, the role of sevoflurane on regulating Ca(2+) channels during the period of rapid brain development is still not well understood. The aim of this study is to explore the effects of sevoflurane on voltage-gated Ca(2+) channels for hippocampal CA1 pyramidal neurons during the period of rapid brain development. 1-week-old Sprague-Dawley rats were randomly divided into 3 groups: control group, 2.1% sevoflurane group (exposed to 2.1% sevoflurane for 6h) and 3% sevoflurane group (exposed to 3% sevoflurane for 6h). Whole-cell patch clamp technique was used. I-V curve, steady-state activation and inactivation curves of Ca(2+) channels were studied in rats of the both 3 treated groups at 5 different ages (1 week, 2 weeks, 3 weeks, 4 and 5 weeks old). After anesthesia with sevoflurane at 1-week-old rats, Ca(2+) channels current density was significantly decreased at week 1 and week 2 (p<0.01). And 3% sevoflurane exposure resulted in a rightward shift in steady-state activation curve at week 1 and week 2, as well as the inactivation curve from week 1 to week 3. However, the 2.1% sevoflurane-induced rightward shift was only found in steady-state inactivation curve of Ca(2+) channels at week 1 and week 2. Both the slope factor (k) of Ca(2+) channels activation and inactivation curves increased by 3% sevoflurane at week 1 (p<0.05). Therefore, early exposure to sevoflurane persistently inhibits Ca(2+) channels activity in hippocampal CA1 pyramidal neurons of developing rats but the development of Ca(2+) channels recovers to normal level at juvenile age. Moreover, the inhibition of 3% sevoflurane on VGCCs is greater than that of 2.1% sevoflurane.

Neonatal Exposure to Sevoflurane in Mice Causes Deficits in Maternal Behavior Later in Adulthood

Background:

In animal models, exposure to general anesthetics induces widespread increases in neuronal apoptosis in the developing brain. Subsequently, abnormalities in brain functioning are found in adulthood, long after the anesthetic exposure. These abnormalities include not only reduced learning abilities but also impaired social behaviors, suggesting pervasive deficits in brain functioning. But the underlying features of these deficits are still largely unknown.

Methods:

Six-day-old C57BL/6 female mice were exposed to 3% sevoflurane for 6 h with or without hydrogen (1.3%) as part of the carrier gas mixture. At 7–9 weeks of age, they were mated with healthy males. The first day after parturition, the maternal behaviors of dams were evaluated. The survival rate of newborn pups was recorded for 6 days after birth.

Results:

Female mice that received neonatal exposure to sevoflurane could mate normally and deliver healthy pups similar to controls. But these dams often left the pups scattered in the cage and nurtured them very little, so that about half of the pups died within a couple of days. Yet, these dams did not show any deficits in olfactory or exploratory behaviors. Notably, pups born to sevoflurane-treated dams were successfully fostered when nursed by control dams. Mice coadministered of hydrogen gas with sevoflurane did not exhibit the deficits of maternal behaviors.

Conclusion:

In an animal model, sevoflurane exposure in the developing brain caused serious impairment of maternal behaviors when fostering their pups, suggesting pervasive impairment of brain functions including innate behavior essential to species survival.

Involvement of the blood-brain barrier opening in cognitive decline in aged rats following orthopedic surgery and high concentration of sevoflurane inhalation

The underlying causes of postoperative cognitive decline (POCD) in old patients remained unelucidated, and there are little descriptions on mechanisms associated with the blood-brain barrier (BBB) disruption during POCD. We therefore tested the effects of orthopedic surgery with different concentrations of sevoflurane for 2 h on the behavior test and the BBB permeability in aged rats. 18-month rats were divided into control group and surgical group with propofol anesthesia (0.7 mgkg(-1) min(-1)) and 1.0 MAC, 1.3 MAC, and 1.5 MAC sevoflurane inhalation for 2 h. We assessed their cognitive function via Y-maze and fear conditioning test on day 1, 3, and 7 after experiments. Animals were then assigned to control group, propofol (2 h, 0.7 mgkg(-1) min(-1)) group, surgery plus propofol group and surgery plus 1.5 MAC sevoflurane inhalation for 2h. Their hippocampal BBB permeability was detected with Evans blue quantification. Alterations of tight junctions in hippocampus were measured with occludin and claudin-5 western blot. Then we assessed matrix metalloproteinase-2,9 (MMP-2,9) via western blot and immunohistochemistry staining at day 1, 3, 7, and 14 after experiments. Surgery impaired cognitive function and increased Evans blue leakage into the hippocampus in aged rats while 2 h of 1.5 MAC sevoflurane inhalation potentiated these effects. Surgery induced occludin protein expression decreases and MMP-2,9 proteins increase and these influences can be enhanced by high concentration of sevoflurane inhalation. In conclusion, 1.5 MAC sevoflurane for 2 h exacerbated cognitive impairment induced by orthopedic surgery in aged rats and the breach in BBB may be involved in this process.

Surgical incision-induced nociception causes cognitive impairment and reduction in synaptic NMDA receptor 2B in mice

Postoperative cognitive dysfunction (POCD) is associated with impairments in daily functioning, and increased morbidity and mortality. However, the causes and neuropathogenesis of POCD remain largely unknown. Uncontrolled pain often occurs postoperatively. We therefore set out to determine the effects of surgical incision-induced nociception on the cognitive function and its underlying mechanisms in 3- and 9-month-old mice. The mice had surgical incision in the hindpaw and then were tested for nociceptive threshold, learning, and memory. Brain levels of NMDA receptor and cyclin-dependent kinase 5 (CDK5) were also assessed. We found that surgical incision-induced nociception in mice led to a decreased freezing time in the tone test (which assesses the hippocampus-independent learning and memory function), but not the context test, of Fear Conditioning System at 3 and 7 d, but not 30 d post incision in 9-month-old, but not 3-month-old mice. Consistently, the surgical incision selectively decreased synaptic NMDA receptor 2B levels in the medial prefrontal cortex, and increased levels of tumor necrosis factor-α and CDK5 in the cortex, but not hippocampus, of the mice. Finally, eutectic mixture of local anesthetics and CDK5 inhibitor, roscovitine, attenuated the surgical incision-induced reduction in the synaptic NMDA receptor 2B levels and learning impairment. These results suggested that surgical incision-induced nociception reduced the synaptic NMDA receptor 2B level in the medial prefrontal cortex of mice, which might lead to hippocampus-independent learning impairment, contributing to POCD. These findings call for further investigation to determine the role of surgical incision-induced nociception in POCD.

Pyrrolidine dithiocarbamate attenuates surgery-induced neuroinflammation and cognitive dysfunction possibly via inhibition of nuclear factor κB

Surgery induces learning and memory impairment. Neuroinflammation may contribute to this impairment. Nuclear factor κB (NF-κB) is an important transcription factor to regulate the expression of inflammatory cytokines. We hypothesize that inhibition of NF-κB by pyrrolidine dithiocarbamate (PDTC) reduces neuroinflammation and the impairment of learning and memory. To test this hypothesis, four-month-old male Fischer 344 rats were subjected to right carotid exploration under propofol and buprenorphine anesthesia. Some rats received two doses of 50mg/kg PDTC given intraperitoneally 30min before and 6h after the surgery. Rats were tested in the Barnes maze and fear conditioning paradigm begun 6days after the surgery. Expression of various proteins related to inflammation was examined in the hippocampus at 24h or 21days after the surgery. Here, surgery, but not anesthesia alone, had a significant effect on prolonging the time needed to identify the target hole during the training sessions of the Barnes maze. Surgery also increased the time for identifying the target hole in the long-term memory test and decreased context-related learning and memory in fear conditioning test. Also, surgery increased nuclear expression of p65, a NF-κB component, decreased cytoplasmic amount of inhibitor of NF-κB, and increased the expression of interleukin-1β, interleukin-6, ionized calcium binding adaptor molecule 1 and active matrix metalloproteinase 9 (MMP-9). Finally, surgery enhanced IgG extravasation in the hippocampus. These surgical effects were attenuated by PDTC. These results suggest that surgery, but not propofol-based anesthesia, induces neuroinflammation and impairment of learning and memory. PDTC attenuates these effects possibly by inhibiting NF-κB activation and the downstream MMP-9 activity.

Early life exposure to sevoflurane impairs adulthood spatial memory in the rat

Sevoflurane is a general anesthetic commonly used in the pediatric setting because it is sweet-smelling, nonflammable, fast acting and has a very short recovery time. Although recent clinical data suggest that early anesthesia exposure is associated with subsequent learning and memory problems, it is difficult to determine the exact scope of developmental neurotoxicity associated with exposure to specific anesthetics such as sevoflurane. This is largely due to inconsistencies in the literature. Thus, in the present studies we evaluated the effect of early life exposure to sevoflurane (1%, 2%, 3% or 4%) on adulthood memory impairment in Sprague-Dawley rats. Animals were exposed to different regimens of sevoflurane anesthesia on postnatal days (PNDs) 3, 7, or 14 or at 7 weeks (P7W) of age and spatial memory performance was assessed in adulthood using the Morris Water Maze (MWM). Rats exposed to sevoflurane exhibited significant memory impairment which was concentration and exposure duration dependent. Disruption of MWM performance was more severe in animals exposed on both PNDs 3 and 7 than in animals exposed on both PNDs 3 and 14. The younger the animal's age at the time of exposure, the more significant the effect on later MWM performance. Compared to the neonates, animals exposed at P7W were relatively insensitive to sevoflurane: memory was impaired in this group only after repeated exposures to low doses or single exposures to high doses. Early life exposure to sevoflurane can result in spatial memory impairments in adulthood and the shorter the interval between exposures, the greater the deficit.

Volatile anesthetics-induced neuroinflammatory and anti-inflammatory responses

Volatile anesthetics have been the major anesthetics used clinically for more than 150 years. They provide all components of general anesthesia and are easy to be applied and monitored with modern equipment and technology. In addition to having anesthetic property, volatile anesthetics have multiple other effects. Many studies have clearly shown that volatile anesthetics can reduce systemic and local inflammatory responses induced by various stimuli in humans and animals. On the other hand, recent animal studies have shown that volatile anesthetics may induce mild neuroinflammation. These dual effects on inflammation may have significant biological implications and are briefly reviewed here.