Quantitative assessment of new cell proliferation in the dentate gyrus and learning after isoflurane or propofol anesthesia in young and aged rats

Propofol produces neurotoxicity by inducing mitochondrial apoptosis

Propofol is a fast and short-acting intravenous anesthetic widely used in clinical anesthesia and intensive care unit sedation. However, its use can cause abnormal effects on the central nervous system. Thus, the purpose of this study was to investigate the mechanism of propofol on primary hippocampal neuron injury. In addition, we aimed to determine whether a correlation exists between propofol and mitochondrial apoptosis-induced neurotoxicity. Hippocampal neurons cultured for 4 days were exposed to different drugs. The treatment groups were divided according to drug exposure into propofol, a rotenone inhibitor, and a coenzyme Q10 agonist groups. The final concentrations of propofol were 1, 10 and 100 µM. The content of ATP and reactive oxygen species (ROS) in the neurons of each group were detected using commercial kits in the culture supernatant after 3 h of drug exposure. Western blotting was used to analyze the expression of apoptosis-related proteins. The JC-1 kit was used to detect the mitochondrial membrane potential. The results revealed that, compared with the non-propofol treatment groups, the expression of apoptosis-related proteins, ATP content, and mitochondrial membrane potential were significantly decreased while the ROS content was markedly increased in the propofol treatment group. In conclusion, propofol treatment promoted damage to hippocampal neuronal mitochondria in a dose-dependent manner. This damage may lead to neuronal apoptosis and neurotoxicity by inducing the inhibition of mitochondrial respiratory chain complex I.

The importance of non-coding RNAs in environmental stress-related developmental brain disorders: A systematic review of evidence associated with exposure to alcohol, anesthetic drugs, nicotine, and viral infections

Brain development is a dynamic and lengthy process that includes cell proliferation, migration, neurogenesis, gliogenesis, synaptogenesis, and pruning. Disruption of any of these developmental events can result in long-term outcomes ranging from brain structural changes, to cognitive and behavioral abnormality, with the mechanisms largely unknown. Emerging evidence suggests non-coding RNAs (ncRNAs) as pivotal molecules that participate in normal brain development and neurodevelopmental disorders. NcRNAs such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are transcribed from the genome but not translated into proteins. Many ncRNAs have been implicated as tuners of cell fate. In this review, we started with an introduction of the current knowledge of lncRNAs and miRNAs, and their potential roles in brain development in health and disorders. We then reviewed and discussed the evidence of ncRNA involvement in abnormal brain development resulted from alcohol, anesthetic drugs, nicotine, and viral infections. The complex connections among these ncRNAs were also discussed, along with potential overlapping ncRNA mechanisms, possible pharmacological targets for therapeutic/neuroprotective interventions, and potential biomarkers for brain developmental disorders.

The Effects of Anesthesia on Adult Hippocampal Neurogenesis

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

Upregulation of miR-496 Rescues Propofol-induced Neurotoxicity by Targeting Rho Associated Coiled-coil Containing Protein Kinase 2 (ROCK2) in Prefrontal Cortical Neurons

OBJECTIVE

Early exposure to general anesthesia in children might be a potentially highrisk factor for learning and behavioral disorders. The mechanism of neurotoxicity induced by general anesthesia was not defined. miR-496 could regulate cerebral injury, while the roles of miR- 496 in neurotoxicity were not elucidated. Therefore, we aimed to investigate the effects of miR- 496 in neurotoxicity induced by propofol.

METHODS

Primary Prefrontal Cortical (PFC) neurons were isolated from neonatal rats and treated with propofol to induce neurotoxicity. Cell viability was detected by (3-(4,5-Dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and cell apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The target relationship of miR-496 and Rho Associated Coiled-Coil Containing Protein Kinase 2 (ROCK2) was explored using luciferase assays.

RESULTS

Propofol decreased cell viability, promoted cell apoptosis, and decreased the expression of miR-496 in PFC neurons in a dose-dependent manner. Overexpression of miR-496 attenuated neurotoxicity induced by propofol in PFC neurons. ROCK2 was a target of miR-496, and miR-496 oppositely modulated the expression of ROCK2. Besides, propofol increased the expression of ROCK2 through inhibiting miR-496 in PFC neurons. Overexpression of miR-496 attenuated propofol- induced neurotoxicity by targeting ROCK2 in PFC neurons.

CONCLUSION

miR-496 was decreased in PFC neurons treated with propofol, and overexpression of miR-496 attenuated propofol-induced neurotoxicity by targeting ROCK2. miR-496 and ROCK2 may be promising targets for protecting propofol-induced neurotoxicity.

L-655,708 Does not Prevent Isoflurane-induced Memory Deficits in Old Mice

Background

General anesthesia and increasing age are two main risk factors for postoperative cognitive dysfunction (POCD). Effective agents for the prevention or treatment of POCD are urgently needed. L-655,708, an inverse agonist of α5 subunit-containing γ-aminobutyric acid subtype A (α5GABA_A) receptors, can prevent anesthesia-induced memory deficits in young animals. However, there is a lack of evidence of its efficacy in old animals.

Methodology

Young (3- to 5-month-old) and old (18- to 20-month-old) mice were given an inhalation of 1.33% isoflurane for 1 hour and their associative memory was evaluated 24 hours after anesthesia using fear-conditioning tests (FCTs). To evaluate the effect of L-655,708, mice received intraperitoneal injections of L-655,708 (0.7 mg/kg) or vehicle 30 minutes before anesthesia.

Results

Old mice exhibited impaired memory and lower hippocampal α5GABA_A levels than young mice under physiological conditions. Pre-injections of L-655,708 significantly alleviated isoflurane-induced memory decline in young mice, but not in old mice.

Conclusions

L-655,708 is not as effective for the prevention of POCD in old mice as it is in young mice. The use of inverse agonists of α5GABA_A in preventing POCD in old patients should be carefully considered.

By regulating miR-182-5p/BCL10/CYCS, sufentanil reduces the apoptosis of umbilical cord mesenchymal stem cells caused by ropivacaine

Sufentanil is a type of opioid analgesic and is usually used to facilitate painless labor in combination with the local anesthetic ropivacaine. One aim of the current study was to investigate the effects of sufentanil and ropivacaine on umbilical cord mesenchymal stem cells (UCMSCs). A second aim of this study was to determine whether sufentanil attenuated the cytotoxicity of ropivacaine in vitro. UCMSCs were divided into 3 groups: one was treated with ropivacaine at a concentration of 50, 100, 200, or 400 μg/mL, another was treated with sufentanil at a concentration of 0.5, 5, 50, or 500 nmol/L, and a third was treated with a combination of ropivacaine at a concentration of 200 μg/mL and sufentanil at a concentration of 0.5, 5, 50, or 500 nmol/L. Results indicated that cell proliferation decreased in cells treated with ropivacaine while it increased in cells treated with sufentanil. In addition, sufentanil limited the inhibitory effect of ropivacaine on UCMSC growth in a dose- and time-dependent manner. Combined treatment with ropivacaine at a concentration of 200 μg/mL and sufentanil at a concentration of 500 nmol/L decreased the proportion of dead and apoptotic UCMSCs, and fewer cells were arrested in the S phase compared to cells treated with ropivacaine. Sufentanil inhibited the apoptosis induced by ropivacaine by increasing miR-182-5p, which regulated the expression of mRNA of the pro-apoptotic genes B-cell lymphoma/leukemia 10 (BCL10) and cytochrome c, somatic (CYCS). Sufentanil also increased the expression of mRNA of anti-apoptotic genes. In short, ropivacaine inhibits the cell viability and induces the apoptosis of UCMSCs in vitro while sufentanil attenuates this apoptosis by regulating miR182-5p/BCL10/CYCS.

Inhibition of α5 GABAA receptors has preventive but not therapeutic effects on isoflurane-induced memory impairment in aged rats

The α5 subunit-containing gamma-amino butyric acid type A receptors (α5 GABAARs) are a distinct subpopulation that are specifically distributed in the mammalian hippocampus and also mediate tonic inhibitory currents in hippocampal neurons. These tonic currents can be enhanced by low-dose isoflurane, which is associated with learning and memory impairment. Inverse agonists of α5 GABAARs, such as L-655,708, are able to reverse the short-term memory deficit caused by low-dose isoflurane in young animals. However, whether these negative allosteric modulators have the same effects on aged rats remains unclear. In the present study, we mainly investigated the effects of L-655,708 on low-dose (1.3%) isoflurane-induced learning and memory impairment in elderly rats. Young (3-month-old) and aged (24-month-old) Wistar rats were randomly assigned to receive L-655,708 0.5 hour before or 23.5 hours after 1.3% isoflurane anesthesia. The Morris Water Maze tests demonstrated that L-655,708 injected before or after anesthesia could reverse the memory deficit in young rats. But in aged rats, application of L-655,708 only before anesthesia showed similar effects. Reverse transcription-polymerase chain reaction showed that low-dose isoflurane decreased the mRNA expression of α5 GABAARs in aging hippocampal neurons but increased that in young animals. These findings indicate that L-655,708 prevented but could not reverse 1.3% isoflurane-induced spatial learning and memory impairment in aged Wistar rats. All experimental procedures and protocols were approved by the Experimental Animal Ethics Committee of Academy of Military Medical Science of China (approval No. NBCDSER-IACUC-2015128) in December 2015.

Repeat propofol anesthesia does not exacerbate plaque deposition or synapse loss in APP/PS1 Alzheimer's disease mice

Background

There is increasing interest in whether anesthetic agents affect the risk or progression of Alzheimer’s disease (AD). To mitigate many of the methodological issues encountered in human retrospective cohort studies we have used a transgenic model of AD to investigate the effect of propofol on AD pathology.

Methods

Six month-old amyloid precursor protein/presenilin 1 (APP/PS1) transgenic AD mice and control mice were exposed to 3 doses of propofol (200 mg/kg) or vehicle, delivered at monthly intervals.

Results

There was no difference in the extent of β-amyloid (Aβ) immunolabeled plaque deposition in APP/PS1 mice in vehicle versus propofol treatment groups. We also detected no difference in plaque-associated synapse loss in APP/PS1 mice following repeat propofol exposure relative to vehicle. Western blotting indicated that there was no difference in post-synaptic density protein 95, synaptophysin or glutamic acid decarboxylase 65/67 expression in control or APP/PS1 mice subjected to repeat propofol treatment relative to vehicle.

Conclusions

These data suggest that repeat propofol anesthesia may not exacerbate plaque deposition or associated synapse loss in AD. Interestingly, this data also provides some of the first evidence suggesting that repeat propofol exposure in adult wild-type mice does not result in robust long-term alterations in the levels of key excitatory and inhibitory synaptic markers.

Electronic supplementary material

The online version of this article (10.1186/s12871-018-0509-5) contains supplementary material, which is available to authorized users.

Hippocampal neurogenesis in the C57BL/6J mice at early adulthood following prenatal alcohol exposure

We examined the effect of chronic prenatal alcohol exposure (PAE) on the process of adult neurogenesis in C57BL/6J mice at early adulthood (PND 56). Pregnant mice, and their in utero litters, were exposed to alcohol, through oral gavage, on gestational days 7-16, with recorded blood alcohol concentrations averaging 184 mg/dL (CA group). Two control groups, sucrose (CAc) and non-treated (NTc) control groups were also examined. The brains of pups at PND 56 from each experimental group were sectioned in a sagittal plane, and stained for Nissl substance with cresyl violet, and immunostained for Ki-67 which labels proliferative cells and doublecortin (DCX) for immature neurons. Morphologically, the neurogenic pattern was identical in all three groups studied. Populations of Ki-67 immunopositive cells in the dentate gyrus were not statistically significantly different between the experimental groups and there were no differences between the sexes. Thus, the PAE in this study does not appear to have a strong effect on the proliferative process in the adult hippocampus. In contrast, the numbers of immature neurons, labeled with DCX, was statistically significantly lower in the prenatal alcohol exposed mice compared with the two control groups. Alcohol significantly lowered the number of DCX hippocampal cells in the male mice, but not in the female mice. This indicates that the PAE appears to lower the rate of conversion of proliferative cells to immature neurons and this effect of alcohol is sexually dimorphic. This lowered number of immature neurons in the hippocampus appears to mirror hippocampal dysfunctions observed in FASD children.

Early postnatal exposure to isoflurane causes cognitive deficits and disrupts development of newborn hippocampal neurons via activation of the mTOR pathway

Clinical and preclinical studies indicate that early postnatal exposure to anesthetics can lead to lasting deficits in learning and other cognitive processes. The mechanism underlying this phenomenon has not been clarified and there is no treatment currently available. Recent evidence suggests that anesthetics might cause persistent deficits in cognitive function by disrupting key events in brain development. The hippocampus, a brain region that is critical for learning and memory, contains a large number of neurons that develop in the early postnatal period, which are thus vulnerable to perturbation by anesthetic exposure. Using an in vivo mouse model we demonstrate abnormal development of dendrite arbors and dendritic spines in newly generated dentate gyrus granule cell neurons of the hippocampus after a clinically relevant isoflurane anesthesia exposure conducted at an early postnatal age. Furthermore, we find that isoflurane causes a sustained increase in activity in the mechanistic target of rapamycin pathway, and that inhibition of this pathway with rapamycin not only reverses the observed changes in neuronal development, but also substantially improves performance on behavioral tasks of spatial learning and memory that are impaired by isoflurane exposure. We conclude that isoflurane disrupts the development of hippocampal neurons generated in the early postnatal period by activating a well-defined neurodevelopmental disease pathway and that this phenotype can be reversed by pharmacologic inhibition.

The United States Food and Drug Administration has recently warned that exposure to anesthetic and sedative drugs during the third trimester of prenatal development and during the first 3 years of life may cause lasting impairments in cognitive function. The mechanisms by which this undesirable side effect occurs are unknown. In this manuscript, we present evidence in mice that early developmental exposure to isoflurane, a canonical general anesthetic, disrupts the appropriate development of neurons in the hippocampus, a brain region associated with learning and memory. Isoflurane also causes up-regulation of the mechanistic target of rapamycin (mTOR) pathway, a signaling system that has been associated with other neurodevelopmental cognitive disorders. Treatment with an inhibitor of the mTOR pathway after isoflurane exposure normalizes neuronal development and also ameliorates the impairments in learning induced by isoflurane. We conclude that early exposure to isoflurane can cause learning deficits via actions on the mTOR pathway, and that this mechanism represents a potentially druggable target to minimize the side effects of anesthetics on the developing brain.

Neurogenesis and developmental anesthetic neurotoxicity

The mechanism by which anesthetics might act on the developing brain in order to cause long term deficits remains incompletely understood. The hippocampus has been identified as a structure that is likely to be involved, as rodent models show numerous deficits in behavioral tasks of learning that are hippocampal-dependent. The hippocampus is an unusual structure in that it is the site of large amounts of neurogenesis postnatally, particularly in the first year of life in humans, and these newly generated neurons are critical to the function of this structure. Intriguingly, neurogenesis is a major developmental event that occurs during postulated windows of vulnerability to developmental anesthetic neurotoxicity across the different species in which it has been studied. In this review, we examine the evidence for anesthetic effects on neurogenesis in the early postnatal period and ask whether neurogenesis should be studied further as a putative mechanism of injury. Multiple anesthetics are considered, and both in vivo and in vitro work is presented. While there is abundant evidence that anesthetics act to suppress neurogenesis at several different phases, evidence of a causal link between these effects and any change in learning behavior remains elusive.

Post-operative cognitive dysfunction at 3 months in adults after non-cardiac surgery: a qualitative systematic review

BACKGROUND

Post-operative cognitive dysfunction is defined as a decline in cognitive functions that occurs after surgery, but different diagnostic criteria and incidences have been reported in medical literature. Our aim was to determine incidence of post-operative cognitive dysfunction 3 months after non-cardiac surgery in adults.

METHODS

A systematic review of available evidence was performed by PRISMA guidelines. A search was done in May-July 2015 on PubMed, EMBASE, CINAHL, LILACS, Scielo, Clinical Trials, and Grey Literature Reports. Inclusion criteria were prospective design studies with patients over 18 years old, surgery under general or regional anesthesia, follow-up for 3 months, and use of a neurocognitive battery for diagnosis. We excluded studies made on cardiac or brain surgery patients. Risk of bias was assessed using tools from National Heart Lung and Blood Institute.

RESULTS

We selected 24 studies. Average age was 68 years. Only five studies reported incidence of cognitive decline for a non-surgical control group. Median number of tests used was 5 (range 3-13). Pooled incidence of post-operative cognitive dysfunction at 3 months was 11.7% [95% CI 10.9-12.5] but with several methodological differences between studies. Increasing age was the most consistent risk factor identified (seven studies).

CONCLUSIONS

Post-operative cognitive dysfunction in patients is frequent, especially in patients over 60 years old. Limitations include methodological differences in studies. Efforts must be made to reach a consensus in definition and diagnosis for future research.

Effect of sevoflurane and halothane anesthesia on cognitive function and immune function in young rats

In the current study, we scrutinized the effect of sevoflurane and halothane on cognitive and immune function in young rats. The rats were divided into following groups: sevoflurane, halothane and sevoflurane + halothane groups, respectively. The rats were regularly treated with the pre-determined treatment. We also scrutinized the serum proinflammatory cytokines including IL-10, IL-4 and IL-2; brain level IL-1β; hippocampal neuronal apoptosis concentration were estimated. The water maze test was performed in rats for the estimation of cognitive ability. During the water maze test, on the 1st day the sevoflurane group showed the latency; sevoflurane and sevoflurane + halothane group demonstrated the declined latency gradually as compared to the control group rats after the 3 days. The latency of the control, halothane, sevoflurane + halothane group rats showed the reduced latency and also showed the reduced crossing circle times. The hippocampal neuron apoptosis was significantly increased in halothane and sevoflurane + halothane group as compared to control group rats, respectively. Control group rats demonstrated the increased neuron apoptosis. The proinflammatory cytokines including IL-10 and IL-4 was significantly higher in sevoflurane, halothane and sevoflurane + halothane group rats after anesthesia and the whole brain IL-1β was significantly decrease in the sevoflurane, halothane and sevoflurane + halothane as compared to control group. Sevoflurane can inhibit the anesthesia effect of halothane on the immune and cognitive function of rats.

Prolonged Treatment with Propofol Transiently Impairs Proliferation but Not Survival of Rat Neural Progenitor Cells In Vitro

Neurocognitive dysfunction is common in survivors of intensive care. Prolonged sedation has been implicated but the mechanisms are unclear. Neurogenesis continues into adulthood and is implicated in learning. The neural progenitor cells (NPC) that drive neurogenesis have receptors for the major classes of sedatives used clinically, suggesting that interruption of neurogenesis may partly contribute to cognitive decline in ICU survivors. Using an in vitro system, we tested the hypothesis that prolonged exposure to propofol concentration- and duration-dependently kills or markedly decreases the proliferation of NPCs. NPCs isolated from embryonic day 14 Sprague-Dawley rat pups were exposed to 0, 2.5, or 5.0 μg/mL of propofol, concentrations consistent with deep clinical anesthesia, for either 4 or 24 hours. Cells were assayed for cell death and proliferation either immediately following propofol exposure or 24 hours later. NPC death and apoptosis were measured by propidium iodine staining and cleaved caspase-3 immunocytochemistry, respectively, while proliferation was measured by EdU incorporation. Staurosporine (1μM for 6h) was used as a positive control for cell death. Cells were analyzed with unbiased high-throughput immunocytochemistry. There was no cell death at either concentration of propofol or duration of exposure. Neither concentration of propofol impaired NPC proliferation when exposure lasted 4 h, but when exposure lasted 24 h, propofol had an anti-proliferative effect at both concentrations (P < 0.0001, propofol vs. control). However, this effect was transient; proliferation returned to baseline 24 h after discontinuation of propofol (P = 0.37, propofol vs. control). The transient but reversible suppression of NPC proliferation, absence of cytotoxicity, and negligible effect on the neural stem cell pool pool suggest that propofol, even in concentrations used for clinical anesthesia, has limited impact on neural progenitor cell biology.

Post-Exposure Exercise Fails to Ameliorate Memory Impairment Induced by Propofol and Ketamine in Developing Rats

Background

This aim of this study was to determine the effects of ketamine-propofol combination on learning and memory, as well as exercise, on anesthetic neurotoxicity.

Material/Methods

A ketamine-propofol combination was administered once (group SKP, Single Ketamine Propofol) on P7 (postnatal day 7) or in 3 treatments on P6, P8, and P10 (group MKP, Multiple Ketamine Propofol). Rat pups in group C (Control) received equivalent volumes of normal saline in 3 injections on P6, P8, and P10. Rats designated MKPR (Multiple Ketamine Propofol and running) and CR (Control and running) began running exercise on P21 on wheels. Learning and memory was assessed by Morris water maze and fear conditioning tests. Hippocampal neurogenesis of rats was detected by BrdU immunofluorescence.

Results

MKP rats had longer latency to platform than group C during training in the Morris water maze; SKP rats stayed in the target quadrant longer than MKP rats during testing (P<0.05). Rats in running groups had shorter latency than non-running rats, but running had no interaction with anesthesia exposure.

Conclusions

Repeat ketamine-propofol combination doses increase risk of memory impairment in developing rats. Running has no impact on anesthetic neurotoxicity.

Effects of docosahexaenoic acid on learning and memory impairment induced by repeated propofol anesthesia in young rats

The aim of the present study was to investigate the effects of docosahexaenoic acid (DHA) on the learning and memory ability of young rats exposed to propofol, and its underlying mechanisms. Sprague Dawley rats (n=60) were randomly divided into six groups: Control group (group A); solvent control group (group B); propofol group (group C); low-dose DHA + propofol group (group D); medium dose DHA + propofol group (group E); and high-dose DHA + propofol group (group F). The Morris water maze (MWM) test was performed to evaluate the rats' learning and memory ability, and tissue samples from the hippocampi of the rats were obtained for biochemical analysis. The results of the MWM test revealed that DHA supplementation administered to young rats led to an evident decrease in the latency to find the maze platform, and a significant increase in the number of platform crossings in groups E and F compared with group C (P<0.05). High-performance liquid chromatography indicated that glutamate concentration levels were significantly lower and γ-aminobutyric acid concentration levels were significantly higher in the hippocampi of group E and F rats treated with DHA compared with group C rats (P<0.05). Furthermore, DHA treatment alleviated the decrease in brain-derived neurotrophic factor levels (P<0.05), and superoxide dismutase (P<0.05) and glutathione peroxidase (P<0.05) activities induced by the administration of propofol. Additionally, DHA treatment decreased malondialdehyde levels in the hippocampi of rats (P<0.05). The aforementioned findings demonstrate that DHA was able to effectively improve learning and memory dysfunction induced by repeated propofol-induced anesthesia in young rats. This data suggests that DHA may be a potential candidate for further preclinical studies aimed at treating postoperative cognitive dysfunction.

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.

Inhibition of propofol anesthesia on functional connectivity between LFPs in PFC during rat working memory task

Working memory (WM) refers to the temporary storage and manipulation of information necessary for performance of complex cognitive tasks. There is a growing interest in whether and how propofol anesthesia inhibits WM function. The aim of this study is to investigate the possible inhibition mechanism of propofol anesthesia based on the functional connections of multi-local field potentials (LFPs) and behavior during WM tasks. Adult SD rats were randomly divided into 3 groups: pro group (0.5 mg·kg⁻¹·min⁻¹,2 h), PRO group (0.9 mg·kg⁻¹·min⁻¹, 2 h) and control group. The experimental data were 16-channel LFPs obtained at prefrontal cortex with implanted microelectrode array in SD rats during WM tasks in Y-maze at 24, 48, 72, 96, 120 hours (day 1-day 5) after propofol anesthesia, and the behavior results of WM were recoded at the same time. Directed transfer function (DTF) method was applied to analyze the connections among LFPs directly. Furthermore, the causal networks were identified by DTF. The clustering coefficient (C), network density (D) and global efficiency (E_global) were selected to describe the functional connectivity quantitatively. The results show that: comparing with the control group, the LFPs functional connectivity in pro group were no significantly difference (p>0.05); the connectivity in PRO group were significantly decreased (p<0.05 at 24 hours, p<0.05 at 48 hours), while no significant difference at 72, 96 and 120 hours for rats (p>0.05), which were consistent with the behavior results. These findings could lead to improved understanding the mechanism of inhibition of anesthesia on WM functions from the view of connections among LFPs.

Regenerative toxicology: the role of stem cells in the development of chronic toxicities

INTRODUCTION

Human stem cell lines and their derivatives, as alternatives to the use of animal cells or cancer cell lines, have been widely discussed as cellular models in predictive toxicology. However, the role of stem cells in the development of long-term toxicities and carcinogenesis has not received great attention so far, despite growing evidence indicating the relationship of stem cell damage to adverse effects later in life. However, testing this in vitro is a scientific/technical challenge in particular due to the complex interplay of factors existing under physiological conditions. Current major research programs in stem cell toxicity are not aiming to demonstrate that stem cells can be targeted by toxicants. Therefore, this knowledge gap needs to be addressed in additional research activities developing technical solutions and defining appropriate experimental designs.

AREAS COVERED

The current review describes selected examples of the role of stem cells in the development of long-term toxicities in the brain, heart or liver and in the development of cancer.

EXPERT OPINION

The presented examples illustrate the need to analyze the contribution of stem cells to chronic toxicity in order to make a final conclusion whether stem cell toxicities are an underestimated risk in mechanism-based safety assessments. This requires the development of predictive in vitro models allowing the assessment of adverse effects to stem cells on chronic toxicity and carcinogenicity.

Mechanistic insights into neurotoxicity induced by anesthetics in the developing brain

Compelling evidence has shown that exposure to anesthetics used in the clinic can cause neurodegeneration in the mammalian developing brain, but the basis of this is not clear. Neurotoxicity induced by exposure to anesthestics in early life involves neuroapoptosis and impairment of neurodevelopmental processes such as neurogenesis, synaptogenesis and immature glial development. These effects may subsequently contribute to behavior abnormalities in later life. In this paper, we reviewed the possible mechanisms of anesthetic-induced neurotoxicity based on new in vitro and in vivo findings. Also, we discussed ways to protect against anesthetic-induced neurotoxicity and their implications for exploring cellular and molecular mechanisms of neuroprotection. These findings help in improving our understanding of developmental neurotoxicology and in avoiding adverse neurological outcomes in anesthesia practice.