Anesthetics interfere with the polarization of developing cortical neurons

A Scoping Review of the Mechanisms Underlying Developmental Anesthetic Neurotoxicity

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

Prolonged exposure of neonatal mice to sevoflurane leads to hyper-ramification in microglia, reduced contacts between microglia and synapses, and defects in adult behavior

Background

Prolonged exposure to general anesthetics during development is known to cause neurobehavioral abnormalities, but the cellular and molecular mechanisms involved are unclear. Microglia are the resident immune cells in the central nervous system and play essential roles in normal brain development.

Materials and methods

In the study, postnatal day 7 (P7) C57BL/6 mice were randomly assigned to two groups. In the sevoflurane (SEVO), mice were exposed to 2.5% sevoflurane for 4 h. In the control group, mice were exposed to carrier gas (30% O2/70% N2) for 4 h. Fixed brain slices from P14 to P21 mice were immunolabeled for ionized calcium-binding adapter molecule 1 (IBA-1) to visualize microglia. The morphological analysis of microglia in the somatosensory cortex was performed using ImageJ and Imaris software. Serial block face scanning electron microscopy (SBF-SEM) was performed to assess the ultrastructure of the microglia and the contacts between microglia and synapse in P14 and P21 mice. The confocal imaging of brain slices was performed to assess microglia surveillance in resting and activated states in P14 and P21 mice. Behavioral tests were used to assess the effect of microglia depletion and repopulation on neurobehavioral abnormalities caused by sevoflurane exposure.

Results

The prolonged exposure of neonatal mice to sevoflurane induced microglia hyper-ramification with an increase in total branch length, arborization area, and branch complexity 14  days after exposure. Prolonged neonatal sevoflurane exposure reduced contacts between microglia and synapses, without affecting the surveillance of microglia in the resting state or responding to laser-induced focal brain injury. These neonatal changes in microglia were associated with anxiety-like behaviors in adult mice. Furthermore, microglial depletion before sevoflurane exposure and subsequent repopulation in the neonatal brain mitigated anxiety-like behaviors caused by sevoflurane exposure.

Conclusion

Our experiments indicate that general anesthetics may harm the developing brain, and microglia may be an essential target of general anesthetic-related developmental neurotoxicity.

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

RATIONALE

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Central Cholinergic Synapse Formation in Optimized Primary Septal-Hippocampal Co-cultures

Septal innervation of basal forebrain cholinergic neurons to the hippocampus is critical for normal learning and memory and is severely degenerated in Alzheimer's disease. To understand the molecular events underlying physiological cholinergic synaptogenesis and remodeling, as well as pathological loss, we developed an optimized primary septal-hippocampal co-culture system. Hippocampal and septal tissue were harvested from embryonic Sprague-Dawley rat brain and cultured together at varying densities, cell ratios, and in the presence of different growth factors. We identified conditions that produced robust septal-hippocampal synapse formation. We used confocal microscopy with primary antibodies and fluorescent ligands to validate that this system was capable of generating developmentally mature cholinergic synapses. Such synapses were comprised of physiological synaptic partners and mimicked the molecular composition of in vivo counterparts. This co-culture system will facilitate the study of the formation, plasticity, and dysfunction of central mammalian cholinergic synapses.

Blockade of the NLRP3/caspase-1 axis attenuates ketamine-induced hippocampus pyroptosis and cognitive impairment in neonatal rats

Background

Multiple studies have revealed that repeated or long-term exposure to ketamine causes neurodegeneration and cognitive dysfunction. Pyroptosis is an inflammatory form of programmed cell death that has been linked to various neurological diseases. However, the role of NLRP3/caspase-1 axis-related pyroptosis in ketamine-induced neurotoxicity and cognitive dysfunction remains uncertain.

Methods

To evaluate whether ketamine caused NLRP3/caspase1-dependent pyroptosis, flow cytometry analysis, western blotting, ELISA test, histopathological analysis, Morris water maze (MWM) test, cell viability assay, and lactate dehydrogenase release (LDH) assay were carried out on PC12 cells, HAPI cells, and 7-day-old rats. In addition, the NLRP3 inhibitor MCC950 or the caspase-1 inhibitor VX-765 was used to investigate the role of the NLRP3/caspase-1 axis in ketamine-induced neurotoxicity and cognitive dysfunction.

Results

Our findings demonstrated that ketamine exposure caused cell damage and increased the levels of pyroptosis in PC12 cells, HAPI cells, and the hippocampus of neonatal rats. After continuous exposure to ketamine, targeting NLRP3 and caspase-1 with MCC950 or VX765 improved pyroptosis, reduced neuropathological damages, and alleviated cognitive dysfunction.

Conclusion

NLRP3/Caspase-1 axis-dependent pyroptosis is involved in ketamine-induced neuroinflammation and cognitive dysfunction, and it provides a promising strategy to treat ketamine-related neurotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02295-9.

Cleft Palate Repair: A New Maxillary Nerve Block Approach

OBJECTIVE

To introduce a different approach for maxillary nerve block (MNB), in cleft palate repair. To reduce the use of opioids during surgery and to prevent frequent respiratory complications by means of an adequate intra and postoperative pain relief.

PATIENTS AND METHODS

A prospective clinical trial was planned, to collect scientific evidences between 2 groups of patients with primary cleft palate, receiving surgery in 2 Pediatric centers of Buenos Aires, utilizing a different protocol.Sixty patients undergoing primary cleft palate repair in both hospitals, from January 2017 to July 2018, by senior surgeons and the same expert anesthesiologists' team, were included.Syndromic and secondary cases, and patients whose parents rejected to participate of this study were excluded. The first group called Hospital A included 45 children, the second group identified as Hospital B was formed by 15 patients.A combination of general whit local anesthesia and a bilateral regional MNB, was used in all the patients of the Hospital A. Utilizing an aspirating syringe, children received 0.15 ml/kg of lidocaine clorhidrate 2% with epinephrine 1:50.000, under direct vision through the spheno palatine holes, just before surgery. A traditional general anesthesia procedure plus local anesthesia, was utilized in all the patients treated at the Hospital B Medial blood pressure and cardiac frequency parameters were tested during induction, along the surgical procedure and in the immediate post op, to detect any sign of pain (12). After surgery, patient reactivity, airway depression symptoms, time of initial feeding and discharge time, were also monitored (13).This study was approved by the Hospitals Ethics Committees of both hospitals, and is in accordance with the 1975 Helsinki Declaration, as amended in 1983. The parents have signed an informed consent form for all the patients included.

RESULTS

Patients of both groups did not show any significant variant in the monitored parameters to detect signals of pain, along the surgery. The rest of controls during and after surgery showed significant differences in favor of the patients of Hospital A.

CONCLUSIONS

Bilateral regional MNB, under direct vision trough the spheno palatine holes results an effective, easy, and safe method for pain relief during and after primary cleft palate repair surgeries.The combination of slight general anesthesia with local anesthesia and regional blocks, results a good option to reduce opioids utilization, to prevent neurotoxicity, respiratory depression, sickness, and vomiting facilitating early feeding and patient discharge.

Activation of nicotinic acetylcholine receptors induces potentiation and synchronization within in vitro hippocampal networks

Nicotinic acetylcholine receptors (nAChRs) are known to play a role in cognitive functions of the hippocampus, such as memory consolidation. Given that they conduct Ca²⁺ and are capable of regulating the release of glutamate and γ-aminobutyric acid (GABA) within the hippocampus, thereby shifting the excitatory-inhibitory ratio, we hypothesized that the activation of nAChRs will result in the potentiation of hippocampal networks and alter synchronization. We used nicotine as a tool to investigate the impact of activation of nAChRs on neuronal network dynamics in primary embryonic rat hippocampal cultures prepared from timed-pregnant Sprague-Dawley rats. We perturbed cultured hippocampal networks with increasing concentrations of bath-applied nicotine and performed network extracellular recordings of action potentials using a microelectrode array. We found that nicotine modulated network dynamics in a concentration-dependent manner; it enhanced firing of action potentials as well as facilitated bursting activity. In addition, we used pharmacological agents to determine the contributions of discrete nAChR subtypes to the observed network dynamics. We found that β4-containing nAChRs are necessary for the observed increases in spiking, bursting, and synchrony, while the activation of α7 nAChRs augments nicotine-mediated network potentiation but is not necessary for its manifestation. We also observed that antagonists of N-methyl-D-aspartate receptors (NMDARs) and group I metabotropic glutamate receptors (mGluRs) partially blocked the effects of nicotine. Furthermore, nicotine exposure promoted autophosphorylation of Ca²⁺ /calmodulin-dependent kinase II (CaMKII) and serine 831 phosphorylation of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunit GluA1. These results suggest that nicotinic receptors induce potentiation and synchronization of hippocampal networks and glutamatergic synaptic transmission. Findings from this work highlight the impact of cholinergic signaling in generating network-wide potentiation in the form of enhanced spiking and bursting dynamics that coincide with molecular correlates of memory such as increased phosphorylation of CaMKII and GluA1. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Using animal models to evaluate the functional consequences of anesthesia during early neurodevelopment

Fifteen years ago Olney and colleagues began using animal models to evaluate the effects of anesthetic and sedative agents (ASAs) on neurodevelopment. The results from ongoing studies indicate that, under certain conditions, exposure to these drugs during development induces an acute elevated apoptotic neurodegenerative response in the brain and long-term functional impairments. These animal models have played a significant role in bringing attention to the possible adverse effects of exposing the developing brain to ASAs when few concerns had been raised previously in the medical community. The apoptotic degenerative response resulting from neonatal exposure to ASAs has been replicated in many studies in both rodents and non-human primates, suggesting that a similar effect may occur in humans. In both rodents and non-human primates, significantly increased levels of apoptotic degeneration are often associated with functional impairments later in life. However, behavioral deficits following developmental ASA exposure have not been consistently reported even when significantly elevated levels of apoptotic degeneration have been documented in animal models. In the present work, we review this literature and propose a rodent model for assessing potential functional deficits following neonatal ASA exposure with special reference to experimental design and procedural issues. Our intent is to improve test sensitivity and replicability for detecting subtle behavioral effects, and thus enhance the translational significance of ASA models.

Anesthetics disrupt growth cone guidance cue sensing through actions on the GABAA α2 receptor mediated by the immature chloride gradient

BACKGROUND

General anesthetics (GAs) may exert harmful effects on the developing brain by disrupting neuronal circuit formation. Anesthetics that act on γ-aminobutyric acid (GABA) receptors can interfere with axonal growth cone guidance, a critical process in the assembly of neuronal circuitry. Here we investigate the mechanism by which isoflurane prevents sensing of the repulsive guidance cue, Semaphorin 3A (Sema3A).

METHODS

Growth cone sensing was assayed by measuring growth cone collapse in dissociated neocortical cultures exposed to recombinant Sema3A in the presence or absence of isoflurane and/or a panel of reagents with specific actions on components of the GABA receptor and chloride ion systems.

RESULTS

Isoflurane exposure prevents Sema3A induced growth cone collapse. A GABA_A α2 specific agonist replicates this effect (36.83 ± 3.417% vs 70.82 ± 2.941%, in the Sema3A induced control group, p < 0.0001), but an α1-specific agonist does not. Both a Na-K-Cl cotransporter 1 antagonism (bumetanide, BUM) and a chloride ionophore (IONO) prevent isoflurane from disrupting growth cone sensing of Sema3A. (65.67 ± 3.775% in Iso + BUM group vs 67.45 ± 3.624% in Sema3A induced control group, 65.34 ± 1.678% in Iso + IONO group vs 68.71 ± 2.071% in Sema3A induced control group, no significant difference) (n = 96 growth cones per group).

CONCLUSION

Our data suggest that the effects of isoflurane on growth cone sensing are mediated by the α2 subunit of the GABA_A receptor and also that they are dependent on the developmental chloride gradient, in which Cl^- exhibits a depolarizing effect. These findings provide a rationale for why immature neurons are particularly susceptible to anesthetic toxicity.

Early Developmental Exposure to Repetitive Long Duration of Midazolam Sedation Causes Behavioral and Synaptic Alterations in a Rodent Model of Neurodevelopment

There is a large body of preclinical literature suggesting that exposure to general anesthetic agents during early life may have harmful effects on brain development. Patients in intensive care settings are often treated for prolonged periods with sedative medications, many of which have mechanisms of action that are similar to general anesthetics. Using in vivo studies of the mouse hippocampus and an in vitro rat cortical neuron model we asked whether there is evidence that repeated, long duration exposure to midazolam, a commonly used sedative in pediatric intensive care practice, has the potential to cause lasting harm to the developing brain. We found that mice that underwent midazolam sedation in early postnatal life exhibited deficits in the performance on Y-maze and fear-conditioning testing at young adult ages. Labeling with a nucleoside analog revealed a reduction in the rate of adult neurogenesis in the hippocampal dentate gyrus, a brain region that has been shown to be vulnerable to developmental anesthetic neurotoxicity. In addition, using immunohistochemistry for synaptic markers we found that the number of presynaptic terminals in the dentate gyrus was reduced, while the number of excitatory postsynaptic terminals was increased. These findings were replicated in a midazolam sedation exposure model in neurons in culture. We conclude that repeated, long duration exposure to midazolam during early development has the potential to result in persistent alterations in the structure and function of the brain.

Pilose antler polypeptide protects against sevoflurane‑mediated neurocyte injury

Pilose antler polypeptide (PAP) is an active substance isolated from the traditional Chinese medicine pilose antler, which possesses multiple biological activities. In the present study, the role and mechanism of PAP in sevoflurane (SEV)-induced neurocyte injury was explored. Cell viability was determined by Cell Counting kit-8 assay. Cell proliferation and apoptosis were analyzed by flow cytometry. Western blotting and reverse transcription-quantitative polymerase chain reaction analysis were used to evaluate the protein and mRNA expression levels, respectively. The results revealed that PAP enhanced the cell viability of SEV-treated nerve cells. In addition, through modulation of apoptosis-associated protein expression, PAP suppressed SEV-induced nerve cell apoptosis. Furthermore, PAP activated the p38 mitogen-activated protein kinase (p38)/c-Jun N-terminal kinase (JNK) pathway in the neurocyte injury model, whereas inhibition of the p38/JNK pathway reversed the beneficial effects produced by PAP. In conclusion, PAP protected against SEV-mediated neurocyte injury via upregulation of the p38/JNK pathway. The present findings suggested that PAP may be an effective agent for neurocyte injury.

Early Developmental Exposure to General Anesthetic Agents in Primary Neuron Culture Disrupts Synapse Formation via Actions on the mTOR Pathway

Human epidemiologic studies and laboratory investigations in animal models suggest that exposure to general anesthetic agents (GAs) have harmful effects on brain development. The mechanism underlying this putative iatrogenic condition is not clear and there are currently no accepted strategies for prophylaxis or treatment. Recent evidence suggests that anesthetics might cause persistent deficits in synaptogenesis by disrupting key events in neurodevelopment. Using an in vitro model consisting of dissociated primary cultured mouse neurons, we demonstrate abnormal pre- and post-synaptic marker expression after a clinically-relevant isoflurane anesthesia exposure is conducted during neuron development. We find that pharmacologic inhibition of the mechanistic target of rapamycin (mTOR) pathway can reverse the observed changes. Isoflurane exposure increases expression of phospho-S6, a marker of mTOR pathway activity, in a concentration-dependent fashion and this effect occurs throughout neuronal development. The mTOR 1 complex (mTORC1) and the mTOR 2 complex (mTORC2) branches of the pathway are both activated by isoflurane exposure and this is reversible with branch-specific inhibitors. Upregulation of mTOR is also seen with sevoflurane and propofol exposure, suggesting that this mechanism of developmental anesthetic neurotoxicity may occur with all the commonly used GAs in pediatric practice. We conclude that GAs disrupt the development of neurons during development by activating a well-defined neurodevelopmental disease pathway and that this phenotype can be reversed by pharmacologic inhibition.

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

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

General Anesthesia and Young Brain: What is New?

Considering that growing population of very young children is exposed to general anesthesia every year, it is of utmost importance to understand how and whether such practice may affect the development and growth of their very immature and vulnerable brains. Compelling evidence from animal studies suggests that an early exposure to general anesthesia is detrimental to normal brain development leading to structural and functional impairments of neurons and glia, and long-lasting impairments in normal emotional and cognitive development. Although the evidence from animal studies is overwhelming and confirmed across species examined from rodents to non-human primates, the evidence from human studies is inconsistent and not conclusive at present. In this review we focus on new developments in animal studies of anesthesia-induced developmental neurotoxicity and summarize recent clinical studies while focusing on outcome measures and exposure variables in terms of their utility for assessing cognitive and behavioral development in children.

An allosteric propofol-binding site in kinesin disrupts kinesin-mediated processive movement on microtubules

Microtubule-based molecular motors mediate transport of intracellular cargo to subdomains in neurons. Previous evidence has suggested that the anesthetic propofol decreases the average run-length potential of the major anterograde transporters kinesin-1 and kinesin-2 without altering their velocity. This effect on kinesin has not been observed with other inhibitors, stimulating considerable interest in the underlying mechanism. Here, we used a photoactive derivative of propofol, meta-azipropofol (AziPm), to search for potential propofol-binding sites in kinesin. Single-molecule motility assays confirmed that AziPm and propofol similarly inhibit kinesin-1 and kinesin-2. We then applied AziPm in semiquantitative radiolabeling and MS microsequencing assays to identify propofol-binding sites within microtubule-kinesin complexes. The radiolabeling experiments suggested preferential AziPm binding to the ATP-bound microtubule-kinesin complex. The photolabeled residues were contained within the kinesin motor domain rather than at the motor domain-β-tubulin interface. No residues within the P-loop of kinesin were photolabeled, indicating an inhibitory mechanism that does not directly affect ATPase activity and has an effect on run length without changing velocity. Our results also indicated that when the kinesin motor interacts with the microtubule during its processive run, a site forms in kinesin to which propofol can then bind and allosterically disrupt the kinesin-microtubule interaction, resulting in kinesin detachment and run termination. The discovery of the propofol-binding allosteric site in kinesin may improve our understanding of the strict coordination of the motor heads during the processive run. We hypothesize that propofol's potent effect on intracellular transport contributes to various components of its anesthetic action.

Isoflurane exposure regulates the cell viability and BDNF expression of astrocytes via upregulation of TREK‑1

Neonatal isoflurane exposure in rodents disrupts hippocampal cognitive functions, including learning and memory, and astrocytes may have an important role in this process. However, the molecular mechanisms underlying this disruption are not fully understood. The present study investigated the role of TWIK‑related K+ channel (TREK‑1) in isoflurane‑induced cognitive impairment. Lentiviruses were used to overexpress or knockdown TREK‑1 in astrocytes exposed to increasing concentrations of isoflurane or O2 for 2 h. Subsequently, the mRNA and protein expression of brain‑derived neurotrophic factor (BDNF), caspase‑3, Bcl‑2‑associated X (Bax) and TREK‑1 was measured by reverse transcription‑ quantitative polymerase chain reaction and western blot analysis, respectively. In addition, cell viability was assessed by a 2‑(4‑Iodophenyl)‑3‑(4‑nitrophenyl)‑5‑(2,4‑disulfophenyl)‑ 2H‑tetrazolium monosodium salt assay. The results demonstrated that, prior to manipulating TREK‑1, isoflurane significantly decreased the cell viability and BDNF expression, and increased Bax, caspase‑3 and TREK‑1 expression was observed. However, TREK‑1 overexpression in astrocytes significantly downregulated BDNF expression, and upregulated Bax and caspase‑3 expression. Furthermore, lentiviral‑mediated short hairpin RNA knockdown of TREK‑1 effectively inhibited the isoflurane‑induced changes in BDNF, Bax and caspase‑3 expression. Taken together, the results of the present study indicate that isoflurane‑induced cell damage in astrocytes may be associated with TREK‑1‑mediated inhibition of BDNF and provide a reference for the safe use of isoflurane anesthesia in infants and children.

The neuroprotective effects of remifentanil on isoflurane-induced apoptosis in the neonatal rat brain

Remifentanil is one of the most frequently prescribed opioids used in combination with inhalation anesthetics in clinical practice, but the effects of such combinations on the developing rat brain are unknown. In our study, we investigated first the potential neurotoxic effects of remifentanil on the developing brain and then the effects of remifentanil on isoflurane-induced apoptosis in the neonatal rat brain following exposure to a nociceptive stimulus. In the first experiment, postnatal day (P) 7 rats were randomly exposed to 30% oxygen, 1.5% isoflurane alone, 1.5% isoflurane and a plantar incision, normal saline, or remifentanil at a low (5 µg·kg^-1·h^-1), moderate (20 µg·kg^-1·h^-1) or high (80 µg·kg^-1·h^-1) dose for 4 h. In the second 4-h experiment, P7 rats were randomly exposed to 1.5% isoflurane, infused with different doses of remifentanil (5, 10, and 20 µg·kg^-1·h^-1), and subjected to a plantar incision. In both experiments, the number of apoptotic neurons in the cortex, hippocampus, and thalamus was assessed after two hours by cleaved caspase-3 or TUNEL staining. Our data showed that unlike 1.5% isoflurane, remifentanil at any dose did not cause significant neuronal apoptosis in any brain section. In addition, in response to a nociceptive stimulus, the infusion of 10 µg·kg^-1·h^-1 remifentanil reduced isoflurane-induced apoptosis in the hippocampus (P = 0.003 in CA1, P = 0.002 in CA3) but not in the cortex or thalamus. Our findings suggest that remifentanil does not induce apoptosis and reduces isoflurane-induced apoptosis in the developing brain.

Insufficient Astrocyte-Derived Brain-Derived Neurotrophic Factor Contributes to Propofol-Induced Neuron Death Through Akt/Glycogen Synthase Kinase 3β/Mitochondrial Fission Pathway

BACKGROUND

Growing animal evidence demonstrates that prolonged exposure to propofol during brain development induces widespread neuronal cell death, but there is little information on the role of astrocytes. Astrocytes can release neurotrophic growth factors such as brain-derived neurotrophic factor (BDNF), which can exert the protective effect on neurons in paracrine fashion. We hypothesize that during propofol anesthesia, BDNF released from developing astrocytes may not be sufficient to prevent propofol-induced neurotoxicity.

METHODS

Hippocampal astrocytes and neurons isolated from neonatal Sprague Dawley rats were exposed to propofol at a clinically relevant dose of 30 μM or dimethyl sulfoxide as control for 6 hours. Propofol-induced cell death was determined by propidium iodide (PI) staining in astrocyte-alone cultures, neuron-alone cultures, or cocultures containing either low or high density of astrocytes (1:9 or 1:1 ratio of astrocytes to neurons ratio [ANR], respectively). The astrocyte-conditioned medium was collected 12 hours after propofol exposure and measured by protein array assay. BDNF concentration in astrocyte-conditioned medium was quantified using enzyme-linked immunosorbent assay. Neuron-alone cultures were treated with BDNF, tyrosine receptor kinase B inhibitor cyclotraxin-B, glycogen synthase kinase 3β (GSK3β) inhibitor CHIR99021, or mitochondrial fission inhibitor Mdivi-1 before propofol exposure. Western blot was performed for quantification of the level of protein kinase B and GSK3β. Mitochondrial shape was visualized through translocase of the outer membrane 20 staining.

RESULTS

Propofol increased cell death in neurons by 1.8-fold (% of PI-positive cells [PI%] = 18.6; 95% confidence interval [CI], 15.2-21.9, P < .05) but did not influence astrocyte viability. The neuronal death was attenuated by a high ANR (1:1 cocultures; fold change [FC] = 1.17, 95% CI, 0.96-1.38, P < .05), but not with a low ANR [1:9 cocultures; FC = 1.87, 95% CI, 1.48-2.26, P > .05]). Astrocytes secreted BDNF in a cell density-dependent way and propofol decreased BDNF secretion from astrocytes. Administration of BDNF, CHIR99021, or Mdivi-1 significantly attenuated the propofol-induced neuronal death and aberrant mitochondria in neuron-alone cultures (FC = 0.8, 95% CI, 0.62-0.98; FC = 1.22, 95% CI, 1.11-1.32; FC = 1.35, 95% CI, 1.16-1.54, respectively, P < .05) and the cocultures with a low ANR (1:9; FC = 0.85, 95% CI, 0.74-0.97; FC = 1.08, 95% CI, 0.84-1.32; FC = 1.25, 95% CI, 1.1-1.39, respectively, P < .05). Blocking BDNF receptor or protein kinase B activity abolished astrocyte-induced neuroprotection in the cocultures with a high ANR (1:1).

CONCLUSIONS

Astrocytes attenuate propofol-induced neurotoxicity through BDNF-mediated cell survival pathway suggesting multiple neuroprotective strategies such as administration of BDNF, astrocyte-conditioned medium, decreasing mitochondrial fission, or inhibition of GSK3β.

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.

Optical coherence tomography to monitor vigabatrin toxicity in children

PURPOSE

The antiepileptic drug vigabatrin is known to cause permanent loss of vision. Both visual field testing and electroretinogram are used to detect retinal damage. Adult data on optical coherence tomography (OCT) shows that retinal nerve fiber layer (RNFL) thinning may be an early indicator of vigabatrin-induced retinal toxicity. The purpose of this study was to investigate whether OCT can detect early vigabatrin-induced retinal toxicity in children.

METHODS

Pediatric patients (≤18 years of age) requiring vigabatrin for seizure control who were followed at our institution were invited to participate. Patients were examined according to manufacturer guidelines, with most examinations taking place under general anesthesia. RNFL thickness was measured by OCT (Stratus Model 3000, Zeiss) and compared to total cumulative dose of vigabatrin. In most cases, indirect ophthalmoscopy, fundus photography, and electroretinography were also performed.

RESULTS

OCT and complete dosing data was available for 19 patients. Patients with tuberous sclerosis (TS, n = 12) received higher cumulative doses (mean, 1463 g) than non-TS patients (mean, 351 g, P = 0.044). RNFL thinning was detected in the nasal (P < 0.01), superior (P < 0.01), and inferior (P < 0.05) quadrants in patients with TS, particularly once cumulative dose exceeded 1500 g.

CONCLUSIONS

In our study population of patients with TS, higher cumulative doses of vigabatrin were associated with RNFL thinning in the nasal, superior, and inferior quadrants. These findings were pronounced once cumulative dose exceeded 1500 g. This pattern of RNFL thinning is similar to what has been shown in adult patients taking vigabatrin.

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.

Report of the fourth PANDA Symposium on "Anesthesia and Neurodevelopment in Children"

On April 12, 2014, the Pediatric Anesthesia and NeuroDevelopment Assessment (PANDA) study team held its fourth biennial scientific symposium at Morgan Stanley Children's Hospital of New York (MS-CHONY). The symposium was organized by the PANDA study team and co-sponsored by the Morgan Stanley Children's Hospital of New York-Presbyterian and the Department of Anesthesiology of Columbia University. The PANDA symposium has become a platform to review current preclinical and clinical data related to anesthetic neurotoxicity, to discuss relevant considerations in study design and approaches to future research among clinicians and researchers, and finally to engage key stakeholders in this controversial public health topic. Program attendants and speakers represented many of the most active investigators in the area of pediatric anesthetic neurotoxicity as well as stakeholders from many different backgrounds outside of anesthesia that provided their own unique perspectives, concerns, and input regarding anesthetic-related neurotoxicity in children.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Review: effects of anesthetics on brain circuit formation

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

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.

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.

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.

Anesthetics interfere with axon guidance in developing mouse neocortical neurons in vitro via a γ-aminobutyric acid type A receptor mechanism

BACKGROUND

The finding that exposure to general anesthetics (GAs) in childhood may increase rates of learning disabilities has raised a concern that anesthetics may interfere with brain development. The generation of neuronal circuits, a complex process in which axons follow guidance cues to dendritic targets, is an unexplored potential target for this type of toxicity.

METHODS

GA exposures were conducted in developing neocortical neurons in culture and in early postnatal neocortical slices overlaid with fluorescently labeled neurons. Axon targeting, growth cone collapse, and axon branching were measured using quantitative fluorescence microscopy.

RESULTS

Isoflurane exposure causes errors in Semaphorin-3A-dependent axon targeting (n = 77 axons) and a disruption of the response of axonal growth cones to Semaphorin-3A (n = 2,358 growth cones). This effect occurs at clinically relevant anesthetic doses of numerous GAs with allosteric activity at γ-aminobutyric acid type A receptors, and it was reproduced with a selective agonist. Isoflurane also inhibits growth cone collapse induced by Netrin-1, but does not interfere branch induction by Netrin-1. Insensitivity to guidance cues caused by isoflurane is seen acutely in growth cones in dissociated culture, and errors in axon targeting in brain slice culture occur at the earliest point at which correct targeting is observed in controls.

CONCLUSIONS

These results demonstrate a generalized inhibitory effect of GAs on repulsive growth cone guidance in the developing neocortex that may occur via a γ-aminobutyric acid type A receptor mechanism. The finding that GAs interfere with axon guidance, and thus potentially with circuit formation, represents a novel form of anesthesia neurotoxicity in brain development.

Preclinical research into the effects of anesthetics on the developing brain: promises and pitfalls

Every year millions of children are treated with anesthetics and sedatives to alleviate pain and distress during invasive procedures. Accumulating evidence suggests the possibility for deleterious effects on the developing brain. This has led to significant concerns among pediatric anesthesiologists and to the formation of the Pediatric Anesthesia NeuroDevelopmental Assessment (PANDA) group and its biannual symposium. Not surprisingly, the majority of the data in this field have thus far been derived through laboratory research. Accordingly, this review summarizes the current state of animal research in this field, introduces some of the findings presented at the PANDA symposium, and addresses some of the difficulties in translating these findings to pediatric anesthesia practice, as discussed during the symposium. The symposium participants' consensus was that significant preclinical and clinical research efforts are still needed to investigate this important concern for child health.