Repeated exposure to propofol impairs spatial learning, inhibits LTP and reduces CaMKIIα in young rats

Nrf2 Ameliorates Sevoflurane-Induced Cognitive Deficits in Aged Mice by Inhibiting Neuroinflammation in the Hippocampus

Perioperative neurocognitive disorders (PND), common complications that occur after anesthetized surgery in elderly patients, are major challenges to our rapidly growing aging population. The transcription factor known as nuclear factor erythroid-2-related factor 2 (Nrf2) is an essential component of the cellular antioxidant response, purportedly contributing to the preservation of cognitive functions such as learning and memory. Nevertheless, the function and intracellular processes involving Nrf2 in PND remain largely unknown. Therefore, we evaluate the influence and fundamental mechanism of Nrf2 on PND in aged mice. To establish the postoperative neurocognitive dysfunction (PND) model, aged mice were subjected to anesthesia via inhalation of 3% sevoflurane for a duration of 2 h. The role of Nrf2 in PND was investigated by administering microinjections of either the adeno-associated virus (AAV)-Nrf2 vector or a null virus vector into the hippocampal CA1 region of aged mice 28 days before exposure to sevoflurane. Various assays including enzyme-linked immunosorbent assay (ELISA), immunofluorescence staining, and western blotting were employed to assess levels of pro-inflammatory cytokines, microglial activation, and the oxidative stress response. Furthermore, synaptic plasticity was evaluated through long-term potentiation (LTP) recording and Golgi staining techniques. Elevated expression of Nrf2 within the hippocampal CA1 region ameliorated sevoflurane-induced cognitive deficits, synaptic plasticity anomalies, and the oxidative stress reaction in aged mice. Furthermore, the activation of microglia and the release of pro-inflammatory cytokines (including IL-6, TNF-α, and IL-1β) within the hippocampus post-sevoflurane exposure were modulated in an Nrf2-dependent fashion. Based on the findings from present research, we conclude that Nrf2 ameliorates sevoflurane-induced cognitive dysfunction by inhibiting hippocampal neuroinflammation, thereby proposing a potential therapeutic target for PND.

NUFIP1-engineered exosomes derived from hUMSCs regulate apoptosis and neurological injury induced by propofol in newborn rats

BACKGROUND

Propofol can increase neurotoxicity in infants but the precise mechanism is still unknown. Our previous study revealed that nuclear FMR1 interacting protein 1 (NUFIP1), a specific ribophagy receptor, can alleviate T cell apoptosis in sepsis. Yet, the effect of NUFIP1-engineered exosomes elicited from human umbilical cord blood mesenchymal stem cells (hUMSCs) on nerve injury induced by propofol remains unclear. This study intended to investigate the effect of NUFIP1-engineered exosomes on propofol-induced nerve damage in neonatal rats.

METHODS

Firstly, NUFIP1-engineered exosomes were extracted from hUMSCs serum and their identification was conducted using transmission electron microscopy (TEM), Flow NanoAnalyzer, quantitative real-time polymerase chain reaction (qRT-PCR), and western blot (WB). Subsequently, the optimal exposure duration and concentration of propofol induced apoptosis were determined in SH-SY5Y cell line using WB. Following this, we co-cultured the NUFIP1-engineered exosomes in the knockdown group (NUFIP1-KD) and overexpression group (NUFIP1-OE) with SH-SY5Y cells and assessed their effects on the apoptosis of SH-SY5Y cells using terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL) assay, Hoechst 33258 staining, WB, and flow cytometry, respectively. Finally, NUFIP1-engineered exosomes were intraperitoneally injected into neonatal rats, and their effects on the learning and memory ability of neonatal rats were observed through the righting reflex and Morris water maze (MWM) test. Hippocampi were extracted from different groups for hematoxylin-eosin (HE) staining, immunohistochemistry, immunofluorescence, and WB to observe their effects on apoptosis in neonatal rats.

RESULTS

TEM, Flow NanoAnalyzer, qRT-PCR, and WB analyses confirmed that the exosomes extracted from hUMSCs serum exhibited the expected morphology, diameter, surface markers, and expression of target genes. This confirmed the successful construction of NUFIP1-KD and NUFIP1-OE-engineered exosomes. Optimal exposure duration and concentration of propofol were determined to be 24 hours and 100 µg/ml, respectively. Co-culture of NUFIP1 engineered exosomes and SH-SY5Y cells resulted in significant up-regulation of pro-apoptotic proteins Bax and c-Caspase-3 in the KD group, while anti-apoptotic protein Bcl-2 was significantly decreased. The OE group showed the opposite trend. TUNEL apoptosis assay, Hoechst 33258 staining, and flow cytometry yielded consistent results. Animal experiments demonstrated that intraperitoneal injection of NUFIP1-KD engineered exosomes prolonged the righting reflex recovery time of newborn rats, and MWM tests revealed a significant diminution in the time and number of newborn rats entering the platform. HE staining, immunohistochemistry, immunofluorescence, and WB results also indicated a significant enhancement in apoptosis in this group. Conversely, the experimental results of neonatal rats in the OE group revealed a certain degree of anti-apoptotic effect.

CONCLUSIONS

NUFIP1-engineered exosomes from hUMSCs have the potential to regulate nerve cell apoptosis and mitigate neurological injury induced by propofol in neonatal rats. Targeting NUFIP1 may hold great significance in ameliorating propofol-induced nerve injury.

Suberoylanilide hydroxamic acid attenuates cognitive impairment in offspring caused by maternal surgery during mid-pregnancy

Some pregnant women have to experience non-obstetric surgery during pregnancy under general anesthesia. Our previous studies showed that maternal exposure to sevoflurane, isoflurane, propofol, and ketamine causes cognitive deficits in offspring. Histone acetylation has been implicated in synaptic plasticity. Propofol is commonly used in non-obstetric procedures on pregnant women. Previous studies in our laboratory showed that maternal propofol exposure in pregnancy impairs learning and memory in offspring by disturbing histone acetylation. The present study aims to investigate whether HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) could attenuate learning and memory deficits in offspring caused by maternal surgery under propofol anesthesia during mid-pregnancy. Maternal rats were exposed to propofol or underwent abdominal surgery under propofol anesthesia during middle pregnancy. The learning and memory abilities of the offspring rats were assessed using the Morris water maze (MWM) test. The protein levels of histone deacetylase 2 (HDAC2), phosphorylated cAMP response-element binding (p-CREB), brain-derived neurotrophic factor (BDNF), and phosphorylated tyrosine kinase B (p-TrkB) in the hippocampus of the offspring rats were evaluated by immunofluorescence staining and western blot. Hippocampal neuroapoptosis was detected by TUNEL staining. Our results showed that maternal propofol exposure during middle pregnancy impaired the water-maze learning and memory of the offspring rats, increased the protein level of HDAC2 and reduced the protein levels of p-CREB, BDNF and p-TrkB in the hippocampus of the offspring, and such effects were exacerbated by surgery. SAHA alleviated the cognitive dysfunction and rescued the changes in the protein levels of p-CREB, BDNF and p-TrkB induced by maternal propofol exposure alone or maternal propofol exposure plus surgery. Therefore, SAHA could be a potential and promising agent for treating the learning and memory deficits in offspring caused by maternal nonobstetric surgery under propofol anesthesia.

Neurotoxic Impact of Individual Anesthetic Agents on the Developing Brain

Concerns about the safety of anesthetic agents in children arose after animal studies revealed disruptions in neurodevelopment after exposure to commonly used anesthetic drugs. These animal studies revealed that volatile inhalational agents, propofol, ketamine, and thiopental may have detrimental effects on neurodevelopment and cognitive function, but dexmedetomidine and xenon have been shown to have neuroprotective properties. The neurocognitive effects of benzodiazepines have not been extensively studied, so their effects on neurodevelopment are undetermined. However, experimental animal models may not truly represent the pathophysiological processes in children. Multiple landmark studies, including the MASK, PANDA, and GAS studies have provided reassurance that brief exposure to anesthesia is not associated with adverse neurocognitive outcomes in infants and children, regardless of the type of anesthetic agent used.

Does propofol definitely improve postoperative cognitive dysfunction?-a review of propofol-related cognitive impairment

Postoperative cognitive dysfunction (POCD) is a common brain function-related complication after surgery. In addition to old age being an independent risk factor, anesthetics are also important predisposing factors. Among them, propofol is the most commonly used intravenous anesthetic in clinical practice. It has a rapid onset, short half-life, and high recovery quality. Many studies report that propofol can attenuate surgery-induced cognitive impairment, however, some other studies reveal that propofol also induces cognitive dysfunction. Therefore, this review summarizes the effects of propofol on the cognition, and discusses possible related mechanisms, which aims to provide some evidence for the follow-up studies.

Neonatal Anesthesia and dysregulation of the Epigenome

Each year, millions of infants and children are anesthetized for medical and surgical procedures. Yet, a substantial body of preclinical evidence suggests that anesthetics are neurotoxins that cause rapid and widespread apoptotic cell death in the brains of infant rodents and non-human primates. These animals have persistent impairments in cognition and behavior many weeks or months after anesthesia exposure, leading us to hypothesize that anesthetics do more than simply kill brain cells. Indeed, anesthetics cause chronic neuropathology in neurons that survive the insult, which then interferes with major aspects of brain development, synaptic plasticity, and neuronal function. Understanding the phenomenon of anesthesia-induced developmental neurotoxicity is of critical public health importance because clinical studies now report that anesthesia in human infancy is associated with cognitive and behavioral deficits. In our search for mechanistic explanations for why a young and pliable brain cannot fully recover from a relatively brief period of anesthesia, we have accumulated evidence that neonatal anesthesia can dysregulate epigenetic tags that influence gene transcription such as histone acetylation and DNA methylation. In this review, we briefly summarize the phenomenon of anesthesia-induced developmental neurotoxicity. We then discuss chronic neuropathology caused by neonatal anesthesia, including disturbances in cognition, socio-affective behavior, neuronal morphology, and synaptic plasticity. Finally, we present evidence of anesthesia-induced genetic and epigenetic dysregulation within the developing brain that may be transmitted intergenerationally to anesthesia-naïve offspring.

Febuxostat Prevents the Cytotoxicity of Propofol in Brain Endothelial Cells

Background and purpose: A high risk of brain injury has been reported with the usage of general anesthetics such as propofol in infants. Experimental data indicated that oxidative stress and inflammation are involved in the neurotoxicity induced by propofol. Febuxostat is a novel anti-gout agent recently reported to exert an anti-inflammatory effect. The present study aims to investigate the protective property of febuxostat against the cytotoxicity of propofol in brain endothelial cells as well as the underlying preliminary mechanism. Methods: The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was utilized to screen the optimized incubation concentration of febuxostat. bEnd.3 brain endothelial cells were stimulated with 2% propofol in the presence or absence of febuxostat (10, 20 μM) for 24 h. The lactate dehydrogenase (LDH) release assay was conducted to detect cytotoxicity. The reactive oxygen species (ROS) levels were evaluated using dichloro-dihydro-fluorescein diacetate (DCFH-DA) staining, and the concentration of reduced glutathione (GSH) was determined using a commercial kit. The expressions of TNF-α, IL-6, IL-12, CXCL-1, PDPN, CXCL8, VCAM-1, and E-selectin were determined using a quantitative real-time polymerase chain reaction (qRT-PCR) and an enzyme-linked immunosorbent assay (ELISA). Western blot and qRT-PCR were utilized to determine the expressions of COX-2 and KLF6. The production of PGE2 was evaluated by ELISA. Results: First, increased LDH release induced by propofol was significantly suppressed by febuxostat. The oxidative stress (elevated ROS levels and decreased GSH level) induced by propofol was alleviated by febuxostat. Second, the upregulated inflammatory factors (TNF-α, IL-6, and IL-12), pro-inflammatory chemokines (CXCL-1, PDPN, and CXCL8), adhesion molecules (VCAM-1 and E-selectin), and inflammatory mediators (COX-2 and PGE2) induced by propofol were greatly downregulated by febuxostat. Lastly, the expression of KLF6 was significantly suppressed by propofol but greatly elevated by febuxostat. Conclusion: Febuxostat prevented the cytotoxicity of propofol in brain endothelial cells by alleviating oxidative stress and inflammatory response through KLF6.

Propofol induces the elevation of intracellular calcium via morphological changes in intracellular organelles, including the endoplasmic reticulum and mitochondria

Propofol, most frequently used as a general anesthetic due to its versatility and short-acting characteristics, is thought to exert its anesthetic actions via GABA_A receptors; however, the precise mechanisms of its adverse action including angialgia remain unclear. We examined the propofol-induced elevation of intracellular calcium and morphological changes in intracellular organelles using SHSY-5Y neuroblastoma cells, COS-7 cells, HEK293 cells, and HUVECs loaded with fluorescent dyes for live imaging. Although propofol (>50 μM) increased intracellular calcium in a dose-dependent manner in these cells, it was not influenced by the elimination of extracellular calcium. The calcium elevation was abolished when intracellular or intraendoplasmic reticulum (ER) calcium was depleted by BAPTA-AM or thapsigargin, respectively, suggesting that calcium was mobilized from the ER. Studies using U-73122, xestospongin C, and dantrolene revealed that propofol-induced calcium elevation was not mediated by G-protein coupled receptors, IP3 receptors, or ryanodine receptors. We performed live imaging of the ER, mitochondria and Golgi apparatus during propofol stimulation using fluorescent dyes. Concomitant with the calcium elevation, the structure of the ER and mitochondria was fragmented and aggregated, and these changes were not reversed during the observation period, suggesting that propofol-induced calcium elevation occurs due to calcium leakage from these organelles. Although the concentration of propofol used in this experiment was greater than that used clinically (30 μM), it is possible that the concentration exceeds 30 μM at the site where propofol is injected, leading the idea that these phenomena might relate to the various propofol-induced adverse effects including angialgia.

The effects of repeated propofol anesthesia on spatial memory and long-term potentiation in infant rats under hypoxic conditions

Propofol is widely used as an intravenous drug for induction and maintenance in general anesthesia. Hypoxemia is a common complication during perianesthesia. We want to know the effect of propofol on spatial memory and LTP (Long-term potentiation) under hypoxic conditions. In this study, 84 seven-day-old Sprague–Dawley rats were randomly assigned into six groups (n = 14)-four control groups: lipid emulsion solvent + 50% oxygen (CO), lipid emulsion solvent + room air (CA), lipid emulsion solvent + 18% oxygen (CH), and propofol + 50% oxygen (propofol–oxygen, PO); and two experiment groups: propofol + room air (propofol–air, PA), and propofol + 18% oxygen (propofol–hypoxia, PH). After receiving propofol (50 mg/kg) or the same volume of intralipid intraperitoneal (5.0 ml/kg), injected once per day for seven consecutive days, the rats were exposed to 18% oxygen, 50% oxygen and air, until recovery of the righting reflex. We found that the apoptotic index and activated caspase-3 increased in the PH group (P < 0.05) compared with the PA group, fEPSP (field excitatory postsynaptic) potential and success induction rate of LTP reduced in all propofol groups (P < 0.05). Compared with the PO group, the fEPSP and success induction rate of LTP reduced significantly in the PA and PH groups (P < 0.05). Moreover, compared with CH group, the average time of escape latency was longer, and the number of platform location crossings was significantly reduced in the PH group (P < 0.05). Thus, we believe that adequate oxygen is very important during propofol anesthesia.

Impact of anesthesia exposure in early development on learning and sensory functions

Each year, millions of children undergo anesthesia, and both human and animal studies have indicated that exposure to anesthesia at an early age can lead to neuronal damage and learning deficiency. However, disorders of sensory functions were not reported in children or animals exposed to anesthesia during infancy, which is surprising, given the significant amount of damage to brain tissue reported in many animal studies. In this review, we discuss the relationship between the systems in the brain that mediate sensory input, spatial learning, and classical conditioning, and how these systems could be affected during anesthesia exposure. Based on previous reports, we conclude that anesthesia can induce structural, functional, and compensatory changes in both sensory and learning systems. Changes in myelination following anesthesia exposure were observed as well as the neurodegeneration in the gray matter across variety of brain regions. Disproportionate cell death between excitatory and inhibitory cells induced by anesthesia exposure can lead to a long-term shift in the excitatory/inhibitory balance, which affects both learning-specific networks and sensory systems. Anesthesia may directly affect synaptic plasticity which is especially critical to learning acquisition. However, sensory systems appear to have better ability to compensate for damage than learning-specific networks.

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.

Repeated neonatal isoflurane exposures in the mouse induce apoptotic degenerative changes in the brain and relatively mild long-term behavioral deficits

Epidemiological studies suggest exposures to anesthetic agents and/or sedative drugs (AASDs) in children under three years old, or pregnant women during the third trimester, may adversely affect brain development. Evidence suggests lengthy or repeated AASD exposures are associated with increased risk of neurobehavioral deficits. Animal models have been valuable in determining the type of acute damage in the developing brain induced by AASD exposures, as well as in elucidating long-term functional consequences. Few studies examining very early exposure to AASDs suggest this may be a critical period for inducing long-term functional consequences, but the impact of repeated exposures at these ages has not yet been assessed. To address this, we exposed mouse pups to a prototypical general anesthetic, isoflurane (ISO, 1.5% for 3 hr), at three early postnatal ages (P3, P5 and P7). We quantified the acute neuroapoptotic response to a single versus repeated exposure, and found age- and brain region-specific effects. We also found that repeated early exposures to ISO induced subtle, sex-specific disruptions to activity levels, motor coordination, anxiety-related behavior and social preference. Our findings provide evidence that repeated ISO exposures may induce behavioral disturbances that are subtle in nature following early repeated exposures to a single AASD.

The recovery from transient cognitive dysfunction induced by propofol was associated with enhanced autophagic flux in normal healthy adult mice

Propofol is the most widely accepted intravenous anesthetic available for clinical use. However, neurotoxicity of propofol in the developing brain has been reported. This study investigated the effects of propofol on cognitive function in normal healthy adult mice. Thirty-three GFP-LC3 adult mice were included. Propofol was injected for anesthesia (n = 22). The sham control (n = 11) received intralipid injections. The mice completed a Y-maze test on 3 and 7 days after being anesthetized. Western blotting, immunofluorescence staining, and transmission electron microscopic (TEM) analyses were performed with their hippocampi. In addition, we conducted a separate ex vivo experiment using organotypic hippocampal slice cultures (OHSCs) to investigate the effects of propofol on induced autophagy. There was a significantly lower percentage of alternation in the Y-maze test on day 3 after propofol anesthesia than the control, but no difference was observed on day 7. Western blot analyses and immunofluorescence assays showed that the levels of cognitive function-related proteins significantly decreased in the propofol group compared to the control on day 3 but had recovered by day 7. In terms of autophagy-related proteins, western blot analyses and immunofluorescence assays showed that propofol increased autophagic induction, flux, and degradation of autophagosomes. Ex vivo experiments showed that propofol enhanced autophagic flux of the induced autophagy. In conclusion, although transient cognitive dysfunction occurred, adult mice recovered their cognitive function after the administration of propofol anesthesia. And this finding may be associated with enhanced autophagic flux.

Neonatal phenobarbital exposure disrupts GABAergic synaptic maturation in rat CA1 neurons

OBJECTIVE

Phenobarbital is the most commonly utilized drug for the treatment of neonatal seizures. The use of phenobarbital continues despite growing evidence that it exerts suboptimal seizure control and is associated with long-term alterations in brain structure, function, and behavior. Alterations following neonatal phenobarbital exposure include acute induction of neuronal apoptosis, disruption of synaptic development in the striatum, and a host of behavioral deficits. These behavioral deficits include those in learning and memory mediated by the hippocampus. However, the synaptic changes caused by acute exposure to phenobarbital that lead to lasting effects on brain function and behavior remain understudied.

METHODS

Postnatal day (P)7 rat pups were treated with phenobarbital (75 mg/kg) or saline. On P13-14 or P29-37, acute slices were prepared and whole-cell patch-clamp recordings were made from CA1 pyramidal neurons.

RESULTS

At P14 we found an increase in miniature inhibitory postsynaptic current (mIPSC) frequency in the phenobarbital-exposed as compared to the saline-exposed group. In addition to this change in mIPSC frequency, the phenobarbital group displayed larger bicuculline-sensitive tonic currents, decreased capacitance and membrane time constant, and a surprising persistence of giant depolarizing potentials. At P29+, the frequency of mIPSCs in the saline-exposed group had increased significantly from the frequency at P14, typical of normal synaptic development; at this age the phenobarbital-exposed group displayed a lower mIPSC frequency than did the control group. Spontaneous inhibitory postsynaptic current (sIPSC) frequency was unaffected at either P14 or P29+.

SIGNIFICANCE

These neurophysiological alterations following phenobarbital exposure provide a potential mechanism by which acute phenobarbital exposure can have a long-lasting impact on brain development and behavior.

Propofol-induced downregulation of NR2B membrane translocation in hippocampus and spatial memory deficits of neonatal mice

BACKGROUND

Thousands of infants and children are undergoing anesthesia around the world every day. But impacts of anesthetics on the developing neural system remain unclear yet. Previous evidence showed that anesthesia might affect the developing neural system. Thus, early-life anesthesia becomes a critical issue in clinical pediatric practice. Hence, propofol, a short-acting and widely applied intravenous anesthetic, has been gaining focus upon neonatal anesthesia.

METHODS

Fifty-four male C57BL/6J mice were randomly divided into following three groups: group D6 intraperitoneally (i.p.) injected propofol (100 mg/kg body weight) once a day from postnatal day 6 (P6) to P11, group D1 administrated propofol (100 mg/kg, i.p.) at P6 solely and administrated normal saline (10 ml/kg, i.p.) from P7 to P11, and group N treated with normal saline (10 ml/kg, i.p.) from P6 to P11 as the control (n = 18 per group). Then, at P28, nine mice were collected randomly from each group for NR2B membrane translocation and phosphorylation analysis, and the rest half in each group were assigned to perform Morris water maze tests from P28 to P35.

RESULTS

Results showed that total protein expression levels of NR2B increased (p < .001) while its membrane translocation decreased (p < .001, n = 9 per group) in the hippocampus but not in the prefrontal cortex of neonatal mice after repeated propofol administration. Phosphorylation levels of NR2B at serine 1303 (D1: p < .05; D6: p < .001, n = 9 per group) and serine 1480 (D1: p < .01, D6: p < .001, n = 9 per group) increased significantly as well in the hippocampus compared with group N. In addition, memory deficits (p < .05, n = 9 per group) were observed in Morris water maze tests of group D6 mice.

CONCLUSIONS

These results suggested that propofol exposure downregulates NR2B membrane translocation and causes spatial memory deficits, with a mediated increased NR2B protein expression and phosphorylation at Ser1303/1480 residues in the hippocampus of neonatal mice.

Recent Insights Into Molecular Mechanisms of Propofol-Induced Developmental Neurotoxicity: Implications for the Protective Strategies

Mounting evidence has demonstrated that general anesthetics could induce developmental neurotoxicity, including acute widespread neuronal cell death, followed by long-term memory and learning abnormalities. Propofol is a commonly used intravenous anesthetic agent for the induction and maintenance of anesthesia and procedural and critical care sedation in children. Compared with other anesthetic drugs, little information is available on its potential contributions to neurotoxicity. Growing evidence from multiple experimental models showed a similar neurotoxic effect of propofol as observed in other anesthetic drugs, raising serious concerns regarding pediatric propofol anesthesia. The aim of this review is to summarize the current findings of propofol-induced developmental neurotoxicity. We first present the evidence of neurotoxicity from animal models, animal cell culture, and human stem cell-derived neuron culture studies. We then discuss the mechanism of propofol-induced developmental neurotoxicity, such as increased cell death in neurons and oligodendrocytes, dysregulation of neurogenesis, abnormal dendritic development, and decreases in neurotrophic factor expression. Recent findings of complex mechanisms of propofol action, including alterations in microRNAs and mitochondrial fission, are discussed as well. An understanding of the toxic effect of propofol and the underlying mechanisms may help to develop effective novel protective or therapeutic strategies for avoiding the neurotoxicity in the developing human brain.

Repeated propofol anesthesia induced downregulation of hippocampal miR-132 and learning and memory impairment of rats

Several studies have reported that neonatal exposure to propofol may cause neurotoxicity in the hippocampus, involving long-term neurodevelopmental impairments. We aimed to detect real-time changes of miR-132 of neonatal rats exposed to propofol anesthesia and to characterize subsequent changes in learning and memory. Seven-day-old Sprague-Dawley rats were injected intraperitoneally with 40mg/kg propofol at 0, 120, and 240 min or with isotonic fat emulsion as controls. Expression levels of miR-132 were assessed, and the mRNA and protein expression levels of p250GAP, a prominent target for miR-132, were evaluated at different time points during development. Dendritic spines were counted, and the learning and memory abilities were also investigated. We found that repeated propofol anesthesia resulted in a significant downregulation of miR-132 levels and a decrease in the number of dendritic spines in the hippocampus leading to learning and memory dysfunction. Therefore, repeated propofol anesthesia induces downregulation of miR-132 and learning and memory impairment in the hippocampus of rats.

The protective effects of propofol against CoCl2-induced HT22 cell hypoxia injury via PP2A/CAMKIIα/nNOS pathway

Background

Perioperative cerebral ischemia/hypoxia could induce hippocampal injury and has been reported to induce cognitive impairment. In this study, we used cobalt chloride (CoCl₂) to build a hypoxia model in mouse hippocampal cell lines. Propofol, a widely used intravenous anesthetic agent, has been demonstrated to have neuroprotective effect. Here, we explored whether and how propofol attenuated CoCl₂-induced mouse hippocampal HT22 cell injury.

Methods

Mouse hippocampal HT22 cells were pretreated with propofol, and then stimulated with CoCl₂. Cell viability was measured by cell counting kit 8 (CCK8). The effect of propofol on CoCl₂-modulated expressions of B-cell lymphoma 2 (Bcl-2), BAX, cleaved caspase 3, phosphatase A2 (PP2A), and the phosphorylation of Ca²⁺/Calmodulin (CaM)-dependent protein kinase II (pCAMKIIα), neuron nitric oxide synthase at Ser¹⁴¹² (pnNOS-Ser¹⁴¹²), neuron nitric oxide synthase at Ser⁸⁴⁷ (pnNOS-Ser⁸⁴⁷) were detected by Western blot analysis.

Results

Compared with control, CoCl₂ treatment could significantly decrease cell viability, which could be reversed by propofol. Further, we found CoCl₂ treatment could up-regulate the expression of PP2A, BAX, cleaved caspase three and cause the phosphorylation of nNOS-Ser¹⁴¹², but it down-regulated the expression of Bcl-2 and the phosphorylation of CAMKIIα and nNOS-Ser⁸⁴⁷. More importantly, these CoCl₂-mediated effects were attentuated by propofol. In addition, we demonstrated that propofol could exert similar effect to that of the PP2A inhibitor (okadaic acid). Further, the PP2A activator (FTY720) and the CAMKIIα inhibitor (KN93) could reverse the neuroprotective effect of propofol.

Conclusion

Our data indicated that propofol could attenuate CoCl₂-induced HT22 cells hypoxia injury via PP2A/CAMKIIα/nNOS pathway.

Neonatal Propofol and Etomidate Exposure Enhance Inhibitory Synaptic Transmission in Hippocampal Cornus Ammonis 1 Pyramidal Neurons

Background:

Propofol and etomidate are the most important intravenous general anesthetics in the current clinical use and that mediate gamma-aminobutyric acid's (GABAergic) synaptic transmission. However, their long-term effects on GABAergic synaptic transmission induced by neonatal propofol or etomidate exposure remain unclear. We investigated the long-term GABAergic neurotransmission alterations, following neonatal propofol and etomidate administration.

Methods:

Sprague-Dawley rat pups at postnatal days 4–6 were underwent 6-h-long propofol-induced or 5-h-long etomidate-induced anesthesia. We performed whole-cell patch-clamp recording from pyramidal cells in the cornus ammonis 1 area of acute hippocampal slices of postnatal 80–90 days. Spontaneous and miniature inhibitory GABAergic currents (spontaneous inhibitory postsynaptic currents [sIPSCs] and miniature inhibitory postsynaptic currents [mIPSCs]) and their kinetic characters were measured. The glutamatergic tonic effect on inhibitory transmission and the effect of bumetanide on neonatal propofol exposure were also examined.

Results:

Neonatal propofol exposure significantly increased the frequency of mIPSCs (from 1.87 ± 0.35 Hz to 3.43 ± 0.51 Hz, P < 0.05) and did not affect the amplitude of mIPSCs and sIPSCs. Both propofol and etomidate slowed the decay time of mIPSCs kinetics (168.39 ± 27.91 ms and 267.02 ± 100.08 ms vs. 68.18 ± 12.43 ms; P < 0.05). Bumetanide significantly blocked the frequency increase and reversed the kinetic alteration of mIPSCs induced by neonatal propofol exposure (3.01 ± 0.45 Hz and 94.30 ± 32.56 ms).

Conclusions:

Neonatal propofol and etomidate exposure has long-term effects on inhibitory GABAergic transmission. Propofol might act at pre- and post-synaptic GABA receptor A (GABA_A) receptors within GABAergic synapses and impairs the glutamatergic tonic input to GABAergic synapses; etomidate might act at the postsynaptic site.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Dexmedetomidine attenuates repeated propofol exposure-induced hippocampal apoptosis, PI3K/Akt/Gsk-3β signaling disruption, and juvenile cognitive deficits in neonatal rats

Propofol is one of the most widely used intravenous anesthetics. However, repeated exposure to propofol may cause neurodegeneration in the developing brain. Dexmedetomidine (Dex), an α2 adrenoceptor agonist, has been previously demonstrated to provide neuroprotection against neuroapoptosis and neurocognitive impairments induced by several anesthetics. Thus, the current study aimed to investigate the effect of Dex on neonatal propofol-induced neuroapoptosis and juvenile spatial learning/memory deficits. Propofol (30 mg/kg) was intraperiotoneally administered to 7‑day‑old Sprague Dawley rats (n=75) three times each day at 90 min intervals for seven consecutive days with or without Dex (75 µg/kg) treatment 20 min prior to propofol injection. Following repeated propofol exposure, reduced Akt and GSK‑3β phosphorylation, increased cleaved caspase‑3 expression levels, an increased Bax/Bcl‑2 ratio, and increased terminal deoxynucleotidyl transferase‑mediated dUTP nick‑end labeling (TUNEL)‑positive cells in the CA1 hippocampal subregion were observed. Morris Water Maze testing at postnatal day 29 also demonstrated spatial learning and memory deficits following propofol treatment compared with the control group. Notably, these changes were significantly attenuated by Dex pretreatment. The results of the current study demonstrated that Dex ameliorates the neurocognitive impairment induced by repeated neonatal propofol challenge in rats, partially via its anti‑apoptotic action and normalization of the disruption to the PI3K/Akt/GSK‑3β signaling pathway. The present study provides preliminary evidence demonstrating the safety of propofol on the neonatal brain and the potential use of dexmedetomidine pretreatment in pediatric patients.

Propofol-Induced Neurotoxicity in the Fetal Animal Brain and Developments in Modifying These Effects-An Updated Review of Propofol Fetal Exposure in Laboratory Animal Studies

In the past twenty years, evidence of neurotoxicity in the developing brain in animal studies from exposure to several general anesthetics has been accumulating. Propofol, a commonly used general anesthetic medication, administered during synaptogenesis, may trigger widespread apoptotic neurodegeneration in the developing brain and long-term neurobehavioral disturbances in both rodents and non-human primates. Despite the growing evidence of the potential neurotoxicity of different anesthetic agents in animal studies, there is no concrete evidence that humans may be similarly affected. However, given the growing evidence of the neurotoxic effects of anesthetics in laboratory studies, it is prudent to further investigate the mechanisms causing these effects and potential ways to mitigate them. Here, we review multiple studies that investigate the effects of in utero propofol exposure and the developmental agents that may modify these deleterious effects.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Detrimental effects of postnatal exposure to propofol on memory and hippocampal LTP in mice

Acute effects of propofol on memory and hippocampal long-term potentiation (LTP) in adult animals were reported. However, long-term effect of early postnatal application of propofol on memory was not totally disclosed. In this study, experiments were designed to verify the mechanisms underlying the long-term detrimental effects of propofol on memory and hippocampal synaptic plasticity. A consecutive propofol protocol from postnatal day 7 was applied to model anesthesia, long term memory and hippocampal synaptic plasticity were detected 2 months later. Our results showed that repeated propofol exposure in early phase affect the memory in the adult phase. Through recording the field excitatory postsynaptic potentials (fEPSPs) at Schaffer colletaral-CA1 synapses, both of basal synaptic transmission and hippocampal LTP were decreased after propofol application. While LTD induced by low frequency stimulation and 3,5-dihydroxyphenylglycine (3,5-DHPG) were not affected. Through analyzing the ultrastructure of dendrite in CA1 region, we found that propofol application decreased the spine density, which was consistent with the decrease of PSD-95 expression. In addition, p-AKT level was reduced after first propofol application. Intracerebroventricular injection of Akt inhibitor could mimic the propofol effects on basal synaptic transmission, hippocampal LTP and memory. Taken together, these results suggested that propofol possibly decreased AKT signaling pathway to restrict the spine development, finally leading to hippocampal LTP impairment and memory deficit.

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

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

Repeated neonatal propofol administration induces sex-dependent long-term impairments on spatial and recognition memory in rats

Propofol is an anesthetic agent that gained wide use because of its fast induction of anesthesia and rapid recovery post-anesthesia. However, previous studies have reported immediate neurodegeneration and long-term impairment in spatial learning and memory from repeated neonatal propofol administration in animals. Yet, none of those studies has explored the sex-specific long-term physical changes and behavioral alterations such as social (sociability and social preference), emotional (anxiety), and other cognitive functions (spatial working, recognition, and avoidance memory) after neonatal propofol treatment. Seven-day-old Wistar-Kyoto (WKY) rats underwent repeated daily intraperitoneal injections of propofol or normal saline for 7 days. Starting fourth week of age and onwards, rats were subjected to behavior tests including open-field, elevated-plus-maze, Y-maze, 3-chamber social interaction, novel-object-recognition, passive-avoidance, and rotarod. Rats were sacrificed at 9 weeks and hippocampal protein expressions were analyzed by Western blot. Results revealed long-term body weight gain alterations in the growing rats and sex-specific impairments in spatial (female) and recognition (male) learning and memory paradigms. A markedly decreased expression of hippocampal NMDA receptor GluN1 subunit in female- and increased expression of AMPA GluR1 subunit protein expression in male rats were also found. Other aspects of behaviors such as locomotor activity and coordination, anxiety, sociability, social preference and avoidance learning and memory were not generally affected. These results suggest that neonatal repeated propofol administration disrupts normal growth and some aspects of neurodevelopment in rats in a sex-specific manner.

Hippocampal long-term potentiation in adult mice after recovery from ketamine anesthesia

Ketamine is frequently used to induce analgesia or anesthesia in laboratory animals, but its effects on learning and memory are poorly characterized. Long-term potentiation (LTP) is considered a cellular mechanism for learning and memory. Ketamine administration immediately abolishes hippocampal LTP in vivo, but whether this effect persists is not known. The authors administered one of two doses of ketamine to adult male C57BL/6 mice and measured LTP in hippocampal slices from the mice 24 h later. Neither LTP induction nor LTP maintenance differed significantly in mice that were administered ketamine compared with mice that were administered saline. The findings suggest that a single intraperitoneal dose of ketamine does not persistently alter LTP in adult male mice.

Systemic or intra-amygdala infusion of an endocannabinoid CB1 receptor antagonist AM251 blocked propofol-induced anterograde amnesia

Propofol is well-known for its anterograde amnesic actions. However, a recent experiment showed that propofol can also produce retrograde memory enhancement effects via an interaction with the endocannabinoid CB1 system. Therefore, the authors hypothesized that the regulating effect of propofol on the endocannabinoid CB1 system might also decrease the anterograde amnesic effect of propofol under some conditions, which might be a risk factor for intraoperative awareness. Since, the basolateral amygdala (BLA) has been confirmed to mediate propofol-induced anterograde amnesia and the BLA contains a high concentration of CB1 receptors, the authors investigated whether and how the endocannabinoid system, particularly the CB1 receptor within BLA, influences propofol-induced anterograde amnesia. Male Sprague-Dawley rats trained with inhibitory avoidance (IA) were systematically pre-trained using a memory-impairing dose of propofol (25 mg/kg). Before propofol administration, rats received an intraperitoneal injection of a CB1 receptor antagonist AM251 (1 mg/kg or 2 mg/kg) or a bilateral intra-BLA injection of AM251 (0.6 ng or 6 ng per 0.5 μl). Twenty-four hours after IA training, the IA retention latency was tested. It was found that systemic or intra-BLA injection of a non-regulating dose of AM251 (2 mg/kg or 6 ng per 0.5 μl, respectively) blocked the memory-impairing effect of propofol. These results indicate that the anterograde amnesic effect of propofol is mediated, in part, by activation of the CB1 cannabinoid receptors in the BLA.