Surgical stress induces brain-derived neurotrophic factor reduction and postoperative cognitive dysfunction via glucocorticoid receptor phosphorylation in aged mice

Recent advances in the crosstalk between the brain-derived neurotrophic factor and glucocorticoids

Brain-derived neurotrophic factor (BDNF), a key neurotrophin within the brain, by selectively activating the TrkB receptor, exerts multimodal effects on neurodevelopment, synaptic plasticity, cellular integrity and neural network dynamics. In parallel, glucocorticoids (GCs), vital steroid hormones, which are secreted by adrenal glands and rapidly diffused across the mammalian body (including the brain), activate two different groups of intracellular receptors, the mineralocorticoid and the glucocorticoid receptors, modulating a wide range of genomic, epigenomic and postgenomic events, also expressed in the neural tissue and implicated in neurodevelopment, synaptic plasticity, cellular homeostasis, cognitive and emotional processing. Recent research evidences indicate that these two major regulatory systems interact at various levels: they share common intracellular downstream pathways, GCs differentially regulate BDNF expression, under certain conditions BDNF antagonises the GC-induced effects on long-term potentiation, neuritic outgrowth and cellular death, while GCs regulate the intraneuronal transportation and the lysosomal degradation of BDNF. Currently, the BDNF-GC crosstalk features have been mainly studied in neurons, although initial findings show that this crosstalk could be equally important for other brain cell types, such as astrocytes. Elucidating the precise neurobiological significance of BDNF-GC interactions in a tempospatial manner, is crucial for understanding the subtleties of brain function and dysfunction, with implications for neurodegenerative and neuroinflammatory diseases, mood disorders and cognitive enhancement strategies.

Integrative analysis of circRNA networks in postoperative cognitive dysfunction

OBJECTIVE

In the quest to decipher the molecular intricacies of Postoperative Cognitive Dysfunction (POCD), this study focused on circular RNA (circRNA) and their regulatory networks.

MATERIALS AND METHODS

Analyzing the Gene Expression Omnibus Series (GSE) 147277 dataset, we pinpointed 10 differentially expressed circRNAs linked to POCD.

RESULTS

The ensuing competing endogenous RNA (ceRNA) network, featuring pivotal players like Homo sapiens(hsa)_circ_0003424 and hsa-miR-193b-5p, provided a comprehensive understanding of the molecular players at play in POCD.

CONCLUSION

Additionally, the Protein-Protein Interaction (PPI) network spotlighted 10 core Hub genes, including phosphatase and tensin homolog (PTEN) and signal transducer and activator of transcription 3(STAT3), shedding light on potential therapeutic targets.

MiR-181a-5p knockdown ameliorates sevoflurane anesthesia-induced neuron injury via regulation of the DDX3X/Wnt/β-catenin signaling axis

Sevoflurane is one of the most widely used inhaled anesthetics. MicroRNAs (miRNAs) have been demonstrated to affect sevoflurane anesthesia-induced neuron damage. The purpose of this study was to investigate the role and mechanism of miR-181a-5p in sevoflurane-induced hippocampal neuronal injury. Primary hippocampal neurons were identified using microscopy and immunofluorescence. The viability and apoptosis of sevoflurane anesthesia-induced neurons were detected by cell counting kit-8 (CCK-8) assay and terminal-deoxynucleoitidyl transferase-mediated nick end-labeling (TUNEL) staining assay, respectively. The levels of apoptosis- and oxidative stress-related proteins as well as the markers in the Wnt/β-catenin signaling pathway were examined by immunoblotting. Enzyme-linked immuno-sorbent assays were performed to examine the levels of inflammatory cytokines. Luciferase reporter assay was conducted to validate the combination between miR-181a-5p and DEAD-box helicase 3, X-linked (DDX3X). Sevoflurane exposure led to significantly inhibited hippocampal neuron viability and elevated miR-181a-5p expression. Knockdown of miR-181a-5p alleviated sevoflurane-induced neuron injury by reducing cell apoptosis, inflammatory response, and oxidative stress. Additionally, DDX3X was targeted and negatively regulated by miR-181a-5p. Moreover, miR-181a-5p inhibitor activated the Wnt/β-catenin pathway via DDX3X in sevoflurane-treated cells. Rescue experiments revealed that DDX3X knockdown or overexpression of Wnt antagonist Dickkopf-1 (DKK1) reversed the suppressive effects of miR-181a-5p inhibitor on cell apoptosis, inflammatory response, and oxidative stress in sevoflurane-treated neuronal cells. MiR-181a-5p ameliorated sevoflurane-triggered neuron injury by regulating the DDX3X/Wnt/β-catenin axis, suggesting the potential of miR-181a-5p as a novel and promising therapeutic target for the treatment of sevoflurane-evoked neurotoxicity.

Electroacupuncture pretreatment preserves telomerase reverse transcriptase function and alleviates postoperative cognitive dysfunction by suppressing oxidative stress and neuroinflammation in aged mice

BACKGROUND

Elderly patients often exhibit postoperative cognitive dysfunction (POCD), a postsurgical decline in memory and executive function. Oxidative stress and neuroinflammation, both pathological characteristics of the aged brain, contribute to this decline. This study posits that electroacupuncture (EA) stimulation, an effective antioxidant and anti-inflammatory modality, may enhance telomerase reverse transcriptase (TERT) function, the catalytic subunit of telomerase known for its protective properties against cellular senescence and oxidative damage, to alleviate POCD in aged mice.

METHODS

The animal POCD model was created by subjecting aged mice to abdominal surgery, followed by EA pretreatment at the Baihui acupoint (GV20). Postoperative cognitive function was gauged using the Morris water maze (MWM) test. Hippocampal TERT mRNA levels and telomerase activity were determined through qPCR and a Telomerase PCR ELISA kit, respectively. Oxidative stress was assessed through superoxide dismutase (SOD), reactive oxygen species (ROS), and malondialdehyde (MDA) levels. Iba-1 immunostaining determined the quantity of hippocampal microglia. Additionally, western blotting assessed TERT, autophagy markers, and proinflammatory cytokines at the protein level.

RESULTS

Abdominal surgery in aged mice significantly decreased telomerase activity and TERT mRNA and protein levels, but increased oxidative stress and neuroinflammation and decreased autophagy in the hippocampus. EA-pretreated mice demonstrated improved postoperative cognitive performance, enhanced telomerase activity, increased TERT protein expression, improved TERT mitochondrial localization, and reduced oxidative damage, autophagy dysfunction, and neuroinflammation. The neuroprotective benefits of EA pretreatment were diminished following TERT knockdown.

CONCLUSIONS

Our findings underscore the significance of TERT function preservation in alleviating surgery-induced oxidative stress and neuroinflammation in aged mice. A novel neuroprotective mechanism of EA stimulation is highlighted, whereby modulation of TERT and telomerase activity reduces oxidative damage and neuroinflammation. Consequently, maintaining TERT function via EA treatment could serve as an effective strategy for managing POCD in elderly patients.

Postoperative Learning and Memory Dysfunction Is More Severe in Males But Is Not Persistent and Transmittable to Next Generation in Young Adult Rats

BACKGROUND

Postoperative cognitive dysfunction (POCD) affects numerous patients each year and is associated with poor outcomes. Currently, the duration of POCD is not known. This preclinical study determined whether POCD was persistent, different between sexes and transmittable to the next generation.

METHODS

Two-month-old Sprague-Dawley rats had left carotid artery exposure under isoflurane anesthesia and their learning and memory were assessed from 5 days, 2 months, and 4 months after surgery. Rats with or without surgery were mated when they were 4 or 6 months old, and the learning and memory of the offspring were tested at 2 months of age.

RESULTS

Males exposed to surgery took a longer time to identify the target box after training sessions in a Barnes maze and had less freezing behavior in context-related fear conditioning than control rats when the tests were started 5 days after surgery. Similarly, female rats had a poorer performance than control rats in the Barnes maze test from 5 days after surgery. However, these poorer performances were not observed when the tests were administered 2 or 4 months after surgery. The offspring of rats with surgery had a performance similar to that of the offspring of control rats.

CONCLUSIONS

Our results suggest that both male and female rats develop POCD but that the learning and memory dysfunction appears to be more severe in male rats. POCD may not be persistent and does not transmit to the next generation.

Mineralocorticoid receptor agonist aldosterone rescues hippocampal neural stem cell proliferation defects and improves postoperative cognitive function in aged mice

OBJECTIVES

Hippocampal neurogenesis is closely related to learning and memory, and hippocampal neurogenesis disorders are involved in the development of many neurodegenerative diseases. Mineralocorticoid receptor (MR) plays a vital role in regulating stress response, neuroendocrine and cognitive functions, and is involved in regulating the integrity and stability of neural networks. However, the potential role of MR in the pathogenesis of postoperative cognitive dysfunction (POCD) is unclear. Therefore, this study evaluated the effect and mechanism of MR activation on postoperative hippocampal neurogenesis and cognitive function in aged mice.

METHODS

18-month-old male Kunming mice were randomly divided into Control group (C group), Surgery group (S group), Surgery+ Aldosterone group (S+Aldo group), Surgery + Wortmannin group (S+Wort group), Surgery + Aldosterone + Wortmannin group (S+Aldo+Wort group). Laparotomy was used to establish an animal model of postoperative cognitive dysfunction. After surgery, mice were intraperitoneally injected with aldosterone (100 ug/kg,150 ug/kg,200 ug/kg) and / or wortmannin (1 mg/kg); One day before the sacrifice, mice were injected intraperitoneally with BrdU (100 mg / kg / time, 3 times in total). Mice were subjected to Morris water maze and field tests at 1, 3, 7, and 14 days after surgery. Immunofluorescence was used to detect the number of BrdU +, Nestin +, BrdU/Nestin + positive cells in the hippocampal dentate gyrus of mice at 1, 3, 7 and 14 days after surgery. Western-blot was used to detect PI3K/Akt/GSK-3β signaling pathway related proteins Akt, p-Akt, GSK-3β, P-GSK-3β expression.

RESULTS

Stress impairs the performance of aged mice in water maze and open field tests, reduces the number of BrdU/Nestin+ cells in the hippocampal dentate gyrus, and inhibits the phosphorylation of Akt and GSK-3β proteins in the hippocampus. Aldosterone treatment promotes P-Akt, P-GSK-3β protein expression and hippocampal neural stem cell proliferation, and improves postoperative cognitive dysfunction. However, wortmannin treatment significantly reversed these effects of aldosterone.

CONCLUSIONS

The mineralocorticoid receptor agonist aldosterone promotes the proliferation of hippocampal neural stem cells and improves cognitive dysfunction in aged mice after surgery, and the mechanism may be related to activation of PI3K/Akt/GSK-3β signaling.

miR-182-5p Delivered by Plasma Exosomes Promotes Sevoflurane-Induced Neuroinflammation and Cognitive Dysfunction in Aged Rats with Postoperative Cognitive Dysfunction by Targeting Brain-Derived Neurotrophic Factor and Activating NF-κB Pathway

The objective of this study was to discuss the possible mechanism and effect of miR-182-5p delivered by plasma exosomes on sevoflurane-induced neuroinflammation and cognitive disorder in aged rats with postoperative cognitive dysfunction (POCD). Firstly, aged POCD rat models were constructed by sevoflurane anesthesia and superior mesenteric artery occlusion. Subsequently, exosomes and miR-182-5p were inhibited by injection of GW4869 and miR-182-5p-sponge, respectively. Then, exosomes were extracted from the plasma of rats in each group, followed by the determination of the morphology and diameters of exosomes as well as the expression of exosome markers CD63 and CD81 by transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and Western blot. Besides, the Morris water maze (MWM) and fear conditioning test were used to evaluate the learning and memory ability of rats; Western blot to detect the expression levels of neurotrophic factors (brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF)) as well as NF-κB pathway-related proteins (p65 and p-p65) in rat hippocampal tissues or PC-12 cells; qRT-PCR to assess the expression levels of miR-182-5p and BDNF in rat plasma, plasma exosomes, hippocampal tissues, and PC-12 cells; ELISA to evaluate the levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β in rat hippocampal tissues; and dual-luciferase reporter assay to verify the targeting relationship between miR-182-5p and BDNF. After examination, the results were obtained as follows. miR-182-5p expression was up-regulated in POCD rats and could be delivered by plasma exosomes. Inhibition of plasma exosomes or miR-182-5p could significantly ameliorate learning and memory disorders; decrease the levels of pro-inflammatory cytokines TNF-α, IL-6, and IL-1β; increase the expression of BDNF and NGF; and inhibit the activity of NF-κB signaling pathway in POCD rat hippocampus. In addition, miR-182-5p could also target and inhibit BDNF. All in all, miR-182-5p delivered by plasma exosomes promotes sevoflurane-induced neuroinflammation and cognitive dysfunction in aged POCD rats by targeting BDNF and activating the NF-κB pathway.

Effects of different types of non-cardiac surgical trauma on hippocampus-dependent memory and neuroinflammation

Background

Older individuals have been reported to suffer from cognitive disorders after surgery. Various types of surgical trauma have been used to establish postoperative cognitive dysfunction (POCD) animal models in preclinical studies. However, few comparative analyses of these animal models were conducted.

Methods

Tibial surgery, abdominal surgery, and extended abdominal surgery were performed on aged ICR mice to establish POCD models. Behavioral tests included open field, novel object recognition, fear conditioning, and Morris water maze tests. The Z-score methodology was adopted to obtain a comprehensive and integrated memory performance profile. The changes in hippocampal neuroinflammation were analyzed by ELISA, PCR, and immunofluorescence.

Results

In this study, we found that each type of non-cardiac surgical trauma has a different effects on locomotor activity. Tibial and extended abdominal surgeries led to more significant cognitive impairment than abdominal surgery. Inflammatory cytokines peaked on postoperative day 1 and decreased to control levels on days 3 and 7. Hippocampal neuroinflammation indicators between the three surgery types on postoperative day 1 had no statistical differences.

Conclusion

Overall, the type and intensity of non-cardiac surgical trauma can affect cognitive behavioral outcomes and central inflammation. The shortcomings and emerging issues of POCD animal research methods need to be further studied and solved.

Preoperative environment enrichment preserved neuroligin 1 expression possibly via epigenetic regulation to reduce postoperative cognitive dysfunction in mice

AIMS

Postoperative cognitive dysfunction (POCD) is a common and significant syndrome. Our previous studies have shown that surgery reduces dendritic arborization and spine density and that environment enrichment (EE) reduces POCD. Neuroligin 1 is a postsynaptic protein involved in the formation of postsynaptic protein complex. This study was designed to determine the role of neuroligin 1 in the protection of EE against POCD and the mechanisms for EE to affect neuroligin 1 expression.

METHODS

Eight-week-old C57BL/6J male mice with or without EE for 3, 7, or 14 days had right carotid artery exposure under isoflurane anesthesia. An anti-neuroligin 1 antibody at 1.5 µg/mouse was injected intracerebroventricularly at one and two weeks before the surgery. Mice were subjected to the Barnes maze and fear conditioning tests from one week after the surgery. Cerebral cortex and hippocampus were harvested after surgery.

RESULTS

Mice with surgery had poorer performance in the Barnes maze and fear conditioning tests than control mice. EE for 2 weeks, but not EE for 3 or 7 days, improved the performance of surgery mice in these tests. Surgery reduced neuroligin 1 in the hippocampus. Preoperative EE for 2 weeks attenuated this reduction. The anti-neuroligin 1 antibody worsened the performance of mice with surgery plus EE in the Barnes maze and fear conditioning tests. Surgery increased histone deacetylase activity and decreased the acetylated histone in the hippocampus. EE attenuated these surgery effects.

CONCLUSION

Our results suggest that preoperative EE for 2 weeks reduces POCD. This effect may be mediated by preserving neuroligin 1 expression via attenuating surgery-induced epigenetic dysregulation in the brain.

Low Skeletal Muscle Mass Is Associated With Perioperative Neurocognitive Disorder Due To Decreased Neurogenesis in Rats

BACKGROUND

Perioperative neurocognitive disorder (PND) is a postsurgical complication associated with neuroinflammation and impaired hippocampal neurogenesis, in which brain-derived neurotrophic factor (BDNF) plays a key role. Sarcopenia refers to age-related muscle loss that causes cognitive decline, muscle atrophy, and postoperative delirium. Rats with tail suspension (TS) were used to represent a low-activity model, which involves decreased hind limb function by TS. This hind limb unloading by TS can induce sarcopenia in 2 weeks. However, the relationship between PND and muscle atrophy is unclear. In this experiment, we investigated whether preoperative muscle atrophy induced by TS would affect neurogenesis and accelerate PND in rats.

METHODS

Sixty 21-week-old rats were assigned to 4 groups: the TS group, the TS with surgery (TS + S) group, the control group, and the control with surgery (control + S) group. After the abdominal manipulation under 3% sevoflurane anesthesia, cognitive function was assessed using the Morris water maze test and a fear-conditioning test. Neurogenesis was evaluated by checking BDNF secretion and immunohistochemical staining in the hippocampus.

RESULTS

The TS + S group showed impaired swimming latency (difference of means = 12.4 versus control + S; 95% confidence interval [CI], 2.0-22.7; P = .016) (difference of means = 15.2 versus TS; 95% CI, 0.4-30.1; P = .043) and path length (difference of means = 147.8 versus control + S; 95% CI, 20.7-274.9; P = .020) in the maze test and cued fear memory (difference of means = -26.0 versus TS; 95% CI, -46.4 to -5.6; P = .006) (difference of means = -22.3 versus control + S; 95% CI, -42.7 to -1.9; P = .026) in the fear-conditioning test. The postoperative levels of BDNF in the TS + S and TS groups were reduced compared with the other groups (P = .002). The number of neural precursors in the dentate gyrus was significantly lower in the TS + S group (P < .001).

CONCLUSIONS

We observed that preoperative hind limb muscle atrophy, indicated by TS, was associated with an increased occurrence of PND through the reduction in BDNF and neurogenesis after abdominal surgery in young adult rats. Therefore, we concluded that preoperative low skeletal muscle mass can induce PND due to impaired postoperative neurogenesis. Our findings might indicate that low-cost perioperative interventions, such as preoperative exercise, is beneficial to preventing PND.

Update on the Mechanism and Treatment of Sevoflurane-Induced Postoperative Cognitive Dysfunction

Sevoflurane is one of the most widely used anesthetics for the induction and maintenance of general anesthesia in surgical patients. Sevoflurane treatment may increase the incidence of postoperative cognitive dysfunction (POCD), and patients with POCD exhibit lower cognitive abilities than before the operation. POCD affects the lives of patients and places an additional burden on patients and their families. Understanding the mechanism of sevoflurane-induced POCD may improve prevention and treatment of POCD. In this paper, we review the diagnosis of POCD, introduce animal models of POCD in clinical research, analyze the possible mechanisms of sevoflurane-induced POCD, and summarize advances in treatment for this condition.

Ginkgolide B‑mediated therapeutic effects on perioperative neurocognitive dysfunction are associated with the inhibition of iNOS‑mediated production of NO

Perioperative neurocognitive dysfunction (PND) is a prevalent neurological complication after anesthesia and surgery. Ginkgolide B (GB) has been suggested to improve lipopolysaccharide-induced learning and memory impairment. The present study aimed to investigate whether GB serves a protective role against PND by inhibiting inducible nitric oxide synthase (iNOS) and nitric oxide (NO). Abdominal surgery was performed on 10- to 12-week-old male C57BL/6 mice under isoflurane anesthesia. Prior to surgery, 1400W (a specific iNOS inhibitor) and GB were administered via intraperitoneal injection. Open field and fear conditioning tests were conducted to assess cognitive function on postoperative days 1 and 3. Biochemical assays were performed to evaluate alterations in NO, malondialdehyde (MDA) and superoxide dismutase (SOD) levels. Western blotting was performed to measure iNOS expression in the hippocampus on postoperative day 1. In addition, hematoxylin and eosin staining was performed to detect the neuronal morphology in the hippocampus. Following treatment with 1400W or GB, surgery-induced cognitive dysfunction was improved. Compared with the control group, the surgery group exhibited significant overproduction of iNOS and MDA in the hippocampus on postoperative day 1. Higher levels of NO were also detected in the hippocampus and prefrontal cortex of the surgery group on postoperative day 1. Furthermore, pretreatment with 1400W or GB significantly inhibited the surgery-induced elevation of NO and MDA in brain tissues. Moreover, GB pretreatment significantly inhibited surgery-induced downregulation of SOD and upregulation of iNOS. Surgery-induced increases in neuronal loss and the Bax/Bcl-2 ratio in the hippocampus were significantly inhibited by pretreatment with GB. Collectively, the results of the present study demonstrated that the therapeutic effects of GB on PND were associated with inhibition of iNOS-induced NO production, increased SOD, and the alleviation of neuronal loss and apoptosis.

The Role of Perioperative Sleep Disturbance in Postoperative Neurocognitive Disorders

Postoperative neurocognitive disorder (PND) increases the length of hospital stay, mortality, and risk of long-term cognitive impairment. Perioperative sleep disturbance is prevalent and commonly ignored and may increase the risk of PND. However, the role of perioperative sleep disturbances in PND remains unclear. Nocturnal sleep plays an indispensable role in learning, memory, and maintenance of cerebral microenvironmental homeostasis. Hospitalized sleep disturbances also increase the incidence of postoperative delirium and cognitive dysfunction. This review summarizes the role of perioperative sleep disturbances in PND and elucidates the potential mechanisms underlying sleep-deprivation-mediated PND. Activated neuroinflammation and oxidative stress; impaired function of the blood-brain barrier and glymphatic pathway; decreased hippocampal brain-derived neurotrophic factor, adult neurogenesis, and sirtuin1 expression; and accumulated amyloid-beta proteins are associated with PND in individuals with perioperative sleep disorders. These findings suggest that the improvement of perioperative sleep might reduce the incidence of postoperative delirium and postoperative cognitive dysfunction. Future studies should further investigate the role of perioperative sleep disturbance in PND.

Aging alters Hv1-mediated microglial polarization and enhances neuroinflammation after peripheral surgery

Perioperative neurocognitive disorders have been widely recognized as common adverse events after surgical intervention. Aging is one of the most important independent risk factors for worsened cognitive outcome, and this deterioration is linked to exacerbated microglia-mediated neuroinflammation in the aged brain. Under pathological stimulation, microglia are capable of polarizing toward proinflammatory M1 and anti-inflammatory M2 phenotypes. In the present study, we examined how aging affects microglial responses and neuroinflammation following peripheral surgery. Adult (2-3 months) and aged (18 months old) male C57/BL6 mice were subjected to tibial fracture or sham surgery. Aged mice exhibited higher level of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in the hippocampus. The expression of synaptic protein synaptophysin (SYP) was also markedly reduced in the aged brain after the surgery. Both adult and aged mice showed significant increases in M1 microglial polarization (CD16/32). In contrast, tibial fracture surgery induced a decreased M2 microglial polarization (CD206, Ym1/2, Arg1) in aged brain but enhanced M2 microglial polarization in adult brain. Aged mice have upregulated voltage-gated proton channel (Hv1) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit expression compared with adult mice. The percentage of CD16/32-positive M1 microglia colabeling with Hv1 was higher in aged mice after tibial fracture surgery. Thus, Hv1/NADPH oxidase upregulation in the aged brain may shift the dynamic equilibrium of microglial activation toward M1 polarization and exaggerate postoperative neuroinflammatory responses after peripheral surgical intervention.

Neuroinflammation and Perioperative Neurocognitive Disorders

Neuroinflammation has become a key hallmark of neurological complications including perioperative pathologies such as postoperative delirium and longer-lasting postoperative cognitive dysfunction. Dysregulated inflammation and neuronal injury are emerging from clinical studies as key features of perioperative neurocognitive disorders. These findings are paralleled by a growing body of preclinical investigations aimed at better understanding how surgery and anesthesia affect the central nervous system and possibly contribute to cognitive decline. Herein, we review the role of postoperative neuroinflammation and underlying mechanisms in immune-to-brain signaling after peripheral surgery.

Histone H3K9 Trimethylation Downregulates the Expression of Brain-Derived Neurotrophic Factor in the Dorsal Hippocampus and Impairs Memory Formation During Anaesthesia and Surgery

Brain-derived neurotrophic factor (BDNF) is essential for cognitive and memory functions. Abnormal BDNF expression in the central nervous system may impair these functions. Anaesthesia and surgery can induce perioperative neurocognitive disorders (PND). Clinical studies show that BDNF expression is decreased in patients presenting with cognitive impairment after anaesthesia and surgery. However, the molecular mechanism is still unclear. Epigenetic regulation plays an important role in cognition. The hypermethylation of H3K9 is crucial for transcriptional silencing and the onset of cognitive disorders. Here, we hypothesised that H3K9 trimethylation repressed BDNF expression and impaired memory formation or recall during anaesthesia and surgery. Laparotomy under isoflurane inhalation anaesthesia, behavioural tests, Western blotting, quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR), chromatin immunoprecipitation (ChIP), and immunohistochemistry were used in this study. BDNF expression was decreased in the hippocampus after anaesthesia and surgery. Cognitive impairment affected memory formation but not recall. The trimethylation of H3K9 downregulated BDNF expression. The overexpression of BDNF or use of exogenous BDNF improved the impairment of memory formation caused by anaesthesia and surgery. Therefore, inhibiting H3K9 trimethylation and increasing the expression of BDNF may help prevent PND in the clinical setting.

Nicotine-Induced Neuroprotection against Cognitive Dysfunction after Partial Hepatectomy Involves Activation of BDNF/TrkB Signaling Pathway and Inhibition of NF-κB Signaling Pathway in Aged Rats

Introduction

The main purpose of this study was to investigate the effects and possible mechanisms of nicotine pre-treatment on postoperative cognitive dysfunction (POCD) in aged rats.

Methods

Nicotine (0.5 mg/kg) was given i.p. immediately after anesthesia induction. After the Morris water maze test was used to evaluate the rats' spatial learning and memory, serum and hippocampal tissues were harvested 1 and 3 days after intervention. Inflammatory cytokines in the serum were evaluated by Enzyme-linked Immunosorbent Assay (ELISA). Brain-derived neurotrophic factor (BDNF), p-TrkB, neuroinflammation cytokines, NF-κB p65, and cleaved caspase-3 were measured by western blotting; neuronal apoptosis in the hippocampal CA1 region was also evaluated by TUNEL staining.

Results

We found that nicotine markedly attenuated the POCD and reduced the elevated levels of inflammatory cytokines in the serum, including IL-1β and high mobility group box-1 (HMGB1), on postoperative day 1. Additionally, nicotine suppressed the surgery-induced release of IL-1β, TNF-ɑ, HMGB1, and NF-κB p65 in the hippocampus on postoperative day 1 and day 3. In addition, operated rats displayed lower BDNF and p-TrkB in the hippocampus on postoperative day 1, returning to baseline by postoperative day 3. However, nicotine pre-treatment clearly reversed the surgical stress-induced decrease in both BDNF and p-TrkB expression in the hippocampus. Furthermore, nicotine pre-treatment significantly alleviated the surgery-induced increase in the neuronal apoptosis in the hippocampus on postoperative day 1 and day 3.

Conclusions

Our results showed that nicotine-induced neuroprotection against POCD may involve activation of the BDNF/TrkB signaling pathway and inhibition of the NF-κB signaling pathway.

Implications

Nicotine has long been considered a potent therapeutic agent for neuroprotection. This study reported the positive effect of nicotine treatment on cognitive dysfunction after partial hepatectomy in aged rats. Furthermore, the underlying mechanism may involve activation of the BDNF/TrkB signaling pathway and inhibition of the NF-κB signaling pathway in the hippocampus.

Cell cycle activation contributes to isoflurane-induced neurotoxicity in the developing brain and the protective effect of CR8

AIMS

It is well established that exposure of common anesthetic isoflurane in early life can induce neuronal apoptosis and long-lasting cognitive deficit, but the underlying mechanisms were not well understood. The cell cycle protein Cyclin B1 plays an important role in the survival of postmitotic neurons. In the present study, we investigated whether cyclin B1-mediated cell cycle activation pathway is a contributing factor in developmental isoflurane neurotoxicity.

METHODS

Postnatal day 7 mice were exposed to 1.2% isoflurane for 6 hours. CR8 (a selective inhibitor of cyclin-dependent kinases) was applied before isoflurane treatment. Brain samples were collected 6 hours after discontinuation of isoflurane, for determination of neurodegenerative biomarkers and cell cycle biomarkers.

RESULTS

We found that isoflurane exposure leads to upregulated expression of cell cycle-related biomarkers Cyclin B1, Phospho-CDK1(Thr-161), Phospho-n-myc and downregulated Phospho-CDK1 (Tyr-15). In addition, isoflurane induced increase in Bcl-xL phosphorylation, cytochrome c release, and caspase-3 activation that resulted in neuronal cell death. Systemic administration of CR8 attenuated isoflurane-induced cell cycle activation and neurodegeneration.

CONCLUSION

These findings suggest the role of cell cycle activation to be a pathophysiological mechanism for isoflurane-induced apoptotic cell death and that treatment with cell cycle inhibitors may provide a possible therapeutic target for prevention of developmental anesthetic neurotoxicity.

Effects of prebiotic galacto-oligosaccharide on postoperative cognitive dysfunction and neuroinflammation through targeting of the gut-brain axis

Background

Surgery-induced neuroinflammation plays an important role in postoperative cognitive dysfunction (POCD). Gut microbiota is a key regulator of neurological inflammation. Nurturing with prebiotics is an effective microbiota manipulation that can regulate host immunity and cognition. The aim of the present study was to test whether administration of the prebiotic Bimuno® (galactooligosaccharide (B-GOS) mixture) could ameliorate POCD and attenuate surgery-induced neuroinflammation through the microbiota-brain-axis.

Methods

Adult rats undergoing abdominal surgery under isoflurane anesthesia were fed with water or prebiotic B-GOS supplementation (15 g/L) for 3 weeks. Novel objective recognition task was employed for testing cognitive changes on postoperative day three. Expression of microglial marker Iba-1 in the hippocampus was assessed by immunohistochemical staining. Expression levels of phenotypic gene markers of activated microglia (M1: iNOS, CD68, CD32; M2: Ym1, CD206, and SOCS3) in hippocampus were determined by quantitative polymerase chain reaction (qPCR). Inflammatory cytokines in the hippocampus were assessed using enzyme-linked immunosorbent assay (ELISA). Feces were collected for microbial community analysis.

Results

Rats exhibited an impairment in novel objective recognition 3 days after surgery compared with control rats (P < .01). In the hippocampus, expressions of Iba-1 and M1 markers of surgical rats were significantly upregulated. Similarly, expressions of SOCS3 and CD206 in the hippocampus were upregulated. Additionally, increasing levels of IL-6 and IL-4 were evident in the hippocampus. Administration of B-GOS significantly alleviated cognitive decline induced by surgery (P < .01). B-GOS-fed rats showed a significantly downregulated activation of microglia and expressions of M1-related genes and SOCS3 and IL-6. While there was no significant difference in expressions of CD206 and Ym1 and IL-4 between the surgical and B-GOS groups. Analysis of gut microbiome found that administration of B-GOS induced a significant change beta diversity of the gut microbiome and proliferation of Bifidobacterium and other potentially anti-inflammatory microbes.

Conclusions

Administration of B-GOS has a beneficial effect on regulating neuroinflammatory and cognitive impairment in a rat model of abdominal surgery and was associated with the manipulation of gut microbiota.

Surgery, neuroinflammation and cognitive impairment

Trauma experienced during surgery can contribute to the development of a systemic inflammatory response that can cause multi-organ dysfunction or even failure. Post-surgical neuroinflammation is a documented phenomenon that results in synaptic impairment, neuronal dysfunction and death, and impaired neurogenesis. Various pro-inflammatory cytokines, such as TNFα, maintain a state of chronic neuroinflammation, manifesting as post-operative cognitive dysfunction and post-operative delirium. Furthermore, elderly patients with post-operative cognitive dysfunction or delirium are three times more likely to experience permanent cognitive impairment or dementia. We conducted a narrative review, considering evidence extracted from various databases including Pubmed, MEDLINE and EMBASE, as well as journals and book reference lists. We found that further pre-clinical and well-powered clinical studies are required to delineate the precise pathogenesis of post-operative delirium and cognitive dysfunction. Despite the burden of post-operative neurological sequelae, clinical studies investigating therapeutic agents, such as dexmedetomidine, ibuprofen and statins, have yielded conflicting results. In addition, evidence supporting novel therapeutic avenues, such as nicotinic and HMGB-1 targeting and remote ischaemic pre-conditioning, is limited and necessitates further investigation.

Sirt1 mediates improvement of isoflurane-induced memory impairment following hyperbaric oxygen preconditioning in middle-aged mice

Hyperbaric oxygen (HBO) preconditioning (PC) has been suggested as a feasible method to provide neuroprotection from postoperative cognitive dysfunction (POCD). However, whether HBO-PC can ameliorate cognitive deficits induced by isoflurane, and the possible mechanism by which it may exert its effect, has not yet been clarified. In the present study, middle-aged mice were exposed to isoflurane anesthesia (1.5 minimal alveolar concentration [MAC]) for 2 h to establish a POCD model. After HBO preconditioning, cognitive function and expression of hippocampal sirtuin 1 (Sirt1), nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) were evaluated 24 h following isoflurane treatment, in the presence or absence of Sirt1 knockdown by short hairpin RNA (shRNA). HBO preconditioning increased the expression of Sirt1, Nrf2, and HO-1 and ameliorated memory dysfunction. Meanwhile, Sirt1 knockdown inhibited the expression of Nrf2 and HO-1 and attenuated the HBO preconditioning-associated memory improvement. Our results suggest that the application of HBO preconditioning is a useful treatment for POCD, and that Sirt1 may be a potential molecular target for POCD therapy.

Curcumin attenuates surgery-induced cognitive dysfunction in aged mice

Post-operative cognitive dysfunction (POCD) is associated with elderly patients undergoing surgery. However, pharmacological treatments for POCD are limited. In this study, we found that curcumin, an active compound derived from Curcuma longa, ameliorated the cognitive dysfunction following abdominal surgery in aged mice. Further, curcumin prevented surgery-induced anti-oxidant enzyme activity. Curcumin also increased brain-derived neurotrophic factor (BDNF)-positive area and expression of pAkt in the brain, suggesting that curcumin activated BDNF signaling in aged mice. Furthermore, curcumin neutralized cholinergic dysfunction involving choline acetyltransferase expression induced by surgery. These results strongly suggested that curcumin prevented cognitive impairments via multiple targets, possibly by increasing the activity of anti-oxidant enzymes, activation of BDNF signaling, and neutralization of cholinergic dysfunction, concurrently. Based on these novel findings, curcumin might be a potential agent in POCD prophylaxis and treatment.

Retinoic acid increases glucocorticoid receptor phosphorylation via cyclin-dependent kinase 5

Glucocorticoid receptor (GR) function is modulated by phosphorylation. As retinoic acid (RA) can activate some cytoplasmic kinases able to phosphorylate GR, we investigated whether RA could modulate GR phosphorylation in neuronal cells in a context of long-term glucocorticoid exposure. A 4-day treatment of dexamethasone (Dex) plus RA, showed that RA potentiated the (Dex)-induced phosphorylation on GR Serine 220 (_pSer220GR) in the nucleus of a hippocampal HT22 cell line. This treatment increased the cytoplasmic ratio of p35/p25 proteins, which are major CDK5 cofactors. Roscovitine, a pharmacological CDK5 inhibitor, or a siRNA against CDK5 prevented RA potentiation of GR phosphorylation. Furthermore, roscovitine counter-acted the effect of RA on GR sensitive target proteins such as BDNF or tissue-transglutaminase. These data help understanding the interaction between RA- and glucocorticoid-signalling pathways, both of which have strong influences on the adult brain.

Orthopedic surgery modulates neuropeptides and BDNF expression at the spinal and hippocampal levels

Pain is a critical component hindering recovery and regaining of function after surgery, particularly in the elderly. Understanding the role of pain signaling after surgery may lead to novel interventions for common complications such as delirium and postoperative cognitive dysfunction. Using a model of tibial fracture with intramedullary pinning in male mice, associated with cognitive deficits, we characterized the effects on the primary somatosensory system. Here we show that tibial fracture with pinning triggers cold allodynia and up-regulates nerve injury and inflammatory markers in dorsal root ganglia (DRGs) and spinal cord up to 2 wk after intervention. At 72 h after surgery, there is an increase in activating transcription factor 3 (ATF3), the neuropeptides galanin and neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF), as well as neuroinflammatory markers including ionized calcium-binding adaptor molecule 1 (Iba1), glial fibrillary acidic protein (GFAP), and the fractalkine receptor CX3CR1 in DRGs. Using an established model of complete transection of the sciatic nerve for comparison, we observed similar but more pronounced changes in these markers. However, protein levels of BDNF remained elevated for a longer period after fracture. In the hippocampus, BDNF protein levels were increased, yet there were no changes in Bdnf mRNA in the parent granule cell bodies. Further, c-Fos was down-regulated in the hippocampus, together with a reduction in neurogenesis in the subgranular zone. Taken together, our results suggest that attenuated BDNF release and signaling in the dentate gyrus may account for cognitive and mental deficits sometimes observed after surgery.

Neuroinflammatory challenges compromise neuronal function in the aging brain: Postoperative cognitive delirium and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that targets memory and cognition, and is the most common form of dementia among the elderly. Although AD itself has been extensively studied, very little is known about early-stage preclinical events and/or mechanisms that may underlie AD pathogenesis. Since the majority of AD cases are sporadic in nature, advancing age remains the greatest known risk factor for AD. However, additional environmental and epigenetic factors are thought to accompany increasing age to play a significant role in the pathogenesis of AD. Postoperative cognitive delirium (POD) is a behavioral syndrome that primarily occurs in elderly patients following a surgical procedure or injury and is characterized by disruptions in cognition. Individuals that experience POD are at an increased risk for developing dementia and AD compared to normal aging individuals. One way in which cognitive function is affected in cases of POD is through activation of the inflammatory cascade following surgery or injury. There is compelling evidence that immune challenges (surgery and/or injury) associated with POD trigger the release of pro-inflammatory cytokines into both the periphery and central nervous system. Thus, it is possible that cognitive impairments following an inflammatory episode may lead to more severe forms of dementia and AD pathogenesis. Here we will discuss the inflammation associated with POD, and highlight the advantages of using POD as a model to study inflammation-evoked cognitive impairment. We will explore the possibility that advancing age and immune challenges may provide mechanistic evidence correlating early life POD with AD. We will review and propose neural mechanisms by which cognitive impairments occur in cases of POD, and discuss how POD may augment the onset of AD.

Diurnal Variation of the Peripheral Cholinergic Antiinflammatory Function in Mice

AIMS

Cholinergic antiinflammatory (CAI) pathway functions importantly in inflammation via α7 nicotinic acetylcholine receptors (α7nAChR). The present work tested circadian rhythm in peripheral CAI activity and validities of CAI activity and glucocorticoids in chronotherapy for lipopolysaccharide (LPS)-induced shock.

METHODS

Vesicular acetylcholine transporter (VAChT) expressed in liver and kidney was examined every 3 h in C57BL/6 mice. Proinflammatory cytokines in serum and survival time in shock were monitored after LPS injection every 3 h. Mifepristone, antagonist of glucocorticoid receptors, and methyllycaconitine (MLA), antagonist of α7nAChR, were administrated before LPS to block antiinflammatory function of endogenous glucocorticoids and acetylcholine.

RESULTS

Both levels of tumor necrosis factor α, interleukin 1β, and interleukin 6 and mortality exhibited diurnal variations with prominent peaks when LPS was given at 15:00, and the minimum mortality occurred at 00:00. Expression of VAChT increased during resting period. MLA increased serum proinflammatory cytokines slightly, but not affected survival rate. Both differences in cytokines and in survival times between LPS injection at 15:00 and 00:00 were eliminated by mifepristone, but not by MLA.

CONCLUSION

Peripheral CAI pathway exerts more powerful antiinflammatory effect during resting period. Glucocorticoids appear to be efficient in chronotherapy for septic shock.

Postoperative cognitive dysfunction and neuroinflammation; Cardiac surgery and abdominal surgery are not the same

Postoperative cognitive dysfunction (POCD) is a debilitating surgical complication, with cardiac surgery patients at particular risk. To gain insight in the mechanisms underlying the higher incidence of POCD after cardiac versus non-cardiac surgery, systemic and central inflammatory changes, alterations in intraneuronal pathways, and cognitive performance were studied after cardiac and abdominal surgery in rats. Male Wistar rats were subjected to ischemia reperfusion of the upper mesenteric artery (abdominal surgery) or the left coronary artery (cardiac surgery). Control rats remained naïve, received anesthesia only, or received thoracic sham surgery. Rats were subjected to affective and cognitive behavioral tests in postoperative week 2. Plasma concentrations of inflammatory factors, and markers for neuroinflammation (NGAL and microglial activity) and the BDNF pathway (BDNF, p38MAPK and DCX) were determined. Spatial memory was impaired after both abdominal and cardiac surgery, but only cardiac surgery impaired spatial learning and object recognition. While all surgical procedures elicited a pronounced acute systemic inflammatory response, NGAL and TNFα levels were particularly increased after abdominal surgery. Conversely, NGAL in plasma and the paraventricular nucleus of the hypothalamus and microglial activity in hippocampus and prefrontal cortex on postoperative day 14 were increased after cardiac, but not abdominal surgery. Both surgery types induced hippocampal alterations in BDNF signaling. These results suggest that POCD after cardiac surgery, compared to non-cardiac surgery, affects different cognitive domains and hence may be more extended rather than more severe. Moreover, while abdominal surgery effects seem limited to hippocampal brain regions, cardiac surgery seems associated with more wide spread alterations in the brain.

Surgery-Induced Hippocampal Angiotensin II Elevation Causes Blood-Brain Barrier Disruption via MMP/TIMP in Aged Rats

Reversible blood-brain barrier (BBB) disruption has been uniformly reported in several animal models of postoperative cognitive dysfunction (POCD). Nevertheless, the precise mechanism underlying this occurrence remains unclear. Using an aged rat model of POCD, we investigated the dynamic changes in expression of molecules involved in BBB disintegration, matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9), as well as three of their endogenous tissue inhibitors of MMP (TIMP-1, -2, -3), and tried to establish the correlation between MMP/TIMP balance and surgery-induced hippocampal BBB disruption. We validated the increased hippocampal expression of angiotensin II (Ang II) and Ang II receptor type 1 (AT1) after surgery. We also found MMP/TIMP imbalance as early as 6 h after surgery, together with increased BBB permeability and decreased expression of Occludin and zonula occludens-1 (ZO-1), as well as increased basal lamina protein laminin at 24 h postsurgery. The AT1 antagonist candesartan restored MMP/TIMP equilibrium and modulated expression of Occludin and laminin, but not ZO-1, thereby improving BBB permeability. These events were accompanied by suppression of the surgery-induced canonical nuclear factor-κB (NF-κB) activation cascade. Nevertheless, AT1 antagonism did not affect nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ) expression. Collectively, these findings suggest that surgery-induced Ang II release impairs BBB integrity by activating NF-κB signaling and disrupting downstream MMP/TIMP balance via AT1 receptor.