Prior infection exacerbates postoperative cognitive dysfunction in aged rats

The potential mechanism of mitochondrial homeostasis in postoperative neurocognitive disorders: an in-depth review

Postoperative neurocognitive disorders (PND) are the most common neurological disorders following surgery and anaesthesia before and within 12 months after surgery, with a high prevalence in the geriatric population. PND can severely deteriorate the quality of life of patients, especially among the elderly, mainly manifested as memory loss, attention, decline and language comprehension disorders, mostly in elderly patients, with an incidence as high as 31%. Previous studies have also raised the possibility of accelerated cognitive decline and underlying neuropathological processes associated with diseases that affect cognitive performance (e.g. Alzheimer's dementia) for reasons related to anaesthesia and surgery. Currently, most research on PND has focused on various molecular pathways, especially in the geriatric population. The various hypotheses that have been proposed regarding the mechanisms imply peripheral neuroinflammation, oxidative stress, mitochondrial homeostasis, synaptic function, autophagy disorder, blood-brain barrier dysfunction, the microbiota-gut-brain axis and lack of neurotrophic support. However, the underlying pathogenesis and molecular mechanisms of PND have not yet been uncovered. Recent research has focused on mitochondrial homeostasis. In this paper, we present a review of various studies to better understand and characterize the mechanisms of associated cognitive dysfunction. As the biochemical basis of PND becomes more clearly defined, future treatments based on mitochondrial homeostasis modulation can prove to be very promising.

Post-operative cognitive dysfunction is exacerbated by high-fat diet via TLR4 and prevented by dietary DHA supplementation

Post-operative cognitive dysfunction (POCD) is an abrupt decline in neurocognitive function arising shortly after surgery and persisting for weeks to months, increasing the risk of dementia diagnosis. Advanced age, obesity, and comorbidities linked to high-fat diet (HFD) consumption such as diabetes and hypertension have been identified as risk factors for POCD, although underlying mechanisms remain unclear. We have previously shown that surgery alone, or 3-days of HFD can each evoke sufficient neuroinflammation to cause memory deficits in aged, but not young rats. The aim of the present study was to determine if HFD consumption before surgery would potentiate and prolong the subsequent neuroinflammatory response and memory deficits, and if so, to determine the extent to which these effects depend on activation of the innate immune receptor TLR4, which both insults are known to stimulate. Young-adult (3mo) & aged (24mo) male F344xBN F1 rats were fed standard chow or HFD for 3-days immediately before sham surgery or laparotomy. In aged rats, the combination of HFD and surgery caused persistent deficits in contextual memory and cued-fear memory, though it was determined that HFD alone was sufficient to cause the long-lasting cued-fear memory deficits. In young adult rats, HFD + surgery caused only cued-fear memory deficits. Elevated proinflammatory gene expression in the hippocampus of both young and aged rats that received HFD + surgery persisted for at least 3-weeks after surgery. In a separate experiment, rats were administered the TLR4-specific antagonist, LPS-RS, immediately before HFD onset, which ameliorated the HFD + surgery-associated neuroinflammation and memory deficits. Similarly, dietary DHA supplementation for 4 weeks prior to HFD onset blunted the neuroinflammatory response to surgery and prevented development of persistent memory deficits. These results suggest that HFD 1) increases risk of persistent POCD-associated memory impairments following surgery in male rats in 2) a TLR4-dependent manner, which 3) can be targeted by DHA supplementation to mitigate development of persistent POCD.

J147 affects cognition and anxiety after surgery in Zucker rats

Vulnerable patients are at risk for neuroinflammation-mediated post-operative complications, including depression (POD) and cognitive dysfunction (POCD). Zucker rats, expressing multiple risk factors for post-operative complications in humans, may provide a clinically relevant model to study pathophysiology and explore potential interventions. J147, a newly developed anti-dementia drug, was shown to prevent POCD in young healthy rats, and improved early post-surgical recovery in Zucker rats. Aim of the present study was to investigate POCD and the therapeutic potential of J147 in male Zucker rats. Risk factors in the Zucker rat strain were evaluated by comparison with lean littermates. Zucker rats were subjected to major abdominal surgery. Acute J147 treatment was provided by a single iv injection (10 mg/kg) at the start of surgery, while chronic J147 treatment was provided in the food (aimed at 30 mg/kg/day), starting one week before surgery and up to end of protocol. Effects on behavior were assessed, and plasma, urine and brain tissue were collected and processed for immunohistochemistry and molecular analyses. Indeed, Zucker rats displayed increased risk factors for POCD, including obesity, high plasma triglycerides, low grade systemic inflammation, impaired spatial learning and decreased neurogenesis. Surgery in Zucker rats reduced exploration and increased anxiety in the Open Field test, impaired short-term spatial memory, induced a shift in circadian rhythm and increased plasma neutrophil gelatinase-associated lipocalin (NGAL), microglia activity in the CA1 and blood brain barrier leakage. Chronic, but not acute J147 treatment reduced anxiety in the Open Field test and protected against the spatial memory decline. Moreover, chronic J147 increased glucose sensitivity. Acute J147 treatment improved long-term spatial memory and reversed the circadian rhythm shift. No anti-inflammatory effects were seen for J147. Although Zucker rats displayed risk factors, surgery did not induce extensive POCD. However, increased anxiety may indicate POD. Treatment with J147 showed positive effects on behavioral and metabolic parameters, but did not affect (neuro)inflammation. The mixed effect of acute and chronic treatment may suggest a combination for optimal treatment.

Systemic inflammation, neuroinflammation and perioperative neurocognitive disorders

Perioperative neurocognitive disorder (PND) is a common disorder following anesthesia and surgery, especially in the elderly. The complex cellular and molecular processes are involved in PND, but the underlying pathogenesis of which remains inconclusive due to conflicting data. A growing body of evidence has been shown that perioperative systemic inflammation plays important roles in the development of PND. We reviewed the relevant literature retrieved by a search in the PubMed database (on July 20, 2023). The search terms used were "delirium", "post operative cognitive dysfunction", "perioperative neurocognitive disorder", "inflammation" and "systemic", alone and in combination. All articles identified were English-language, full-text papers. The ones cited in the review are those that make a substantial contribution to the knowledge about systemic inflammation and PNDs. The aim of this review is to bring together the latest evidence for the understanding of how perioperative systemic inflammation mediates neuroinflammation and brain injury, how the inflammation is regulated and how we can translate these findings into prevention and/or treatment for PND.

Prevention of Postoperative Cognitive Dysfunction by Minocycline in Elderly Patients after Total Knee Arthroplasty: A Randomized, Double-blind, Placebo-controlled Clinical Trial

BACKGROUND

There are no effective pharmacologic interventions for preventing postoperative cognitive dysfunction in daily practice. Since the antibiotic minocycline is known to suppress postoperative neuroinflammation, this study hypothesized and investigated whether minocycline might have a preventive effect on postoperative cognitive dysfunction after noncardiac surgery.

METHODS

This study included patients aged more than 60 yr undergoing total knee arthroplasty under general anesthesia. They were randomly assigned to minocycline and placebo groups, to orally receive 100 mg of minocycline or placebo twice daily from the day before surgery until the seventh day after surgery. Cognitive function was evaluated before surgery, and 1 week and 3 months after surgery, using a battery of four cognitive function tests, including Visual Verbal Learning Test, Trail Making Test, Stroop Color and Word Test, and Letter-Digit Coding Task. Additionally, 30 healthy volunteers were subjected to the same tests as the patients to examine the learning effect of repeated tests. The occurrence of postoperative cognitive dysfunction was judged from the results of the neurocognitive test battery, with consideration of the learning effect. The secondary endpoints were the effects of minocycline on postoperative delirium and postoperative pain.

RESULTS

A total of 100 patients were randomized to the minocycline group, and 102 were randomized to the placebo group. The average age of patients was 75 yr. Evaluation showed no significant difference in the incidence of postoperative cognitive dysfunction between the minocycline and placebo groups at both 1 week (8 of 90 [8.9%] vs. 4 of 95 [4.2%]; odds ratio, 2.22 [95% CI, 0.64 to 7.65]; P = 0.240) and 3 months (15.3 of 90 [17.0%] vs. 15.3 of 95 [16.1%]; odds ratio, 1.07 [95% CI, 0.49 to 2.32]; P = 0.889) postoperatively. Missing data 3 months after surgery were corrected by the multiple imputation method. There were no differences between the two groups in postoperative delirium and postoperative pain.

CONCLUSIONS

Minocycline is likely to have no preventive effect on postoperative cognitive dysfunction.

EDITOR’S PERSPECTIVE

Age-Related Perioperative Neurocognitive Disorders: Experimental Models and Druggable Targets

With the worldwide increase in life span, surgical patients are becoming older and have a greater propensity for postoperative cognitive impairment, either new onset or through deterioration of an existing condition; in both conditions, knowledge of the patient's preoperative cognitive function and postoperative cognitive trajectory is imperative. We describe the clinical utility of a tablet-based technique for rapid assessment of the memory and attentiveness domains required for executive function. The pathogenic mechanisms for perioperative neurocognitive disorders have been investigated in animal models in which excessive and/or prolonged postoperative neuroinflammation has emerged as a likely contender. The cellular and molecular species involved in postoperative neuroinflammation are the putative targets for future therapeutic interventions that are efficacious and do not interfere with the surgical patient's healing process.

Whole body vibration, an alternative for exercise to improve recovery from surgery?

Although exercise is usually associated with beneficial effects on physical and mental health, patients recovering from surgery may be hampered to perform active exercise. Whole body vibration (WBV) is suggested a passive alternative for physical training. Aim of the present study was to explore the therapeutic potential of WBV compared to physical exercise during early post-surgery recovery.

Male three months old Wistar rats underwent major abdominal surgery. Starting the day after surgery, rats were subjected to either daily WBV or exercise (treadmill running) for 15 consecutive days. Control rats underwent pseudo treatment. During the first week after surgery, effects of interventions were obtained from continuous recording of hemodynamic parameters, body temperature and activity (via an implanted transducer). Behavioral tests were performed during the second post-surgical week to evaluate anxiety-like behavior, short and long-term memory functions, cognitive flexibility and motor performance. Animals were sacrificed 15 days after surgery and brain tissue was collected for analysis of hippocampal neuroinflammation and neurogenesis.

Surgery significantly impacted all parameters measured during the first post-surgery week, irrespective of the type of surgery. Effect on cognitive performance was limited to cognitive flexibility; both WBV and exercise prevented the surgery-induced decline. Exercise, but not WBV increased anxiety-like behavior and grip strength. WBV as well as exercise prevented the surgery-induced declined neurogenesis, but surgery-associated hippocampal neuroinflammation was not affected.

Our results indicated that active exercise and WBV share similar therapeutic potentials in the prevention of surgery induced decline in cognitive flexibility and hippocampal neurogenesis. In contrast to exercise, WBV did not increase anxiety-like behavior. Since neither intervention affected hippocampal neuroinflammation, other mechanisms and/or brain areas may be involved in the behavioral effects. Taken together, we conclude that WBV may provide a relevant alternative to active exercise during the early stage of post-operative recovery.

•

Both whole body vibration (WBV) and running exercise restored the reduced cognitive flexibility caused by surgery.

•

WBV as well as active exercise prevented surgery-induced declined neurogenesis.

•

Active exercise, but not WBV, induced anxiety-like behavior after surgery.

•

Neither WBV nor active exercise affected surgery-induced neuroinflammation.

•

Neither WBV nor active exercise influenced hemodynamic recovery from surgery.

The Impact of Inflammation and General Anesthesia on Memory and Executive Function in Mice

BACKGROUND

Perioperative neurocognitive disorders (PNDs) are complex, multifactorial conditions that are associated with poor long-term outcomes. Inflammation and exposure to general anesthetic drugs are likely contributing factors; however, the relative impact of each factor alone versus the combination of these factors remains poorly understood. The goal of this study was to compare the relative impact of inflammation, general anesthesia, and the combination of both factors on memory and executive function.

METHODS

To induce neuroinflammation at the time of exposure to an anesthetic drug, adult male mice were treated with lipopolysaccharide (LPS) or vehicle. One day later, they were anesthetized with etomidate (or vehicle). Levels of proinflammatory cytokines were measured in the hippocampus and cortex 24 hours after LPS treatment. Recognition memory and executive function were assessed starting 24 hours after anesthesia using the novel object recognition assay and the puzzle box, respectively. Data are expressed as mean (or median) differences (95% confidence interval).

RESULTS

LPS induced neuroinflammation, as indicated by elevated levels of proinflammatory cytokines, including interleukin-1β (LPS versus control, hippocampus: 3.49 pg/mg [2.06-4.92], P < .001; cortex: 2.60 pg/mg [0.83-4.40], P = .010) and tumor necrosis factor-α (hippocampus: 3.50 pg/mg [0.83-11.82], P = .002; cortex: 2.38 pg/mg [0.44-4.31], P = .021). Recognition memory was impaired in mice treated with LPS, as evinced by a lack of preference for the novel object (novel versus familiar: 1.03 seconds [-1.25 to 3.30], P = .689), but not in mice treated with etomidate alone (novel versus familiar: 2.38 seconds [0.15-4.60], P = .031). Mice cotreated with both LPS and etomidate also exhibited memory deficits (novel versus familiar: 1.40 seconds [-0.83 to 3.62], P = .383). In the puzzle box, mice treated with either LPS or etomidate alone showed no deficits. However, the combination of LPS and etomidate caused deficits in problem-solving tasks (door open task: -0.21 seconds [-0.40 to -0.01], P = .037; plug task: -0.30 seconds [-0.50 to -0.10], P < .001; log values versus control), indicating impaired executive function.

CONCLUSIONS

Impairments in recognition memory were driven by inflammation. Deficits in executive function were only observed in mice cotreated with LPS and etomidate. Thus, an interplay between inflammation and etomidate anesthesia led to cognitive deficits that were not observed with either factor alone. These findings suggest that inflammation and anesthetic drugs may interact synergistically, or their combination may unmask covert or latent deficits induced by each factor alone, leading to PNDs.

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.

Electro-Acupuncture Pretreatment Ameliorates Anesthesia and Surgery-Induced Cognitive Dysfunction Via Inhibiting Mitochondrial Injury and nEuroapoptosis in Aged Rats

Postoperative cognitive dysfunction (POCD) remains one of the most common complications following anesthesia and surgery (AS) in the elderly population. Calcium-mediated mitochondrial injury has been proved to induce cognitive impairment in a variety of neurologic diseases. In the current study we determined whether electro-acupuncture (EA) pretreatment ameliorated AS-induced POCD in aged rats, as well as the underlying mechanism. Eighty SD rats (18 months, male) were randomly assigned into four groups (n = 20): C, C + EA, POCD and EA + POCD. Rats in Group POCD and EA + POCD were subjected to exploratory laparotomy under sevoflurane anesthesia. Rats of Group C + EA and EA + POCD received a 5-day EA stimulation at Hegu, Neiguan and Zusanli acupoints before AS. At 3rd day after AS, open field test along with Morris water maze test were employed to examine the cognitive function of aged rats. Then hippocampal tissues were stripped and hippocampal neuronal amount, expression level of cleaved caspase-9 level, cytochrome c (Cyt C), cleaved caspase-3 level, Bcl-2, Bax, ROS expression level, apoptosis rate, mitochondrial membrane potential (MMP), cytosolic calcium concentration ([Ca²⁺]c), opening level of mitochondrial permeability transition pore (mPTP) and ultrastructure of hippocampal neurons were detected separately. EA pretreatment inhibited AS-induced cognitive dysfunction. Furthermore, EA pretreatment decreased level of [Ca²⁺]c, MMP, mPTP, ROS and hippocampal mitochondrial disruption and enhanced neuronal amount. In addition, EA pretreatment notably reduced the AS-induced increased level of cleaved caspase-9, cleaved caspase-3 and expression of Cyt c, Bax/Bcl-2 ratio, as well as neuronal apoptosis rate in aged rats. EA pretreatment ameliorates AS-induced POCD in aged rats, the potential mechanism may be associated with inhibiting calcium overload and ameliorating mitochondrial injury and neuroapoptosis in hippocampal neurons.

Cerebral infarction after cardiac surgery

Cerebral infarction, a common central nervous system complication after adult cardiac surgery, is one of the main factors leading to the poor prognosis of cardiac surgery patients besides cardiac insufficiency. However, there is currently no effective treatment for cerebral infarction. Therefore, early prevention and diagnosis of postoperative cerebral infarction are particularly important. There are many factors and mechanisms during and after cardiac surgery that play an important role in the occurrence of postoperative cerebral infarction, such as intraoperative embolism, systemic inflammatory response syndrome, atrial fibrillation, temperature regulation, blood pressure control, use of postoperative blood products, and so forth. The mechanism by which most risk factors act on the human body, leading to postoperative cerebral infarction, is not well understood, and further research is needed. Therefore, this paper aims to summarize and explain the relevant risk factors, mechanisms, clinical signs, imaging characteristics, and early diagnosis methods of cerebral infarction complications after cardiac surgery, and provides useful data for the establishment of related diagnosis and treatment standards.

Enteral enriched nutrition to prevent cognitive dysfunction after surgery; a study in rats

Background

Inflammation plays an important role in postoperative cognitive dysfunction (POCD), particularly in elderly patients. Enteral enriched nutrition was shown to inhibit the response on inflammatory stimuli. Aim of the present study was to explore the therapeutic potential of enteral enriched nutrition in our rat model for POCD. The anticipated mechanism of action was examined in young rats, while responses in the target group of elderly patients were evaluated in old rats.

Methods

Male 3 and 23 months old Wistar rats received a bolus of enteral fat/protein-enriched nutrition 2 ​h and 30 ​min before surgery. The inflammatory response was evaluated by systemic inflammation markers and brain microglia activity. Additionally, in old rats, the role of the gut-brain axis was studied by microbiome analyses of faecal samples. Days 9–14 after surgery, rats were subjected to cognitive testing. Day 16, rats were sacrificed and brains were collected for immunohistochemistry.

Results

In young rats, enriched nutrition improved long-term spatial learning and memory in the Morris Water Maze, reduced plasma IL1-β and VEGF levels, but left microglia activity and neurogenesis unaffected. In contrast, in old rats, enriched nutrition improved short-term memory in the novel object- and novel location recognition tests, but impaired development of long-term memory in the Morris Water Maze. Systemic inflammation was not affected, but microglia activity seemed even increased. Gut integrity and microbiome were not affected.

Conclusion

Enteral enriched nutrition before surgery in young rats indeed reduced systemic inflammation and improved cognitive performance after surgery, whereas old rats showed a mixed favorable/unfavorable cognitive response, without effect on systemic inflammation. Anti-inflammatory effects of enriched nutrition were not reflected in decreased microglia activity. Neither was an important role for the gut-brain axis observed. Since the relatively straight forward effects of enriched nutrition in young rats could not be shown in old rats, as indicated by a mixed beneficial/detrimental cognitive outcome in the latter, caution is advised by translating effects seen in younger patients to older ones.

•

Enriched nutrition reduced inflammation after surgery in young rats.

•

Enriched nutrition improved postoperative cognitive outcome in young rats.

•

Enteral enriched nutrition did not inhibit neuroinflammation.

•

Effects in young rats do not predict effects in old rats.

•

Enteral enriched nutrition caused mixed improved/declined cognition in old rats.

NLRP3 inflammasomes are involved in the progression of postoperative cognitive dysfunction: from mechanism to treatment

Postoperative cognitive dysfunction (POCD) involves patient memory and learning decline after surgery. POCD not only presents challenges for postoperative nursing and recovery but may also cause permanent brain damage for patients, including children and the aged, with vulnerable central nervous systems. Its occurrence is mainly influenced by surgical trauma, anesthetics, and the health condition of the patient. There is a lack of imaging and experimental diagnosis; therefore, patients can only be diagnosed by clinical observation, which may underestimate the morbidity, resulting in decreased treatment efficacy. Except for symptomatic support therapy, there is a relative lack of effective drugs specific for the treatment of POCD, because the precise mechanism of POCD remains to be determined. One current hypothesis is that postoperative inflammation promotes the progression of POCD. Accumulating research has indicated that overactivation of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasomes contribute to the POCD progression, suggesting that targeting NLRP3 inflammasomes may be an effective therapy to treat POCD. In this review, we summarize recent studies and systematically describe the pathogenesis, treatment progression, and potential treatment options of targeting NLRP3 inflammasomes in POCD patients.

Acute pre-operative ibuprofen improves cognition in a rat model for postoperative cognitive dysfunction

BACKGROUND

Inflammation is considered a key factor in the development of postoperative cognitive dysfunction (POCD). Therefore, we hypothesized that pre-operative anti-inflammatory treatment with ibuprofen would inhibit POCD in our rat-model.

METHODS

Male Wistar rats of 3 or 23 months old received a single injection of ibuprofen (15 mg/kg i.p.) or were control handled before abdominal surgery. Timed blood and fecal samples were collected for analyses of inflammation markers and gut microbiome changes. Behavioral testing was performed from 9 to 14 days after surgery, in the open field, novel object- and novel location-recognition tests and Morris water maze. Neuroinflammation and neurogenesis were assessed by immune histochemistry after sacrifice on postoperative day 14.

RESULTS

Ibuprofen improved short-term spatial memory in the novel location recognition test, and increased hippocampal neurogenesis. However, these effects were associated with increased hippocampal microglia activity. Whereas plasma cytokine levels (IL1-β, IL6, IL10, and TNFα) were not significantly affected, VEGF levels increased and IFABP levels decreased after ibuprofen. Long-term memory in the Morris water maze was not significantly improved by ibuprofen. The gut microbiome was neither significantly affected by surgery nor by ibuprofen treatment. In general, effects in aged rats appeared similar to those in young rats, though less pronounced.

CONCLUSION

A single injection of ibuprofen before surgery improved hippocampus-associated short-term memory after surgery and increased neurogenesis. However, this favorable outcome seemed not attributable to inhibition of (neuro)inflammation. Potential contributions of intestinal and blood-brain barrier integrity need further investigation. Although less pronounced compared to young rats, effects in aged rats indicate that even elderly individuals could benefit from ibuprofen treatment.

Anesthesia and surgery induce cognitive dysfunction in elderly male mice: the role of gut microbiota

It is well known that the incidence of postoperative cognitive dysfunction (POCD) is high in elderly patients. The pathogenesis and therapeutic mechanisms of POCD, however, have not yet been completely elucidated. The effects of gut microbiota, particularly in terms of regulating brain function, have gradually attracted increasing attention. In this study, we investigated the potential role of gut microbiota in POCD in aged male mice and attempted to determine whether alterations in gut microbiota would be helpful in the diagnosis of POCD. POCD and non-POCD mice were classified by hierarchical cluster analysis of behavioral results. Additionally, α- and β-diversity of gut microbiota showed a differential profile between the groups. In total, 24 gut bacteria were significantly altered in POCD mice compared with those in non-POCD mice, in which 13 gut bacteria were significantly correlated with escape latency in the Morris water maze test (MWMT). Remarkably, receiver operating characteristic curves revealed that the Dehalobacteriaceae family and Dehalobacterium genus are potentially important bacteria for the diagnosis of POCD. These findings indicate that alterations in the composition of gut microbiota are probably involved in the pathogenesis of POCD in aged mice. Novel therapeutic strategies regulating specific gut bacteria may be helpful for the prevention and treatment of POCD.

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.

Repeated social defeat induces transient glial activation and brain hypometabolism: A positron emission tomography imaging study

Psychosocial stress is a risk factor for the development of depression. Recent evidence suggests that glial activation could contribute to the development of depressive-like behaviour. This study aimed to evaluate in vivo whether repeated social defeat (RSD) induces short- and long-term inflammatory and metabolic alterations in the brain through positron emission tomography (PET). Male Wistar rats ( n = 40) were exposed to RSD by dominant Long-Evans rats on five consecutive days. Behavioural and biochemical alterations were assessed at baseline, day 5/6 and day 24/25 after the RSD protocol. Glial activation (11C-PK11195 PET) and changes in brain metabolism (18F-FDG PET) were evaluated on day 6, 11 and 25 (short-term), and at 3 and 6 months (long-term). Defeated rats showed transient depressive- and anxiety-like behaviour, increased corticosterone and brain IL-1β levels, as well as glial activation and brain hypometabolism in the first month after RSD. During the third- and six-month follow-up, no between-group differences in any investigated parameter were found. Therefore, non-invasive PET imaging demonstrated that RSD induces transient glial activation and reduces brain glucose metabolism in rats. These imaging findings were associated with stress-induced behavioural changes and support the hypothesis that neuroinflammation could be a contributing factor in the development of depression.

Neurocognitive Function after Cardiac Surgery: From Phenotypes to Mechanisms

For half a century, it has been known that some patients experience neurocognitive dysfunction after cardiac surgery; however, defining its incidence, course, and causes remains challenging and controversial. Various terms have been used to describe neurocognitive dysfunction at different times after cardiac surgery, ranging from "postoperative delirium" to "postoperative cognitive dysfunction or decline." Delirium is a clinical diagnosis included in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Postoperative cognitive dysfunction is not included in the DSM-5 and has been heterogeneously defined, though a recent international nomenclature effort has proposed standardized definitions for it. Here, the authors discuss pathophysiologic mechanisms that may underlie these complications, review the literature on methods to prevent them, and discuss novel approaches to understand their etiology that may lead to novel treatment strategies. Future studies should measure both delirium and postoperative cognitive dysfunction to help clarify the relationship between these important postoperative complications.

Hippocampal microglia modifications in C57Bl/6 Pahenu2 and BTBR Pahenu2 phenylketonuria (PKU) mice depend on the genetic background, irrespective of disturbed sleep patterns

Toxic levels of phenylalanine in blood and brain is a characteristic of (untreated) phenylketonuria (PKU), leading to cognitive deficits in PKU mice. In addition, our recent findings showed that PKU mice (as well as PKU patients) have a disturbed sleep/wake cycle. As a consequence, sleep loss may contribute to cognitive deficits in PKU. Sleep loss has been linked to increased activation of microglia in the hippocampus. In this study, we set out to examine morphological features of the microglia population in the hippocampus of the mouse PKU model, using both the C57Bl/6 and the BTBR strain and their wild-type controls (age 5.3 ± 0.5 months; n = 16 per group, both males and females; n = 8 each). Microglial activation is reflected by retraction and thickening of the dendritic branches and an increase in cell body size of a microglial cell. Such morphological changes of microglia were studied by way of immunohistochemical staining for Iba-1, a microglia-specific calcium binding protein. We measured the number of microglia in seven subregions of the dorsal hippocampus. The level of microglial activation was determined, based on the ratio between the soma size and total cell size (soma size plus the area covered by the dendritic branches). Results showed subtle but statistical significant activation of hippocampal microglia in the C57Bl6, but not in the BTBR, PKU mice when compared with their wild-type controls. Also the total number of microglia was higher in the C57Bl/6 PKU (compared to the wild-type) mouse, but not in the BTBR PKU mouse. It is concluded that the C57Bl/6 PKU mouse has mildly higher microglia activity, which may support rather than hamper hippocampal homeostasis. The results further indicate that high levels of phenylalanine or disturbed sleep patterns do not consequently cause hippocampal microglial activation in the PKU mouse. It is currently unknown why the two PKU mouse strains show these differences in number and activation level of their hippocampal microglia, and to what extent it influences hippocampal functioning. Further scrutinizing the role of microglia functioning in the context of PKU is therefore warranted.

Brain changes due to hypoxia during light anaesthesia can be prevented by deepening anaesthesia; a study in rats

In anaesthetic practice the risk of cerebral ischemic/hypoxic damage is thought to be attenuated by deep anaesthesia. The rationale is that deeper anaesthesia reduces cerebral oxygen demand more than light anaesthesia, thereby increasing the tolerance to ischemia or hypoxia. However, evidence to support this is scarce. We thus investigated the influence of light versus deep anaesthesia on the responses of rat brains to a period of hypoxia. In the first experiment we exposed adult male Wistar rats to deep or light propofol anaesthesia and then performed [18F]- Fludeoxyglucose (FDG) Positron Emission Tomography (PET) scans to verify the extent of cerebral metabolic suppression. In subsequent experiments, rats were subjected to light/deep propofol anaesthesia and then exposed to a period of hypoxia or ongoing normoxia (n = 9-11 per group). A further 5 rats, not exposed to anaesthesia or hypoxia, served as controls. Four days later a Novel Object Recognition (NOR) test was performed to assess mood and cognition. After another 4 days, the animals were sacrificed for later immunohistochemical analyses of neurogenesis/neuroplasticity (Doublecortin; DCX), Brain Derived Neurotrophic Factor (BDNF) expression and neuroinflammation (Ionized calcium-binding adaptor protein-1; Iba-1) in hippocampal and piriform cortex slices. The hippocampi of rats subjected to hypoxia during light anaesthesia showed lower DCX positivity, and therefore lower neurogenesis, but higher BDNF levels and microglia hyper-ramification. Exploration was reduced, but no significant effect on NOR was observed. In the piriform cortex, higher DCX positivity was observed, associated with neuroplasticity. All these effects were attenuated by deep anaesthesia. Deepening anaesthesia attenuated the brain changes associated with hypoxia. Hypoxia during light anaesthesia had a prolonged effect on the brain, but no impairment in cognitive function was observed. Although reduced hippocampal neurogenesis may be considered unfavourable, higher BDNF expression, associated with microglia hyper-ramification may suggest activation of repair mechanisms. Increased neuroplasticity observed in the piriform cortex supports this, and might reflect a prolonged state of alertness rather than damage.

The Role of Neuroinflammation in Postoperative Cognitive Dysfunction: Moving From Hypothesis to Treatment

Postoperative cognitive dysfunction (POCD) is a common complication of the surgical experience and is common in the elderly and patients with preexisting neurocognitive disorders. Animal and human studies suggest that neuroinflammation from either surgery or anesthesia is a major contributor to the development of POCD. Moreover, a large and growing body of literature has focused on identifying potential risk factors for the development of POCD, as well as identifying candidate treatments based on the neuroinflammatory hypothesis. However, variability in animal models and clinical cohorts makes it difficult to interpret the results of such studies, and represents a barrier for the development of treatment options for POCD. Here, we present a broad topical review of the literature supporting the role of neuroinflammation in POCD. We provide an overview of the cellular and molecular mechanisms underlying the pathogenesis of POCD from pre-clinical and human studies. We offer a brief discussion of the ongoing debate on the root cause of POCD. We conclude with a list of current and hypothesized treatments for POCD, with a focus on recent and current human randomized clinical trials.

Hypertonic saline for prevention of delirium in geriatric patients who underwent hip surgery

BACKGROUND

Postoperative delirium (POD) is a common disorder in the elderly patients, and neuroinflammation is the possible underlying mechanism. This study is designed to determine whether or not hypertonic saline (HS) pre-injection can alleviate POD in aged patients.

METHODS

This prospective study recruited 120 geriatric patients who underwent hip surgery. The patients were randomly divided into two groups: control group (NS group) and HS group. Patients in the NS group were pre-injected with 4 mL/kg isotonic saline, and those in the HS group were pre-injected with 4 mL/kg 7.5% HS. All 120 patients were then subjected to general anesthesia. Blood samples were extracted to detect the concentration of inflammatory factors, namely, IL-1β, IL-6, IL-10, and TNF-α, and the nerve injury factor S100β. Flow cytometry was used to detect the number of monocytes in peripheral venous blood and evaluate the relationship of inflammation to delirium. The nursing delirium screening scale (Nu-DESC) was used to determine cognitive function 1 to 3 days postoperatively.

RESULTS

Analysis using random-effect multivariable logistic regression indicated that HS administration before anesthesia was associated with a low risk of POD (odds ratio [OR], 0.13; 95% CI, 0.04 to 0.41; P = 0.001) and few CD14 + CD16+ monocytes (β = - 0.61; 95% CI, - 0.74 to - 0.48; P = 0.000) the following day. When the association between HS and delirium was controlled for CD14 + CD16+ monocytes, the effect size became nonsignificant (odds ratio [OR], 0.86; 95% CI, 0.14 to 5.33; P = 0.874). TNF-α was significantly associated with POD (odds ratio [OR], 1.10; 95% CI, 1.05 to 1.16; P = 0.000). However, IL-1β, IL-6, IL-10, and S100β were not significantly related to POD.

CONCLUSION

HS can alleviate POD in geriatric patients and may inhibit the secretion of inflammatory factors by monocytes.

An update on anesthetics and impact on the brain

INTRODUCTION

While anesthetics are indispensable clinical tools and generally considered safe and effective, a growing concern over the potential neurotoxicity of anesthesia or specific anesthetic agents has called into question the safety of general anesthetics, especially when administered at extremes of age. Areas covered: This article reviews and updates research findings on the safety of anesthesia and anesthetics in terms of long-term neurotoxicity, with particular focus on postoperative cognitive dysfunctions, Alzheimer's disease and dementias, developing brain, post-operative depression and autism spectrum disorder. Expert opinion: Exposure to general anesthetics is potentially harmful to the human brain, and the consequent long-term cognitive deficits should be classified as an iatrogenic pathology, and considered a public health problem. The fact that in laboratory and clinical research only certain anesthetic agents and techniques, but not others, appear to be involved, raises the problem on what is the safest and the least safe anesthetic to maximize anesthesia efficiency, avoid occurrence of adverse events, and ensure patient safety. New trends in research are moving toward the theory that neuroinflammation could be the hallmark of, or could have a pivotal role in, several neurological disorders.

The aminoestrogen prolame increases recognition memory and hippocampal neuronal spine density in aged mice

The aging brain shows biochemical and morphological changes in the dendrites of pyramidal neurons from the limbic system associated with memory loss. Prolame (N-(3-hydroxy-1,3,5 (10)-estratrien-17β-yl)-3-hydroxypropylamine) is a non-feminizing aminoestrogen with antithrombotic activity that prevents neuronal deterioration, oxidative stress, and neuroinflammation. Our aim was to evaluate the effect of prolame on motor and cognitive processes, as well as its influence on the dendritic morphology of neurons at the CA1, CA3, and granule cells of the dentate gyrus (DG) regions of hippocampus (HP), and medium spiny neurons of the nucleus accumbens (NAcc) of aged mice. Dendritic morphology was assessed with the Golgi-Cox stain procedure followed by Sholl analysis. Prolame (60 µg/kg) was subcutaneously injected daily for 60 days in 18-month-old mice. Immediately after treatment, locomotor activity in a new environment and recognition memory using the Novel Object Recognition Task (NORT) were evaluated. Prolame-treated mice showed a significant increase in the long-term exploration quotient, but locomotor activity was not modified in comparison to control animals. Prolame-treated mice showed a significant increase in dendritic spines density and dendritic length in neurons of the CA1, CA3, and DG regions of the HP, whereas dendrites of neurons in the NAcc remained unmodified. In conclusion, prolame administration promotes hippocampal plasticity processes but not in the NAcc neurons of aged mice, thus improving long-term recognition memory. Prolame could become a pharmacological alternative to prevent or delay the brain aging process, and thus the emergence of neurodegenerative diseases that affect memory.

WHOLE BODY VIBRATION IMPROVES ATTENTION AND MOTOR PERFORMANCE IN MICE DEPENDING ON THE DURATION OF THE WHOLE-BODY VIBRATION SESSION

Background:

Whole body vibration (WBV) is a form of physical stimulation via mechanical vibrations transmitted to a subject. It is assumed that WBV induces sensory stimulation in cortical brain regions through the activation of skin and muscle receptors responding to the vibration. The effects of WBV on muscle strength are well described. However, little is known about the impact of WBV on the brain. Recently, it was shown in humans that WBV improves attention in an acute WBV protocol. Preclinical research is needed to unravel the underlying brain mechanism. As a first step, we examined whether chronic WBV improves attention in mice.

Material and Methods:

A custom made vibrating platform for mice with low intensity vibrations was used. Male CD1 mice (3 months of age) received five weeks WBV (30 Hz; 1.9 G), five days a week with sessions of five (n=12) or 30 (n=10) minutes. Control mice (pseudo-WBV; n=12 and 10 for the five and 30 minute sessions, respectively) were treated in a similar way, but did not receive the actual vibration. Object recognition tasks were used as an attention test (novel and spatial object recognition – the primary outcome measure). A Balance beam was used for motor performance, serving as a secondary outcome measure.

Results:

WBV sessions of five (but not WBV sessions of 30 minutes) improved balance beam performance (mice gained 28% in time needed to cross the beam) and novel object recognition (mice paid significantly more attention to the novel object) as compared to pseudo WBV, but no change was found for spatial object performance (mice did not notice the relocation). Although 30 minutes WBV sessions were not beneficial, it did not impair either attention or motor performance.

Conclusion:

These results show that brief sessions of WBV improve, next to motor performance, attention for object recognition, but not spatial cues of the objects. The selective improvement of attention in mice opens the avenue to unravel the underlying brain mechanisms.

Pathophysiological and behavioral effects of systemic inflammation in aged and diseased rodents with relevance to delirium: A systematic review

Delirium is a frequent outcome for aged and demented patients that suffer a systemic inflammatory insult. Animal models that reconstruct these etiological processes have potential to provide a better understanding of the pathophysiology of delirium. Therefore, we systematically reviewed animal studies in which systemic inflammation was superimposed on aged or diseased animal models. In total, 77 studies were identified. Aged animals were challenged with a bacterial endotoxin in 29 studies, 25 studies superimposed surgery on aged animals, and in 6 studies a bacterial infection, Escherichia coli (E. coli), was used. Diseased animals were challenged with a bacterial endotoxin in 15 studies, two studies examined effects of the cytokine IL-1β, and one study used polyinosinic:polycytidilic acid (poly I:C). This systematic review analyzed the impact of systemic inflammation on the production of inflammatory and neurotoxic mediators in peripheral blood, cerebrospinal fluid (CSF), and on the central nervous system (CNS). Moreover, concomitant behavioral and cognitive symptoms were also evaluated. Finally, outcomes of behavioral and cognitive tests from animal studies were compared to features and symptoms present in delirious patients.

Neuroinflammation Induced by Surgery Does Not Impair the Reference Memory of Young Adult Mice

Postoperative cognitive dysfunction (POCD) increases morbidity and mortality after surgery. But the underlying mechanism is not clear yet. While age is now accepted as the top one risk factor for POCD, results from studies investigating postoperative cognitive functions in adults have been controversial, and data about the very young adult individuals are lacking. The present study investigated the spatial reference memory, IL-1β, IL-6, and microglia activation changes in the hippocampus in 2-month-old mice after anesthesia and surgery. We found that hippocampal IL-1β and IL-6 increased at 6 hours after surgery. Microglia were profoundly activated in the hippocampus 6 to 24 hours after surgery. However, no significant behavior changes were found in these mice. These results indicate that although anesthesia and surgery led to neuroinflammation, the latter was insufficient to impair the spatial reference memory of young adult mice.

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.

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.