Postoperative cognitive dysfunction is made persistent with morphine treatment in aged rats

Aged mice exhibit faster acquisition of intravenous opioid self-administration with variable effects on intake

Although opioid abuse is more prevalent in young individuals, the rates of opioid use, overdose, and use disorders continue to climb among the elderly. Little is known about the biology underlying abuse potential in a healthy, aged population, in part due to technical and logistical difficulties testing intravenous self-administration in aged rodents. The goal of this study was to address a critical gap in the literature regarding age-dependent effects in opioid (remifentanil and fentanyl) self-administration. Male and female C57Bl/6J and C57Bl/6NJ mice were divided into young (mean: 19 weeks) and old (mean: 101 weeks) groups and were trained to self-administer intravenous fentanyl or remifentanil in daily operant sessions. Acquisition, intake, and cue-responding after forced abstinence were measured for both drugs, and a dose-response curve and dose-escalation were conducted for remifentanil and fentanyl, respectively. Surprisingly, old mice learned to self-administer both remifentanil and fentanyl faster and more accurately than young mice. Baseline intake of remifentanil was also greater in old mice compared to the young group; however, we did not see increased intake of fentanyl with age at either dose tested. Furthermore, old mice showed greater responding for cues previously associated with remifentanil after a forced abstinence, but this result was not observed with fentanyl. This first report of opioid self-administration in greater than 20-month-old mice suggests that old mice have an increased vulnerability for opioid use compared to younger counterparts, underscoring the importance of future work to uncover the biological mechanisms that are responsible.

Postoperative analgesia with morphine promoting microglial activation and neuroinflammation induced by surgery aggravates perioperative neurocognitive dysfunction in aged mice

Introduction

Perioperative neurocognitive dysfunction (PND) is a significant challenge for patients who need surgery worldwide. Morphine can trigger an intense inflammatory reaction in the central nervous system (CNS) at the same time as analgesia, thus adverse effects aggravating PND. Microglia polarization is closely involved in the regulation of neuroinflammation and the TLR4/MyD88/NF-κB signaling pathway. However, the mechanisms of morphine analgesia aggravating PND impairment remain unclear.

Methods

Tibial fracture surgery was performed in 18 months old male C57BL/6 J mice to mimic human orthopedic surgery and postoperative analgesia with morphine hypodermic or ropivacaine. Levels of inflammatory factors in the hippocampus, activation, and phenotype of microglia, an essential protein of TLR4/MyD88/NF-κB signal pathway, synaptic plasticity, and hippocampal-dependent memory function were evaluated after surgery and postoperative analgesia.

Results

Morphine postoperative analgesia increased the expression of pro-inflammatory cytokines IL-1 β, IL-6, and TNF-α, decreased the level of anti-inflammatory IL-10, aggravated the activation of microglia and the destruction of synaptic plasticity in the hippocampus, resulting in hippocampal neuron loss, a significant decrease in the number of synapses and cognitive impairment in aged mice. In addition, the aggravation of neuroinflammatory response and the activation of microglia may be mediated by TLR4/MyD88/NF- κ B signal pathway.

Conclusion

Our results demonstrate that morphine postoperative analgesia may aggravate microglia activation and neuroinflammation in the hippocampus by regulating the TLR4/MyD88/NF- κ B signal pathway and inhibiting the synaptic plasticity hippocampal neurons. It aggravated the acute cognitive decline and cognitive impairment after tibial fracture in elderly mice.

Peripartum buprenorphine and oxycodone exposure impair maternal behavior and increase neuroinflammation in new mother rats

7 % of pregnant people use opioids. Opioid use during pregnancy can negatively impact maternal and offspring health. Medications for opioid use disorder (MOUD), commonly buprenorphine, are the recommended treatment for opioid use disorder during pregnancy to prevent cycles of withdrawal and relapse. In addition to effects on opioid receptors, opioids have strong binding affinity to toll-like receptor (TLR) 4, an immune cell receptor, and thereby impact neuroinflammatory signaling. We have previously shown that neuroimmune alterations are important for the display of maternal behavior. Here, we used a rodent model to assess the impact of chronic peripartum opioid exposure or MOUD on maternal caregiving and neuroinflammation in the postpartum brain. Female rats were exposed to vehicle (VEH), buprenorphine (BUP) to model MOUD, or oxycodone (OXY), to model peripartum drug use, before, during, and after pregnancy. Opioid exposure reduced gestation length and maternal weight gain. Postpartum maternal caretaking behaviors, including pup retrieval, huddling and nursing, and pup-directed sniffing and licking, were reduced in opioid-exposed mothers. Following behavioral testing, tissue was collected from brain regions important for maternal caretaking, including the prefrontal cortex (PFC), nucleus accumbens (NAc), preoptic area (POA), amygdala (AMY), and periaqueductal grey (PAG). Immunofluorescent labeling showed that BUP increased astrocyte labeling, while OXY increased microglia labeling in the PAG, but not other regions. Gene expression analysis also showed regional and treatment differences in immune transcripts. BUP and OXY increased TLR4 in the PFC. BUP increased TNF in the NAc but decreased IL1β in the POA. OXY increased CD68 in the POA, and IL1β, TNF, and TLR4 in the PAG. Together, these results provide novel evidence of peripartum neuroimmune alterations following chronic opioid exposure that could be mediating maternal care deficits. This work provides a foundation to explore the extent to which modulation of neuroimmune activation may be a potential intervention for caregiving deficits in mothers exposed to opioids during pregnancy.

The NF-κB pathway: Key players in neurocognitive functions and related disorders

Perioperative neurocognitive disorder (PND) is a common complication of surgical anesthesia, yet its precise etiology remains unclear. Neuroinflammation is a key feature of PND, influenced by both patient -related and surgical variables. The nuclear factor-κB (NF-κB) transcription factor family plays a critical role in regulating the body's immunological proinflammatory response, which is pivotal in the development of PND. Surgery and anesthesia trigger the activation of the NF-κB signaling pathway, leading to the initiation of inflammatory cascades, disruption of the blood-brain barrier, and neuronal injury. Immune cells and glial cells are central to these pathological processes in PND. Furthermore, this study explores the interactions between NF-κB and various signaling molecules, including Tlr4, P2X, α7-nAChR, ROS, HIF-1α, PI3K/Ak, MicroRNA, Circular RNA, and histone deacetylases, within the context of PND. Targeting NF-κB as a therapeutic approach for PND shows promise as a potential treatment strategy.

Morphine induces inflammatory responses via both TLR4 and cGAS-STING signaling pathways

BACKGROUND

Opioid activation of the microglia or macrophage Toll-like receptor 4 (TLR4) and associated inflammatory cytokine release are implicated in opioid-induced hyperalgesia and tolerance. The cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS-STING) signaling pathway, activated by double-stranded DNA including mitochondrial DNA (mtDNA), has emerged as another key mediator of inflammatory responses. This study tested the hypothesis that morphine induces immune inflammatory responses in microglia and macrophages involving TLR4 and cGAS-STING pathway.

METHODS

BV2 microglia and Raw 264.7 (Raw) macrophage cells were exposed to morphine with and without a STING inhibitor (C176) for 6 h or TLR 4 inhibitor (TAK242) for 24 h. Western blotting and RT-qPCR analyses assessed TLR4, cGAS, STING, nuclear factor-kappa B (NF-κB), and pro-inflammatory cytokine expression. Morphine-induced mitochondria dysfunction was quantified by reactive oxygen species (ROS) release using MitoSOX, mtDNA release by immunofluorescence, and RT-qPCR. Polarization of BV2 and Raw cells was assessed by inducible nitric oxide (iNOS) and CD86 expression. The role of mtDNA on morphine-related inflammation was investigated by mtDNA depletion of the cells with ethidium bromide (EtBr) or cell transfection of mtDNA extracted from morphine-treated cells.

RESULTS

Morphine significantly increased the expression of TLR4, cGAS, STING, p65 NF-κB, and cytokines (IL-6 and TNF-α) in BV2 and Raw cells. Morphine-induced mitochondrial dysfunction by increased ROS and mtDNA release; the increased iNOS and CD86 evidenced inflammatory M1-like phenotype polarization. TLR4 and STING inhibitors reduced morphine-induced cytokine release in both cell types. The transfection of mtDNA activated inflammatory signaling proteins, cytokine release, and polarization. Conversely, mtDNA depletion led to the reversal of these effects.

CONCLUSION

Morphine activates the cGAS-STING pathway in macrophage cell types. Inhibition of the STING pathway can be an additional method to overcome immune cell inflammation-related morphine tolerance and opioid-induced hyperalgesia.

Decoding paradoxical links of cytokine markers in cognition: Cross talk between physiology, inflammaging, and Alzheimer's disease- related cognitive decline

Recent research has revolutionized our understanding of memory consolidation by emphasizing the critical role of astrocytes, microglia, and immune cells in through cytokine signaling. Cytokines, compact proteins, play pivotal roles in neuronal development, synaptic transmission, and normal aging. This review explores the cellular mechanisms contributing to cognitive decline in inflammaging and Alzheimer's disease, highlighting the paradoxical effects of most studied cytokines (IL-1, IL-6, TNF-α) in brain function, which act as a double-edged sword in brain physiology, acting both as facilitators of healthy cognitive function and as a potential contributor to cognitive decline.

Short-term high fat diet impairs memory, exacerbates the neuroimmune response, and evokes synaptic degradation via a complement-dependent mechanism in a mouse model of Alzheimer's disease

Alzheimer's Disease (AD) is a neurodegenerative disease characterized by profound memory impairments, synaptic loss, neuroinflammation, and hallmark pathological markers. High-fat diet (HFD) consumption increases the risk of developing AD even after controlling for metabolic syndrome, pointing to a role of the diet itself in increasing risk. In AD, the complement system, an arm of the immune system which normally tags redundant or damaged synapses for pruning, becomes pathologically overactivated leading to tagging of healthy synapses. While the unhealthy diet to AD link is strong, the underlying mechanisms are not well understood in part due to confounding variables associated with long-term HFD which can independently influence the brain. Therefore, we experimented with a short-term diet regimen to isolate the diet's impact on brain function without causing obesity. This project investigated the effect of short-term HFD on 1) memory, 2) neuroinflammation including complement, 3) AD pathology markers, 4) synaptic markers, and 5) in vitro microglial synaptic phagocytosis in the 3xTg-AD mouse model. Following the consumption of either standard chow or HFD, 3xTg-AD and non-Tg mice were tested for memory impairments. In a separate cohort of mice, levels of hippocampal inflammatory markers, complement proteins, AD pathology markers, and synaptic markers were measured. For the last set of experiments, BV2 microglial phagocytosis of synapses was evaluated. Synaptoneurosomes isolated from the hippocampus of 3xTg-AD mice fed chow or HFD were incubated with equal numbers of BV2 microglia. The number of BV2 microglia that phagocytosed synaptoneurosomes was tracked over time with a live-cell imaging assay. Finally, we incubated BV2 microglia with a complement receptor inhibitor (NIF) and repeated the assay. Behavioral analysis showed 3xTg-AD mice had significantly impaired long-term contextual and cued fear memory compared to non-Tg mice that was further impaired by HFD. HFD significantly increased inflammatory markers and complement expression while decreasing synaptic marker expression only in 3xTg-AD mice, without altering AD pathology markers. Synaptoneurosomes from HFD-fed 3xTg-AD mice were phagocytosed at a significantly higher rate than those from chow-fed mice, suggesting the synapses were altered by HFD. The complement receptor inhibitor blocked this effect in a dose-dependent manner, demonstrating the HFD-mediated increase in phagocytosis was complement dependent. This study indicates HFD consumption increases neuroinflammation and over-activates the complement cascade in 3xTg-AD mice, resulting in poorer memory. The in vitro data point to complement as a potential mechanistic culprit and therapeutic target underlying HFD's influence in increasing cognitive vulnerability to AD.

Aged mice exhibit faster acquisition of intravenous opioid self-administration with variable effects on intake

Although opioid abuse is more prevalent in young individuals, opioid use, overdose, and use disorders continue to climb at a rapid rate among the elderly. Little is known about abuse potential in a healthy aged population, in part due to technical and logistical difficulties testing intravenous self-administration in aged rodents. The goal of this study was to address the critical gap in the literature regarding age-dependent differences in opioid (remifentanil and fentanyl) self-administration between old and young mice. Male and female mice were grouped into young (mean: 19 weeks) and old (mean: 101 weeks), and were trained to self-administer intravenous fentanyl or remifentanil in daily sessions. In both old and young mice, acquisition, intake, and cue-responding after forced abstinence were measured for both drugs, and a dose-response curve (remifentanil) and dose-escalation (fentanyl) were conducted. Surprisingly, old mice learned to self-administer both remifentanil and fentanyl faster and more accurately than young mice. Baseline intake of remifentanil was also substantially greater in old mice compared to their young counterparts; however, we did not see increased intake of fentanyl with age at either dose tested. Further, compared to young mice, the old mice showed a greater incubation of responding for cues previously associated with remifentanil after a forced abstinence, but again this was not observed with fentanyl. Together these data suggest that an aged population may have an increased drug-abuse vulnerability for opioids compared to young counterparts and underscore the importance of future work on mechanisms responsible for this increased vulnerability.

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.

Role and mechanism of esketamine in improving postoperative cognitive dysfunction in aged mice through the TLR4/MyD88/p38 MAPK pathway

Postoperative cognitive dysfunction (POCD) is a significant concern for the elderly population worldwide. This study explored the effects of esketamine on aged mice with POCD and investigate its mechanism of action involving the TLR4/MyD88/MAPK pathway. We administrated esketamine, along with lipopolysaccharide or anisomycin, to the aged POCD mouse models. We assessed their cognitive function using the Morris water maze test. Additionally, we evaluated histopathological changes/neuronal apoptosis in the mouse hippocampal CA1 area through HE/TUNEL stainings. Furthermore, we measured IL-1β/IL-6/TNF-α/TLR4/MyD88/MAPK (p-p38/p38) levels in mouse hippocampal tissues using ELISA/RT-qPCR/Western blotting. Lastly, we analyzed the interaction between TLR4 and MyD88 using a co-immunoprecipitation assay. Our findings showed that esketamine effectively mitigated POCD in aged mice. This was evident from the improved cognitive performance observed in the Morris water maze test, characterized by reduced escape latency/increased number of platform crossing/a higher percentage of time spent in the target quadrant. Furthermore, esketamine exhibited a protective effect against neuronal apoptosis and reduced the levels of inflammatory factors. These findings suggest that esketamine exerts an anti-inflammatory effect by downregulating TLR4/MyD88, thereby attenuating the inflammatory response associated with POCD. Additionally, esketamine suppressed the p38 MAPK pathway by inhibiting the TLR4/MyD88 signaling cascade. Esketamine demonstrated its efficacy in improving postoperative inflammation and cognitive impairment in aged mice by inhibiting the TLR4/MyD88 pathway. The activation of p38 MAPK signaling diminished the beneficial effects of esketamine in aged POCD mice. Collectively, the underlying mechanism of esketamine in mitigating POCD in aged mice involves the suppression of the TLR4/MyD88/p38 MAPK pathway.

Morphine aggravates inflammatory, behavioral, and hippocampal structural deficits in septic rats

Although pain and sepsis are comorbidities of intensive care units, reported data on whether pain control by opioid analgesics could alter inflammatory and end-organ damage caused by sepsis remain inconclusive. Here, we tested the hypothesis that morphine, the gold standard narcotic analgesic, modifies behavioral and hippocampal structural defects induced by sepsis in male rats. Sepsis was induced with cecal ligation and puncture (CLP) and behavioral studies were undertaken 24 h later in septic and/or morphine-treated animals. The induction of sepsis or exposure to morphine (7 mg/kg) elicited similar: (i) falls in systolic blood pressure, (ii) alterations in spatial memory and learning tested by the Morris water maze, and (iii) depression of exploratory behavior measured by the new object recognition test. These hemodynamic and cognitive defects were significantly exaggerated in septic rats treated with morphine compared with individual interventions. Similar patterns of amplified inflammatory (IL-1β) and histopathological signs of hippocampal damage were noted in morphine-treated septic rats. Additionally, the presence of intact opioid receptors is mandatory for the induction of behavioral and hemodynamic effects of morphine because no such effects were observed when the receptors were blocked by naloxone. That said, our findings suggest that morphine provokes sepsis manifestations of inflammation and interrelated hemodynamic, behavioral, and hippocampal deficits.

Neurocognitive Effect of Biased µ-Opioid Receptor Agonist Oliceridine, a Utility Function Analysis and Comparison with Morphine

BACKGROUND

Oliceridine (Olinvyk) is a μ-opioid receptor agonist that in contrast to conventional opioids preferentially engages the G-protein-coupled signaling pathway. This study was designed to determine the utility function of oliceridine versus morphine based on neurocognitive tests and cold pressor test.

METHODS

The study had a randomized, double-blind, placebo-controlled, partial block three-way crossover design. Experiments were performed in 20 male and female volunteers. The subjects received intravenous oliceridine (1 or 3 mg; cohorts of 10 subjects/dose), morphine (5 or 10 mg; cohorts of 10 subjects/dose), or placebo on three separate occasions. Before and after dosing, neurocognitive tests, cold pressor test, and plasma drug concentrations were obtained at regular intervals. Population pharmacokinetic-pharmacodynamic analyses served as the basis for construction of a utility function, which is an objective function of probability of benefit minus probability of harm. Antinociception served as the measure of benefit, and slowing of saccadic peak velocity and increased body sway as the measures of neurocognitive harm.

RESULTS

The oliceridine and morphine C50 values, i.e., the effect-site concentrations causing 50% effect, were as follows: antinociception, 13 ± 2 and 23 ± 7 ng/ml; saccadic peak velocity, 90 ± 14 and 54 ± 15 ng/ml; and body sway, 10 ± 2 and 5.6 ± 0.8 ng/ml, respectively. The ratio oliceridine/morphine of the therapeutic indices, C50(benefit)/C50(harm), were 0.34 (95% CI, 0.17 to 0.7; P < 0.01) for saccadic peak velocity and 0.33 (0.16 to 0.50; P < 0.01) for body sway. The oliceridine utility was positive across the effect-site concentration 5 to 77 ng/ml, indicative of a greater probability of benefit than harm. The morphine utility was not significantly different from 0 from 0 to 100 ng/ml. Over the concentration range 15 to 50 ng/ml, the oliceridine utility was superior to that of morphine (P < 0.01). Similar observations were made for body sway.

CONCLUSIONS

These data indicate that over the clinical concentration range, oliceridine is an analgesic with a favorable safety profile over morphine when considering analgesia and neurocognitive function.

EDITOR’S PERSPECTIVE

Inhibition of adult hippocampal neurogenesis induced by postoperative CD8 + T-cell infiltration is associated with cognitive decline later following surgery in adult mice

BACKGROUND

Some patients show persistent cognitive decline for weeks, months or even years after surgery, which seriously affects their long-term prognosis and quality of life. However, most previous basic studies have focused mainly on the mechanisms of early postoperative cognitive decline, whereas cognitive decline in the longer term after surgery is less well-understood. The subgranular zone of the dentate gyrus exhibits life-long neurogenesis, supporting hippocampus-dependent learning and memory.

MAIN TEXT

The aim of this study was to investigate whether adult hippocampal neurogenesis (AHN) involves in cognitive decline later following surgery and to further explore the roles of CD8 + T lymphocytes infiltrating the hippocampal parenchyma after surgery in this pathological process. Cognitive function was examined in adult mice that underwent laparotomy combined with partial hepatectomy, and the results showed that cognitive decline persisted in mice who underwent surgery during the first postoperative month, even though there was a trend toward continuous improvement over time. Significantly decreased numbers of DCX + cells, BrdU + cells, and BrdU + /DCX + cells were observed on day 8 after surgery, and a significantly decreased number of NeuN + /BrdU + cells was observed on day 28 after surgery, which indicated inhibition of AHN. After surgery, T lymphocytes, the majority of which were CD8 + T cells, infiltrated the hippocampus and secreted Interferon-γ (IFN-γ). Depletion of CD8 + T cells could inhibit the increase of IFN-γ synthesis, improve hippocampal neurogenesis, and improve postoperative cognitive function. Hippocampal microinjection of IFN-γ neutralizing antibody or adeno-associated virus to knock down IFN-γ receptor 1 (IFNGR1) could also partially attenuate the inhibition of AHN and improve postoperative cognitive function.

CONCLUSIONS

These results demonstrate that postoperative infiltration of CD8 + T cells into the hippocampus and subsequent secretion of IFN-γ contribute to the inhibition of AHN and cognitive decline later following surgery.

3-Methyladenine ameliorates surgery-induced anxiety-like behaviors in aged mice by inhibiting autophagy-induced excessive oxidative stress

BACKGROUND

Postoperative anxiety is a common surgical complication in older patients. Research has recently linked excessive autophagy to several neurological disorders, including anxiety. This study aimed to determine whether 3-Methyladenine (3-MA) administration reduced anxiety-like behaviors in a mouse model following abdominal exploratory laparotomy.

METHODS

An abdominal exploratory laparotomy model of postoperative anxiety was established using male C57BL/6 mice aged 20 months. 3-MA (6, 30, and 150 mg/ml) was administered via intracerebroventricular immediately following surgery. The mice were assessed 14 days after surgery using the marble burying, elevated plus maze tests, and local field potential recording in the amygdala. The levels of expression of phosphorylated-Akt, Beclin-1, LC3B, nuclear factor erythroid 2-related factor 2 (Nrf2)-occupied regions in NeuN-positive cells, superoxide dismutase (SOD) activity, malondialdehyde (MDA), and glutathione (GSH) were measured at 24 h after surgery.

RESULTS

The injection of 3-MA reversed the increased number of marbles buried, decreased time spent in the open arm, and enhanced θ oscillation power after 14 days of abdominal exploratory laparotomy. In addition, administration of 3-MA reduced the ratio of phosphorylated- to total-Akt, decreased expression in Beclin-1 and LC3B, attenuated MDA levels, and increased the ratio of Nrf2-occupied areas in NeuN-positive cells, SOD activity, and GSH levels under abdominal exploratory laparotomy conditions.

CONCLUSIONS

3-MA improved anxiety-like behaviors in aged mice undergoing abdominal exploratory laparotomy by inhibiting excessive autophagy-induced oxidative stress. These results suggest that 3-MA could be an effective treatment for postoperative anxiety.

Short-term high-fat diet consumption impairs synaptic plasticity in the aged hippocampus via IL-1 signaling

More Americans are consuming diets higher in saturated fats and refined sugars than ever before. These trends could have serious consequences for the older population because high-fat diet (HFD) consumption, known to induce neuroinflammation, has been shown to accelerate and aggravate memory declines. We have previously demonstrated that short-term HFD consumption, which does not evoke obesity-related comorbidities, produced profound impairments to hippocampal-dependent memory in aged rats. These impairments were precipitated by increases in proinflammatory cytokines, primarily interleukin-1 beta (IL-1β). Here, we explored the extent to which short-term HFD consumption disrupts hippocampal synaptic plasticity, as measured by long-term potentiation (LTP), in young adult and aged rats. We demonstrated that (1) HFD disrupted late-phase LTP in the hippocampus of aged, but not young adult rats, (2) HFD did not disrupt early-phase LTP, and (3) blockade of the IL-1 receptor rescued L-LTP in aged HFD-fed rats. These findings suggest that hippocampal memory impairments in aged rats following HFD consumption occur through the deterioration of synaptic plasticity and that IL-1β is a critical driver of that deterioration.

NLRP3-GABA signaling pathway contributes to the pathogenesis of impulsive-like behaviors and cognitive deficits in aged mice

BACKGROUND

Perioperative neurocognitive disorders (PND), such as delirium and cognitive impairment, are commonly encountered complications in aged patients. The inhibitory neurotransmitter γ-aminobutyric acid (GABA) is aberrantly synthesized from reactive astrocytes following inflammatory stimulation and is implicated in the pathophysiology of neurodegenerative diseases. Additionally, the activation of NOD-like receptor protein 3 (NLRP3) inflammasome is involved in PND. Herein, we aimed to investigate whether the NLRP3-GABA signaling pathway contributes to the pathogenesis of aging mice's PND.

METHODS

24-month-old C57BL/6 and astrocyte-specific NLRP3 knockout male mice were used to establish a PND model via tibial fracture surgery. The monoamine oxidase-B (MAOB) inhibitor selegiline (1 mg/kg) was intraperitoneally administered once a day for 7 days after the surgery. PND, including impulsive-like behaviors and cognitive impairment, was evaluated by open field test, elevated plus maze, and fear conditioning. Thereafter, pathological changes of neurodegeneration were explored by western blot and immunofluorescence assays.

RESULTS

Selegiline administration significantly ameliorated TF-induced impulsive-like behaviors and reduced excessive GABA production in reactive hippocampal astrocytes. Moreover, astrocyte-specific NLRP3 knockout mice reversed TF-induced impulsive-like and cognitive impairment behaviors, decreased GABA levels in reactive astrocytes, ameliorated NLRP3-associated inflammatory responses during the early stage, and restored neuronal degeneration in the hippocampus.

CONCLUSIONS

Our findings suggest that anesthesia and surgical procedures trigger neuroinflammation and cognitive deficits, which may be due to NLRP3-GABA activation in the hippocampus of aged mice.

Comparison of the effects of remimazolam and dexmedetomidine on early postoperative cognitive function in elderly patients with gastric cancer

Purpose

To compare the effects of remimazolam and dexmedetomidine on early postoperative cognitive dysfunction (POCD) in aged gastric cancer patients.

Methods

From June to December 2022, 104 elderly patients (aged 65-80 years) received laparoscopic radical resection of gastric cancer at the First Affiliated Hospital of Nanchang University. Using the random number table approach, the patients were separated into three groups: remimazolam (Group R), dexmedetomidine (Group D), and saline (Group C). The primary outcome was the incidence of POCD, and secondary outcomes included TNF-α and S-100β protein concentrations, hemodynamics, VAS scores, anesthesia recovery indicators, and the occurrence of adverse events within 48 h postoperatively.

Results

At 3 and 7 days after surgery, there were no statistically significant differences in the incidence of POCD, the MMSE and MoCA scores between groups R and D (p > 0.05). However, compared to the saline group, both groups had higher MMSE and MoCA scores and decreased incidences of POCD. These differences were statistically significant (p < 0.05). Between group R and group D, there were no statistically significant changes (p > 0.05) in the levels of TNF-α and S-100β protein at the three time points (at the end of the surgery, 1 day later, and 3 days later). Even though neither group's concentration of the two factors was as high as that of the saline group, the differences were statistically significant (p < 0.05). At all three time points-following induction (T2), 30 min into the operation (T3), and at the conclusion of the surgery (T4)-the heart rate and blood pressure in group R were greater than those in groups D and C. Statistics showed that the differences were significant (p < 0.05). The incidence of intraoperative hypotension was highest in group D and lowest in group R (p < 0.05). The dose of propofol and remifentanil, group C > group R > group D. Extubation and PACU residence times did not differ statistically significantly (p > 0.05) between the three groups. There was no significant difference in VAS scores between groups R and D after 24 h postoperatively (p > 0.05), although both had lower scores than group C, and the difference was statistically significant (p < 0.05). The VAS scores between the three groups at 72 h (T6) and 7 days (T7) were not statistically significant (p > 0.05). Adverse reactions such as respiratory depression, hypotension, bradycardia, agitation, drowsiness, and nausea and vomiting had the lowest incidence in group R and the highest incidence in group C (p < 0.05).

Conclusion

Remimazolam is similarly beneficial as dexmedetomidine in lowering the incidence of early POCD in aged patients after radical gastric cancer resection, probably due to reduced inflammatory response.

Inhibition of PINK1-Mediated Mitophagy Contributes to Postoperative Cognitive Dysfunction through Activation of Caspase-3/GSDME-Dependent Pyroptosis

PTEN-induced kinase 1 (PINK1)-mediated mitophagy and caspase-1/gasdermin D canonical pyroptosis pathways have been implicated in the pathogenesis of postoperative cognitive dysfunction (POCD). However, gasdermin E (GSDME), another recently identified executioner of pyroptosis that can be specifically cleaved by caspase-3, is highly expressed in the brain and neurons. This study aimed to ascertain whether PINK1-dependent mitophagy governs postoperative cognitive capacity through caspase-3/GSDME. Twelve month old male Sprague-Dawley rats underwent exploratory laparotomy under isoflurane anesthesia. Lipopolysaccharide (LPS)-primed SH-SY5Y cells were used to mimic postsurgical neuroinflammation. For the interventional study, rats were administered with adeno-associated virus serotype 9 (AAV9)-mediated silencing of Pink1 and/or caspase-3 inhibitor Ac-DEVD-CHO (Ac-DC). SH-SY5Y cells were treated with siPINK1 and/or Ac-DC. Cognitive performance was assessed using the Morris water maze test. The mitophagy- and pyroptosis-related parameters were determined in the hippocampus and SH-SY5Y cells. Anesthesia/surgery and LPS caused defective PINK1-mediated mitophagy and activation of caspase-3/GSDME-dependent pyroptosis. AAV-9 mediated Pink1 overexpression mitigated cognitive impairment and caspase-3/GSDME-dependent pyroptosis. Conversely, inhibition of PINK1 aggravates POCD and overactivates neuronal pyroptosis. These abnormalities were rescued by Ac-DC treatment. Collectively, PINK1-mediated mitophagy regulates anesthesia and surgery-induced cognitive impairment by negatively affecting the caspase-3/GSDME pyroptosis pathway, which provides a promising therapeutic target for POCD.

Young adult and aged female rats are vulnerable to amygdala-dependent, but not hippocampus-dependent, memory impairment following short-term high-fat diet

Global populations are increasingly consuming diets high in saturated fats and refined carbohydrates, and such diets have been well-associated with heightened inflammation and neurological dysfunction. Notably, older individuals are particularly vulnerable to the impact of unhealthy diet on cognition, even after a single meal, and pre-clinical rodent studies have demonstrated that short-term consumption of high-fat diet (HFD) induces marked increases in neuroinflammation and cognitive impairment. Unfortunately though, to date, most studies on the topic of nutrition and cognition, especially in aging, have been performed only in male rodents. This is especially concerning given that older females are more vulnerable to develop certain memory deficits and/or severe memory-related pathologies than males. Thus, the aim of the present study was to determine the extent to which short-term HFD consumption impacts memory function and neuroinflammation in female rats. Young adult (3 months) and aged (20-22 months) female rats were fed HFD for 3 days. Using contextual fear conditioning, we found that HFD had no effect on long-term contextual memory (hippocampus-dependent) at either age, but impaired long-term auditory-cued memory (amygdala-dependent) regardless of age. Gene expression of Il-1β was markedly dysregulated in the amygdala, but not hippocampus, of both young and aged rats after 3 days of HFD. Interestingly, modulation of IL-1 signaling via central administration of the IL-1 receptor antagonist (which we have previously demonstrated to be protective in males) had no impact on memory function following the HFD in females. Investigation of the memory-associated gene Pacap and its receptor Pac1r revealed differential effects of HFD on their expression in the hippocampus and amygdala. Specifically, HFD induced increased expression of Pacap and Pac1r in the hippocampus, whereas decreased Pacap was observed in the amygdala. Collectively, these data suggest that both young adult and aged female rats are vulnerable to amygdala-dependent (but not hippocampus-dependent) memory impairments following short-term HFD consumption, and identify potential mechanisms related to IL-1β and PACAP signaling in these differential effects. Notably, these findings are strikingly different than those previously reported in male rats using the same diet regimen and behavioral paradigms, and highlight the importance of examining potential sex differences in the context of neuroimmune-associated cognitive dysfunction.

Acute pain management and long term outcomes

PURPOSE OF REVIEW

The acute inflammatory reaction induced by tissue trauma causes pain but also promotes recovery. Recovery is highly variable among peoples. Effective acute pain (AP) management is very important but remains suboptimal what could affect long term outcomes. The review questions the impact of either failure or effectiveness of AP treatments and the choice of analgesic drugs on different long-term outcomes after tissue trauma.

RECENT FINDINGS

Pain control during mobilization is mandatory to reduce the risk of complications which exacerbate and prolong the inflammatory response to trauma, impairing physical recovery. Common analgesic treatments show considerable variability in effectiveness among peoples what argues for an urgent need to develop personalized AP management, that is, finding better responders to common analgesics and targeting challenging patients for more invasive procedures. Optimal multimodal analgesia to spare opioids administration remains a priority as opioids may enhance neuroinflammation, which underlies pain persistence and precipitates neurocognitive decline in frail patients. Finally, recent findings demonstrate that AP treatments which modulate nociceptive and inflammatory pain should be used with caution as drugs which inhibit inflammation like nonsteroidal antiinflammatory drugs and corticoids might interfere with natural recovery processes.

SUMMARY

Effective and safe AP management is of far greater importance than previously realized. Evidence of suboptimal AP management in many patients and recent reports pointing out the impact of current treatments on long term outcomes argue for further research in the field.

Abdominal surgery plus sevoflurane exposure induces abnormal emotional changes and cognitive dysfunction in aged rats

BACKGROUND

Cognitive impairment, which includes perioperative psychological distress and cognitive dysfunction, can be determined by preoperative and post-operative neuropsychological tests. Several mechanisms have been proposed regarding the two-way communication between the immune system and the brain after surgery. We aimed to understand the mechanisms underlying perioperative neurocognitive disorders (PND) in elderly rats using an experimental abdominal surgery model.

METHODS

24-month-old SD rats were exposed to the abdominal surgery model (AEL) under 3% anesthesia. On day 15 and day 30 post-surgery, fractional anisotropy (FA) using diffusion kurtosis imaging (DKI) was measured. From day 25 to day 30 post-surgery, behavioral tests, including open field test (OFT), Morris water maze (MWM), novel object recognition (NOR), force swimming test (FST), and elevated plus maze (EPM), were performed. Then, the rats were euthanized to perform pathological analysis and western blot measurement.

RESULTS

The rats exposed to AEL surgical treatment demonstrated significantly decreased time crossing the platform in the MWM, decreased recognition index in the NOR, reduced time in the open arm in the EPM, increased immobility time in the FST, and increased number of crossings in the OFT. Aged rats, after AEL exposure, further demonstrated decreased FA in the mPFC, nucleus accumbens (NAc), and hippocampus, together with reduced MAP2 intensity, attenuation of GAD65, VGlut2, CHAT, and phosphorylated P38MAPK expression, and increased reactive astrocytes and microglia.

CONCLUSIONS

In this study, the aged rats exposed to abdominal surgery demonstrated both emotional changes and cognitive dysfunction, which may be associated with neuronal degeneration and reduced phosphorylated P38MAPK.

CD8+ T cells contribute to diet-induced memory deficits in aged male rats

We have previously shown that short-term (3-day) high fat diet (HFD) consumption induces a neuroinflammatory response and subsequent impairment of long-term memory in aged, but not young adult, male rats. However, the immune cell phenotypes driving this proinflammatory response are not well understood. Previously, we showed that microglia isolated from young and aged rats fed a HFD express similar levels of priming and proinflammatory transcripts, suggesting that additional factors may drive the exaggerated neuroinflammatory response selectively observed in aged HFD-fed rats. It is established that T cells infiltrate both the young and especially the aged central nervous system (CNS) and contribute to immune surveillance of the parenchyma. Thus, we investigated the modulating role of short-term HFD on T cell presence in the CNS in aged rats using bulk RNA sequencing and flow cytometry. RNA sequencing results indicate that aging and HFD altered the expression of genes and signaling pathways associated with T cell signaling, immune cell trafficking, and neuroinflammation. Moreover, flow cytometry data showed that aging alone increased CD4+ and CD8+ T cell presence in the brain and that CD8+, but not CD4+, T cells were further increased in aged rats fed a HFD. Based on these data, we selectively depleted circulating CD8+ T cells via an intravenous injection of an anti-CD8 antibody in aged rats prior to 3 days of HFD to infer the functional role these cells may be playing in long-term memory and neuroinflammation. Results indicate that peripheral depletion of CD8+ T cells lowered hippocampal cytokine levels and prevented the HFD-induced i) increase in brain CD8+ T cells, ii) memory impairment, and iii) alterations in pre- and post-synaptic structures in the hippocampus and amygdala. Together, these data indicate a substantial role for CD8+ T cells in mediating diet-induced memory impairments in aged male rats.

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.

Selective TLR4 Antagonism Prevents and Reverses Morphine-Induced Persistent Postoperative Cognitive Dysfunction, Dysregulation of Synaptic Elements, and Impaired BDNF Signaling in Aged Male Rats

Perioperative neurocognitive disorders (PNDs) are characterized by confusion, difficulty with executive function, and episodic memory impairment in the hours to months following a surgical procedure. Postoperative cognitive dysfunction (POCD) represents such impairments that last beyond 30 d postsurgery and is associated with increased risk of comorbidities, progression to dementia, and higher mortality. While it is clear that neuroinflammation plays a key role in PND development, what factors underlie shorter self-resolving versus persistent PNDs remains unclear. We have previously shown that postoperative morphine treatment extends POCD from 4 d (without morphine) to at least 8 weeks (with morphine) in aged male rats, and that this effect is likely dependent on the proinflammatory capabilities of morphine via activation of toll-like receptor 4 (TLR4). Here, we extend these findings to show that TLR4 blockade, using the selective TLR4 antagonist lipopolysaccharide from the bacterium Rhodobacter sphaeroides (LPS-RS Ultrapure), ameliorates morphine-induced POCD in aged male rats. Using either a single central preoperative treatment or a 1 week postoperative central treatment regimen, we demonstrate that TLR4 antagonism (1) prevents and reverses the long-term memory impairment associated with surgery and morphine treatment, (2) ameliorates morphine-induced dysregulation of the postsynaptic proteins postsynaptic density 95 and synaptopodin, (3) mitigates reductions in mature BDNF, and (4) prevents decreased activation of the BDNF receptor TrkB (tropomyosin-related kinase B), all at 4 weeks postsurgery. We also reveal that LPS-RS Ultrapure likely exerts its beneficial effects by preventing endogenous danger signal HMGB1 (high-mobility group box 1) from activating TLR4, rather than by blocking continuous activation by morphine or its metabolites. These findings suggest TLR4 as a promising therapeutic target to prevent or treat PNDs.SIGNIFICANCE STATEMENT With humans living longer than ever, it is crucial that we identify mechanisms that contribute to aging-related vulnerability to cognitive impairment. Here, we show that the innate immune receptor toll-like receptor 4 (TLR4) is a key mediator of cognitive dysfunction in aged rodents following surgery and postoperative morphine treatment. Inhibition of TLR4 both prevented and reversed surgery plus morphine-associated memory impairment, dysregulation of synaptic elements, and reduced BDNF signaling. Together, these findings implicate TLR4 in the development of postoperative cognitive dysfunction, providing mechanistic insight and novel therapeutic targets for the treatment of cognitive impairments following immune challenges such as surgery in older individuals.

Modulation of Small RNA Signatures by Astrocytes on Early Neurodegeneration Stages; Implications for Biomarker Discovery

Diagnosis of neurodegenerative disease (NDD) is complex, therefore simpler, less invasive, more accurate biomarkers are needed. small non-coding RNA (sncRNA) dysregulates in NDDs and sncRNA signatures have been explored for the diagnosis of NDDs, however, the performance of previous biomarkers is still better. Astrocyte dysfunction promotes neurodegeneration and thus derived scnRNA signatures could provide a more precise way to identify of changes related to NDD course and pathogenesis, and it could be useful for the dissection of mechanistic insights operating in NDD. Often sncRNA are transported outside the cell by the action of secreted particles such as extracellular vesicles (EV), which protect sncRNA from degradation. Furthermore, EV associated sncRNA can cross the BBB to be found in easier to obtain peripheral samples, EVs also inherit cell-specific surface markers that can be used for the identification of Astrocyte Derived Extracellular Vesicles (ADEVs) in a peripheral sample. By the study of the sncRNA transported in ADEVs it is possible to identify astrocyte specific sncRNA signatures that could show astrocyte dysfunction in a more simpler manner than previous methods. However, sncRNA signatures in ADEV are not a copy of intracellular transcriptome and methodological aspects such as the yield of sncRNA produced in ADEV or the variable amount of ADEV captured after separation protocols must be considered. Here we review the role as signaling molecules of ADEV derived sncRNA dysregulated in conditions associated with risk of neurodegeneration, providing an explanation of why to choose ADEV for the identification of astrocyte-specific transcriptome. Finally, we discuss possible limitations of this approach and the need to improve the detection limits of sncRNA for the use of ADEV derived sncRNA signatures.

Toll-like receptor-mediated neuroinflammation: relevance for cognitive dysfunctions

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) with a well-documented role in the innate and adaptive immune responses. Interestingly, TLR activation has also been linked to several brain functions including neurogenesis and synaptogenesis. Increasing evidence supports TLR involvement in peripheral and central inflammation underlying normal aging and the pathogenesis of clinical conditions characterized by cognitive decline. These include not only major neurodegenerative diseases but also traumatic brain injuries, surgeries, and alcohol consumption- and chemotherapy-induced cognitive impairment. We first summarize the physiological roles of TLRs in the nervous system, and then illustrate the emerging involvement of TLRs in cognitive functions, pointing to these receptors as novel enticing pharmacological targets to develop more efficient drugs for the treatment of cognitive impairment.

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.

The role of plant-based products in the prevention of neurological complications

BACKGROUND

Neurological complications are most likely to be fatal and cause loss of ability to function or care for self. These include Alzheimer's disease and cognitive impairment. The main aim of the review is to determine the effects of various drugs and their cognitive risk with the need to opt for herbal therapy as an adjuvant in treating neurological conditions like Alzheimer's disease with lesser-known side effects. The Methodology: Involved a detailed literature survey which was performed through an online database, such as Science Direct, Google Scholar, Scopus, Cochrane, and PubMed. The study included randomized trials and original research conducted by herbal supplements on animal models to assess expression of upregulation of signalling pathways. Various studies involved in treating dementia, neurological disorders, Alzheimer disease, cognitive dysfunction were included.

RESULTS

Found that various studies involved plant-based products were showing improvement in prevention of disease and signalling pathways with lesser-known side effects.

CONCLUSION

It was observed that plant-based products play a major role in the prevention of neurological complications. Herbal medicines could most suitably prevent Alzheimer's risk with less known side effects in contrast with the existing treatment patterns. However, to improve the utility of herbal medicines, more evidences from in vitro, in vivo, and clinical trials need to be addressed.

Necrostatin-1 Against Sevoflurane-Induced Cognitive Dysfunction Involves Activation of BDNF/TrkB Pathway and Inhibition of Necroptosis in Aged Rats

Postoperative cognitive dysfunction (POCD) induced by anesthesia or surgery has become a common complication in the aged population. Sevoflurane, a clinical inhalation anesthetic, could stimulate calcium overload and necroptosis to POCD. In addition, necroptosis inhibitor necrostatin-1 (Nec-1) alleviated cognitive impairment caused by multiple causes, including postoperative cognitive impairment. However, whether Nec-1 exerts a neuroprotective effect on POCD via calcium and necroptosis remains unclear. We anesthetized Sprague-Dawley rats with sevoflurane to construct the POCD model and to explore the mechanism underlying neuroprotective effects of Nec-1 in POCD. Rats were treated with Nec-1 (6.25 mg/kg) 1 h prior to anesthesia. Open field test and Morris water maze were employed to detect the cognitive function. In this study, rats exposed to sevoflurane displayed cognitive dysfunction without changes in spontaneous activity; however, the sevoflurane-induced POCD could be relieved by Nec-1 pretreatment. Nec-1 decreased sevoflurane-induced calcium overload and calpain activity in the hippocampus. In addition, Nec-1 alleviated the expression of p-RIPK1, RIPK1, p-RIPK3, RIPK3, p-MLKL and MLKL. Furthermore, Nec-1 remarkably increased BDNF and p-TrkB/TrkB expression in the hippocampus of aged rats. Ultimately, our research manifests evidence that Nec-1 may play a neuroprotective role against sevoflurane-induced cognitive impairment via the increase of BDNF/TrkB and suppression of necroptosis-related pathway.

VRT-043198 Ameliorates Surgery-Induced Neurocognitive Disorders by Restoring the NGF and BNDF Expression in Aged Mice

BACKGROUND

Perioperative neurocognitive disorders (PND) are common surgical complications in the elderly. Pyroptosis-associated inflammation has been suggested to participate in a series of neurocognitive diseases, including Alzheimer's disease. Given that VRT-043198 can reportedly inhibit caspase-1-induced pyroptosis, this study sought to determine whether VRT-043198 reduced PND in a mouse model following abdominal exploratory laparotomy.

METHODS

20-month-old male C57/BL mice were used to establish an abdominal exploratory laparotomy (AEL) model of PND. VRT-043198 (1, 10 and 100 mg/kg) was administered intraperitoneally immediately after surgery. Thirty days post-surgery, the mice were evaluated in the Morris water maze test. Their number of neurons, neurotrophin nerve growth factor (NGF) levels and brain-derived neurotrophic factor (BDNF) were measured. In the hippocampus, A1-type astrocytes and M1-type microglia were assessed using an immunofluorescence assay and Western blot, respectively. Caspase-1 activity, IL-1β, IL-18, and PPAR-γ were also measured 24h after surgery.

RESULTS

VRT-043198 administration increased the time to cross the platform and increased the ratio of distance and time in the targeted quadrant after surgery. Furthermore, it was found that VRT-043198 restored neuronal amount, increased NGF and BDNF and decreased the number of A1-type astrocytes and M1-type microglia. VRT-043198 also attenuated caspase-1 activity, downregulated IL-1β and IL-18, but increased PPAR-γ 24h post-surgery.

CONCLUSION

VRT-043198 improved PND in aged mice after abdominal exploratory laparotomy by restoring the NGF and BNDF expression. These results indicate that VRT-043198 may be a potential therapy for PND.

Clemastine Ameliorates Perioperative Neurocognitive Disorder in Aged Mice Caused by Anesthesia and Surgery

Perioperative neurocognitive disorder (PND) leads to progressive deterioration of cognitive function, especially in aged patients. Demyelination is closely associated with cognitive dysfunction. However, the relationship between PND and demyelination remains unclear. Here we showed that demyelination was related to the pathogenesis of PND. Clemastine, an antihistamine with potency in remyelination, was predicted to have a potential therapeutic effect on PND by next-generation sequencing and bioinformatics in our previous study. In the present study, it was given at 10 mg/kg per day for 2 weeks to evaluate the effects on PND in aged mice. We found that clemastine ameliorated PND and reduced the expression levels of inflammatory factors such as tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β). Further investigation suggested clemastine increased the expression of oligodendrocyte transcription factor 2 (OLIG2) and myelin basic protein (MBP) to enhance remyelination by inhibiting the overactivation of the WNT/β-catenin pathway. At the same time, the expression of post-synaptic density protein 95 (PSD95, or DLG4), brain-derived neurotrophic factor (BDNF), synaptosomal-associated protein 25 (SNAP25) and neuronal nuclei (NEUN) were also improved. Our results suggested that clemastine might be a therapy for PND caused by anesthetic and surgical factors in aged patients.

The Perfect Cytokine Storm: How Peripheral Immune Challenges Impact Brain Plasticity & Memory Function in Aging

Precipitous declines in cognitive function can occur in older individuals following a variety of peripheral immune insults, such as surgery, infection, injury, and unhealthy diet. Aging is associated with numerous changes to the immune system that shed some light on why this abrupt cognitive deterioration may occur. Normally, peripheral-to-brain immune signaling is tightly regulated and advantageous; communication between the two systems is bi-directional, via either humoral or neural routes. Following an immune challenge, production, secretion, and translocation of cytokines into the brain is critical to the development of adaptive sickness behaviors. However, aging is normally associated with neuroinflammatory priming, notably microglial sensitization. Microglia are the brain's innate immune cells and become sensitized with advanced age, such that upon immune stimulation they will mount more exaggerated neuroimmune responses. The resultant elevation of pro-inflammatory cytokine expression, namely IL-1β, has profound effects on synaptic plasticity and, consequentially, cognition. In this review, we (1) investigate the processes which lead to aberrantly elevated inflammatory cytokine expression in the aged brain and (2) examine the impact of the pro-inflammatory cytokine IL-1β on brain plasticity mechanisms, including its effects on BDNF, AMPA and NMDA receptor-mediated long-term potentiation.

Restoration of Proresolution Pathway with Exogenous Resolvin D1 Prevents Sevoflurane-Induced Cognitive Decline by Attenuating Neuroinflammation in the Hippocampus in Rats with Type 2 Diabetes Mellitus

Sevoflurane (SEV), a commonly used volatile anesthetic, has been shown to cause cognitive decline in diabetic rats by aggregating neuroinflammation in the hippocampus, but the underlying mechanisms are unknown. Recent evidence suggests that neuroinflammation could be a consequence of failure to resolve inflammation by specialized pro-resolving lipid mediators including resolvin D1 (RvD1). Here we first examined whether type 2 diabetes mellitus (DM) alters RvD1 proresolution pathway. Diabetic Goto-Kakizaki (GK) rats and non-diabetic Wistar rats received control or 2.6% SEV exposure for 4 h. Seven days after exposure, GK control rats, compared with Wistar control rats, had significantly lower RvD1 levels in plasma and CSF and decreased RvD1 receptor FPR2 expression in the hippocampus. SEV increased RvD1 levels in plasma and CSF and FPR2 expression in the hippocampus in Wistar rats but not in GK rats. We next examined whether RvD1 treatment of GK rats can prevent SEV-induced neuroinflammation and cognitive decline. GK rats received control, SEV or SEV and once-daily treatment with exogenous RvD1 (0.2 ug/kg, ip) for 7 days. RvD1 administration markedly increased RvD1 levels in plasma and CSF and FPR2 expression in the hippocampus in GK rats received SEV. Compared with GK control rats, GK rats received SEV exhibited shorter freezing times in trace fear conditioning task, which was accompanied by increased microglia activity and pro-inflammatory cytokine expression in the hippocampus. RvD1 administration attenuated SEV-induced increases in microglia activity and pro-inflammatory cytokine expression in the hippocampus, preventing cognitive decline in GK rats. Notably, neither SEV nor RvD1 altered metabolic parameters in GK rats. The results suggest that RvD1 proresolution pathway is impaired in the brain of diabetic GK rats. which may enhance the susceptibility to SEV, contributing to neuroinflammation and cognitive decline. Restoration of RvD1 proresolution pathway in diabetic GK rats with exogenous RvD1 can prevent SEV-induced cognitive decline by attenuating neuroinflammation in the hippocampus.

Toll-like receptor 2 activation and up-regulation by high mobility group box-1 contribute to post-operative neuroinflammation and cognitive dysfunction in mice

Post-operative cognitive dysfunction (POCD) is common and is associated with poor clinical outcome. Toll-like receptor (TLR) 3 and 4 have been implied in the development of POCD. The role of TLR2, a major brain TLR, in POCD is not clear. High mobility group box-1 (HMGB1) is a delayed inflammatory mediator and may play a role in POCD. The interaction between HMGB1 and TLRs in the perioperative period is not known. We hypothesize that TLR2 contributes to the development of POCD and that HMGB1 regulates TLR2 for this effect. To test these hypotheses, 6- to 8-week old male mice were subjected to right carotid artery exposure under isoflurane anesthesia. CU-CPT22, a TLR1/TLR2 inhibitor, at 3 mg/kg was injected intraperitoneally 30 min before surgery and 1 day after surgery. Glycyrrhizin, a HMGB1 antagonist, at 200 mg/kg was injected intraperitoneally 30 min before surgery. Mice were subjected to Barnes maze and fear conditioning tests from 1 week after surgery. Hippocampus and cerebral cortex were harvested 6 hr or 12 hr after the surgery for Western blotting, ELISA, immunofluorescent staining, and chromatin immunoprecipitation. There were neuroinflammation and impairment of learning and memory in mice with surgery. Surgery increased the expression of TLR2 and TLR4 but not TLR9 in the brain of CD-1 male mice. CU-CPT22 attenuated surgery-induced neuroinflammation and cognitive impairment. Similarly, surgery induced neuroinflammation and cognitive dysfunction in C57BL/6J mice but not in TLR2^-/- mice. TLR2 staining appeared in neurons and microglia. Surgery increased HMGB1 in the cell nuclei of the cerebral cortex and hippocampus. Glycyrrhizin ameliorated this increase and the increase of TLR2 in the hippocampus after surgery. Surgery also increased the amount of tlr2 DNA precipitated by an anti-HMGB1 antibody in the hippocampus. Our results suggest that TLR2 contributes to surgery-induced neuroinflammation and cognitive impairment. HMGB1 up-regulates TLR2 expression in the hippocampus after surgery to facilitate this contribution. Thus, TLR2 and HMGB1 are potential targets for reducing POCD.

Buprenorphine alters microglia and astrocytes acutely following diffuse traumatic brain injury

Traumatic brain injury (TBI) is a common phenomenon, accounting for significant cost and adverse health effects. While there is information about focal pathologies following TBI, knowledge of more diffuse processes is lacking, particularly regarding how analgesics affect this pathology. As buprenorphine is the most commonly used analgesic in experimental TBI models, this study investigated the acute effects of the opioid analgesic buprenorphine (Bup-SR-Lab) on diffuse neuronal/glial pathology, neuroinflammation, cell damage, and systemic physiology. We utilized a model of central fluid percussion injury (CFPI) in adult male rats treated with a single subcutaneous bolus of Bup-SR-Lab or saline 15 min post-injury. Microscopic assessments were performed at 1 day post-injury. Cell impermeable dextran was infused intraventricularly prior to sacrifice to assess neuronal membrane disruption. Axonal injury was assessed by investigating labeling of the anterogradely transported amyloid precursor protein. Neuroinflammation was assessed by analyzing Iba-1 + microglial and GFAP + astrocyte histological/morphological features as well as cytokine levels in both regions of interest (ROIs). Myelin pathology was assessed by evaluating the expression of myelin basic protein (MBP) and the propensity of MBP + myelin debris. Acute physiologic data showed no difference between groups except for reduction in weight loss following cFPI in Bup treated animals compared to saline. There were no discernable differences in axonal injury or membrane disruption between treatment groups. Cytokine levels were consistent between Bup and saline treated animals, however, microglia and astrocytes revealed region specific histological changes at 1d following Bup treatment. Myelin integrity and overall MBP expression showed no differences between Bup and saline treated animals, but there were significant regional differences in MBP expression between the cortex and thalamus. These data suggest effects of Bup treatment on weight following CFPI and potential regional specificity of Bup-associated microglial and astrocyte alterations, but very little change in other acute pathology at 1-day post-injury. Overall, this preliminary study indicates that use of Bup-SR-Lab in preclinical work does have effects on acute glial pathology, however, longer term studies will be needed to assess potential effects of Bup treatment on more chronic pathological progressions.