Systemic lipopolysaccharide administration impairs retrieval of context-object discrimination, but not spatial, memory: Evidence for selective disruption of specific hippocampus-dependent memory functions during acute neuroinflammation

The clinical efficacy of Olibanum gum chewing in patients with Mild-to-Moderate Alzheimer disease: A randomized Parallel-Design controlled trial

BACKGROUND

Alzheimer's disease is a common neurodegenerative disorder in elderly with progressive decline in cognitive functions. This study aimed to investigate the possible memory-improving effects of Olibanum on patients with Alzheimer's disease.

RESEARCH DESIGN AND METHOD

This double-blind, randomized clinical trial was carried out on 72 participants aged 50-75 years. The intervention group (n = 36) received 1.6 g/day of olibanum chewing gum for 18 weeks. The placebo group (n = 36) received chewing gum without olibanum. Neuropsychological assessments were performed at baseline, every 4 weeks, and after 18 weeks of the intervention.

RESULTS

There was no significant difference between (MD: 0.84, 95%CI: -1.10 to 2.78, p = 0.392) at baseline. Both groups had linear improvements over time. There was no significant difference between two groups regarding the improvements after the intervention (F = 0.157, p = 0.693). There were no significant differences between the groups for MMSE score (Mini-Mental State Examination) after the intervention (F = 0.141, p = 0.708).

CONCLUSIONS

This study revealed that 18 weeks of gum chewing with Olibanum did not change the neuropsychological status. More clinical studies are needed to confirm these findings.

D-ribose-L-cysteine exhibits restorative neurobehavioral functions through modulation of neurochemical activities and inhibition oxido-inflammatory perturbations in rats exposed to polychlorinated biphenyl

Polychlorinated biphenyl (PCB) is potentially harmful environmental toxicant causing cognitive decline with depressive features. PCB-induced behavioral deficits are associated with neurochemical dysfunctions, immune changes, and oxidative stress. This study investigated the neuroprotective effects of D-ribose-L-cysteine (DRLC), a neuroprotective precursor element of glutathione on PCB-induced neurobehavioral impairments. Following the initial 15 days of PCB (2 mg/kg) exposure to rats, DRLC (50 mg/kg) was given orally for an additional 15 days, from days 16 to 30. Animals were assessed for behavioral effect such as changes in locomotion, cognition, and depression. Oxidative/nitrergic stress markers; antioxidant regulatory proteins paraoxonase-1 (PON-1), heme oxygenase-1 (HO-1), nuclear factor erythroid 2-related factor 2 (Nfr2), NADPH oxidase-1 (NOX-1), NAD(P)H quinone oxidoreductase 1 (NQO1), and neuroinflammation (NF-kβ, and TNF-α); and neurochemical metabolizing enzymes (acetylcholinesterase (AChE), monoamine oxidase-A and -B (MAO-A, MAO-B)) were carried out. The PCB-induced decline in locomotion, cognitive performance, and depressive-like features were reversed by DRLC. More specifically, PCB-induced oxidative and nitrergic stress, typified by reduced levels GSH, CAT, and SOD, accompanied by elevated MDA and nitrite were attenuated by DRLC. Additionally, DRLC restored the neuroinflammatory milieu indicated by decreased NF-kβ and TNF-α levels toward normal. Hyperactivities of AChE, MAO-A, MAO-B, PON-1, and NOX-1 levels as well as Nfr2, NQO1, and PON-1 due to PCB exposure were mitigated by DLRC. Our results suggest DRLC as a prospective neurotherapeutic agent against PCB-induced neurobehavioral impairments such as cognitive deficit and depressive-like feature through antioxidative and anti-nitrergic stress, anti-neuroinflammation, inhibition of brain metabolizing enzymes, and normalization of neurochemical homeostasis.

Interleukin-15 alters hippocampal synaptic transmission and impairs episodic memory formation in mice

Cytokines are potent immunomodulators exerting pleiotropic effects in the central nervous system (CNS). They influence neuronal functions and circuit activities with effects on memory processes and behaviors. Here, we unravel a neuromodulatory activity of interleukin-15 (IL-15) in mouse brain. Acute exposure of hippocampal slices to IL-15 enhances gamma-aminobutyricacid (GABA) release and reduces glutamatergic currents, while chronic treatment with IL-15 increases the frequency of hippocampal miniature inhibitory synaptic transmission and impairs memory formation in the novel object recognition (NOR) test. Moreover, we describe that serotonin is involved in mediating the hippocampal effects of IL-15, because a selective 5-HT3A receptor antagonist prevents the effects on inhibitory neurotransmission and ameliorates mice performance in the NOR test. These findings provide new insights into the modulatory activities of cytokines in the CNS, with implications on behavior.

Avanafil mediated dual inhibition of IKKβ and TNFR1 in an experimental paradigm of Alzheimer's disease: in silico and in vivo approach

In Alzheimer's disease pathology, inhibitors of nuclear factor kappa-β kinase subunit β (IKKB) and Tumor necrosis factor receptor 1 (TNFR1) signaling are linked to neuroinflammation-mediated cognitive decline. We explored the role of a phosphodiesterase 5 inhibitor (PDE5I) with dual antagonistic action on IKKB and TNFR1 to inhibit nuclear factor kappa B (NF-kB) and curb neuroinflammation. In the in silico approach, the FDA-approved Zinc 15 library was docked with IKKB and TNFR1. The top compound with dual antagonistic action on IKKB and TNFR1 was selected based on bonding and non-bonding interactions. Further, induced fit docking (IFD), molecular mechanics-generalized Born and surface area (MMGBSA), and molecular dynamic studies were carried out and evaluated. Lipopolysaccharide (LPS) administration caused a neuroinflammation-mediated cognitive decline in mice. Two doses of avanafil were administered for 28 days while LPS was administered for 10 days. Morris water maze (MWM) along with the passive avoidance test (PAT) were carried out. Concurrently brain levels of inflammatory markers, oxidative parameters, amyloid beta (Aβ), IKKB and NF-kB levels were estimated. Avanafil produced good IKKB and TNFR1 binding ability. It interacted with crucial inhibitory amino acids of IKKB and TNFR1. MD analysis predicted good stability of avanafil with TNFR1 and IKKB. Avanafil 6 mg/kg could significantly improve performance in MWM, PAT and oxidative parameters and reduce Aβ levels and inflammatory markers. As compared to avanafil 3 mg/kg, 6 mg/kg dose was found to exert better efficacy against elevated Aβ , neuroinflammatory cytokines and oxidative markers while improving behavioural parameters.Communicated by Ramaswamy H. Sarma.

Genes Involved by Dexamethasone in Prevention of Long-Term Memory Impairment Caused by Lipopolysaccharide-Induced Neuroinflammation

Inflammatory activation within the brain is linked to a decrease in cognitive abilities; however, the molecular mechanisms implicated in the development of inflammatory-related cognitive dysfunction and its prevention are poorly understood. This study compared the responses of hippocampal transcriptomes 3 months after the striatal infusion of lipopolysaccharide (LPS; 30 µg), resulting in memory loss, or with dexamethasone (DEX; 5 mg/kg intraperitoneal) pretreatment, which abolished the long-term LPS-induced memory impairment. After LPS treatment, a significant elevation in the expression of immunity/inflammatory-linked genes, including chemokines (Cxcl13), cytokines (Il1b and Tnfsf13b), and major histocompatibility complex (MHC) class II members (Cd74, RT1-Ba, RT1-Bb, RT1-Da, and RT1-Db1) was observed. DEX pretreatment did not change the expression of these genes, but significantly affected the expression of genes encoding ion channels, primarily calcium and potassium channels, regulators of glutamate (Slc1a2, Grm5, Grin2a), and GABA (Gabrr2, Gabrb2) neurotransmission, which enriched in such GO biological processes as "Regulation of transmembrane transport", "Cognition", "Learning", "Neurogenesis", and "Nervous system development". Taken together, these data suggest that (1) pretreatment with DEX did not markedly affect LPS-induced prolonged inflammatory response; (2) DEX pretreatment can affect processes associated with glutamatergic signaling and nervous system development, possibly involved in the recovery of memory impairment induced by LPS.

Study on the Mechanism of Jiaotai Pill Intervention on Insomnia Animal Model Based on Gut Microbiome and Metabolomics

Background

With the continuous advancement of clinical application and experimental research of JTP, the application prospect of JTP in nervous system diseases and metabolic diseases is becoming increasingly clear. Jiaotai Pill (JTP) is a traditional Chinese medicine formula for insomnia, consisting of Coptidis rhizoma and Cinnamomi cortex, which dates back to Han Shi Yi Tong in the Ming Dynasty of China.

Objective

Based on the brain-gut axis theory, this paper aims to explore the potential mechanism of JTP in the intervention of insomnia by using intestinal microbiome and metabolomics technology, taking the animal model of insomnia as the research object, so as to provide experimental basis for its further application and research.

Methods

The insomnia mouse model was induced by intraperitoneal injection of para-chlorophenylalanine (PCPA). The clinical equivalent dose of JTP was administered by gavage for one week. The efficacy of JTP was evaluated by behavioral tests, serum biochemical detection, and brain histomorphological observation. The contents of cecum were analyzed by microbiomics and metabolomics.

Results

The results show that insomnia caused by PCPA led to daytime dysfunction, higher HPA axis hormone levels, and morphologically impaired hippocampus. JTP reversed these anomalies. Omics research indicates that JTP significantly reduced gut α diversity; at the phylum level, JTP reduced the relative abundance of Firmicutes, Deferribacterota, Cyanobacteria, and Actinobacteriota and increased the relative abundance of Verrucomicrobiota, Proteobacteria, and Desulfobacterota. At the genus level, JTP reduced the relative abundance of Muribaculaceae, Lachnospiraceae_NK4A136_group, Alistipes, Colidextribacter, Muribaculum, and Mucispirillum and increased the relative abundance of Bacteroides and Akkermansia. JTP also reversed the activation of the linoleic acid metabolism pathway induced by insomnia. The combined analysis of omics suggests that JTP may play a role by regulating the inflammatory state of the body. Further gene expression analysis of brain tissue confirmed this.

Conclusions

We hypothesize that JTP may achieve insomnia relief by eliminating inflammation-causing bacteria in the gut and reducing inflammation levels through the brain-gut axis, pointing to potential targets and pathways for future research on JTP.

Conditioned place avoidance is associated with a distinct hippocampal phenotype, partly preserved pattern separation, and reduced reactive oxygen species production after stress

Stress is associated with contextual memory deficits, which may mediate avoidance of trauma-associated contexts in posttraumatic stress disorder. These deficits may emerge from impaired pattern separation, the independent representation of similar experiences by the dentate gyrus-Cornu Ammonis 3 (DG-CA3) circuit of the dorsal hippocampus, which allows for appropriate behavioral responses to specific environmental stimuli. Neurogenesis in the DG is controlled by mitochondrial reactive oxygen species (ROS) production, and may contribute to pattern separation. In Experiment 1, we performed RNA sequencing of the dorsal hippocampus 16 days after stress in rats that either develop conditioned place avoidance to a predator urine-associated context (Avoiders), or do not (Non-Avoiders). Weighted genome correlational network analysis showed that increased expression of oxidative phosphorylation-associated gene transcripts and decreased expression of gene transcripts for axon guidance and insulin signaling were associated with avoidance behavior. Based on these data, in Experiment 2, we hypothesized that Avoiders would exhibit elevated hippocampal (HPC) ROS production and degraded object pattern separation (OPS) compared with Nonavoiders. Stress impaired pattern separation performance in Non-Avoider and Avoider rats compared with nonstressed Controls, but surprisingly, Avoiders exhibited partly preserved pattern separation performance and significantly lower ROS production compared with Non-Avoiders. Lower ROS production was associated with better OPS performance in Stressed rats, but ROS production was not associated with OPS performance in Controls. These results suggest a strong negative association between HPC ROS production and pattern separation after stress, and that stress effects on these outcome variables may be associated with avoidance of a stress-paired context.

Effects of sex and pro-inflammatory cytokines on context discrimination memory

In learning and memory tasks, immune overactivation is associated with impaired performance, while normal immune activation is associated with optimal performance. In one specific domain of memory, context discrimination memory, peripheral immune stimulation has been shown to impair performance on the context-object discrimination memory task in male rats. In order to evaluate potential sex differences in this task, as well as potential mechanisms for the memory impairment, we evaluated the ability of peripheral immune stimulation to impair task performance in both males and females. Next, we examined whether treatment with interleukin-1 receptor antagonist (IL-1ra), a receptor antagonist for the pro-inflammatory cytokine interleukin (IL)-1β, was able to rescue the memory deficit. We examined microglial morphology in the hippocampus and cytokine mRNA and protein expression in the hippocampus and the periphery. Male rats displayed memory impairment in response to LPS, and this impairment was not rescued by IL-1ra. Female rats did not have significant memory impairments and IL-1ra administration improved memory following inflammation. A subset of cytokines and chemokines were increased only in LPS-treated males. Inflammation alone did not alter microglia morphology, but IL-1ra did in certain sub-regions of the hippocampus. Together, these results indicate that sex differences exist in the ability of a peripheral immune stimulus to influence context discrimination memory and specific cytokine signals may be altered in impaired males. This study highlights the importance of sex differences in response to inflammatory challenges, especially related to memory impairments in context discrimination memory.

HMGB1 mediates synaptic loss and cognitive impairment in an animal model of sepsis-associated encephalopathy

BACKGROUND

Microglial activation-mediated neuroinflammation is one of the essential pathogenic mechanisms of sepsis-associated encephalopathy (SAE). Mounting evidence suggests that high mobility group box-1 protein (HMGB1) plays a pivotal role in neuroinflammation and SAE, yet the mechanism by which HMGB1 induces cognitive impairment in SAE remains unclear. Therefore, this study aimed to investigate the mechanism of HMGB1 underlying cognitive impairment in SAE.

METHODS

An SAE model was established by cecal ligation and puncture (CLP); animals in the sham group underwent cecum exposure alone without ligation and perforation. Mice in the inflachromene (ICM) group were continuously injected with ICM intraperitoneally at a daily dose of 10 mg/kg for 9 days starting 1 h before the CLP operation. The open field, novel object recognition, and Y maze tests were performed on days 14-18 after surgery to assess locomotor activity and cognitive function. HMGB1 secretion, the state of microglia, and neuronal activity were measured by immunofluorescence. Golgi staining was performed to detect changes in neuronal morphology and dendritic spine density. In vitro electrophysiology was performed to detect changes in long-term potentiation (LTP) in the CA1 of the hippocampus. In vivo electrophysiology was performed to detect the changes in neural oscillation of the hippocampus.

RESULTS

CLP-induced cognitive impairment was accompanied by increased HMGB1 secretion and microglial activation. The phagocytic capacity of microglia was enhanced, resulting in aberrant pruning of excitatory synapses in the hippocampus. The loss of excitatory synapses reduced neuronal activity, impaired LTP, and decreased theta oscillation in the hippocampus. Inhibiting HMGB1 secretion by ICM treatment reversed these changes.

CONCLUSIONS

HMGB1 induces microglial activation, aberrant synaptic pruning, and neuron dysfunction in an animal model of SAE, leading to cognitive impairment. These results suggest that HMGB1 might be a target for SAE treatment.

Paeoniflorin Attenuates Lipopolysaccharide-Induced Cognitive Dysfunction by Inhibition of Amyloidogenesis in Mice

Alzheimer's disease (AD) is a neurodegenerative disease, associated with progressive cognitive impairment and memory loss. In the present study, we examined the protective effects of paeoniflorin against memory loss and cognitive decline in lipopolysaccharide (LPS)-induced mice. Treatment with paeoniflorin alleviated LPS-induced neurobehavioral dysfunction, as confirmed by behavioral tests, including the T-maze test, novel-object recognition test, and Morris water maze test. LPS stimulated the amyloidogenic pathway-related proteins (amyloid precursor protein, APP; β-site APP cleavage enzyme, BACE; presenilin1, PS1; presenilin2, PS2) expression in the brain. However, paeoniflorin decreased APP, BACE, PS1, and PS2 protein levels. Therefore, paeoniflorin reverses LPS-induced cognitive impairment via inhibition of the amyloidogenic pathway in mice, which suggests that paeoniflorin may be useful in the prevention of neuroinflammation related to AD.

Interactions of alcohol and combination antiretroviral (cART) drug in diabetic male Sprague Dawley rats: Hippocampal perturbations and toxicosis

Hippocampal pathology in diabetes is constantly investigated but the resultant health impact of the concomitant presence of alcohol and combined antiretroviral therapy (cART) in diabetes requires further studies to delineate toxicities inimical to hippocampal normal function. Forty-eight male Sprague Dawley rats were divided into eight groups (n = 6): negative control (NC), alcohol (AL), cART (AV), alcohol-cART (AA), diabetic control (DB), diabetes-alcohol (DAL), diabetes-cART (DAV), and diabetes-alcohol-cART (DAA) exposure groups. Following diabetes induction and sub-chronic (90 days) treatment exposure, hippocampal homogenates were profiled for pro-inflammatory cytokines and oxidative stress (MDA and GPx) using immunoassay, while apoptotic genes (BAX, Bcl₂, and Caspase-3), insulin receptor genes (INSR and IRS-1), and blood-brain barrier (BBB) junctional proteins (claudin-5, and occludin) gene expression were assessed using qPCR. Histomorphology of hippocampal neuronal number, nuclei area, and volume of dentate gyrus and neurogenesis were accessed using Giemsa stain, Ki67, and DCX histochemistry respectively. A central hippocampal effect that underpins all treatments is the reduction of DG neuronal number and antioxidant (GPx), highlighting the venerability of the hippocampal dentate gyrus neurons to diabetes, alcohol, cART, and their combinatorial interactions. Additionally, elevated BAX, Bcl_2, and IRS1 mRNA levels in the DAL group, and their downregulation in AA, suggests IRS-1-regulated apoptosis due to differential modulating effects of alcohol treatment in diabetes (DAL) in contrast to alcohol with cART (AA). Although the interaction in AA therapy ameliorated the independent alcohol and cART effects on MDA levels, pro-inflammatory cytokines, and DCX, the interaction in AA exacerbated a deficiency in the expression of INSR, IRS-1 (insulin sensitivity), and BBB mRNA which are implicated in the pathogenies of diabetes. Furthermore, the diabetic comorbidity groups (DAV, DAL, and DAA) all share a central effect of elevated hippocampal oxidative stress, BAX, and Caspase-3 mRNA expression with the reduced number of hippocampal neurons, dentate gyrus volume, and neurogenesis, highlighting neurodegenerative and cognitive deficiency implication of these comorbidity treatments. Considering these findings, assessment of hippocampal well-being in patients with these comorbidities/treatment combinations is invaluable and caution is advised particularly in alcohol use with cART prophylaxis in diabetes.

Anti-Inflammatory Activity of Panduratin A against LPS-Induced Microglial Activation

Uncontrolled and excessive microglial activation is known to contribute to inflammation-mediated neurodegeneration. Therefore, reducing neurotoxic microglial activation may serve as a new approach to preventing neurodegeneration. Here, we investigated the anti-inflammatory effects of panduratin A against microglial activation induced by lipopolysaccharides (LPS) in the SIMA9 microglial cell line. We initially examined the anti-inflammatory properties of panduratin A by measuring LPS-induced nitric oxide (NO) production and the levels of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6). Panduratin A significantly reduced NO levels and pro-inflammatory cytokines’ production and secretion. In addition, panduratin A enhanced the production of anti-inflammatory cytokines IL-4 and IL-10. The anti-inflammatory effects of panduratin A are related to the suppression of the NF-κB signaling pathway. Together, these results demonstrate the anti-inflammatory properties of panduratin A against LPS-induced microglial activation, suggesting panduratin A has the potential to be further developed as a new agent for the prevention of neuroinflammation-associated neurodegenerative diseases.

Periodontal microorganisms and Alzheimer disease - A causative relationship?

In the initiation or exacerbation of Alzheimer disease, the dissemination of oral microorganisms into the brain tissue or the low‐level systemic inflammation have been speculated to play a role. However, the impact of oral microorganisms, such as Porphyromonas gingivalis, on the pathogenesis of Alzheimer disease and the potential causative relationship is still unclear. The present review has critically reviewed the literature by examining the following aspects: (a) the oral microbiome and the immune response in the elderly population, (b) human studies on the association between periodontal and gut microorganisms and Alzheimer disease, (c) animal and in vitro studies on microorganisms and Alzheimer disease, and (d) preventive and therapeutic approaches. Factors contributing to microbial dysbiosis seem to be aging, local inflammation, systemic diseases, wearing of dentures, living in nursing homes and no access to adequate oral hygiene measures. Porphyromonas gingivalis was detectable in post‐mortem brain samples. Microbiome analyses of saliva samples or oral biofilms showed a decreased microbial diversity and a different composition in Alzheimer disease compared to cognitively healthy subjects. Many in‐vitro and animal studies underline the potential of P gingivalis to induce Alzheimer disease‐related alterations. In animal models, recurring applications of P gingivalis or its components increased pro‐inflammatory mediators and β‐amyloid in the brain and deteriorated the animals' cognitive performance. Since periodontitis is the result of a disturbed microbial homoeostasis, an effect of periodontal therapy on the oral microbiome and host response related to cognitive parameters may be suggested and should be elucidated in further clinical trials.

Neuroprotective and memory enhancing effects of Zataria multiflora in lipopolysaccharide-treated rats

The study was aimed to evaluate the effects of hydro-ethanol extract Zataria multiflora on the brain tissue oxidative damage, and hippocampal interleukin-6 (IL-6) as well as learning and memory capacity in lipopolysaccharide (LPS) - challenged rats. The rats were randomized into five groups as follow: Control group: Rats were treated with saline, LPS group: Rats were treated with LPS 1.00 mg kg-1, ZM50, ZM100 and ZM200 groups in which the rats were treated with Z. multiflora extract (50.00, 100 or 200 mg kg-1 per day, respectively). The treatments including extract or vehicle were administered intraperitoneally ‎and given three days before the behavioral tests and were continued within a6-day behavioral experiment. Injection of LPS was daily done before the behavioral tests. Finally, the brains were collected for biochemical evaluations. Although LPS administration prolonged the latency in Morris water maze and shortened the latency to enter the dark chamber in passive avoidance test, ZM extract restored these changes to approach control group values. Also, LPS increased IL-6, malondialdehyde (MDA) and nitric oxide (NO) metabolites levels and lowered thiol, superoxide dismutase (SOD) and catalase (CAT) levels in the brain, however, Z. multiflora extract reduced IL-6, MDA and NO metabolites concentrations, but increased thiol content, SOD, and CAT levels. The results of this study showed that Z. multiflora ameliorated learning and memory dysfunction in LPS - challenged rats by alleviating of inflammatory responses and brain tissue oxidative damage.

Exercise to spot the differences: a framework for the effect of exercise on hippocampal pattern separation in humans

Exercise has a beneficial effect on mental health and cognitive functioning, but the exact underlying mechanisms remain largely unknown. In this review, we focus on the effect of exercise on hippocampal pattern separation, which is a key component of episodic memory. Research has associated exercise with improvements in pattern separation. We propose an integrated framework mechanistically explaining this relationship. The framework is divided into three pathways, describing the pro-neuroplastic, anti-inflammatory and hormonal effects of exercise. The pathways are heavily intertwined and may result in functional and structural changes in the hippocampus. These changes can ultimately affect pattern separation through direct and indirect connections. The proposed framework might guide future research on the effect of exercise on pattern separation in the hippocampus.

Resistance-exercise training attenuates LPS-induced astrocyte remodeling and neuroinflammatory cytokine expression in female Wistar rats

Neuroinflammation is an early detectable marker of mild cognitive impairment, the transition state between normal cognition and dementia. Resistance-exercise training can attenuate the cognitive decline observed in patients with mild cognitive impairment. However, the underlying mechanisms of resistance training effects are largely unknown. To further elucidate mechanisms of the known cognitive health benefits from resistance-exercise training, we tested if three weeks of resistance-exercise training could ameliorate lipopolysaccharide-induced neuroinflammation. Five-week-old female Wistar rats received intracerebroventricular injections of lipopolysaccharides to induce neuroinflammation and cognitive impairment. Rats then underwent three weeks of progressive ladder climbing to recapitulate resistance-exercise training in humans. Cognition was assessed towards the end of the training period by novelty object recognition testing. Neuroinflammation was measured one and 24-hours after the last resistance-exercise training workout. Resistance-exercise training ameliorated cognitive impairment, diminished lipopolysaccharide-induced neuroinflammatory cytokine expression, and attenuated astrocyte remodeling in the dentate gyrus 24-hours post exercise. Here, we provide evidence that the ladder-climbing model of resistance-exercise training in rats can improve cognition as early as three weeks. Additionally, these data support the hypothesis that resistance exercise can reduce lipopolysaccharide-induced neuroinflammation in the dentate gyrus.

Involvement of striatal oxido-inflammatory, nitrosative and decreased cholinergic activity in neurobehavioral alteration in adult rat model with oral co-exposure to erythrosine and tartrazine

Overuse or overconsumption of food additive or colorant cannot be ignored in our society and there are several reports of it harmful effect on the body system. This study investigated the toxicity effect of tartrazine and erythrosine (ET, 50:50) on neurobehavioral alteration, striatal oxido-nitrosative and pro-inflammatory stress and striatal acetylcholinesterase activity in experimental rat model. Rats were co-exposed to ET (2 mg/kg, 6 mg/kg and 10 mg/kg) and distilled water (control), p.o for 6 weeks. The change in neurobehavioral function (Open field test, Forced swimming test and Tail suspension test), Lipid peroxidation (Malonaldehyde, MDA), Antioxidants (Glutathione, GSH; Catalase, CAT) Nitrite, Pro-inflammatory cytokine (Tumor necrosis factor-alpha, TNF-α) and Acetylcholinesterase (AChE) activity were evaluated. Results showed significant decrease in neurobehavioral functions after co-exposure to ET. Moreover, there were significant increase in MDA and Nitrite level, significant decrease in the concentration of GSH and CAT and a significant increase TNF-α concentration and AChE activity after co-exposure to ET. Oral co-exposure to tartrazine and erythrosine induced decrease in locomotion and exploration, increase anxiety and depression-like behavior and altered the cholinergic system through upregulation of oxido-nitrosative stress, pro-inflammatory cytokine and acetylcholinesterase activity.

Acute neuroinflammation increases excitability of prefrontal parvalbumin interneurons and their functional recruitment during novel object recognition

There is an emerging body of literature suggesting that unlike the chronic neuroinflammatory response, acute neuroinflammation is self-regulated and is beneficial for central nervous system homeostasis and cognitive integrity. However, the neurophysiological alterations upon acute neuroinflammation and their implications on cognitive function remain poorly understood. In the present study, we reliably established a mouse model of acute and self-limiting neuroinflammation by administering a single intraperitoneal injection of low-dose lipopolysaccharide, which induced reversible sickness behavior and increased pro-inflammatory cytokine expression in the medial prefrontal cortex (mPFC). During acute neuroinflammation, fast-spiking parvalbumin-expressing interneurons (PV interneurons) in the mPFC exhibited a hyperexcitable phenotype exemplified by increased input resistance, decreased rheobase current, and a higher frequency of action potentials. Furthermore, PV interneurons in the prelimbic subregion of the mPFC were excessively recruited into circuits supporting novel object recognition memory, which remained intact after acute neuroinflammation. Together, our findings suggest that alterations in PV neuronal excitability resulting from acute neuroinflammation may mediate neuronal recruitment and confer a beneficial outcome on functional integrity of NOR circuit in the mPFC.

Adult hippocampal neurogenesis in the context of lipopolysaccharide-induced neuroinflammation: A molecular, cellular and behavioral review

The continuous generation of new neurons occurs in at least two well-defined niches in the adult rodent brain. One of these areas is the subgranular zone of the dentate gyrus (DG) in the hippocampus. While the DG is associated with contextual and spatial learning and memory, hippocampal neurogenesis is necessary for pattern separation. Hippocampal neurogenesis begins with the activation of neural stem cells and culminates with the maturation and functional integration of a portion of the newly generated glutamatergic neurons into the hippocampal circuits. The neurogenic process is continuously modulated by intrinsic factors, one of which is neuroinflammation. The administration of lipopolysaccharide (LPS) has been widely used as a model of neuroinflammation and has yielded a body of evidence for unveiling the detrimental impact of inflammation upon the neurogenic process. This work aims to provide a comprehensive overview of the current knowledge on the effects of the systemic and central administration of LPS upon the different stages of neurogenesis and discuss their effects at the molecular, cellular, and behavioral levels.

Ginsenoside Re exhibits neuroprotective effects by inhibiting neuroinflammation via CAMK/MAPK/NF‑κB signaling in microglia

Ginsenoside Re (G-Re) is a panaxatriol saponin and one of the pharmacologically active natural constituents of ginseng (Panax ginseng C.A. Meyer). G-Re has antioxidant, anti-inflammatory and antidiabetic effects. The present study aimed to investigate the effects of G-Re on neuroinflammatory responses in lipopolysaccharide (LPS)-stimulated microglia and its protective effects on hippocampal neurons. Cytokine levels were measured using ELISA and reactive oxygen species (ROS) levels were assessed using flow cytometry and fluorescence microscopy. Protein levels of inflammatory molecules and kinase activity were assessed by western blotting. Cell viability was assessed by MTT assay; apoptosis was estimated by Annexin V apoptosis assay. The results revealed that G-Re significantly inhibited the production of IL-6, TNF-α, nitric oxide (NO) and ROS in BV2 microglial cells, and that of NO in mouse primary microglia, without affecting cell viability. G-Re also inhibited the nuclear translocation of NF-κB, and phosphorylation and degradation of IκB-α. In addition, G-Re dose-dependently suppressed LPS-mediated phosphorylation of Ca²⁺/calmodulin-dependent protein kinase (CAMK)2, CAMK4, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinases (JNK). Moreover, the conditioned medium from LPS-stimulated microglial cells induced HT22 hippocampal neuronal cell death, whereas that from microglial cells incubated with both LPS and G-Re ameliorated HT22 cell death in a dose-dependent manner. These results suggested that G-Re suppressed the production of pro-inflammatory mediators by blocking CAMK/ERK/JNK/NF-κB signaling in microglial cells and protected hippocampal cells by reducing these inflammatory and neurotoxic factors released from microglial cells. The present findings indicated that G-Re may be a potential treatment option for neuroinflammatory disorders and could have therapeutic potential for various neurodegenerative diseases.

The effects of early-life immune activation on microglia-mediated neuronal remodeling and the associated ontogeny of hippocampal-dependent learning in juvenile rats

Many neurodevelopmental disorders and associated learning deficits have been linked to early-life immune activation or ongoing immune dysregulation (Laskaris et al., 2016; O'Connor et al., 2014; Frick et al., 2013). Neuroscientists have begun to understand how the maturation of neural circuits allows for the emergence of cognitive and learning behaviors; yet we know very little about how these developing neural circuits are perturbed by certain events, including risk-factors such as early-life immune activation and immune dysregulation. To answer these questions, we examined the impact of early-life immune activation on the emergence of hippocampal-dependent learning in juvenile male and female rats using a well-characterized hippocampal-dependent learning task and we investigated the corresponding, dynamic multicellular interactions in the hippocampus that may contribute to these learning deficits. We found that even low levels of immune activation can result in hippocampal-depedent learning deficits days later, but only when this activation occurs during a sensitive period of development. The initial immune response and associated cytokine production in the hippocampus resolved within 24 h, several days prior to the observed learning deficit, but notably the initial immune response was followed by altered microglial-neuronal communication and synapse remodeling that changed the structure of hippocampal neurons during this period of juvenile brain development. We conclude that immune activation or dysregulation during a sensitive period of hippocampal development can precipitate the emergence of learning deficits via a multi-cellular process that may be initiated by, but not the direct result of the initial cytokine response. SIGNIFICANCE STATEMENT: Many neurodevelopmental disorders have been linked to early-life immune activation or immune dysregulation; however, very little is known about how dynamic changes in neuroimmune cells mediate the transition from normal brain function to the early stages of cognitive disorders, or how changes in immune signaling are subsequently integrated into developing neuronal networks. The current experiments examined the consequences of immune activation on the cellular and molecular changes that accompany the emergence of learning deficits during a sensitive period of hippocampal development. These findings have the potential to significantly advance our understanding of how early-life immune activation or dysregulation can result in the emergence of cognitive and learning deficits that are the largest source of years lived with disability in humans.

Neuroprotective effects of Levisticum officinale on LPS-induced spatial learning and memory impairments through neurotrophic, anti-inflammatory, and antioxidant properties

Levisticum officinale (Apiaceae) has been identified as a medicinal plant in traditional medicine, with the anti-inflammatory, antioxidant, and anticholinesterase activities. The present study aims to evaluate the effects of Levisticum officinale extract (LOE) on lipopolysaccharide (LPS)-induced learning and memory deficits and to examine its potential mechanisms. LOE was administered to adult male Wistar rats at doses of 100, 200, and 400 mg kg-1 for a week. Later, LPS was intraperitoneally injected at a dose of 1 mg kg-1 to induce neuroinflammation, and treatment with LOE continued for 3 more weeks. Behavioral, biochemical, and molecular analyses were performed at the end of the experiment. Moreover, quantitative immunohistochemical assessments of the expression of Ki-67 (intracellular proliferation marker) in the hippocampus were performed. The results revealed that LPS injection caused spatial memory impairment in the rats. Daily LOE treatment at applied doses for 4 weeks attenuated spatial learning and memory deficits in LPS-injected rats. Furthermore, LPS significantly increased the mRNA expression level of interleukin-6 in the hippocampus, which was accompanied by decreased brain-derived neurotrophic factor (BDNF) mRNA expression levels. Moreover, LPS increased the levels of malondialdehyde, reduced the antioxidant enzyme activities of catalase and superoxide dismutase in the hippocampus, and impaired neurogenesis. However, pre-treatment with LOE at a dose of 100 mg kg-1 significantly reversed the LPS-induced changes, and improved neurogenesis. In conclusion, the beneficial effect of LOE on the improvement of learning and memory could be attributed to its anti-inflammatory and antioxidant activities, along with its ability to increase BDNF expression and neurogenesis in the hippocampus.

Altered acoustic startle, prepulse facilitation, and object recognition memory produced by corticosterone withdrawal in male rats

The symptoms of human depression often include cognitive deficits. However, cognition is not frequently included in the behavioral assessments conducted in preclinical models of depression. For example, it is well known that repeated corticosterone (CORT) injections in rodents produce depression-like behavior as measured by the forced swim test, sucrose preference test, and tail suspension test, but the cognitive impairments produced by repeated CORT have not been thoroughly examined. The purpose of this experiment was to assess the effect of repeated CORT injections on several versions of object recognition memory and modulation of the acoustic startle response by relatively low intensity prepulses, along with the more traditional assessment of depression-like behavior using the forced swim test. Rats received 21 days of CORT (40 mg/kg) or vehicle injections followed by a battery of behavioral tests. Importantly, during behavioral testing CORT treatment did not occur (CORT withdrawal). Corticosterone decreased body weight, increased immobility in the forced swim test, lowered startle amplitudes, and facilitated responding to trials with a short interval (30 ms) between the prepulse and pulse. Corticosterone also impaired both object location and object-in-place recognition memory, while sparing performance on object recognition memory. Collectively, our data suggest that CORT produces selective disruptions in prepulse facilitation, object location, and object-in-place recognition memory, and that these impairments should be considered as part of the phenotype produced by repeated CORT, and perhaps chronic stress.

Cognitive complications of cancer and cancer-related treatments - Novel paradigms

As advances in diagnostics and therapeutic strategies in oncology have increased the number of cancer survivors, the investigation of the mechanisms associated with long-term cognitive complications of cancer treatment has become an important topic of interest. The neurotoxic effects of chemotherapeutic agents have been described in pre-clinical and clinical research. In vitro and rodent studies have identified some underlying mechanisms contributing to chemotherapy-induced neurotoxicity and cognitive impairment for various chemotherapy drugs and other cancer treatments. However, investigation of the direct biological effects of cancer and other potential contributing factors in the pathogenesis of cancer-related cognitive impairment (CRCI) has only recently come into focus. This review will highlight evidence from pre-clinical tumor-bearing rodent models suggesting that cancer influences the cognitive and behavioral changes reported in human cancer populations through direct or indirect pathways that alter the normal neuroinflammatory responses, induce structural brain deficits, and decrease neurogenesis. We reflect on human clinical cancer research indicating that cognitive and behavioral changes precede cancer treatment in some malignancies. We also highlight implications for future areas of CRCI research based on novel findings on the interplay between cancer, chemotherapy, inflammation, tau pathology, and dysregulation of the microbiota-gut-brain axis.

Partial microglial depletion is associated with impaired hippocampal synaptic and cognitive function in young and aged rats

The role of microglia in mediating age-related changes in cognition and hippocampal synaptic function was examined by microglial depletion and replenishment using PLX3397. We observed age-related differences in microglial number and morphology, as well as increased Iba-1 expression, indicating microglial activation. PLX3397 treatment decreased microglial number, with aged rats exhibiting the lowest density. Young rats exhibited increased expression of pro-inflammatory cytokines during depletion and repopulation and maintenance of Iba-1 levels despite reduced microglial number. For aged rats, several cytokines increased with depletion and recovered during repopulation; however, aged rats did not fully recover microglial cell number or Iba-1 expression during repopulation, with a recovery comparable to young control levels rather than aged controls. Hippocampal CA3-CA1 synaptic transmission was impaired with age, and microglial depletion was associated with decreased total synaptic transmission in young and aged rats. A robust decline in N-methyl-d-aspartate-receptor-mediated synaptic transmission arose in young depleted rats specifically. Microglial replenishment normalized depletion-induced synaptic function to control levels; however, recovery of aged animals did not mirror young. Microglial depletion was associated with decreased context-object discrimination memory in both age groups, which recovered with microglial repopulation. Aged rats displayed impaired contextual and cued fear memory, and microglial replenishment did not recover their memory to the level of young. The current study indicates that cognitive function and synaptic transmission benefit from the support of aged microglia and are hindered by removal of these cells. Replenishment of microglia in aging did not ameliorate age-related cognitive impairments or senescent synaptic function.

Irradiation of the head reduces adult hippocampal neurogenesis and impairs spatial memory, but leaves overall health intact in rats

Treatment of brain cancer, glioma, can cause cognitive impairment as a side-effect, possibly because it disrupts the integrity of the hippocampus, a structure vital for normal memory. Radiotherapy is commonly used to treat glioma, but the effects of irradiation on the brain are still poorly understood, and other biological effects have not been extensively studied. Here, we exposed healthy adult male rats to moderate-dose irradiation of the head. We found no effect of irradiation on systemic inflammation, weight gain or gut microbiota diversity, although it increased the abundance of Bacteroidaceae family, namely Bacteroides genus in the gut microbiota. Irradiation had no effect on long-term potentiation in the CA3-CA1 synapse or endogenous hippocampal electrophysiology, but it did reduce adult hippocampal neurogenesis and impaired short-term spatial recognition memory. However, no overall cognitive impairment was observed. To summarize, our results suggest that in adult male rats head irradiation does not compromise health or cognition overall even though the number of new, adult-born hippocampal neurons is decreased. Thus, the sole effects of head irradiation on the body, brain and cognition might be less harmful than previously thought, and the cognitive decline experienced by cancer patients might originate from physiological and mental effects of the disease itself. Therefore, to increase the translational value of animal studies, the effects of irradiation should be studied together with cancer, in older animals, using varying irradiation protocols and doses.

Reversal of lipopolysaccharide-induced learning and memory deficits by agmatine in mice

MATERIALS AND METHODS

Learning and memory functions in animals were evaluated by using Novel object recognition (NOR) and Morris water maze (MWM) tests. Following 7 days of LPS administration, animals were subjected to NOR test on Day-8 and MWM test on Days-9 to 13 for the assessment of recognition and spatial learning and memory, respectively.

RESULTS

LPS administration produced significant deficits in recognition and spatial memory in mice after seven days of LPS administration. In LPS pre-treated mice, agmatine treatment on Day-8 resulted in the increased exploration to the novel object. Agmatine treatment (Day 8-12) in mice showed reduction in the escape latency and time spent in the target quadrant (probe trial) in the MWM test. However, co-administration of agmatine with LPS in mice for 7 days showed higher discrimination index in NOR test on Day-8. This co-administration also decreased escape latency and time spent in the target quadrant in MWM test on Days 9-13 as compared to LPS control group.

CONCLUSION

Results implies the protective and curative effects of agmatine against LPS-induced loss of memory functions in experimental animals.HighlightsSubchronic but not acute lipopolysaccharides induce memory deficitsLipopolysaccharides impairs recognition and spatial memory in mice.Agmatine prevents lipopolysaccharides-induced loss of memory.Agmatine reverses deficits in learning and memory by lipopolysaccharides.

Chronic Neuroinflammation Induced by Lipopolysaccharide Injection into the Third Ventricle Induces Behavioral Changes

The existence of Gram-negative bacteria in the brain, regardless of underlying immune status has been demonstrated by recent studies. The colocalization of lipopolysaccharide (LPS) with Aβ_1-40/42 in amyloid plaques supports the hypothesis that brain microbes may be the cause, triggering chronic neuroinflammation, leading to Alzheimer's disease (AD). To investigate the behavioral changes induced by infectious neuroinflammation, we chose the third ventricle as the site of a single LPS injection (20 μg or 80 μg) in male Wistar rats to avoid mechanical injury to forebrain structures while inducing widespread inflammation throughout the brain. Chronic neuroinflammation induced by LPS resulted in depressive-like behaviors and the impairment of spatial learning; however, there was no evidence of the development of pathological hallmarks (e.g., the phosphorylation of tau) for 10 months following LPS injection. The acceleration of cholesterol metabolism via CYP46A1 and the retardation of cholesterol synthesis via HMGCR were observed in the hippocampus of rats treated with either low-dose or high-dose LPS. The rate-limiting enzymes of cholesterol metabolism (CYP46A1) in SH-SY5Y cells and synthesis (HMGCR) in U251 cells were altered by inflammation stimulators, including LPS, IL-1β, and TNF-α, through the TLR4/MyD88/NF-κB signaling pathway. The data suggest that chronic neuroinflammation provoked by the administration of LPS into the third ventricle may induce depressive-like symptoms and that the loss of cholesterol might be a biomarker of chronic neuroinflammation. The lack of pathological hallmarks of AD in our model indicates that Gram-negative bacteria infection might not be a single cause of AD.

The effects of pre-treatment with olibanum and its constituent, boswellic acid on synaptic plasticity impairments induced by lipopolysaccharide in rats

OBJECTIVE

Olibanum (OLIB) and its component boswellic acid (BOSA) are suggested to have anti-inflammatory, anti-oxidant and neuroprotective effects. In the present work, we examined effect of OLIB, and BOSA on the synaptic plasticity impairment and oxidative stress indicators in a rat model of neuro-inflammation induced by lipopolysaccharide (LPS).

MATERIALS AND METHODS

Forty rats were divided into the following four groups: (1) Control, (2) LPS, (3) OLIB (200 mg/kg), and (4) BOSA (10 mg/kg). The animals were pre-treated with OLIB extract, BOSA or the vehicle 30 min before LPS (1 mg/kg) administration, for 6 days. On the 6^th day, electrophysiological recording was done. Long-term potentiation (LTP) from CA1 area of hippocampus was assessed. The animals were then sacrificed and their brains were removed for evaluation of the levels of interleukin-6 (IL-6), nitric oxide (NO) metabolites, malondialdehyde (MDA), thiol, superoxide dismutase (SOD) and catalase (CAT) in the cortex.

RESULTS

Administration of LPS decreased amplitude (p<0.001) and slope (p<0.01) of field excitatory postsynaptic potential (fEPSP). Pre-treatment enhanced these parameters (p<0.05 to p<0.001). LPS also increased cortical levels of IL-6 (P<0.01), NO, and MDA (p<0.001) while decreased thiol, SOD (p<0.001), and CAT (p<0.05). OLIB and BOSA diminished IL-6 (p<0.05-p<0.001), NO (p<0.01-p<0.001) and MDA level (p<0.01 and p<0.001, respectively) while improved SOD (p<0.05 and p<0.001, respectively), CAT (p<0.05 and p<0.001, respectively) and thiol content (p<0.001).

CONCLUSION

The results showed that OLIB and BOSA could improve synaptic plasticity impairment induced by LPS as shown by a decrease in an inflammation indicator along with the anti-oxidant effects.

Effects of crocin on spatial or aversive learning and memory impairments induced by lipopolysaccharide in rats

OBJECTIVE

Neuroinflammation and oxidative stress play essential roles in the pathogenesis and progression of neurodegenerative diseases, such as Alzheimer's disease. Crocin, main active constituent of Crocus sativus L. (saffron), possesses anti-inflammatory, anti-apoptotic and anti-oxidative capacity. The aim of the present study was to investigate the neuroprotective effect of crocin on lipopolysaccharide (LPS)-induced learning and memory deficits and neuroinflammation in rats.

MATERIALS AND METHODS

The animals were randomly classified into four groups, including control, LPS, crocin 50 and crocin 100. The rats were treated with either crocin (50 and 100 mg/kg) or saline for a week. Later, LPS (1 mg/kg, i.p.) or saline was administered, and treatments with crocin or saline were continued for 3 more weeks. The behavioral tasks for spatial and aversive memories were performed by the Morris water maze and passive avoidance tasks from post-injection days 18 to 24. Furthermore, the levels of interleukine-1β, lipid peroxidation and total thiol were assayed in the hippocampus and cerebral cortex.

RESULTS

Our results demonstrated that treatment of LPS-treated rats with crocin decreased the escape latency in the Morris water maze and increased the time spent in the target quadrant in the probe trial. Moreover, crocin increased step-through latency in the passive avoidance test. However, there was no significant difference in the oxidative and neuroinflammatory responses among the experimental groups.

CONCLUSION

Pretreatment with crocin attenuates spatial or aversive learning and memory deficits in LPS-treated rats.

Inhibitory effect of carvacrol on lipopolysaccharide-induced memory impairment in rats

Neuroinflammation is an important process underlying a wide variety of neurodegenerative diseases. Carvacrol (CAR) is a phenolic monoterpene commonly used as a food additive due to its antibacterial properties, but it has also been shown to exhibit strong antioxidative, anti-inflammatory, and neuroprotective effects. Here, we sought to investigate the effects of CAR on inflammation in the hippocampus and prefrontal cortex, as well as the molecular mechanisms underlying these effects. In our study, lipopolysaccharide was injected into the lateral ventricle of rats to induce memory impairment and neuroinflammation. Daily administration of CAR (25, 50, and 100 mg/kg) for 21 days improved recognition, discrimination, and memory impairments relative to untreated controls. CAR administration significantly attenuated expression of several inflammatory factors in the brain, including interleukin-1β, tumor necrosis factor-α, and cyclooxygenase-2. In addition, CAR significantly increased expression of brain-derived neurotrophic factor (BDNF) mRNA, and decreased expression of Toll-like receptor 4 (TLR4) mRNA. Taken together, these results show that CAR can improve memory impairment caused by neuroinflammation. This cognitive enhancement is due to the anti-inflammatory effects of CAR medicated by its regulation of BDNF and TLR4. Thus, CAR has significant potential as an inhibitor of memory degeneration in neurodegenerative diseases.

N-Docosahexanoylethanolamine Reduces Microglial Activation and Improves Hippocampal Plasticity in a Murine Model of Neuroinflammation

Chronic neuroinflammation is a common pathogenetic link in the development of various neurological and neurodegenerative diseases. Thus, a detailed study of neuroinflammation and the development of drugs that reduce or eliminate the negative effect of neuroinflammation on cognitive processes are among the top priorities of modern neurobiology. N-docosahexanoylethanolamine (DHEA, synaptamide) is an endogenous metabolite and structural analog of anandamide, an essential endocannabinoid produced from arachidonic acid. Our study aims to elucidate the pharmacological activity of synaptamide in lipopolysaccharide (LPS)-induced neuroinflammation. Memory deficits in animals were determined using behavioral tests. To study the effects of LPS (750 µg/kg/day, 7 days) and synaptamide (10 mg/kg/day, 7 days) on synaptic plasticity, long-term potentiation was examined in the CA1 area of acute hippocampal slices. The Golgi-Cox method allowed us to assess neuronal morphology. The production of inflammatory factors and receptors was assessed using ELISA and immunohistochemistry. During the study, functional, structural, and plastic changes within the hippocampus were identified. We found a beneficial effect of synaptamide on hippocampal synaptic plasticity and morphological characteristics of neurons. Synaptamide treatment recovered hippocampal neurogenesis, suppressed microglial activation, and significantly improved hippocampus-dependent memory. The basis of the phenomena described above is probably the powerful anti-inflammatory activity of synaptamide, as shown in our study and several previous works.

What animal models can tell us about long-term cognitive dysfunction following sepsis: A systematic review

Survivors of sepsis often develop long-term cognitive impairments. This review aimed at exploring the results of the behavioral tools and tests which have been used to evaluate cognitive dysfunction in different animal models of sepsis. Two independent investigators searched for sepsis- and cognition-related keywords. 6323 publications were found, of which 355 were selected based on their title, and 226 of these were chosen based on manuscript review. LPS was used to induce sepsis in 171 studies, while CLP was used in 55 studies. Inhibitory avoidance was the most widely used method for assessing aversive memory, followed by fear conditioning and continuous multi-trial inhibitory avoidance. With regard to non-aversive memory, most studies used the water maze, open-field, object recognition, Y-maze, plus maze, and radial maze tests. Both CLP and LPS models of sepsis were effective in inducing short- and long-term behavioral impairment. Our findings help elucidate the mechanisms involved in the pathophysiology of sepsis-induced cognitive changes, as well as the available methods and tests used to study this in animal models.

Pharmacological inhibition of phosphodiesterase 7 enhances consolidation processes of spatial memory

Augmentation of cAMP signaling through inhibition of phosphodiesterases (PDE) is known to enhance plasticity and memory. Inhibition of PDE4 enhances consolidation into memory, but less is known about the role of other cAMP specific PDEs. Here, we tested the effects of oral treatment with a selective inhibitor of PDE7 of nanomolar potency on spatial and contextual memory. In an object location task, doses of 0.3-3 mg/kg administered 3 h after training dose-dependently attenuated time-dependent forgetting in rats. Significant enhancement of memory occurred at a dose of 3 mg/kg with corresponding brain levels consistent with PDE7 inhibition. The same dose given prior to training augmented contextual fear conditioning. In mice, daily dosing before training enhanced spatial memory in two different incremental learning paradigms in the Barnes Maze. Drug treated mice made significantly less errors locating the escape in a probe-test 24 h after the end of training, and they exhibited hippocampal-dependent spatial search strategies more frequently than controls, which tended to show serial sampling of escape locations. Acquisition and short-term memory, in contrast, were unaffected. Our data provide evidence for a role of PDE7 in the consolidation of hippocampal-dependent memory. We suggest that targeting PDE7 for memory enhancement may provide an alternative to PDE4 inhibitors, which tend to have undesirable gastrointestinal side-effects.

Chrysophyllum albidum (African star apple) fruit-supplemented diet enhances cognitive functions and attenuates lipopolysaccharide-induced memory impairment, oxidative stress, and release of proinflammatory cytokines

Purpose

Fruit-based supplement has an important role in protecting the brain against oxido-inflammatory stress. Chrysophyllum albidum fruit contained several phytonutrients that possess antioxidants and anti-inflammatory properties. Hence, this study investigated the effect of C. albidum fruit supplemented diet (CAFD) on cognitive functions and lipopolysaccharide (LPS)-induced memory impairment and oxido-inflammatory response in mice.

Methods

Mice were randomized into two experiments. Experiment 1 with naïve mice contained four groups (n = 6) while experiment 2 with LPS contains five groups (n = 6). Mice in experiments 1 and 2 were fed on CAFD (5%, 10%, and 20%) in naïve (6 weeks) and LPS (250 μg/kg, i.p.) in the 7th week, respectively. Cognitive performance was tested using Y-maze test (YMT) and novel object recognition test (NORT) in the naïve and LPS mice. Brain samples were obtained for determination of oxido-inflammatory parameters and acetylcholinesterase activity.

Results

The CAFD significantly enhanced cognitive performance in the YMT and NORT in naïve and LPS mice, as evidenced by increased % alternation and discrimination index, respectively. CAFD supplementation significantly reduced acetylcholinesterase enzyme activity while it attenuated depletion of reduced glutathione and catalase activities in brains of naive and LPS-treated animals. The CAFD significantly reduced LPS-induced increased malondialdehyde levels in mice brains. CAFD supplementation significantly attenuated LPS-induced pro-inflammatory cytokines (IL-6, TNF-α) in mice brains.

Conclusion

Chrysophyllum albidum fruit supplementation in diet enhances memory function and prevents cognitive deficits induced by LPS via mechanisms associated with inhibition of oxidative stress-related processes, acetylcholinesterase activity, and pro-inflammatory mediators.

Ellagic Acid Inhibits Neuroinflammation and Cognitive Impairment Induced by Lipopolysaccharides

Neuroinflammation is a predisposing factor for the development of cognitive impairment and dementia. Among the new molecules that are currently being studied, ellagic acid (EA) has stood out for its neuroprotective properties. The present study investigated the effects of ellagic acid in the object recognition test, oxidative stress, cholinergic neurotransmission, glial cell expression, and phosphorylated Tau protein expression. For this, 32 male Wistar rats received an intraperitoneal (IP) application of lipopolysaccharides (LPS) at a dose of 250 µg/kg or 0.9% saline solution (SAL) for 8 days. Two hours after the IP injections, the animals received 100 mg/kg of EA or SAL via intragastric gavage. Behavioral parameters (open field test and object recognition) were performed on days 5, 6, and 7 of the experimental periods. The results showed that the treatment with EA in the LPS group was able to inhibit cognitive impairment, modulate the immune system response by significantly reducing glial cell expression, attenuating phosphorylated Tau and oxidative damage with consequent improvement in the antioxidant system, as well as preventing the increase of acetylcholinesterase activity. Thus, the neuroprotective effects of EA and its therapeutic potential in cognitive disorders secondary to neuroinflammation were demonstrated.

Acute Nicotine Treatment Alleviates LPS-Induced Impairment of Fear Memory Reconsolidation Through AMPK Activation and CRTC1 Upregulation in Hippocampus

BACKGROUND

Fear memory is a fundamental capability for animals and humans to survive. Its impairment results in the disability to avoid danger. When memory is reactivated, a reconsolidation process, which can be disrupted by various stimuli, including inflammation, is required to become permanent. Nicotine has been shown to improve cognitive deficits induced by inflammation and other stimuli. Therefore, in the present study, we investigated the effect of nicotine on lipopolysaccharide (LPS)-induced impairment of fear memory reconsolidation and the underlying mechanism.

METHODS

Step-through inhibitory avoidance task was recruited to study fear memory of rat, i.p. LPS (0.5 mg/kg) treatment was used to induce inflammation, and western blot and immunostaining were applied to detect protein expression and distribution in medial prefrontal cortex and hippocampus.

RESULTS

Our data showed that LPS induced fear memory reconsolidation impairment without affecting retrieval. In addition, LPS significantly increased inflammation factors tumor necrosis factor-α and interleukin-1 beta and decreased CREB-regulated transcription coactivator 1 (CRTC1) expression and adenosine monophosphate-activated protein kinase (AMPK) activation in hippocampus. More importantly, LPS significantly decreased CRTC1 expression and AMPK activation in neurons by activating microglia cells. Of note, either nicotine treatment or activation of AMPK by intracerebroventricular infusion of metformin reduced LPS-induced impairment of fear memory reconsolidation and ameliorated inflammation factor tumor necrosis factor-α and interleukin-1 beta as well as the expression of CRTC1.

CONCLUSIONS

In conclusion, our results showed that acute nicotine treatment alleviates LPS-induced impairment of fear memory reconsolidation through activation of AMPK and upregulation of CRTC1 in hippocampus.

Translocator protein 18 kDa: a potential therapeutic biomarker for post traumatic stress disorder

Post traumatic stress disorder (PTSD) is widely regarded as a stress-related and trauma disorder. The symptoms of PTSD are characterized as a spectrum of vulnerabilities after the exposure to an extremely traumatic stressor. Considering as one of complex mental disorders, little progress has been made toward its diagnostic biomarkers, despite the involvement of PTSD has been studied. Many studies into the underlying neurobiology of PTSD implicated the dysfunction of neurosteroids biosynthesis and neuorinflammatory processes. Translocator protein 18 kDa (TSPO) has been considered as one of the promising therapeutic biomarkers for neurological stress disorders (like PTSD, depression, anxiety, et al) without the benzodiazepine-like side effects. This protein participates in the formation of neurosteroids and modulation of neuroinflammation. The review outlines current knowledge involving the role of TSPO in the neuropathology of PTSD and the anti-PTSD-like effects of TSPO ligands.

Transient neonatal sleep fragmentation results in long-term neuroinflammation and cognitive impairment in a rabbit model

Sleep fragmentation is an increase in sleep-wake transitions without an overall decrease in total sleep time. Sleep fragmentation is well documented during acute and chronic hospitalization and can result in delirium and memory problems in children. Sleep fragmentation is also often noted in neurodevelopmental disorders. However, it is unclear how sleep fragmentation independent of disease affects brain development and function. We hypothesized that acute sleep fragmentation during the neonatal period in otherwise healthy animals would result in neuroinflammation and would be associated with abnormalities in cognitive development. The orbital shaker method was used to fragment sleep for 72 h in postnatal day 3 New Zealand white rabbit kits (fragmentation group). To control for maternal separation, the sham group was separated from the dam and maintained in the same conditions without undergoing sleep fragmentation. A naïve control group remained with the dam. Kits underwent behavioral testing with novel object recognition and spontaneous alternation T-maze tests at 2-3 weeks post-fragmentation and were sacrificed 3-50 days after fragmentation. Sleep fragmentation resulted in acute and chronic changes in microglial morphology in the hippocampus and cortex, and regional differences in mRNA expression of pro- and anti-inflammatory cytokines at 3, 7 and 50 days post-fragmentation. Impaired novel object recognition and a longer latency in T-maze task completion were noted in the fragmented kits. This was in spite of normalization of sleep architecture noted at 2 months of age in these kits. The results indicate that transient neonatal sleep fragmentation results in short-term and long-term immune alterations in the brain, along with diminished performance in cognitive tasks long-term.

D-Ribose-L-cysteine attenuates lipopolysaccharide-induced memory deficits through inhibition of oxidative stress, release of proinflammatory cytokines, and nuclear factor-kappa B expression in mice

D-Ribose-L-cysteine (DRLC), an analog of cysteine that boosts glutathione (GSH) content, has been reported to mitigate oxidative stress-mediated diseases. This study seeks to evaluate the effects of DRLC on memory deficits and the biochemical and histo-morphological changes induced by lipopolysaccharide (LPS) in mice. Male Swiss mice (n = 10) were pre-treated orally with three doses of DRLC (25 mg/kg, 50 mg/kg, and 100 mg/kg), donepezil (1 mg/kg), or vehicle (saline) for 30 min prior to the intraperitoneal injection of LPS (0.25 mg/kg) daily for 7 days. Memory functions were evaluated using the Y-maze, object recognition, and social recognition tests. The specific brain regions (prefrontal cortex and hippocampus) were evaluated to determine oxidative stress biomarkers (malondialdehyde, GSH, and catalase), acetyl-cholinesterase activity, proinflammatory cytokines (tumor necrosis factor-α and interleukin-6), expression of nuclear factor-kappa B (NF-κB), and neuronal cell morphology. DRLC (25-100 mg/kg) reversed the memory deficits in the LPS-treated mice (p < 0.05). The increased oxidative stress and proinflammatory cytokines in the brain regions of the LPS-treated mice were significantly (p < 0.05) reduced by DRLC. DRLC (50 mg/kg and 100 mg/kg) also reduced acetyl-cholinesterase activity and decreased NF-κB expression in the brains of LPS-treated mice. Finally, it attenuated the cytoarchitectural distortions and loss of neuronal cells of the prefrontal cortex and hippocampus that were induced by LPS in mice. The results of this study suggest that DRLC attenuates memory deficit induced by LPS in mice through mechanisms related to the inhibition of oxidative stress, release of proinflammatory cytokines, and expression of NF-κB in mice.

Complement activation sustains neuroinflammation and deteriorates adult neurogenesis and spatial memory impairment in rat hippocampus following sleep deprivation

BACKGROUND

An association between neuroinflammation, reduced adult neurogenesis, and cognitive impairment has been established in sleep deprivation (SD). Complement receptors are expressed on neuronal and glial cells, thus, regulate the neuroinflammation, neurogenesis and learning/memory. However, understanding of the effect of SD on the brain-immune system interaction associated with cognitive dysfunction and its mechanisms is obscure. We hypothesized that complement activation induced changes in inflammatory and neurogenesis related proteins might be involved in the cognitive impairment during SD.

METHODOLOGY

Adult male Sprague Dawley rats were used. Rats were sleep deprived for 48 h using a novel automated SD apparatus. Dosage of BrdU (50 mg/kg/day, i.p. in 0.07 N NaOH), complement C3a receptor antagonist (C3aRA; SB290157; 1 mg/kg/day, i.p.) in 1.16% v/v PBS and complement C5a receptor antagonist (C5aRA; W-54011; 1 mg/kg/day, i.p.) in normal saline were used. Rats were subjected to spatial memory evaluation following SD. Hippocampal tissue was collected for biochemical, molecular, and immunohistochemical studies. T-test and ANOVA were used for the statistical analysis.

RESULTS

An up-regulation in the levels of complement components (C3, C5, C3a, C5a) and receptors (C3aR and C5aR) in hippocampus, displayed the complement activation during SD. Selective antagonism of C3aR/C5aR improved the spatial memory performance of sleep-deprived rats. C3aR antagonist (C3aRA) or C5aR antagonist (C5aRA) treatment inhibited the gliosis, maintained inflammatory cytokines balance in hippocampus during SD. Complement C3aR/C5aR antagonism improved hippocampal adult neurogenesis via up-regulating the BDNF level following SD. Administration of C3aRA and C5aRA significantly maintained synaptic homeostasis in hippocampus after SD. Gene expression analysis showed down-regulation in the mRNA levels of signal transduction pathways (Notch and Wnt), differentiation and axogenous proteins, which were found to be improved after C3aRA/C5aRA treatment. These findings were validated at protein and cellular level. Changes in the corticosterone level and ATP-adenosine-NO pathway were established as the key mechanisms underlying complement activation mediated consequences of SD.

CONCLUSION

Our study suggests complement (C3a-C3aR and C5a-C5aR) activation as the novel mechanism underlying spatial memory impairment via promoting neuroinflammation and adult neurogenesis decline in hippocampus during SD, thereby, complement (C3aR/C5aR) antagonist may serve as the novel therapeutics to improve the SD mediated consequences.

Effect of Systemic Inflammation on Rat Attentional Function and Neuroinflammation: Possible Protective Role for Food Restriction

Background: Aging is characterized by subtle cognitive decline, which correlates with increased peripheral inflammation. Acute activation of the peripheral immune system, via lipopolysaccharide (LPS) injection, elicits deficits in hippocampal-dependent spatial memory. Little is known concerning the effect of chronic inflammation on prefrontal cortex (PFC)-dependent vigilance. We examined the impact of repeated LPS injections in young and middle-age rats on the 5-choice serial reaction time task (5-CSRTT), expecting repeated LPS treatment to induce attentional deficits with greater disruption in middle-age. Methods: Male Fischer-344 rats, 4- and 12-months-old, were food restricted and trained on the 5-CSRTT. Once rats reached criterion, they were injected with LPS (1 mg/kg, i.p.) weekly for 4 weeks and testing started 48 h after each injection. To examine the possibility that mild food restriction inherent to the behavioral task influenced inflammation markers, a second group of food-restricted or ad-lib-fed rats was assessed for cytokine changes 48 h after one injection. Results: Performing LPS-treated rats exhibited a sickness response, manifesting as reduced initiated and completed trials during the first week but recovered by the second week of testing. After the first week, LPS-treated rats continued to exhibit longer response latencies, despite no change in food retrieval latency, suggestive of LPS-induced cognitive slowing. Similarly, LPS-induced impairment of attention was observed as increased omissions with heightened cognitive demand and increased age. Repeated LPS-treatment increased the level of PFC IL-1α, and PFC IL-6 was marginally higher in middle-age rats. No effect of age or treatment was observed for plasma cytokines in performing rats. Histological examination of microglia indicated increased colocalization of Iba1+ and CD68+ cells from middle-age relative to young rats. Examination of food restriction demonstrated an attenuation of age- and LPS-related increases in plasma cytokine levels. Conclusions: Systemic inflammation, induced through LPS treatment, impaired attentional function, which was independent of sickness and exacerbated by increased cognitive demand and increased age. Additional studies revealed that food restriction, associated with the task, attenuated markers of neuroinflammation and plasma cytokines. The results emphasize the need for improved methods for modeling low-level chronic systemic inflammation to effectively examine its impact on attention during aging.

Active Fraction Combination from Liuwei Dihuang Decoction (LW-AFC) Alleviated the LPS-Induced Long-Term Potentiation Impairment and Glial Cells Activation in Hippocampus of Mice by Modulating Immune Responses

Neuroinflammation is known as a typical feature associated with many neurodegenerative diseases including Alzheimer's disease (AD) and impairs the synaptic plasticity of the hippocampus. LW-AFC is an active fraction combination being extracted from Liuwei Dihuang decoction, a classic traditional Chinese medicine prescription. This study aimed to investigate the effects of LW-AFC on synaptic plasticity in mice with lipopolysaccharide (LPS) treatment. The results showed that the administration of LPS caused fever and long-term potentiation (LTP) impairment in mice. The pretreatment with LW-AFC had an antipyretic effect on fever and improved the impaired LTP induced by LPS, alleviated the microglia and astrocytes activation in the hippocampus, regulated the abnormal T-lymphocyte subpopulation in the spleen and blood caused by LPS, and reduced the aberrant secretion of cytokines in the brain and plasma. The compounds paeoniflorin, morroniside, and loganic acid in LW-AFC regulated the TNF-α secretion in non-LPS- and LPS-stimulated BV-2 cells. These data suggest that LW-AFC improves the LPS-induced impairment of LTP and alleviates the activation of glial cells in the hippocampus, which might be associated with modulating immune responses.

Determining the biological associates of acute cold pressor post-encoding stress effects on human memory: The role of salivary interleukin-1β

Stress generally hurts many aspects of memory, but an interesting finding to emerge from the stress and memory literature is that stress that occurs shortly after learning (i.e., post-encoding stress) usually benefits memory. Although this effect is well established, the biological mechanisms underpinning this effect are not-especially in humans. We addressed this gap in the present study by collecting saliva samples from 80 participants who were randomized to a post-encoding stress (i.e., cold pressor for 3 min) or control task (i.e., warm water for 3 min) and 48 h later completed a recognition memory task. Saliva was collected both prior to and 15 min after the offset of (18 min after the onset of) the stress/control manipulation. Drawing on animal and human work, we examined how five stress-responsive biomarkers-cortisol, salivary α-amylase, progesterone, estradiol, and the proinflammatory cytokine interleukin (IL)-1β, all assessed in saliva-related to the effects of stress on memory. We found that stress enhanced recollection of negative images and that these effects were selectively related to salivary IL-1β. Moreover, we found that the beneficial effects of stress on memory were statistically mediated by salivary IL-1β. We found no robust associations-either linear or quadratic-between memory and any other biomarker, nor did we find significant interactions between biomarkers in predicting memory. These results suggest that immune system activity indexed by salivary IL-1β may play an important role in contributing to post-encoding stress effects on human memory.

The effects of exercise on hippocampal inflammatory cytokine levels, brain oxidative stress markers and memory impairments induced by lipopolysaccharide in rats

The exercise effects on behavioral tests, hippocampal and cortical oxidative stress, and hippocampal inflammatory cytokines of lipopolysaccharide (LPS) administered rats were investigated. The rats were divided into four groups (N = 8): (1) control; (2) moderate training (MT, 15 m/min, 30 min/day, 9 weeks); (3) LPS (1 mg/kg LPS) and (4) LPS + MT (1 mg/kg LPS; 15 m/min, 30 min/day, 9 weeks). LPS was injected 2 h before the behavioral experiments during the last week of training. Finally, the rats' brain were removed for biochemical assessments. LPS increased escape latency and traveled distance to reach the platform in Morris water maze (MWM) test (P < 0.05-P < 0.001). In the passive avoidance (PA) test, LPS decreased the latency to enter the dark compartment and the time spent in the light compartment and increased the time spent in the dark compartment (P < 0.01-P < 0.001), while MT improved the rats performances in MWM and PA tests (P < 0.01-P < 0.001). Additionally, LPS increased tumor necrosis factor α (TNF-α), interleukin 1 beta (IL-1β) and C-reactive protein levels in the hippocampal tissues, malondialdehyde (MDA) and nitric oxide metabolite in hippocampal and cortical tissues, and decreased thiol contents and catalase (CAT) and superoxide dismutase (SOD) activity in hippocampal and cortical tissues compared to the control group (P < 0.01-P < 0.001); while moderate training decreased the levels of TNF-α, IL-1β and MDA; increased thiol contents, and SOD and CAT activity in the LPS + MT compared to the LPS group (P < 0.001). These results indicated that moderate training improved LPS-induced learning and memory impairments by attenuating the hippocampal cytokine levels and brain oxidative damage.