Lipopolysaccharide induces memory-processing deficits in day-old chicks

Investigation of the Immunomodulatory and Neuroprotective Properties of Nigella sativa Oil in Experimental Systemic and Neuroinflammation

Nigella sativa (NS) is a promising medicinal plant with diverse therapeutic properties. This study aimed to investigate the impact of NS oil (NSO) on memory functions in rats with LPS (lipopolysaccharide)-induced neuroinflammation, as well as its effect on serum levels of inflammatory cytokines, neuropeptide Y (NPY) and brain-derived neurotrophic factor (BDNF). Male rats were divided into four groups: control, LPS-control, LPS+NSO 3 and 5 mL/kg. Neuroinflammation was induced by a single intraperitoneal LPS injection (2 mg/kg). The novel object recognition test (NORT) and Y-maze were used for the evaluation of memory processes. Recognition index (RI) and % spontaneous alteration (%SA) were registered, respectively. Blood samples for TNF-α, IL-1β, IL-10, BDNF, and NPY serum levels were taken. Thymoquinone, the active compound of the oil, was detected by high-performance liquid chromatography. NSO administration resulted in an improvement in spatial and episodic memory, as evidenced by increased % SA and RI compared to LPS-control. Treatment with NSO led to a significant reduction in pro-inflammatory cytokines and NPY, along with an increase in IL-10 and BDNF levels, when compared to LPS-control. In conclusion, NSO enhances BDNF production and regulates pro- and anti-inflammatory cytokines release, which probably contributes to the observed cognitive improvement in animals with experimental neuroinflammation.

The microbiota-gut-brain axis in hippocampus-dependent learning and memory: current state and future challenges

A fundamental shift in neuroscience suggests bidirectional interaction of gut microbiota with the healthy and dysfunctional brain. This microbiota-gut-brain axis has mainly been investigated in stress-related psychopathology (e.g. depression, anxiety). The hippocampus, a key structure in both the healthy brain and psychopathologies, is implicated by work in rodents that suggests gut microbiota substantially impact hippocampal-dependent learning and memory. However, understanding microbiota-hippocampus mechanisms in health and disease, and translation to humans, is hampered by the absence of a coherent evaluative approach. We review the current knowledge regarding four main gut microbiota-hippocampus routes in rodents: through the vagus nerve; via the hypothalamus-pituitary-adrenal-axis; by metabolism of neuroactive substances; and through modulation of host inflammation. Next, we suggest an approach including testing (biomarkers of) the four routes as a function of the influence of gut microbiota (composition) on hippocampal-dependent (dys)functioning. We argue that such an approach is necessary to proceed from the current state of preclinical research to beneficial application in humans to optimise microbiota-based strategies to treat and enhance hippocampal-dependent memory (dys)functions.

Lipopolysaccharide-Induced Immunological Tolerance in Monocyte-Derived Dendritic Cells

Bacterial lipopolysaccharides (LPS), also referred to as endotoxins, are major outer surface membrane components present on almost all Gram-negative bacteria and are major determinants of sepsis-related clinical complications including septic shock. LPS acts as a strong stimulator of innate or natural immunity in a wide variety of eukaryotic species ranging from insects to humans including specific effects on the adaptive immune system. However, following immune stimulation, lipopolysaccharide can induce tolerance which is an essential immune-homeostatic response that prevents overactivation of the inflammatory response. The tolerance induced by LPS is a state of reduced immune responsiveness due to persistent and repeated challenges, resulting in decreased expression of pro-inflammatory modulators and up-regulation of antimicrobials and other mediators that promote a reduction of inflammation. The presence of environmental-derived LPS may play a key role in decreasing autoimmune diseases and gut tolerance to the plethora of ingested antigens. The use of LPS may be an important immune adjuvant as demonstrated by the promotion of IDO1 increase when present in the fusion protein complex of CTB-INS (a chimera of the cholera toxin B subunit linked to proinsulin) that inhibits human monocyte-derived DC (moDC) activation, which may act through an IDO1-dependent pathway. The resultant state of DC tolerance can be further enhanced by the presence of residual E. coli lipopolysaccharide (LPS) which is almost always present in partially purified CTB-INS preparations. The approach to using an adjuvant with an autoantigen in immunotherapy promises effective treatment for devastating tissue-specific autoimmune diseases like multiple sclerosis (MS) and type 1 diabetes (T1D).

Folecitin Isolated from Hypericum oblongifolium Exerts Neuroprotection against Lipopolysaccharide-Induced Neuronal Synapse and Memory Dysfunction via p-AKT/Nrf-2/HO-1 Signalling Pathway

Neurodegenerative diseases, especially Alzheimer's disease (AD), are characterised with neuronal synapse and memory dysfunction, and thus, there is an urgent need to find novel therapeutic medicines that can target different pathways to restore the deficits. In this investigation, we assessed the medicinal potency of folecitin (a flavonoid isolated from Hypericum oblongifolium Wall.) against lipopolysaccharide (LPS)-induced amyloidogenic amyloid beta (Aβ) production pathway-mediated memory impairment in mice. The LPS was administered intraperitonially (i.p.) 250 μg/kg/day for 3 consecutive weeks, followed by the coadministration of folecitin (30 mg/kg/day) with LPS for the last two weeks (2^nd and 3^rd week). The expression of various proteins involved in synapse, neuronal death, and Aβ generation was evaluated using the Western blot approach. Results indicated that folecitin significantly decreased LPS-induced apoptotic proteins; expressed BAX, PARP-1, and caspase-3 proteins; and inhibited BACE1 that cleaves transmembrane amyloid precursor protein and the amyloidogenic Aβ production pathway. Folecitin restored both preneural and postneuronal synapse, accompanied by the improvement in memory impairment. Moreover, folecitin significantly activated endogenous antioxidant proteins Nrf-2 and HO-1 by stimulating the phosphorylation of Akt proteins. These findings indicate that folecitin might be a promising target for developing novel medication to treat neurodegenerative disorders caused by neurotoxins.

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.

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.

Porphyromonas gingivalis lipopolysaccharide induces cognitive dysfunction, mediated by neuronal inflammation via activation of the TLR4 signaling pathway in C57BL/6 mice

Background

Porphyromonas gingivalis lipopolysaccharide (P. gingivalis-LPS) is one of the major pathogenic factors of chronic periodontitis (CP). Few reports on the correlation between P. gingivalis-LPS and cognitive function exist. Thus, the present study aimed to investigate the effects of P. gingivalis-LPS on cognitive function and the associated underlying mechanism in C57BL/6 mice.

Methods

The C57BL/6 mice were injected with P. gingivalis-LPS (5 mg kg⁻¹) either with or without Toll-like receptor 4 (TLR4) inhibitor (TAK-242, 5 mg kg⁻¹). After 7 days, behavioral alterations were assessed with the open field test (OFT), Morris water maze (MWM) test, and passive avoidance test (PAT). The activation of astrocytes and microglia in the cerebral cortex and hippocampus of mice was observed by immunohistochemistry. The expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8), TLRs (TLR2, TLR3, and TLR4), and CD14 and the activation of the NF-κB signaling pathway (IRAK1, p65, and p-p65) in the cerebral cortex of the mice were evaluated by RT-PCR, ELISA, and western blot.

Results

The OFT showed that P. gingivalis-LPS did not affect the initiative and activity of mice. Administration of P. gingivalis-LPS significantly impaired spatial learning and memory during the MWM test and attenuated the ability of passive avoidance learning during the PAT. Both astrocytes and microglia were activated in the cortex and hippocampus. The messenger RNA (mRNA) and protein expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8) was upregulated by P. gingivalis-LPS in the cortex. In addition, the TLR4/NF-κB signaling pathway was activated (TLR4, CD14, IRAK1, and p-p65). These effects were effectively alleviated by TAK-242.

Conclusions

Administration of P. gingivalis-LPS can lead to learning and memory impairment in C57BL/6 mice. This impairment is mediated by activation of the TLR4 signaling pathway. Our study suggests that P. gingivalis-LPS-induced neuroinflammation plays an important role in cognitive impairment. It also reveals that endotoxins of periodontal pathogens could represent a risk factor for cognitive disorders.

Lipopolysaccharide-Induced Spatial Memory and Synaptic Plasticity Impairment Is Preventable by Captopril

Introduction. Renin-angiotensin system has a role in inflammation and also is involved in many brain functions such as learning, memory, and emotion. Neuroimmune factors have been proposed as the contributors to the pathogenesis of memory impairments. In the present study, the effect of captopril on spatial memory and synaptic plasticity impairments induced by lipopolysaccharide (LPS) was investigated. Methods. The rats were divided and treated into control (saline), LPS (1 mg/kg), LPS-captopril (LPS-Capto; 50 mg/kg captopril before LPS), and captopril groups (50 mg/kg) before saline. Morris water maze was done. Long-term potentiation (LTP) from CA1 area of hippocampus was assessed by 100 Hz stimulation in the ipsilateral Schaffer collateral pathway. Results. In the LPS group, the spent time and traveled path to reach the platform were longer than those in the control, while, in the LPS-Capto group, they were shorter than those in the LPS group. Moreover, the slope and amplitude of field excitatory postsynaptic potential (fEPSP) decreased in the LPS group, as compared to the control group, whereas, in the LPS-Capto group, they increased compared to the LPS group. Conclusion. The results of the present study showed that captopril improved the LPS-induced memory and LTP impairments induced by LPS in rats. Further investigations are required in order to better understand the exact responsible mechanism(s).

The effects of L-arginine on spatial memory and synaptic plasticity impairments induced by lipopolysaccharide

Background:

An important role of nitric oxide (NO) in neuroinflammation has been suggested. It is also suggested that NO has a critical role in learning and memory. Neuro-inflammation induced by lipopolysaccharide (LPS) has been reported that deteriorates learning and memory. The effect of L-arginine (LA) as a precursor of NO on LPS-induced spatial learning and memory and neuronal plasticity impairment was evaluated.

Materials and Methods:

The animals were grouped into: (1) Control, (2) LPS, (3) LA-LPS, and (4) LA. The rats received intraperitoneally LPS (1 mg/kg) 2 h before experiments and LA (200 mg/kg) 30 min before LPS. The animals were examined in Morris water maze (MWM). Long-term potentiation (LTP) from CA₁ area of the hippocampus was also assessed by 100 Hz stimulation in the ipsilateral Schaffer collateral pathway.

Results:

In MWM, time latency and traveled path were higher in LPS group than the control group (P < 0.001) whereas in LA-LPS group they were shorter than LPS group (P < 0.001). The amplitude and slope of field excitatory postsynaptic potential (fEPSP) decreased in LPS group compared to control group (P < 0.05 and P < 0.01) whereas, there was not any significant difference in these parameters between LPS and LA-LPS groups.

Conclusion:

Administration of LPS impaired spatial memory and synaptic plasticity. Although LA ameliorated deleterious effects of LPS on learning of spatial tasks, it could not restore LPS-induced LTP impairment.

Systemic inflammation impairs respiratory chemoreflexes and plasticity

Many lung and central nervous system disorders require robust and appropriate physiological responses to assure adequate breathing. Factors undermining the efficacy of ventilatory control will diminish the ability to compensate for pathology, threatening life itself. Although most of these same disorders are associated with systemic and/or neuroinflammation, and inflammation affects neural function, we are only beginning to understand interactions between inflammation and any aspect of ventilatory control (e.g. sensory receptors, rhythm generation, chemoreflexes, plasticity). Here we review available evidence, and present limited new data suggesting that systemic (or neural) inflammation impairs two key elements of ventilatory control: chemoreflexes and respiratory motor (versus sensory) plasticity. Achieving an understanding of mechanisms whereby inflammation undermines ventilatory control is fundamental since inflammation may diminish the capacity for natural, compensatory responses during pathological states, and the ability to harness respiratory plasticity as a therapeutic strategy in the treatment of devastating breathing disorders, such as during cervical spinal injury or motor neuron disease.

Spinal glia modulate both adaptive and pathological processes

Recent research indicates that glial cells control complex functions within the nervous system. For example, it has been shown that glial cells contribute to the development of pathological pain, the process of long-term potentiation, and the formation of memories. These data suggest that glial cell activation exerts both adaptive and pathological effects within the CNS. To extend this line of work, the present study investigated the role of glia in spinal learning and spinal learning deficits using the spinal instrumental learning paradigm. In this paradigm rats are transected at the second thoracic vertebra (T2) and given shock to one hind limb whenever the limb is extended (controllable shock). Over time these subjects exhibit an increase in flexion duration that reduces net shock exposure. However, when spinalized rats are exposed to uncontrollable shock or inflammatory stimuli prior to testing with controllable shock, they exhibit a learning deficit. To examine the role of glial in this paradigm, spinal glial cells were pharmacologically inhibited through the use of fluorocitrate. Our results indicate that glia are involved in the acquisition, but not maintenance, of spinal learning. Furthermore, the data indicate that glial cells are involved in the development of both shock and inflammation-induced learning deficits. These findings are consistent with prior research indicating that glial cells are involved in both adaptive and pathological processes within the spinal cord.

Polyinosinic:polycytidylic acid induces memory processing deficits in the day-old chick

Anecdotal and experimental evidence has demonstrated that humans and animals exhibit physiological and cognitive alterations in response to sickness and injury. It is now clear that these changes are due to the actions of proinflammatory cytokines. The current study examined the effects of peripheral administration of polyinosinic:polycytidylic acid, a synthetic double-stranded viral RNA, on the memory processes of day-old chicks trained on a single trial passive avoidance task. Polyinosinic:polycytidylic acid impaired performance on the passive avoidance task in a dose-dependent manner. Maximal deficits were observed when 5 g/kg polyinosinic:polycytidylic acid was administered 120 min before training. Tests for retention revealed that interference in memory consolidation appeared between 30 and 40 min after training. These results indicate an inhibitory effect of polyinosinic:polycytidylic acid on the processes of memory formation at the transition from intermediate-term memory phase (A) to intermediate-term memory phase (B) of the Gibbs and Ng model of memory formation. The study also investigated the pyrogenic actions of polyinosinic:polycytidylic acid, and examined the effect of pretreatment with ketoprofen, a cyclooxygenase inhibitor. Significant rises in body temperature were observed 30 min after injection of polyinosinic:polycytidylic acid. Inhibition of cyclooxygenase by ketoprofen ameliorated the polyinosinic:polycytidylic acid-induced deficits in retention and attenuated the increase in body temperature. These results demonstrate that polyinosinic:polycytidylic acid induces memory processing deficits and is pyrogenic in the day-old chick and that these effects are cyclooxygenase-dependent.

The potential impact of sickness-motivated behavior on the expression of neuropsychiatric disturbances in systemic lupus erythematosus

Activation of the peripheral immune system is often accompanied by changes in cognition, ingestive behavior, sleep pattern, and sexual drive; collectively referred to as sickness behavior. Mounting evidence suggests that sickness behavior may be a purposeful attempt on the part of an organism to conserve energy and thereby facilitate recuperation. Illnesses characterized by chronic, uncontrolled immune reactivity such as systemic lupus erythematosus are also frequently associated with impaired emotionality and cognition; which, unlike sickness behavior, are conventionally thought to emanate from fixed structural lesions of the brain. Clinical observations, however, indicate that the neuropsychiatric disturbances in lupus may wax and wane in intensity and suggest the hypothesis that sickness-motivated behavior may significantly influence the neuropsychiatric manifestations of systemic lupus erythematosus and, perhaps, those of other autoimmune diseases associated with neuroinflammation. The hypothesis that patients with systemic lupus erythematosus undergo a reorganization of their motivational priorities, which influences cognitive performance and emotional output, may be examined using validated behavior paradigms in autoimmune MRL-MpJ-Tnfrsf6(lpr) (MRL-lpr/lpr) mice that spontaneously develop a lupus-like illness accompanied by disturbances in cognition and emotionality. Confirming that sickness-motivated behavior contributes to the aberrations in cognition and emotionality exhibited by an experimental model of systemic lupus erythematosus might have important therapeutic and prognostic implications by invoking the possibility that similar motivational effects may be influencing cognitive and/or emotional output in patients with neuropsychiatric lupus.

Minocycline reduces lipopolysaccharide-induced neurological dysfunction and brain injury in the neonatal rat

Preferential brain white matter injury and hypomyelination induced by intracerebral administration of the endotoxin lipopolysaccharide (LPS) in the neonatal rat brain has been characterized as associated with the activation of microglia. To examine whether inhibition of microglial activation might provide protection against LPS-induced brain injury and behavioral deficits, minocycline (45 mg/kg) was administered intraperitoneally 12 hr before and immediately after an LPS (1 mg/kg) intracerebral injection in postnatal day 5 (P5) Sprague-Dawley rats and then every 24 hr for 3 days. Brain injury and myelination were examined on postnatal day 21 and the tests for neurobehavioral toxicity were carried out from P3 to P21. LPS administration resulted in severe white matter injury, enlarged ventricles, deficits in the hippocampus, loss of oligodendrocytes and tyrosine hydroxylase neurons, damage to axons and dendrites, and impaired myelination as indicated by the decrease in myelin basic protein immunostaining in the P21 rat brain. LPS administration also significantly affected physical development (body weight) and neurobehavioral performance, such as righting reflex, wire hanging maneuver, cliff avoidance, locomotor activity, gait analysis, and responses in the elevated plus-maze and passive avoidance task. Treatment with minocycline significantly attenuated the LPS-induced brain injury and improved neurobehavioral performance. The protective effect of minocycline was associated with its ability to attenuate LPS-induced microglial activation. These results suggest that inhibition of microglial activation by minocycline may have long-term protective effects in the neonatal brain on infection-induced brain injury and associated neurologic dysfunction in the rat.

Suppressed fever and hypersensitivity responses in chicks prenatally exposed to opiates

We have established procedures to reliably induce opiate dependence in the chick embryo via in ovo injection, early in embryonic development, of the long-acting and potent opiate N-desmethyl-l-alpha-noracetylmethadol (NLAAM). Prior studies found that there is continual exposure to NLAAM throughout embryogenesis and shortly after hatching there are signs of spontaneous withdrawal. In the present study, we used three doses of NLAAM (2.5, 5, and 10 mg/kg egg weight) to determine if prenatal opiate exposure followed by postnatal withdrawal interfered with appropriate neural-endocrine-immune interactions in the young chick. To ensure that effects were not a consequence of inappropriately large doses, we first examined acute and chronic toxicity and additional characteristics of postnatal opiate withdrawal. We then measured the corticosterone and fever responses to LPS stimulation during the withdrawal period. After the conclusion of opiate withdrawal, we assessed the hypersensitivity response to phytohemagglutinin (PHA). The fever response to LPS and the hypersensitivity response to PHA were suppressed by prenatal opiate exposure and postnatal withdrawal. The corticosterone response to LPS was not affected, but there were exaggerated corticosterone responses to saline injection in chicks exposed in ovo to NLAAM. It was unlikely that the effects of prenatal NLAAM were the result of toxicity, as little chronic toxicity was seen with the lower two doses of NLAAM, doses that yielded significant suppressions of neural-endocrine-immune responses. However, effects found in the chicks treated with 10 mg NLAAM/kg may have been partly related to the greater toxicity and/or protracted postnatal withdrawal in this group.

Lipopolysaccharide induces biochemical alterations in chicks trained on the passive avoidance learning task

We have recently shown that activation of the immune system with lipopolysaccharide (LPS) results in memory-processing deficits for the passive avoidance learning task in the day-old chick. The current study examined two important issues in understanding the mechanisms underlying these memory deficits associated with immune system activation, namely, whether LPS (1) impairs Na(+)/K(+)-ATPase functioning and (2) increases corticosterone (CORT) concentrations in chicks trained on the task. As the effects of LPS on sickness behavior have only previously been characterized in older chickens, this study also tested whether LPS is able to produce similar alterations in day-old chicks. LPS decreased brain Na(+)/K(+)-ATPase activity and increased plasma concentrations of CORT in chicks trained on the passive avoidance learning task. These findings give an insight into some of the mechanisms that may be responsible for the LPS-induced memory-processing deficits. Consistent with previous research in older chickens, LPS increased body temperature in a dose-dependent manner, however, only the lowest dose of LPS tested significantly decreased food intake in the day-old chicks.

Behavioral and motivational effects of immune-system activation

Immune-system activity induces changes in animal behavior such as decreased food intake, decreased exploratory behavior, increased sleep, and impaired cognitive functioning. These changes are mediated by proinflammatory cytokines, and the administration of cytokines produces the same profile of behavior change as do infection and inflammation. Results demonstrating differential effects of immune-system activation depending on environmental contingencies and physiological states support the hypothesis that the behavioral effects of immune activity may be mediated by motivation. In this article, the author outlines the behavioral changes induced by immune-system activation and discusses evidence for a motivational analysis of immune-induced behavior change and the potential involvement of motivation in human sickness behavior.