Characterization of a rat model to study acute neuroinflammation on histopathological, biochemical and functional outcomes

Ambiguous Contribution of Glucocorticosteroids to Acute Neuroinflammation in the Hippocampus of Rat

Effects of modulation of glucocorticoid and mineralocorticoid receptors (GR and MR, respectively) on acute neuroinflammatory response were studied in the dorsal (DH) and ventral (VH) parts of the hippocampus of male Wistar rats. Local neuroinflammatory response was induced by administration of bacterial lipopolysaccharide (LPS) to the DH. The modulation of GR and MR was performed by dexamethasone (GR activation), mifepristone, and spironolactone (GR and MR inhibition, respectively). Experimental drugs were delivered to the dentate gyrus of the DH bilaterally by stereotaxic injections. Dexamethasone, mifepristone, and spironolactone were administered either alone (basal conditions) or in combination with LPS (neuroinflammatory conditions). Changes in expression levels of neuroinflammation-related genes and morphology of microglia 3 days after intrahippocampal administration of above substances were assessed. Dexamethasone alone induced a weak proinflammatory response in the hippocampal tissue, while neither mifepristone nor spironolactone showed significant effects. During LPS-induced neuroinflammation, GR activation suppressed expression of selected inflammatory genes, though it did not prevent appearance of activated forms of microglia. In contrast to GR activation, GR or MR inhibition had virtually no influence on LPS-induced inflammatory response. The results suggest glucocorticosteroids ambiguously modulate specific aspects of neuroinflammatory response in the hippocampus of rats at molecular and cellular levels.

Neurochemical effects of sepsis on the brain

Sepsis is a life-threatening organ dysfunction triggered by a dysregulated host immune response to eliminate an infection. After the host immune response is activated, a complex, dynamic, and time-dependent process is triggered. This process promotes the production of inflammatory mediators, including acute-phase proteins, complement system proteins, cytokines, chemokines, and antimicrobial peptides, which are required to initiate an inflammatory environment for eliminating the invading pathogen. The physiological response of this sepsis-induced systemic inflammation can affect blood-brain barrier (BBB) function; subsequently, endothelial cells produce inflammatory mediators, including cytokines, chemokines, and matrix metalloproteinases (MMPs) that degrade tight junction (TJ) proteins and decrease BBB function. The resulting BBB permeability allows peripheral immune cells from the bloodstream to enter the brain, which then release a range of inflammatory mediators and activate glial cells. The activated microglia and astrocytes release reactive oxygen species (ROS), cytokines, chemokines, and neurochemicals, initiate mitochondrial dysfunction and neuronal damage, and exacerbate the inflammatory milieu in the brain. These changes trigger sepsis-associated encephalopathy (SAE), which has the potential to increase cognitive deterioration and susceptibility to cognitive decline later in life.

Rosmarinic acid attenuates lipopolysaccharide-induced neuroinflammation and cognitive impairment in rats

It has been recently demonstrated that rosmarinic acid (RA) through modulation in the amyloidogenic pathway exhibit neuroprotective potential in Alzheimer's disease. However, its effects on non-amyloidogenic pathways such as neuroinflammation (NI) and oxidative stress have not been elucidated carefully. Hence, this study aimed to investigate the effect of RA on cognitive function, cortical and hippocampal oxidant-antioxidant balance, and proinflammatory cytokines production in lipopolysaccharide (LPS)-induced NI in rats. NI was induced by intracerebroventricular injection of LPS (50 μg/20 μL; 10 μL into each ventricle) in Wistar rats. RA (25 and 50 mg/kg.) was intraperitoneally administrated to the experimental groups 30 min before the LPS injection and continued once per day for seven days. Cognitive function was investigated by the Y-maze test, and the production of proinflammatory cytokines and oxidative stress markers were evaluated in their hippocampi (HIP) and prefrontal cortex (PFC). In addition, neuronal damage was evaluated in the HIP subfields histologically. The RA administration could alleviate cognitive impairments caused by NI in LPS-treated rats as evidenced by improved working memory and attenuated neuronal injury in the HIP subfields. RA treatment in a dose-dependent manner prevented the overproduction of tumor necrosis factor-alpha (TNF-α), interleukin 1 beta (IL-1β), and IL-6 in both the HIP and PFC. RA significantly alleviated the HIP and PFC levels of malondialdehyde (MDA) and nitric oxide (NOx) and enhanced the superoxide dismutase (SOD) activity. These findings demonstrated that RA could also exert its neuroprotective effects by modulating non-amyloidogenic pathways such as inflammation and oxidative stress.

Preclinical Evaluation of TSPO and MAO-B PET Radiotracers in an LPS Model of Neuroinflammation

Discovery of novel PET radiotracers targeting neuroinflammation (microglia and astrocytes) is actively pursued. Employing a lipopolysaccharide (LPS) rat model, this longitudinal study evaluated the translocator protein 18-kDa radiotracer [¹⁸F]FEPPA (primarily microglia) and monoamine oxidase B radiotracers [¹¹C]L-deprenyl and [¹¹C]SL25.1188 (astrocytes preferred). Increased [¹⁸F]FEPPA binding peaked at 1 week in LPS-injected striatum whereas increased lazabemide-sensitive [¹¹C]L-deprenyl binding developed later. No increase in radiotracer uptake was observed for [¹¹C]SL25.1188. The unilateral intrastriatal LPS rat model may serve as a useful tool for benchmarking PET tracers targeted toward distinct phases of neuroinflammatory reactions involving both microglia and astrocytes.

Simvastatin Prevents Long-Term Cognitive Deficits in Sepsis Survivor Rats by Reducing Neuroinflammation and Neurodegeneration

Sepsis-associated encephalopathy causes brain dysfunction that can result in cognitive impairments in sepsis survivor patients. In previous work, we showed that simvastatin attenuated oxidative stress in brain structures related to memory in septic rats. However, there is still a need to evaluate the long-term impact of simvastatin administration on brain neurodegenerative processes and cognitive damage in sepsis survivors. Here, we investigated the possible neuroprotective role of simvastatin in neuroinflammation, and neurodegeneration conditions of brain structures related to memory in rats at 10 days after sepsis survival. Male Wistar rats (250-300 g) were submitted to cecal ligation and puncture (CLP, n = 42) or remained as non-manipulated (naïve, n = 30). Both groups were treated (before and after the surgery) by gavage with simvastatin (20 mg/kg) or an equivalent volume of saline and observed for 10 days. Simvastatin-treated rats that survived to sepsis showed a reduction in the levels of nitrate, IL1-β, and IL-6 and an increase in Bcl-2 protein expression in the prefrontal cortex and hippocampus, and synaptophysin only in the hippocampus. Immunofluorescence revealed a reduction of glial activation, neurodegeneration, apoptosis, and amyloid aggregates confirmed by quantification of GFAP, Iba-1, phospho Ser₃₉₆-tau, total tau, cleaved caspase-3, and thioflavin-S in the prefrontal cortex and hippocampus. In addition, treated animals presented better performance in tasks involving habituation memory, discriminative, and aversive memory. These results suggest that statins exert a neuroprotective role by upregulation of the Bcl-2 and gliosis reduction, which may prevent the cognitive deficit observed in sepsis survivor animals.

Immune Profile in Blood Following Non-convulsive Epileptic Seizures in Rats

Non-convulsive status epilepticus (NCSE) is a prolonged epileptic seizure with subtle symptoms that may delay clinical diagnosis. Emerging experimental evidence shows brain pathology and epilepsy development following NCSE. New diagnostic/prognostic tools are therefore needed for earlier and better stratification of treatment. Here we examined whether NCSE initiates a peripheral immune response in blood serum from rats that experienced electrically-induced NCSE. ELISA analysis showed an acute transient increase in serum protein levels including interleukin-6 6 h post-NCSE, similar to the immune reaction in the brain. At 4 weeks post-NCSE, when 75% of rats subjected to NCSE had also developed spontaneous seizures, several immune proteins were altered. In particular, markers associated with microglia, macrophages and antigen presenting cells, such as CD68, MHCII, and galectin-3, were increased and the T-cell marker CD4 was decreased in serum compared to both non-stimulated controls and NCSE rats without spontaneous seizures, without correlation to interictal epileptiform activity. Analyses of serum following intracerebral injection of lipopolysaccharide (LPS) showed an acute increase in interleukin-6, but at 4 weeks unaltered levels of MHCII and galectin-3, an increase in CD8 and CD11b and a decrease in CD68. None of the increased serum protein levels after NCSE or LPS could be confirmed in spleen tissue. Our data identifies the possibility to detect peripheral changes in serum protein levels following NCSE, which may be related to the development of subsequent spontaneous seizures.

Tb II-I, a Fraction Isolated from Tityus bahiensis Scorpion Venom, Alters Cytokines': Level and Induces Seizures When Intrahippocampally Injected in Rats

Scorpion venoms are composed of several substances with different pharmacological activities. Neurotoxins exert their effects by targeting ion channels resulting in toxic effects to mammals, insects and crustaceans. Tb II-I, a fraction isolated from Tityus bahiensis scorpion venom, was investigated for its ability to induce neurological and immune-inflammatory effects. Two putative β-sodium channel toxins were identified in this fraction, Tb2 II and Tb 4, the latter having been completely sequenced by mass spectrometry. Male Wistar rats, stereotaxically implanted with intrahippocampal cannulas and electrodes, were injected with Tb II-I (2 µg/2 µL) via the intrahippocampal route. The behavior, electrographic activity and cellular integrity of the animals were analyzed and the intracerebral level of cytokines determined. Tb II-I injection induced seizures and damage in the hippocampus. These alterations were correlated with the changes in the level of the cytokines tumoral necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Therefore, the binding of Tb II-I to its target in the central nervous system may induce inflammation resulting in neuropathological and behavioral alterations.

Brain Oxidative Stress During Experimental Sepsis Is Attenuated by Simvastatin Administration

During sepsis, brain damage is associated with oxidative stress due to overproduction of reactive oxygen species (ROS). Although there are recent reports about the benefits of statins in experimental sepsis and endotoxemia in peripheral organs, little is known about their effects in the CNS. Here, we investigated the antioxidant properties of simvastatin and its possible neuroprotective role during experimental sepsis. Male Wistar rats (250-300 g) were submitted to cecal ligation and puncture (CLP, n = 34) or remained as non-manipulated (naive, n = 34). Both groups were treated by gavage with simvastatin (20 mg/kg) or an equivalent volume of saline. The animals submitted to CLP were treated 4 days before and 48 h after surgery. One animal group was decapitated and the blood and brain were collected to quantify plasma levels of cytokines and assess astrogliosis and apoptosis in the prefrontal cortex and hippocampus. Another group was perfused with PBS (0.01 M), and the same brain structures were dissected to analyze oxidative damage. The CLP rats treated with simvastatin showed a reduction in nitric oxide (P < 0.05), IL1-β (P < 0.001), IL-6 (P < 0.01), and TBARS levels (P < 0.001) and an increase in catalase activity (P < 0.01), citrate synthase enzyme (P < 0.05), and normalized GSH/GSSG ratio. In addition, the histopathological analysis showed a reduction (P < 0.001) in reactive astrocytes and caspase 3-positive apoptotic cells. The results suggest a possible neuroprotective effect of simvastatin in structures responsible for spatial learning and memory and indicate the need for behavioral studies evaluating the impact on cognitive damage, as frequently seen in patients surviving sepsis.

The role of IL-1β and glutamate in the effects of lipopolysaccharide on the hippocampal electrical kindling of seizures

In our study, we used rapid electrical hippocampal kindling and in vivo microdialysis methods to assess the involvement of inflammatory mediators: lipopolysaccharide (LPS) and proinflammatory interleukin-1β (IL-1β) in mechanisms of epileptogenesis. We observed, that both, LPS and IL-1β, administered into stimulated hippocampus, accelerated kindling process. LPS also increased the expression of IL-1β in stimulated hippocampus in kindled rats. In vivo acute LPS perfusion, via a microdialysis cannula implanted into the naïve rat's hippocampus, produced an increase in extracellular glutamate release. We suppose, that particularly IL-1β action and increased glutamate concentration may significantly contribute to LPS effects on kindling development.

TLR4-activated microglia require IFN-γ to induce severe neuronal dysfunction and death in situ

Microglia (tissue-resident macrophages) represent the main cell type of the innate immune system in the CNS; however, the mechanisms that control the activation of microglia are widely unknown. We systematically explored microglial activation and functional microglia-neuron interactions in organotypic hippocampal slice cultures, i.e., postnatal cortical tissue that lacks adaptive immunity. We applied electrophysiological recordings of local field potential and extracellular K(+) concentration, immunohistochemistry, design-based stereology, morphometry, Sholl analysis, and biochemical analyses. We show that chronic activation with either bacterial lipopolysaccharide through Toll-like receptor 4 (TLR4) or leukocyte cytokine IFN-γ induces reactive phenotypes in microglia associated with morphological changes, population expansion, CD11b and CD68 up-regulation, and proinflammatory cytokine (IL-1β, TNF-α, IL-6) and nitric oxide (NO) release. Notably, these reactive phenotypes only moderately alter intrinsic neuronal excitability and gamma oscillations (30-100 Hz), which emerge from precise synaptic communication of glutamatergic pyramidal cells and fast-spiking, parvalbumin-positive GABAergic interneurons, in local hippocampal networks. Short-term synaptic plasticity and extracellular potassium homeostasis during neural excitation, also reflecting astrocyte function, are unaffected. In contrast, the coactivation of TLR4 and IFN-γ receptors results in neuronal dysfunction and death, caused mainly by enhanced microglial inducible nitric oxide synthase (iNOS) expression and NO release, because iNOS inhibition is neuroprotective. Thus, activation of TLR4 in microglia in situ requires concomitant IFN-γ receptor signaling from peripheral immune cells, such as T helper type 1 and natural killer cells, to unleash neurotoxicity and inflammation-induced neurodegeneration. Our findings provide crucial mechanistic insight into the complex process of microglia activation, with relevance to several neurologic and psychiatric disorders.

Methionine sulfoxide reductase A negatively controls microglia-mediated neuroinflammation via inhibiting ROS/MAPKs/NF-κB signaling pathways through a catalytic antioxidant function

AIMS

Oxidative burst is one of the earliest biochemical events in the inflammatory activation of microglia. Here, we investigated the potential role of methionine sulfoxide reductase A (MsrA), a key antioxidant enzyme, in the control of microglia-mediated neuroinflammation.

RESULTS

MsrA was detected in rat microglia and its expression was upregulated on microglial activation. Silencing of MsrA exacerbated lipopolysaccharide (LPS)-induced activation of microglia and the production of inflammatory markers, indicating that MsrA may function as an endogenous protective mechanism for limiting uncontrolled neuroinflammation. Application of exogenous MsrA by transducing Tat-rMsrA fusion protein into microglia attenuated LPS-induced neuroinflammatory events, which was indicated by an increased Iba1 (a specific microglial marker) expression and the secretion of pro-inflammatory cytokines, and this attenuation was accompanied by inhibiting multiple signaling pathways such as p38 and ERK mitogen-activated protein kinases (MAPKs) and nuclear factor kappaB (NF-κB). These effects were due to MsrA-mediated reactive oxygen species (ROS) elimination, which may be derived from a catalytic effect of MsrA on the reaction of methionine with ROS. Furthermore, the transduction of Tat-rMsrA fusion protein suppressed the activation of microglia and the expression of pro-inflammatory factors in a rat model of neuroinflammation in vivo.

INNOVATION

This study provides the first direct evidence for the biological significance of MsrA in microglia-mediated neuroinflammation.

CONCLUSION

Our data provide a profound insight into the role of endogenous antioxidative defense systems such as MsrA in the control of microglial function.

Neuroinflammation induced by intracerebroventricular injection of microbial neuraminidase

In the present paper, we describe the facts that took place in the rat brain after a single injection of the enzyme neuraminidase from Clostridium perfringens into the right lateral ventricle. After injection, it diffused through the cerebrospinal fluid of the ipsilateral ventricle and the third ventricle, and about 400 μm into the periventricular brain parenchyma. The expression of ICAM1 in the endothelial cells of the periventricular vessels, IBA1 in microglia, and GFAP in astrocytes notably increased in the regions reached by the injected neuraminidase. The subependymal microglia and the ventricular macrophages begun to express IL1β and some appeared to cross the ependymal layer. After about 4 h of the injection, leukocytes migrated from large venules of the affected choroid plexus, the meninges and the local subependyma, and infiltrated the brain. The invading cells arrived orderly: first neutrophils, then macrophage-monocytes, and last CD8α-positive T-lymphocytes and B-lymphocytes. Leukocytes in the ventricles and the perivascular zones penetrated the brain parenchyma passing through the ependyma and the glia limitans. Thus, it is likely that a great part of the damage produced by microorganism invading the brain may be due to their neuraminidase content.

The role of interleukin-1β in the pentylenetetrazole-induced kindling of seizures, in the rat hippocampus

Because the contribution of inflammatory mediators to seizure disorders is unclear, we investigated the changes in the expression of interleukin-1β (IL-β) and its receptor - IL-1 receptor type 1 (IL-1R1), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the rat hippocampus at different stages of pentylenetetrazole (PTZ)-induced kindling. The occurrence and progressive development of seizures were induced by repeated systemic administration of PTZ, a non-competitive antagonist of the γ-aminobutyric acid type A (GABAA) receptor at a subconvulsive dose of 30 mg/kg. We also examined the effects of continuous intracerebroventricular administration of IL-1β and lipopolysaccharide (LPS) in this model of epilepsy using subcutaneously implanted osmotic mini-pumps. We observed enhanced IL-1R1 expression in the dentate gyrus (DG) at different stages of kindling, whereas the elevated IL-1β level was distinctive to fully kindled seizures. We did not detect significant changes in the concentration of IL-6 or TNF-α throughout the kindling process. LPS accelerated transiently the process of kindling, while IL-1β showed a predisposition to delay kindling acquisition. Our study supports the concept of seizure-related modifications in brain cytokine production during epileptogenesis. Although some evidence indicates a proconvulsant property of IL-1β activity, it cannot be ruled out that the alterations in IL-1 system reflect the activation of endogenous protective mechanisms with respect to the kindling of seizures.

Attenuated mRNA expression of inflammatory mediators in neonatal rat lung following lipopolysaccharide treatment

Neonates are known to exhibit increased susceptibility to bacterial and viral infections and increasing evidence demonstrates that the increased susceptibility is related to their attenuated immune response to infections. The lung is equipped with an innate defense system involving both cellular and humoral mediators. The present study was performed to characterize the expression of inflammatory mediators in the lung of neonatal rats in comparison with older animals. Rats at postnatal day 1 (P1), P21, and P70 were treated with saline or 0.25 mg/kg lipopolysaccharide (LPS) via intraperitoneal injection. Two hours later, animals were sacrificed and the transcriptional response of key inflammatory mediators and enzyme activity of myeloperoxidase (MPO) in the lung of these animals were examined. LPS-induced messenger RNA (mRNA) expression of pro-inflammatory cytokines, namely interleukin (IL)-1β, IL-6, and tumor necrosis factor-α, antiinflammatory cytokines, namely IL-10 and IL-1 receptor antagonist (IL-1ra), and chemokines, namely macrophage inflammatory protein (MIP)-1β, MIP-2, and monocyte chemotactic protein-1, in P1 lung was much reduced compared to that in P21 and P70 animals at 2 hours postinjection. These data suggest that LPS-induced transcriptional response of cytokines and chemokines was much reduced in P1 lung even though the protein levels of these genes were not ascertained and mRNA levels of these genes may not reflect their final protein levels. MPO activity in LPS-treated P1 lung was also significantly attenuated compared to that in LPS-treated P70 lung, suggesting impaired neutrophil infiltration in P1 lung at 2 hours following LPS treatment. In parallel, the baseline mRNA expression of LPS-binding protein (LBP) in P1 lung was much lower than that in P21 and P70 lungs. While the protein level of LBP was not examined and the mRNA level of LBP may not reflect its final protein level, the reduced transcriptional response of cytokines and chemokines in P1 lung at 2 hours following LPS treatment may be attributed to lower LBP expression in P1 lung as compared to P21 and P70 lungs.

Upregulation of connexins 30 and 32 gap junctions in rat hippocampus at transcription level by chronic central injection of lipopolysaccharide

BACKGROUND

Gap junctions composed of connexins (Cx) are functional in cell defense by propagation of toxic/death molecules to neighboring cells. Hippocampus, one of the brain regions with particular vulnerability to damage, has a wide network of gap junctions. Functional response of astrocytic Cx30 and neuronal Cx32 to hippocampal damage is unknown.

METHODS

We infused lipopolysaccharide (LPS) intracerebroventricularly (2.5 mug/rat) once daily for two weeks to create neuroinflammation. The mRNA and protein levels of the Cx were measured in the hippocampus after 1st, 7th and 14th injection by real-time PCR and Western-blot techniques.

RESULTS

A significant increase in Cx32 and Cx30 gene expression was observed after 7th and 14th injection of LPS with no significant change in their protein abundance.

CONCLUSION

Transcriptional overexpression of hippocampal Cx30 and Cx32 could be an adaptive response to production of intracellular toxic molecules but it is not accompanied with post- transcriptional overexpression and might have no functional impact.

Effect of chronic intracerebroventricluar administration of lipopolysaccharide on connexin43 protein expression in rat hippocampus

BACKGROUND

Hippocampal damages, which are accompanied by inflammation, are among the main causes of epilepsy acquisition. We previously reported that chronic intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS) modulates epileptogenesis in rats. There is a network of gap junction channels in the hippocampus that contribute to epileptogenesis. Gap junction channels are formed by oligomeric protein subunits called connexins (Cx). Astrocytic Cx43 and neuronal Cx36 are expressed in the hippocampus. In order to find out the possible role of gap junctions in seizure-modulating effect of LPS and neuroinflammation, we studied the effect of central administration of LPS on expression of Cx36 and Cx43 in rat hippocampus.

METHODS

LPS, 2.5 mug/rat/day, was injected i.c.v. to male Wistar rats for 14 days. mRNA and protein abundance of Cx36, Cx43 and IL1-β were measured in rat hippocampus by real time-PCR, Western blot and ELISA techniques, at the beginning, in the middle, and at the end of the treatment period.

RESULTS

IL1-β protein level was significantly increased 6 h after first injection of LPS. Cx36 and Cx43 mRNA expression did not alter during chronic administration of LPS. A selective decrease in Cx43 protein expression was observed after 7 injections of LPS.

CONCLUSION

It is suggested that Cx43 containing gap junctions in the hippocampus is down-regulated in response to chronic injection of LPS. This event can inhibit propagation of toxic and noxious molecules to neighboring cells and modulate hippocampal excitability and epileptogenesis.

The dual role of the neuroinflammatory response after ischemic stroke: modulatory effects of hypothermia

Neuroinflammation is a key element in the ischemic cascade after cerebral ischemia that results in cell damage and death in the subacute phase. However, anti-inflammatory drugs do not improve outcome in clinical settings suggesting that the neuroinflammatory response after an ischemic stroke is not entirely detrimental. This review describes the different key players in neuroinflammation and their possible detrimental and protective effects in stroke. Because of its inhibitory influence on several pathways of the ischemic cascade, hypothermia has been introduced as a promising neuroprotective strategy. This review also discusses the influence of hypothermia on the neuroinflammatory response. We conclude that hypothermia exerts both stimulating and inhibiting effects on different aspects of neuroinflammation and hypothesize that these effects are key to neuroprotection.

Attenuation of astrogliosis and modulation of endothelial growth factor receptor in lipid rafts by simvastatin after traumatic brain injury

OBJECT

The authors' previous studies have demonstrated that simvastatin treatment promotes neuronal survival and reduces inflammatory cytokine release from astrocytes after traumatic brain injury (TBI) in rats. Since reactive astrocytes produce inflammation mediators, in the current study the authors investigated the effect of simvastatin on astrocyte activation after TBI and its underlying signaling mechanisms.

METHODS

Saline or simvastatin (1 mg/kg) was orally administered to rats starting at Day 1 after TBI and then daily for 14 days. Rats were killed at 1, 3, 7, and 14 days after treatment. Brain sections and tissues were prepared for immunohistochemical staining and Western blot analysis, respectively. Cultured astrocytes were subjected to oxygen-glucose deprivation (OGD) and followed by immunocytochemical staining with glial fibrillary acidic protein/caveolin-1 and Western blot analysis. Lipid rafts were isolated from the cell lysate and Western blotting was carried out to detect the changes in epidermal growth factor receptor (EGFR) expression and phosphorylation in the lipid rafts.

RESULTS

Simvastatin significantly promoted neuronal survival after TBI and attenuated activation of astrocytes. Simvastatin modified the caveolin-1 expression in lipid rafts in astrocyte cell membrane, suppressed the phosphorylation of EGFR in lipid rafts of astrocytes after OGD, and inhibited the OGD-induced interleukin-1 production.

CONCLUSIONS

These data suggest that simvastatin reduces reactive astrogliosis and rescues neuronal cells after TBI. These beneficial effects of simvastatin may be mediated by inhibiting astrocyte activation after TBI through modifying the caveolin-1 expression in lipid rafts and the subsequent modulation of EGFR phosphorylation in lipid rafts.

The acute phase response and soman-induced status epilepticus: temporal, regional and cellular changes in rat brain cytokine concentrations

Background

Neuroinflammation occurs following brain injury, including soman (GD) induced status epilepticus (SE), and may contribute to loss of neural tissue and declined behavioral function. However, little is known about this important pathological process following GD exposure. Limited transcriptional information on a small number of brain-expressed inflammatory mediators has been shown following GD-induced SE and even less information on protein upregulation has been elucidated. The purpose of this study is to further characterize the regional and temporal progression of the neuroinflammatory process following acute GD-induced SE.

Methods

The protein levels of 10 cytokines was quantified using bead multiplex immunoassays in damaged brain regions (i.e., piriform cortex, hippocampus and thalamus) up to 72 hours following seizure onset. Those factors showing significant changes were then localized to neural cells using fluorescent IHC.

Results

A significant concentration increase was observed in all injured brain regions for four acute phase response (APR) induction cytokines: interleukin (IL)-1α, IL-1β, IL-6, and tumor necrosis factor (TNF)-α. Increases in these APR cytokines corresponded both temporally and regionally to areas of known seizure damage and neuronal death. Neurotoxic cytokines IL-1α and IL-1β were primarily expressed by activated microglia whereas the potentially neuroprotective cytokine IL-6 was expressed by neurons and hypertrophic astrocytes.

Conclusions

Increases in neurotoxic cytokines likely play an active role in the progression of GD-induced SE neuropathology though the exact role that these and other cytokines play in this process require further study.

Lipopolysaccharide produces dose-dependent reductions of the acoustic startle response without impairing prepulse inhibition in male rats

This study examined the dose-dependent effects of Lipopolysaccharide (LPS) on the acoustic startle response and prepulse inhibition (PPI) in male Long-Evans rats. LPS is known to stimulate the innate immune system and result in behavior modifications referred to as "sickness behaviors". The purpose of this study was to assess the ability of LPS to modulate sensorimotor reflexes (Startle-Only trials) and/or sensory processing (PPI trials). Rats were injected intraperitoneally with LPS (50, 100 or 200 microg/kg LPS, n=9/group) or saline vehicle (n=14) on 2 test days 72 h apart. Subjects were placed in a familiar startle box apparatus where startle response magnitudes were recorded following 115 dB Startle-Only trials and PPI trials (with prepulses at +3, +6 and +12 dB above background noise). Analysis of Startle-Only trials indicated a significant dose-dependent effect of LPS on Test Day 1. The 200 microg/kg LPS group exhibited significantly reduced startle response magnitude relative to all other treatments. On the PPI trials no LPS groups displayed significantly different performance from vehicle controls. Also, DayxDrug interactions for both Startle-Only and PPI trial types indicated behavioral tolerance to LPS. LPS reduced the acoustic startle response in a dose-dependent manner on Test Day 1. From the PPI data, it is evident that all treatment groups elicited near-normal inhibition levels indicating adequate sensory function. In combination, the results suggest that the range of sickness behaviors following LPS-administration to adult rats includes decreased non-voluntary motor activity as reflected by reduced startle magnitude.

Triptolide inhibits COX-2 expression via NF-kappa B pathway in astrocytes

Previous investigations have showed that triptolide possessed potent anti-inflammatory and immunosuppressive properties. In the present study, we examined the protective effects of triptolide on the inflammatory response induced by bacterial lipopolysaccharide (LPS) both in vivo and in vitro. Intrahippocampal injection of LPS (4 microg) in rats significantly increased the immunoreactivity of glial fibrillary acid protein (GFAP) and cyclooxygenase-2 (COX-2) in the injected region, which was reduced by pretreatment with triptolide (10-50 microg/kg) for 5d. In the cultured human differentiated A172 astroglial cells, LPS (1mg/L) increased the expression of COX-2 mRNA and protein, the production of prostaglandin E(2) (PGE(2)) and the DNA binding activity of NF-kappa B, which were markedly attenuated by pretreatment with triptolide (0.2-5 microg/L) for 1h. These results suggested that the protective effect of triptolide on neuroinflammation is mediated by decreasing COX-2 expression, at least partly, via the inhibition of NF-kappa B signaling pathway.

Chemokines regulate the migration of neural progenitors to sites of neuroinflammation

Many studies have shown that transplanted or endogenous neural progenitor cells will migrate toward damaged areas of the brain. However, the mechanism underlying this effect is not clear. Here we report that, using hippocampal slice cultures, grafted neural progenitor cells (NPs) migrate toward areas of neuroinflammation and that chemokines are a major regulator of this process. Migration of NPs was observed after injecting an inflammatory stimulus into the area of the fimbria and transplanting enhanced green fluorescent protein (EGFP)-labeled NPs into the dentate gyrus of cultured hippocampal slices. Three to 7 d after transplantation, EGFP-NPs in control slices showed little tendency to migrate and had differentiated into neurons and glia. In contrast, in slices injected with inflammatory stimuli, EGFP-NPs migrated toward the site of the injection. NPs in these slices also survived less well. The inflammatory stimuli used were a combination of the cytokines tumor necrosis factor-alpha and interferon-gamma, the bacterial toxin lipopolysaccharide, the human immunodeficiency virus-1 coat protein glycoprotein 120, or a beta-amyloid-expressing adenovirus. We showed that these inflammatory stimuli increased the synthesis of numerous chemokines and cytokines by hippocampal slices. When EGFP-NPs from CC chemokine receptor CCR2 knock-out mice were transplanted into slices, they exhibited little migration toward sites of inflammation. Similarly, wild-type EGFP-NPs exhibited little migration toward inflammatory sites when transplanted into slices prepared from monocyte chemoattractant protein-1 (MCP-1) knock-out mice. These data indicate that factors secreted by sites of neuroinflammation are attractive to neural progenitors and suggest that chemokines such as MCP-1 play an important role in this process.

Selective inhibition of inducible nitric oxide synthase reduces neurological deficit but not cerebral edema following traumatic brain injury

The role of inducible nitric oxide synthase (iNOS) in cerebral edema and neurological deficit following traumatic brain injury (TBI) is not yet clear-cut. Therefore, the aim of this study was to investigate the effect of three different iNOS inhibitors on cerebral edema and functional outcome after TBI. First, the time courses of blood--brain barrier (BBB) breakdown, cerebral edema, and neurological deficit were studied in a rat model of fluid percussion-induced TBI. The permeability of BBB to Evans blue was increased from 1 h to 24 h after TBI. Consistently, a significant increase in brain water content (BWC) was observed at 6 and 24 h post-TBI. A deficit in sensorimotor neurological functions was also observed from 6 h to 7 days with a maximum 24 h after TBI. Second, a single dose of aminoguanidine (AG; 100 mg/kg, i.p.), L-N-iminoethyl-lysine (L-NIL; 20 mg/kg, i.p.), or N-[3-(aminomethyl)benzyl]acetamide (1400W; 20 mg/kg, s.c.) was administered at 6 h post-TBI. Treatment with AG reduced by 71% the increase in BWC evaluated at 24 h, while L-NIL and 1400W had no effect. In contrast, the three iNOS inhibitors reduced the neurological deficit from 30% to 40%. Third, 1400W (20 mg/kg, s.c.) was administered at 5 min, 8 and 16 h post-TBI. Although this treatment paradigm had no effect on cerebral edema evaluated at 24 h, it significantly reduced the neurological deficit and iNOS activity. In conclusion, iNOS contributes to post-TBI neurological deficit but not to cerebral edema. The beneficial effect of iNOS inhibitors is not due to their anti-edematous effect, and the reduction of cerebral edema by AG is unlikely related to iNOS inhibition. The 6 h therapeutic window of iNOS inhibitors could allow their use in the treatment of functional deficit at the acute phase of TBI.

Endothelial influences on cerebrovascular tone

The cerebrovascular endothelium exerts a profound influence on cerebral vessels and cerebral blood flow. This review summarizes current knowledge of various dilator and constrictor mechanisms intrinsic to the cerebrovascular endothelium. The endothelium contributes to the resting tone of cerebral arteries and arterioles by tonically releasing nitric oxide (NO•). Dilations can occur by stimulated release of NO•, endothelium-derived hyperpolarization factor, or prostanoids. During pathological conditions, the dilator influence of the endothelium can turn to that of constriction by a variety of mechanisms, including decreased NO• bioavailability and release of endothelin-1. The endothelium may participate in neurovascular coupling by conducting local dilations to upstream arteries. Further study of the cerebrovascular endothelium is critical for understanding the pathogenesis of a number of pathological conditions, including stroke, traumatic brain injury, and subarachnoid hemorrhage.