The neuron-astrocyte-microglia triad in normal brain ageing and in a model of neuroinflammation in the rat hippocampus

An improved method for growing neurons: Comparison with standard protocols

BACKGROUND

Since different culturing parameters - such as media composition or cell density - lead to different experimental results, it is important to define the protocol used for neuronal cultures. The vital role of astrocytes in maintaining homeostasis of neurons - both in vivo and in vitro - is well established: the majority of improved culturing conditions for primary dissociated neuronal cultures rely on astrocytes.

NEW METHOD

Our culturing protocol is based on a novel serum-free preparation of astrocyte - conditioned medium (ACM). We compared the proposed ACM culturing method with other two commonly used methods Neurobasal/B27- and FBS- based media. We performed morphometric characterization by immunocytochemistry and functional analysis by calcium imaging for all three culture methods at 1, 7, 14 and 60days in vitro (DIV).

RESULTS

ACM-based cultures gave the best results for all tested criteria, i.e. growth cone's size and shape, neuronal outgrowth and branching, network activity and synchronization, maturation and long-term survival. The differences were more pronounced when compared with FBS-based medium. Neurobasal/B27 cultures were comparable to ACM for young cultures (DIV1), but not for culturing times longer than DIV7.

COMPARISON WITH EXISTING METHOD(S)

ACM-based cultures showed more robust neuronal outgrowth at DIV1. At DIV7 and 60, the activity of neuronal network grown in ACM had a more vigorous spontaneous electrical activity and a higher degree of synchronization.

CONCLUSIONS

We propose our ACM-based culture protocol as an improved and more suitable method for both short- and long-term neuronal cultures.

Age-associated physiological and pathological changes at the blood-brain barrier: A review

The age-associated decline of the neurological and cognitive functions becomes more and more serious challenge for the developed countries with the increasing number of aged populations. The morphological and biochemical changes in the aging brain are the subjects of many extended research projects worldwide for a long time. However, the crucial role of the blood-brain barrier (BBB) impairment and disruption in the pathological processes in age-associated neurodegenerative disorders received special attention just for a few years. This article gives an overview on the major elements of the blood-brain barrier and its supporting mechanisms and also on their alterations during development, physiological aging process and age-associated neurodegenerative disorders (Alzheimer's disease, multiple sclerosis, Parkinson's disease, pharmacoresistant epilepsy). Besides the morphological alterations of the cellular elements (endothelial cells, astrocytes, pericytes, microglia, neuronal elements) of the BBB and neurovascular unit, the changes of the barrier at molecular level (tight junction proteins, adheres junction proteins, membrane transporters, basal lamina, extracellular matrix) are also summarized. The recognition of new players and initiators of the process of neurodegeneration at the level of the BBB may offer new avenues for novel therapeutic approaches for the treatment of numerous chronic neurodegenerative disorders currently without effective medication.

Diet-induced cellular neuroinflammation in the hypothalamus: Mechanistic insights from investigation of neurons and microglia

Diet-induced obesity can lead to detrimental chronic disorders. The severity of this global epidemic has encouraged ongoing research to characterize the mechanisms underlying obesity and its comorbidities. Recent evidence suggests that saturated fatty acids (SFA) in high-fat diets rapidly generate inflammation in the arcuate nucleus of the hypothalamus (ARC), which centrally regulates whole-body energy homeostasis. Herein, we will review the roles of hypothalamic neurons and resident microglia in the initiation of SFA-induced hypothalamic inflammation. Particularly, we focus on neuronal and microglial free fatty acid-sensing and capacity to produce inflammatory signaling. We also outline a potential role of peripherally-derived monocytes in this inflammation. And finally, we explore synaptic plasticity as a mechanism through which hypothalamic inflammation can modulate ARC circuitry, and thus disrupt energy homeostasis.

Inflammatory Response in the CNS: Friend or Foe?

Inflammatory reactions could be both beneficial and detrimental to the brain, depending on strengths of their activation in various stages of neurodegeneration. Mild activation of microglia and astrocytes usually reveals neuroprotective effects and ameliorates early symptoms of neurodegeneration; for instance, released cytokines help maintain synaptic plasticity and modulate neuronal excitability, and stimulated toll-like receptors (TLRs) promote neurogenesis and neurite outgrowth. However, strong activation of glial cells gives rise to cytokine overexpression/dysregulation, which accelerates neurodegeneration. Altered mutual regulation of p53 protein, a major tumor suppressor, and NF-κB, the major regulator of inflammation, seems to be crucial for the shift from beneficial to detrimental effects of neuroinflammatory reactions in neurodegeneration. Therapeutic intervention in the p53-NF-κB axis and modulation of TLR activity are future challenges to cope with neurodegeneration.

Effect of acrylamide-induced neurotoxicity in a primary astrocytes/microglial co-culture model

Acrylamide (AA), is a common food contaminant generated by heat processing. Astrocytes and microglia are the two major glial cell types in the brain that play pivotal but different roles in maintaining optimal brain function. The objective of this study is to investigate the neurotoxicity of AA, using a primary astrocytes/microglia co-culture model. Co-cultural cells obtained from Balb/c mice were cultured and treated with 0-1.0mM AA for 24-96h. Cell viability, reactive oxygen species (ROS) generation, oxidative end produces formation and glutathione (GSH) levels were measured. The expression of nuclear-E2-related factor 2(Nrf2), and nuclear factor kappa-beta (NF-κB) and selected down-stream genes were measured. Results showed that AA treatment led toa dose-dependent toxicity. Oxidative stress was induced as indicated by an increase of ROS, a decrease of GSH levels, and an increase in the formation of 4-hydroxynonenal-adduct and 8-hydroxy-2-deoxyguanosine-adduct. Both Nrf2 and NF-κB pathway contributed to the initiation of oxidative stress but the timing of two factors was different. Nrf2 and its related downstream genes were activated earlier than that in NF-κB pathway. In conclusion, AA-induced neurotoxicity attribute to oxidative stress via Nrf2 and NF-κB pathway. Moreover, the co-culture cell model was proven to be a viable model to study AA neurotoxicity.

Acute neuroinflammation provokes intracellular acidification in mouse hippocampus

Background

Maintaining pH levels within the physiological norm is an important component of brain homeostasis. However, in some pathological or physiological conditions, the capacity of the pH regulatory system could be overpowered by various factors resulting in a transient or permanent alteration in pH levels. Such changes are often observed in pathological conditions associated with neuroinflammation. We hypothesized that neuroinflammation itself is a factor affecting pH levels in neural tissue. To assess this hypothesis, we examined the effects of acute LPS-induced neuroinflammation on intra- and extracellular pH (pHi and pHo) levels in the CA1 region of mouse hippocampus.

Methods

Acute neuroinflammation was induced using two approaches: (1) in vivo by i.p. injections of LPS (5 mg/kg) and (2) in vitro by incubating hippocampal slices of naïve animals in the LPS-containing media (1 μg/mL, 1 h at 35 °C). Standard techniques were used to prepare hippocampal slices. pHi was measured using ratiometric pH-sensitive fluorescent dye BCECF-AM. pHo was assessed using calibrated pH-sensitive micropipettes. The presence of neuroinflammation was verified with immunohistochemistry (IL-1β and Iba1) and ELISA (IL-1β and TNF-α).

Results

A significant reduction of pHi was observed in the slices of the LPS-injected 3-month-old (LPS 7.13 ± 0.03; Sal 7.22 ± 0.03; p = 0.043, r = 0.43) and 19-month-old (LPS 6.78 ± 0.08; Sal 7.13 ± 0.03; p = 0.0001, r = 0.32) mice. In contrast, the levels of pHo within the slice, measured in 19-month-old animals, were not affected (LPS 7.27 ± 0.02; Sal 7.26 ± 0.02; p = 0.6, r = 0.13). A reduction of pHi was also observed in the LPS-treated slices during the interval 3.5–7 h after the LPS exposure (LPS 6.92 ± 0.07; Veh 7.28 ± 0.05; p = 0.0001, r = 0.46).

Conclusions

Acute LPS-induced neuroinflammation results in a significant intracellular acidification of the CA1 neurons in mouse hippocampus, while the pHo remains largely unchanged. Such changes may represent a specific protective reaction of neural tissue in unfavorable external conditions or be a part of the pathological process.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0747-8) contains supplementary material, which is available to authorized users.

Maternal inflammation leads to impaired glutamate homeostasis and up-regulation of glutamate carboxypeptidase II in activated microglia in the fetal/newborn rabbit brain

Astrocyte dysfunction and excessive activation of glutamatergic systems have been implicated in a number of neurologic disorders, including periventricular leukomalacia (PVL) and cerebral palsy (CP). However, the role of chorioamnionitis on glutamate homeostasis in the fetal and neonatal brains is not clearly understood. We have previously shown that intrauterine endotoxin administration results in intense microglial 'activation' and increased pro-inflammatory cytokines in the periventricular region (PVR) of the neonatal rabbit brain. In this study, we assessed the effect of maternal inflammation on key components of the glutamate pathway and its relationship to astrocyte and microglial activation in the fetal and neonatal New Zealand white rabbit brain. We found that intrauterine endotoxin exposure at gestational day 28 (G28) induced acute and prolonged glutamate elevation in the PVR of fetal (G29, 1day post-injury) and postnatal day 1 (PND1, 3days post-injury) brains along with prominent morphological changes in the astrocytes (soma hypertrophy and retracted processes) in the white matter tracts. There was a significant increase in glutaminase and N-Methyl-d-Aspartate receptor (NMDAR) NR2 subunit expression along with decreased glial L-glutamate transporter 1 (GLT-1) in the PVR at G29, that would promote acute dysregulation of glutamate homeostasis. This was accompanied with significantly decreased TGF-β1 at PND1 in CP kits indicating ongoing neuroinflammation. We also show for the first time that glutamate carboxypeptidase II (GCPII) was significantly increased in the activated microglia at the periventricular white matter area in both G29 and PND1 CP kits. This was confirmed by in vitro studies demonstrating that LPS activated primary microglia markedly upregulate GCPII enzymatic activity. These results suggest that maternal intrauterine endotoxin exposure results in early onset and long-lasting dysregulation of glutamate homeostasis, which may be mediated by impaired astrocyte function and GCPII upregulation in activated microglia.

The neuron-astrocyte-microglia triad involvement in neuroinflammaging mechanisms in the CA3 hippocampus of memory-impaired aged rats

We examined the effects of inflammaging on memory encoding, and qualitative and quantitative modifications on proinflammatory proteins, apoptosis, neurodegeneration and morphological changes of neuron-astrocyte-microglia triads in CA3 Stratum Pyramidale (SP), Stratum Lucidum (SL) and Stratum Radiatum (SR) of young (3months) and aged rats (20months). Aged rats showed short-term memory impairments in the inhibitory avoidance task, increased expression of iNOS and activation of p38MAPK in SP, increase of apoptotic neurons in SP and of ectopic neurons in SL, and decrease of CA3 pyramidal neurons. The number of astrocytes and their branches length decreased in the three CA3 subregions of aged rats, with morphological signs of clasmatodendrosis. Total and activated microglia increased in the three CA3 subregions of aged rats. In aged rats CA3, astrocytes surrounded ectopic degenerating neurons forming "micro scars" around them. Astrocyte branches infiltrated the neuronal cell body, and, together with activated microglia formed "triads". In the triads, significantly more numerous in CA3 SL and SR of aged rats, astrocytes and microglia cooperated in fragmentation and phagocytosis of ectopic neurons. Inflammaging-induced modifications of astrocytes and microglia in CA3 of aged rats may help clearing neuronal debris derived from low-grade inflammation and apoptosis. These events might be common mechanisms underlying many neurodegenerative processes. The frequency to which they appear might depend upon, or might be the cause of, the burden and severity of neurodegeneration. Targeting the triads may represent a therapeutic strategy which may control inflammatory processes and spread of further cellular damage to neighboring cells.

Purinergic P2Y1 Receptors Control Rapid Expression of Plasma Membrane Processes in Hippocampal Astrocytes

Astrocytes regulate neuronal activity and blood brain barrier through tiny plasma membrane branches or astrocytic processes (APs) making contact with synapses and brain vessels. Several transmitters released by astrocytes and exerting their action on several receptor classes expressed by astrocytes themselves influence their physiology. Here we found that APs are dynamically modulated by purines. In live imaging experiments carried out in rat hippocampal astrocytes, Gq-coupled P2Y1 receptor blockade with the selective antagonist MRS2179 (1 μM) or inhibition of its effector phospholipase C using U73122 (3 μM) produced APs retraction, while stimulation of the same receptor with the selective agonist 2MeSADP (100 μM) increased their number. Since astrocytes, among other transmitters, release ATP by several mechanisms including connexin hemichannels, we used the connexin hemichannel inhibitor carbenoxolone (100 μM) and APs retraction was observed. In our system we then measured expression or function of channels important for modulation of volume transmission and K+ buffering, aquaporin-4, and K+ inward rectifying (Kir) channels, respectively. Aquaporin-4 expression level did not change whereas, in whole-cell patch-clamp recordings performed to measure Kir current, we observed an increase in K+ current in all conditions where APs number was reduced. These data are supporting the idea of a dynamic modulation of astrocytic processes by purinergic signal, strengthening the role of purines in brain homeostasis.

Microglial activation during epileptogenesis in a mouse model of tuberous sclerosis complex

OBJECTIVE

Tuberous sclerosis complex (TSC) is a genetic disorder, characterized by tumor formation in multiple organs and severe neurologic manifestations, including epilepsy, intellectual disability, and autism. Abnormalities of both neurons and astrocytes have been implicated in contributing to the neurologic phenotype of TSC, but the role of microglia in TSC has not been investigated. The objectives of this study were to characterize microglial activation in a mouse model of TSC, involving conditional inactivation of the Tsc1 gene predominantly in glial cells (Tsc1(GFAP) CKO mice), and to test the hypothesis that microglial activation contributes to epileptogenesis in this mouse model.

METHODS

Microglial and astrocyte activation was examined in Tsc1(GFAP) CKO mice by ionized calcium binding adaptor molecule 1 and glial fibrillary acidic protein immunohistochemistry. Cytokine and chemokine expression was evaluated with quantitative polymerase chain reaction. Seizures were monitored by video-electroencephalography (EEG). The effect of minocycline in inhibiting microglial and astrocyte activation, cytokine expression, and seizures was tested.

RESULTS

Microglial cell number and size were increased in cortex and hippocampus of 3- to 4-week-old Tsc1(GFAP) CKO mice, which correlated with the onset of seizures. Minocycline treatment prevented the increase in number and cell size of microglia in 4-week-old Tsc1(GFAP) CKO mice. However, minocycline treatment had no effect on astrocyte proliferation and cytokine/chemokine expression and the progression of seizures in Tsc1(GFAP) CKO mice.

SIGNIFICANCE

Microglia cell number and size are abnormal in Tsc1(GFAP) CKO mice, and minocycline treatment inhibits this microglia activation, but does not suppress seizures. Microglia may play a role in the neurologic manifestations of TSC, but additional studies are needed in other models and human studies to determine whether microglia are critical for epileptogenesis in TSC.

Anti-inflammatory Function of Phyllostachys Edulis Extract in the Hippocampus of HIV-1 Transgenic Rats

HIV induces neuroinflammation. We evaluated the anti-inflammatory effect of an extract from bamboo Phyllostachys edulis in the hippocampus of HIV-1 transgenic (TG) rats. Five (5) one-month-old TG rats and 5 Fisher 344 (F344) rats were fed a control diet, another 5 TG rats were fed the control diet supplemented with bamboo extract (BEX, 11 grams dry mass per 4057 Kcal). After 9 months of dietary treatment, the gene and protein expression of interleukin 1 beta (IL-1β), glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba1), and the protein expression p65 and c-Jun were analyzed in the hippocampus. Compared to the F344 rats, the TG rats fed control diet showed significantly higher protein expression of GFAP and c-Jun, and mRNA and protein levels of IL-1β. BEX supplement to the TG rats significantly lowered protein expressions of GFAP, p65, and c-Jun, and showed a trend to decrease the protein expression of IL-1β. Compared to the TG rats, TG+BEX rats also downregulated the mRNA levels of IL-1β and TNFα. In summary, neuroinflammation mediated by the NFκB and AP-1 pathways in the hippocampus of the TG rats was effectively abolished by dietary supplement of BEX.

Clasmatodendrosis and β-amyloidosis in aging hippocampus

Alterations of the tightly interwoven neuron/astrocyte interactions are frequent traits of aging, but also favor neurodegenerative diseases, such as Alzheimer disease (AD). These alterations reflect impairments of the innate responses to inflammation-related processes, such as β-amyloid (Aβ) burdening. Multidisciplinary studies, spanning from the tissue to the molecular level, are needed to assess how neuron/astrocyte interactions are influenced by aging. Our study addressed this requirement by joining fluorescence-lifetime imaging microscopy/phasor multiphoton analysis with confocal microscopy, implemented with a novel method to separate spectrally overlapped immunofluorescence and Aβ autofluorescence. By comparing data from young control rats, chronically inflamed rats, and old rats, we identified age-specific alterations of neuron/astrocyte interactions in the hippocampus. We found a correlation between Aβ aggregation (+300 and +800% of aggregated Aβ peptide in chronically inflamed and oldvs.control rats, respectively) and fragmentation (clasmatodendrosis) of astrocyte projections (APJs) (+250 and +1300% of APJ fragments in chronically inflamed and oldvs.control rats, respectively). Clasmatodendrosis, in aged rats, associates with impairment of astrocyte-mediated Aβ clearance (-45% of Aβ deposits on APJs, and +33% of Aβ deposits on neurons in oldvs.chronically inflamed rats). Furthermore, APJ fragments colocalize with Aβ deposits and are involved in novel Aβ-mediated adhesions between neurons. These data define the effects of Aβ deposition on astrocyte/neuron interactions as a key topic in AD biology.-Mercatelli, R., Lana, D., Bucciantini, M., Giovannini, M. G., Cerbai, F., Quercioli, F., Zecchi-Orlandini, S., Delfino, G., Wenk, G. L., Nos, D. Clasmatodendrosis and β-amyloidosis in aging hippocampus.

Characteristic Changes of Astrocyte and Microglia in Rat Striatum Induced by 3-NP and MCAO

Our previous studies had confirmed that both 3-NP and MCAO induced the behavioral defect as well as striatal neuronal injury and loss in experimental rats. This study aimed to examine different response forms of striatal astrocyte and microglia in 3-NP and MCAO rat models. The present results showed that the immunoreaction for GFAP was extremely weak in the lesioned core of striatum, but in the transition zone of 3-NP model and the penumbra zone of MCAO model, GFAP+ cells showed strong hypertrophic and proliferative changes. Statistical analysis for the number, size and integral optical density (IOD) of GFAP+ cells showed significant differences when compared with their controls and compared between the core and the transition zone or the penumbra zone, respectively, but no differences between the 3-NP and MCAO groups. However, Iba-1+ cells showed obvious hypertrophy and proliferation in the injured striatum in the 3-NP and the MCAO models, especially in the transition zone of 3-NP model and the penumbra zone of MCAO model. These Iba-1+ cells displayed two characteristic forms as branching cells with thick processes and amoeboid cells with thin processes. Statistical analysis showed that the number, size and IOD of Iba-1+ cells were significantly increased in the cores and the transition zone of 3-NP group and the penumbra zone of MCAO group than that of the controls, and the immune response of Iba-1 was stronger in the MCAO group than in the 3-NP group. The present results suggested that characteristic responses of astrocyte and microglia in the 3-NP and the MCAO models display their different effects on the pathological process of brain injury.

Astrocytic CCAAT/Enhancer-Binding Protein Delta Contributes to Glial Scar Formation and Impairs Functional Recovery After Spinal Cord Injury

After spinal cord injury, inflammatory reaction induces the aggregation of astrocytes to form a glial scar that eventually blocks axonal regeneration. Transcription factor CCAAT/enhancer-binding protein delta (C/EBPδ) is a regulatory protein of genes responsive to inflammatory factors, but its role in glial scar formation after spinal cord injury remains unknown. By using a model of moderate spinal cord contusion injury at the mid-thoracic level, we found that C/EBPδ was expressed mostly in the reactive astrocytes bordering the lesion in wild-type mice from 7 days after the injury. C/EBPδ-deficient mice showed reduced glial scar formation, more residual white matter, and better motor function recovery compared with wild-type mice 28 days after the injury. Upon interleukin (IL)-1β stimulation in vitro, the increased expression of C/EBPδ in reactive astrocytes inhibited RhoA expression and, subsequently, the ability of astrocyte migration. However, these reactive astrocytes also produced an increased amount of matrix metalloproteinase-3, which promoted the migration of non-IL-1β-treated, inactive astrocytes. Although the involvement of other non-astroglial C/EBPδ cannot be entirely excluded, our studies suggest that astrocytic C/EBPδ is integral to the inflammatory cascades leading to glial scar formation after spinal cord injury.

Rodent models of neuroinflammation for Alzheimer's disease

Alzheimer's disease remains incurable, and the failures of current disease-modifying strategies for Alzheimer's disease could be attributed to a lack of in vivo models that recapitulate the underlying etiology of late-onset Alzheimer's disease. The etiology of late-onset Alzheimer's disease is not based on mutations related to amyloid-β (Aβ) or tau production which are currently the basis of in vivo models of Alzheimer's disease. It has recently been suggested that mechanisms like chronic neuroinflammation may occur prior to amyloid-β and tau pathologies in late-onset Alzheimer's disease. The aim of this study is to analyze the characteristics of rodent models of neuroinflammation in late-onset Alzheimer's disease. Our search criteria were based on characteristics of an idealistic disease model that should recapitulate causes, symptoms, and lesions in a chronological order similar to the actual disease. Therefore, a model based on the inflammation hypothesis of late-onset Alzheimer's disease should include the following features: (i) primary chronic neuroinflammation, (ii) manifestations of memory and cognitive impairment, and (iii) late development of tau and Aβ pathologies. The following models fit the pre-defined criteria: lipopolysaccharide- and PolyI:C-induced models of immune challenge; streptozotocin-, okadaic acid-, and colchicine neurotoxin-induced neuroinflammation models, as well as interleukin-1β, anti-nerve growth factor and p25 transgenic models. Among these models, streptozotocin, PolyI:C-induced, and p25 neuroinflammation models are compatible with the inflammation hypothesis of Alzheimer's disease.

Seizure-induced oxidative stress in temporal lobe epilepsy

An insult to the brain (such as the first seizure) causes excitotoxicity, neuroinflammation, and production of reactive oxygen/nitrogen species (ROS/RNS). ROS and RNS produced during status epilepticus (SE) overwhelm the mitochondrial natural antioxidant defense mechanism. This leads to mitochondrial dysfunction and damage to the mitochondrial DNA. This in turn affects synthesis of various enzyme complexes that are involved in electron transport chain. Resultant effects that occur during epileptogenesis include lipid peroxidation, reactive gliosis, hippocampal neurodegeneration, reorganization of neural networks, and hypersynchronicity. These factors predispose the brain to spontaneous recurrent seizures (SRS), which ultimately establish into temporal lobe epilepsy (TLE). This review discusses some of these issues. Though antiepileptic drugs (AEDs) are beneficial to control/suppress seizures, their long term usage has been shown to increase ROS/RNS in animal models and human patients. In established TLE, ROS/RNS are shown to be harmful as they can increase the susceptibility to SRS. Further, in this paper, we review briefly the data from animal models and human TLE patients on the adverse effects of antiepileptic medications and the plausible ameliorating effects of antioxidants as an adjunct therapy.

Lipopolysaccharide-induced sepsis induces long-lasting affective changes in the mouse

Post-septic encephalopathy is a poorly understood condition in survivors of sepsis that is characterised by cognitive and affective impairments. In this study we have sought to better understand this condition by undertaking a comprehensive behavioural and cognitive assessment of mice who had previously survived sepsis. Mice were treated with lipopolysaccharide (LPS; 5mg/kg) and one month after this assessed on a battery of tests. Post-septic animals were found to display significantly more immobility in the tail suspension test and show a significantly decreased sucrose preference. Acute fluoxetine treatment reversed the increase in immobility in the tail suspension test in post-septic animals. Post-septic animals also showed less overall exploratory behaviour in the novel object recognition task and also showed increased anxiety-like behaviour in the elevated plus maze. Post-septic mice did not show signs of cognitive impairment, as assessed in the Morris watermaze, the 8-arm radial maze or on preference for the novel object in the novel object recognition task. Immunohistochemical analysis revealed significant upregulation of the microglial marker CD-11b, F4/80 and IBA-1 in the hippocampus of post-septic animals, as well as significant downregulation of the plasticity-related immediate early gene products ARC and EGR1. We also observed a decrease in neural stem cell proliferation in the dentate gyrus of post-septic animals as judged by BrdU incorporation. Co-treatment with the NF-κB pathway inhibitor PDTC attenuated the long-lasting effects of LPS on most of the affected parameters, but not on neural stem cell proliferation. These results show that LPS-induced sepsis in the mouse is followed by long-lasting increases in depressive- and anxiety-like behaviours, as well as by changes in neuroinflammatory- and neural plasticity-associated factors, and that attenuation of the severity of sepsis by PDTC attenuates many of these effects.

Hippocampal spatial position evaluation on MRI for research and clinical practice

In clinical practice as well as in many volumetric studies we use different reorientations of the brain position towards x and y axis on the magnetic resonance imaging (MRI) scans. In order to find out whether it has an overall effect on the resulting 2D data, manual hippocampal area measurements and rotation variability of the brain (in two reoriented axes) and the skull were performed in 23 Alzheimer's disease patients and 31 healthy controls. After the MRI scanning, native brain scans (nat) were reoriented into the two different artificial planes (anterior commissure – posterior commissure axis (AC-PC) and hippocampal horizontal long axis (hipp)). Hippocampal area and temporal horn of the lateral ventricle was measured manually using freeware Image J program. We found that 1) hippocampal area of nat images is larger compared to hipp images, area of the nat images is equal to the AC-PC images and area of the hipp images is smaller compared to AC-PC images, 2) hippocampal area together with the area of the temporal horn for nat images is larger compared to hipp images, area of the hipp images is smaller compared to the AC-PC images and area of the nat images is smaller compared to the AC-PC images. The conclusion is that the measured area of the hippocampus in the native MRI is almost the same as the area of MRI reoriented only into the AC-PC axis. Therefore, when performing 2D area studies of the hippocampus or in the clinical practice we recommend usage of not-reoriented MRI images or to reorient them into the AC-PC axis. Surprising finding was that rotation of both AC-PC and hipp line towards x-axis among patients varies up to 35° and the same is true for the skull rotation so that it is not only a matter of the brain position.

Lithium prevents parkinsonian behavioral and striatal phenotypes in an aged parkin mutant transgenic mouse model

Lithium has long been used as a treatment for the psychiatric disease bipolar disorder. However, previous studies suggest that lithium provides neuroprotective effects in neurodegenerative diseases such as Parkinson's disease (PD) and Alzheimer's disease. The exact mechanism by which lithium exerts these effects still remains unclear. In the present study, we evaluated the effects of low-dose lithium treatment in an aged mouse model expressing a parkin mutation within dopaminergic neurons. We found that low-dose lithium treatment prevented motor impairment as demonstrated by the open field test, pole test, and rearing behavior. Furthermore, lithium prevented dopaminergic striatal degeneration in parkin animals. We also found that parkin-induced striatal astrogliosis and microglial activation were prevented by lithium treatment. Our results further corroborate the use of this parkin mutant transgenic mouse line as a model for PD for testing novel therapeutics. The findings of the present study also provide further validation that lithium could be re-purposed as a therapy for PD and suggest that anti-inflammatory effects may contribute to its neuroprotective mechanisms.

The neuron-astrocyte-microglia triad in a rat model of chronic cerebral hypoperfusion: protective effect of dipyridamole

Chronic cerebral hypoperfusion during aging may cause progressive neurodegeneration as ischemic conditions persist. Proper functioning of the interplay between neurons and glia is fundamental for the functional organization of the brain. The aim of our research was to study the pathophysiological mechanisms, and particularly the derangement of the interplay between neurons and astrocytes-microglia with the formation of "triads," in a model of chronic cerebral hypoperfusion induced by the two-vessel occlusion (2VO) in adult Wistar rats (n = 15). The protective effect of dipyridamole given during the early phases after 2VO (4 mg/kg/day i.v., the first 7 days after 2VO) was verified (n = 15). Sham-operated rats (n = 15) were used as controls. Immunofluorescent triple staining of neurons (NeuN), astrocytes (GFAP), and microglia (IBA1) was performed 90 days after 2VO. We found significantly higher amount of "ectopic" neurons, neuronal debris and apoptotic neurons in CA1 Str. Radiatum and Str. Pyramidale of 2VO rats. In CA1 Str. Radiatum of 2VO rats the amount of astrocytes (cells/mm(2)) did not increase. In some instances several astrocytes surrounded ectopic neurons and formed a "micro scar" around them. Astrocyte branches could infiltrate the cell body of ectopic neurons, and, together with activated microglia cells formed the "triads." In the triad, significantly more numerous in CA1 Str. Radiatum of 2VO than in sham rats, astrocytes and microglia cooperated in the phagocytosis of ectopic neurons. These events might be common mechanisms underlying many neurodegenerative processes. The frequency to which they appear might depend upon, or might be the cause of, the burden and severity of neurodegeneration. Dypiridamole significantly reverted all the above described events. The protective effect of chronic administration of dipyridamole might be a consequence of its vasodilatory, antioxidant and anti-inflammatory role during the early phases after 2VO.

Increased levels and activity of cathepsins B and D in kainate-induced toxicity

Administration of kainic acid induces acute seizures that result in the loss of neurons, gliosis and reorganization of mossy fiber pathways in the hippocampus resembling those observed in human temporal lobe epilepsy. Although these structural changes have been well characterized, the mechanisms underlying the degeneration of neurons following administration of kainic acid remain unclear. Since the lysosomal enzymes, cathepsins B and D, are known to be involved in the loss of neurons and clearance of degenerative materials in a variety of experimental conditions, we evaluated their potential roles in kainic acid-treated rats. In parallel, we also measured the levels and expression of insulin-like growth factor-II/mannose 6-phosphate (IGF-II/M6P) receptors, which mediate the intracellular trafficking of these enzymes, in kainic acid-treated rats. Our results showed that systemic administration of kainic acid evoked severe loss of neurons along with hypertrophy of astrocytes and microglia in the hippocampus of the adult rat brain. The levels and activity of cathepsins B and D increased with time in the hippocampus of kainic acid-treated rats compared to the saline-injected control animals. The expression of both cathepsins B and D, as evident by immunolabeling studies, was also markedly increased in activated astrocytes and microglia of the kainic acid-treated rats. Additionally, cytosolic levels of the cathepsins were enhanced along with cytochrome c and to some extent Bax in the hippocampus in kainic acid-treated rats. These changes were accompanied by appearance of cleaved caspase-3-positive neurons in the hippocampus of kainic acid-treated animals. The levels of IGF-II/M6P receptors, on the other hand, were not significantly altered, but these receptors were found to be present in a subset of reactive astrocytes following administration of kainic acid. These results, taken together, suggest that enhanced levels/expression and activity of lysosomal enzymes may have a role in the loss of neurons and/or clearance of degenerative materials observed in kainic acid-treated rats.

Aging, the metabolic syndrome, and ischemic stroke: redefining the approach for studying the blood-brain barrier in a complex neurological disease

The blood-brain barrier (BBB) has many important functions in maintaining the brain's immune-privileged status. Endothelial cells, astrocytes, and pericytes have important roles in preserving vasculature integrity. As we age, cell senescence can contribute to BBB compromise. The compromised BBB allows an influx of inflammatory cytokines to enter the brain. These cytokines lead to neuronal and glial damage. Ultimately, the functional changes within the brain can cause age-related disease. One of the most prominent age-related diseases is ischemic stroke. Stroke is the largest cause of disability and is third largest cause of mortality in the United States. The biggest risk factors for stroke, besides age, are results of the metabolic syndrome. The metabolic syndrome, if unchecked, quickly advances to outcomes that include diabetes, hypertension, cardiovascular disease, and obesity. The contribution from these comorbidities to BBB compromise is great. Some of the common molecular pathways activated include: endoplasmic reticulum stress, reactive oxygen species formation, and glutamate excitotoxicity. In this chapter, we examine how age-related changes to cells within the central nervous system interact with comorbidities. We then look at how comorbidities lead to increased risk for stroke through BBB disruption. Finally, we discuss key molecular pathways of interest with a focus on therapeutic targets that warrant further investigation.

Astrocytic and microglial response in experimentally induced diabetic rat brain

Diabetes Mellitus is associated with increased risk of cognitive and behavioural disorders with hitherto undeciphered role of glia. Glia as majority population in brain serve several vital functions, thus require pertinent revelation to further explicate the mechanisms affecting the brain function following diabetes. In this study we have evaluated glial changes in terms of phenotypic switching, proliferation and expression of activation cell surface markers and associated cellular degeneration in hippocampus following STZ-induced diabetes and caused cognitive impairments. Experimental diabetes was induced in Wistar rats by a single dose of STZ (45 mg/kg body weight; intraperitoneally) and changes were studied in 2nd, 4th and 6th week post diabetes confirmation using Barnes maze and T-maze test, immunohistochemistry and image analysis. An increase in GFAP expression sequentially from 2nd to 6th weeks of diabetes was analogous with the phenotypic changes and increased astrocyte number. Elevated level of S100β with defined stellate morphology further confirmed the astrocytosis following diabetes. Enhanced level of Iba-1 and MHC-II revealed the corroborated microglial activation and proliferation following diabetes, which was unresolved till date. Increased caspase-3 activity induced profound cell death upto 6th weeks post diabetes confirmation. Such caspase 3 mediated cellular damage with a concomitant activation of the astrocytes and microglia suggests that diabetes linked cell death activates the astrocytes and microglia in hippocampus which further underpin the progression and severity of brain disorders resulting in cognitive and behavioural impairments.

Melatonin and oestrogen treatments were able to improve neuroinflammation and apoptotic processes in dentate gyrus of old ovariectomized female rats

The aim of this study was to determine the outcomes of oestrogen and melatonin treatments following long-term ovarian hormone depletion on neuroinflammation and apoptotic processes in dentate gyrus of hippocampi. Forty-six female Wistar rats of 22 months of age were used. Twelve of them remained intact, and the other 34 were ovariectomized at 12 months of age. Ovariectomized animals were divided into three groups and treated for 10 weeks with oestrogens, melatonin or saline. All rats were killed by decapitation at 24 months of age, and dentate gyri were collected. A group of 2 month-old intact female rats was used as young control. The levels of pro-inflammatory cytokines and heat shock protein 70 (HSP 70) were analysed by ELISA. The expressions of TNFα, IL1β, GFAP, nNOS, iNOS, HO-1, NFκB, Bax, Bad, AIF, Bcl2 and SIRT1 genes were detected by real-time (RT)-PCR. Western blots were used to measure the protein expression of NFκB p65, NFκB p50/105, IκBα, IκBβ, p38 MAPK, MAP-2 and synapsin I. We have assessed the ability of 17β-oestradiol and melatonin administration to downregulate markers of neuroinflammation in the dentate gyrus of ovariectomized female rats. Results indicated that 17β-oestradiol and melatonin treatments were able to significantly decrease expression of pro-inflammatory cytokines, iNOS and HO-1 in the hippocampus when compared to non-treated animals. A similar age- and long-term ovarian hormone depletion- related increase in GFAP was also attenuated after both melatonin and oestradiol treatments. In a similar way to oestradiol, melatonin decreased the activation of p38 MAPK and NFκB pathways. The treatments enhanced the levels of synaptic molecules synapsin I and MAP-2 and have been shown to modulate the pro-antiapoptotic ratio favouring the second and to increase SIRT1 expression. These findings support the potential therapeutic role of melatonin and oestradiol as protective anti-inflammatory agents for the central nervous system during menopause.

Aging reduces glial uptake and promotes extracellular accumulation of Aβ from a lentiviral vector

We used a lentiviral system for expressing secreted human Aβ in the brains of young and old APOE knock-in mice. This system allowed us to examine Aβ metabolism in vivo, and test the effects of both aging and APOE genotype, two of the strongest risk factors for Alzheimer’s disease. We injected the Aβ_1-42 lentivirus into the motor cortex of young (2 month old) and old (20–22 month old) APOE3 and APOE4 mice. After 2 weeks of lentiviral expression, we analyzed the pattern of Aβ accumulation, glial activation, and phosphor-tau. In young mice, Aβ accumulated mainly within neurons with no evidence of extracellular Aβ. Significantly higher levels of intraneuronal Aβ were observed in APOE4 mice compared to APOE3 mice. In old mice, APOE4 predisposed again to higher levels of Aβ accumulation, but the Aβ was mainly in extracellular spaces. In younger mice, we also observed Aβ in microglia but not astrocytes. The numbers of microglia containing Aβ were significantly higher in APOE3 mice compared to APOE4 mice, and were significantly lower in both genetic backgrounds with aging. The astrocytes in old mice were activated to a greater extent in the brain regions where Aβ was introduced, an effect that was again increased by the presence of APOE4. Finally, phospho-tau accumulated in the region of Aβ expression, with evidence of extracellular phospho-tau increasing with aging. These data suggest that APOE4 predisposes to less microglial clearance of Aβ, leading to more intraneuronal accumulation. In older brains, decreased clearance leads to more extracellular Aβ, and more downstream consequences relating to astrocyte activation and phospho-tau accumulation. We conclude that both aging and APOE genotype affect pathways related to Aβ metabolism by microglia.

Selective estrogen receptor modulators regulate reactive microglia after penetrating brain injury

Following brain injury, microglia assume a reactive-like state and secrete pro-inflammatory molecules that can potentiate damage. A therapeutic strategy that may limit microgliosis is of potential interest. In this context, selective estrogen receptor modulators, such as raloxifene and tamoxifen, are known to reduce microglia activation induced by neuroinflammatory stimuli in young animals. In the present study, we have assessed whether raloxifene and tamoxifen are able to affect microglia activation after brain injury in young and aged animals in time points relevant to clinics, which is hours after brain trauma. Volume fraction of MHC-II(+) microglia was estimated according to the point-counting method of Weibel within a distance of 350 μm from the lateral border of the wound, and cellular morphology was measured by fractal analysis. Two groups of animals were studied: (1) young rats, ovariectomized at 2 months of age; and (2) aged rats, ovariectomized at 18 months of age. Fifteen days after ovariectomy animals received a stab wound brain injury and the treatment with estrogenic compounds. Our findings indicate that raloxifene and tamoxifen reduced microglia activation in both young and aged animals. Although the volume fraction of reactive microglia was found lower in aged animals, this was accompanied by important changes in cell morphology, where aged microglia assume a bushier and hyperplasic aspect when compared to young microglia. These data suggest that early regulation of microglia activation provides a mechanism by which selective estrogen receptors modulators (SERMs) may exert a neuroprotective effect in the setting of a brain trauma.

Morphological changes in the suprachiasmatic nucleus of aging female marmosets (Callithrix jacchus)

The suprachiasmatic nuclei (SCN) are pointed to as the mammals central circadian pacemaker. Aged animals show internal time disruption possibly caused by morphological and neurochemical changes in SCN components. Some studies reported changes of neuronal cells and neuroglia in the SCN of rats and nonhuman primates during aging. The effects of senescence on morphological aspects in SCN are important for understanding some alterations in biological rhythms expression. Therefore, our aim was to perform a comparative study of the morphological aspects of SCN in adult and aged female marmoset. Morphometric analysis of SCN was performed using Nissl staining, NeuN-IR, GFAP-IR, and CB-IR. A significant decrease in the SCN cells staining with Nissl, NeuN, and CB were observed in aged female marmosets compared to adults, while a significant increase in glial cells was found in aged marmosets, thus suggesting compensatory process due to neuronal loss evoked by aging.

Increase of zinc finger protein 179 in response to CCAAT/enhancer binding protein delta conferring an antiapoptotic effect in astrocytes of Alzheimer's disease

Reactive astrogliosis is a cellular manifestation of neuroinflammation and occurs in response to all forms and severities of the central nervous system (CNS)'s injury and disease. Both astroglial proliferation and antiapoptotic processes are aspects of astrogliosis. However, the underlying mechanism of this response remains poorly understood. In addition, little is known about why activated astrocytes are more resistant to stress and inflammation. CCAAT/enhancer binding protein delta (CEBPD) is a transcription factor found in activated astrocytes that surround β-amyloid plaques. In this study, we found that astrocytes activation was attenuated in the cortex and hippocampus of APPswe/PS1 E9 (AppTg)/Cebpd (-/-)mice. Furthermore, an increase in apoptotic astrocytes was observed in AppTg/Cebpd (-/-)mice, suggesting that CEBPD plays a functional role in enhancing the antiapoptotic ability of astrocytes. We found that Zinc Finger Protein 179 (ZNF179) was a CEBPD-regulated gene that played an antiapoptotic, but not proliferative, role in astrocytes. The transcriptions of the proapoptotic genes, insulin-like growth factor binding protein 3 (IGFBP3) and BCL2-interacting killer (BIK), were suppressed by ZNF179 via its interaction with the promyelocytic leukemia zinc finger (PLZF) protein in astrocytes. This study provides the first evidence that ZNF179, PLZF, IGFBP3, and BIK contributed to the novel CEBPD-induced antiapoptotic feature of astrocytes.

Neuroglia in ageing and disease

The proper operation of the mammalian brain requires dynamic interactions between neurones and glial cells. Various types of glial cells are susceptible to morpho-functional changes in a variety of brain pathological states, including toxicity, neurodevelopmental, neurodegenerative and psychiatric disorders. Morphological modifications include a change in the glial cell size and shape; the latter is evident by changes of the appearance and number of peripheral processes. The most blatant morphological change is associated with the alteration of the sheer number of neuroglia cells in the brain. Functionally, glial cells can undergo various metabolic and biochemical changes, the majority of which reflect upon homeostasis of neurotransmitters, in particular that of glutamate, as well as on defence mechanisms provided by neuroglia. Not only glial cells exhibit changes associated with the pathology of the brain but they also change with brain aging.

Surveillance, phagocytosis, and inflammation: how never-resting microglia influence adult hippocampal neurogenesis

Microglia cells are the major orchestrator of the brain inflammatory response. As such, they are traditionally studied in various contexts of trauma, injury, and disease, where they are well-known for regulating a wide range of physiological processes by their release of proinflammatory cytokines, reactive oxygen species, and trophic factors, among other crucial mediators. In the last few years, however, this classical view of microglia was challenged by a series of discoveries showing their active and positive contribution to normal brain functions. In light of these discoveries, surveillant microglia are now emerging as an important effector of cellular plasticity in the healthy brain, alongside astrocytes and other types of inflammatory cells. Here, we will review the roles of microglia in adult hippocampal neurogenesis and their regulation by inflammation during chronic stress, aging, and neurodegenerative diseases, with a particular emphasis on their underlying molecular mechanisms and their functional consequences for learning and memory.

Therapeutic and space radiation exposure of mouse brain causes impaired DNA repair response and premature senescence by chronic oxidant production

Despite recent epidemiological evidences linking radiation exposure and a number of human ailments including cancer, mechanistic understanding of how radiation inflicts long-term changes in cerebral cortex, which regulates important neuronal functions, remains obscure. The current study dissects molecular events relevant to pathology in cerebral cortex of 6 to 8 weeks old female C57BL/6J mice two and twelve months after exposure to a γ radiation dose (2 Gy) commonly employed in fractionated radiotherapy. For a comparative study, effects of 1.6 Gy heavy ion 56Fe radiation on cerebral cortex were also investigated, which has implications for space exploration. Radiation exposure was associated with increased chronic oxidative stress, oxidative DNA damage, lipid peroxidation, and apoptosis. These results when considered with decreased cortical thickness, activation of cell-cycle arrest pathway, and inhibition of DNA double strand break repair factors led us to conclude to our knowledge for the first time that radiation caused aging-like pathology in cerebral cortical cells and changes after heavy ion radiation were more pronounced than γ radiation.

Role of stress, depression, and aging in cognitive decline and Alzheimer's disease

Late-onset Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most common cause of progressive cognitive dysfunction and dementia. Despite considerable progress in elucidating the molecular pathology of this disease, we are not yet close to unraveling its etiopathogenesis. A battery of neurotoxic modifiers may underpin neurocognitive pathology via deleterious heterogeneous pathologic impact in brain regions, including the hippocampus. Three important neurotoxic factors being addressed here include aging, stress, and depression. Unraveling "upstream pathologies" due to these disparate neurotoxic entities, vis-à-vis cognitive impairment involving hippocampal dysfunction, is of paramount importance. Persistent systemic inflammation triggers and sustains neuroinflammation. The latter targets several brain regions including the hippocampus causing upregulation of amyloid beta and neurofibrillary tangles, synaptic and neuronal degeneration, gray matter volume atrophy, and progressive cognitive decline. However, what is the fundamental source of this peripheral inflammation in aging, stress, and depression? This chapter highlights and delineates the inflammatory involvement-i.e., from its inception from gut to systemic inflammation to neuroinflammation. It highlights an upregulated cascade in which gut-microbiota-related dysbiosis generates lipopolysaccharides (LPS), which enhances inflammation and gut's leakiness, and through a Web of interactions, it induces stress and depression. This may increase neuronal dysfunction and apoptosis, promote learning and memory impairment, and enhance vulnerability to cognitive decline.

Age-associated alterations in the time-dependent profile of pro- and anti-inflammatory proteins within the hippocampus in response to acute exposure to interleukin-1β

The pro-inflammatory cytokine IL-1β is known to play a role in several models of aging, neuroinflammation, and neurodegenerative diseases. Here, we document a detailed time- and age-dependent pattern of pro- and anti-inflammatory biomarkers following bilateral intrahippocampal injection of interleukin-1β. During the first 12h several pro- and anti-inflammatory cytokines increased in the aged (24 mo old) rats, some of which returned to baseline levels by 24h post-injection while others remained elevated for 72 h post-injection. In contrast, no such increases were observed in the young (3 mo old) rats. Interestingly, young rats up-regulated mRNA of two pro-inflammatory cytokines, interleukin-1β and tumor necrosis factor-α, but did not translate these transcripts into functional proteins, which may be related to expression of suppressor of cytokine signaling type-2. These results contribute to our understanding of how neuroinflammation may contribute to the pathogenesis of age-related neurodegenerative disorders due to an age-related bias towards a hyper-reactive immune response that is not selective for a pro- or anti-inflammatory phenotype following an inflammatory stimulus.

Dual effects of noradrenaline on astroglial production of chemokines and pro-inflammatory mediators

Background

Noradrenaline (NA) is known to limit neuroinflammation. However, the previously described induction by NA of a chemokine involved in the progression of immune/inflammatory processes, such as chemokine (C-C motif) ligand 2 (CCL2)/monocyte chemotactic protein-1 (MCP-1), apparently contradicts NA anti-inflammatory actions. In the current study we analyzed NA regulation of astroglial chemokine (C-X3-C motif) ligand 1 (CX3CL1), also known as fractalkine, another chemokine to which both neuroprotective and neurodegenerative actions have been attributed. In addition, NA effects on other chemokines and pro-inflammatory mediators were also analyzed.

Methods

Primary astrocyte-enriched cultures were obtained from neonatal Wistar rats. These cells were incubated for different time durations with combinations of NA and lipopolysaccharide (LPS). The expression and synthesis of different proteins was measured by RT-PCR and enzyme-linked immunosorbent assay (ELISA) or enzyme immunoassays. Data were analyzed by one-way analysis of variance (ANOVA), followed by Newman-Keuls multiple comparison tests.

Results

The data presented here show that in control conditions, NA induces the production of CX3CL1 in rat cultured astrocytes, but in the presence of an inflammatory stimulus, such as LPS, NA has the opposite effect inhibiting CX3CL1 production. This inversion of NA effect was also observed for MCP-1. Based on the observation of this dual action, NA regulation of different chemokines and pro-inflammatory cytokines was also analyzed, observing that in most cases NA exerts an inhibitory effect in the presence of LPS. One characteristic exception was the induction of cyclooxygenase-2 (COX-2), where a summative effect was detected for both LPS and NA.

Conclusion

These data suggest that NA effects on astrocytes can adapt to the presence of an inflammatory agent reducing the production of certain cytokines, while in basal conditions NA may have the opposite effect and help to maintain moderate levels of these cytokines.

Neurovascular unit in chronic pain

Chronic pain is a debilitating condition with major socioeconomic impact, whose neurobiological basis is still not clear. An involvement of the neurovascular unit (NVU) has been recently proposed. In particular, the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB), two NVU key players, may be affected during the development of chronic pain; in particular, transient permeabilization of the barrier is suggested by several inflammatory- and nerve-injury-based pain models, and we argue that the clarification of molecular BBB/BSCB permeabilization events will shed new light in understanding chronic pain mechanisms. Possible biases in experiments supporting this theory and its translational potentials are discussed. Moving beyond an exclusive focus on the role of the endothelium, we propose that our understanding of the mechanisms subserving chronic pain will benefit from the extension of research efforts to the NVU as a whole. In this view, the available evidence on the interaction between analgesic drugs and the NVU is here reviewed. Chronic pain comorbidities, such as neuroinflammatory and neurodegenerative diseases, are also discussed in view of NVU changes, together with innovative pharmacological solutions targeting NVU components in chronic pain treatment.

Riluzole partially rescues age-associated, but not LPS-induced, loss of glutamate transporters and spatial memory

Impaired memory may result from synaptic glutamatergic dysregulation related to chronic neuroinflammation. GLT1 is the primary excitatory amino acid transporter responsible for regulating extracellular glutamate levels in the hippocampus. We tested the hypothesis that if impaired spatial memory results from increased extracellular glutamate due to age or experimentally induced chronic neuroinflammation in the hippocampus, then pharmacological augmentation of the glutamate transporter GLT1 will attenuate deficits in a hippocampal-dependent spatial memory task. The profile of inflammation-related genes and proteins associated with normal aging, or chronic neuroinflammation experimentally-induced via a four-week LPS infusion into the IV(th) ventricle, were correlated with performance in the Morris water maze following treatment with Riluzole, a drug that can enhance glutamate clearance by increasing GLT1 expression. Age-associated inflammation was qualitatively different from LPS-induced neuro-inflammation in young rats. LPS produced a pro-inflammatory phenotype characterized by increased IL-1ß expression in the hippocampus, whereas aging was not associated with a strong central pro-inflammatory response but with a mixed peripheral immune phenotype. Riluzole attenuated the spatial memory impairment, the elevation of serum cytokines and the decrease in GLT1 gene expression in Aged rats, but had no effect on young rats infused with LPS. Our findings highlight the therapeutic potential of reducing glutamatergic function upon memory impairment in neurodegenerative diseases associated with aging.