Age and meloxicam modify the response of the glutamate vesicular transporters (VGLUTs) after transient global cerebral ischemia in the rat brain

Microvascular damage, neuroinflammation and extracellular matrix remodeling in Col18a1 knockout mice as a model for early cerebral small vessel disease

Collagen type XVIII (COL18) is an abundant heparan sulfate proteoglycan in vascular basement membranes. Here, we asked (i) if the loss of COL18 would result in blood-brain barrier (BBB) breakdown, pathological alterations of small arteries and capillaries and neuroinflammation as found in cerebral small vessel disease (CSVD) and (ii) if such changes may be associated with remodeling of synapses and neural extracellular matrix (ECM). We found that 5-month-old Col18a1-/- mice had elevated BBB permeability for mouse IgG in the deep gray matter, and intravascular erythrocyte accumulations were observed brain-wide in capillaries and arterioles. BBB permeability increased with age and affected cortical regions and the hippocampus in 12-month-old Col18a1-/- mice. None of the Col18a1-/- mice displayed hallmarks of advanced CSVD, such as hemorrhages, and did not show perivascular space enlargement. Col18a1 deficiency-induced BBB leakage was accompanied by activation of microglia and astrocytes, a loss of aggrecan in the ECM of perineuronal nets associated with fast-spiking inhibitory interneurons and accumulation of the perisynaptic ECM proteoglycan brevican and the microglial complement protein C1q at excitatory synapses. As the pathway underlying these regulations, we found increased signaling through the TGF-ß1/Smad3/TIMP-3 cascade. We verified the pivotal role of COL18 for small vessel wall structure in CSVD by demonstrating the protein's involvement in vascular remodeling in autopsy brains from patients with cerebral hypertensive arteriopathy. Our study highlights an association between the alterations of perivascular ECM, extracellular proteolysis, and perineuronal/perisynaptic ECM, as a possible substrate of synaptic and cognitive alterations in CSVD.

Inhibition of Vesicular Glutamate Transporters (VGLUTs) with Chicago Sky Blue 6B Before Focal Cerebral Ischemia Offers Neuroprotection

Brain ischemia is one of the leading causes of death and long-term disability in the world. Interruption of the blood supply to the brain is a direct stimulus for many pathological events. The massive vesicular release of glutamate (Glu) after ischemia onset induces excitotoxicity, which is a potent stress on neurons. Loading of presynaptic vesicles with Glu is the first step of glutamatergic neurotransmission. Vesicular glutamate transporters 1, 2, and 3 (VGLUT1, 2, and 3) are the main players involved in filling presynaptic vesicles with Glu. VGLUT1 and VGLUT2 are expressed mainly in glutamatergic neurons. Therefore, the possibility of pharmacological modulation to prevent ischemia-related brain damage is attractive. In this study, we aimed to determine the effect of focal cerebral ischemia on the spatiotemporal expression of VGLUT1 and VGLUT2 in rats. Next, we investigated the influence of VGLUT inhibition with Chicago Sky Blue 6B (CSB6B) on Glu release and stroke outcome. The effect of CSB6B pretreatment on infarct volume and neurological deficit was compared with a reference model of ischemic preconditioning. The results of this study indicate that ischemia upregulated the expression of VGLUT1 in the cerebral cortex and in the dorsal striatum 3 days after ischemia onset. The expression of VGLUT2 was elevated in the dorsal striatum and in the cerebral cortex 24 h and 3 days after ischemia, respectively. Microdialysis revealed that pretreatment with CSB6B significantly reduced the extracellular Glu concentration. Altogether, this study shows that inhibition of VGLUTs might be a promising therapeutic strategy for the future.

Excitatory Synaptic Transmission in Ischemic Stroke: A New Outlet for Classical Neuroprotective Strategies

Stroke is one of the leading causes of death and disability in the world, of which ischemia accounts for the majority. There is growing evidence of changes in synaptic connections and neural network functions in the brain of stroke patients. Currently, the studies on these neurobiological alterations mainly focus on the principle of glutamate excitotoxicity, and the corresponding neuroprotective strategies are limited to blocking the overactivation of ionic glutamate receptors. Nevertheless, it is disappointing that these treatments often fail because of the unspecificity and serious side effects of the tested drugs in clinical trials. Thus, in the prevention and treatment of stroke, finding and developing new targets of neuroprotective intervention is still the focus and goal of research in this field. In this review, we focus on the whole processes of glutamatergic synaptic transmission and highlight the pathological changes underlying each link to help develop potential therapeutic strategies for ischemic brain damage. These strategies include: (1) controlling the synaptic or extra-synaptic release of glutamate, (2) selectively blocking the action of the glutamate receptor NMDAR subunit, (3) increasing glutamate metabolism, and reuptake in the brain and blood, and (4) regulating the glutamate system by GABA receptors and the microbiota–gut–brain axis. Based on these latest findings, it is expected to promote a substantial understanding of the complex glutamate signal transduction mechanism, thereby providing excellent neuroprotection research direction for human ischemic stroke (IS).

Potential Therapeutic Effects of Mi-Jian-Chang-Pu Decoction on Neurochemical and Metabolic Changes of Cerebral Ischemia-Reperfusion Injury in Rats

As a traditional Chinese medicine formula, Mi-Jian-Chang-Pu decoction (MJCPD) has been successfully used in patients with language dysfunction and hemiplegia after ischemic stroke (IS). Given the excellent protective effects of MJCPD against nerve damage caused by IS in clinical settings, the present investigation mainly focused on its underlying mechanism on ischemia-reperfusion (IR) injury. Firstly, by applying the MCAO-induced cerebral IR injury rats, the efficacy of MJCPD on IS was estimated using the neurological deficit score, TTC, HE, and IHC staining, and neurochemical measurements. Secondly, an UHPLC-QTOF-MS/MS-based nontargeted metabolomics was developed to elucidate the characteristic metabolites. MJCPD groups showed significant improvements in the neurological score, infarction volume, and histomorphology, and the changes of GSH, GSSG, GSH-PX, GSSG/GSH, LDH, L-LA, IL-6, TNF-α, and VEGF-c were also reversed to normal levels after the intervention compared to the MCAO model group. Metabolomics profiling identified 21 different metabolites in the model group vs. the sham group, 10 of which were significantly recovered after treatment of MJCPD, and those 10 metabolites were all related to the oxidative stress process including glucose, fatty acid, amino acid, glutamine, and phospholipid metabolisms. Therefore, MJCPD might protect against IS by inhibiting oxidative stress during IR.

miR-204-5p is sponged by TUG1 to aggravate neuron damage induced by focal cerebral ischemia and reperfusion injury through upregulating COX2

Studies have reported that miR-204-5p is involved in multiple biological processes. However, little is known about the expression and mechanism of miR-204-5p in cerebral ischemia and reperfusion injury. This study found that miR-204-5p expression was significantly downregulated in the blood of patients with ischemic stroke, MCAO/R rat brains, and OGD/R neurons. Overexpression of miR-204-5p markedly reduced infarct volume and neurological impairment and alleviated the inflammatory response in vivo. miR-204-5p promoted neuronal viability and reduced apoptotic cells in vitro. Mechanically, miR-204-5p was negatively regulated by the expression lncRNA TUG1 upstream and down-regulated COX2 expression downstream. Therefore, the TUG1/miR-204-5p/COX2 axis was involved in ischemia and reperfusion-induced neuronal damage. This finding may provide a novel strategy for the treatment of cerebral ischemia and reperfusion injury.

A New Player in the Hippocampus: A Review on VGLUT3+ Neurons and Their Role in the Regulation of Hippocampal Activity and Behaviour

Glutamate is the most abundant excitatory amino acid in the central nervous system. Neurons using glutamate as a neurotransmitter can be characterised by vesicular glutamate transporters (VGLUTs). Among the three subtypes, VGLUT3 is unique, co-localising with other "classical" neurotransmitters, such as the inhibitory GABA. Glutamate, manipulated by VGLUT3, can modulate the packaging as well as the release of other neurotransmitters and serve as a retrograde signal through its release from the somata and dendrites. Its contribution to sensory processes (including seeing, hearing, and mechanosensation) is well characterised. However, its involvement in learning and memory can only be assumed based on its prominent hippocampal presence. Although VGLUT3-expressing neurons are detectable in the hippocampus, most of the hippocampal VGLUT3 positivity can be found on nerve terminals, presumably coming from the median raphe. This hippocampal glutamatergic network plays a pivotal role in several important processes (e.g., learning and memory, emotions, epilepsy, cardiovascular regulation). Indirect information from anatomical studies and KO mice strains suggests the contribution of local VGLUT3-positive hippocampal neurons as well as afferentations in these events. However, further studies making use of more specific tools (e.g., Cre-mice, opto- and chemogenetics) are needed to confirm these assumptions.

An Overview of Stroke: Mechanism, In vivo Experimental Models Thereof, and Neuroprotective Agents

BACKGROUND

Stroke is one of the causes of death and disability globally. Brain attack is because of the acute presentation of stroke, which highlights the requirement for decisive action to treat it.

OBJECTIVE

The mechanism and in-vivo experimental models of stroke with various neuroprotective agents are highlighted in this review.

METHOD

The damaging mechanisms may proceed by rapid, nonspecific cell lysis (necrosis) or by the active form of cell death (apoptosis or necroptosis), depending upon the duration and severity and of the ischemic insult.

RESULTS

Identification of injury mediators and pathways in a variety of experimental animal models of global cerebral ischemia has directed to explore the target-specific cytoprotective strategies, which are critical to clinical brain injury outcomes.

CONCLUSION

The injury mechanism, available encouraging medicaments thereof, and outcomes of natural and modern medicines for ischemia have been summarized. In spite of available therapeutic agents (thrombolytics, calcium channel blockers, NMDA receptor antagonists and antioxidants), there is a need for an ideal drug for strokes.

Fluoxetine suppresses inflammatory reaction in microglia under OGD/R challenge via modulation of NF-κB signaling

We aimed to investigate the anti-inflammatory role of fluoxetine, a selective serotonin reuptake inhibitor, in microglia (MG) and the mechanisms under oxygen glucose deprivation/reoxygenation (OGD/R). An OGD/R model on BV-2 cells was used for the study of microglia under ischemia/reperfusion injury in ischemic stroke. Lentiviral transfection was applied to knock down IκB-α. Enzyme-linked immunosorbent assay (ELISA) was used for detecting levels of TNF-α, IL-1β, and IL-6, and real-time PCR was used to assess the expression of IκB-α protein. Western blotting was applied to analyze NF-κB-signaling related proteins and Cell Counting Kit-8 (CCK-8) was used for assessing cell viability. Molecular docking and drug affinity responsive target stability (DARTS) assay were used for the detection of the interaction between IκB-α and fluoxetine. We found that fluoxetine decreased the levels of TNF-α, IL-1β, and IL-6 in supernatant as well as NF-κB subunits p65 and p50 in BV-2 cells under OGD/R. Fluoxetine significantly increased the level of IκB-α through the inhibition of IκB-α ubiquitylation and promoted the bonding of IκB-α and fluoxetine in BV-2 cells under OGD/R. Knocking down IκB-α attenuated the decreasing effect of TNF-α, IL-1β, and IL-6 as well as p65 and p50 in BV-2 cells under OGD/R led to by fluoxetine. In conclusion, our present study demonstrated the anti-inflammatory role of fluoxetine and its mechanisms related to the modulation of NF-κB-related signaling in MG under ischemia/reperfusion challenge.

Stability and Function of Hippocampal Mossy Fiber Synapses Depend on Bcl11b/Ctip2

Structural and functional plasticity of synapses are critical neuronal mechanisms underlying learning and memory. While activity-dependent regulation of synaptic strength has been extensively studied, much less is known about the transcriptional control of synapse maintenance and plasticity. Hippocampal mossy fiber (MF) synapses connect dentate granule cells to CA3 pyramidal neurons and are important for spatial memory formation and consolidation. The transcription factor Bcl11b/Ctip2 is expressed in dentate granule cells and required for postnatal hippocampal development. Ablation of Bcl11b/Ctip2 in the adult hippocampus results in impaired adult neurogenesis and spatial memory. The molecular mechanisms underlying the behavioral impairment remained unclear. Here we show that selective deletion of Bcl11b/Ctip2 in the adult mouse hippocampus leads to a rapid loss of excitatory synapses in CA3 as well as reduced ultrastructural complexity of remaining mossy fiber boutons (MFBs). Moreover, a dramatic decline of long-term potentiation (LTP) of the dentate gyrus-CA3 (DG-CA3) projection is caused by adult loss of Bcl11b/Ctip2. Differential transcriptomics revealed the deregulation of genes associated with synaptic transmission in mutants. Together, our data suggest Bcl11b/Ctip2 to regulate maintenance and function of MF synapses in the adult hippocampus.

Regional-specific effects of cerebral ischemia/reperfusion and dehydroepiandrosterone on synaptic NMDAR/PSD-95 complex in male Wistar rats

Excessive glutamate efflux and N-methyl-D-aspartate receptor (NMDAR) over-activation represent well-known hallmarks of cerebral ischemia/reperfusion (I/R) injury, still, expression of proteins involved in this aspect of I/R pathophysiology show inconsistent data. Neurosteroid dehydroepiandrosterone (DHEA) has been proposed as potent NMDAR modulator, but its influence on I/R-induced changes up to date remains questionable. Therefore, I/R-governed alteration of vesicular glutamate transporter 1 (vGluT1), synaptic NMDAR subunit composition, postsynaptic density protein 95 (PSD-95) and neuronal morphology alone or following DHEA treatment were examined. For that purpose, adult male Wistar rats were treated with a single dose of vehicle or DHEA (20 mg/kg i.p.) 4 h following sham operation or 15 min bilateral common carotid artery occlusion. Western blot was used for analyses of synaptic protein expressions in hippocampus and prefrontal cortex, while neuronal morphology was assessed using Nissl staining. Regional-specific postischemic changes were detected on protein level i.e. signs of neuronal damage in CA1 area was accompanied with hippocampal vGluT1, NR1, NR2B enhancement and PSD-95 decrement, while histological changes observed in layer III were associated with decreased NR1 subunit in prefrontal cortex. Under physiological conditions DHEA had no effect on protein and histological appearance, while in ischemic milieu it restored hippocampal PSD-95 and NR1 in prefrontal cortex to the control level. Along with intact neurons, ones characterized by morphology observed in I/R group were also present. Future studies involving NMDAR-related intracellular signaling and immunohistochemical analysis will reveal precise effects of I/R and DHEA treatment in selected brain regions.

Glutamatergic and central cholinergic dysfunction in the CA1, CA2 and CA3 fields on spatial learning and memory in chronic cerebral ischemia-Induced vascular dementia of rats

Chronic cerebral ischemia (CCI) is associated with cognitive decline in aging, vascular dementia and Alzheimer's disease. Substantial evidence has shown that chronic cerebral ischemia may cause cognitive impairment, but the underlying neurobiological mechanism is poorly understood so far. In the present study, we used a rat model of chronic cerebral ischemia by permanent bilateral common carotid artery occlusion (BCCAO) to investigate the alterations of glutamatergic and central cholinergic dysfunction, and their causal relationship with the cognitive deficits induced by chronic cerebral ischemia. We found that BCCAO rats exhibited spatial learning and memory impairments dysfunction 3 month after BCCAO. Meanwhile, vGluT levels as well as glutamatergic and central cholinergic positive neurons in the hippocampus CA1-3 field significantly decreased. The protection of glutamergic and cholinergic neurons or regulating glutamate and central cholinergic levels in hippocampal subregion may have beneficial effects on cognitive impairments associated with the possible mechanism in CCI-induced vascular dementia.

Meloxicam prevents COX-2-mediated post-surgical inflammation but not pain following laparotomy in mice

BACKGROUND

Inflammation is thought to be a major contributor to post-surgical pain, so non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used analgesics. However, compared to rats, considerably less is known as to how successfully these prevent pain in mice.

METHODS

A fluorescent COX-2 selective probe was used for the first time to evaluate the post-surgical anti-inflammatory effects of meloxicam, and automated behaviour analyses (HomeCageScan; HCS), the Mouse Grimace Scale (MGS) and body weight changes to assess its pain-preventative properties. Groups of 8-9 BALB/c mice were subcutaneously injected with saline (0.3 mL) or meloxicam at (1, 5 or 20 mg/kg) 1 h before a 1.5-cm midline laparotomy. The probe or a control dye (2 mg/kg) was injected intravenously 3 h later. Imaging was used to quantify inflammation at 7, 24 and 48 h following surgery. HCS data and MGS scores were respectively obtained from video recordings and photographs before surgery and 24 h later.

RESULTS

Post-surgical inflammation was dose dependently reduced by meloxicam; with 5 or 20 mg/kg being most effective compared to saline. However, all mice lost weight, MGS scores increased and behavioural activity was reduced by surgery for at least 24 h with no perceivable beneficial effect of meloxicam on any of these potentially pain-associated changes.

CONCLUSIONS

Although meloxicam prevented inflammation, even large doses did not prevent post-laparotomy pain possibly arising due to a range of factors, including, but not limited to inflammation. MGS scoring can be applied by very naïve assessors and so should be effective for cage-side use.

Retinal aging in the diurnal Chilean rodent (Octodon degus): histological, ultrastructural and neurochemical alterations of the vertical information processing pathway

The retina is sensitive to age-dependent degeneration. To find suitable animal models to understand and map this process has particular importance. The degu (Octodon degus) is a diurnal rodent with dichromatic color vision. Its retinal structure is similar to that in humans in many respects, therefore, it is well suited to study retinal aging. Histological, cell type-specific and ultrastructural alterations were examined in 6-, 12- and 36-months old degus. The characteristic layers of the retina were present at all ages, but slightly loosened tissue structure could be observed in 36-month-old animals both at light and electron microscopic levels. Elevated Glial fibrillary acidic protein (GFAP) expression was observed in Müller glial cells in aging retinas. The number of rod bipolar cells and the ganglion cells was reduced in the aging specimens, while that of cone bipolar cells remained unchanged. Other age-related differences were detected at ultrastructural level: alteration of the retinal pigment epithelium and degenerated photoreceptor cells were evident. Ribbon synapses were sparse and often differed in morphology from those in the young animals. These results support our hypothesis that (i) the rod pathway seems to be more sensitive than the cone pathway to age-related cell loss; (ii) structural changes in the basement membrane of pigment epithelial cells can be one of the early signs of degenerative processes; (iii) the loss of synaptic proteins especially from those of the ribbon synapses are characteristic; and (iv) the degu retina may be a suitable model for studying retinal aging.

Glutamate receptor and transporter modifications in rat organotypic hippocampal slice cultures exposed to oxygen-glucose deprivation: the contribution of cyclooxygenase-2

Meloxicam is a non-steroidal anti-inflammatory drug which has been reported to lessen the ischemic transcriptional effects in some of the glutamatergic system genes as well as to decrease the infarct volume in in vivo assays. In this study, we show how the presence of meloxicam decreases cell mortality in assays of oxygen-glucose deprivation (OGD) in rat organotypic hippocampal slices culture. Mortality was measured using propidium iodide. Transcript levels of some glutamatergic system genes, including vesicular and membrane glutamate transporters (VGLUT1, VGLUT2, GLAST-1A, GLT-1, and EAAC-1) and some glutamatergic receptor subunits (NMDA receptor, GluN1, GluN2A and GluN2B subunits and AMPA receptor, GluA1 and GluA2 subunits) were measured by real-time PCR (qPCR). The transcription of vesicular glutamate transporters and glutamatergic receptor subunits, but not membrane glutamate transporters, was modified by the presence of meloxicam. The study demonstrates the neuroprotective role of meloxicam in organotypic hippocampal slice cultures and shows how meloxicam is able to selectively increase or decrease the OGD-induced changes in the expression of the different glutamatergic system genes studied here. We suggest that the neuroprotective role of meloxicam could be due to a modification in the balance of the expression of some glutamatergic receptor subunits, leading to a different stoichiometry of receptors such as NMDA or AMPA. Thus, meloxicam would decrease the excitotoxicity induced by OGD.

Glutamate transporters in brain ischemia: to modulate or not?

In this review, we briefly describe glutamate (Glu) metabolism and its specific transports and receptors in the central nervous system (CNS). Thereafter, we focus on excitatory amino acid transporters, cystine/glutamate antiporters (system xc-) and vesicular glutamate transporters, specifically addressing their location and roles in CNS and the molecular mechanisms underlying the regulation of Glu transporters. We provide evidence from in vitro or in vivo studies concerning alterations in Glu transporter expression in response to hypoxia or ischemia, including limited human data that supports the role of Glu transporters in stroke patients. Moreover, the potential to induce brain tolerance to ischemia through modulation of the expression and/or activities of Glu transporters is also discussed. Finally we present strategies involving the application of ischemic preconditioning and pharmacological agents, eg β-lactam antibiotics, amitriptyline, riluzole and N-acetylcysteine, which result in the significant protection of nervous tissues against ischemia.