PFOS Elicits Cytotoxicity in Neuron Through Astrocyte-Derived CaMKII-DLG1 Signaling In Vitro Rat Hippocampal Model

Both epidemiological investigation and animal experiments demonstrated that pre-/postnatal exposure to perfluorooctane sulfonic acid (PFOS) could induce neurodevelopmental disorders. Previous studies showed that astrocyte was involved in PFOS-induced neurotoxicity, while little information is available. In the present study, the role of astrocyte-derived calmodulin-dependent protein kinase II (CaMKII)-phosphorylated discs large homolog 1 (DLG1) signaling in PFOS eliciting cytotoxicity in neuron was explored with primary cultured hippocampal astrocyte and neuron. The application of PFOS showed a decreased cell viability, synapse length and glutamate transporter 1 (GLT-1) expression, but an increased CaMKII, DLG1 and cyclic AMP response element binding protein (CREB) expression in primary cultured astrocyte. With 2-(2-hydroxyethylamino)-6-aminohexylcarbamic acid tert-butyl ester-9-isopropylpurine (CK59), the CaMKII inhibitor, the disturbed cell viability and molecules induced by PFOS could be alleviated (CREB expression was excluded) in astrocytes. The cytotoxic effect of neuron exposed to astrocyte conditional medium collected from PFOS (PFOS-ACM) pretreated with CK59 was also decreased. These results indicated that PFOS mediated GLT-1 expression through astrocyte-derived CaMKII-DLG signaling, which might be associated with injuries on neurons. The present study gave an insight in further exploration of mechanism in PFOS-induced neurotoxicity.

Suppression of presynaptic corticostriatal glutamate activity attenuates L-dopa-induced dyskinesia in 6-OHDA-lesioned Parkinson's disease mice

A common adverse effect of Parkinson's disease (PD) treatment is L-dopa-induced dyskinesia (LID). This condition results from both dopamine (DA)-dependent and DA-independent mechanisms, as glutamate inputs from corticostriatal projection neurons impact DA-responsive medium spiny neurons in the striatum to cause the dyskinetic behaviors. In this study, we explored whether suppression of presynaptic corticostriatal glutamate inputs might affect the behavioral and biochemical outcomes associated with LID. We first established an animal model in which 6-hydroxydopamine (6-OHDA)-lesioned mice were treated daily with L-dopa (10 mg/kg, i.p.) for 2 weeks; these mice developed stereotypical abnormal involuntary movements (AIMs). When the mice were pretreated with the NMDA antagonist, amantadine, we observed suppression of AIMs and reductions of phosphorylated ERK1/2 and NR2B in the striatum. We then took an optogenetic approach to manipulate glutamatergic activity. Slc17a6 (vGluT2)-Cre mice were injected with pAAV5-Ef1a-DIO-eNpHR3.0-mCherry and received optic fiber implants in either the M1 motor cortex or dorsolateral striatum. Optogenetic inactivation at either optic fiber implant location could successfully reduce the intensity of AIMs after 6-OHDA lesioning and L-dopa treatment. Both optical manipulation strategies also suppressed phospho-ERK1/2 and phospho-NR2B signals in the striatum. Finally, we performed intrastriatal injections of LDN 212320 in the dyskenesic mice to enhance expression of glutamate uptake transporter GLT-1. Sixteen hours after the LDN 212320 treatment, L-dopa-induced AIMs were reduced along with the levels of striatal phospho-ERK1/2 and phospho-NR2B. Together, our results affirm a critical role of corticostriatal glutamate neurons in LID and strongly suggest that diminishing synaptic glutamate, either by suppression of neuronal activity or by upregulation of GLT-1, could be an effective approach for managing LID.

Chronic social defeat stress induces the down-regulation of the Nedd4L-GLT-1 ubiquitination pathway in the prefrontal cortex of mice

Stressful life events contribute to the onset of major depressive disorder (MDD). We recently demonstrated abnormalities in ubiquitination in the pathophysiology of MDD. However, the underlying molecular mechanisms remain unclear. We investigated the involvement of the ubiquitination system-mediated glutamatergic dysfunction in social impairment induced by chronic social defeat stress (CSDS). Adult C57BL/6J mice were exposed to aggressor ICR male mice for 10 consecutive days. Social impairment was induced by CSDS in the social interaction test 1 days after the last stress exposure. In terms of brain microdialysis, CSDS reduced depolarization-evoked glutamate release in the prefrontal cortex (PFC), which was reversed by a glutamate transporter 1 (GLT-1) inhibitor. Interestingly, the expression of ubiquitinated, but not total GLT-1, was decreased in the PFC of mice exposed to CSDS. The expression of neural precursor cells expressing developmentally downregulated gene 4-like (Nedd4L: E3 ligase for GLT-1), and ubiquitin-conjugating enzyme E2D2 (Ube2d2: E2 ubiquitin-conjugating enzyme for Nedd4L) was also reduced in CSDS mice. Furthermore, the downregulation of the Nedd4L-GLT-1 ubiquitination pathway decreased SIT ratio, but up-regulation increased it even in non-CSDS mice. Taken together, the decrease in GLT-1 ubiquitination may reduce the release of extracellular glutamate induced by high-potassium stimulation, which may lead to social impairment, while we could not find differences in GLT-1 ubiquitination between susceptible and resistant CSDS mice. In conclusion, GLT-1 ubiquitination could play a crucial role in the pathophysiology of MDD and is an attractive target for the development of novel antidepressants.

Identification of PS1/gamma-secretase and glutamate transporter GLT-1 interaction sites

The recently discovered interaction between Presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for generating amyloid-β peptides, and GLT-1, a major glutamate transporter in the brain (EAAT2), provides a mechanistic link between these two key factors involved in Alzheimer's disease (AD) pathology. Modulating this interaction can be crucial to understand the consequence of such crosstalk in AD context and beyond. However, the interaction sites between these two proteins are unknown. Herein, we utilized an alanine scanning approach coupled with FRET-based fluorescence lifetime imaging microscopy to identify the interaction sites between PS1 and GLT-1 in their native environment within intact cells. We found that GLT-1 residues at position 276 to 279 (TM5) and PS1 residues at position 249 to 252 (TM6) are crucial for GLT-1-PS1 interaction. These results have been cross validated using AlphaFold Multimer prediction. To further investigate whether this interaction of endogenously expressed GLT-1 and PS1 can be prevented in primary neurons, we designed PS1/GLT-1 cell-permeable peptides (CPPs) targeting the PS1 or GLT-1 binding site. We used HIV TAT domain to allow for cell penetration which was assayed in neurons. First, we assessed the toxicity and penetration of CPPs by confocal microscopy. Next, to ensure the efficiency of CPPs, we monitored the modulation of GLT-1-PS1 interaction in intact neurons by fluorescence lifetime imaging microscopy. We saw significantly less interaction between PS1 and GLT-1 with both CPPs. Our study establishes a new tool to study the functional aspect of GLT-1-PS1 interaction and its relevance in normal physiology and AD models.

High-frequency repetitive transcranial magnetic stimulation improves depressive-like behaviors in CUMS-induced rats by modulating astrocyte GLT-1 to reduce glutamate toxicity

Impaired glutamate recycling plays an important role in the pathophysiology of depression, and it has been demonstrated that glutamate transporter-1 (GLT-1) on astrocytes is involved in glutamate uptake. Studies have shown that repetitive transcranial magnetic stimulation (rTMS) is effective in treating depression, however, the exact mechanism of rTMS treatment remains unclear. Here, we used a chronic unpredictable mild stress (CUMS) protocol to induce depression-like behaviors in rats followed by rTMS treatment. Behavioral assessment was primarily through SPT, FST, OFT and body weight. Histological analysis focused on GFAP and GLT-1 expression, synaptic plasticity, apoptosis and PI3K/Akt/CREB pathway-related proteins. The results showed that rTMS treatment increased sucrose preference, improved locomotor activity, shortened immobility time as well as increased body weight. And rTMS intervention reversed the elevated glutamate concentration in the hippocampus of CUMS rats using an ELISA kit. Moreover, rTMS ameliorated the reduction in GFAP and GLT-1 expression, alleviated the decrease in BDNF, PSD95 and synapsin-1 expression, also reversed the expression levels of BAX and Bcl2 in the hippocampus of CUMS-induced rats. Moreover, rTMS also increased the protein phosphorylation level of PI3K/Akt/CREB pathway. These results suggest that rTMS treatment ameliorates depression-like behaviors in the rat model by reversing the reduction of GLT-1 on astrocytes and reducing glutamate accumulation in the synaptic cleft, which in turn ameliorates synaptic plasticity damage and neuronal apoptosis. The regulation of GLT-1 by rTMS may be through the PI3K/Akt/CREB pathway.

Ceftriaxone Modulates Ubiquitination of α-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionic Acid Receptors to Improve Long-Term Potentiation Impairment Induced by Exogenous β-Amyloid in a Glutamate Transporter-1 Dependent Manner

Α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) are crucial for properties of synaptic plasticity, such as long-term potentiation (LTP). LTP impairment can occur early in the onset of Alzheimer's disease (AD). The downregulation or decreased abundance of AMPAR expression in the postsynaptic membrane is closely associated with LTP impairment. Ceftriaxone (Cef) can improve LTP impairment in the early stages of AD in a mouse model. The purpose of this study was to explore the mechanism underlying this process from the aspects of AMPAR expression and ubiquitination degree. In this study, we found that β-amyloid (Aβ) treatment induced hippocampal LTP impairment and AMPAR downregulation and ubiquitination. Cef pretreatment ameliorated Aβ-induced hippocampal LTP impairment, reduced AMPAR ubiquitination, and increased AMPAR expression, especially in the plasma membrane, in Aβ-treated mice. Administration of USP46 siRNA and DHK (a specific blocker of glutamate transporter-1) significantly inhibited the above effects of Cef, suggesting a role for anti-AMPAR ubiquitination and upregulation of glutamate transporter-1 (GLT-1) in the Cef-induced improvements mentioned above. The above findings demonstrate that pretreatment with Cef effectively mitigated Aβ-induced impairment of hippocampal LTP by suppressing the ubiquitination process of AMPARs in a GLT-1-dependent manner. These results provide novel insights into the underlying mechanisms elucidating the anti-AD by Cef.

GLT-1a glutamate transporter nanocluster localization is associated with astrocytic actin and neuronal Kv2 clusters at sites of neuron-astrocyte contact

Introduction: Astrocytic GLT-1 glutamate transporters ensure the fidelity of glutamic neurotransmission by spatially and temporally limiting glutamate signals. The ability to limit neuronal hyperactivity relies on the localization and diffusion of GLT-1 on the astrocytic surface, however, little is known about the underlying mechanisms. We show that two isoforms of GLT-1, GLT-1a and GLT-1b, form nanoclusters on the surface of transfected astrocytes and HEK-293 cells. Methods: We used both fixed and live cell super-resolution imaging of fluorescent protein and epitope tagged proteins in co-cultures of rat astrocytes and neurons. Immunofluorescence techniques were also used. GLT1 diffusion was assessed via single particle tracking and fluorescence recovery after photobleach (FRAP). Results: We found GLT-1a, but not GLT-1b, nanoclusters concentrated adjacent to actin filaments which was maintained after addition of glutamate. GLT-1a nanocluster concentration near actin filaments was prevented by expression of a cytosolic GLT-1a C-terminus, suggesting the C-terminus is involved in the localization adjacent to cortical actin. Using super-resolution imaging, we show that astrocytic GLT-1a and actin co-localize in net-like structures around neuronal Kv2.1 clusters at points of neuron/astrocyte contact. Conclusion: Overall, these data describe a novel relationship between GLT-1a and cortical actin filaments, which localizes GLT-1a near neuronal structures responsive to ischemic insult.

Effects of Beta Lactams on Behavioral Outcomes of Substance Use Disorders: A Meta-Analysis of Preclinical Studies

INTRODUCTION

Preclinical studies demonstrated that beta-lactams have neuroprotective effects in conditions involving glutamate neuroexcitotoxicity, including substance use disorders (SUDs). This meta-analysis aims to analyze the existing evidences on the effects of beta-lactams as glutamate transporter 1 (GLT-1) upregulators in animal models of SUDs, identification of gaps in the literature, and setting the stage for potential translation into clinical phases.

METHODS

Meta-analysis was conducted on preclinical studies retrieved systematically from MEDLINE and ScienceDirect databases. Abused substances were identified by refereeing to the National Institute on Drug Abuse (NIDA). The results were quantitatively described with a focus on the behavioral outcomes. Treatment effect sizes were described using standardized mean difference, and they were pooled using random effect model. I2-statistic was used to assess heterogeneity, and Funnel plot and Egger's test were used for assessment of publication bias.

RESULTS

Literature search yielded a total of 71 studies that were eligible to be included in the analysis. Through these studies, the effects of beta-lactams were evaluated in animal models of nicotine, cannabis, amphetamines, synthetic cathinone, opioids, ethanol, and cocaine use disorders as well as steroids-related aggressive behaviors. Meta-analysis showed that treatments with beta-lactams consistently reduced the pooled undesired effects of the abused substances in several paradigms, including drug-self administration, conditioned place preference, drug seeking behaviors, hyperlocomotion, withdrawal syndromes, tolerance to analgesic effects, hyperalgesia, and hyperthermia.

CONCLUSION

This meta-analysis revealed that enhancing GLT-1 expression in the brain through beta-lactams seemed to be a promising treatment approach in the context of substance use disorders, as indicated by results in animal models.

Clavulanic Acid and its Potential Therapeutic Effects on the Central Nervous System

Clavulanic acid (CLAV) is a non-antibiotic β-lactam that has been used since the late 1970s as a β-lactamase inhibitor in combination with amoxicillin, another ß-lactam with antibiotic activity. Its long-observed adverse reaction profile allows it to say that CLAV is a well-tolerated drug with mainly mild adverse reactions. Interestingly, in 2005, it was discovered that β-lactams enhance the astrocytic expression of GLT-1, a glutamate transporter essential for maintaining synaptic glutamate homeostasis involved in several pathologies of the central nervous system (CNS). This finding, along with a favorable pharmacokinetic profile, prompted the appearance of several studies that intended to evaluate the effect of CLAV in preclinical disease models. Studies have revealed that CLAV can increase GLT-1 expression in the nucleus accumbens (NAcc), medial prefrontal cortex (PFC), and spinal cord of rodents, to affect glutamate and dopaminergic neurotransmission, and exert an anti-inflammatory effect by modulating the levels of the cytokines TNF-α and interleukin 10 (IL-10). CLAV has been tested with positive results in preclinical models of epilepsy, addiction, stroke, neuropathic and inflammatory pain, dementia, Parkinson's disease, and sexual and anxiety behavior. These properties make CLAV a potential therapeutic drug if repurposed. Therefore, this review aims to gather information on CLAV's effect on preclinical neurological disease models and to give some perspectives on its potential therapeutic use in some diseases of the CNS.

PS1/gamma-secretase acts as rogue chaperone of glutamate transporter EAAT2/GLT-1 in Alzheimer's disease

The recently discovered interaction between presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for the generation of amyloid-β(Aβ) peptides, and GLT-1, the major glutamate transporter in the brain (EAAT2 in the human) may provide a mechanistic link between two important pathological aspects of Alzheimer's disease (AD): abnormal Aβoccurrence and neuronal network hyperactivity. In the current study, we employed a FRET-based approach, fluorescence lifetime imaging microscopy (FLIM), to characterize the PS1/GLT-1 interaction in its native environment in the brain tissue of sporadic AD (sAD) patients. There was significantly less interaction between PS1 and GLT-1 in sAD brains, compared to tissue from patients with frontotemporal lobar degeneration (FTLD), or non-demented age-matched controls. Since PS1 has been shown to adopt pathogenic "closed" conformation in sAD but not in FTLD, we assessed the impact of changes in PS1 conformation on the interaction. Familial AD (fAD) PS1 mutations which induce a "closed" PS1 conformation similar to that in sAD brain and gamma-secretase modulators (GSMs) which induce a "relaxed" conformation, reduced and increased the interaction, respectively. This indicates that PS1 conformation seems to have a direct effect on the interaction with GLT-1. Furthermore, using biotinylation/streptavidin pull-down, western blotting, and cycloheximide chase assays, we determined that the presence of PS1 increased GLT-1 cell surface expression and GLT-1 homomultimer formation, but did not impact GLT-1 protein stability. Together, the current findings suggest that the newly described PS1/GLT-1 interaction endows PS1 with chaperone activity, modulating GLT-1 transport to the cell surface and stabilizing the dimeric-trimeric states of the protein. The diminished PS1/GLT-1 interaction suggests that these functions of the interaction may not work properly in AD.

Kainic Acid-Induced Excitotoxicity Leads to the Activation of Heat Shock Response

Heat shock response (HSR) which is regulated by heat shock factor 1 (HSF1) is the most important mechanism and the major regulator that prevents protein aggregation in neurodegenerative diseases. Excitotoxicity, which is the accumulation of excess glutamate in synaptic cleft, is observed in age-dependent neurodegenerative diseases and also in stroke, epilepsy, and brain trauma. Only a few studies in the literature show the link between excitotoxicity and HSR. In this study, we aimed to show the molecular mechanism underlying this link. We applied heat shock (HS) treatment and induced excitotoxicity with kainic acid (KA) in neuroblastoma (SHSY-5Y) and glia (immortalized human astrocytes (IHA)) cells. We observed that, only in SHSY-5Y cells, heat shock preconditioning increases cell survival after KA treatment. GLT-1 mRNA expression is increased as a result of KA treatment and HS due to the elevation of HSF1 binding to GLT-1 promoter which was induced by HSF1 phosphorylation and sumolation in SHSY-5Y cells. Additionally, glutamine synthetase and glutaminase expressions are increased after HS preconditioning in SHSY-5Y cells indicating that HS activates glutamate metabolism modulators and accelerates the glutamate cycle. In glia cells, we did not observe the effect of HS preconditioning. In summary, heat shock preconditioning might be protective against excitotoxicity-related cell death and degeneration.

Marrow Mesenchymal Stem Cell-Derived Exosomes Upregulate Astrocytic Glutamate Transporter-1 Expression via miR-124/mTOR Pathway against Oxygen-Glucose Deprivation/Reperfusion Injury

BACKGROUND

Experimental investigations have reported the efficacy of marrow mesenchymal stem cell-derived exosomes (MSC-Exos) for the treatment of ischemic stroke. The therapeutic mechanism, however, is still unknown. The purpose of the study is to show whether MSC-Exos increases astrocytic glutamate transporter-1 (GLT-1) expression in response to ischemic stroke and to investigate further mechanisms.

METHODS AND RESULTS

An in vitro ischemia model (oxygen-glucose deprivation/reperfusion, OGD/R) was used. MSC-Exos was identified by Western blot (WB) and transmission electron microscopy (TEM). To further investigate the mechanism, MSC-Exos, miR-124 inhibitor, and mimics, and a mTOR pathway inhibitor (rapamycin, Rap) were used. The interaction between GLT-1 and miR-124 was analyzed by luciferase reporter assay. The GLT-1 RNA expression and miR-124 was assessed by quantitative real-time polymerase chain reaction (qRTPCR). The protein expressions of GLT-1, S6, and pS6 were detected by WB. Results demonstrated that MSC-Exos successfully inhibited the decrease of GLT-1 and miR-124 expression and the increase of pS6 expression in astrocytes after OGD/R. miR-124 inhibitor suppressed the effect of MSC-Exos on GLT-1 upregulation after OGD/R. Rapamycin notably decreased pS6 expression with significantly higher GLT-1 expression in astrocytes injured by OGD/R. Luciferase activity of the reporter harboring the wild-type or mutant GLT-1 3'UTR was not inhibited by miR-124 mimics. Further results showed that the inhibiting effect of MSC-Exos on pS6 expression and promoting effect of MSC-Exos on GLT-1 expression could be reversed by miR-124 inhibitor after OGD/R; meanwhile, the above conditions could be reversed again by rapamycin.

CONCLUSIONS

Results show that miR-124 and the mTOR pathway are involved in regulation of MSC-Exos on GLT-1 expression in astrocytes injured by OGD/R. miR-124 does not directly target GLT-1. MSC-Exos upregulates GLT-1 expression via the miR-124/mTOR pathway in astrocytes injured by OGD/R.

Effects of Chronic Hydrocodone Exposure and Ceftriaxone on the Expression of Astrocytic Glutamate Transporters in Mesocorticolimbic Brain Regions of C57/BL Mice

Exposure to opioids can lead to the alteration of several neurotransmitters. Among these neurotransmitters, glutamate is thought to be involved in opioid dependence. Glutamate neurotransmission is mainly regulated by astrocytic glutamate transporters such as glutamate transporter 1 (GLT-1) and cystine/glutamate antiporter (xCT). Our laboratory has shown that exposure to lower doses of hydrocodone reduced the expression of xCT in the nucleus accumbens (NAc) and the hippocampus. In the present study, we investigated the effects of chronic exposure to hydrocodone, and tested ceftriaxone as a GLT-1 upregulator in mesocorticolimbic brain regions such as the NAc, the amygdala (AMY), and the dorsomedial prefrontal cortex (dmPFC). Eight-week-old male mice were divided into three groups: (1) the saline vehicle control group; (2) the hydrocodone group; and (3) the hydrocodone + ceftriaxone group. Mice were injected with hydrocodone (10 mg/kg, i.p.) or saline for 14 days. On day seven, the hydrocodone/ceftriaxone group was injected with ceftriaxone (200 mg/kg, i.p.) for last seven days. Chronic exposure to hydrocodone reduced the expression of GLT-1, xCT, protein kinase B (AKT), extracellular signal-regulated kinases (ERK), and c-Jun N-terminal Kinase (JNK) in NAc, AMY, and dmPFC. However, hydrocodone exposure increased the expression of G-protein-coupled metabotropic glutamate receptors (mGluR5) in the NAc, AMY, and dmPFC. Importantly, ceftriaxone treatment normalized the expression of mGluR5, GLT-1, and xCT in all these brain regions, except for xCT in the AMY. Importantly, ceftriaxone treatment attenuated hydrocodone-induced downregulation of signaling pathways such as AKT, ERK, and JNK expression in the NAc, AMY, and dmPFC. These findings demonstrate that ceftriaxone has potential therapeutic effects in reversing hydrocodone-induced downregulation of GLT-1 and xCT in selected reward brain regions, and this might be mediated through the downstream kinase signaling pathways such as AKT, ERK, and JNK.

Yueju volatile oil plays an integral role in the antidepressant effect by up-regulating ERK/AKT-mediated GLT-1 expression to clear glutamate

Phytochemical investigation of the volatile oil of Yueju (YJVO) and its constituent herbs induced the detection of 52 compounds in YJVO, mainly monoterpenes and sesquiterpenes as well as a small amount of aromatic and aliphatic compounds. 5 of these compounds were found only in the YJVO instead of the volatile oil of its constituent herbs. The anti-depressant effect of YJVO was proved by behavioral tests in chronic unpredictable mild stress (CUMS) mice. An acute oral toxicity evaluation determined the LD50 of YJVO was 5.780 mL/kg. Doppler ultrasound and laser speckle imaging have detected that the YJVO could improve depression-related cerebral blood flow. In addition, related neurotransmitters and proteins were analyzed through targeted metabolomics and immunofluorescence. The potential antidepressant mechanisms of YJVO related to significantly decreasing Glu in CUMS mice by up-regulating the ERK/AKT-mediated expression of GLT-1.

Nanoassemblies from the aqueous extract of roasted coffee beans modulate the behavioral and molecular effects of smoking withdrawal-induced anxiety in female rats

Antioxidant-rich plant extracts have demonstrated tremendous value as inflammatory modulators and as nanomaterial precursors. Chronic cigarette smoking alters neurotransmitter systems, particularly the glutamatergic system, and produces neuroinflammation. This study aimed to investigate the behavioral and molecular correlates of cigarette smoking withdrawal-induced anxiety-like behavior in rats, and whether these effects could be mitigated by the administration of antioxidant nanoassemblies prepared by spontaneous oxidation of dark-roasted Arabica coffee bean aqueous extracts. Four experimental groups of female Sprague-Dawley rats were randomly assigned to: (i) a control group that was only exposed to room air, (ii) a COF group that was administered 20 mg/kg of the coffee nanoassemblies by oral gavage, (iii) a SMOK group that was exposed to cigarette smoke and was given an oral gavage of distilled water, (iv) and a SMOK + COF group that was exposed to cigarette smoke and administered 20 mg/kg of the coffee nanoassemblies. Animals were exposed to cigarette smoke for 2 h per day, five days per week, with a 2-day withdrawal period each week. At the end of the 4th week, rats began receiving either distilled water or the coffee nanoassemblies before being exposed to cigarette smoke for 21 additional days. Weekly behavioral tests revealed that cigarette smoking withdrawal exacerbated anxiety, while the administration of the coffee nanoassemblies reduced this effect. The effect of cigarette smoking on astroglial glutamate transporters and nuclear factor kappa B (NF-κB) expression in brain subregions was also measured. Smoking reduced the relative mRNA and protein levels of the glutamate transporter 1 (GLT-1) and the cystine/glutamate antiporter (xCT), and increased the levels of NF-κB, but these effects were attenuated by the coffee nanoassemblies. Thus, administration of the antioxidant nanoassemblies decreased the negative effects of cigarette smoke, which included neuroinflammation, changes in glutamate transporters' expression, and a rise in anxiety-like behavior.

Glutamate-Transporter Unbinding in Probabilistic Synaptic Environment Facilitates Activation of Distant NMDA Receptors

Once outside the synaptic cleft, the excitatory neurotransmitter glutamate is rapidly bound by its high-affinity transporters, which are expressed in abundance on the surface of perisynaptic astroglia. While this binding and the subsequent uptake of glutamate constrain excitatory transmission mainly within individual synapses, there is growing evidence for the physiologically important extrasynaptic actions of glutamate. However, the mechanistic explanation and the scope of such actions remain obscure. Furthermore, a significant proportion of glutamate molecules initially bound by transporters could be released back into the extracellular space before being translocated into astrocytes. To understand the implications of such effects, we simulated the release, diffusion, and transporter and receptor interactions of glutamate molecules in the synaptic environment. The latter was represented via trial-by-trial stochastic generation of astroglial and neuronal elements in the brain neuropil (overlapping spheroids of varied sizes), rather than using the 'average' morphology, thus reflecting the probabilistic nature of neuropil architectonics. Our simulations predict significant activation of high-affinity receptors, such as receptors of the NMDA type, at distances beyond half-micron from the glutamate release site, with glutamate-transporter unbinding playing an important role. These theoretical predictions are consistent with recent glutamate imaging data, thus lending support to the concept of significant volume-transmitted actions of glutamate in the brain.

Ceftriaxone and selenium mitigate seizures and neuronal injury in pentylenetetrazole-kindled rats: Oxidative stress and inflammatory pathway

Epilepsy is one of the most serious worldwide neurological disorders that lead to the cognitive-psychosocial insults in recurrent seizures. About one third of the patients are drug-resistant, so innovative drugs are needed to manage seizures to improve the quality of life. Ceftriaxone is a cephalosporin antibiotic that increases the expression of glutamate transporters-1 and improves the neurobehavioral effects caused by increased glutamate level in the CNS. Selenium is well known antioxidant. The present study aimed to investigate ceftriaxone and selenium therapeutic effects against epilepsy in rats. Epilepsy was induced by PTZ given at a dose (50 mg/kg I.P) on alternative days for 13 days. Eighty rats were randomly divided into 8 groups: Group1-2; normal and vehicle control, Group 3; PTZ group, Group 4-8; kindled rats received selenium, ceftriaxone100, ceftriaxone200, selenium + ceftriaxone100 and selenium + ceftriaxone200 mg/kg/day respectively for a week. At the end of the study, behavioral tests were performed. Oxidative stress, inflammatory markers, neurotransmitters and GLT-1 were measured in brain tissue homogenate. Brain histopathological investigation was also done. PTZ-kindled rats exhibited increased Racine score, besides behavioral tests and histopathological changes, significant elevation in oxidative stress and inflammatory markers, with decrease in serotonin, dopamine, GABA levels and GLT-1 expressions. Selenium and Ceftriaxone alone or combined treatment decreased Racine score with remarkable improvement in behavioral and histopathological changes. The antioxidant enzymes, neurotransmitters and GLT-1 expressions were increased, along with reduced TNF-α, IL-1 levels. Current study showed that selenium + ceftriaxone100 group represents a possible approach to improve epilepsy particularly through inhibiting oxidative stress and inflammation.

Fenpropathrin Induces GLT-1 Ubiquitination and Increases IL-6 Secretion through the Mdm2-p53 Pathway

Human exposure to fenpropathrin, a widely used pesticide, is linked to Parkinson's-like symptoms in the body. However, a specific pathogenic mechanism is still unclear. This study found that fenpropathrin increased the expression of murine double minute 2 (Mdm2) and reduced the expression of p53. Fenpropathrin stimulated the expression of neural precursor cell expressed, developmentally down-regulated 4-like (Nedd4L) and promoted the secretion of the inflammatory cytokine interleukin-6 (IL-6) through the Mdm2-p53 pathway. Nedd4L, a ubiquitin ligase, mediated the ubiquitination degradation of glutamate transporter 1 (GLT-1), resulting in glutamate accumulation and excitotoxicity aggravation. Our findings elucidate part of the pathogenic mechanism of fenpropathrin toxicity and provide scientific evidence to help develop guidance for pesticide control and environmental protection.

The Regulation of GLT-1 Degradation Pathway by SIRT4

Glial cells give rise to glioblastoma multiform as a primary brain tumor. In glioblastomas, neurons are destroyed via excitotoxicity which is the accumulation of excess glutamate in synaptic cavity. Glutamate Transporter 1 (GLT-1) is the main transporter that absorbs the excessive glutamate. Sirtuin 4 (SIRT4) was shown to have a potential protective role against excitotoxicity in previous studies. In this study, the regulation of dynamic GLT-1 expression by SIRT4 was analyzed in glia (immortalized human astrocytes) and glioblastoma (U87) cells. The expression of GLT-1 dimers and trimers were reduced and the ubiquitination of GLT-1 was increased in glioblastoma cells when SIRT4 was silenced; however GLT-1 monomer was not affected. In glia cells, SIRT4 reduction did not affect GLT-1 monomer, dimer, trimer expression or the ubiquitination of GLT-1. The phosphorylation of Nedd4-2 and the expression of PKC did not change in glioblastoma cells when SIRT4 was silenced but increased in glia cells. We also showed that SIRT4 deacetylates PKC in glia cells. In addition, GLT-1 was shown to be deacetylated by SIRT4 which might be a priority for ubiquitination. Therefore, we conclude that GLT-1 expression is regulated differently in glia and glioblastoma cells. SIRT4 activators or inhibitors of ubiquitination may be used to prevent excitotoxicity in glioblastomas.

Inhibition of mGluR5 alters BDNF/TrkB and GLT-1 expression in the prefrontal cortex and hippocampus and ameliorates PTSD-like behavior in rats

RATIONALE AND OBJECTIVE

Post-traumatic stress disorder (PTSD) is a prevalent and debilitating psychiatric disorder. However, its specific etiological mechanism remains unclear. Previous studies have shown that traumatic stress changes metabotropic glutamate receptor 5 (mGluR5) expression in the hippocampus (HIP) and prefrontal cortex (PFC). More importantly, mGluR5 expression is often accompanied by alterations in brain-derived neurotrophic factor (BDNF). Furthermore, BDNF/tropomyosin-associated kinase B (TrkB) signaling plays multiple roles, including roles in neuroplasticity and antidepressant activity, by regulating glutamate transporter-1 (GLT-1) expression. This study aims to explore the effects of inhibiting mGluR5 on PTSD-like behaviors and BDNF, TrkB, and GLT-1 expression in the HIP and PFC of inevitable foot shock (IFS)-treated rats.

METHODS

Seven-day IFS was used to establish a PTSD rat model, and 2-methyl-6-(phenylethynyl)-pyridine (MPEP) (10 mg/kg, intraperitoneal injection) was used to inhibit the activity of mGluR5 during IFS in rats. After modeling, behavioral changes and mGluR5, BDNF, TrkB, and GLT-1 expression in the PFC and HIP were examined.

RESULTS

First, the IFS procedure induced PTSD-like behavior. Second, IFS increased the expression of mGluR5 and decreased BDNF, TrkB, and GLT-1 expression in the PFC and HIP. Third, the mGluR5 antagonist blocked the above behavioral and molecular alterations.

CONCLUSIONS

mGluR5 was involved in IFS-induced PTSD-like behavior by changing BDNF, TrkB, and GLT-1 expression.

Age-Associated Upregulation of Glutamate Transporters and Glutamine Synthetase in Senescent Astrocytes In Vitro and in the Mouse and Human Hippocampus

Aging is marked by complex and progressive physiological changes, including in the glutamatergic system, that lead to a decline of brain function. Increased content of senescent cells in the brain, such as glial cells, has been reported to impact cognition both in animal models and human tissue during normal aging and in the context of neurodegenerative disease. Changes in the glutamatergic synaptic activity rely on the glutamate-glutamine cycle, in which astrocytes handle glutamate taken up from synapses and provide glutamine for neurons, thus maintaining excitatory neurotransmission. However, the mechanisms of glutamate homeostasis in brain aging are still poorly understood. Herein, we showed that mouse senescent astrocytes in vitro undergo upregulation of GLT-1, GLAST, and glutamine synthetase (GS), along with the increased enzymatic activity of GS and [³H]-D-aspartate uptake. Furthermore, we observed higher levels of GS and increased [³H]-D-aspartate uptake in the hippocampus of aged mice, although the activity of GS was similar between young and old mice. Analysis of a previously available RNAseq dataset of mice at different ages revealed upregulation of GLAST and GS mRNA levels in hippocampal astrocytes during aging. Corroborating these rodent data, we showed an increased number of GS + cells, and GS and GLT-1 levels/intensity in the hippocampus of elderly humans. Our data suggest that aged astrocytes undergo molecular and functional changes that control glutamate-glutamine homeostasis upon brain aging.

Revealing the contribution of astrocytes to glutamatergic neuronal transmission

Research on glutamatergic neurotransmission has focused mainly on the function of presynaptic and postsynaptic neurons, leaving astrocytes with a secondary role only to ensure successful neurotransmission. However, recent evidence indicates that astrocytes contribute actively and even regulate neuronal transmission at different levels. This review establishes a framework by comparing glutamatergic components between neurons and astrocytes to examine how astrocytes modulate or otherwise influence neuronal transmission. We have included the most recent findings about the role of astrocytes in neurotransmission, allowing us to understand the complex network of neuron-astrocyte interactions. However, despite the knowledge of synaptic modulation by astrocytes, their contribution to specific physiological and pathological conditions remains to be elucidated. A full understanding of the astrocyte's role in neuronal processing could open fruitful new frontiers in the development of therapeutic applications.

Acetylsalicylic acid reduces cigarette smoke withdrawal-induced anxiety in rats via modulating the expression of NFĸB, GLT-1, and xCT

Background: Chronic exposure to cigarette smoke produces neuroinflammation and long-term changes in neurotransmitter systems, especially glutamatergic systems. Objective: We examined the effects of cigarette smoke on astroglial glutamate transporters as well as NF-κB expression in mesocorticolimbic brain regions, prefrontal cortex (PFC) and nucleus accumbens (NAc). The behavioral consequences of cigarette smoke exposure were assessed using open field (OF) and light/dark (LD) tests to assess withdrawal-induced anxiety-like behavior. Methods: Sprague-Dawley rats were randomly assigned to five experimental groups: a control group exposed only to standard room air, a cigarette smoke exposed group treated with saline vehicle, two cigarette smoke exposed groups treated with acetylsalicylic acid (ASA) (15 mg/kg and 30 mg/kg, respectively), and a group treated only with ASA (30 mg/kg). Cigarette smoke exposure was performed for 2 h/day, 5 days/week, for 31 days. Behavioral tests were conducted weekly, 24 h after cigarette smoke exposure, during acute withdrawal. At the end of week 4, rats were given either saline or ASA 45 min before cigarette exposure for 11 days. Results: Cigarette smoke increased withdrawal-induced anxiety, and 30 mg/kg ASA attenuated this effect. Cigarette smoke exposure increased the relative mRNA and protein expression of nuclear factor ĸB (NFĸB) in PFC and NAc, and ASA treatment reversed this effect. Also, cigarette smoke decreased the relative mRNA and protein expression of glutamate transporter1 (GLT-1) and the cystine-glutamate transporter (xCT) in the PFC and the NAc, while ASA treatment normalized their expression. Conclusion: Cigarette smoke caused neuroinflammation, alterations in glutamate transporter expression, and increased anxiety-like behavior, and these effects were attenuated by acetylsalicylic acid treatment.

Upregulation of glutamate transporter 1 by mTOR/Akt pathway in astrocyte culture during oxygen-glucose deprivation and reoxygenation

Astrocyte-specific glutamate transporter subtype 1 (GLT-1) plays an important role in influencing glutamate excitatory toxicity and preventing the death of excitatory toxic neurons. Although the mammalian target of rapamycin (mTOR)/protein kinase B(Akt)/nuclear factor kappa B signaling cascade is involved in the upregulation of astrocytic GLT-1 in oxygen-glucose deprivation (OGD), it is unclear whether the mTOR/Akt pathway is involved in astrocytic GLT-1 upregulation in OGD and reoxygenation (OGD/R). In this study, we found that the treatment of cultured astrocytes with rapamycin and triciribine led to the decreased astrocytes' protrusions, smaller nuclei, and an increased apoptotic rate. The inhibitors of mTOR complex 1 significantly increased the expression levels of phosphorylated Akt-Ser473 (p-Akt), phosphorylated Akt-Thr308(p-Akt), and GLT-1, while Akt-specific inhibitors blocked GLT-1 expression, suggesting that the mTOR/Akt pathway is involved in GLT-1 upregulation. We further demonstrated that astrocytes under OGD/R adapted to environmental changes through the mTOR/Akt pathway, mainly by altering cell morphology and apoptosis and upregulating the expression levels of p-Akt and GLT-1. Our results suggested that astrocytes may adapt to short-term ischemic-reperfusion injury by regulating cell morphology, apoptosis and GLT-1 upregulation.

Glutamatergic systems in neuropathic pain and emerging non-opioid therapies

Neuropathic pain, a disease of the somatosensory nervous system, afflicts many individuals and adequate management with current pharmacotherapies remains elusive. The glutamatergic system of neurons, receptors and transporters are intimately involved in pain but, to date, there have been few drugs developed that therapeutically modulate this system. Glutamate transporters, or excitatory amino acid transporters (EAATs), remove excess glutamate around pain transmitting neurons to decrease nociception suggesting that the modulation of glutamate transporters may represent a novel approach to the treatment of pain. This review highlights and summarizes (1) the physiology of the glutamatergic system in neuropathic pain, (2) the preclinical evidence for dysregulation of glutamate transport in animal pain models, and (3) emerging novel therapies that modulate glutamate transporters. Successful drug discovery requires continuous focus on basic and translational methods to fully elucidate the etiologies of this disease to enable the development of targeted therapies. Increasing the efficacy of astrocytic EAATs may serve as a new way to successfully treat those suffering from this devastating disease.

LncRNA BIRF Promotes Brain Ischemic Tolerance Induced By Cerebral Ischemic Preconditioning Through Upregulating GLT-1 via Sponging miR-330-5p

Long noncoding RNAs (lncRNAs) play an important regulatory role in various diseases. However, the role of lncRNAs in brain ischemic tolerance (BIT) induced by cerebral ischemic preconditioning (CIPC) is still unknown. The lncRNA profile of rat cortical astrocytes pretreated with ischemic preconditioning was analyzed by high-throughput sequencing. The results of Cell-Counting Kit-8 (CCK-8) assay showed that a novel lncRNA, NONRATT009133.2, which we referred to as brain ischemia-related factor (BIRF), was highly correlated with BIT. Through bioinformatics analysis, we predicted that BIRF, miR-330-5p, and GLT-1 (also named Slc1a2) might constitute a ceRNA regulatory network in the induction of BIT. We found that BIRF was upregulated by CIPC, which promoted GLT-1 expression and BIT induction. BIRF could directly bind to miR-330-5p. Furthermore, miR-330-5p directly targeted GLT-1, and miR-330-5p inhibited both GLT-1 expression and BIT induction in vitro and in vivo. Moreover, BIRF acts as a molecular sponge to competitively bind to miR-330-5p with GLT-1 mRNA, while the miR-330-5p inhibitor reversed all the effects of BIRF siRNA on GLT-1 expression and neuronal vitality. Taken together, our results demonstrate the important roles of the BIRF/miR-330-5p/GLT-1 axis in the induction of BIT by CIPC. BIRF may be a potentially effective therapeutic strategy against stroke injury.

Interactive role of acid sensing ion channels and glutamatergic system in opioid dependence

Dysregulation in glutamatergic receptors and transporters has been found to mediate drugs of abuse, including morphine. Among glutamate receptors, ionotropic glutamate receptors (iGluRs) are altered with exposure to drugs of abuse. Acid-sensing ion channels (ASICs) are ligand (H+)-gated channels, which are expressed at the excitatory synaptic clefts and play a role in drug dependence. Overexpression of a specific ASIC subtype, ASIC1a, attenuated reinstatement of cocaine. ASICs are revealed to be involved in cocaine and morphine seeking behaviors, and these effects are mediated through modulation of glutamatergic receptors. In this review, we discussed the interactive role of ASICs and glutamate receptors, mainly iGluRs, in opioid dependence. ASICs are also expressed in astrocytes and are suggested to be involved on regulating glutamate uptake. However, little is known about the coupling between ASICs and the astroglial glutamate transporters. In addition, this review discussed the role of nitric oxide in the modulation of ASIC function and potentially opioid dependence. We also discussed the role of ASICs in the modulation of the function of both glutamatergic receptors in post-synaptic neurons and glutamatergic transporters in astrocytes in animals exposed to drugs of abuse.

Extracellular tau oligomers affect extracellular glutamate handling by astrocytes through downregulation of GLT-1 expression and impairment of NKA1A2 function

AIMS

Several studies reported that astrocytes support neuronal communication by the release of gliotransmitters, including ATP and glutamate. Astrocytes also play a fundamental role in buffering extracellular glutamate in the synaptic cleft, thus limiting the risk of excitotoxicity in neurons. We previously demonstrated that extracellular tau oligomers (ex-oTau), by specifically targeting astrocytes, affect glutamate-dependent synaptic transmission via a reduction in gliotransmitter release. The aim of this work was to determine if ex-oTau also impair the ability of astrocytes to uptake extracellular glutamate, thus further contributing to ex-oTau-dependent neuronal dysfunction.

METHODS

Primary cultures of astrocytes and organotypic brain slices were exposed to ex-oTau (200 nM) for 1 hour. Extracellular glutamate buffering by astrocytes was studied by: Na⁺ imaging; electrophysiological recordings; high-performance liquid chromatography; Western blot and immunofluorescence. Experimental paradigms avoiding ex-oTau internalization (i.e., heparin pre-treatment and amyloid precursor protein knockout astrocytes) were used to dissect intracellular vs. extracellular effects of oTau.

RESULTS

Ex-oTau uploading in astrocytes significantly affected glutamate-transporter-1 expression and function, thus impinging on glutamate buffering activity. Ex-oTau also reduced Na-K-ATPase activity because of pump mislocalization on the plasma membrane, with no significant changes in expression. This effect was independent of oTau internalization and it caused Na⁺ overload and membrane depolarization in ex-oTau-targeted astrocytes.

CONCLUSIONS

Ex-oTau exerted a complex action on astrocytes, at both intracellular and extracellular levels. The net effect was dysregulated glutamate signalling in terms of both release and uptake that relied on reduced expression of glutamate-transporter-1, altered function and localization of NKA1A1, and NKA1A2. Consequently, Na⁺ gradients and all Na⁺ -dependent transports were affected.

Minocycline prevents chronic restraint stress-induced vulnerability to developing cocaine self-administration and associated glutamatergic mechanisms: a potential role of microglia

Stressful experience-induced cocaine-related behaviors are associated with a significant impairment of glutamatergic mechanisms in the Nucleus Accumbens core (NAcore). The hallmarks of disrupted glutamate homeostasis following restraint stress are the enduring imbalance of glutamate efflux after a cocaine stimulus and increased basal concentrations of extracellular glutamate attributed to GLT-1 downregulation in the NAcore. Glutamate transmission is tightly linked to microglia functioning. However, the role of microglia in the biological basis of stress-induced addictive behaviors is still unknown. By using minocycline, a potent inhibitor of microglia activation with anti-inflammatory properties, we determined whether microglia could aid chronic restraint stress (CRS)-induced glutamate homeostasis disruption in the NAcore, underpinning stress-induced cocaine self-administration. In this study, adult male rats were restrained for 2 h/day for seven days (day 1-7). From day 16 until completing the experimental protocol, animals received a vehicle or minocycline treatment (30 mg/Kg/12h i.p.). On day 21, animals were assigned to microscopic, biochemical, neurochemical or behavioral studies. We confirm that the CRS-induced facilitation of cocaine self-administration is associated with enduring GLT-1 downregulation, an increase of basal extracellular glutamate and postsynaptic structural plasticity in the NAcore. These alterations were strongly related to the CRS-induced reactive microglia and increased TNF-α mRNA and protein expression, since by administering minocycline, the impaired glutamate homeostasis and the facilitation of cocaine self-administration were prevented. Our findings are the first to demonstrate that minocycline suppresses the CRS-induced facilitation of cocaine self-administration and glutamate homeostasis disruption in the NAcore. A role of microglia is proposed for the development of glutamatergic mechanisms underpinning stress-induced vulnerability to cocaine addiction.

The GLT-1 enhancer clavulanic acid suppresses cocaine place preference behavior and reduces GCPII activity and protein levels in the rat nucleus accumbens

The β-lactam antibiotic ceftriaxone (CTX) is a glutamate transporter subtype 1 (GLT-1) enhancer that reduces cocaine reinforcing efficacy and relapse in rats, but pharmacokinetic liabilities limit translational utility. An attractive alternative is clavulanic acid (CLAV), a structurally related β-lactamase inhibitor and component of FDA-approved Augmentin. CLAV retains the GLT-1 enhancing effects of CTX but displays greater oral bioavailability, brain penetrability and negligible antibacterial activity. CLAV reduces morphine conditioned place preference (CPP) and ethanol consumption in rats, but knowledge about the efficacy of CLAV in preclinical models of drug addiction remains sparse. Here, we investigated effects of CLAV (10 mg/kg, IP) on the acquisition, expression, and maintenance of cocaine CPP in rats, and on two glutamate biomarkers associated with cocaine dependence, GLT-1 and glutamate carboxypeptidase II (GCPII). CLAV administered during cocaine conditioning (10 mg/kg, IP x 4 d) did not affect the development of cocaine CPP. However, a single CLAV injection, administered after the conditioning phase, reduced the expression of cocaine CPP. In rats with established cocaine preference, repeated CLAV administration facilitated extinction of cocaine CPP. In the nucleus accumbens, acute CLAV exposure reduced GCPII protein levels and activity, and a 10-d CLAV treatment regimen enhanced GLT-1 levels. These results suggest that CLAV reduces expression and maintenance of cocaine CPP but lacks effect against development of CPP. Moreover, the ability of a single injection of CLAV to reduce both GCPII activity and protein levels, as well as expression of cocaine CPP, points toward studying GCPII as a therapeutic target of CLAV.

Clozapine induces astrocyte-dependent FDG-PET hypometabolism

PURPOSE

Advances in functional imaging allowed us to visualize brain glucose metabolism in vivo and non-invasively with [¹⁸F]fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) imaging. In the past decades, FDG-PET has been instrumental in the understanding of brain function in health and disease. The source of the FDG-PET signal has been attributed to neuronal uptake, with hypometabolism being considered as a direct index of neuronal dysfunction or death. However, other brain cells are also metabolically active, including astrocytes. Based on the astrocyte-neuron lactate shuttle hypothesis, the activation of the glutamate transporter 1 (GLT-1) acts as a trigger for glucose uptake by astrocytes. With this in mind, we investigated glucose utilization changes after pharmacologically downregulating GLT-1 with clozapine (CLO), an anti-psychotic drug.

METHODS

Adult male Wistar rats (control, n = 14; CLO, n = 12) received CLO (25/35 mg kg^-1) for 6 weeks. CLO effects were evaluated in vivo with FDG-PET and cortical tissue was used to evaluate glutamate uptake and GLT-1 and GLAST levels. CLO treatment effects were also assessed in cortical astrocyte cultures (glucose and glutamate uptake, GLT-1 and GLAST levels) and in cortical neuronal cultures (glucose uptake).

RESULTS

CLO markedly reduced in vivo brain glucose metabolism in several brain areas, especially in the cortex. Ex vivo analyses demonstrated decreased cortical glutamate transport along with GLT-1 mRNA and protein downregulation. In astrocyte cultures, CLO decreased GLT-1 density as well as glutamate and glucose uptake. By contrast, in cortical neuronal cultures, CLO did not affect glucose uptake.

CONCLUSION

This work provides in vivo demonstration that GLT-1 downregulation induces astrocyte-dependent cortical FDG-PET hypometabolism-mimicking the hypometabolic signature seen in people developing dementia-and adds further evidence that astrocytes are key contributors of the FDG-PET signal.

Rapid Regulation of Glutamate Transport: Where Do We Go from Here?

Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). A family of five Na⁺-dependent transporters maintain low levels of extracellular glutamate and shape excitatory signaling. Shortly after the research group of the person being honored in this special issue (Dr. Baruch Kanner) cloned one of these transporters, his group and several others showed that their activity can be acutely (within minutes to hours) regulated. Since this time, several different signals and post-translational modifications have been implicated in the regulation of these transporters. In this review, we will provide a brief introduction to the distribution and function of this family of glutamate transporters. This will be followed by a discussion of the signals that rapidly control the activity and/or localization of these transporters, including protein kinase C, ubiquitination, glutamate transporter substrates, nitrosylation, and palmitoylation. We also include the results of our attempts to define the role of palmitoylation in the regulation of GLT-1 in crude synaptosomes. In some cases, the mechanisms have been fairly well-defined, but in others, the mechanisms are not understood. In several cases, contradictory phenomena have been observed by more than one group; we describe these studies with the goal of identifying the opportunities for advancing the field. Abnormal glutamatergic signaling has been implicated in a wide variety of psychiatric and neurologic disorders. Although recent studies have begun to link regulation of glutamate transporters to the pathogenesis of these disorders, it will be difficult to determine how regulation influences signaling or pathophysiology of glutamate without a better understanding of the mechanisms involved.

Astrocytes in Addictive Disorders

Astroglia are key regulators of synaptic function, playing central roles in homeostatic ion buffering, energy dynamics, transmitter uptake, maintenance of neurotransmitter pools, and regulation of synaptic plasticity through release of neuroactive chemicals. Given the myriad of crucial homeostatic and signaling functions attributed to astrocytes and the variety of neurotransmitter receptors expressed by astroglia, they serve as prime cellular candidates for establishing maladaptive synaptic plasticity following drug exposure. Initial studies on astroglia and addiction have placed drug-mediated disruptions in the homeostatic regulation of glutamate as a central aspect of relapse vulnerability. However, the generation of sophisticated tools to study and manipulate astroglia have proven that the interaction between addictive substances, astroglia, and relapse-relevant synaptic plasticity extends far beyond the homeostatic regulation of glutamate. Here we present astroglial systems impacted by drug exposure and discuss how changes in astroglial biology contribute to addiction biology.

Melatonin Blocks Morphine-Induced Place Preference: Involvement of GLT-1, NF-κB, BDNF, and CREB in the Nucleus Accumbens

Opioid addiction remains a widespread issue despite continuous attempts by the FDA to help maintain abstinence. Melatonin is a neurohormone considered to be involved only in the neuroendocrine and reproductive systems; however, recent reports have demonstrated its potential to attenuate drug addiction and dependence. Cumulative studies have suggested that melatonin can attenuate the rewarding effects of several drugs of abuse, including opioids. This study aimed to investigate the effect of melatonin (50 mg/kg) on morphine (5 mg/kg) to produce place preference. We also investigated the effect of melatonin and morphine on the expression of GLT-1, BDNF, NF-κB, and CREB within the nucleus accumbens. Male Wistar rats were divided into control, morphine, melatonin, and the morphine + melatonin groups. The study involved a two-phase habituation phase from day 1 to day 3 and an acquisition phase from day 5 to day 14. The conditioned place preference (CPP) score, distance traveled, resting time, ambulatory count, and total activity count were measured for all animals. Rats that received morphine showed a significant increase in CPP score compared to those in the control group. Morphine treatment reduced the mRNA expression of GLT-1, BDNF, and CREB and increased that of NF-κB. However, melatonin treatment administered 30 min before morphine treatment attenuated morphine place preference and reversed GLT-1, BDNF, NF-κB, and CREB expression levels. In conclusion, the study results indicate, for the first time, the new potential targets of melatonin in modulating morphine-induced CPP.

Astrocytic transcription factor REST upregulates glutamate transporter EAAT2, protecting dopaminergic neurons from manganese-induced excitotoxicity

Chronic exposure to high levels of manganese (Mn) leads to manganism, a neurological disorder with similar symptoms to those inherent to Parkinson's disease. However, the underlying mechanisms of this pathological condition have yet to be established. Since the human excitatory amino acid transporter 2 (EAAT2) (glutamate transporter 1 in rodents) is predominantly expressed in astrocytes and its dysregulation is involved in Mn-induced excitotoxic neuronal injury, characterization of the mechanisms that mediate the Mn-induced impairment in EAAT2 function is crucial for the development of novel therapeutics against Mn neurotoxicity. Repressor element 1-silencing transcription factor (REST) exerts protective effects in many neurodegenerative diseases. But the effects of REST on EAAT2 expression and ensuing neuroprotection are unknown. Given that the EAAT2 promoter contains REST binding sites, the present study investigated the role of REST in EAAT2 expression at the transcriptional level in astrocytes and Mn-induced neurotoxicity in an astrocyte–neuron coculture system. The results reveal that astrocytic REST positively regulates EAAT2 expression with the recruitment of an epigenetic modifier, cAMP response element-binding protein–binding protein/p300, to its consensus binding sites in the EAAT2 promoter. Moreover, astrocytic overexpression of REST attenuates Mn-induced reduction in EAAT2 expression, leading to attenuation of glutamate-induced neurotoxicity in the astrocyte–neuron coculture system. Our findings demonstrate that astrocytic REST plays a critical role in protection against Mn-induced neurotoxicity by attenuating Mn-induced EAAT2 repression and the ensuing excitotoxic dopaminergic neuronal injury. This indicates that astrocytic REST could be a potential molecular target for the treatment of Mn toxicity and other neurological disorders associated with EAAT2 dysregulation.

Induction of Parkinsonian-Like Changes via Targeted Downregulation of Astrocytic Glutamate Transporter GLT-1 in the Striatum

BACKGROUND

Previous investigations have suggested that decreased expression of glutamate transporter-1 (GLT-1) is involved in glutamate excitotoxicity and contribute to the development of Parkinson's disease (PD), GLT-1 is decreased in animal models of PD. GLT-1 is mainly expressed in astrocytes, and the striatum is a GLT-1-rich brain area.

OBJECTIVE

The aim was to explore the function and mechanism of astrocytic GLT-1 in PD-like changes.

METHODS

In the study, PD-like changes and their molecular mechanism in rodents were tested by a behavioral assessment, micro-positron emission tomography/computed tomography (PET/CT), western blotting, immunohistochemical and immunofluorescence staining, and high performance liquid chromatography pre-column derivatization with O-pthaldialdehida after downregulating astrocytic GLT-1 in vivo and in vitro.

RESULTS

In vivo, after 6 weeks of brain stereotactic injection of adeno-associated virus into the striatum, rats in the astrocytic GLT-1 knockdown group showed poorer motor performance, abnormal gait, and depression-like feature; but no olfactory disorders. The results of micro-PET/CT and western blotting indicated that the dopaminergic system was impaired in astrocytic GLT-1 knockdown rats. Similarly, tyrosine hydroxylase (TH) positive immune-staining in neurons of astrocytic GLT-1 knockdown rats showed deficit in cell count. In vitro, knockdown of astrocytic GLT-1 via RNA interference led to morphological injury of TH-positive neurons, which may be related to the abnormal calcium signal induced by glutamate accumulation after GLT-1 knockdown. Furthermore, the GLT-1 agonist ceftriaxone showed a protective effect on TH-positive neuron impairment.

CONCLUSION

The present findings may shed new light on the future prevention and treatment of PD based on blocking glutamate excitotoxicity.

Upregulation of heat-shock protein HSP-70 and glutamate transporter-1/glutamine synthetase in the striatum and hippocampus in haloperidol-induced dopamine-supersensitivity-state rats

BACKGROUND

The excessive blockade of dopamine D2 receptors (DRD2s) with long-term antipsychotic treatment is known to induce a dopamine supersensitivity state (DSS). The mechanism of DSS is speculated to be a compensatory up-regulation of DRD2s, but an excess blockade of DRD2s can also cause glutamatergic neuronal damage. Herein, we investigated whether antipsychotic-induced neuronal damage plays a role in the development of DSS.

METHODS

Haloperidol (HAL; 0.75 mg/kg/day for 14 days) or vehicle was administered to rats via an osmotic mini-pump. Haloperidol-treated rats were divided into groups of DSS rats and non-DSS rats based on their voluntary locomotion data. We then determined the tissue levels of glutamate transporter-1 (GLT-1)/glutamine synthetase (GS) and heat shock protein-70 (HSP-70) in the rats' brain regions.

RESULTS

The levels of HSP-70 in the striatum and CA-3 region of the DSS rats were significantly higher than those of the control and non-DSS rats, whereas the dentate gyrus HSP-70 levels in both the DSS and non-DSS rats were increased versus the controls. The levels of GLT-1/GS in the CA-3 and nucleus accumbens were increased in the DSS rats.

CONCLUSIONS

These results suggest that the DSS rats experienced striatal neuronal damage and indicate that a HAL-induced upregulation of HSP-70 and the GLT-1/GS system in the CA3 may be involved in the development of DSS. It remains unknown why the non-DSS rats did not suffer neuronal damage. In view of the need for therapeutic strategies for treatment-resistant schizophrenia, dopamine supersensitivity psychosis, and tardive dyskinesia, further investigations of our findings are warranted.

Obesity-induced astrocyte dysfunction impairs heterosynaptic plasticity in the orbitofrontal cortex

Overconsumption of highly palatable, energy-dense food is considered a key driver of the obesity pandemic. The orbitofrontal cortex (OFC) is critical for reward valuation of gustatory signals, yet how the OFC adapts to obesogenic diets is poorly understood. Here, we show that extended access to a cafeteria diet impairs astrocyte glutamate clearance, which leads to a heterosynaptic depression of GABA transmission onto pyramidal neurons of the OFC. This decrease in GABA tone is due to an increase in extrasynaptic glutamate, which acts via metabotropic glutamate receptors to liberate endocannabinoids. This impairs the induction of endocannabinoid-mediated long-term plasticity. The nutritional supplement, N-acetylcysteine rescues this cascade of synaptic impairments by restoring astrocytic glutamate transport. Together, our findings indicate that obesity targets astrocytes to disrupt the delicate balance between excitatory and inhibitory transmission in the OFC.

The p38 MAPK/NF-κB pathway mediates GLT-1 up-regulation during cerebral ischemic preconditioning-induced brain ischemic tolerance in rats

Our previous finding suggests that p38 MAPK contributes to the GLT-1 upregulation during induction of brain ischemic tolerance by cerebral ischemic preconditioning (CIP), however, the underlying mechanism is still unclear. Here, we investigated the molecular mechanisms underlying the CIP-induced GLT-1 upregulation by using Western blotting, Co-immunoprecipitation (Co-IP), electrophoretic mobility shift assay (EMSA) and thionin staining in rat hippocampus CA1 subset. We found that application of BAY11-7082 (an inhibitor of NF-κB), or dihydrokainate (an inhibitor of GLT-1), or SB203580 (an inhibitor of p38 MAPK) could attenuate the CIP-induced neuronal protection in hippocampus CA1 region of rats. Moreover, CIP caused rapid activation of NF-κB, as evidenced by nuclear translocation of NF-κB p50 protein, which led to active p50/p65 dimer formation and increased DNA binding activity. GLT-1 was also increased after CIP. Pretreatment with BAY11-7082 blocked the CIP-induced GLT-1 upregulation. The above results suggest that NF-κB participates in GLT-1 up-regulation during the induction of brain ischemic tolerance by CIP. We also found that pretreatment with SB203580 caused significant reduction of NF-κB p50 protein in nucleus, NF-κB p50/p65 dimer nuclear translocation and DNA binding activity of NF-κB. Together, we conclude that p38 MAPK/NF-κB pathway participates in the mediation of GLT-1 up-regulation during the induction of brain ischemic tolerance induced by CIP.

Pharmacological evidence for the concept of spare glutamate transporters

Through the efficient clearance of extracellular glutamate, high affinity astrocytic glutamate transporters constantly shape excitatory neurotransmission in terms of duration and spreading. Even though the glutamate transporter GLT-1 (also known as EAAT2/SLC1A2) is amongst the most abundant proteins in the mammalian brain, its density and activity are tightly regulated. In order to study the influence of changes in the expression of GLT-1 on glutamate uptake capacity, we have developed a model in HEK cells where the density of the transporter can be manipulated thanks to a tetracycline-inducible promoter. Exposing the cells to doxycycline concentration-dependently increased GLT-1 expression and substrate uptake velocity. However, beyond a certain level of induction, increasing the density of transporters at the cell surface failed to increase the maximal uptake. This suggested the progressive generation of a pool of spare transporters, a hypothesis that was further validated using the selective GLT-1 blocker WAY-213613 of which potency was influenced by the density of the transporters. The curve showing inhibition of uptake by increasing concentrations of WAY-213613 was indeed progressively rightward shifted when tested in cells where the transporter density was robustly induced. As largely documented in the context of cell-surface receptors, the existence of 'spare' glutamate transporters in the nervous tissue and particularly in astrocytes could impact on the consequences of physiological or pathological regulation of these transporters.

Targeted overexpression of glutamate transporter-1 reduces seizures and attenuates pathological changes in a mouse model of epilepsy

Astrocytic glutamate transporters are crucial for glutamate homeostasis in the brain, and dysregulation of these transporters can contribute to the development of epilepsy. Glutamate transporter-1 (GLT-1) is responsible for the majority of glutamate uptake in the dorsal forebrain and has been shown to be reduced at epileptic foci in patients and preclinical models of temporal lobe epilepsy (TLE). Current antiepileptic drugs (AEDs) work primarily by targeting neurons directly through suppression of excitatory neurotransmission or enhancement of inhibitory neurotransmission, which can lead to both behavioral and psychiatric side effects. This study investigates the therapeutic capacity of astrocyte-specific AAV-mediated GLT-1 expression in the intrahippocampal kainic acid (IHKA) model of TLE. In this study, we used Western blot analysis, immunohistochemistry, and long-term-video EEG monitoring to demonstrate that cell-type-specific upregulation of GLT-1 in astrocytes is neuroprotective at early time points during epileptogenesis, reduces seizure frequency and total time spent in seizures, and eliminates large behavioral seizures in the IHKA model of epilepsy. Our findings suggest that targeting glutamate uptake is a promising therapeutic strategy for the treatment of epilepsy.

Downregulation of astroglial glutamate transporter GLT-1 in the lateral habenula is associated with depressive-like behaviors in a rat model of Parkinson's disease

Recent studies show that neuron-glial communication plays an important role in neurological diseases. Particularly, dysfunction of astroglial glutamate transporter GLT-1 has been involved in various neuropsychiatric disorders, including Parkinson's disease (PD) and depression. Our previous studies indicated hyperactivity of neurons in the lateral habenula (LHb) of hemiparkinsonian rats with depressive-like behaviors. Thus, we hypothesized that impaired expression or function of GLT-1 in the LHb might be a potential contributor to LHb hyperactivity, which consequently induces PD-related depression. In the study, unilateral lesions of the substantia nigra pars compacta (SNc) by 6-hydroxydopamine in rats induced depressive-like behaviors and resulted in neuronal hyperactivity as well as increased glutamate levels in the LHb compared to sham-lesioned rats. Intra-LHb injection of GLT-1 inhibitor WAY-213613 induced the depressive-like behaviors in both groups, but the dose producing behavioral effects in the lesioned rats was lower than that of sham-lesioned rats. In the two groups of rats, WAY-213613 increased the firing rate of LHb neurons and extracellular levels of glutamate, and these excitatory effects in the lesioned rats lasted longer than those in sham-lesioned rats. The functional changes of the GLT-1 which primarily expresses in astrocytes in the LHb may attribute to its downregulation after degeneration of the nigrostriatal pathway. Bioinformatics analysis showed that GLT-1 is correlated with various biomarkers of PD and depression risks. Collectively, our study suggests that astroglial GLT-1 in the LHb regulates the firing activity of the neurons, whereupon its downregulation and dysfunction are closely associated with PD-related depression.

Ceftriaxone regulates glutamate production and vesicular assembly in presynaptic terminals through GLT-1 in APP/PS1 mice

Perturbations in the glutamate-glutamine cycle and glutamate release from presynaptic terminals have been involved in the development of cognitive deficits in Alzheimer's disease (AD) patients and mouse models. Glutamate transporter-1 (GLT-1) removes glutamate from the synaptic cleft and transports it into astrocytes, where it is used as substrate for the glutamate-glutamine cycle. Ceftriaxone has been reported to improve cognitive deficits in AD mice by increasing GLT-1 expression, glutamate transformation to glutamine, and glutamine efflux from astrocytes. However, the impact of ceftriaxone on glutamine metabolism in neurons is unknown. The present study aimed to investigate whether ceftriaxone regulated the production and vesicular assembly of glutamate in the presynaptic terminals of neurons and to determine GLT-1 involvement in this process. We used the amyloid precursor protein (APP)/presenilin-1 (PS1) AD mouse model and GLT-1 knockdown APP/PS1 (GLT-1^+/-/APP/PS1) mice. The expression levels of sodium-coupled neutral amino-acid transporter 1 (SNAT1) and vesicular glutamate transporters 1 and 2 (VGLUT1/2) were analyzed by immunofluorescence and immunohistochemistry staining as well as by Western blotting. Glutaminase activity was assayed by fluorometry. Ceftriaxone treatment significantly increased SNAT1 expression and glutaminase activity in neurons in APP/PS1 mice. Similarly, VGLUT1/2 levels were increased in the presynaptic terminals of APP/PS1 mice treated with ceftriaxone. The deletion of one GLT-1 allele in APP/PS1 mice prevented the ceftriaxone-induced upregulation of SNAT1 and VGLUT1/2 expression, indicating that GLT-1 played an important role in ceftriaxone effect. Based on the role of SNAT1, glutaminase, and VGLUT1/2 in the glutamate-glutamine cycle in neurons, the present results suggested that ceftriaxone improved the production and vesicular assembly of glutamate as a neurotransmitter in presynaptic terminals by acting on GLT-1 in APP/PS1 mice.

Ceftriaxone Reduces Waterpipe Tobacco Smoke Withdrawal-induced Anxiety in rats via Modulating the Expression of TNF-α/NFĸB, Nrf2, and GLT-1

Tobacco exposure has been linked to neuroinflammation and adaptive/maladaptive changes in neurotransmitter systems, including in glutamatergic systems. We examined the effects of waterpipe tobacco smoke (WTS) on inflammatory mediators and astroglial glutamate transporters in mesocorticolimbic brain regions including the prefrontal cortex (PFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). The behavioral consequences of WTS exposure on withdrawal-induced anxiety-like behavior were assessed using elevated plus maze (EPM) and open field (OF) tests. Male Sprague-Dawley rats were randomly assigned to 3 experimental groups: a control group exposed only to standard room air, a WTS exposed group treated with saline vehicle, and a WTS exposed group treated with ceftriaxone. WTS exposure was performed for 2 h/day, 5 days/week, for 4 weeks. Behavioral tests (EPM and OF) were conducted weekly 24 h after WTS exposure, during acute withdrawal. During week 4, rats were given either saline or ceftriaxone (200 mg/kg i.p.) 30 min before WTS exposure. WTS increased withdrawal-induced anxiety, and ceftriaxone attenuated this effect. WTS exposure increased the relative mRNA levels for nuclear factor ĸB (NFĸB), tumor necrosis factor-α (TNF-α), and brain-derived neurotrophic factor (BDNF) in the PFC, NAc and VTA, and ceftriaxone treatment reversed these effects. In addition, WTS decreased the relative mRNA of nuclear factor erythroid 2 related factor 2 (Nrf2), glutamate transporter 1 (GLT-1) and cystine-glutamate transporter (xCT) in PFC, NAc and VTA, and ceftriaxone treatment normalized their expression. WTS caused neuroinflammation, alteration in relative mRNA glutamate transport expression, and increased anxiety-like behavior, and these effects were attenuated by ceftriaxone treatment.

The investigation of glutamate transporter 1 (GLT-1) degradation pathway in glioblastoma cells

Glioblastoma multiform is a primary brain tumor derived from glial cells. The aim of this study is to investigate how glutamate metabolism is regulated by glutamate transporter 1 (GLT-1) degradation pathway in glioblastoma and glial cell lines. The protein expression levels of GLT-1, total ubiquitin, protein kinase C (PKC) proteins involved in the GLT-1 degradation pathway were measured by the western blot technique. Additionally, in glial and glioblastoma cells, the level of glutamate accumulated in the medium and the lysates was measured with the glutamate assay. GLT-1 protein expression was increased significantly in glioblastoma cells. The expression levels of the PKC protein and total ubiquitin were found to be decreased in glioblastoma cells although not significantly. The glutamate accumulated in the medium and lysates of glioblastoma cells is reduced compared to glial cells. Further research regarding excitotoxicity in glioblastoma focusing on GLT-1 degradation or activation pathway may create new opportunities of drug and treatment development.

MiR-30a-5p Regulates GLT-1 Function via a PKCα-Mediated Ubiquitin Degradation Pathway in a Mouse Model of Parkinson's Disease

Glutamate excitotoxicity is caused by dysfunctional glutamate transporters and plays an important role in the pathogenesis of Parkinson's disease (PD); however, the mechanisms that underlie the regulation of glutamate transporters in PD are still not fully elucidated. MicroRNAs(miRNA), which are abundant in astrocytes and neurons, have been reported to play key roles in regulating the translation of glutamate-transporter mRNA. In this study, we hypothesized that the miR-30a-5p contributes to the pathogenesis of PD by regulating the ubiquitin-mediated degradation of glutamate transporter 1 (GLT-1). We demonstrated that short-hairpin RNA-mediated knockdown of miR-30a-5p ameliorated motor deficits and pathological changes like astrogliosis and reactive microgliosis in a mouse model of PD (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice). Western blotting and immunofluorescent labeling revealed that miR-30a-5p suppressed the expression and function of GLT-1 in MPTP-treated mice and specifically in astrocytes treated with 1-methyl-4-phenylpyridinium (MPP⁺) (cell model of PD). Both in vitro and in vivo, we found that miR-30a-5p knockdown promoted glutamate uptake and increased GLT-1 expression by hindering GLT-1 ubiquitination and subsequent degradation in a PKCα-dependent manner. Therefore, we conclude that miR-30a-5p represents a potential therapeutic target for the treatment of PD.

Rapid recycling of glutamate transporters on the astroglial surface

Glutamate uptake by astroglial transporters confines excitatory transmission to the synaptic cleft. The efficiency of this mechanism depends on the transporter dynamics in the astrocyte membrane, which remains poorly understood. Here, we visualise the main glial glutamate transporter GLT1 by generating its pH-sensitive fluorescent analogue, GLT1-SEP. Fluorescence recovery after photobleaching-based imaging shows that 70-75% of GLT1-SEP dwell on the surface of rat brain astroglia, recycling with a lifetime of ~22 s. Genetic deletion of the C-terminus accelerates GLT1-SEP membrane turnover while disrupting its surface pattern, as revealed by single-molecule localisation microscopy. Excitatory activity boosts surface mobility of GLT1-SEP, involving its C-terminus, metabotropic glutamate receptors, intracellular Ca2+, and calcineurin-phosphatase activity, but not the broad-range kinase activity. The results suggest that membrane turnover, rather than lateral diffusion, is the main 'redeployment' route for the immobile fraction (20-30%) of surface-expressed GLT1. This finding reveals an important mechanism helping to control extrasynaptic escape of glutamate.

Potential Benefits of N-Acetylcysteine in Preventing Pregabalin-Induced Seeking-Like Behavior

Substance-use disorder is globally prevalent and responsible for numerous social and medical problems. Pregabalin (Lyrica), typically used to treat diabetic neuropathy, has recently emerged as a drug of abuse. Drug abuse is associated with several neuronal changes, including the downregulation of glutamate transporters such as glutamate transporter 1 and cystine/glutamate antiporter. We investigated the effects of N-acetylcysteine, a glutamate transporter 1 and xCT upregulator, on pregabalin addiction using a conditioned place preference paradigm. Pregabalin (60 mg/kg) was found to induce conditioned place preference when compared to a vehicle. A 100 mg/kg dose of N-acetylcysteine was found to block pregabalin-seeking behaviors. These results support previous findings showing that glutamate transporters play an important role in pregabalin-induced seeking behaviors. N-acetylcysteine may represent a beneficial agent in preventing the abuse potential of pregabalin.

Hydrogen enriched saline alleviates morphine tolerance via inhibiting neuroinflammation, GLT-1, GS nitration and NMDA receptor trafficking and functioning in the spinal cord of rats

The development and maintenance of morphine tolerance showed association with neuroinflammation and dysfunction of central glutamatergic system (such as nitration of glutamate transporter). Recent evidence indicated that hydrogen could reduce the levels of neuroinflammation and oxidative stress, but its role in morphine tolerance has not been studied. The rats were intrathecally administered with morphine (10 μg/10 μL each time, twice/day for 5 days). Hydrogen enriched saline (HS) or saline was given intraperitoneally at 1, 3 and 10 mL/kg for 10 min before each dose of morphine administration. The tail-flick latency, mechanical threshold and thermal latency were assessed one day (baseline) before and daily for up to 5 days during morphine injection. The pro-inflammatory cytokine expressions [tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), IL-6)] (by western blotting), astrocyte activation (by immunofluorescence and western blotting), and nitration of glutamate transporter-1 (GLT-1) and glutamine synthetase (GS) (by immunoprecipitation), membrane and total expression of N-methyl-d-aspartic acid (NMDA) receptor NR1 and NR2B subunits were carried out in the spinal dorsal horns. Chronic morphine administration induced antinociceptive tolerance, and together led to increased TNF-α, IL-1β and IL-6 expression, astrocyte activation, GLT-1 and GS nitration, increased membrane and total NR1, NR2B expression. Injection of HS attenuated morphine tolerance in a dose-dependent manner, decreased proinflammatory cytokine expression, inhibited astrocyte activation, decreased GLT-1 and GS nitration, and inhibited membrane trafficking of NMDA receptor. Our result showed that hydrogen pretreatment prevented morphine tolerance by reducing neuroinflammation, GLT-1, GS nitration, NMDA receptor trafficking in the spinal dorsal horn. Pretreatment with hydrogen might be considered as a novel therapeutic strategy for the prevention of morphine tolerance.

Fractional anisotropy from diffusion tensor imaging correlates with acute astrocyte and myelin swelling in neonatal swine models of excitotoxic and hypoxic-ischemic brain injury

The specific cytopathology that causes abnormal fractional anisotropy (FA) and mean diffusivity (MD) from diffusion tensor imaging (DTI) after neonatal hypoxia-ischemia (HI) is not completely understood. The panoply of cell types in the brain might contribute differentially to changes in DTI metrics. Because glia are the predominant cell type in brain, we hypothesized that changes in FA and MD would signify perturbations in glial microstructure. Using a 3-Tesla clinical scanner, we conducted in vivo DTI MRI in nine neonatal piglets at 20-96 h after excitotoxic brain injury from striatal quinolinic acid injection or global HI. FA and MD from putamen, caudate, and internal capsule in toto were correlated with astrocyte swelling, neuronal excitotoxicity, and white matter injury. Low FA correlated with more swollen astrocytes immunophenotyped by aquaporin-4 (AQP4), glial fibrillary acidic protein (GFAP), and glutamate transporter-1 (GLT-1). Low FA was also related to the loss of neurons with perineuronal GLT-1+ astrocyte decorations, large myelin swellings, lower myelin density, and oligodendrocyte cell death identified by 2',3'-cyclic nucleotide 3'-phosphodiesterase, bridging integrator-1, and nuclear morphology. MD correlated with degenerating oligodendrocytes and depletion of normal GFAP+ astrocytes but not with astrocyte or myelin swelling. We conclude that FA is associated with cytotoxic edema in astrocytes and oligodendrocyte processes as well as myelin injury at the cellular level. MD can detect glial cell death and loss, but it may not discern subtle pathology in swollen astrocytes, oligodendrocytes, or myelin. This study provides a cytopathologic basis for interpreting DTI in the neonatal brain after HI.