• Astrocytes
• Glutamate transporters: GLT-1
• Migraine
• Na/K pump
• Pain
• Spreading depolarization

Cannabinoids and their derivatives attract strong interest due to the tremendous potential of their psychoactive effects for treating psychiatric disorders and symptoms. However, their clinical application is restricted by various side-effects such as impaired coordination, anxiety, and learning and memory disability. Adverse impact on dorsal striatum-dependent learning is an important side-effect of cannabinoids. As one of the most important forms of learning mediated by the dorsal striatum, reinforcement learning is characterized by an initial association learning phase, followed by habit learning. While the effects of cannabinoids on habit learning have been well-studied, little is known about how cannabinoids influence the initial phase of reinforcement learning.

We found that acute activation of cannabinoid receptor type 1 (CB1R) by the synthetic cannabinoid HU210 induced dose-dependent impairment of association learning, which could be alleviated by intra-dorsomedial striatum (DMS) injection of CB1R antagonist. Moreover, acute exposure to HU210 elicited enhanced synaptic transmission in striatonigral “direct” pathway medium spiny neurons (MSNs) but not indirect pathway neurons in DMS. Intriguingly, enhancement of synaptic transmission that is also observed after learning was abolished by HU210, indicating cannabinoid system might disrupt reinforcement learning by confounding synaptic plasticity normally required for learning. Remarkably, the impaired response-reinforcer learning was also induced by selectively enhancing the D1-MSN (MSN that selectively expresses the dopamine receptor type 1) activity by virally expressing excitatory hM3Dq DREADD (designer receptor exclusively activated by a designer drug), which could be rescued by specifically silencing the D1-MSN activity via hM4Di DREADD.

Our findings demonstrate dose-dependent deleterious effects of cannabinoids on association learning by disrupting plasticity change required for learning associated with the striatal direct pathway, which furthers our understanding of the side-effects of cannabinoids and the underlying mechanisms.

The online version contains supplementary material available at 10.1186/s12915-022-01307-1.

• Chemogenetics
• D1 MSNs
• DREADD
• HU210
• Intracranial injection
• Learning impairment
• Reinforcement learning

GLT-1, the major glutamate transporter in the mammalian central nervous system, is expressed in presynaptic terminals that use glutamate as a neurotransmitter, in addition to astrocytes. It is widely assumed that glutamate homeostasis is regulated primarily by glutamate transporters expressed in astrocytes, leaving the function of GLT-1 in neurons relatively unexplored. We generated conditional GLT-1 knockout (KO) mouse lines to understand the cell-specific functions of GLT-1. We found that stimulus-evoked field extracellular postsynaptic potentials (fEPSPs) recorded in the CA1 region of the hippocampus were normal in the astrocytic GLT-1 KO but were reduced and often absent in the neuronal GLT-1 KO at 40 weeks. The failure of fEPSP generation in the neuronal GLT-1 KO was also observed in slices from 20 weeks old mice but not consistently from 10 weeks old mice. Using an extracellular FRET-based glutamate sensor, we found no difference in stimulus-evoked glutamate accumulation in the neuronal GLT-1 KO, suggesting a postsynaptic cause of the transmission failure. We hypothesized that excitotoxicity underlies the failure of functional recovery of slices from the neuronal GLT-1 KO. Consistent with this hypothesis, the non-competitive NMDA receptor antagonist MK801, when present in the ACSF during the recovery period following cutting of slices, promoted full restoration of fEPSP generation. The inclusion of an enzymatic glutamate scavenging system in the ACSF conferred partial protection. Excitotoxicity might be due to excess release or accumulation of excitatory amino acids, or to metabolic perturbation resulting in increased vulnerability to NMDA receptor activation. Previous studies have demonstrated a defect in the utilization of glutamate by synaptic mitochondria and aspartate production in the synGLT-1 KO in vivo, and we found evidence for similar metabolic perturbations in the slice preparation. In addition, mitochondrial cristae density was higher in synaptic mitochondria in the CA1 region in 20–25 weeks old synGLT-1 KO mice in the CA1 region, suggesting compensation for loss of axon terminal GLT-1 by increased mitochondrial efficiency. These data suggest that GLT-1 expressed in presynaptic terminals serves an important role in the regulation of vulnerability to excitotoxicity, and this regulation may be related to the metabolic role of GLT-1 expressed in glutamatergic axon terminals.

• Alzheimer’s disease
• aging
• excitotoxicity glutamatergic
• homeostasis
• mitochondria
• neurodegeneration
• repair

• EAAC1
• Excitatory amino acid transporter
• GLAST
• GLT-1
• Glutamate transport
• Protein kinase C

• GABA transporter
• Glutamate transporter
• Glycine transporter
• Liposomes
• Reconstitution
• Scientific history

• Amino Acid Transport System X-AG
• GABA Plasma Membrane Transport Proteins
• Glutamates
• Glycine/metabolism
• gamma-Aminobutyric Acid/metabolism

• 240844 Norges Forskningsråd
• SAF2017-84235-R Ministerio de Economía, Industria y Competitividad, Gobierno de España
• UNIFOR-FRIMED Universitetet i Oslo
• SERTA Universitetet i Oslo
• Anders Jahres Fond til Vitenskapens Fremme Anders Jahres Fond til Vitenskapens Fremme
• Unger Vetlesen Medical Fund Unger Vetlesen Medical Fund
• University of Oslo (incl Oslo University Hospital)

• Antipsychotic
• Astrocyte
• DSS
• Dopamine supersensitivity state
• GLT-1
• GS
• Glutamate transporter-1
• Glutamine synthetase
• HSP-70
• Heat shock protein-70

Alzheimer’s disease (AD) is a neuropathological disorder characterized by the presence and accumulation of amyloid-beta plaques and neurofibrillary tangles. Glutamate dysregulation and the concept of glutamatergic excitotoxicity have been frequently described in the pathogenesis of a variety of neurodegenerative disorders and are postulated to play a major role in the progression of AD. In particular, alterations in homeostatic mechanisms, such as glutamate uptake, have been implicated in AD. An association with excitatory amino acid transporter 2 (EAAT2), the main glutamate uptake transporter, dysfunction has also been described. Several animal and few human studies examined EAAT2 expression in multiple brain regions in AD but studies of the hippocampus, the most severely affected brain region, are scarce. Therefore, this study aims to assess alterations in the expression of EAAT2 qualitatively and quantitatively through DAB immunohistochemistry (IHC) and immunofluorescence within the hippocampus, subiculum, entorhinal cortex, and superior temporal gyrus (STG) regions, between human AD and control cases. Although no significant EAAT2 density changes were observed between control and AD cases, there appeared to be increased transporter expression most likely localized to fine astrocytic branches in the neuropil as seen on both DAB IHC and immunofluorescence. Therefore, individual astrocytes are not outlined by EAAT2 staining and are not easily recognizable in the CA1–3 and dentate gyrus regions of AD cases, but the altered expression patterns observed between AD and control hippocampal cases could indicate alterations in glutamate recycling and potentially disturbed glutamatergic homeostasis. In conclusion, no significant EAAT2 density changes were found between control and AD cases, but the observed spatial differences in transporter expression and their functional significance will have to be further explored.

• Alzheimer’s disease
• EAAT2
• entorhinal cortex
• glutamate transporter
• hippocampus
• subiculum
• superior temporal gyrus

• GABA
• dopamine
• glutamate
• surface mobility
• transporter
• uptake

• Astrocyte
• Depression
• Glutamate transporter-1
• Glutamine synthetase
• Learned helplessness
• Resilience

• Parkinson’s disease
• cell replacement
• dopaminergic neuron
• machine learning
• progenitor
• radial glia
• single cell
• stem cell

• astrocytes
• glutamate
• glutamate transporters
• migraine
• spreading depression

Episodic ataxia type 6 is an inherited neurological condition characterized by combined ataxia and epilepsy. A severe form of this disease with episodes combining ataxia, epilepsy and hemiplegia was recently associated with a proline to arginine substitution at position 290 of the excitatory amino acid transporter 1 in a heterozygous patient. The excitatory amino acid transporter 1 is the predominant glial glutamate transporter in the cerebellum. However, this glutamate transporter also functions as an anion channel and earlier work in heterologous expression systems demonstrated that the mutation impairs the glutamate transport rate, while increasing channel activity. To understand how these changes cause ataxia, we developed a constitutive transgenic mouse model. Transgenic mice display epilepsy, ataxia and cerebellar atrophy and, thus, closely resemble the human disease. We observed increased glutamate-activated chloride efflux in Bergmann glia that triggers the apoptosis of these cells during infancy. The loss of Bergmann glia results in reduced glutamate uptake and impaired neural network formation in the cerebellar cortex. This study shows how gain-of-function of glutamate transporter-associated anion channels causes ataxia through modifying cerebellar development.

• Bergmann glia
• chloride homeostasis
• episodic ataxia
• glial apoptosis
• glutamate transporters

• Huntington's
• TCA cycle
• anaplerosis
• aspartate
• bioenergetics
• neurodegeneration

• Alcohol dependence
• Amygdala
• Glutamate
• Glutamate receptors
• Glutamate transporters
• Hippocampus
• NAc
• PFC
• Striatum
• VTA

Glutamate is the predominant excitatory neurotransmitter in the human brain and it has been shown that prolonged activation of the glutamatergic system leads to nerve damage and cell death. Following release from the pre-synaptic neuron and synaptic transmission, glutamate is either taken up into the pre-synaptic neuron or neighbouring glia by transmembrane glutamate transporters. Excitatory amino acid transporter (EAAT) 1 and EAAT2 are Na⁺-dependant glutamate transporters expressed predominantly in glia cells of the central nervous system. As the most abundant glutamate transporters, their primary role is to modulate levels of glutamatergic excitability and prevent spill over of glutamate beyond the synapse. This role is facilitated through the binding and transportation of glutamate into astrocytes and microglia. The function of EAAT1 and EAAT2 is heavily regulated at the levels of gene expression, post-transcriptional splicing, glycosylation states and cell-surface trafficking of the protein. Both glutamatergic dysfunction and glial dysfunction have been proposed to be involved in psychiatric disorder. This review will present an overview of the roles that EAAT1 and EAAT2 play in modulating glutamatergic activity in the human brain, and mount an argument that these two transporters could be involved in the aetiologies of schizophrenia and affective disorders as well as represent potential drug targets for novel therapies for those disorders.

• Glia
• Excitatory amino acid transporter
• Psychiatry
• Affective disorders
• Glutamate transporter
• Glutamate
• Schizophrenia

• Excitatory amino acid transporter 2
• Glutamate metabolism
• Glutamate uptake
• Presynaptic
• Syn1-cre
• Synaptosomes

• Alzheimer’s disease
• Blood brain barrier
• Cholesterol homeostasis
• Neurodegeneration
• Neurovascular unit
• Oxysterols

• Animals
• Blood-Brain Barrier/metabolism
• Blood-Brain Barrier/pathology
• Brain Diseases/metabolism
• Brain Diseases/pathology
• Cholesterol/metabolism
• Humans
• Nerve Degeneration/metabolism
• Nerve Degeneration/pathology
• Neurons/metabolism
• Neurons/pathology

• Bergmann glia
• EAAT
• fluorescence lifetime imaging
• glial chloride switch

• Ceftriaxone
• Glutamate transporter
• Ischemia
• Medial prefrontal cortex
• Postpartum depression

• Axon-terminals
• Conditional knockout
• EAAT2
• Glutamate transporter
• Glutamate uptake
• Synaptosomes

• EAAT3
• Glutamate transporter

• Addiction
• Aging
• Glutamate homeostasis
• Glutamate-glutamine cycle
• Metabolism
• Mitochondria
• Neurodegeneration
• Schizophrenia
• Synaptic plasticity
• Synaptogenesis

• Astrocytes
• EAAC1
• EAAT
• GLAST
• GLT-1
• Glu uptake
• Transcriptional regulation

• ATP-Binding Cassette Transporters/metabolism
• Amino Acid Transport System X-AG/metabolism
• Animals
• Astrocytes/metabolism
• Glutamic Acid/metabolism
• Humans
• Neurons/metabolism
• Signal Transduction
• Transcription Factors/metabolism

• R01 NS092067 NINDS NIH HHS

• Astrocytes
• Depression
• Glia
• Glutamatergic synapse
• Major depressive disorder

• glia
• ischemia
• plasticity
• seizures
• spillover
• transport

• DAB
• EAATs
• EM
• EtOH
• LTD
• LTP
• N-methyl-d-aspartate
• NMDA
• PB
• PBS
• PMI
• PSD
• astrocytes
• diaminobenzidine
• electron microscopic
• electron microscopy
• ethanol
• excitatory amino acid transporters
• glutamate transporter
• long-term depression
• long-term potentiation
• mitochondria
• phosphate buffer
• phosphate-buffered saline
• postmortem interval
• postsynaptic density
• rER
• rough endoplasmic reticulum
• ultrastructure

• Adult
• Aged
• Animals
• Astrocytes/metabolism
• Astrocytes/ultrastructure
• Excitatory Amino Acid Transporter 1/genetics
• Excitatory Amino Acid Transporter 1/metabolism
• Excitatory Amino Acid Transporter 2
• Female
• Glutamate Plasma Membrane Transport Proteins/metabolism
• Humans
• Male
• Mice, Knockout
• Microscopy, Electron
• Middle Aged
• Neurons/metabolism
• Neurons/ultrastructure
• Prefrontal Cortex/blood supply
• Prefrontal Cortex/metabolism
• Prefrontal Cortex/ultrastructure
• Species Specificity

• MH074016 NIMH NIH HHS
• MH087752 NIMH NIH HHS
• K08 MH074016 NIMH NIH HHS
• R01 MH094445 NIMH NIH HHS
• R21 MH087752 NIMH NIH HHS
• MH094445 NIMH NIH HHS

• glutamate uptake
• eaat2
• eaat1
• eaat3
• slc1a2
• slc1a1
• slc1a3
• glutamate
• glutamate transporter
• immunocytochemistry
• neuropil

• Animals
• Blood-Brain Barrier/metabolism
• Brain/metabolism
• Glutamate Plasma Membrane Transport Proteins/metabolism
• Glutamic Acid/metabolism
• Glutamine/metabolism
• Humans
• Neurotransmitter Agents/metabolism

• Bipolar disorder
• Glutamate
• Glutamate transporters
• Hippocampus
• In situ hybridization
• Laser capture microdissection
• Major depression disorder
• Microarray

• Astrocytes/metabolism
• Blotting, Western
• Cerebral Cortex/embryology
• Cerebral Cortex/growth & development
• Cerebral Cortex/metabolism
• Child, Preschool
• Excitatory Amino Acid Transporter 2/analysis
• Excitatory Amino Acid Transporter 2/biosynthesis
• Fetus
• Humans
• Immunohistochemistry
• Infant
• Infant, Newborn
• Neurogenesis/physiology
• Neurons/metabolism

• R01 NS066019 NINDS NIH HHS
• NS041883 NINDS NIH HHS
• NS066019 NINDS NIH HHS
• P30 HD018655 NICHD NIH HHS
• HD18655 NICHD NIH HHS
• R01 NS041883 NINDS NIH HHS

• BGT1
• EAAT1
• EAAT2
• GABA uptake
• GAT1
• GAT2
• GAT3
• glutamate uptake

• EAAT2
• GABA
• GLAST
• GLT-1
• epigallocatechin-monogallate
• glutamate
• glutamate dehydrogenase
• sodium-dependent uptake

• P30 HD026979 NICHD NIH HHS
• R01 NS077773 NINDS NIH HHS

Glioblastoma multiforme is the most malignant type of primary brain tumor with a poor prognosis. These tumors consist of a heterogeneous population of malignant cells, including well-differentiated tumor cells and less differentiated cells with stem cell properties. These cancer stem cells, known as brain tumor initiating cells, likely contribute to glioma recurrence, as they are highly invasive, mobile, resistant to radiation and chemotherapy, and have the capacity to self-renew. Glioblastoma tumor cells release excitotoxic levels of glutamate, which may be a key process in the death of peritumoral neurons, formation of necrosis, local inflammation, and glioma-related seizures. Moreover, elevated glutamate levels in the tumor may act in paracrine and autocrine manner to activate glutamate receptors on glioblastoma tumor cells, resulting in proliferation and invasion. Using a previously described culturing condition that selectively promotes the growth of brain tumor initiating cells, which express the stem cell markers nestin and SOX-2, we characterize the expression of α-amino-3-hydroxy-5-methyl-4-isozolepropionic acid (AMPA)-type glutamate receptor subunits in brain tumor initiating cells derived from glioblastomas. Here we show for the first time that glioblastoma brain tumor initiating cells express high concentrations of functional calcium-permeable AMPA receptors, compared to the differentiated tumor cultures consisting of non-stem cells. Up-regulated calcium-permeable AMPA receptor expression was confirmed by immunoblotting, immunocytochemistry, and intracellular calcium imaging in response to specific agonists. Our findings raise the possibility that glutamate secretion in the GBM tumor microenvironment may stimulate brain tumor derived cancer stem cells.

• Calcium/metabolism
• Gene Expression Regulation, Neoplastic/genetics
• Gene Expression Regulation, Neoplastic/physiology
• Glioblastoma/metabolism
• Humans
• Immunoblotting
• Immunohistochemistry
• Neoplastic Stem Cells/metabolism
• Receptors, AMPA/metabolism
• Tumor Cells, Cultured

• F32 NS073326 NINDS NIH HHS
• F32NS073326-01 NINDS NIH HHS

• Animals
• Brain/drug effects
• Brain/metabolism
• Brain/physiology
• Brain Chemistry/drug effects
• Brain Chemistry/physiology
• Disease Models, Animal
• Excitatory Amino Acid Transporter 2/biosynthesis
• Excitatory Amino Acid Transporter 2/genetics
• Fluoxetine/pharmacology
• Gene Expression Regulation/drug effects
• Glutamic Acid/metabolism
• Male
• Rats
• Rats, Sprague-Dawley

• G0700102 Medical Research Council

We used light and electron microscopic immunocytochemical techniques to analyze the distribution, cellular and synaptic localization of EAAT2, the main glutamate transporter, in normal human neocortex. EAAT2a-immunoreactivity (ir) was in all layers and consisted of small neuropilar puncta and rare cells. In white matter EAAT2a+ cells were numerous. Electron microscopic studies showed that in gray matter ∼77% of immunoreactive elements were astrocytic processes, ∼14% axon terminals, ∼2.8% dendrites, whereas ∼5% were unidentifiable. In white matter, ∼81% were astrocytic processes, ∼17% were myelinated axons, and ∼2.0% were unidentified. EAAT2a-ir was never in microglial cells and oligodendrocytes. Pre-embedding electron microscopy showed that ∼67% of EAAT2a expressed at (or in the vicinity of) asymmetric synapses was in astrocytes, ∼17% in axon terminals, while ∼13% was both in astrocytes and in axons. Post-embedding electron microscopy studies showed that in astrocytic processes contacting asymmetric synapses and in axon terminals, gold particle density was ∼25.1 and ∼2.8 particles/μm², respectively, and was concentrated in a membrane region extending for ∼300 nm from the active zone edge. Besides representing the first detailed description of EAAT2a in human cerebral cortex, these findings may contribute to understanding its role in the pathophysiology of neuropsychiatric diseases.

• EAAT2
• Glutamate transporters
• human neocortex
• immunogold post-embedding electron microscopy

GLT-1 eGFP BAC reporter transgenic adult mice were used to detect GLT-1 gene expression in individual cells of CA1, CA3 and SI, and eGFP fluorescence was measured to analyze quantitatively GLT-1 promoter activity in different cells of neocortex and hippocampus. Virtually all GFAP+ astrocytes were eGFP+; we also found that about 80% of neurons in CA3 pyramidal layer, 10–70% of neurons in I-VI layers of SI and rare neurons in all strata of CA1 and in strata oriens and radiatum of CA3 were eGFP+. Analysis of eGFP intensity showed that astrocytes had a higher GLT-1 promoter activity in SI than in CA1 and CA3, and that neurons had the highest levels of GLT-1 promoter activity in CA3 stratum pyramidale and in layer VI of SI. Finally, we observed that the intensity of GLT-1 promoter activity in neurons is 1–20% of that measured in astrocytes. These results showed that in the hippocampus and neocortex GLT-1 promoter activity is observed in astrocytes and neurons, detailed the distribution of GLT-1 expressing neurons, and indicated that GLT-1 promoter activity in both astrocytes and neurons varies in different brain regions.

• GLT-1/EAAT2
• astrocytes
• glutamate transporters
• hippocampus
• neocortex
• neurons