Glutamate Receptor Gene Expression Research Articles

Early effects of 16O radiation on neuronal morphology and cognition in a murine model

Astronauts exposed to high linear energy transfer radiation may experience cognitive injury. The pathogenesis of this injury is unknown but may involve glutamate receptors or modifications to dendritic structure and/or dendritic spine density and morphology. Glutamate is the major excitatory neurotransmitter in the central nervous system, where it acts on ionotropic and metabotropic glutamate receptors located at the presynaptic terminal and in the postsynaptic membrane at synapses in the hippocampus. Dendritic spines are sites of excitatory synaptic transmission, and changes in spine structure and dendrite morphology are thought to be morphological correlates of altered brain function associated with hippocampal-dependent learning and memory. The aim of the current study is to assess whether behavior, glutamate receptor gene expression, and dendritic structure in the hippocampus are altered in mice after early exposure to 16O radiation in mice. Two weeks post-irradiation, animals were tested for hippocampus-dependent cognitive performance in the Y-maze. During Y-maze testing, mice exposed to 0.1 Gy and 0.25 Gy radiation failed to distinguish the novel arm, spending approximately the same amount of time in all 3 arms during the retention trial. Exposure to 16O significantly reduced the expression of Nr1 and GluR1 in the hippocampus and modulated spine morphology in the dentate gyrus and cornu Ammon 1 within the hippocampus. The present data provide evidence that 16O radiation has early deleterious effects on mature neurons that are associated with hippocampal learning and memory.

THC Treatment Alters Glutamate Receptor Gene Expression in Human Stem Cell-Derived Neurons

Given the cognitive and behavioral effects following in utero Δ9-tetrahydrocannabinol (THC) exposure that have been reported in humans and rodents, it is critical to understand the precise consequences of THC on developing human neurons. Here, we utilize excitatory neurons derived from human-induced pluripotent stem cells (hiPSCs), and report that in vitro THC exposure reduced expression of glutamate receptor subunit genes (GRIA1, GRIA2, GRIN2A, and GRIN2B). By expanding these studies across hiPSC-derived neurons from individuals with a variety of genotypes, we believe that a hiPSC-based model will facilitate studies of the interaction of THC exposure and the genetic risk factors underlying neuropsychiatric disease vulnerability.

Evolution of song complexity in Bengalese finches could mirror the emergence of human language

Bengalese finches (BFs) are a domesticated strain of wild white-rumped munias imported from China to Japan 250 years ago. Bengalese songs are composed of multiple chunks of song notes, and each chunk is a combination of 2–5 song notes. Furthermore, chunks are arranged in a finite-state probabilistic automaton. We studied how and why BFs sing such complex songs. We found the following: (1) ancestral strains sing simpler songs; (2) there is high learning specificity in white-rumped munias but not in BFs; (3) BFs have larger song control nuclei and higher glutamate receptor gene expression levels than white-rumped munias; (4) both BFs and white-rumped munia females prefer complex songs as measured by the nest string assay, and males with complex songs are physically fitter than males with simpler songs. These results indicated the sexual selection scenario of song complexity in Bengalese finches. We further examined factors related to domestication. We examined songs of white-rumped munias in subpopulations of Taiwan. Where there is a sympatric species with white-rumped munias, songs were simpler. This led to a hypothesis that in the wild, songs needed to be simple to secure species identification, but under domestication this constraint was unnecessary. Based on these results, we extended our research into the socio-emotional domain. All indexes suggested that white-rumped munias have higher levels of stress and social shyness, which should be adaptive in natural environments, but could limit opportunities for learning complex songs. Evolution of song complexity involves factors related to the strength of sexual selection and relaxation of species identification as well as socio-emotional factors because of domestication. The results of the present study on BFs should be useful in discussing the possible biological origins of human speech relating to proximate and ultimate factors.

Journal Digest

Journal Digest

Sex differences in glutamate receptor gene expression in major depression and suicide.

Accumulating data indicate that the glutamate system is disrupted in major depressive disorder (MDD), and recent clinical research suggests that ketamine, an antagonist of the N-methyl-d-aspartate (NMDA) glutamate receptor (GluR), has rapid antidepressant efficacy. Here we report findings from gene expression studies of a large cohort of postmortem subjects, including subjects with MDD and controls. Our data reveal higher expression levels of the majority of glutamatergic genes tested in the dorsolateral prefrontal cortex (DLPFC) in MDD (F21,59=2.32, P=0.006). Posthoc data indicate that these gene expression differences occurred mostly in the female subjects. Higher expression levels of GRIN1, GRIN2A-D, GRIA2-4, GRIK1-2, GRM1, GRM4, GRM5 and GRM7 were detected in the female patients with MDD. In contrast, GRM5 expression was lower in male MDD patients relative to male controls. When MDD suicides were compared with MDD non-suicides, GRIN2B, GRIK3 and GRM2 were expressed at higher levels in the suicides. Higher expression levels were detected for several additional genes, but these were not statistically significant after correction for multiple comparisons. In summary, our analyses indicate a generalized disruption of the regulation of the GluRs in the DLPFC of females with MDD, with more specific GluR alterations in the suicides and in the male groups. These data reveal further evidence that, in addition to the NMDA receptor, the AMPA, kainate and the metabotropic GluRs may be targets for the development of rapidly acting antidepressant drugs.

Cell type-specific in vivo expression of genes encoding signalling molecules in the brain in response to chronic mild stress and chronic treatment with fluoxetine.

Previously, we reported that chronic treatment with fluoxetine increased gene expression of 5-hydroxytryptamine receptor 2B (5-HT2BR), cytosolic phospholipase 2α (cPLA2α), glutamate receptor, ionotropic kainate 2 (GluK2) and adenosine deaminase acting on RNA 2 (ADAR2), in cultured astrocytes and astrocytes freshly isolated from transgenic mice tagged with an astrocyte-specific marker. In contrast, neurones isolated from transgenic mice tagged with a neurone-specific marker and exposed to fluoxetine showed an increase in gene expression of glutamate receptor, ionotropic kainate 4 (GluK4) and 5-hydroxytryptamine receptor 2C (5-HT2CR). In a mouse model of anhedonia, the downregulation of 5-HT2BR, cPLA2α, ADAR2 and GluK4 but not GluK2 and 5-HT2CR was detected. To investigate the effects of chronic mild stress (CMS) and/or fluoxetine treatment on gene expression of 5-HT2BR, 5-HT2CR, cPLA2α, ADAR2, GluK2 and GluK4 specifically in astrocytes and neurones. Transgenic mice tagged with either astrocyte- or neurone-specific markers were exposed to the CMS. Real-time PCR was applied to determine expression of messenger RNA (mRNA). We found that (i) mRNAs of the 5-HT2BR and cPLA2α in astrocytes and GluK4 in neurones were significantly reduced in mice that became anhedonic; the mRNA levels were restored by fluoxetine treatment; (ii) ADAR2 in astrocytes was decreased by the CMS but showed no response to fluoxetine in anhedonic animals; (iii) neither GluK2 expression in astrocytes nor 5-HT2CR expression in neurones were affected in anhedonic animals, although expression of 5-HT2CR mRNA was upregulated by fluoxetine. Our results indicate that the effects of chronic treatment with fluoxetine are not only dependent on the cell type studied but also on the development of anhedonia. This suggests that fluoxetine may affect major depression (MD) patients and healthy people in a different manner.

Glutamatergic circuits in the song system of Zebra Finch brain determined by gene expression of Vglut2 and Glutamate receptors

The songbird brain has a system of interconnected nuclei that are specialized for singing and song learning. Electrophysiological findings indicate a role for the glutamatergic neurons in the song system. Vesicular glutamate transporter 2 (vGluT2) is considered to be a specific biomarker of glutamatergic neurons in birds. Neurons receiving glutamatergic afferents express mRNA of ionotropic glutamate receptor subunits. This study examined expression of vGluT2 and glutamate receptor subunit mRNAs in nuclei of the song pathways of male zebra finch brain by in situ hybridization. VGluT2 mRNA was revealed high density of expression in the song nuclei, namely HVC, lateral magnocellular nucleus of the anterior nidopallium, and robust nucleus of the arcopallium. Area X did not show expression of vGluT2 mRNA. Nuclei in the descending motor pathway (dorsomedial nucleus of the intercollicular complex and retroambigual nucleus) were expressed vGluT2 mRNA. Target nuclei of vGluT2 mRNA-expressing nuclei showed hybridization signals for mRNAs of ionotropic glutamate receptor subunits. At least one of five subunit mRNAs (GluA1, GluA4, GluK1, GluN1, GluN2A) was expressed in song nuclei. The present findings support the existence of glutamatergic circuits in the song system in songbirds. DOI: http://dx.doi.org/10.3329/ralf.v1i1.22356 Res. Agric., Livest. Fish.1(1): 61-70, Dec 2014

Chronic SO2 inhalation above environmental standard impairs neuronal behavior and represses glutamate receptor gene expression and memory-related kinase activation via neuroinflammation in rats

Sulfur dioxide (SO2), as a ubiquitous air pollutant implicated in the genesis of pulmonary disease, is now being considered to be involved in neurotoxicity and increased risk for hospitalization of brain disorders. However, comparatively little is known about the impact of chronically SO2 inhalation on neuronal function. In the present study, by exposing male Wistar rats to SO2 at 3.50 and 7.00mg/m3 (approximately 1225 and 2450ppb, 4.08–8.16 (24h average concentration) times higher than the EPA standard for environmental air concentrations) or filtered air for 90 days, we investigated the impact of chronic SO2 inhalation on performance in Morris water maze, and probed the accompanying neurobiological effects, including activity-regulated cytoskeletal associated gene (Arc) and glutamate receptor gene expression, memory-related kinase level and inflammatory cytokine release in the hippocampus. Here, we found that SO2 exposure reduced the number of target zone crossings and time spent in the target quadrant during the test session in the spatial memory retention of the Morris water maze. Following the neuro-functional abnormality, we detected that SO2 inhalation reduced the expression of Arc and glutamate receptor subunits (GluR1, GluR2, NR1, NR2A, and NR2B) with a concentration-dependent property in comparison to controls. Additionally, the expression of memory kinases was attenuated statistically in the animals receiving the higher concentration, including protein kinase A (PKA), protein kinase C (PKC) and calcium/calmodulin-dependent protein kinaseIIα (CaMKIIα). And the inflammatory cytokine release was increased in rats exposed to SO2. Taken together, our results suggest that long-term exposure to SO2 air pollution at concentrations above the environmental standard in rats impaired spatial learning and memory, and indicate a close link between the neurobiological changes highlighted in the brain and the behavioral disturbances.

Physical activity correlates with glutamate receptor gene expression in spinally-projecting RVLM neurons: A laser capture microdissection study

Physical inactivity is an important risk factor in the development of cardiovascular disease. The rostral ventrolateral portion of the medulla (RVLM) is composed of heterogeneous populations of neurons that are involved in the regulation of the cardiovascular system. Because of functional heterogeneity, studying the changes in the gene expression of this specific population of neurons within the RVLM is challenging. In the present study, a fluorescent retrograde tracer was injected into the spinal cord to specifically label bulbospinal RVLM neurons in sedentary and active rats. Laser capture microdissection (LCM) was then employed to collect the fluorescently labeled neurons from sections encompassing the rostrocaudal extent of the RVLM. RNA extracted from the neurons was used in qRT-PCR analysis. Changes in gene expression levels of glutamate and GABA receptor subunits were compared between sedentary and physically active rats. GLUR3 subunit showed a significant negative correlation between total running distance and its relative gene expression in active rats. There were no significant difference in the gene expression of NMDA (NR1, NR2A, NR2B, NR2C and NR2D), AMPA (GLUR1, GLUR2 and GLUR3) and GABAA (GABAA1 and GABAA2) receptor subunits. Overall, the present study demonstrates the feasibility of utilizing LCM to investigate the gene expression changes in a specific population of neurons in the RVLM. Correlation studies suggest that physical activity could contribute to neuroplasticity in the RVLM.

Modulation of gene expression of adenosine and metabotropic glutamate receptors in rat's neuronal cells exposed to L-glutamate and [60]fullerene.

L-Glutamate (L-Glu) has been often associated not only to fundamental physiological roles, as learning and memory, but also to neuronal cell death and the genesis and development of important neurodegenerative diseases. Herein we studied the variation in the adenosine and metabotropic glutamate receptors expression induced by L-Glu treatment in rat's cortical neurons. The possibility to have structural alteration of the cells induced by L-Glu (100 nM, 1 and 10 microM) has been addressed, studying the modulation of microtubule associated protein-2 (MAP-2) and neurofilament heavy polypeptide (NEFH), natively associated proteins to the dendritic shape maintenance. Results showed that the proposed treatments were not destabilizing the cells, so the L-Glu concentrations were acceptable to investigate fluctuation in receptors expression, which were studied by RT-PCR. Interestingly, C60 fullerene derivative t3ss elicited a protective effect against glutamate toxicity, as demonstrated by MTT assay. In addition, t3ss compound exerted a different effect on the adenosine and metabotropic glutamate receptors analyzed. Interestingly, A(2A) and mGlu1 mRNAs were significantly decreased in conditions were t3ss neuroprotected cortical neurons from L-Glu toxicity. In summary, t3ss protects neurons from glutamate toxicity in a process that appears to be associated with the modulation of the gene expression of adenosine and metabotropic glutamate receptors.

Acute mechanisms underlying antibody effects in anti-N-methyl-D-aspartate receptor encephalitis.

ObjectiveA severe but treatable form of immune-mediated encephalitis is associated with antibodies in serum and cerebrospinal fluid (CSF) against the GluN1 subunit of the N-methyl-D-aspartate receptor (NMDAR). Prolonged exposure of hippocampal neurons to antibodies from patients with anti-NMDAR encephalitis caused a reversible decrease in the synaptic localization and function of NMDARs. However, acute effects of the antibodies, fate of the internalized receptors, type of neurons affected, and whether neurons develop compensatory homeostatic mechanisms were unknown and are the focus of this study.MethodsDissociated hippocampal neuron cultures and rodent brain sections were used for immunocytochemical, physiological, and molecular studies.ResultsPatient antibodies bind to NMDARs throughout the rodent brain, and decrease NMDAR cluster density in both excitatory and inhibitory hippocampal neurons. They rapidly increase the internalization rate of surface NMDAR clusters, independent of receptor activity. This internalization likely accounts for the observed decrease in NMDAR-mediated currents, as no evidence of direct blockade was detected. Once internalized, antibody-bound NMDARs traffic through both recycling endosomes and lysosomes, similar to pharmacologically induced NMDAR endocytosis. The antibodies are responsible for receptor internalization, as their depletion from CSF abrogates these effects in hippocampal neurons. We find that although anti-NMDAR antibodies do not induce compensatory changes in glutamate receptor gene expression, they cause a decrease in inhibitory synapse density onto excitatory hippocampal neurons.InterpretationOur data support an antibody-mediated mechanism of disease pathogenesis driven by immunoglobulin-induced receptor internalization. Antibody-mediated downregulation of surface NMDARs engages homeostatic synaptic plasticity mechanisms, which may inadvertently contribute to disease progression. Ann Neurol 2014;76:108–119

Elevated gene expression of glutamate receptors in noradrenergic neurons from the locus coeruleus in major depression.

Glutamate receptors are promising drug targets for the treatment of urgent suicide ideation and chronic major depressive disorder (MDD) that may lead to suicide completion. Antagonists of glutamatergic NMDA receptors reduce depressive symptoms faster than traditional antidepressants, with beneficial effects occurring within hours. Glutamate is the prominent excitatory input to the noradrenergic locus coeruleus (LC). The LC is activated by stress in part through this glutamatergic input. Evidence has accrued demonstrating that the LC may be overactive in MDD, while treatment with traditional antidepressants reduces LC activity. Pathological alterations of both glutamatergic and noradrenergic systems have been observed in depressive disorders, raising the prospect that disrupted glutamate-norepinephrine interactions may be a central component to depression and suicide pathobiology. This study examined the gene expression levels of glutamate receptors in post-mortem noradrenergic LC neurons from subjects with MDD (most died by suicide) and matched psychiatrically normal controls. Gene expression levels of glutamate receptors or receptor subunits were measured in LC neurons collected by laser capture microdissection. MDD subjects exhibited significantly higher expression levels of the NMDA receptor subunit genes, GRIN2B and GRIN2C, and the metabotropic receptor genes, GRM4 and GRM5, in LC neurons. Gene expression levels of these receptors in pyramidal neurons from prefrontal cortex (BA10) did not reveal abnormalities in MDD. These findings implicate disrupted glutamatergic-noradrenergic interactions at the level of the stress-sensitive LC in MDD and suicide, and provide a theoretical mechanism by which glutamate antagonists may exert rapid antidepressant effects.

Ovarian steroids increase PSD-95 expression and dendritic spines in the dorsal raphe of ovariectomized macaques

Estradiol (E) and progesterone (P) promote spinogenesis in several brain areas. Intracellular signaling cascades that promote spinogenesis involve RhoGTPases, glutamate signaling and synapse assembly. We found that in serotonin neurons, E ± P administration increases (a) gene and protein expression of RhoGTPases, (b) gene expression of glutamate receptors, and (c) gene expression of pivotal synapse assembly proteins. Therefore, in this study we determined whether structural changes in dendritic spines in the dorsal raphe follow the observed changes in gene and protein expression. Dendritic spines were examined with immunogold silver staining of a spine marker protein, postsynaptic density-95 (PSD-95) and with Golgi staining. In the PSD-95 study, adult Ovx monkeys received placebo, E, P, or E + P for 1 month (n = 3/group). Sections were immunostained for PSD-95 and the number of PSD-95-positive puncta was determined with stereology. E, P, and E + P treatment significantly increased the total number of PSD-95-positive puncta (ANOVA, P = 0.04). In the golgi study, adult Ovx monkeys received placebo, E or E + P for 1 month (n = 3-4) and the midbrain was golgi-stained. A total of 80 neurons were analyzed with Neurolucida software. There was a significant difference in spine density that depended on branch order (two-way ANOVA). E + P treatment significantly increased spine density in higher-order (3°-5°) dendritic branches relative to Ovx group (Bonferroni, P < 0.05). In summary, E + P leads to the elaboration of dendritic spines on dorsal raphe neurons. The ability of E to induce PSD-95, but not actual spines, suggests either a sampling or time lag issue. Increased spinogenesis on serotonin dendrites would facilitate excitatory glutamatergic input and, in turn, increase serotonin neurotransmission throughout the brain.

Gene expression of NMDA receptor subunits using laser capture microdissection in the rostral ventrolateral medulla (RVLM) of sedentary versus physically active rats.

The RVLM is important in tonic and reflex control of blood pressure and sympathetic nerve activity (SNA). We have observed enhanced SNA responses in sedentary versus physically active rats after microinjection of glutamate in the RVLM. Changes in glutamate receptor gene expression in the RVLM may contribute to enhanced responses in sedentary rats. In order to test this hypothesis, active (voluntary running for 15–18 wks) and sedentary (no running) rats were injected with Fluorogold (5%) at spinal levels T9‐T10 (n=5 ea). Brainstems were cryosectioned at 8μm for laser capture microdissection of bulbospinal RVLM neurons. RNA was isolated to analyze changes in gene expression of NMDA receptor subunits (NR2A‐D) using RT‐PCR. Gene expression was normalized to a housekeeping gene (HPRT). Preliminary results suggest that expression of NR2A‐D is not different between groups. However, within active rats, total running distance was significantly correlated to NR2C gene expression (r2=0.87, p&lt;0.05). These findings suggest that physical activity contributes to NR2C neuroplasticity in the RVLM. However further studies are needed to address whether NMDA receptor protein expression contributes to enhanced responses in sedentary rats. (R01HL096787; DC007733)

Altered expression of synapse and glutamate related genes in post-mortem hippocampus of depressed subjects

Major depressive disorder (MDD) has been linked to changes in function and activity of the hippocampus, one of the central limbic regions involved in regulation of emotions and mood. The exact cellular and molecular mechanisms underlying hippocampal plasticity in response to stress are yet to be fully characterized. In this study, we examined the genetic profile of micro-dissected subfields of post-mortem hippocampus from subjects diagnosed with MDD and comparison subjects matched for sex, race and age. Gene expression profiles of the dentate gyrus and CA1 were assessed by 48K human HEEBO whole genome microarrays and a subgroup of identified genes was confirmed by real-time polymerase chain reaction (qPCR). Pathway analysis revealed altered expression of several gene families, including cytoskeletal proteins involved in rearrangement of neuronal processes. Based on this and evidence of hippocampal neuronal atrophy in MDD, we focused on the expression of cytoskeletal, synaptic and glutamate receptor genes. Our findings demonstrate significant dysregulation of synaptic function/structure related genes SNAP25, DLG2 (SAP93), and MAP1A, and 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor subunit genes GLUR1 and GLUR3. Several of these human target genes were similarly dysregulated in a rat model of chronic unpredictable stress and the effects reversed by antidepressant treatment. Together, these studies provide new evidence that disruption of synaptic and glutamatergic signalling pathways contribute to the pathophysiology underlying MDD and provide interesting targets for novel therapeutic interventions.

Effects of 18-kDa translocator protein knockdown on gene expression of glutamate receptors, transporters, and metabolism, and on cell viability affected by glutamate

Previously, several important roles for glutamate have been described for the biology of primary brain tumors. For example, glutamate has been suggested to promote glioma cell proliferation by the activation of the 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid (AMPA) subtype of glutamate receptors. In the present study, we determined the potential regulatory roles of the 18-kDa translocator protein (TSPO) in the glutamatergic system in relation to cell death of brain tumor cells through knockdown of the TSPO by genetic manipulation. With microarray analysis and validation of gene expression of particular genes using real-time PCR, we found effects because of small inhibitory RNA knockdown of the TSPO in human U118MG glioblastoma cells on gene expression of glutamate receptors, glutamate transporters, and enzymes for glutamate metabolism. We also applied antisense RNA to silence TSPO in rat C6 glioblastoma cells and assayed the effects on DNA fragmentation, indicative of apoptosis, because of glutamate exposure. In particular, the effects of TSPO silencing in human U118MG cells related to glutamate metabolism indicate a net effect of a reduction in glutamate levels, which may potentially protect the cells in question from cell death. The TSPO knockdown in C6 cells showed that TSPO is required for the induction of apoptosis because of glutamate exposure. These findings show that interactions between the TSPO and the glutamatergic system may play a role in tumor development of glioblastoma cells. This may also have implications for our understanding of the involvement of the TSPO in secondary brain damage and neurodegenerative diseases.

Ovarian steroids increase glutamatergic related gene expression in serotonin neurons of macaques

Dendritic spines are the elementary structural units of neuronal plasticity and their proliferation and stabilization involve components of glutamate neurotransmission. In a model of hormone replacement therapy (HT), we sought the effect of estradiol (E) and progesterone (P) on gene expression related to glutamate neurotransmission in a laser captured preparation enriched for serotonin neurons from rhesus macaques. Microarray analysis was conducted (n=2 animals/treatment) and then confirmed for pivotal genes with qRT-PCR on additional laser captured material (n=3 animals/treatment). Ovariectomized rhesus macaques were treated with either placebo, E or E+P via Silastic implants for 1month prior to euthanasia. The midbrain was obtained, sectioned and immunostained for TPH. TPH-positive neurons were laser captured using an Arcturus Laser Dissection Microscope (Pixel II). RNA from laser captured serotonin neurons (n=2 animals/treatment) was hybridized to Rhesus Affymetrix GeneChips for screening purposes. There was a 2-fold or greater change in the expression of 28 probe sets related to glutamate processes in E and E+P treated animals. Quantitative (q) RT-PCR was conducted for 11 genes with a custom Taqman PCR array containing monkey specific primers and analyzed with ANOVA followed by Bonferroni's test. The log of the relative expression values indicated that in general, the responses to E and E+P were similar. Comparison of the relative expression or log relative expression in Ovx-controls to combined E and E+P treated groups with t-tests showed a significant increase in AMPA1 (GRIA1), AMPA2 (GRIA2), AMPA4 (GRIA4), NMDA2a (GRIN2A), metabotrophic glutamate receptor (GRM1), glutamine synthetase (GLUL), glutamate dehydrogenase (GLUD), glutamate cysteine ligase modifier subunit (GCLM), the glutamate transporter 2 (SLC1A2) and the glutamate transporter 3 (SLC1A3) with steroid treatment. There was no effect of steroid treatment on gene expression of the glutamate cysteine ligase catalytic subunit (GCLC). These data suggest that ovarian steroids target gene expression of ionotrophic and metabotrophic glutamate receptors in serotonin neurons. These receptors are present on dendritic spines and are necessary for spine maturation. The mRNAs coding for glutamate-related enzymes and transporters are likely derived from astrocytes or glutamate-containing terminals. Their induction by ovarian steroids indicates a complex upregulation of multiple components in the glutamate cycle and antioxidation, in addition to spine proliferation.

Glutamate receptor ion channels: structure, regulation, and function.

The mammalian ionotropic glutamate receptor family encodes 18 gene products that coassemble to form ligand-gated ion channels containing an agonist recognition site, a transmembrane ion permeation pathway, and gating elements that couple agonist-induced conformational changes to the opening or closing of the permeation pore. Glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system and are localized on neuronal and non-neuronal cells. These receptors regulate a broad spectrum of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors are postulated to play important roles in numerous neurological diseases and have attracted intense scrutiny. The description of glutamate receptor structure, including its transmembrane elements, reveals a complex assembly of multiple semiautonomous extracellular domains linked to a pore-forming element with striking resemblance to an inverted potassium channel. In this review we discuss International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.

Cholinergic and glutamergic receptor functional regulation in long-term, low dose somatotropin and insulin treatment to ageing rats: Rejuvenation of brain function

The role of somatotropin and insulin treatment in the regulation of neurotransmitter levels in the ageing brain is not fully established. We evaluated the long-term, low dose effects of somatotropin and insulin on acetylcholine and glutamate receptor subtypes functional regulation in the cerebral cortex of young (4–16 weeks) and old rats (60–90 weeks). Somatotropin and insulin treated young rats showed significant upregulation in muscarinic M1 and M3 expression whereas in old rats, somatotropin and insulin treatment downregulated M1 and M3 expression. N-methyl- d-aspartate and metabotropic glutamate receptor gene expression were significantly downregulated with somatotropin treatment while insulin treatment showed upregulation in both young and old rats. Acetylcholine esterase activity showed a decrease with age and after somatotropin and insulin treatment, the activity increased in both young and old rats. Electroencephalogram studies confirmed the brain wave activity in both young and old somatotropin and insulin treated rats. The results highlight long-term low dose somatotropin and insulin treatment in regulating cholinergic and glutamergic receptors subtypes in ageing rats and rejuvenation of brain function.

Alterations in gene expression of glutamate receptors and exocytosis-related factors by a hydroxylated-polychlorinated biphenyl in the developing rat brain

Polychlorinated biphenyls (PCBs), major environmental hormonally active agents, are metabolized into hydroxylated PCBs in the liver to facilitate excretion. Some of hydroxylated PCBs also have potencies disturbing endogenous hormonal activities at least in vitro. Hormonal activities of hydroxylated PCBs raise a possibility of their interfering with normal brain development which is strictly regulated by endogenous hormones. We investigated whether and how prenatal exposure to a congener of hydroxylated PCBs (4-OH-2′,3,3′,4′,5′-penta CB; 4-OH-PCB106) having activities to disrupt thyroid hormone-dependent signals in vitro could perturb normal gene expression in the developing brain in vivo. Pregnant rats were exposed to 4-OH-PCB106 subcutaneously at the dose of 1.0 mg/(kg day) from day 7 of gestation to postnatal day 1. Then three brain regions (cerebral cortex, hippocampus and striatum) were obtained from offspring on postnatal day 1 and subjected to further gene expression analyses. Comprehensive analyses of mRNA expression by oligo DNA microarrays and subsequent validations by quantitative RT-PCR revealed that prenatal exposure to 4-OH-PCB106 affected mRNA expression of glutamate receptors as well as that of thyroid hormone-responsive genes in region-specific manners. Concomitantly 4-OH-PCB106 exposure increased mRNA expression of genes related to exocytosis in the three brain regions. These results raise the possibility that prenatal exposure to some hydroxylated PCBs with thyroid hormone-disrupting potencies leads to abnormal brain development via perturbations on the expression of genes involved in glutamatergic neurotransmission.