Changes In Glutamate Receptors Research Articles

Neuroprotective effects of quinpirole on lithium chloride pilocarpine-induced epilepsy in rats and its underlying mechanisms

IntroductionEpilepsy is a common neurological disorder that presents with challenging mechanisms and treatment strategies. This study investigated the neuroprotective effects of quinpirole on lithium chloride pilocarpine-induced epileptic rats and explored its potential mechanisms.MethodsLithium chloride pilocarpine was used to induce an epileptic model in rats, and the effects of quinpirole on seizure symptoms and cognitive function were evaluated. The Racine scoring method, electroencephalography, and Morris water maze test were used to assess seizure severity and learning and memory functions in rats in the epileptic group. Additionally, immunohistochemistry and Western blot techniques were used to analyze the protein expression levels and morphological changes in glutamate receptor 2 (GluR2; GRIA2), BAX, and BCL2 in the hippocampi of rats in the epileptic group.ResultsFirst, it was confirmed that the symptoms in rats in the epileptic group were consistent with features of epilepsy. Furthermore, these rats demonstrated decreased learning and memory function in the Morris water maze test. Additionally, gene and protein levels of GluR2 in the hippocampi of rats in the epileptic group were significantly reduced.Quinpirole treatment significantly delayed seizure onset and decreased the mortality rate after the induction of a seizure. Furthermore, electroencephalography showed a significant decrease in the frequency of the spike waves. In the Morris water maze test, rats from the quinpirole treatment group demonstrated a shorter latency period to reach the platform and an increased number of crossings through the target quadrant. Network pharmacology analysis revealed a close association between quinpirole and GluR2 as well as its involvement in the cAMP signaling pathway, cocaine addiction, and dopaminergic synapses.Furthermore, immunohistochemistry and Western blot analysis showed that quinpirole treatment resulted in a denser arrangement and a more regular morphology of the granule cells in the hippocampi of rats in the epileptic group. Additionally, quinpirole treatment decreased the protein expression of BAX and increased the protein expression of BCL2.ConclusionThe current study demonstrated that quinpirole exerted neuroprotective effects in the epileptic rat model induced by lithium chloride pilocarpine. Additionally, it was found that the treatment not only alleviated the rats' seizure symptoms, but also improved their learning and memory abilities. This improvement was linked to the modulation of protein expression levels of GLUR2, BAX, and BCL2. These findings provided clues that would be important for further investigation of the therapeutic potential of quinpirole and its underlying mechanisms for epilepsy treatment.

Cross-modality supervised image restoration enables nanoscale tracking of synaptic plasticity in living mice

Learning is thought to involve changes in glutamate receptors at synapses, submicron structures that mediate communication between neurons in the central nervous system. Due to their small size and high density, synapses are difficult to resolve in vivo, limiting our ability to directly relate receptor dynamics to animal behavior. Here we developed a combination of computational and biological methods to overcome these challenges. First, we trained a deep-learning image-restoration algorithm that combines the advantages of ex vivo super-resolution and in vivo imaging modalities to overcome limitations specific to each optical system. When applied to in vivo images from transgenic mice expressing fluorescently labeled glutamate receptors, this restoration algorithm super-resolved synapses, enabling the tracking of behavior-associated synaptic plasticity with high spatial resolution. This method demonstrates the capabilities of image enhancement to learn from ex vivo data and imaging techniques to improve in vivo imaging resolution.

Differential alterations of entorhinal versus CA3 impact on ventral CA1 pyramidal neurons in 5xFAD mice.

Most hippocampal physiologic studies in Alzheimer disease (AD) have focused on memory circuit dysfunction in dorsal CA1. Ventral CA1 (vCA1) has received little attention, despite evidence supporting its increased susceptibility and its role in mood and affective symptoms, which play a prominent role in AD. We aimed to study the effect of amyloid pathology on circuit dysfunction in vCA1 using 5xFAD mice. We evaluated intrinsic excitability of vCA1 pyramidal neurons (PNs) as well as the impact of two distinct inputs onto their apical dendrite: entorhinal cortex (EC) input onto the distal compartment and CA3 inputs onto the proximal compartment. Acute ventral hippocampal slices were prepared from 12-14 month old 5xFAD and age-matched wild type (WT) mice. Whole cell patch clamp recordings were performed on vCA1 PNs. EC and CA3 input responses were elicited with extracellular stimulation of stratum lacunosum moleculare and stratum radiatum. We also addressed presynaptic function (paired pulse ratio), dendritic excitability (decay time constant of synaptic response), and intrinsic excitability (resting membrane potential, input resistance, sag ratio, firing rate). The EC stimulus-response curve reduced in 5xFAD vs. WT mice (n=6-10 PNs; p=0.0096) with a peak reduction of ∼33% (1.5mV vs. 1.0mV). In these same cells, the CA3 stimulus-response curve was also reduced (p<0.0001) but to a much larger extent of ∼67% at the peak (4.3mV vs. 1.4mV). The paired pulse ratio and response decay time constant were not affected with either input. Lastly, there were no statistically significant changes in intrinsic excitability measures. In 5xFAD mice, vCA1 PN circuit dysfunction is dominated by synaptic not intrinsic excitability changes. These changes are not in presynaptic function or postsynaptic ion currents, suggesting glutamate receptor changes or spine loss as alternative mechanisms. Moreover, these alterations are much more evident in CA3 versus EC input responses, perhaps driven by the inherent differences of the proximal and distal dendritic compartment. As such, with amyloidosis, vCA1 PN output shifts from being heavily dependent on CA3 input to being nearly equivalently dependent on EC input. These changes are important for understanding the circuit basis of mood and affect dysfunction in AD.

Endocannabinoids Released in the Ventral Tegmental Area During Copulation to Satiety Modulate Changes in Glutamate Receptors Associated With Synaptic Plasticity Processes.

Endocannabinoids modulate mesolimbic (MSL) dopamine (DA) neurons firing at the ventral tegmental area (VTA). These neurons are activated by copulation, increasing DA release in nucleus accumbens (NAcc). Copulation to satiety in male rats implies repeated ejaculation within a short period (around 2.5 h), during which NAcc dopamine concentrations remain elevated, suggesting continuous neuronal activation. During the 72 h that follow copulation to satiety, males exhibit long-lasting changes suggestive of brain plasticity processes. Enhanced DA neuron activity triggers the synthesis and release of endocannabinoids (eCBs) in the VTA, which participate in several long-term synaptic plasticity processes. Blockade of cannabinoid type 1 receptors (CB1Rs) during copulation to satiety interferes with the appearance of the plastic changes. Glutamatergic inputs to the VTA express CB1Rs and contribute to DA neuron burst firing and synaptic plasticity. We hypothesized that eCBs, released during copulation to satiety, would activate VTA CB1Rs and modulate synaptic plasticity processes involving glutamatergic transmission. To test this hypothesis, we determined changes in VTA CB1R density, phosphorylation, and internalization in rats that copulated to satiety 24 h earlier as compared both to animals that ejaculated only once and to sexually experienced unmated males. Changes in glutamate AMPAR and NMDAR densities and subunit composition and in ERK1/2 activation were determined in the VTA of males that copulated to satiety in the presence or absence of AM251, a CB1R antagonist. The CB1R density decreased and the proportion of phosphorylated CB1Rs increased in the animals that copulated compared to control rats. The CB1R internalization was detected only in sexually satiated males. A decrease in α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor (AMPAR) density, blocked by AM251 pretreatment, and an increase in the proportion of GluA2-AMPARs occurred in sexually satiated rats. GluN2A- N-methyl-D-aspartate receptor (NMDAR) expression decreased, and GluN2B-NMDARs increased in these animals, both of which were prevented by AM251 pre-treatment. An increase in phosphorylated ERK1/2 emerged in males copulating to satiety in the presence of AM251. Results demonstrate that during copulation to satiety, eCBs activate CB1Rs in the VTA, producing changes in glutamate receptors compatible with a reduced neuronal activation. These changes could play a role in the induction of the long-lasting physiological changes that characterize sexually satiated rats.

Metaplastic Effects of Ketamine and MK-801 on Glutamate Receptors Expression in Rat Medial Prefrontal Cortex and Hippocampus

Ketamine and MK-801 by blocking NMDA receptors may induce reinforcing effects as well as schizophrenia-like symptoms. Recent results showed that ketamine can also effectively reverse depressive signs in patients’ refractory to standard therapies. This evidence clearly points to the need of characterization of effects of these NMDARs antagonists on relevant brain areas for mood disorders. The aim of the present study was to investigate the molecular changes occurring at glutamatergic synapses 24 h after ketamine or MK-801 treatment in the rat medial prefrontal cortex (mPFC) and hippocampus (Hipp). In particular, we analyzed the levels of the glutamate transporter-1 (GLT-1), NMDA receptors, AMPA receptors subunits, and related scaffolding proteins. In the homogenate, we found a general decrease of protein levels, whereas their changes in the post-synaptic density were more complex. In fact, ketamine in the mPFC decreased the level of GLT-1 and increased the level of GluN2B, GluA1, GluA2, and scaffolding proteins, likely indicating a pattern of enhanced excitability. On the other hand, MK-801 only induced sparse changes with apparently no correlation to functional modification. Differently from mPFC, in Hipp, both substances reduced or caused no changes of glutamate receptors and scaffolding proteins expression. Ketamine decreased NMDA receptors while increased AMPA receptors subunit ratios, an effect indicative of permissive metaplastic modulation; conversely, MK-801 only decreased the latter, possibly representing a blockade of further synaptic plasticity. Taken together, these findings indicate a fine tuning of glutamatergic synapses by ketamine compared to MK-801 both in the mPFC and Hipp.

Psychosocial Crowding Stress-Induced Changes in Synaptic Transmission and Glutamate Receptor Expression in the Rat Frontal Cortex.

This study demonstrates how exposure to psychosocial crowding stress (CS) for 3, 7, and 14 days affects glutamate synapse functioning and signal transduction in the frontal cortex (FC) of rats. CS effects on synaptic activity were evaluated in FC slices of the primary motor cortex (M1) by measuring field potential (FP) amplitude, paired-pulse ratio (PPR), and long-term potentiation (LTP). Protein expression of GluA1, GluN2B mGluR1a/5, VGLUT1, and VGLUT2 was assessed in FC by western blot. The body’s response to CS was evaluated by measuring body weight and the plasma level of plasma corticosterone (CORT), adrenocorticotropic hormone (ACTH), and interleukin 1 beta (IL1B). CS 3 14d increased FP and attenuated LTP in M1, while PPR was augmented in CS 14d. The expression of GluA1, GluN2B, and mGluR1a/5 was up-regulated in CS 3d and downregulated in CS 14d. VGLUTs expression tended to increase in CS 7d. The failure to blunt the effects of chronic CS on FP and LTP in M1 suggests the impairment of habituation mechanisms by psychosocial stressors. PPR augmented by chronic CS with increased VGLUTs level in the CS 7d indicates that prolonged CS exposure changed presynaptic signaling within the FC. The CS bidirectional profile of changes in glutamate receptors’ expression seems to be a common mechanism evoked by stress in the FC.

Behavioral, Oxidative, and Biochemical Effects of Omega-3 on an Ovariectomized Rat Model of Menopause.

ObjectivesMenopause induces changes in neuronal transmission, leading to anxiety and depression. Changes in the brain's glutamate levels cause psychological behavior in postmenopausal women. Omega-3 has been studied to improve some of these behaviors.MethodsTwenty-four female Wistar rats were divided into four groups: sham-operated treated with water (SO-W), sham-operated treated with omega-3 (SO-O), ovariectomized (OVX) treated with water (OVX-W), and bilateral OVX treated with omega-3 (OVX-O). These treatments were performed for 20 days via gavage, before and after surgery, totaling 40 days.ResultsIn the forced swimming, elevated plus-maze, and open field tests to assess behaviors, such as depression and anxiety, omega-3 improved these behaviors in both treated groups. The levels of thiobarbituric acid reactive substances (TBARS) in the brain were not different between the groups; however, there was a significant decrease in the catalase activity in the SO-O group compared with the SO-W group (P < 0.05). The glutamate level in the cerebrospinal fluid (CSF) was elevated in the SO-O group (P < 0.001) but not in the OVX-W or OVX-O groups.ConclusionsThese results bring novel data when related to the glutamatergic system in the SO-O group. This has suggested that the action mechanism of omega-3 was not dependent on glutamate levels in the CSF of the OVX group, but it played a regulatory role in the sham-operated animals. To confirm this, more studies are needed to explore this field when relating to the estrogen and glutamate receptor changes in specific brain regions.

Glutamate Receptor Plasticity in Brainstem Respiratory Nuclei Following Chronic Hypercapnia in Goats

Patients that retain CO2 with respiratory diseases such as chronic obstructive pulmonary disease (COPD) have worse prognoses and higher mortality rates than those with equal impairment of lung function without hypercapnia. However, little is known about the effects of chronic hypercapnia on the neurochemical mechanisms controlling brainstem respiratory nuclei (BRN). Common mechanisms of neuroplasticity involve changes in glutamate receptor expression/phosphorylation to modulate synaptic strength and network excitability, driven by changes in both AMPA (GluR) and NMDA (GluN) glutamate receptors. Accordingly, herein we tested the hypothesis that changes occur in glutamatergic signaling within the BRN during exposure to chronically elevated inspired CO2 (InCO2) induced hypercapnia. Healthy goats were euthanized after either 24 hours or 30 days of chronic exposure to 6% InCO2 or room air. The brainstems were extracted for western blot analyses to assess GluR and GluN receptor expression and phosphorylation state within the BRN. Compared to room air control goats, the following significant (P&lt;0.05) changes were found after 24 hours of exposure to chronic hypercapnia: 1) AMPA receptor expression was greater, and NMDA receptor expression lower within the rostral solitary complex. 2) NMDA receptor expression/phosphorylation and APMA receptor phosphorylation were lower within the rostral ventrolateral medulla (VLM), while AMPA receptor expression/phosphorylation were greater in the caudal VLM. 3) AMPA receptor expression/phosphorylation were lower within the rostral retrotrapezoid nucleus. And, 4) NMDA receptor expression was greater within the caudal Raphe nucleus. The data indicate that within 24 hours of chronic hypercapnia changes have occurred in four BRN in GluR/GluN signaling which may contribute to an attenuated CO2‐induced hyperpnea and attenuated CO2 chemoreflex between 1 and 24 hours of hypercapnia (J. Physiol. 2018). GluR/GluN changes found at 24 hours of hypercapnia had returned to control levels after 30 days of hypercapnia. However, compared to room air control goats, the following significant (P&lt;0.05) changes were found following 30 days of hypercapnia: 1) NMDA receptor phosphorylation was greater in the caudal ventral respiratory column, and 2) AMPA receptor expression was greater in the caudal RTN. The changes in GluR/GluN signaling between 24 hours and 30 days of chronic InCO2 may contribute to a sustained hyperpnea and normalization of the CO2 chemoreflex at 30 days.Support or Funding Information‐Department of Veteran Affairs ‐NIH Grant 007852This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Role of glutamate and its receptors in migraine with reference to amitriptyline and transcranial magnetic stimulation therapy

Glutamate plays an important role in migraine pathogenesis but there is paucity of studies on glutamate in migraine subtypes, effect of treatment on glutamate levels and the changes in glutamate receptors. In this study we report the glutamate levels and changes in glutamate receptors following amitriptyline (AMT) or repetitive Transcranial Magnetic Stimulation (rTMS) therapy.One hundred and fifty migraine patients having more than 4 migraine attacks per month were included. Thirty patients were treated with AMT and 120 with rTMS; 24 patients received 3 sessions, 36 received single session of rTMS and 60 patients received sham stimulation. The severity of headache was assessed by VAS score, Migraine Index (MI) and frequency of headache. Good outcome was defined by 50% improvement in headache frequency; severity and MI. Plasma glutamate level were measured by enzyme linked immunosorbant assay and relative expression of NR2B and mGluR3 receptors by real time polymerase chain reaction. The changes in these parameters before and after treatment were measured and correlated with the clinical parameters.Glutamate levels (P = 0.006) and NR2B receptor expressions (P < 0.001) were significantly higher in migraine patients compared to the controls. Chronic migraine patients had higher glutamate level (P = 0.05). Glutamate and NR2B receptor declined after treatment (P < 0.001). There was a decline in glutamate levels following rTMS (P = 0.03), sham stimulation (P = 0.05) and AMT treatment (P = 0.003). NR2B receptors also declined after rTMS (P = 0.005) and AMT treatment (P = 0.01). It can be concluded that migraine is associated with high plasma glutamate and NR2B receptor which decline following AMT or rTMS therapy.

DMD‐10 and its Potential Effect on Regulation of the Glutamate Receptor GLR‐1 in C. elegans

An organism's nervous system processes decisions on how to respond to their environment. Studying how proteins of the nervous system are regulated enables us to identify how an organism responds to its environment and alters its behavior. In our lab, we study glutamate receptors, specifically GLR‐1. Glutamate is used for communication between neurons, and changes in glutamate receptors are believed to play an important role in learning and memory. The DAF‐7/TGF‐β signaling pathway regulates GLR‐1 in C. elegans and mutants in the DAF‐7/TGF‐β signaling pathway have increased GLR‐1. However, the mechanism through which GLR‐1 levels are increased in the daf‐7 mutant worms is unknown. My research addressed how GLR‐1 levels were increased in the daf‐7 worms. I explored the possibility that the transcription factor DMD‐10 is affected in the daf‐7 mutants, and then in turn affects GLR‐1. We tested this by measuring spontaneous reversals (a GLR‐1 dependent behavior) in both single mutant and double mutant worms. If DMD‐10 is affected in the daf‐7 mutants, we predict that the dmd‐10; daf‐7 double mutants would have fewer reversals than the daf‐7 mutant. The dmd‐10; daf‐7 double mutants did not have fewer spontaneous reversals than the single daf‐7 mutant, which suggests that the DAF‐7/TGF‐β signaling pathway does not use DMD‐10 to alter levels of GLR‐1. However, the dmd‐10 single mutant had fewer reversals than the wildtype, suggesting that DMD‐10 is required for normal reversals. The results of this experiment suggested that although DMD‐10 is not involved in DAF‐7/TGF‐β regulation of GLR‐1, it may have an independent effect on GLR‐1. My current research is aimed at determining if DMD‐10 is involved in the regulation of GLR‐1. I have generated a strain of dmd‐10 mutant worms that expresses GFP‐tagged GLR‐1 (GLR‐1::GFP). Imaging of GLR‐1::GFP in wild type and dmd‐10 mutant worms will allow us to test if DMD‐10 is involved in GLR‐1 regulation. This strain is being analyzed for total levels of GLR‐1::GFP using western blotting and will indicate if DMD‐10 is reducing total levels of GLR‐1. Synaptic levels of GLR‐1::GFP will be analyzed using fluorescence imaging that provides information on the location of GLR‐1 and whether it is localized in the cell body or synapses. Together, these results will indicate if DMD‐10 is affecting GLR‐1 and will give us insight into how regulation is occurring.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Perfluorooctane sulfonate induces neuronal vulnerability by decreasing GluR2 expression.

Perfluorooctane sulfonate (PFOS) is a persistent environmental contaminant. Although studies have described PFOS-induced neurotoxicity in animal brains and neuronal cells, the molecular mechanisms of PFOS-induced neurotoxicity based on the distribution properties, especially during developmental periods, have not been clarified. To clarify the mechanisms of PFOS-induced neuronal vulnerability during developmental periods, we examined changes in glutamate receptor 2 (GluR2) expression and related neurotoxicity in PFOS-treated primary cortical neurons and neonatal rat brains. Exposure of cortical neurons to 1μM PFOS for 9days resulted in decreased α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluR2 expression, which subsequently enhanced vulnerability to glutamate by increasing intracellular Ca2+ concentrations. The brain-plasma ratio of PFOS in pups was approximately five times higher than that in dams, although there were no differences in liver-plasma ratio between dams and pups. GluR2 expression in pup cerebral cortex decreased after exposure to 2.0mg/kg PFOS, and kainic acid induced histopathological abnormalities in PFOS-exposed pups. Our findings suggest that decreased neuronal GluR2 expression is involved in PFOS-induced neurotoxicity, especially during the fetal and neonatal periods.

Ethanol-Associated Changes in Glutamate Reward Neurocircuitry: A Minireview of Clinical and Preclinical Genetic Findings.

Herein, we have reviewed the role of glutamate, the major excitatory neurotransmitter in the brain, in a number of neurochemical, -physiological, and -behavioral processes mediating the development of alcohol dependence. The findings discussed include results from both preclinical as well as neuroimaging and postmortem clinical studies. Expression levels for a number of glutamate-associated genes and/or proteins are modulated by alcohol abuse and dependence. These changes in expression include metabotropic receptors and ionotropic receptor subunits as well as different glutamate transporters. Moreover, these changes in gene expression parallel the pharmacologic manipulation of these same receptors and transporters. Some of these gene expression changes may have predated alcohol abuse and dependence because a number of glutamate-associated polymorphisms are related to a genetic predisposition to develop alcohol dependence. Other glutamate-associated polymorphisms are linked to age at the onset of alcohol-dependence and initial level of response/sensitivity to alcohol. Finally, findings of innate and/or ethanol-induced glutamate-associated gene expression differences/changes observed in a genetic animal model of alcoholism, the P rat, are summarized. Overall, the existing literature indicates that changes in glutamate receptors, transporters, enzymes, and scaffolding proteins are crucial for the development of alcohol dependence and there is a substantial genetic component to these effects. This indicates that continued research into the genetic underpinnings of these glutamate-associated effects will provide important novel molecular targets for treating alcohol abuse and dependence.

Changes in glutamate receptors in dyskinetic parkinsonian monkeys after unilateral subthalamotomy.

Unilateral subthalamotomy is a surgical procedure that may be used to alleviate disabling levodopa-induced dyskinesias (LIDs) in patients with Parkinson disease (PD). However, the mechanisms involved in LID remain largely unknown. The subthalamic nucleus (STN) is the sole glutamatergic nucleus within the basal ganglia, and its lesion may produce changes in glutamate receptors in various areas of the basal ganglia. The authors aimed to investigate the biochemical changes in glutamate receptors in striatal and pallidal regions of the basal ganglia after lesion of the STN in parkinsonian macaque monkeys. The authors treated 12 female ovariectomized monkeys with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to induce PD-like symptoms, treated 8 of these animals with 3,4-dihydroxy-l-phenylalanine (L-DOPA; levodopa) to induce LID, and performed unilateral subthalamotomy in 4 of these 8 monkeys. Four additional monkeys were treated with saline only and were used as controls. The MPTP monkeys had previously been shown to respond behaviorally to lower doses of levodopa after the STN lesion. Autoradiography of slices from postmortem brain tissues was used to visualize changes in the specific binding of striatal and pallidal ionotropic glutamate receptors (that is, of the α-amino-3-hydroxy 5-methyl-4-isoxazole propionate [AMPA] and N-methyl-d-aspartate [NMDA] NR1/NR2B subunit receptors) and of metabotropic glutamate (mGlu) receptors (that is, mGlu2/3 and mGlu5 receptors). The specific binding and distribution of glutamate receptors in the basal ganglia of the levodopa-treated, STN-lesioned MPTP monkeys were compared with those in the saline-treated control monkeys and in the saline-treated and levodopa-treated MPTP monkeys. The autoradiographic results indicated that none of the pharmacological and surgical treatments produced changes in the specific binding of AMPA receptors in the basal ganglia. Levodopa treatment increased the specific binding of NMDA receptors in the basal ganglia. Subthalamotomy reversed these increases in the striatum, but in the globus pallidus (GP), the subthalamotomy reversed these increases only contralaterally. Levodopa treatment reversed MPTP-induced increases in mGlu2/3 receptors only in the GP. mGlu2/3 receptor-specific binding in the striatum and GP decreased bilaterally in the levodopa-treated, STN-lesioned MPTP monkeys compared with the other 3 groups. Compared with mGlu5 receptor-specific binding in the control monkeys, that of the levodopa-treated MPTP monkeys increased in the dorsal putamen and remained unchanged in the caudate nucleus and in the GP. These results implicate glutamate receptors in the previously observed benefits of unilateral subthalamotomy to improve motor control.

Sequential expression of cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor in rat hippocampal neurons after fluid percussion injury.

Traumatic brain injury causes gene expression changes in different brain regions. Occurrence and development of traumatic brain injury are closely related, involving expression of three factors, namely cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor. However, little is known about the correlation of these three factors and brain neuronal injury. In this study, primary cultured rat hippocampal neurons were subjected to fluid percussion injury according to Scott's method, with some modifications. RT-PCR and semi-quantitative immunocytochemical staining was used to measure the expression levels of cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor. Our results found that cyclooxygenase-2 expression were firstly increased post-injury, and then decreased. Both mRNA and protein expression levels reached peaks at 8 and 12 hours post-injury, respectively. Similar sequential changes in glutamate receptor 2 were observed, with highest levels mRNA and protein expression at 8 and 12 hours post-injury respectively. On the contrary, the expressions of platelet activating factor receptor were firstly decreased post-injury, and then increased. Both mRNA and protein expression levels reached the lowest levels at 8 and 12 hours post-injury, respectively. Totally, our findings suggest that these three factors are involved in occurrence and development of hippocampal neuronal injury.

Binge alcohol drinking by mice requires intact group 1 metabotropic glutamate receptor signaling within the central nucleus of the amygdala.

Despite the fact that binge alcohol drinking (intake resulting in blood alcohol concentrations (BACs) 80 mg% within a 2-h period) is the most prevalent form of alcohol-use disorders (AUD), a large knowledge gap exists regarding how this form of AUD influences neural circuits mediating alcohol reinforcement. The present study employed integrative approaches to examine the functional relevance of binge drinking-induced changes in glutamate receptors, their associated scaffolding proteins and certain signaling molecules within the central nucleus of the amygdala (CeA). A 30-day history of binge alcohol drinking (for example, 4-5 g kg(-1) per 2 h(-1)) elevated CeA levels of mGluR1, GluN2B, Homer2a/b and phospholipase C (PLC) β3, without significantly altering protein expression within the adjacent basolateral amygdala. An intra-CeA infusion of mGluR1, mGluR5 and PLC inhibitors all dose-dependently reduced binge intake, without influencing sucrose drinking. The effects of co-infusing mGluR1 and PLC inhibitors were additive, whereas those of coinhibiting mGluR5 and PLC were not, indicating that the efficacy of mGluR1 blockade to lower binge intake involves a pathway independent of PLC activation. The efficacy of mGluR1, mGluR5 and PLC inhibitors to reduce binge intake depended upon intact Homer2 expression as revealed through neuropharmacological studies of Homer2 null mutant mice. Collectively, these data indicate binge alcohol-induced increases in Group1 mGluR signaling within the CeA as a neuroadaptation maintaining excessive alcohol intake, which may contribute to the propensity to binge drink.

WHAT PROTEOMICS WILL ADD TO OUR UNDERSTANDING OF THE NEUROPATHOLOGY OF SCHIZOPHRENIA

Recent data suggest abnormalities of glutamate transmission in schizophrenia. While many findings of abnormal glutamate receptor expression in schizophrenia have been published, findings are subtle or even contradictory. These conflicting studies on the expression of these receptors leads to a reconsideration of the “glutamate hypothesis of schizophrenia” as not “too many” or “too few” receptors, but rather one of alterations in the cell biological processes that manage the total pool of receptors. Recent data point to abnormalities of glutamate receptor trafficking, delivery, dendritic localization, recycling, and degradation in the brain in schizophrenia. In this study, we extend our findings of abnormalities of intracellular trafficking of the AMPA subtype of glutamate receptor in schizophrenia. AMPA receptor trafficking starts in the endoplasmic reticulum (ER), in which AMPA receptor subunits are postranslationaly N-glycosylated. N-linked high mannose containing sugars added to AMPA subunits, which are trimmed and replaced by more elaborate sugars in the Golgi, after which AMPA subunits are trafficked for insertion into the plasma membrane. We assayed N-glycosylation status of AMPA subunits in prefrontal cortex in schizophrenia. N-glycosylation was assessed following digestion with endoglycosidase H (Endo H), which removes immature high mannose containing sugars, or with peptide-Nglycosidase F (PNGase F), which removes all N-linked sugars. We found that both GluR2 and GluR4 were sensitive to Endo H and PNGase F treatment, indicating that they are N-glycosylated; neither GluR1 nor GluR3 are N-glycosylated in human brain. GluR2 was found to have less N-linked high mannose and/or hybrid sugars in schizophrenia. This was confirmed by immunoprecipitation of GluR2 and probing with Concavalin A, a mannose-specific lectin. GluR2 immunoprecipitated from schizophrenia cortex was significantly less reactive to Con A comparing to the comparison group. These results indicate that GluR2 is abnormally glycosylated in schizophrenia, consistent with abnormal assembly or trafficking of the AMPA receptor. Abnormalities of glycosylation in schizophrenia may be more extensive, as we also have preliminary results suggesting abnormalities of Nglycosylation of NMDA subunits and two of the glutamate transporters. These results suggest that there are changes in glutamate receptors in schizophrenia that involve abnormalities of intracellular processes that effectively reduce receptor function even though total cellular levels of these receptors may be normal. Such findings are important because they point to the complexity of molecular and intracellular abnormalities in schizophrenia, and highlight novel sites that may be profitably targeted for drug.

ABNORMAL N-GLYCOSYLATION OF PROTEINS OF THE GLUTAMATE SYNAPSE IN SCHIZOPHRENIA

Recent data suggest abnormalities of glutamate transmission in schizophrenia. While many findings of abnormal glutamate receptor expression in schizophrenia have been published, findings are subtle or even contradictory. These conflicting studies on the expression of these receptors leads to a reconsideration of the “glutamate hypothesis of schizophrenia” as not “too many” or “too few” receptors, but rather one of alterations in the cell biological processes that manage the total pool of receptors. Recent data point to abnormalities of glutamate receptor trafficking, delivery, dendritic localization, recycling, and degradation in the brain in schizophrenia. In this study, we extend our findings of abnormalities of intracellular trafficking of the AMPA subtype of glutamate receptor in schizophrenia. AMPA receptor trafficking starts in the endoplasmic reticulum (ER), in which AMPA receptor subunits are postranslationaly N-glycosylated. N-linked high mannose containing sugars added to AMPA subunits, which are trimmed and replaced by more elaborate sugars in the Golgi, after which AMPA subunits are trafficked for insertion into the plasma membrane. We assayed N-glycosylation status of AMPA subunits in prefrontal cortex in schizophrenia. N-glycosylation was assessed following digestion with endoglycosidase H (Endo H), which removes immature high mannose containing sugars, or with peptide-Nglycosidase F (PNGase F), which removes all N-linked sugars. We found that both GluR2 and GluR4 were sensitive to Endo H and PNGase F treatment, indicating that they are N-glycosylated; neither GluR1 nor GluR3 are N-glycosylated in human brain. GluR2 was found to have less N-linked high mannose and/or hybrid sugars in schizophrenia. This was confirmed by immunoprecipitation of GluR2 and probing with Concavalin A, a mannose-specific lectin. GluR2 immunoprecipitated from schizophrenia cortex was significantly less reactive to Con A comparing to the comparison group. These results indicate that GluR2 is abnormally glycosylated in schizophrenia, consistent with abnormal assembly or trafficking of the AMPA receptor. Abnormalities of glycosylation in schizophrenia may be more extensive, as we also have preliminary results suggesting abnormalities of Nglycosylation of NMDA subunits and two of the glutamate transporters. These results suggest that there are changes in glutamate receptors in schizophrenia that involve abnormalities of intracellular processes that effectively reduce receptor function even though total cellular levels of these receptors may be normal. Such findings are important because they point to the complexity of molecular and intracellular abnormalities in schizophrenia, and highlight novel sites that may be profitably targeted for drug.

Brain-derived neurotrophic factor modulates the severity of cognitive alterations induced by mutant huntingtin: Involvement of phospholipaseCγ activity and glutamate receptor expression

The involvement of brain-derived neurotrophic factor (BDNF) in cognitive processes and the decrease in its expression in Huntington's disease suggest that this neurotrophin may play a role in learning impairment during the disease progression. We therefore analyzed the onset and severity of cognitive deficits in two different mouse models with the same mutant huntingtin but with different levels of BDNF (R6/1 and R6/1:BDNF+/− mice). We observed that BDNF modulates cognitive function in different learning tasks, even before the onset of motor symptoms. R6/1:BDNF+/− mice showed earlier and more accentuated cognitive impairment than R6/1 mice at 5 weeks of age in discrimination learning; at 5 weeks of age in procedural learning; and at 9 weeks of age in alternation learning. At the earliest age at which cognitive impairment was detected, electrophysiological analysis was performed in the hippocampus. All mutant genotypes showed reduced hippocampal long term potentiation (LTP) with respect to wild type but did not show differences between them. Thus, we evaluated the involvement of BDNF-trkB signaling and glutamate receptor expression in the hippocampus of these mice. We observed a decrease in phospholipaseCγ activity, but not ERK, in R61, BDNF+/− and R6/1:BDNF+/− hippocampus at the age when LTP was altered. However, a specific decrease in the expression of glutamate receptors NR1, NR2A and GluR1 was detected only in R6/1:BDNF+/− hippocampus. Therefore, these results show that BDNF modulates the learning and memory alterations induced by mutant huntingtin. This interaction leads to intracellular changes, such as specific changes in glutamate receptors and in BDNF-trkB signaling through phospholipaseCγ.

Topiramate-Induced Psychosis in an Individual With Alcohol Dependent

Sir: Topiramate, an antiepileptic drug, has been shown to reduce alcohol craving and heavy drinking and to improve abstinence among alcohol-dependent individuals.1 By potentiating the inhibitory effects of γ-aminobutyric acid (GABA)2 and depressing the excitatory action of kainate on α-amino-3-hy-droxy-5-methylisoxazole-4-propionic acid (AMPA) glutamate receptors,3 topiramate reduces mesocorticolimbic dopamine activity, which is a crucial pathway by which alcohol exerts its rewarding effects.4–6 Doses of up to 300 mg per day have been effective in reducing craving in alcoholdependent patients. The drug is started at a low dose and increased slowly to avoid adverse effects. Psychiatric side effects occur in up to 23.9% of patients with epilepsy7 and are related to a personal or family history of psychiatric illness and rapid dose escalation. These psychiatric side effects include depression, anxiety, aggression, cognitive slowing, and psychosis. Topiramate has also been reported to precipitate psychosis in patients with schizophrenia8 and mood disorder.9 Case report. Mr. A, a 42-year-old man, was admitted to our Deaddiction Centre in January 2005 with a diagnosis of alcohol dependence syndrome (according to ICD-10 criteria) and presented with delirium tremens. The patient had a history of alcohol consumption for the last 15 years and had developed features of salience, tolerance, craving, and loss of control over drinking over the last 8 years. He presented with tremors; irritability; insomnia; loss of appetite; auditory, visual, and tactile hallucinations; disorientation; and clouding of consciousness, all of which began after 24 hours of abstinence. He had a history of possible withdrawal seizures in the past. There was no history of psychosis. There was a family history of alcohol dependence in his father and 2 male siblings. There was no family history of psychosis or mood disorder. Laboratory findings were within normal limits. The patient was started on a detoxification regimen with lorazepam, 16 mg per day PO in tapering doses, and vitamin supplementation. His withdrawal symptoms subsided within 48 hours, with hallucinations subsiding within 24 hours. After detoxification for 10 days, the patient was started on topiramate 25 mg per day as long-term medication for alcohol dependence. On the third day after starting topiramate, the patient suddenly awoke at around 1:00 a.m., looked anxious, and reported that he could hear “voices calling out to him from hell” and discussing his death. He continued to hear these voices even after he was fully awake. He remained anxious, apprehensive, and distressed for the next 30 minutes and was sedated with intravenous haloperidol 10 mg and lorazepam 4 mg, both of which had to be repeated after 2 hours. During this episode, there was no disorientation, clouding of consciousness, or tremulousness. After topiramate was stopped, these psychotic symptoms remitted completely within 48 hours and did not recur. Topiramate has been hypothesized to induce psychosis as a result of its antiglutamatergic properties in the nucleus accumbens and prefrontal cortex.8 Brief psychosis was the most common presentation in a series of patients with epilepsy.7 As patients with alcohol dependence syndrome show changes in glutamate receptors, especially during withdrawal,6 they may be more sensitive to the effects of topiramate. To the best of our knowledge, this is the first report of topiramate precipitating psychosis in a patient with alcohol dependence. It is possible that patients presenting with alcohol withdrawal are more susceptible to this particular adverse effect.

Glutamate receptor changes associated with transient anoxia/hypoglycaemia in hippocampal slice cultures

Transient anoxia/hypoglycaemia in organotypic hippocampal slice cultures, a model of transient brain ischaemia, ultimately results in delayed cell death. Although the mechanisms underlying this delayed death remain unknown, an increase in excitatory drive has been postulated. We report here that transient anoxia/hypoglycaemia in rat hippocampal slice cultures resulted in a 70-80% enhancement of evoked, alpha-amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid (AMPA) receptor-mediated, excitatory responses lasting over 60 min. This effect was prevented by blockade of N-methyl-d-aspartate (NMDA) receptors, did not involve changes of paired-pulse facilitation ratio, but was associated with a 50% increase in amplitude, but not frequency, of spontaneous miniature excitatory postsynaptic currents (mEPSCs). Consistent with this, paired recordings revealed the appearance of AMPA receptor-mediated EPSCs at previously silent synapses and occlusion by prior induction of long-term potentiation (LTP). Transient anoxia/hypoglycaemia further resulted in a 63% potentiation of evoked NMDA receptor-dependent synaptic responses, accounting for the 20% increase in ratio of AMPA to NMDA responses. No change in rectification properties of AMPA receptor-mediated currents could be detected within the first hour following anoxia/hypoglycaemia-induced potentiation. Western blot analyses of slice cultures exposed to either control conditions or a short anoxia/hypoglycaemia revealed a marked, 50-70% increase of GluR1, GluR2/3 and NR1 subunits 1 h, but not 15 min, after the anoxic/hypoglycaemic episode. This increase was blocked by an inhibitor of protein synthesis. Together these results indicate that a transient anoxia/hypoglycaemia is associated with a marked enhancement of excitatory transmission sharing similarities with the mechanisms underlying LTP, and is correlated with an increased synthesis of excitatory receptor subunits.