Glutamatergic Receptor Antagonists Research Articles

The Role of the Rodent Insula in Anxiety.

The human insula has been consistently reported to be overactivated in all anxiety disorders, activation which has been suggested to be proportional to the level of anxiety and shown to decrease with effective anxiolytic treatment. Nonetheless, studies evaluating the direct role of the insula in anxiety are lacking. Here, we set out to investigate the role of the rodent insula in anxiety by either inactivating different insular regions via microinjections of glutamatergic AMPA receptor antagonist CNQX or activating them by microinjection of GABA receptor antagonist bicuculline in rats, before measuring anxiety-like behavior using the elevated plus maze. Inactivation of caudal and medial insular regions induced anxiogenic effects, while their activation induced anxiolytic effects. In contrast, inactivation of more rostral areas induced anxiolytic effects and their activation, anxiogenic effects. These results suggest that the insula in the rat has a role in the modulation of anxiety-like behavior in rats, showing regional differences; rostral regions have an anxiogenic role, while medial and caudal regions have an anxiolytic role, with a transition area around bregma +0.5. The present study suggests that the insula has a direct role in anxiety.

S-ketamine reduces marble burying behaviour: Involvement of ventromedial orbitofrontal cortex and AMPA receptors

Previous clinical and pre-clinical studies suggest the involvement of ventromedial orbitofrontal cortex (vmOFC) and glutamatergic neurotransmission in obsessive-compulsive disorder (OCD). Ketamine, an NMDA glutamatergic receptor antagonist, has shown a rapid and long-lasting antidepressant effect, but its anti-compulsive effect has been scarcely investigated. The antidepressant effect of ketamine involves NMDA receptor blockade, AMPA receptor activation, increased serotonin (5-HT) release and attenuation of nitric oxide (NO) synthesis. It is not known if these mechanisms are involved in ketamine-induced anti-compulsive effect. Therefore, we firstly investigated the effect of S-ketamine in the marble-burying test (MBT), a model for screening of drugs with potential to treat OCD. Then, we evaluated whether ketamine effects in the MBT would involve the vmOFC, be dependent on AMPA receptors, facilitation of serotonergic neurotransmission and inhibition of nitrergic pathway. Our results showed that single systemic (10 mg/kg) and intra-vmOFC (10 nmol/side) administration of S-ketamine reduces marble burying behaviour (MBB) without affecting spontaneous locomotors activity. Pre-treatment with NBQX (3 mg/kg; AMPA receptor antagonist) blocked the reduction of MBB induced by S-ketamine. However, pre-treatment with p-CPA (150 mg/kg/day; a 5-HT synthesis inhibitor), WAY100635 (3 mg/kg; a 5-HT1A receptor antagonist), or L-arginine (500 mg/kg; a nitric oxide precursor) did not counteract S-ketamine effect in the MBT. In contrast, associating sub-effective doses of L-NAME (10 mg/kg; NOS inhibitor) and S-ketamine (3 mg/kg) decreased MBB. In conclusion, the reduction of MBB by S-ketamine strengthens its possible anti-compulsive effect. The vmOFC is involved in this S-ketamine effect, which is dependent on the activation of AMPA receptors.

Efficacy of Ketamine in the Treatment of Substance Use Disorders: A Systematic Review.

Background: Despite advances in behavioral and pharmacotherapy interventions, substance use disorders (SUDs) are frequently refractory to treatment. Glutamatergic dysregulation has received increasing attention as one common neuropathology across multiple substances of abuse. Ketamine is a potent N-methyl-D-aspartate (NMDA) glutamatergic receptor antagonist which has been found to be effective in the treatment of severe depression. Here we review the literature on the efficacy of ketamine in the treatment of SUDs.Methods: A systematic review of the PubMed, Scopus, and ClinicalTrials.gov databases was undertaken to identify completed and ongoing human studies of the effectiveness of ketamine in the treatment of SUDs between January 1997 and January 2018.Results and conclusion: Seven completed studies were identified. Two studies focused on alcohol use disorder, two focused on cocaine use disorder, and three focused on opioid use disorder. Both cocaine studies found improvements in craving, motivation, and decreased cocaine use rates, although studies were limited by small sample sizes, a homogeneous population and short follow-up. Studies of alcohol and opioid use disorders found improvement in abstinence rates in the ketamine group, with significant between-group effects noted for up to two years following a single infusion, although these were not placebo-controlled trials. These results suggest that ketamine may facilitate abstinence across multiple substances of abuse and warrants broader investigation in addiction treatment. We conclude with an overview of the six ongoing studies of ketamine in the treatment of alcohol, cocaine, cannabis, and opioid use disorders and discuss future directions in this emerging area of research.

1/f electrophysiological spectra in resting and drug-induced states can be explained by the dynamics of multiple oscillatory relaxation processes

Neurophysiological recordings are dominated by arhythmical activity whose spectra can be characterised by power-law functions, and on this basis are often referred to as reflecting scale-free brain dynamics (1/fβ). Relatively little is known regarding the neural generators and temporal dynamics of this arhythmical behaviour compared to rhythmical behaviour. Here we used Irregularly Resampled AutoSpectral Analysis (IRASA) to quantify β, in both the high (5–100 Hz, βhf) and low frequency bands (0.1–2.5 Hz, βlf) in MEG/EEG/ECoG recordings and to separate arhythmical from rhythmical modes of activity, such as, alpha rhythms. In MEG/EEG/ECoG data, we demonstrate that oscillatory alpha power dynamically correlates over time with βhf and similarly, participants with higher rhythmical alpha power have higher βhf. In a series of pharmaco-MEG investigations using the GABA reuptake inhibitor tiagabine, the glutamatergic AMPA receptor antagonist perampanel, the NMDA receptor antagonist ketamine and the mixed partial serotonergic agonist LSD, a variety of effects on both βhf and βlf were observed. Additionally, strong modulations of βhf were seen in monkey ECoG data during general anaesthesia using propofol and ketamine. We develop and test a unifying model which can explain, the 1/f nature of electrophysiological spectra, their dynamic interaction with oscillatory rhythms as well as the sensitivity of 1/f activity to drug interventions by considering electrophysiological spectra as being generated by a collection of stochastically perturbed damped oscillators having a distribution of relaxation rates.

Intracerebroventricular Injection of NMDA Receptor Antagonist Affects l-Arginine Induced Food Intake in Neonatal Layer Chicks

Nowadays inquiry of possible interplay between different neurotransmitters in brain function is one of the major fields of interest for researchers. In the current study, we aimed to survey interaction between glutamatergic and nitrergic systems on food intake in layers. In this regards, total of 308 one-day-old female layer-type chicks divided to 28 groups of 11 individuals in 7 defined experiments. All chickens were kept 3 h food deprived and used for intracerebroventricular (ICV) injection in the 5 day olds. In experiments 1–5, treatment groups received ICV injection of 10 µl control solution, l-arginine (precursor of NO synthesis; 800 nmol). In addition, birds administrated by different antagonists of glutamatergic receptors including MK-801 (NMDA receptor antagonist; 15 nmol), CNQX (AMPA/kainate receptor antagonist; 390 nmol), AIDA (mGLUR1 glutamate receptor antagonist; 2 nmol), LY341495 (mGLUR2 glutamate receptor antagonist; 150 nmol), UBP1112 (mGLUR3 glutamate receptor antagonist; 2 nmol) besides combination of mentioned antagonists of glutamatergic receptors + l-arginine (800 nmol). In the experiment 6, groups injected by control solution, glutamate (300 nmol), l-NAME (100 nmol) besides combination of both drugs. In the experiment 7, birds were ICV injected by control solution, glutamate (75 nmol), l-arginine (200 nmol) and combination of glutamate + l-arginine. Then cumulative food intake measured as following a known amount of a diet was given to the animals after 30, 60 and 120 min post injection. Based on the results, administration of MK-801 (15 nmol) significantly attenuated hypophagic effect induced by l-arginine (800 nmol) in neonatal chicks (P 0.05). Furthermore, co-administration of sub-effective doses of glutamate with l-arginine made significant hypophagic effect in comparison with control group and any of treatment group, which received sole glutamate or only l-arginine (P < 0.05). As a conclusion, it seems central glutamatergic system is modulating hypophagic effect induced by nitrergic system through NMDA receptor in neonatal layer chicks. Apparently, l-arginine and glutamate neurotransmitters showed synergistic effect on regulating food intake in layers.

Spontaneously hypertensive rats exhibit higher sensitivity to ethanol-induced hypotensive effects: Role of NMDA receptors and nitric oxide in rostral ventrolateral medulla.

Intake of ethanol (alcohol) affects cardiovascular function. Acute ethanol intake has been shown to lower blood pressure (BP) in hypertensive patients. The present study was undertaken to examine the effects and mechanisms of acute administration of ethanol on BP in hypertensive and normotensive rats. Ethanol was given by intraperitoneal (i.p.) injection in male spontaneously hypertensive rats (SHRs) and the normotensive Wistar-Kyoto rats (WKYs). BP responses were measured in free-moving conscious rats or in urethane-anesthetized rats. Inhibitors were applied by bilateral microinjection into the rostral ventrolateral medulla (RVLM). Nitric oxide (NO•) levels and glutamate levels were determined by nitrate and nitrite (NOx) analyzer and HPLC-ECD, respectively. Intraperitoneal (i.p.) injection of ethanol (1.6g/kg) caused a significant decrease in BP in free-moving or in anesthetized SHRs but not in WKYs. A higher dose (3.2g/kg) of ethanol decreased BP in both SHRs and WKYs, although the depressor responses in SHRs occurred significantly earlier than those in WKYs. The blood ethanol concentrations 60min after injection were similar in SHRs and WKYs. Bilateral microinjection of nitric oxide synthase (NOS) inhibitors or glutamatergic NMDA receptor antagonists into the RVLM 5min after administration of ethanol significantly inhibited the ethanol-induced depressor effects in SHRs. The levels of NOx and glutamate release in the RVLM following ethanol administration and the NOx content in the RVLM areas 30min after administration were significantly increased in SHRs, but not in WKYs. Our results showed that SHRs were more sensitive to ethanol-induced hypotensive effects than WKYs because of augmentation of ethanol-induced expression of the glutamatergic NMDA receptor/NO• signal in the RVLM of SHRs.

Systematic investigation of the response reliability of optogenetically enforced activity patterns in developing cortical networks in vitro as a prerequisite for studying the effects of modified electrical activity patterns on cell death in developing cortical networks

Systematic investigation of the response reliability of optogenetically enforced activity patterns in developing cortical networks in vitro as a prerequisite for studying the effects of modified electrical activity patterns on cell death in developing cortical networks

Both Ketamine and NBQX Attenuate Alcohol-Withdrawal Induced Depression in Male Rats.

The co-morbidity between heavy drinking and depression can negatively influence successful cessation of alcohol use. Since ketamine, a glutamatergic NMDA receptor antagonist, has shown promise as a quick-acting antidepressant, we studied its effects specifically on alcohol withdrawal-induced depression. We also evaluated the effects of NBQX an AMPA/kainate receptor antagonist, because some of the effects of ketamine are proposed to be indirectly mediated through these receptors. Adult male Wistar rats were exposed daily to ethanol via inhalation chambers 4 h/day for 7 days (blood alcohol concentration=160 mg%), followed by daily intraperitoneal injections of ketamine (2.5 mg/kg), NBQX (5mg/kg), alone or in combination. Eighteen hours later, open field locomotor activity (OFLA) followed by forced swim test (FST) were performed. The animals were sacrificed 2 h later for evaluation of brain-derived neurotrophic factor (BDNF) in the hippocampus. Alcohol withdrawal did not affect OFLA, but caused an increase in immobility in FST, suggesting induction of “depressive-like” helplessness. Both ketamine and NBQX normalized the swimming score in FST. The combination of the two drugs, however, cancelled each other’s effect. Parallel to these behavioral observations, both ketamine and NBQX normalized the reduction in hippocampal BDNF caused by alcohol withdrawal. Here also, the combination of the two drugs cancelled each other’s effect. These results suggest that either NMDA or AMPA/kainate receptor antagonists, acting at least partially through hippocampal BDNF, may be of therapeutic potential in alcohol use disorder.

A Microfluidic Platform for the Characterisation of CNS Active Compounds

New in vitro technologies that assess neuronal excitability and the derived synaptic activity within a controlled microenvironment would be beneficial for the characterisation of compounds proposed to affect central nervous system (CNS) function. Here, a microfluidic system with computer controlled compound perfusion is presented that offers a novel methodology for the pharmacological profiling of CNS acting compounds based on calcium imaging readouts. Using this system, multiple applications of the excitatory amino acid glutamate (10 nM–1 mM) elicited reproducible and reversible transient increases in intracellular calcium, allowing the generation of a concentration response curve. In addition, the system allows pharmacological investigations to be performed as evidenced by application of glutamatergic receptor antagonists, reversibly inhibiting glutamate-induced increases in intracellular calcium. Importantly, repeated glutamate applications elicited significant increases in the synaptically driven activation of the adjacent, environmentally isolated neuronal network. Therefore, the proposed new methodology will enable neuropharmacological analysis of CNS active compounds whilst simultaneously determining their effect on synaptic connectivity.

Memantine, an NMDA Receptor Antagonist, Prevents Thyroxin-induced Hypertension, but Not Cardiac Remodeling.

Stimulation of glutamatergic tone has been causally linked to myocardial pathogenesis and amplified systemic blood pressure (BP). Memantine, a noncompetitive N-methyl-D-aspartate glutamatergic receptor (NMDA-R) antagonist, has been proposed to be an active cardioprotective drug. However, the efficacy of memantine and subsequently the possible involvement of the NMDA-R in the thyroxin (T4)-induced cardiovascular complications have never been investigated. We examined the effect of memantine (30 mg·kg·d) on the T4 (500 μg·kg·d)-provoked increase in mouse BP, cardiac hypertrophy indicated by enlarged overall myocardial mass, and reformed reactions of the contractile myocardium both in vivo and ex vivo after 2 weeks of treatment. Memantine alone did not result in any cardiovascular pathology in mice. Instead, memantine significantly prevented the T4-triggered systemic hypertension. But, it did not reverse cardiac hypertrophy, coupled in vivo left ventricular dysfunction (LV) or ex vivo right ventricular (RV) papillary muscle contractile alterations of the T4-treated mice. Our results openly direct the cardiovascular safety and tolerability of memantine therapy. Yet, extra research is necessary to endorse these prospective advantageous outcomes. Also, we believe that this is the first study to inspect the possible role of NMDA-R in the T4-stimulated cardiovascular disorders and concluded that NMDA-R could play a key role in the T4-induced hypertension.

Carbachol-induced network oscillations in an in vitro limbic system brain slice

We employed simultaneous field potential recordings from CA3, subiculum and entorhinal cortex in an in vitro brain slice preparation to understand the involvement of these limbic areas in the generation of the field potential oscillations that are induced by bath application of the muscarinic receptor agonist carbachol. Regularly spaced oscillations that mainly presented at theta frequency range (5–12Hz) occurred synchronously in all three structures in the presence of carbachol. These oscillations, which disappeared when slices were perfused with pirenzepine or with glutamatergic receptor antagonists, were categorized as short (<4s) and long (>4s) with short events oscillating at higher frequencies than long events. Field oscillations were highly synchronized between regions and latency analysis revealed that they often initiated in the entorhinal cortex later than in the other two structures. Blocking GABAA receptors modified the activity patterns of both short and long oscillations and decreased their coherence in the theta frequency range. Finally, blocking KCC2 activity disclosed a pattern of recurrent short oscillations. Our results suggest that in the presence of carbachol both subiculum and CA3 most often drive theta generators in the entorhinal cortex and that these oscillations are influenced but not abolished by altering GABAA receptor signaling.

Assessments in Primary Parkinson Syndrome for comparison between Monodopaminergic and Multi-target Anti-parkinsonian Pharmacotherapies

In this review, the altered functions of neurotransmitters and neuropeptides in the extrapyramidal system in primary Parkinson syndrome are pointed out. In this syndrome, an altered neurotransmitter balance in the nuclei of the extrapyramidal system with hypoactivity of the dopaminergic and GABAergic neurotransmitter systems and hypoactivity of the muscarinic cholinergic and glutamatergic neurotransmitter systems occurs. Serotonin counteracts dopamine deficiency in the putamen via 5-HT2A receptors. Neuropeptides have a modulating function and influence the mentioned neurotransmitter systems. Neurotensin antagonists, at NTS1 receptors, and antagonists, at the mu opioid receptor, could have a therapeutic function in the anti-Parkinsonian pharmacotherapy. A scheme including the possible neural combinations in the neuronal system and considering the mentioned alterations of the neuroactive substances is described. A scientific problem to be investigated is, whether a multi-target pharmacological treatment, i.e. add-on drugs such as agonists of the s2 nicotinic cholinergic receptor, A2A adenosine antagonists, 5 metabotropic glutamatergic receptor antagonists and/or NTS1 receptor antagonists could exert a neuroprotective effect on dopaminergic neurons and may be slow down the progression of the disease. In clinical studies with Parkinsonian patients, a main goal must be to compare a cohort of Parkinsonian patients receiving a mono-dopaminergic pharmacotherapy with patients receiving multi-target anti-Parkinsonian pharmacotherapy. The motor and cognitive functions could be assessed by assessment tools, and imaging examination techniques should be applied in order to assess the generally progressive course of the illness.

Behavioural Assessment of the A2a/NR2B Combination in the Unilateral 6-OHDA-Lesioned Rat Model: A New Method to Examine the Therapeutic Potential of Non-Dopaminergic Drugs.

In Parkinson’s disease (PD), dopaminergic therapies are often associated with the development of motor complications. Attention has therefore been focused on the use of non-dopaminergic drugs. This study developed a new behavioural method capable of demonstrating the added value of combining adenosinergic and glutamatergic receptor antagonists in unilateral 6-OHDA lesioned rats. Rats were dosed orally with Tozadenant, a selective A2A receptor antagonist, and three different doses of Radiprodil, an NR2B-selective NMDA receptor antagonist. The drugs were given alone or in combination and rats were placed in an open-field for behavioural monitoring. Video recordings were automatically analysed. Five different behaviours were scored: distance traveled, ipsi- and contraversive turns, body position, and space occupancy. The results show that A2A or NR2B receptor antagonists given alone or in combination did not produce enhanced turning as observed with an active dose of L-Dopa/benserazide. Instead the treated rats maintained a straight body position, were able to shift from one direction to the other and occupied a significantly larger space in the arena. The highest “Tozadenant/Radiprodil” dose combination significantly increased all five behavioural parameters recorded compared to rats treated with vehicle or the same doses of the drugs alone. Our data suggest that the A2A/NR2B antagonist combination may be able to stimulate motor activity to a similar level as that achieved by L-Dopa but in the absence of the side-effects that are associated with dopaminergic hyperstimulation. If these results translate into the clinic, this combination could represent an alternative symptomatic treatment option for PD.

A novel mechanism for the anticonvulsant effect of furosemide in rat hippocampus in vitro

Though both in vivo and in vitro studies have demonstrated an anticonvulsant effect of the loop diuretic furosemide, the precise mechanism behind this effect is still debated. The current study investigates the effect of furosemide on Cs-induced epileptiform activity (Cs-FP) evoked in area CA1 of rat hippocampal slices in the presence of Cs+ (5mM) and ionotropic glutamatergic and GABAergic receptor antagonists. As this model diverges in several respects from other epilepsy models it can offer new insight into the mechanism behind the anticonvulsive effect of furosemide. The present study shows that furosemide suppresses the Cs-FP in a dose-dependent manner with a near complete block at concentrations≥1.25mM. Because furosemide targets several types of ion transporters we examined the effect of more selective antagonists. Bumetanide (20μM), which selectively inhibits the Na–K–2Cl co-transporter (NKCC1), had no significant effect on the Cs-FP. VU0240551 (10μM), a selective antagonist of the K–Cl co-transporter (KCC2), reduced the ictal-like phase by 51.73±8.5% without affecting the interictal-like phase of the Cs-FP. DIDS (50μM), a nonselective antagonist of Cl−/HCO3−-exchangers, Na+–HCO3−-cotransporters, chloride channels and KCC2, suppressed the ictal-like phase by 60.8±8.1% without affecting the interictal-like phase. At 500μM, DIDS completely suppressed the Cs-FP. Based on these results we propose that the anticonvulsant action of furosemide in the Cs+-model is exerted through blockade of the neuronal KCC2 and Na+-independent Cl−/HCO3−-exchanger (AE3) leading to stabilization of the activity-induced intracellular acidification in CA1 pyramidal neurons.

Inhibition of PDE2A, but not PDE9A, modulates presynaptic short-term plasticity measured by paired-pulse facilitation in the CA1 region of the hippocampus.

Phosphodiesterase (PDE) inhibitors are currently considered promising therapeutic targets for treatment of cognitive impairment in diseases such as Schizophrenia and Alzheimer's disease. Inhibitors of PDE2A and PDE9A have emerged as potential candidates shown to improve synaptic plasticity and memory function in animals. However, the functional relevance of their putative different localization in the neuron is not understood. Thus, this study aims at elucidating potential presynaptic effects of PDE2A inhibition in comparison to the inhibition of PDE9A. For this purpose, we used paired-pulse facilitation (PPF), a model of short-term synaptic plasticity related to presynaptic function. First, we performed a series of experiments to validate the model in acute rat hippocampal slices using several reference substances including calcium channel blockers, glutamatergic receptor antagonists, and GPCR agonists. Second, we analysed the effect of PDE2A and PDE9A inhibition and their role regulating the influence that the second messengers cAMP and cGMP exert on basal transmission. Our results show that the interplay between the adenylyl cyclase activator forskolin, the soluble guanylyl cyclase activator BAY 41-8543 and the PDE2A inhibitor PF-999 reveals a primarily presynaptic mechanism of action of PDE2A inhibition. On the contrary, inhibition of PDE9A did not alter PPF under similar conditions. In conclusion, these data provide new evidence supporting a role of PDE2A modulating short-term synaptic plasticity. Moreover, this function of PDE2A is suggested to rely on an active modulation of the cAMP hydrolysis as a response to changes in cGMP levels at the presynaptic level.

Synchronous inhibitory potentials precede seizure-like events in acute models of focal limbic seizures.

Interictal spikes in models of focal seizures and epilepsies are sustained by the synchronous activation of glutamatergic and GABAergic networks. The nature of population spikes associated with seizure initiation (pre-ictal spikes; PSs) is still undetermined. We analyzed the networks involved in the generation of both interictal and PSs in acute models of limbic cortex ictogenesis induced by pharmacological manipulations. Simultaneous extracellular and intracellular recordings from both principal cells and interneurons were performed in the medial entorhinal cortex of the in vitro isolated guinea pig brain during focal interictal and ictal discharges induced in the limbic network by intracortical and brief arterial infusions of either bicuculline methiodide (BMI) or 4-aminopyridine (4AP). Local application of BMI in the entorhinal cortex did not induce seizure-like events (SLEs), but did generate periodic interictal spikes sensitive to the glutamatergic non-NMDA receptor antagonist DNQX. Unlike local applications, arterial perfusion of either BMI or 4AP induced focal limbic SLEs. PSs just ahead of SLE were associated with hyperpolarizing potentials coupled with a complete blockade of firing in principal cells and burst discharges in putative interneurons. Interictal population spikes recorded from principal neurons between two SLEs correlated with a depolarizing potential. We demonstrate in two models of acute limbic SLE that PS events are different from interictal spikes and are sustained by synchronous activation of inhibitory networks. Our findings support a prominent role of synchronous network inhibition in the initiation of a focal seizure.

Effects of cannabinoid and glutamate receptor antagonists and their interactions on learning and memory in male rats

IntroductionDespite previous findings on the effects of cannabinoid and glutamatergic systems on learning and memory, the effects of the combined stimulation or the simultaneous inactivation of these two systems on learning and memory have not been studied. In addition, it is not clear whether the effects of the cannabinoid system on learning and memory occur through the modulation of glutamatergic synaptic transmission. Hence, in this study, we examined the effects of the simultaneous inactivation of the cannabinoid and glutamatergic systems on learning and memory using a passive avoidance (PA) test in rats. Materials and methodsOn the test day, AM251, which is a CB1 cannabinoid receptor antagonist; MK-801, which is a glutamate receptor antagonist; or both substances were injected intraperitoneally into male Wistar rats 30min before placing the animal in a shuttle box. A learning test (acquisition) was then performed, and a retrieval test was performed the following day. ResultsLearning and memory in the PA test were significantly different among the groups. The CB1 receptor antagonist improved the scores on the PA acquisition and retention tests. However, the glutamatergic receptor antagonist decreased the acquisition and retrieval scores on the PA task. The CB1 receptor antagonist partly decreased the glutamatergic receptor antagonist effects on PA learning and memory. ConclusionsThese results indicated that the acute administration of a CB1 antagonist improved cognitive performance on a PA task in normal rats and that a glutamate-related mechanism may underlie the antagonism of cannabinoid by AM251 in learning and memory.

The influence of glutamatergic receptor antagonists on biochemical and ultrastructural changes in myelin membranes of rats subjected to experimental autoimmune encephalomyelitis.

Elevated extracellular glutamate in the synaptic cleft causes overactivation of glutamate receptors and kills neurons by an excitotoxic mechanism. Recent studies have shown that glutamate can also lead to toxic injury of white matter oligodendrocytes in myelin sheaths and consequently to axon demyelination. The present study was performed using the rodent model of multiple sclerosis known as experimental autoimmune encephalomyelitis (EAE). The aim of the study was to test the effects of the glutamatergic receptor antagonists amantadine and memantine (antagonists of NMDA receptors), LY 367384 (an antagonist of mGluR1), and MPEP (an mGluR5 antagonist) on the development of neurological symptoms in immunized animals, morphological changes in cerebral myelin, and expression of mRNA of the principal myelin proteins PLP, MBP, MOG, MAG, and CNPase. Pharmacological inhibition of NMDA receptors by amantadine and memantine was found to suppress neurological symptoms in EAE rats, whereas antagonists of the group I metabotropic glutamate receptors (mGluRs G I) did not function positively. In the symptomatic phase of the disease we observed destruction of myelin sheaths via electron microscopy and decreased levels of mRNA for all of the principal myelin proteins. The results reveal that glutamate receptor antagonists have a positive effect on the expression of mRNA MBP and glycoproteins MAG and MOG but not on myelin ultrastructure.

Modulation of glutamate transport and receptor binding by glutamate receptor antagonists in EAE rat brain.

The etiology of multiple sclerosis (MS) is currently unknown. However, one potential mechanism involved in the disease may be excitotoxicity. The elevation of glutamate in cerebrospinal fluid, as well as changes in the expression of glutamate receptors (iGluRs and mGluRs) and excitatory amino acid transporters (EAATs), have been observed in the brains of MS patients and animals subjected to experimental autoimmune encephalomyelitis (EAE), which is the predominant animal model used to investigate the pathophysiology of MS. In the present paper, the effects of glutamatergic receptor antagonists, including amantadine, memantine, LY 367583, and MPEP, on glutamate transport, the expression of mRNA of glutamate transporters (EAATs), the kinetic parameters of ligand binding to N-methyl-D-aspartate (NMDA) receptors, and the morphology of nerve endings in EAE rat brains were investigated. The extracellular level of glutamate in the brain is primarily regulated by astrocytic glutamate transporter 1 (GLT-1) and glutamate-aspartate transporter (GLAST). Excess glutamate is taken up from the synaptic space and metabolized by astrocytes. Thus, the extracellular level of glutamate decreases, which protects neurons from excitotoxicity. Our investigations showed changes in the expression of EAAT mRNA, glutamate transport (uptake and release) by synaptosomal and glial plasmalemmal vesicle fractions, and ligand binding to NMDA receptors; these effects were partially reversed after the treatment of EAE rats with the NMDA antagonists amantadine and memantine. The antagonists of group I metabotropic glutamate receptors (mGluRs), including LY 367385 and MPEP, did not exert any effect on the examined parameters. These results suggest that disturbances in these mechanisms may play a role in the processes associated with glutamate excitotoxicity and the progressive brain damage in EAE.

An organotypic brain slice preparation from adult patients with temporal lobe epilepsy.

A long-term in vitro preparation of diseased brain tissue would facilitate work on human pathologies. Organotypic tissue cultures retain an appropriate neuronal form, spatial arrangement, connectivity and electrical activity over several weeks. However, they are typically prepared with tissue from immature animals. In work using tissue from adult animals or humans, survival times longer than a few days have not been reported and it is not clear that pathological neuronal activities are retained. We modified tissue preparation procedures and used a defined culture medium to make organotypic cultures of temporal lobe tissue obtained after operations on adult patients with pharmaco-resistant mesial temporal lobe epilepsies. Organototypic culture preparation and maintenance techniques were judged on criteria of morphology and the generation of epileptiform activities. Short-duration (30-100 ms) interictal-like population activities were initiated spontaneously in either the subiculum, dentate gyrus or the CA2/CA3 region, but not the cortex, for up to 3-4 weeks in culture. Ictal-like discharges, of duration greater than 10s, were induced by convulsants. Epileptiform activities were modulated by both glutamatergic and GABAergic receptor antagonists. Our methods now permit the maintenance in organotypic culture of epileptic adult human tissue, generating appropriate epileptiform activity over 3-4 weeks. We have shown that characteristic morphology and pathological activities are maintained in organotypic cultures of adult human tissue. These cultures should permit studies on the effects of prolonged drug treatments and long-term procedures such as viral transduction.