Non-competitive Antagonist Research Articles

Non-competitive AMPA glutamate receptors antagonism by perampanel as a strategy to counteract hippocampal hyper-excitability and cognitive deficits in cerebral amyloidosis

Pathological accumulation of Aβ oligomers has been linked to neuronal networks hyperexcitability, potentially underpinned by glutamatergic AMPA receptors (AMPARs) dysfunction. We aimed to investigate whether the non-competitive block of AMPARs was able to counteract the alteration of hippocampal epileptic threshold, and of synaptic plasticity linked to Aβ oligomers accumulation, being this glutamate receptor a valuable specific therapeutic target. In this work, we showed that the non-competitive AMPARs antagonist perampanel (PER) which, per se, did not affect physiological synaptic transmission, was able to counteract Aβ-induced hyperexcitability. Moreover, AMPAR antagonism was able to counteract Aβ-induced hippocampal LTP impairment and hippocampal-based cognitive deficits in Aβ oligomers-injected mice, while retaining antiseizure efficacy. Beside this, AMPAR antagonism was also able to reduce the increased expression of proinflammatory cytokines in this mice model, also suggesting the presence of an anti-inflammatory activity. Thus, targeting AMPARs might be a valuable strategy to reduce both hippocampal networks hyperexcitability and synaptic plasticity deficits induced by Aβ oligomers accumulation.

RBIO-08. MEMANTINE INCREASES DENDRITIC ARBORIZATION OF IMMATURE NEURONS AFTER IRRADIATION WITH NO EVIDENCE OF DISRUPTION IN THE NORMAL BRAIN FUNCTION

Abstract Cranial irradiation (IR) is a cornerstone in the treatment of high-grade pediatric brain tumors. While lifesaving, it is associated with severe sequalae in 50-90 % of the survivors, as they often show disabling cognitive dysfunction, declined IQ, impaired processing speed, anxiety and posttraumatic stress symptoms, resulting in poorer academic accomplishments and social isolation. Memantine (Mem) is a non-competitive NMDA receptor antagonist and a potent enhancer of neural plasticity. While an improvement in cognition in post-IR cancer survivors and in synaptic plasticity in association to hippocampal neurogenesis have been documented, the exact mechanisms underlying Mem’s actions are poorly understood. The goal of this project is to further dissect the actions of Mem and identify factors that contribute to hippocampal neurogenesis. To this end, 20-day-old C57BL6/J mice were subjected to a single dose of 7 Gy whole brain irradiation and then supplied with Mem in the drinking water (10 mg/kg/day) to obtain a steady-state plasma concentration of the drug. Two weeks after IR, Sholl analysis of the morphology of the newborn neurons of Mem treated animals showed a statistically significant increase in coverage area (500 µm2 vs. 250 µm2, p < 0,0001) and number of dendrites (15 vs. 5, p < 0,0001) compared to non-treated individuals. Bulk-RNA sequencing analysis revealed 9 differentially expressed genes (alpha=0.1) between the hippocampal cell populations of Mem and vehicle-treated IR mice, which are related to protein folding and the programmed cell death machinery. At six weeks after IR, Mem treatment maintains the gamma oscillatory dynamics in the hippocampal CA3 region (~2x10-9 V2 in non-IR, ~1x109 V2 in IR), but with no apparent recovery to the sham levels. These results emphasize the strong neurogenic effect that Mem exerts on the surviving newborn neurons, while also highlighting Mem’s low toxicity and impact on the normal function of the brain.

The psychotomimetic ketamine disrupts the transfer of late sensory information in the corticothalamic network.

In prodromal and early schizophrenia, disorders of attention and perception are associated with structural and chemical brain abnormalities and with dysfunctional corticothalamic networks exhibiting disturbed brain rhythms. The underlying mechanisms are elusive. The non-competitive NMDA receptor antagonist ketamine simulates the symptoms of prodromal and early schizophrenia, including disturbances in ongoing and task & sensory-related broadband beta-/gamma-frequency (17-29 Hz/30-80 Hz) oscillations in corticothalamic networks. In normal healthy subjects and rodents, complex integration processes, like sensory perception, induce transient, large-scale synchronised beta/gamma oscillations in a time window of a few hundred ms (200-700 ms) after the presentation of the object of attention (e.g., sensory stimulation). Our goal was to use an electrophysiological multisite network approach to investigate, in lightly anesthetised rats, the effects of a single psychotomimetic dose (2.5mg/kg, subcutaneous) of ketamine on sensory stimulus-induced oscillations. Ketamine transiently increased the power of baseline beta/gamma oscillations and decreased sensory-induced beta/gamma oscillations. In addition, it disrupted information transferability in both the somatosensory thalamus and the related cortex and decreased the sensory-induced thalamocortical connectivity in the broadband gamma range. The present findings support the hypothesis that NMDA receptor antagonism disrupts the transfer of perceptual information in the somatosensory cortico-thalamo-cortical system.

Sustained MK-801 induced deficit in a novel probabilistic reversal learning task.

Cognitive flexibility, the ability to adapt to unexpected changes, is critical for healthy environmental and social interactions, and thus to everyday functioning. In neuropsychiatric diseases, cognitive flexibility is often impaired and treatment options are lacking. Probabilistic reversal learning (PRL) is commonly used to measure cognitive flexibility in rodents and humans. In PRL tasks, subjects must sample choice options and, from probabilistic feedback, find the current best choice which then changes without warning. However, in rodents, pharmacological models of human cognitive impairment tend to disrupt only the first (or few) of several contingency reversals, making quantitative assessment of behavioral effects difficult. To address this limitation, we developed a novel rat PRL where reversals occur at relatively long intervals in time that demonstrates increased sensitivity to the non-competitive NMDA receptor antagonist MK-801. Here, we quantitively compare behavior in time-based PRL with a widely used task where reversals occur based on choice behavior. In time-based PRL, MK-801 induced sustained reversal learning deficits both in time and across reversal blocks but, at the same dose, only transient weak effects in performance-based PRL. Moreover, time-based PRL yielded better estimates of behavior and reinforcement learning model parameters, which opens meaningful pharmacological windows to efficiently test and develop novel drugs preclinically with the goal of improving cognitive impairment in human patients.

O010 / #862 FRONTOPARIETAL TDCS DECREASES PSYCHOSIS-RELEVANT OSCILLOPATHIES: A PRECLINICAL PROOF OF THERAPEUTIC CONCEPT: TRACK 2: BRAIN STIMULATION

During the prodromal phase of schizophrenia with its complex and insidious clinical picture, EEG recordings detect widespread oscillation disturbances (or oscillopathies) during the wake-sleep cycle. Neural oscillations are electro-biomarkers of the connectivity state within systems. A single systemic psychotomimetic administration of ketamine, a non-competitive NMDA glutamate receptor antagonist, transiently reproduces the oscillopathies with a clinical picture reminiscent of the psychosis prodrome.

S3556 Unique Approach to Refractory Nausea With Ketamine Infusion

Introduction: Functional refractory nausea is defined as nausea that persists for more than 4 weeks. Nausea can result from complex interactions between afferent and efferent pathways of the central nervous system and gastrointestinal tract. Management of refractory nausea, especially if it is associated with migraines, can be difficult to treat as conventional therapies such antiemetic and prokinetics are ineffective. We present a case of functional refractory nausea that was incidentally treated successfully with ketamine infusion. Case Description/Methods: A 37-year-old male with a history of pancreatic insufficiency, migraines, and chronic refractory nausea since 2016 with recurrent ED visits presented this time with headache and nausea for 7 days. He had tried multiple prophylactic medications at home including triptans and muscle relaxers without relief. For his nausea he tried ondansetron but it only provided temporary relief for 15-20 minutes. In the ED, the patient received prochlorperazine, diphenhydramine, and ketorolac for his headache and nausea. He continued to complain of his symptoms and was subsequentially given 20.4 milligram of ketamine infusion over 1 hour with resolution of his headache as expected. Surprisingly, the patient’s nausea concomitantly resolved with the ketamine infusion. After discharge, he was followed in GI clinic after one week and 3 months where he stated he was completely free of nausea without the use of his prophylactic medications. Discussion: Functional refractory nausea has been associated with decreased quality of life for patients. This presents as an economic burden in terms of health care costs and resources with recurrent admissions and ED visits. Conventional treatments for nausea include the use of antiemetics and prokinetics to name a few. The use of ketamine infusion has only been reported in one other case study for abortive and prophylactic therapy for nausea. Ketamine is a noncompetitive antagonist to N-methyl-d-aspartate receptor. The mechanism by which it helps with refractory nausea is still unclear but it is believed to be related to reduction of neural transmissions by ketamine. Ketamine is a generic medication that is cost effective. Side effects of ketamine are dose dependent and include cystitis and liver toxicity, which is unlikely with the doses given for nausea treatment. This case represents incidental resolution of nausea with ketamine administration and more studies are required for its role in abortive and prophylactic therapy.

Antibiotics versus no treatment for asymptomatic bacteriuria in residents of aged care facilities: a systematic review and meta-analysis

l-Glutamate (Glu) activates at least eight different G protein-coupled receptors known as metabotropic glutamate (mGlu) receptors, which mostly act as regulators of synaptic transmission. These receptors consist of two domains: an extracellular domain in which agonists bind and a transmembrane heptahelix region involved in G protein activation. Although new mGlu receptor agonists and antagonists have been described, few are selective for a single mGlu subtype. Here, we have examined the effects of a novel compound, BAY36-7620 [(3a<i>S</i>,6a<i>S</i>)- 6a-Naphtalen-2-ylmethyl-5-methyliden-hexahydro-cyclopental[<i>c</i>]furan-1-on], on mGlu receptors (mGlu1–8), transiently expressed in human embryonic kidney 293 cells. BAY36-7620 is a potent (IC₅₀ = 0.16 μM) and selective antagonist at mGlu1 receptors and inhibits &gt;60% of mGlu1a receptor constitutive activity (IC⁵⁰ = 0.38 μM). BAY36-7620 is therefore the first described mGlu1 receptor inverse agonist. To address the mechanism of action of BAY36-7620, Glu dose-response curves were performed in the presence of increasing concentrations of BAY36-7620. The results show that BAY36-7620 largely decreases the maximal effect of Glu. Moreover, BAY36-7620 did not displace the [³H]quisqualate binding from the Glu-binding pocket, further indicating that BAY36-7620 is a noncompetitive mGlu1 antagonist. Studies of chimeric receptors containing regions of mGlu1 and regions of DmGluA, mGlu2, or mGlu5, revealed that the transmembrane region of mGlu1 is necessary for activity of BAY36-7620. Transmembrane helices 4 to 7 are shown to play a critical role in the selectivity of BAY36-7620. This specific site of action of BAY36-7620 differs from that of competitive antagonists and indicates that the transmembrane region plays a pivotal role in the agonist-independent activity of this receptor. BAY36-7620 will be useful to further delineate the functional importance of the mGlu1 receptor, including its putative agonist-independent activity.

The effects and mechanism of environmental enrichment on MK-801 induced cognitive impairment in rodents with schizophrenia.

Schizophrenia is a severe mental disorder characterized by positive, negative, and cognitive symptoms. Cognitive symptoms are a kind of symptoms with high incidence and great impact on patients. There is no effective treatment in clinical practice. N-methyl-d-aspartic acid (NMDA) receptor hypofunction may be an important cause of cognitive symptoms. MK-801 (also named Dizocilpine), a noncompetitive antagonist of NMDA receptor, is often used to construct a model of NMDA receptor dysfunction. In terms of treatment, environmental enrichment (EE) as an environmental intervention can effectively improve the symptoms of cognitive impairment in rodents. In this paper, we first briefly introduce the background of cognitive symptoms and EE in schizophrenia, and then investigate the manifestations of MK-801 induced cognitive impairment, the improvement of EE on these cognitive impairments based on the MK-801 induced schizophrenia rodent models, and the possible mechanism of EE in improving cognitive symptoms. This article reviews the literature in recent years, which provides an important reference for MK-801 to construct a cognitive symptom model of schizophrenia and the mechanism of EE in improving cognitive symptoms of schizophrenia.

Memantine associated with ventricular-subcutaneous shunt promotes behavioral improvement, reduces reactive astrogliosis and cell death in juvenile hydrocephalic rats

Hydrocephalus is defined as the accumulation of cerebrospinal fluid in the brain ventricles. The usual treatment of hydrocephalus is surgical (shunt), but not all patients can undergo treatment immediately after diagnosis. Thus, neuroprotective measures were tested to minimize the tissue damage involved. Memantine is a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, which has shown a neuroprotective action in neurodegenerative diseases. This study aimed to evaluate the neuroprotective response of memantine in animals treated with or without a ventricular-subcutaneous shunt. Seven-day-old male Wistar rats induced by intracisternal injection of kaolin were used, divided into five groups: intact control (n = 10), hydrocephalic (n = 10), hydrocephalic treated with memantine (20 mg/kg/day) (n = 10), hydrocephalic treated with shunt (n = 10), hydrocephalic treated with shunt and memantine (20 mg/kg/day) (n = 10). Memantine administration was started on the day after hydrocephalus induction and continued until the last day of the experimental period, totaling 21 consecutive days of drug application. The CSF shunt surgery was performed seven days after hydrocephalus induction. Behavioral tests (open field, and modified Morris water maze), histological, and immunohistochemical evaluations were performed. Treatment with memantine resulted in significant improvement (p < 0.05) in sensorimotor development, preservation of spatial memory, reduction of astrocytic reaction in the corpus callosum, cortex, and germinal matrix. When associated with the shunt, it has also been shown to reduce the cell death cascade. It is concluded that memantine is a promising adjuvant drug with beneficial potential for the treatment of lesions secondary to hydrocephalus.

Comprehensive metabolomic characterization of the hippocampus in a ketamine mouse model of schizophrenia

Ketamine is a noncompetitive antagonist of N-methyl-D-aspartate receptors (NMDARs). We have shown that ketamine can induce cognitive impairments and schizophrenia-like symptoms in mice. However, the detailed metabolic profile changes in the progression of ketamine-induced schizophrenia-like symptoms are still not fully elucidated. In this study, an ultra-performance liquid chromatography-Q-Exactive hybrid quadrupole-Orbitrap mass spectrometry-based untargeted hippocampus high-throughput metabolomics method was first performed to screen for potential biomarkers in a schizophrenia-like state in a chronically administered ketamine-induced mouse model. Our results identified that the amino acid and energy metabolism pathways were significantly affected in mouse models of ketamine-induced schizophrenia. The detailed amino acid profiles were subsequently quantified in the hippocampus. The results showed that ketamine dramatically decreased the Lys, Gly, and Ser levels while significantly increasing the Gln level and relative Glu-to-GABA ratio. Our study suggested that Gln, Gly and Ser metabolism disturbances might be involved in ketamine-induced schizophrenia-like phenotypes. This research offers a fresh viewpoint for creating new neuroleptic medications and contributes to understanding the mechanisms underlying ketamine-induced schizophrenia.

The rat takes the cheese: a novel model of CFTR-dependent chronic bacterial airway infection

Pharmacological mechanisms involved in nicotine-induced seizures were investigated in mice by testing the ability of several nicotinic agonists in producing seizures after peripheral administration. In addition, nicotinic antagonists such as hexamethonium, mecamylamine, dihydro-β-erythroidine, and methyllycaconitine citrate (MLA) were used in combination with nicotine. We also examined the involvement of calcium channels, <i>N</i>-methyl-d-aspartate receptors, and nitric oxide formation in nicotine-induced seizures. Our results showed that the peripheral administration of nicotine produced seizures in a stereospecific and mecamylamine-sensitive manner. Nicotine-induced seizures are centrally mediated and involve the activation of α7 along with other nicotinic receptor subunits. Indeed, MLA, an α7-antagonist, blocked the effects of nicotine after peripheral and central administration. The extent of α4β2-receptor subtype involvement in nicotine-induced seizures was difficult to assess. On one hand, we observed that dihydro-β-erythroidine (a competitive antagonist) failed to block the effects of nicotine. In addition, a poor correlation was found between binding affinity for³H-nicotine-labeled sites (predominantly α4β2) and seizures potency for several nicotinic agonists. On the other hand, mecamylamine, a noncompetitive antagonist, blocked nicotine-induced seizures more potently than MLA. Furthermore, its potency in blocking seizures was in the same general dose range of other nicotinic effects that are not α7 mediated. These results suggest that this receptor subtype does not play a major role in nicotine-induced seizures. Our findings also suggest that nicotine enhances the release of glutamate either directly or indirectly (membrane depolarization that opens L-type calcium channels). Glutamate release in turn stimulates<i>N</i>-methyl-d-aspartate receptors, thus triggering the cascade of events leading to nitric oxide formation and possibly seizure production.

Thermal grill illusion of pain in patients with chronic pain: a clinical marker of central sensitization?

The thermal grill illusion of pain (TGIP) is a paradoxical burning pain sensation elicited by the simultaneous application of innocuous cutaneous warm and cold stimuli with a thermode ("thermal grill") consisting of interlaced heated and cooled bars. Its neurophysiological mechanisms are unclear, but TGIP may have some mechanisms in common with pathological pain, including central sensitization in particular, through the involvement of N-methyl- d -aspartate receptors. However, few studies have investigated TGIP in patients with chronic pain and its clinical relevance is uncertain. We hypothesized that the TGIP would be increased in comparison with controls in patients with fibromyalgia or irritable bowel syndrome, which are regarded as typical "nociplastic" primary pain syndromes related to changes in central pain processing. We compared the sensations elicited by a large range of combinations of temperature differentials between the warm and cold bars of a thermal grill applied to the hand between patients with fibromyalgia (n = 30) or irritable bowel syndrome (n= 30) and controls (n = 30). The percentage of TGIP responses and the intensity and unpleasantness of TGIP were significantly greater in patients than controls. Furthermore, positive correlations were found between TGIP intensity and clinical pain intensity and between TGIP intensity and the cold pain threshold measured on the hand. These results are consistent with our working hypothesis of shared mechanisms between TGIP and clinical pain mechanisms in patients with nociplastic chronic pain syndromes and suggest that TGIP might represent a clinical marker of central sensitization in these patients.

Analytical strategy to document horse fatalities related to Oenanthe crocata poisoning

To report the analytical procedure that was developed and applied to identify oenanthotoxin (OT) and its metabolite 2,3-dihydro-oenanthotoxin (2,3DHOT) in biological and vegetal samples using both LC-DAD and LC-HRMS methods in two cases of equine fatal intoxication by Oenanthe crocata. : (case#1) a 7-year-old Arabian horse was found dead within one hour after the ingestion of «wild carrots», and was autopsied the following day. The gross and microscopic examination was unremarkable, except the presence of several root pieces in the animal's stomach. Sections of the same roots found on the site showed hexagonal subdivisions and a yellowish latex. These findings were consistent with Hemlock water-dropwort (Oenanthe crocata) and confirmed by an experienced botanist. (case#2) an 8-year-old pony was unexpectedly found dead and autopsied two days later. The body conservation was poor; the only significant finding was the presence of several root pieces of undetermined origin in the stomach. Autopsy samples (root pieces found in the stomach, stomach content, liver, kidney, and spleen of case#1; stomach content of case#2) were stored at -20 °C before analysis, while the on-site roots (case#1) were stored at room temperature. After grinding organ samples, 1 to 10 g were extracted using methanol (5 mL), vortex mixed for 30 seconds, and kept at 4 °C for 2 hours. These methanolic suspensions were centrifuged firstly at 2500 g for 10 min, then the supernatant was secondly centrifugated at 8000 g for 14 min. In order to enhance detection sensitivity, one mL of each supernatant from the liver, kidney, and spleen samples was dried under nitrogen and then each extract was resuspended with 100 μL of methanol. Extracts were analysed using two analytical methods (LC-DAD and LC-HRMS) both using the same ACQUITY HSS C18 column (150 × 2 mm, 20 μm) for chromatographic separation. The acquired data were analysed using Empower 3 (LC-DAD) and Unify and Progenesis QI softwares (LC-HRMS) for investigation of specific fragmentation spectra of identified substances. Thanks to combined analytical data (i.e. characteristic UV spectra [Kite. J Chrom B. 2006;838:63-70.] together with specific fragmentation HRMS spectra), oenanthotoxin (OT) and its hydrogenated metabolite, 2,3-dihydro-oenanthotoxin (2,3DHOT*), were identified (case#1) in roots found on the siteand in the stomach content, in the stomach content, kidney, and liver (*also in spleen), and (case#2) in the stomach content. In France, three species of the Apiaceae family can cause life threatening poisoning: the Hemlock (Cicuta virosa), the big Hemlock (Conium maculatum) and the Hemlock water-dropwort (Oenanthe crocata). In the latter one, OT and 2,3DHOT act as non-competitive antagonists of GABA receptors. Clinical signs of poisoning in horses (non-vomiting animals) are dominated by hypersalivation, mydriasis, muscle tremors, respiratory distress, and convulsions, but sometimes sudden death is observed. In humans, the clinical signs are completed/supplemented by ataxia, bruxism, hallucinations, nausea, and vomiting seizures; they occur between 15 min and 10 hours after ingestion [Schep. Clin Tox.2009;47:270–278.]. Analytical detection of Oenanthe crocata toxins in biological samples is a challenge due to their instability (e.g. OT and 2,3DHOT stabilities in post-mortem samples is unknown), the lack of commercially available analytical standards, and the exceptionally low response of these toxins using mass spectrometry detection. Nevertheless, identification of OT and 2,3DHOT can be performed using a combination of LC-DAD and LC-HMRS (for enhanced detection in organs, e.g. liver) methods, in order to support poisoning diagnosis. In this context, we consider that the reported analytical data can be helpful to diagnose oenanthotoxin poisonings.

Memantine has a nicotinic neuroprotective pathway in acute hippocampal slices after an NMDA insult

Memantine is a non-competitive antagonist with a moderate affinity to the N-methyl-d-Aspartate (NMDA) receptor. The present study assessed memantine's neuroprotective activity using electrophysiology of ex-vivo hippocampal slices. Interestingly, a nicotinic component was necessary for memantine's neuroprotection (NP). Memantine demonstrated a bell-shaped dose-response curve of NP against NMDA. Memantine was neuroprotective at concentrations below 3 μM, but the NP declined at higher concentrations (>3 μM) when memantine inhibits the NMDA receptor. Additional evidence that memantine NP is mediated by an alternate mechanism independent of the inhibition of the NMDA receptor is supported by its ability to protect neurons when applied before or after the NMDA insult and in the presence of D(−)-2-Amino-5-phosphonopentanoic acid (APV), the standard NMDA receptor inhibitor. We found several similarities between the memantine NP mechanism and the neuroprotective nicotinic drug, the 4R cembranoid. Memantine's NP requires the release of acetylcholine, the activation of α4β2, and is independent of MEK/MAPK signaling. Both 4R and memantine require the activation of PI3K/AKT for NP against NMDA-mediated excitotoxicity, although at different concentrations. In conclusion, our studies show memantine is neuroprotective through a nicotinic pathway, similar to the nicotinic drug 4R. This information leads to a better understanding of memantine's mechanisms of action and explains its dose-dependent effectiveness in Alzheimer's and other neurological disorders.

Picrotoxin Delineates Different Transport Configurations for Malate and γ Aminobutyric Acid through TaALMT1.

Simple SummaryGamma aminobutyric acid (GABA) a non-protein amino acid is an archaic signalling molecule for cellular communication across all kingdoms of life with distinct signalling roles in animals. Emerging research establishes GABA as a signalling molecule in planta. GABA modulates numerous developmental processes and negatively regulates root growth, stomatal aperture, and anion flux under abiotic stress. A putative GABA binding site with homology to the mammalian GABA binding site has been identified in a family of proteins (Aluminium Activated Malate Transporters -ALMT) involved in mediating anion flux and conferring plant aluminium tolerance. Studies have shown that ALMTs are regulated by GABA and transport both anions and GABA. To gain further insights into the mechanism of GABA regulation, it is essential to differentiate between the two transport modes. Pharmacological agents used to characterise mammalian GABA receptors have proved useful in gaining insights into GABA regulation of plant processes. In this study, picrotoxin an inhibitor of anion flux in mammalian GABA receptors was used to investigate the pathways for anion and GABA transport in ALMTs. Results suggest that picrotoxin inhibits anion flux but not GABA flux and can be used to gain further insights into mechanism of GABA regulation of plant proteins.Plant-derived pharmacological agents have been used extensively to dissect the structure–function relationships of mammalian GABA receptors and ion channels. Picrotoxin is a non-competitive antagonist of mammalian GABAA receptors. Here, we report that picrotoxin inhibits the anion (malate) efflux mediated by wheat (Triticum aestivum) ALMT1 but has no effect on GABA transport. The EC50 for inhibition was 0.14 nM and 0.18 nM when the ALMTs were expressed in tobacco BY2 cells and in Xenopus oocytes, respectively. Patch clamping of the oocyte plasma membrane expressing wheat ALMT1 showed that picrotoxin inhibited malate currents from both sides of the membrane. These results demonstrate that picrotoxin inhibits anion efflux effectively and can be used as a new inhibitor to study the ion fluxes mediated by ALMT proteins that allow either GABA or anion transport.

Memantine ameliorates the impairment of social behaviors induced by a single social defeat stress as juveniles

Clinically, juveniles are more sensitive to stress than adults, and exposure to stress as juveniles prolongs psychiatric symptoms and causes treatment resistance. However, the efficacy of antidepressants for juveniles with psychiatric disorders is unknown. In the present study, we investigated whether the expression or development of impaired social behavior was attenuated by memantine, a non-competitive NMDA receptor antagonist. In addition, we clarified the molecular mechanisms related to intracellular signal transduction through NMDA receptors and the ameliorating effect of memantine in mice with impaired social behavior. Acute administration of memantine before the social interaction test, but not before exposure to social defeat stress, attenuated social behavioral impairment. A single social defeat stress increased the phosphorylation of NMDA receptor subunit GluN2A and extracellular-signal-related kinase 1/2 (ERK1/2). Memantine inhibited the increase of phosphorylated GluN2A and ERK1/2 resulting from social interaction behavior. In both GluN2A deficient and pharmacological blockaded mice, social behavioral impairment was not observed in the social interaction test through regulation of ERK1/2 phosphorylation. These findings suggest that memantine ameliorates social behavioral impairment in mice exposed to a single social defeat stress as juveniles by regulating the NMDA receptor and subsequent ERK1/2 signaling activation. Memantine may constitute a novel therapeutic drug for stress-related psychiatric disorders in juveniles with adverse juvenile experiences.

Astrocyte Activation, but not Microglia, Is Associated with the Experimental Mouse Model of Schizophrenia Induced by Chronic Ketamine.

Ketamine is a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors. Many experimental studies have shown that ketamine can induce cognitive impairments and schizophrenia-like symptoms. While much data have demonstrated that glial cells are associated with the pathophysiology of psychiatric disorders, including schizophrenia, the response of glial cells to ketamine and its significance to schizophrenia are not clear. The present study was intended to explore whether chronic ketamine treatment would induce behavioral and glial changes in mice. First, ketamine was used to stimulate behavioral abnormalities similar to schizophrenia evaluated by the open field test, elevated plus-maze test, Y maze test, novel object recognition test, and tail suspension test. Secondly, histopathology and Nissl staining were performed. Meanwhile, immunofluorescence was used to evaluate the expression levels of IBA-1 (a microglial marker) and GFAP (an astrocyte marker) in the mouse hippocampus for any change. Then, ELISA was used to analyze proinflammatory cytokine levels for any change. Our results showed that ketamine (25mg/kg, i.p., qid, 12days) induced anxiety, recognition deficits, and neuronal injury in the hippocampus. Moreover, chronic ketamine treatment enhanced GFAP expression in CA1 and DG regions of the hippocampus but did not influence the expression of IBA-1. Ketamine also increased the levels of IL-1β, IL-6, and TNF-α in the mouse hippocampus. Our study created a new procedure for ketamine administration, which successfully induce negative symptoms and cognitive-behavioral defects in schizophrenia by chronic ketamine. This study furtherrevealed that an increase in astrocytosis, but not microglia, is associated with the mouse model of schizophrenia caused by ketamine. In summary, hippocampal astrocytes may be involved in the pathophysiology of ketamine-induced schizophrenia-like phenotypes through reactive transformation and regulation of neuroinflammation.

Sustained vascular contractile response induced by an R- and S-epimer of the ergot alkaloid ergocristine and attenuation by a noncompetitive antagonist.

Vasoconstriction is a known effect associated with ergot alkaloid consumption. The vascular contractile responses are often sustained for an extended period after exposure. Ergot alkaloids exist in two molecular configurations, the C-8-(R)-isomer (R-epimer) and the C-8-(S)-isomer (S-epimer). The sustained vascular contractile response to the R-epimers has been studied previously, unlike the S-epimers which are thought to be biologically inactive. Additionally, antagonists have been utilized to attenuate the vascular contraction associated with the R-epimers of ergot alkaloids utilizing ex vivo techniques. This study utilized an arterial tissue bath to examine and compare the sustained vascular contractile response attributed to ergocristine (R) and ergocristinine (S) using dissected bovine metatarsal arteries. The contractile blocking effect of a noncompetitive alpha-adrenergic antagonist, phenoxybenzamine (POB), was also investigated in precontracted arteries. Arteries (n = 6/epimer) were exposed to a single dose of ergocristine or ergocristinine (1 × 10−6 M in buffer). Each of the epimer doses was followed by a POB (1 × 10−3 M) or methanol (control) treatment at 90 min and the response was observed for another 90 min. Both epimers produced a sustained contractile response over the 180-min incubation period in the control groups. The R-epimer caused a greater sustained contractile response from 60 to 180 min post epimer exposure, compared to the S-epimer (P < 0.05, generalized estimating equations, independent t-test). Phenoxybenzamine caused a decrease in the contractile response induced by ergocristine and ergocristinine from 105 to 180 min, compared to the control (P < 0.05, generalized estimating equations, paired t-test). Overall, these results demonstrate the presence of a sustained vascular contractile response attributed to the R- and S-epimer of an ergot alkaloid with differences in contractile response between the epimers, suggesting differences in receptor binding mechanisms. Furthermore, this study demonstrated that a noncompetitive antagonist could attenuate the sustained arterial contractile effects of both ergot configurations ex vivo. Additional investigation into S-epimers of ergot alkaloids is needed. This research contributes to the understanding of the ergot epimer-vascular receptor binding mechanisms, which may support the investigation of different approaches of minimizing ergot toxicity in livestock.

The Notable Articles Project

Studies are presented of the interaction of aromatic amine noncompetitive antagonists with the receptor-rich (post-synaptic) membranes isolated from <i>Torpedo marmorata</i> electric organ. When present at micromolar concentrations, methyl iodide quaternary derivatives of the potent non-competitive antagonists proadifen and dimethisoquin increase the affinity of the membrane-bound nicotinic receptor for [³H]acetylcholine and [¹⁴C]dimethyltubocurarine. The equilibrium binding of [¹⁴C]meproadifen (2-(diethylmethylamino)ethyl-2,2-diphenyl valerate) to the receptor-rich membranes is characterized by an ultracentrifugatiom assay. When all acetylcholine binding sites are occupied by the agonist carbamylcholine or the antagonist tubocurarine, [¹⁴C]meproadifen is bound with a dissociation constant <i>K_D</i> = 0.5 µM to a number of sites equal to one-quarter the number of α-neurotoxin binding sites. That high affinity binding site is found in the receptor-rich membranes and not in other membrane fractions isolated from <i>Torpedo</i> electric organ. Other non-competitive aromatic amino antagonists including dimethisoquin, proadifen, and prilocaine displace [¹⁴C]meproadifen, as does perhydrohistrionicotoxin. It is concluded that there is a specific site of binding for the aromatic amine non-competitive antagonists in the isolated nicotinic post-synaptic membrane that is distinct from the site of binding of acetylcholine. Analysis of the interaction of [¹⁴C]meproadifen with the receptor-rich membranes in the absence of cholinergic ligands indicates that under these circumstances the ligand binds weakly to both the anesthetic binding site and the acetylcholine binding site (<i>K_D</i> = 5 µM). The functional significance of the specific binding site for the aromatic amine non-competitive antagonists is discussed in terms of its possible relation to the site of ion translocatiom and to the mechanism of receptor desensitization.

The Promising Effect of Colchicine on Random-Pattern Skin Flap Survival in Rats: Glutamate Pathway.

Random-pattern skin flap is a conventional procedure in reconstructive surgery, yet partial or complete flap necrosis has remained a major issue. Herein, we investigated the potential effects of colchicine on skin flap survival through the glutamate pathway and N-methyl-D-aspartate (NMDA) receptors. Wistar male rats were injected multiple doses of colchicine intraperitoneally (0.02, 0.05, 0.1, and 0.4mg/kg) before the surgery. MK-801 (a noncompetitive NMDA receptor antagonist) was administered in combination with colchicine to assess the role of glutamate. Histopathological evaluation; quantitative assessment of glutamate, IL-6, and TNF-α; and the expression of NR2A-type NMDA receptors were performed in the skin tissue. Colchicine 0.05mg/kg could significantly promote flap survival compared to the control group (P<0.001), while administration of MK-801 (0.05mg/kg) reversed the effect of colchicine (0.05mg/kg) (P<0.001). Levels of IL-6 and TNF-α decreased, and the expression of NR2A-type NMDA receptors was enhanced in the flap tissue of colchicine 0.05mg/kg group compared to the controls. Also, glutamate level significantly increased after the administration of colchicine 0.05mg/kg compared to the controls (P<0.05). We found that colchicine could improve skin flap survival remarkably in rats that have undergone skin flap surgery through the glutamate pathway and NMDA receptors.