Cocaine facilitates protein synthesis-dependent LTP: The role of metabotropic glutamate receptors

Cocaine addiction alters synaptic plasticity in many brain areas involved in learning and memory processes, including the hippocampus. Long-term potentiation (LTP) is one of the best studied examples of hippocampal synaptic plasticity and it is considered as one of the molecular basis of learning and memory. We previously demonstrated that in the presence of cocaine, a long lasting form of hippocampal LTP is induced by a single pulse of high frequency stimulation, which in normal conditions evokes only an early form of LTP. In this study, we further explore the molecular basis of this modulation of synaptic plasticity by cocaine. By performing pharmacological experiments on hippocampal slices, we were able to show that cocaine converts early LTP to a form of LTP dependent on protein synthesis, probably through the cAMP-dependent protein kinase and extracellular signal-regulated kinase signaling cascades. We also found that metabotropic glutamate receptors are involved in this phenomenon. These studies further clarify the molecular machinery used by cocaine to alter synaptic plasticity and modulate learning and memory processes.     

Stimulation of synaptoneurosome glutamate release by monomeric and fibrillated α‐synuclein

The α‐synuclein protein exists in vivo in a variety of covalently modified and aggregated forms associated with Parkinson's disease (PD) pathology. However, the specific proteoform structures involved with neuropathological disease mechanisms are not clearly defined. Since α‐synuclein plays a role in presynaptic neurotransmitter release, an in vitro enzyme‐based assay was developed to measure glutamate release from mouse forebrain synaptoneurosomes (SNs) enriched in synaptic endings. Glutamate measurements utilizing SNs from various mouse genotypes (WT, over‐expressers, knock‐outs) suggested a concentration dependence of α‐synuclein on calcium/depolarization‐dependent presynaptic glutamate release from forebrain terminals. In vitro reconstitution experiments with recombinant human α‐synuclein proteoforms including monomers and aggregated forms (fibrils, oligomers) produced further evidence of this functional impact. Notably, brief exogenous applications of fibrillated forms of α‐synuclein enhanced SN glutamate release but monomeric forms did not, suggesting preferential membrane penetration and toxicity by the aggregated forms. However, when applied to brain tissue sections just prior to homogenization, both monomeric and fibrillated forms stimulated glutamate release. Immuno‐gold and transmission electron microscopy (TEM) detected exogenous fibrillated α‐synuclein associated with numerous SN membranous structures including synaptic terminals. Western blots and immuno‐gold TEM were consistent with SN internalization of α‐synuclein. Additional studies revealed no evidence of gross disruption of SN membrane integrity or glutamate transporter function by exogenous α‐synuclein. Overall excitotoxicity, due to enhanced glutamate release in the face of either overexpressed monomeric α‐synuclein or extrasynaptic exposure to fibrillated α‐synuclein, should be considered as a potential neuropathological pathway during the progression of PD and other synucleinopathies. © 2017 Wiley Periodicals, Inc.     

Pathological Role for Exocytotic Glutamate Release from Astrocytes in Hepatic Encephalopathy

Liver failure can lead to generalized hyperammonemia, which is thought to be the underlying cause of hepatic encephalopathy. This neuropsychiatric syndrome is accompanied by functional changes of astrocytes. These glial cells enter ammonia-induced self-amplifying cycle characterized by brain oedema, oxidative and osmotic stress that causes modification of proteins and RNA. Consequently, protein expression and function are affected, including that of glutamine synthetase and plasmalemmal glutamate transporters, leading to glutamate excitotoxicity; Ca²⁺-dependent exocytotic glutamate release from astrocytes contributes to this extracellular glutamate overload.     

ACAM2000: a newly licensed cell culture-based live vaccinia smallpox vaccine

Importance of the field: Migraine is an episodic, substantially inherited brain disorder affecting 15% of adults in Western Europe and North America, and is one of the commonest reasons for patients to see their physicians. While the World Health Organization considers that severe migraine can be as disabling as quadriplegia, unfortunately the condition remains undertreated. Until the 1990s, specific migraine therapies were limited to ergot derivatives.

Areas covered in this review: The triptans, serotonin 5-HT_1B/1D receptor agonists, revolutionized the acute management of migraine patients. However, although the triptans are generally effective and safe, not all patients can take them and many do not respond especially to oral therapies. Recently, progress has been made on the therapeutic front, particularly with new acute treatments. This review will focus on the therapeutic potential of ADX10059, a metabotropic glutamate receptor 5, negative allosteric modulator (mGluR5 NAM), in migraine. Data from a proof-of-concept study in episodic migraineurs demonstrated a significant improvement following acute treatment. A large European multicenter, randomized, double-blind, placebo-controlled, parallel-group, dose-ranging study is currently investigating the efficacy, safety and tolerability of the compound for migraine prevention.

What the reader will gain: The reader will have the basic principles of migraine management and the potential for glutamate-targeted approaches.

Take home message: Targeting glutamatergic transmission in migraine may provide a novel preventive therapy that is effective and well-tolerated.     

Antibodies to glutamate receptor subtype 3 (GluR3) are found in some patients suffering from epilepsy as the main disease,but not in patients whose epilepsy accompanies antiphospholipid syndrome or Sneddon's syndrome

Autoantibodies (Ab's) to the “B” peptide (amino acids 372–395) of glutamate/AMPA receptor subtype 3 (GluR3) are found in serum and cerebrospinal fluid of some patients with different types of epilepsy. Since such anti-GluR3B Ab's can activate and/or kill neurons in vitro and in vivo, they may contribute to epilepsy.

To investigate whether anti-GluR3B Ab's may also be relevant to epilepsy when it accompanies some autoimmune-diseases, we tested for these Ab's in patients suffering from epilepsy that accompanies anti-phospholipid syndrome (APS) or Sneddon's syndrome (SNS), both being autoimmune-diseases with frequent neurological complications. We tested 77 pediatric patients whose epilepsy is their main disease; 31 adult patients whose epilepsy accompanies APS (primary or SLE-associated) or SNS; 45 epilepsy-free APS and SNS patients; and 90 healthy controls. Compared to the controls, significantly elevated anti-GluR3B Ab's were found in 22/77 (29%) patients whose epilepsy is their main disease, but in none of the patients whose seizures accompany APS or SNS. Yet, all the APS and SNS patients harbored the characteristic anti-phospholipid Ab's (aPL), directed against cardiolipin and β2-glycoprotein I, and had lupus anti-coagulant. Thus, anti-GluR3B Ab's are not crossreactive with aPL, and not produced as a non-specific consequence of seizures on the one hand, or autoimmune-diseases on the other.

Taken together with new findings accumulated recently in our lab, we suggest that anti-GluR3B Ab's are produced primarily in the periphery due to specific/non-specific “irritation” of the immune system, and that once they reach the brain via a leaky blood–brain barrier they may cause neuronal/glial damage and facilitate the outburst of epilepsy and additional neurological abnormalities. In contrast, the presence of anti-GluR3B Ab's does not seem to increase the probability of developing APS, SNS or the seizures that often accompany these autoimmune-diseases. These findings may have important diagnostic and therapeutic implications.     

Protection in Glutamate-Induced Neurotoxicity by Imidazoline Receptor Agonist Moxonidine

In the present study we investigated the effects of mixed imidazoline-1 and α₂-adrenoceptor agonist, moxonidine, in glutamate-induced neurotoxicity in frontal cortical cell cultures of rat pups by dye exclusion test. Also, phosphorylated p38 mitogen activated protein kinases (p-p38 MAPK) levels were determined from rat frontal cortical tissue homogenates by two dimensional gel electrophoresis and semidry western blotting. Glutamate at a concentration of 10^?6 M was found neurotoxic when applied for 16 hr in cell cultures. Dead cell mean scores were 12.8 ± 0.5 for control and 52.3 ± 4.8 for glutamate (p < .001). On the other hand, p-p38 MAPK levels start to increase at a glutamate concentration of 10^?7 M for 20 min application. Moxonidine was found to have an U-shape neuroprotective effect in glutamate-induced neurotoxicity in neuronal cell culture experiments. Even though moxonidine did not induce neurotoxicity alone between the doses of 10^?8 to 10^?4 M concentrations in cell culture series, it caused the reduction of glutamate-induced dead cell population 23.07 ± 3.6% in 10^?6 M and 26.7 ± 2.1% in 10^?5 M concentrations (p <.001 for both, in respect to control values). The protective effect of moxonidine was confirmed in 10^?8 and 10^?7 M, but not in higher concentrations in glutamate neurotoxicity in gel electrophoresis and western blotting of p-p38 MAPK levels. In addition to other studies that revealed an antihypertensive feature of moxonidine, we demonstrated a possible partial neuroprotective role in lower doses for it in glutamate-mediated neurotoxicity model.     

Perineuronal nets protect fast-spiking interneurons against oxidative stress

A hallmark of schizophrenia pathophysiology is the dysfunction of cortical inhibitory GABA neurons expressing parvalbumin, which are essential for coordinating neuronal synchrony during various sensory and cognitive tasks. The high metabolic requirements of these fast-spiking cells may render them susceptible to redox dysregulation and oxidative stress. Using mice carrying a genetic redox imbalance, we demonstrate that extracellular perineuronal nets, which constitute a specialized polyanionic matrix enwrapping most of these interneurons as they mature, play a critical role in the protection against oxidative stress. These nets limit the effect of genetically impaired antioxidant systems and/or excessive reactive oxygen species produced by severe environmental insults. We observe an inverse relationship between the robustness of the perineuronal nets around parvalbumin cells and the degree of intracellular oxidative stress they display. Enzymatic degradation of the perineuronal nets renders mature parvalbumin cells and fast rhythmic neuronal synchrony more susceptible to oxidative stress. In parallel, parvalbumin cells enwrapped with mature perineuronal nets are better protected than immature parvalbumin cells surrounded by less-condensed perineuronal nets. Although the perineuronal nets act as a protective shield, they are also themselves sensitive to excess oxidative stress. The protection might therefore reflect a balance between the oxidative burden on perineuronal net degradation and the capacity of the system to maintain the nets. Abnormal perineuronal nets, as observed in the postmortem patient brain, may thus underlie the vulnerability and functional impairment of pivotal inhibitory circuits in schizophrenia.     

Inhibition of microRNA-181 reduces forebrain ischemia-induced neuronal loss

MicroRNA (miRNA), miR-181a, is enriched in the brain, and inhibition of miR-181a reduced astrocyte death in vitro and infarct volume after stroke in vivo. This study investigated the role of miR-181a in neuronal injury in vitro and hippocampal neuronal loss in vivo after forebrain ischemia. miR-181a levels were altered by transfection with mimic or antagomir. N2a cells subjected to serum deprivation and oxidative stress showed less cell death when miR-181a was reduced and increased death when miR-181a increased; protection was associated with increased Bcl-2 protein. In contrast, transfected primary neurons did not show altered levels of cell death when miR-181a levels changed. Naive male rats and rats stereotactically infused with miR-181a antagomir or control were subjected to forebrain ischemia and cornus ammonis (CA)1 neuronal survival and protein levels were assessed. Forebrain ischemia increased miR-181a expression and decreased Bcl-2 protein in the hippocampal CA1 region. miR-181a antagomir reduced miR-181a levels, reduced CA1 neuronal loss, increased Bcl-2 protein, and significantly prevented the decrease of glutamate transporter 1. Thus, miR-181a antagomir reduced evidence of astrocyte dysfunction and increased CA1 neuronal survival. miR-181a inhibition is thus a potential target in the setting of forebrain or global cerebral ischemia as well as focal ischemia.     

Trends and changes in Clostridium difficile diagnostic policies and their impact on the proportion of positive samples: a national survey

In June 2012, Israeli guidelines for laboratories were published defining the recommended methods for diagnosis of Clostridium difficile infection (CDI). We conducted this survey to examine the effects of the new recommendations on the proportions of rejected and positive samples by the different methods. A survey was mailed to the directors of all general hospital (GH) and health maintenance organization (HMO) clinical microbiology laboratories. The report was divided into two periods, before and after implementation of the guidelines. Surveys were completed by 13/28 GH laboratories and 5/6 HMO laboratories. All 18 of these laboratories used C. difficile toxin (CDT) enzyme immunoassay alone during the first period of the survey. In the second period, nine laboratories (Group A) used CDT-PCR: two of them used this method exclusively while the other seven used it to resolve most (>90%) of the discrepant results (glutamate dehydrogenase antigen (GDH) +/CDT−]. The other nine laboratories (Group B) used combined GDH/CDT assay, using CDT PCR in only a minority (< 20%) of GDH+/CDT− cases. The overall proportion of rejected samples increased from 9.5% in the first period to 13.9% in the second (p <0.001). Between the first and second periods the proportion of positive samples increased from 9.0% to 11.6% in group A laboratories (p <0.001), but decreased from 12.9% to 9.7% in group B laboratories (p <0.001). Implementation of the guidelines has resulted in a significant increase in the proportion of rejected samples and in the proportion testing positive, suggesting more appropriate test utilization and improved sensitivity in the laboratory diagnosis of CDI.