Ultrasound modulates neuronal potassium currents via ionotropic glutamate receptors

BACKGROUND

Focused ultrasound stimulation (FUS) has the potential to provide non-invasive neuromodulation of deep brain regions with unparalleled spatial precision. However, the cellular and molecular consequences of ultrasound stimulation on neurons remains poorly understood. We previously reported that ultrasound stimulation induces increases in neuronal excitability that persist for hours following stimulation in vitro. In the present study we sought to further elucidate the molecular mechanisms by which ultrasound regulates neuronal excitability and synaptic function.

OBJECTIVES

To determine the effect of ultrasound stimulation on voltage-gated ion channel function and synaptic plasticity.

METHODS

Primary rat cortical neurons were exposed to a 40 s, 200 kHz pulsed ultrasound stimulus or sham-stimulus. Whole-cell patch clamp electrophysiology, quantitative proteomics and high-resolution confocal microscopy were employed to determine the effects of ultrasound stimulation on molecular regulators of neuronal excitability and synaptic function.

RESULTS

We find that ultrasound exposure elicits sustained but reversible increases in whole-cell potassium currents. In addition, we find that ultrasound exposure activates synaptic signalling cascades that result in marked increases in excitatory synaptic transmission. Finally, we demonstrate the requirement of ionotropic glutamate receptor (AMPAR/NMDAR) activation for ultrasound-induced modulation of neuronal potassium currents.

CONCLUSION

These results suggest specific patterns of pulsed ultrasound can induce contemporaneous enhancement of both neuronal excitability and synaptic function, with implications for the application of FUS in experimental and therapeutic settings. Further study is now required to deduce the precise molecular mechanisms through which these changes occur.

Synthesis and pharmacological characterisation of arctigenin analogues as antagonists of AMPA and kainate receptors

(-)-Arctigenin and a series of new analogues have been synthesised and then tested for their potential as AMPA and kainate receptor antagonists of human homomeric GluA1 and GluK2 receptors expressed in HEK293 cells using a Ca²⁺ influx assay. In general, these compounds showed antagonist activity at both receptors with greater activity evident at AMPARs. Schild analysis indicates that a spirocyclic analogue 6c acts as a non-competitive antagonist. Molecular docking studies in which 6c was docked into the X-ray crystal structure of the GluA2 tetramer suggest that (-)-arctigenin and its analogues bind in the transmembrane domain in a similar manner to the known AMPA receptor non-competitive antagonists GYKI53655 and the antiepileptic drug perampanel. The arctigenin derivatives described herein may serve as novel leads for the development of drugs for the treatment of epilepsy.

21st century excitatory amino acid research: A Q & A with Jeff Watkins and Dick Evans

In 1981 Jeff Watkins and Dick Evans wrote what was to become a seminal review on excitatory amino acids (EAAs) and their receptors (Watkins and Evans, 1981). Bringing together various lines of evidence dating back over several decades on: the distribution in the nervous system of putative amino acid neurotransmitters; enzymes involved in their production and metabolism; the uptake and release of amino acids; binding of EAAs to membranes; the pharmacological action of endogenous excitatory amino acids and their synthetic analogues, and notably the actions of antagonists for the excitations caused by both nerve stimulation and exogenous agonists, often using pharmacological tools developed by Jeff and his colleagues, they provided a compelling account for EAAs, especially l-glutamate, as a bona fide neurotransmitter in the nervous system. The rest, as they say, is history, but far from being consigned to history, EAA research is in rude health well into the 21st Century as this series of Special Issues of Neuropharmacology exemplifies. With EAAs and their receptors flourishing across a wide range of disciplines and clinical conditions, we enter into a dialogue with two of the most prominent and influential figures in the early days of EAA research: Jeff Watkins and Dick Evans.

Age-Dependent Shift of AMPA Receptors From Synapses to Intracellular Compartments in Alzheimer's Disease: Immunocytochemical Analysis of the CA1 Hippocampal Region in APP/PS1 Transgenic Mouse Model

Synapse loss occurs early in Alzheimer’s disease (AD) patients and animal models. Alterations at synaptic level are a major morphological correlate of the memory deficits and related symptoms of AD. Given the predominant roles of synaptic AMPA receptors (AMPARs) in excitatory synaptic transmission in the brain, changes in their dynamic regulation are also implicated in the pathophysiology of AD. Here, we used immunolocalization techniques to analyze the expression and subcellular distribution of AMPARs in the hippocampal region of APP/PS1 mouse model of AD. Immunoblots and histoblots revealed that the total amount of AMPARs and their regional expression pattern in the hippocampus was similar in APP/PS1 mice and in age-matched wild type mice. At the ultrastructural level, two synapse populations were examined using SDS-digested freeze-fracture replica labeling in the stratum radiatum in mice: (i) on spines of CA1 pyramidal cells; and (ii) on randomly found dendritic shafts of CA1 interneurons. While 1- and 6-months-old APP/PS1 mice exhibited no change, we observed a significant reduction at 12 months in AMPAR density at synapses in both pyramidal cells and interneurons, compared to wild-type. This reduction of AMPARs in dendritic spines was accompanied by a significant increase in AMPAR subunit proteins identified in intracellular compartments. Our data demonstrate an age-dependent reduction of synaptic AMPARs in APP/PS1 mice, which may contribute to impaired learning and memory at later stages of AD.

Cell-Based Enzyme-Linked Immunosorbent Assay (Cell-ELISA) Analysis of Native and Recombinant Glutamate Receptors

Glutamate receptors (GluRs) located primarily on the membranes of neurons and glial cells are responsible for excitatory synaptic transmission in the central nervous system. The transport of GluRs to the cell surface is a highly regulated dynamic process that determines neuronal excitability and synaptic responses. The molecular and cellular mechanisms of GluR trafficking are often studied in cell cultures. These studies require sensitive techniques that allow the measurement of total and surface-expressed GluRs in cell populations. The cell-based enzyme-linked immunosorbent assay (cell-ELISA) combines steps of direct immunochemical labelling of cell cultures and ELISA. It can be used for quantitative comparisons of surface-expressed and total protein contents of various cell cultures. While several cell-ELISA protocols are available for different cell types, in this chapter we describe the procedure that we have applied for the investigation of quantitative changes in the cell surface expression of recombinant ionotropic glutamate receptors (iGluRs) in adherent human embryonic kidney 293 (HEK293) cells and endogenous iGluR proteins in primary neuronal cultures.

Assembly and Trafficking of Homomeric and Heteromeric Kainate Receptors with Impaired Ligand Binding Sites

Kainate receptors (KARs) are a subfamily of ionotropic glutamate receptors (iGluRs) mediating excitatory synaptic transmission. Cell surface expressed KARs modulate the excitability of neuronal networks. The transfer of iGluRs from the endoplasmic reticulum (ER) to the cell surface requires occupation of the agonist binding sites. Here we used molecular modelling to produce a range of ligand binding domain (LBD) point mutants of GluK1-3 KAR subunits with and without altered agonist efficacy to further investigate the role of glutamate binding in surface trafficking and activation of homomeric and heteromeric KARs using endoglycosidase digestion, cell surface biotinylation and imaging of changes in intracellular Ca²⁺ concentration [Ca²⁺]_i. Mutations of conserved amino acid residues in the LBD that disrupt agonist binding to GluK1-3 (GluK1-T675V, GluK2-A487L, GluK2-T659V and GluK3-T661V) reduced both the total expression levels and cell surface delivery of all of these mutant subunits compared to the corresponding wild type in transiently transfected human embryonic kidney 293 (HEK293) cells. In contrast, the exchange of non-conserved residues in the LBD that convert antagonist selectivity of GluK1-3 (GluK1-T503A, GluK2-A487T, GluK3-T489A, GluK1-N705S/S706N, GluK2-S689N/N690S, GluK3-N691S) did not alter the biosynthesis and trafficking of subunit proteins. Co-assembly of mutant GluK2 with an impaired LBD and wild type GluK5 subunits enables the cell surface expression of both subunits. However, [Ca²⁺]_i imaging indicates that the occupancy of both GluK2 and GluK5 LBDs is required for the full activation of GluK2/GluK5 heteromeric KAR channels.

Joined supernumerary mandibular teeth in the premolar region: Report of a Hungarian archeological case

Supernumerary teeth are those that are additional to the normal complement. They may occur in any region of the dental arch and have been reported in both the primary and the permanent dentitions. The etiology of supernumerary teeth is still not clearly understood, but several theories have been suggested for their occurrence. The investigated material were the remains from the Bácsalmás-Óalmás burial site (from the 16th-17th centuries), where 472 skeletons were excavated from 1993 to 2003. For the purpose of this study, the dentitions of 164 adult individuals were examined. The examination was carried out using macromorphological methods, radiographic analysis and a dial caliper were applied. This paper describes a supernumerary tooth of an adult female skeleton. On the labial surface of the first mandibular premolar an extra tooth was observed.Radiographic examination of the fused teeth indicated that the crown of the premolar had fused incompletely with the crown of the extra tooth. The position of the extra tooth could have been the result of gemination of the tooth germ or the elaboration of the buccal cingulum. The cranium of the examined individual showed some mongoloid morphologic features, too. Our presumption about the formation of the supernumerary tooth may have contributed to the theories of the occurrence of supernumeraries. The sporadic occurrence of this anomaly was reported in recent and archaeological skeletal collections. This study showed that multiple permanent dental formation was present in past Hungarian populations, representing a contribution to the history of dental anomalies.

New tool to tackle Alzheimer's disease: amyloid-β protofibril-selective antibody AbSL: An Editorial Highlight for 'The conformational epitope for a new Aβ42 protofibril-selective antibody partially overlaps with the peptide N-terminal region' on page 736

This Editorial highlights a study by Colvin et al. (2017) in the current issue of Journal of Neurochemistry, in which the authors describe the development and characterisation of a new rabbit antibody (termed antibody St. Louis; AbSL) that preferentially recognises amyloid-β (Aβ) protein 42 (Aβ42) protofibrils over other Aβ species.

Variants of the EAAT2 Glutamate Transporter Gene Promoter Are Associated with Cerebral Palsy in Preterm Infants

Preterm delivery is associated with neurodevelopmental impairment caused by environmental and genetic factors. Dysfunction of the excitatory amino acid transporter 2 (EAAT2) and the resultant impaired glutamate uptake can lead to neurological disorders. In this study, we investigated the role of single nucleotide polymorphisms (SNPs; g.-200C>A and g.-181A>C) in the EAAT2 promoter in susceptibility to brain injury and neurodisability in very preterm infants born at or before 32-week gestation. DNA isolated from newborns’ dried blood spots were used for pyrosequencing to detect both SNPs. Association between EAAT2 genotypes and cerebral palsy, cystic periventricular leukomalacia and a low developmental score was then assessed. The two SNPs were concordant in 89.4% of infants resulting in three common genotypes all carrying two C and two A alleles in different combinations. However, in 10.6% of cases, non-concordance was found, generating six additional rare genotypes. The A alleles at both loci appeared to be detrimental and consequently, the risk of developing cerebral palsy increased four- and sixfold for each additional detrimental allele at -200 and -181 bp, respectively. The two SNPs altered the regulation of the EAAT2 promoter activity and glutamate homeostasis. This study highlights the significance of glutamate in the pathogenesis of preterm brain injury and subsequent development of cerebral palsy and neurodevelopmental disabilities. Furthermore, the described EAAT2 SNPs may be an early biomarker of vulnerability to neurodisability and may aid the development of targeted treatment strategies.

Association between neonatal resuscitation and a single nucleotide polymorphism rs1835740

AIM

The aim of this work was to test whether three single nucleotide polymorphisms (SNPs) implicated in glutamate homoeostasis or signalling and cellular survival are associated with birth condition.

METHODS

This study is drawn from the Avon Longitudinal Study of Parents and Children. A total of 7611 term infants were genotyped and patient outcome data retrieved from routine medical records. Exposure measures were the presence of one or more minor alleles in one of 3 SNPs (rs2284411, rs2498804, rs1835740). The primary outcome was the need for resuscitation at birth.

RESULTS

For SNP rs1835740, infants homozygous for the minor allele compared to wild type were more likely to need resuscitation (9.2% vs. 7.0%, p = 0.041), while the odds ratio for resuscitation was associated with each increasing minor allele [OR 1.17 (1.01-1.35)]. Population attributable risk fraction was 6.5%. There was no evidence that the other two SNPs investigated were associated with birth condition.

CONCLUSION

We have tested three candidate SNPs to measure any association with birth condition. The study revealed that the rs1835740 was associated with the need for resuscitation and Apgar scores, with a substantial population impact.

Is riluzole a new drug for Alzheimer's disease?

This Editorial highlights a study by Hunsberger et al. (2015) in the current issue of Journal of Neurochemistry, in which the authors explore the effects of riluzole (R) treatment on tau-P301L transgenic mice. The authors employed a comprehensive analysis of possible restorative effects of the drug by examining glutamate levels in subregions of the hippocampus, expression of tau and its hyper-phosphorylated forms, and memory function using behavioral tests. The authors report a simultaneous reduction in glutamate reuptake and an increase in glutamate release in the tau-P301L model, both of which are ameliorated with riluzole treatment. The authors' findings have implications for our understanding of synaptic transmission mechanisms also associated with Alzheimer's disease pathology.

Assessment of heat provocation tests on the human gingiva: the effect of periodontal disease and smoking

Periodontal inflammation is associated with morphological changes in the blood vessels which may influence the regulation of gingival blood flow (GBF). Our aim was to adapt the heat provocation test to the human gingiva to assess vascular reactivity in periodontal inflammation.

METHOD

GBF was recorded by Laser Doppler Flowmetry before and after heat provocation in healthy volunteers (n = 50). Heat was generated either by warm saline or a halogen lamp. The latter method was also utilized for a heat test in non-smoking and smoking patients with periodontal inflammation. The circulatory parameters were correlated to the inflammatory marker, i.e. gingival crevicular fluid (GCF) production measured by Periotron.

RESULTS

Local application of heat caused a rapid, significant and transient increase in GBF regardless of the method used. The increase in the speed and not in the concentration of moving blood cells was responsible for increased GBF. Higher GCF values were correlated with increased peak flow, flux pulse amplitude and faster restoration of GBF after the test in non-smokers, but not in smokers.

CONCLUSIONS

The heat test could be a valuable tool to check the vascular reactivity of gingival vessels. Moderate periodontal inflammation may facilitate gingival vascular responsiveness which can be suppressed by smoking.

Unusual spinal tuberculosis in an Avar Age skeleton (Csongrád-Felgyő, Ürmös-tanya, Hungary): A morphological and biomolecular study

The paleopathological analysis of a well-preserved young adult female skeleton from the AD 7-8th century (Avar Age) in Hungary revealed multiple lytic lesions in all of the thoracic and lumbar vertebral bodies. The lesions were characterized by smooth marginal zones and space-occupying mass appearance. The considerable loss of spongy bone in the thoracolumbar vertebrae resulted in angular deformity and fusion, characteristic of the healing stage of TB. Osteolytic lesions were also observed on the vertebral processes, ribs and sternum. On the endocranial surface, abnormal blood vessel impressions were revealed, indicating some kind of meningitis. The X-ray and CT analysis of the affected bones detected abnormal structures and cystic zones of destruction. The lesions were however not always bordered by areas of increased density, which is typical in cystic TB. Vertebral remains were also subjected to biomolecular analysis in two different laboratories, which attested the presence of Mycobacterium tuberculosis complex (MTBC) DNA and supported the paleopathological diagnosis of TB. Spoligotyping analysis confirmed the presence of MTBC DNA and more specifically an infection caused by bacteria belonging to the M. tuberculosis lineage. This case study provides new data for the paleoepidemiology of TB in this geographical area and historical period, and draws attention to the great variability of TB lesions in the human skeleton.

Nutrient stress alters the glycosylation status of LGR5 resulting in reduced protein stability and membrane localisation in colorectal tumour cells: implications for targeting cancer stem cells

BACKGROUND

LGR5 is an important marker of intestinal stem cells and performs its vital functions at the cell membrane. Despite the importance of LGR5 to both normal and cancer stem cell biology, it is not known how microenvironmental stress affects the expression and subcellular distribution of the protein.

METHODS

Nutrient stress was induced through glucose starvation. Glycosylation status was assessed using endoglycosidase or tunicamycin treatment. Flow cytometry and confocal microscopy were used to assess subcellular distribution of LGR5.

RESULTS

Glucose deprivation altered the glycosylation status of LGR5 resulting in reduced protein stability and cell surface expression. Furthermore, inhibiting LGR5 glycosylation resulted in depleted surface expression and reduced localisation in the cis-Golgi network.

CONCLUSIONS

Nutrient stress within a tumour microenvironment has the capacity to alter LGR5 protein stability and membrane localisation through modulation of LGR5 glycosylation status. As LGR5 surface localisation is required for enhanced Wnt signalling, this is the first report to show a mechanism by which the microenvironment could affect LGR5 function.

Target- and input-dependent organization of AMPA and NMDA receptors in synaptic connections of the cochlear nucleus

We examined the synaptic structure, quantity, and distribution of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)- and N-methyl-D-aspartate (NMDA)-type glutamate receptors (AMPARs and NMDARs, respectively) in rat cochlear nuclei by a highly sensitive freeze-fracture replica labeling technique. Four excitatory synapses formed by two distinct inputs, auditory nerve (AN) and parallel fibers (PF), on different cell types were analyzed. These excitatory synapse types included AN synapses on bushy cells (AN-BC synapses) and fusiform cells (AN-FC synapses) and PF synapses on FC (PF-FC synapses) and cartwheel cell spines (PF-CwC synapses). Immunogold labeling revealed differences in synaptic structure as well as AMPAR and NMDAR number and/or density in both AN and PF synapses, indicating a target-dependent organization. The immunogold receptor labeling also identified differences in the synaptic organization of FCs based on AN or PF connections, indicating an input-dependent organization in FCs. Among the four excitatory synapse types, the AN-BC synapses were the smallest and had the most densely packed intramembrane particles (IMPs), whereas the PF-CwC synapses were the largest and had sparsely packed IMPs. All four synapse types showed positive correlations between the IMP-cluster area and the AMPAR number, indicating a common intrasynapse-type relationship for glutamatergic synapses. Immunogold particles for AMPARs were distributed over the entire area of individual AN synapses; PF synapses often showed synaptic areas devoid of labeling. The gold-labeling for NMDARs occurred in a mosaic fashion, with less positive correlations between the IMP-cluster area and the NMDAR number. Our observations reveal target- and input-dependent features in the structure, number, and organization of AMPARs and NMDARs in AN and PF synapses.

Detection of three closely located single nucleotide polymorphisms in the EAAT2 promoter: comparison of single-strand conformational polymorphism (SSCP), pyrosequencing and Sanger sequencing

Background

Single-strand conformational polymorphism (SSCP) is still a frequently used genotyping method across different fields for the detection of single nucleotide polymorphisms (SNPs) due to its simplicity, requirement for basic equipment accessible in most laboratories and low cost. This technique was previously used to detect rs4354668:A > C (g.-181A > C) SNP in the promoter of astroglial glutamate transporter (EAAT2) and the same approach was initially used here to investigate this promoter region in a cohort of newborns.

Results

Unexpectedly, four distinct DNA migration patterns were identified by SSCP. Sanger sequencing revealed two additional SNPs: g.-200C > A and g.-168C > T giving a rise to a total of ten EAAT2 promoter variants. SSCP failed to distinguish these variants reliably and thus pyrosequencing assays were developed. g.-168C > T was found in heterozygous form in one infant only with minor allele frequency (MAF) of 0.0023. In contrast, g.-200C > A and -181A > C were more common (with MAF of 0.46 and 0.49, respectively) and showed string evidence of linkage disequilibrium (LD). In a systematic comparison, 16% of samples were miss-classified by SSCP with 25-31% errors in the identification of the wild-type and homozygote mutant genotypes compared to pyrosequencing or Sanger sequencing. In contrast, SSCP and pyrosequencing of an unrelated single SNP (rs1835740:C > T), showed 94% concordance.

Conclusion

Our data suggest that SSCP cannot always detect reliably several closely located SNPs. Furthermore, caution is needed in the interpretation of the association studies linking only one of the co-inherited SNPs in the EAAT2 promoter to human diseases.

Isolation of human genomic DNA for genetic analysis from premature neonates: a comparison between newborn dried blood spots, whole blood and umbilical cord tissue

Background

Genotyping requires biological sample collection that must be reliable, convenient and acceptable for patients and clinicians. Finding the most optimal procedure of sample collection for premature neonates who have a very limited blood volume is a particular challenge. The aim of the current study was to evaluate the use of umbilical cord (UC) tissue and newborn dried blood spot (DBS)-extracted genomic DNA (gDNA) as an alternative to venous blood-derived gDNA from premature neonates for molecular genetic analysis.

All samples were obtained from premature newborn infants between 24-32 weeks of gestation. Paired blood and UC samples were collected from 31 study participants. gDNA was extracted from ethylenediaminetetraacetic acid (EDTA) anticoagulant-treated blood samples (~500 μl) and newborn DBSs (n = 723) using QIAamp DNA Micro kit (Qiagen Ltd., Crawley, UK); and from UC using Qiagen DNAeasy Blood and Tissue kit (Qiagen Ltd., Crawley, UK). gDNA was quantified and purity confirmed by measuring the A₂₆₀:A₂₈₀ ratio. PCR amplification and pyrosequencing was carried out to determine suitability of the gDNA for molecular genetic analysis. Minor allele frequency of two unrelated single nucleotide polymorphisms (SNPs) was calculated using the entire cohort.

Results

Both whole blood samples and UC tissue provided good quality and yield of gDNA, which was considerably less from newborn DBS. The gDNA purity was also reduced after 3 years of storage of the newborn DBS. PCR amplification of three unrelated genes resulted in clear products in all whole blood and UC samples and 86%-100% of newborn DBS. Genotyping using pyrosequencing showed 100% concordance in the paired UC and whole blood samples. Minor allele frequencies of the two SNPs indicated that no maternal gDNA contamination occurred in the genotyping of the UC samples.

Conclusions

gDNAs from all three sources are suitable for standard PCR and pyrosequencing assays. Given that UC provide good quality and quantity gDNA with 100% concordance in the genetic analysis with whole blood, it can replace blood sampling from premature infants. This is likely to reduce the stress and potential side effects associated with invasive sample collection and thus, greatly facilitate participant recruitment for genetic studies.

MyRIP interaction with MyoVa on secretory granules is controlled by the cAMP-PKA pathway

Myosin- and Rab-interacting protein is not a classic receptor for MyoVa on large, dense-core secretory granules (SGs), but it aids in PKA-dependent phosphorylation of MyoVa-associated proteins on SGs in endocrine and neuroendocrine cells.

Myosin- and Rab-interacting protein (MyRIP), which belongs to the protein kinase A (PKA)–anchoring family, is implicated in hormone secretion. However, its mechanism of action is not fully elucidated. Here we investigate the role of MyRIP in myosin Va (MyoVa)-dependent secretory granule (SG) transport and secretion in pancreatic beta cells. These cells solely express the brain isoform of MyoVa (BR-MyoVa), which is a key motor protein in SG transport. In vitro pull-down, coimmunoprecipitation, and colocalization studies revealed that MyRIP does not interact with BR-MyoVa in glucose-stimulated pancreatic beta cells, suggesting that, contrary to previous notions, MyRIP does not link this motor protein to SGs. Glucose-stimulated insulin secretion is augmented by incretin hormones, which increase cAMP levels and leads to MyRIP phosphorylation, its interaction with BR-MyoVa, and phosphorylation of the BR-MyoVa receptor rabphilin-3A (Rph-3A). Rph-3A phosphorylation on Ser-234 was inhibited by small interfering RNA knockdown of MyRIP, which also reduced cAMP-mediated hormone secretion. Demonstrating the importance of this phosphorylation, nonphosphorylatable and phosphomimic Rph-3A mutants significantly altered hormone release when PKA was activated. These data suggest that MyRIP only forms a functional protein complex with BR-MyoVa on SGs when cAMP is elevated and under this condition facilitates phosphorylation of SG-associated proteins, which in turn can enhance secretion.

The NMDA receptor as a target for cognitive enhancement

NMDA receptors (NMDARs) play an important role in neural plasticity including long-term potentiation and long-term depression, which are likely to explain their importance for learning and memory. Cognitive decline is a major problem facing an ageing human population, so much so that its reversal has become an important goal for scientific research and pharmaceutical development. Enhancement of NMDAR function is a core strategy toward this goal. In this review we indicate some of the major ways of potentiating NMDAR function by both direct and indirect modulation. There is good evidence that both positive and negative modulation can enhance function suggesting that a subtle approach correcting imbalances in particular clinical situations will be required. Excessive activation and the resultant deleterious effects will need to be carefully avoided. Finally we describe some novel positive allosteric modulators of NMDARs, with some subunit selectivity, and show initial evidence of their ability to affect NMDAR mediated events. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Piperazine-2,3-dicarboxylic acid derivatives as dual antagonists of NMDA and GluK1-containing kainate receptors

Competitive N-methyl-d-aspartate receptor (NMDAR) antagonists bind to the GluN2 subunit, of which there are four types (GluN2A-D). We report that some N(1)-substituted derivatives of cis-piperazine-2,3-dicarboxylic acid display improved relative affinity for GluN2C and GluN2D versus GluN2A and GluN2B. These derivatives also display subtype selectivity among the more distantly related kainate receptor family. Compounds 18i and (-)-4 were the most potent kainate receptor antagonists, and 18i was selective for GluK1 versus GluK2, GluK3 and AMPA receptors. Modeling studies revealed structural features required for activity at GluK1 subunits and suggested that S674 was vital for antagonist activity. Consistent with this hypothesis, replacing the equivalent residue in GluK3 (alanine) with a serine imparts 18i antagonist activity. Antagonists with dual GluN2D and GluK1 antagonist activity may have beneficial effects in various neurological disorders. Consistent with this idea, antagonist 18i (30 mg/kg ip) showed antinociceptive effects in an animal model of mild nerve injury.

Developmental regulation of G protein-gated inwardly-rectifying K+ (GIRK/Kir3) channel subunits in the brain

G protein-gated inwardly-rectifying K(+) (GIRK/family 3 of inwardly-rectifying K(+) ) channels are coupled to neurotransmitter action and can play important roles in modulating neuronal excitability. We investigated the temporal and spatial expression of GIRK1, GIRK2 and GIRK3 subunits in the developing and adult brain of mice and rats using biochemical, immunohistochemical and immunoelectron microscopic techniques. At all ages analysed, the overall distribution patterns of GIRK1-3 were very similar, with high expression levels in the neocortex, cerebellum, hippocampus and thalamus. Focusing on the hippocampus, histoblotting and immunohistochemistry showed that GIRK1-3 protein levels increased with age, and this was accompanied by a shift in the subcellular localization of the subunits. Early in development (postnatal day 5), GIRK subunits were predominantly localized to the endoplasmic reticulum in the pyramidal cells, but by postnatal day 60 they were mostly found along the plasma membrane. During development, GIRK1 and GIRK2 were found primarily at postsynaptic sites, whereas GIRK3 was predominantly detected at presynaptic sites. In addition, GIRK1 and GIRK2 expression on the spine plasma membrane showed identical proximal-to-distal gradients that differed from GIRK3 distribution. Furthermore, although GIRK1 was never found within the postsynaptic density (PSD), the level of GIRK2 in the PSD progressively increased and GIRK3 did not change in the PSD during development. Together, these findings shed new light on the developmental regulation and subcellular diversity of neuronal GIRK channels, and support the contention that distinct subpopulations of GIRK channels exert separable influences on neuronal excitability. The ability to selectively target specific subpopulations of GIRK channels may prove effective in the treatment of disorders of excitability.

Molecular mechanism of myosin Va recruitment to dense core secretory granules

The brain-spliced isoform of Myosin Va (BR-MyoVa) plays an important role in the transport of dense core secretory granules (SGs) to the plasma membrane in hormone and neuropeptide-producing cells. The molecular composition of the protein complex that recruits BR-MyoVa to SGs and regulates its function has not been identified to date. We have identified interaction between SG-associated proteins granuphilin-a/b (Gran-a/b), BR-MyoVa and Rab27a, a member of the Rab family of GTPases. Gran-a/b-BR-MyoVa interaction is direct, involves regions downstream of the Rab27-binding domain, and the C-terminal part of Gran-a determines exon specificity. MyoVa and Gran-a/b are partially colocalised on SGs and disruption of Gran-a/b-BR-MyoVa binding results in a perinuclear accumulation of SGs which augments nutrient-stimulated hormone secretion in pancreatic beta-cells. These results indicate the existence of at least another binding partner of BR-MyoVa that was identified as rabphilin-3A (Rph-3A). BR-MyoVa-Rph-3A interaction is also direct and enhanced when secretion is activated. The BR-MyoVa-Rph-3A and BR-MyoVa-Gran-a/b complexes are linked to a different subset of SGs, and simultaneous inhibition of these complexes nearly completely blocks stimulated hormone release. This study demonstrates that multiple binding partners of BR-MyoVa regulate SG transport, and this molecular mechanism is universally used by neuronal, endocrine and neuroendocrine cells.

Removal of nonspecific binding proteins from cell and tissue extracts using 2-aminobenzimidazole-tethered affinity resin

Cellular drug target identification through affinity chromatography is often hindered by the quantity of nonspecific binders, such as cytoskeletal and heat shock proteins. Thus, we prepared a 2-aminobenzimidazole-tethered depletion resin designed for removal of these proteins, and tested it on human lung carcinoma cell and rat tissue extracts. Column-bound proteins were identified by two-dimensional gel electrophoresis and MS. Among others, tubulins, actins and heat shock proteins were successfully depleted. Due to the reduction of these highly abundant proteins detection of potential drug targets is considerably facilitated in the pre-purified samples.

Long-term potentiation in cultured hippocampal neurons

Studies performed on low-density primary neuronal cultures have enabled dissection of molecular and cellular changes during N-methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation (LTP). Various electrophysiological and chemical induction protocols were developed for the persistent enhancement of excitatory synaptic transmission in hippocampal neuronal cultures. The characterisation of these plasticity models confirmed that they share many key properties with the LTP of CA1 neurons, extensively studied in hippocampal slices using electrophysiological techniques. For example, LTP in dissociated hippocampal neuronal cultures is also dependent on Ca(2+) influx through post-synaptic NMDA receptors, subsequent activation and autophosphorylation of the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and an increase in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor insertion at the post-synaptic membrane. The availability of models of LTP in cultured hippocampal neurons significantly facilitated the monitoring of changes in endogenous postsynaptic receptor proteins and the investigation of the associated signalling mechanisms that underlie LTP. A central feature of LTP of excitatory synapses is the recruitment of AMPA receptors at the postsynaptic site. Results from the use of cell culture-based models started to establish the mechanism by which synaptic input controls a neuron's ability to modify its synapses in LTP. This review focuses on key features of various LTP induction protocols in dissociated hippocampal neuronal cultures and the applications of these plasticity models for the investigation of activity-induced changes in native AMPA receptors.

Influence of shear viscosity of quark-gluon plasma on elliptic flow in ultrarelativistic heavy-ion collisions

We investigate the influence of a temperature-dependent shear viscosity over entropy density ratio η/s on the transverse momentum spectra and elliptic flow of hadrons in ultrarelativistic heavy-ion collisions. We find that the elliptic flow in √S(NN)=200  GeV Au+Au collisions at RHIC is dominated by the viscosity in the hadronic phase and in the phase transition region, but largely insensitive to the viscosity of the quark-gluon plasma (QGP). At the highest LHC energy, the elliptic flow becomes sensitive to the QGP viscosity and insensitive to the hadronic viscosity.

LTP in hippocampal neurons is associated with a CaMKII-mediated increase in GluA1 surface expression

The use of hippocampal dissociated neuronal cultures has enabled the study of molecular changes in endogenous native proteins associated with long-term potentiation. Using immunofluorescence labelling of the active (Thr286-phosphorylated) alpha-Ca(2+) /calmodulin-dependent protein kinase II (CaMKII) we found that CaMKII activity was increased by transient (3 × 1 s) depolarisation in 18- to 21-day-old cultures but not in 9- to 11-day-old cultures. The increase in Thr286 phosphorylation of CaMKII required the activation of NMDA receptors and was greatly attenuated by the CaMKII inhibitor KN-62. We compared the effects of transient depolarisation on the surface expression of GluA1 and GluA2 subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor and found a preferential recruitment of the GluA1 subunit. CaMKII inhibition prevented this NMDA receptor-dependent delivery of GluA1 to the cell surface. CaMKII activation is therefore an important factor in the activity-dependent recruitment of native GluA1 subunit-containing alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors to the cell surface of hippocampal neurons.

Mapping the ligand binding sites of kainate receptors: molecular determinants of subunit-selective binding of the antagonist [3H]UBP310

Kainate receptors (KARs) modulate synaptic transmission and plasticity, and their dysfunction has been linked to several disease states such as epilepsy and chronic pain. KARs are tetramers formed from five different subunits. GluK1-3 are low affinity kainate binding subunits, whereas GluK4/5 bind kainate with high affinity. A number of these subunits can be present in any given cell type, and different combinations of subunits confer different properties to KARs. Here we report the characterization of a new GluK1 subunit-selective radiolabeled antagonist (S)-1-(2-amino-2-carboxyethyl)-3-(2-carboxythiophene-3-yl-methyl)-5-methylpyrimidine-2,4-dione ([(3)H]UBP310) using human recombinant KARs. [(3)H]UBP310 binds to GluK1 with low nanomolar affinity (K(D) = 21 ± 7 nM) but shows no specific binding to GluK2. However, [(3)H]UBP310 also binds to GluK3 (K(D) = 0.65 ± 0.19 μM) but with ~30-fold lower affinity than that observed for GluK1. Competition [(3)H]UBP310 binding experiments on GluK1 revealed the same rank order of affinity of known GluK1-selective ligands as reported previously in functional assays. Nonconserved residues in GluK1-3 adjudged in modeling studies to be important in determining the GluK1 selectivity of UBP310 were point-mutated to switch residues between subunits. None of the mutations altered the expression or trafficking of KAR subunits. Whereas GluK1-T503A mutation diminished [(3)H]UBP310 binding, GluK2-A487T mutation rescued it. Likewise, whereas GluK1-N705S/S706N mutation decreased, GluK3-N691S mutation increased [(3)H]UBP310 binding activity. These data show that Ala487 in GluK2 and Asn691 in GluK3 are important determinants in reducing the affinity of UBP310 for these subunits. Insights from these modeling and point mutation studies will aid the development of new subunit-selective KAR antagonists.

Assembly and intracellular distribution of kainate receptors is determined by RNA editing and subunit composition

Kainate receptors (KARs) modulate neuronal network activity. The molecular mechanisms that control the assembly and trafficking of KARs are unclear. Here, we examined the role of Q/R editing and subunit composition on KAR subunit assembly and subcellular distribution. The majority of GluK2 subunits undergo editing at the Q/R site in the channel pore loop. Cell surface biotinylation, cross-linking, Endoglycosidase-H analysis and gradient separation of KAR subunit assembly states revealed that Q/R editing reduces oligomerization, endoplasmic reticulum (ER) export, plasma membrane expression and stability of homomeric GluK2-containing KARs. These results indicate that Q/R editing of GluK2 may orchestrate channel subunit composition during KAR assembly in the ER. GluK2/GluK5 heteromers are the most abundant KAR subtype in the brain. While subcellular fractionation of brain tissue confirmed that both GluK2/3 and GluK5 are present in synaptosomes and tightly associated with post-synaptic density fractions, biochemical analysis revealed that endogenous GluK2/3 subunits show less complete assembly and trafficking compared with GluK5. In transgenic mice, the loss of the key assembly partner GluK2 leads to dramatic reduction in GluK5 expression. These results support the idea that the assembly and intracellular distribution of KARs is determined by RNA editing at the Q/R site and subunit composition.

Metabotropic glutamate receptor-mediated long-term depression: molecular mechanisms

The ability to modify synaptic transmission between neurons is a fundamental process of the nervous system that is involved in development, learning, and disease. Thus, synaptic plasticity is the ability to bidirectionally modify transmission, where long-term potentiation and long-term depression (LTD) represent the best characterized forms of plasticity. In the hippocampus, two main forms of LTD coexist that are mediated by activation of either N-methyl-d-aspartic acid receptors (NMDARs) or metabotropic glutamate receptors (mGluRs). Compared with NMDAR-LTD, mGluR-LTD is less well understood, but recent advances have started to delineate the underlying mechanisms. mGluR-LTD at CA3:CA1 synapses in the hippocampus can be induced either by synaptic stimulation or by bath application of the group I selective agonist (R,S)-3,5-dihydroxyphenylglycine. Multiple signaling mechanisms have been implicated in mGluR-LTD, illustrating the complexity of this form of plasticity. This review provides an overview of recent studies investigating the molecular mechanisms underlying hippocampal mGluR-LTD. It highlights the role of key molecular components and signaling pathways that are involved in the induction and expression of mGluR-LTD and considers how the different signaling pathways may work together to elicit a persistent reduction in synaptic transmission.

Disruption of the interaction between myosin VI and SAP97 is associated with a reduction in the number of AMPARs at hippocampal synapses

Myosin VI is an actin-based motor protein that is enriched at the postsynaptic density and appears to interact with alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-type glutamate receptors (AMPARs) via synapse associated protein 97 (SAP97). Here, we find that a Flag epitope-tagged dominant negative construct that inhibits the interaction between SAP97 and myosin VI (Flag-myoVI-DN) causes a dramatic reduction in the number of synapses and the surface expression of AMPARs in cultured hippocampal neurons. Furthermore, we find that Flag-myoVI-DN also prevents the rapid delivery of AMPARs to synapses that can be induced by the transient activation of N-methyl-d-aspartate receptors. The Flag-myoVI-DN induced decrease in surface AMPARs is not because of reduced AMPAR subunit protein synthesis. Using whole-cell recording, we show that Flag-myoVI-DN also prevents the activity-induced increase in miniature excitatory postsynaptic current frequency that is normally associated with recruitment of AMPARs to the cell surface at synaptic sites that lack these receptors (i.e. 'silent' synapses). Together, these results indicate that myosin VI/SAP97 plays an important role in trafficking and activity-dependent recruitment of AMPARs to synapses.

Effects of dietary vegetable oil supplementation on fillet quality traits, chemical and fatty acid composition of African catfish (<i>Clarias gariepinus</i>)

Abstract. The effects of dietary fish oil (FO), soybean oil (SO) and linseed oil (LO) (12 % crude fat content each) in African catfish (Clarias gariepinus) diets were tested on the fillet flesh quality, chemical and fatty acid (FA) composition, after 3 and 6 weeks of feeding. The bodyweight gain of fish and the fillet dry matter, crude protein and crude fat content was not different among the divergent treatments. High (>20 %) total n3 FA supplementation significantly increased the moisture loss of fillet (FO, LO). Applying the simple FA dilution model (JOBLING 2004a, 2004b), the incorporation dynamics of the most largely dosed FAs were accurately predictable after 3 weeks (R² between observed and estimated data for total n3 FAs: FO 0.95, LO 0.73 and for α-linolenic acid, LO 0.97). In the fillet FA composition the metabolism of n3 acids was more pronounced. The large provision of α-linolenic acid (LO) had a pronounced effect on the longchain, polyunsaturated n3 FA proportions (eicosapentaenoic and docosapentaenoic acids), while no effect was experienced on docosahexaenoic acid. This study suggests that daily bodyweight gain is not, while fillet flesh quality and FA composition is slightly compromised when fish oil is substituted for vegetable oils.

Relativistic shock waves in viscous gluon matter

We solve the relativistic Riemann problem in viscous gluon matter employing a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio eta/s from zero to infinity. We show that an eta/s ratio larger than 0.2 prevents the development of well-defined shock waves on time scales typical for ultrarelativistic heavy-ion collisions. Comparisons with viscous hydrodynamic calculations confirm our findings.

Modification of ionotropic glutamate receptor-mediated processes in the rat hippocampus following repeated, brief seizures

The seizure-induced molecular and functional alterations of glutamatergic transmission in the hippocampus have been investigated. Daily repeated epileptic seizures were induced for 12 days by intraperitoneal administration of 4-aminopyridine (4-AP; 4.5 mg/kg) in adult Wistar rats. The seizure symptoms were evaluated on the Racine's scale. One day after the last injection, the brains were removed for in vitro electrophysiological experiments and immunohistochemical analysis. The glutamate receptor subunits NR1, NR2A, NR2B, GluR1, GluR1(flop), GluR2, and KA-2 were studied using the histoblotting method. The semi-quantitative analysis of subunit immunoreactivities in hippocampal layers was performed with densitometry. In the hippocampus, increase of GluR1, GluR1(flop) and NR2B immunostaining was observed in most of the areas and layers. The significant decrease of GluR2 staining intensity was observed in the CA1 and dentate gyrus. Calcium permeability of hippocampal neurons was tested by a cobalt uptake assay in hippocampal slices. The uptake of cobalt increased in the CA1 area and dentate gyrus, but not in the CA3 region following 4-AP treatment. Effects of AMPA and NMDA (N-methyl-d-aspartate) glutamate receptor antagonists (1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466) and D-APV respectively) were measured in hippocampal slices using extracellular recording. Analysis of the population spikes revealed the reduced effectiveness of the AMPA receptor antagonist GYKI 52466, while the effect of the NMDA receptor antagonist d-(2R)-amino-5-phosphonovaleric acid was similar to controls. The results demonstrated that repeated convulsions induced structural and functional changes in AMPA receptor-mediated transmission, while NMDA and kainate receptor systems displayed only alterations in receptor subunit composition.

Tyrosine dephosphorylation regulates AMPAR internalisation in mGluR-LTD

Long-term depression (LTD) can be induced at hippocampal CA1 synapses by activation of either NMDA receptors (NMDARs) or group I metabotropic glutamate receptors (mGluRs), using their selective agonists NMDA and (RS)-3,5-dihydroxyphenylglycine (DHPG), respectively. Recent studies revealed that DHPG-LTD is dependent on activation of postsynaptic protein tyrosine phosphatases (PTPs), which transiently dephosphorylate tyrosine residues in AMPA receptors (AMPARs). Here we show that while both endogenous GluR2 and GluR3 AMPAR subunits are tyrosine phosphorylated at basal activity, only GluR2 is dephosphorylated in DHPG-LTD. The tyrosine dephosphorylation of GluR2 does not occur in NMDA-LTD. Conversely, while NMDA-LTD is associated with the dephosphorylation of GluR1-serine-845, DHPG-LTD does not alter the phosphorylation of this site. The increased AMPAR endocytosis in DHPG-LTD is PTP-dependent and involves tyrosine dephosphorylation of cell surface AMPARs. Together, these results indicate that the subunit selective tyrosine dephosphorylation of surface GluR2 regulates AMPAR internalisation in DHPG-LTD but not in NMDA-LTD in the hippocampus.

Leflunomide and its metabolite A771726 are high affinity substrates of BCRP: implications for drug resistance

BACKGROUND

Earlier publications have suggested a possible role for the efflux transporter breast cancer resistance protein (BCRP) in acquired resistance to disease-modifying antirheumatic drugs (DMARDs) such as leflunomide and its metabolite A771726 (teriflunomide). However, there is no direct evidence that BCRP interacts with these drugs.

OBJECTIVES

To characterise the interaction between BCRP transporter and leflunomide and its active metabolite A771726, with emphasis on the nature of the interaction (substrate or inhibitor) and the kinetic characterisation of the interactions.

METHODS

Different in vitro membrane-based methods (ATPase and vesicular transport assay) using BCRP-HAM-Sf9 membrane preparations and cellular assays (Hoechst assay and cytotoxicity assay) were performed on PLB985-BCRP and HEK293-BCRP cell lines overexpressing BCRP.

RESULTS

In all assays used, an interaction between the investigated drugs and BCRP was detected. In the vesicular transport assay, both leflunomide and its metabolite inhibited BCRP-mediated methotrexate transport. Both compounds are likely substrates of BCRP as shown by the vanadate-sensitive ATPase assay. In line with the membrane assays, leflunomide and A771726 inhibited BCRP-mediated Hoechst efflux from PLB985-BCRP cells. In the cytotoxicity assay, overexpression of BCRP conferred 20.6-fold and 7.5-fold resistance to HEK293 cells against leflunomide and A771726, respectively. The resistance could be reversed by Ko134, a specific inhibitor of BCRP.

CONCLUSION

Based on these results, BCRP could play an important role in the resistance to leflunomide and A771726 via interactions with these drugs. BCRP may also mediate drug-drug interactions when leflunomide is administered with other BCRP substrate drugs such as methotrexate.

Number and density of AMPA receptors in individual synapses in the rat cerebellum as revealed by SDS-digested freeze-fracture replica labeling

The number of AMPA receptor (AMPAR) is the major determinant of synaptic strength at glutamatergic synapses, but little is known about the absolute number and density of AMPARs in individual synapses. Using SDS-digested freeze-fracture replica labeling, which has high detection efficiency comparable with electrophysiological noise analysis for functional AMPAR, we analyzed three kinds of excitatory synapses in the molecular layer of the adult rat cerebellum. In parallel fiber (PF)-Purkinje cell (PC) synapses, we found large variability in the number (38.1 +/- 34.4 particles per synapse, mean +/- SD; range, 2-178 particles per synapse) and density (437 +/- 277 particles/microm2; range, 48-1210 particles/microm2) of immunogold-labeled AMPARs. Two-dimensional view and high sensitivity of this method revealed irregular-shaped small AMPAR clusters within synapses. Climbing fiber (CF)-PC synapses had higher number of AMPAR labeling (68.6 +/- 34.5 particles per synapse) than PF-PC and PF-interneuron synapses (36.8 +/- 14.4 particles per synapse). Furthermore, AMPAR density at CF-PC and PF-interneuron synapses was approximately five times higher and more uniform than that at PF-PC synapses. These results suggest input- and target-dependent regulation of AMPAR-mediated synaptic strength.

Cholesterol potentiates ABCG2 activity in a heterologous expression system: improved in vitro model to study function of human ABCG2

ABCG2, a transporter of the ATP-binding cassette family, is known to play a prominent role in the absorption, distribution, metabolism, and excretion of xenobiotics. Drug-transporter interactions are commonly screened by high-throughput systems using transfected insect and/or human cell lines. The determination of ABCG2-ATPase activity is one method to identify ABCG2 substrate and inhibitors. We demonstrate that the ATPase activities of the human ABCG2 transfected Sf9 cell membranes (MXR-Sf9) and ABCG2-overexpressing human cell membranes (MXR-M) differ. Variation due to disparity in the glycosylation level of the protein had no effect on the transporter. The influence of cholesterol on ABCG2-ATPase activity was investigated because the lipid compositions of insect and human cells are largely different from each other. Differences in cholesterol content, shown by cholesterol loading and depletion experiments, conferred the difference in stimulation of basal ABCG2-ATPase of the two cell membranes. Basal ABCG2-ATPase activity could be stimulated by sulfasalazine, prazosin, and topotecan, known substrates of ABCG2 in cholesterol-loaded MXR-Sf9 and MXR-M cell membranes. In contrast, ABCG2-ATPase could not be stimulated in MXR-Sf9 or in cholesterol-depleted MXR-M membranes. Moreover, cholesterol loading significantly improved the drug transport into inside-out membrane vesicles prepared from MXR-Sf9 cells. MXR-M and cholesterol-loaded MXR-Sf9 cell membranes displayed similar ABCG2-ATPase activity and vesicular transport. Our study indicates an essential role of membrane cholesterol for the function of ABCG2.

mGluR5 is involved in dendrite differentiation and excitatory synaptic transmission in NTERA2 human embryonic carcinoma cell-derived neurons

The pluripotent human embryonic carcinoma cell line NTERA2 readily differentiates into neurons when exposed to retinoic acid in vitro. These neurons show characteristic morphology with long processes and they express neuronal markers TUJ-1 and NeuN. NTERA2-derived neurons can regulate Ca2+ signalling through ionotropic glutamate (iGluR) and muscarinic receptors (mAChRs). Little is known, however, about the role of metabotropic glutamate receptors (mGluRs) in these neurons. Here we show that NTERA2-derived neurons express functional mGluR5, which is involved in Ca2+ signalling. Blocking mGluR5 activity at early stages of differentiation leads to fewer dendrites and a reduction in miniature excitatory postsynaptic currents (mEPSCs). Furthermore, cells cultured in the presence of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) show reduced N-methyl-D-aspartate (NMDA) receptor-mediated Ca2+ mobilisation but increased alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor Ca2+ permeability. During normal neuronal development, the edited GluR2 renders AMPARs Ca2+ impermeable. The increased Ca2+ permeability of AMPARs in MPEP-treated neurons is due to the reduced expression of GluR2 subunit protein. Thus, mGluR5 activity at early stages of differentiation is likely to play a role in the development of multipotent cell-derived neurons.

Developing oligodendrocytes express functional GABA(B) receptors that stimulate cell proliferation and migration

GABA(B) receptors (GABA(B)Rs) are involved in early events during neuronal development. The presence of GABA(B)Rs in developing oligodendrocytes has not been established. Using immunofluorescent co-localization, we have identified GABA(B)R proteins in O4 marker-positive oligodendrocyte precursor cells (OPCs) in 4-day-old mouse brain periventricular white matter. In culture, OPCs, differentiated oligodendrocytes (DOs) and type 2 astrocytes (ASTs) express both the GABA(B1abcdf) and GABA(B2) subunits of the GABA(B)R. Using semiquantitative PCR analysis with GABA(B)R isoform-selective primers we found that the expression level of GABA(B1abd) was substantially higher in OPCs or ASTs than in DOs. In contrast, the GABA(B2) isoform showed a similar level of expression in OPCs and DOs, and a significantly higher level in ASTs. This indicates that the expression of GABA(B1) and GABA(B2) subunits are under independent control during oligodendroglial development. Activation of GABA(B)Rs using the selective agonist baclofen demonstrated that these receptors are functionally active and negatively coupled to adenylyl cyclase. Manipulation of GABA(B)R activity had no effect on OPC migration in a conventional agarose drop assay, whereas baclofen significantly increased OPC migration in a more sensitive transwell microchamber-based assay. Exposure of cultured OPCs to baclofen increased their proliferation, providing evidence for a functional role of GABA(B)Rs in oligodendrocyte development. The presence of GABA(B)Rs in developing oligodendrocytes provides a new mechanism for neuronal-glial interactions during development and may offer a novel target for promoting remyelination following white matter injury.

Oligodendroglial metabotropic glutamate receptors are developmentally regulated and involved in the prevention of apoptosis

Oligodendrocytes (OLs) are responsible for axon myelination and are the principal cells targeted in preterm white matter injury. The cellular and molecular mechanisms involved in white matter development and immature OL injury are incompletely understood. Metabotropic glutamate receptors (mGluRs) modulate neuronal development and survival, and have recently been identified in oligodendrocyte progenitor cells (OPCs). Using the highly homogeneous CG-4 OPC line and O4 marker-immunoselected primary OLs, we established the differentiation stage-specific expression profile of mGluR3 and mGluR5 mRNAs and proteins in the oligodendroglial lineage and type-2-astrocytes (ASTs). Our quantitative analysis indicated no changes in mGluR3, but a significant down-regulation of mGluR5a mRNA and protein expression during differentiation of OPCs into OLs or ASTs. The down-regulation of mGluR5a had functional consequences, with significantly fewer OLs and ASTs than OPCs responding to the group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine with intracellular Ca(2+) concentration oscillations. Neither stimulation nor inhibition of mGluR3 or mGluR5 altered OPC migration, suggesting that these receptors do not play prominent roles in the regulation of OPC motility. The activation of mGluR5 completely protected OPCs and substantially reduced staurosporine-induced apoptosis in OLs. This suggests that the down-regulation of mGluR5 in premyelinating OLs is likely to contribute to their increased vulnerability, and that the targeting of mGluR5 may be a potential therapeutic strategy for future development.

Calcium and NeuroD2 control the development of thalamocortical communication

Donald Hebb postulated the existence of a mechanism of activity-dependent transcription and synaptic modification almost 60 years ago. While the details of this process are still unclear, a new study by Ince-Dunn et al. in this issue of Neuron indicates that NeuroD2, a calcium-regulated transcription factor, plays a central role in thalamocortical synaptic maturation.

Lateral entorhinal cortex lesions rearrange afferents, glutamate receptors, increase seizure latency and suppress seizure-induced c-fos expression in the hippocampus of adult rat

The entorhinal cortex (EC) provides the predominant excitatory drive to the hippocampal CA1 and subicular neurones in chronic epilepsy. Here we analysed the effects of one-sided lateral EC (LEC) and temporoammonic (alvear) path lesion on the development and properties of 4-aminopyridine-induced seizures. Electroencephalography (EEG) analysis of freely moving rats identified that the lesion increased the latency of the hippocampal seizure significantly and decreased the number of brief convulsions. Seizure-induced neuronal c-fos expression was reduced in every hippocampal area following LEC lesion. Immunocytochemical analysis 40 days after the ablation of the LEC identified sprouting of cholinergic and calretinin-containing axons into the dentate molecular layer. Region and subunit specific changes in the expression of ionotropic glutamate receptors (iGluRs) were identified. Although the total amount of AMPA receptor subunits remained unchanged, GluR1(flop) displayed a significant decrease in the CA1 region. An increase in NR1 and NR2B N-methyl-d-aspartate (NMDA) receptor subunits and KA-2 kainate receptor subunit was identified in the deafferented layers of the hippocampus. These results further emphasize the importance of the lateral entorhinal area in the spread and regulation of hippocampal seizures and highlight the potential role of the rewiring of afferents and rearrangement of iGluRs in the dentate gyrus in hippocampal convulsive activity.

Toxicity and degradation of benefin in chicken embryos

The herbicide formulation Flubalex (20% benefin) was applied, ROSS 308 embryonated hen eggs were treated on day 12 of incubation period. The pesticide was diluted in water to a concentration level of 3.0%, and the emulsion was injected into the air space in a volume of 0.1 ml/egg, or hen's eggs were treated by the immersion technique. Residues of benefin were measured in the samples on days 13, 15 and 19 of the incubation of chicken embryos, and morphological examinations were performed simultaneously. After the immersion treatment the mortality rate of embryos was remarkable compared to the injection treatment. Analytical chemistry data showed the concentration of the active ingredient which was 3.5 times higher on day 13 of incubation in the samples after immersion treatment than after the injection of benefin. This resulted an increased incidence rate of mortality. On day 19 of hatching period the benefin concentration was practically similar independently of treatment method. No macro- and microscopic alterations were seen.