Therapeutics for dementia and Alzheimer's disease: New directions for precision medicine.

LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Inflammation: maladies, models, mechanisms and molecules.

The continued focus of attention on the diversity of mechanisms underpinning inflammation has improved our understanding of the potential to target specific pathways in the inflammatory network to achieve meaningful therapeutic gains. In this themed issue of the British Journal of Pharmacology our scope was deliberately broad, ranging across both acute and chronic disease in various organs. Pro- and anti-inflammatory mechanisms receive attention as does the phenotype of macrophages. Whilst the manifestations of neuro-inflammation are less obvious than those in peripheral tissues, central innate and adaptive immunity in brain and the M1/M2 phenotypes of microglia are topics of special interest. The contributions to the inflammatory milieu of cytokines, chemokines and associated signalling cascades are considered. Overall, the coverage herein advances the basic science underpinning our understanding of inflammation and emphasizes its importance in different pathologies.

Astrocyte and microglial control of glutamatergic signalling: a primer on understanding the disruptive role of chronic stress.

It is now well established that chronic stress can induce significant structural remodelling of astrocytes and microglia. Until recently, however, the full significance of these morphological disturbances has remained unclear. Clues to the significance of astroglial re-organisation following stress are beginning to emerge from a compelling literature describing how astrocytes contribute to glutamatergic neurotransmission. The present review briefly summarises these two fields of research, identifies points of overlap and, in doing so, pin-points future research directions for stress neurobiology. Ultimately, understanding how chronic stress can disrupt the interactions of astrocytes and microglia with neurones has the potential in the future to improve the development of therapeutics designed to treat stress-related illnesses such as depression.

Mitochondrial pharmacology: energy, injury and beyond.

While the mitochondrion has long fascinated biologists and the sheer diversity of druggable targets has made it attractive for potential drug development, there has been little success translatable to the clinic. Given the diversity of inborn errors of metabolism and mitochondrial diseases, mitochondrially mediated oxidative stress (myopathies, reperfusion injury, Parkinson's disease, ageing) and the consequences of disturbed energetics (circulatory shock, diabetes, cancer), the potential for meaningful gain with novel drugs targeting mitochondrial mechanisms is huge both in terms of patient quality of life and health care costs. In this themed issue of the British Journal of Pharmacology, we highlight the key directions of the contemporary advances in the field of mitochondrial biology, emerging drug targets and new molecules which are close to clinical application. Authors' contributions are diverse both in terms of species and organs in which the mitochondrially related studies are performed, and from the perspectives of mechanisms under study. Defined roles of mitochondria in disease are updated and previously unknown contributions to disease are described in terms of the interface between basic science and pathological relevance.

Links between L-glutamate transporters, Na+/K+-ATPase and cytoskeleton in astrocytes: evidence following inhibition with rottlerin.

Astrocytes are plastic cells that play key roles in brain physiology and pathology, including via their glutamate transporters, excitatory amino acid transporter (EAAT)1 and EAAT2, maintaining low extracellular glutamate concentrations and protecting against excitotoxic neuronal injury. Alterations in cell surface expression of EAATs and astrocytic cytoskeleton are important for regulating transporter activity. This study employed the actions of rottlerin, to interrogate the regulation of EAAT activity, expression and localization, and interfaces with Na(+)/K(+)-ATPase and astrocytic morphology. EAAT activity and expression were determined in primary cultures of mouse astrocytes in the presence of and after rottlerin removal, with or without trafficking inhibitors, using uptake ([(3)H]d-aspartate, (86)Rb(+)) and molecular analyses. Astrocytic morphology and EAAT localization were investigated using Western blotting and immunocytochemistry, in concert with image analysis of glial fibrillary acidic protein, F-actin and EAAT1/2. Rottlerin induced a time-dependent inhibition of glutamate transport (Vmax). Rapid changes in cytoskeletal arrangement were observed and immunoblotting revealed increases in EAAT2 total and cell surface expression, despite reduced EAAT activity. Rottlerin-induced inhibition was reversible and its rate was increased by monensin co-treatment. Rottlerin inhibited, while monensin stimulated Na(+)/K(+)-ATPase. Removal of rottlerin rapidly elevated Na(+)/K(+)-ATPase activity beyond control levels, while co-treatment with monensin failed to stimulate the Na(+)/K(+)-ATPase. These data reveal inhibition of EAAT activity by rottlerin is not associated with loss of EAATs at the cell surface, but rather linked to cytoskeletal rearrangement, and inhibition of the Na(+)/K(+)-ATPase. Rapid recovery of Na(+)/K(+)-ATPase activity, and subsequent restoration of glutamate uptake indicates that astrocytic morphology and EAAT activity are co-regulated by a tightly coupled, homeostatic relationship between l-glutamate uptake, the electrochemical gradient and the activity of the Na(+)/K(+)-ATPase.

The Concise Guide to PHARMACOLOGY 2013/14: overview.

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties from the IUPHAR database. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. This compilation of the major pharmacological targets is divided into seven areas of focus: G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors & Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and GRAC and provides a permanent, citable, point-in-time record that will survive database updates.

The Rho kinase inhibitor Fasudil up-regulates astrocytic glutamate transport subsequent to actin remodelling in murine cultured astrocytes.

BACKGROUND AND PURPOSE: Glutamate transporters play a major role in maintaining brain homeostasis and the astrocytic transporters, EAAT1 and EAAT2, are functionally dominant. Astrocytic excitatory amino acid transporters (EAATs) play important roles in various neuropathologies wherein astrocytes undergo cytoskeletal changes. Astrocytic plasticity is well documented, but the interface between EAAT function, actin and the astrocytic cytoskeleton is poorly understood. Because Rho kinase (ROCK) is a key determinant of actin polymerization, we investigated the effects of ROCK inhibitors on EAAT activity and astrocytic morphology. EXPERIMENTAL APPROACH: The functional activity of glutamate transport was determined in murine cultured astrocytes after exposure to the ROCK inhibitors Fasudil (HA-1077) and Y27632 using biochemical, molecular and morphological approaches. Cytochemical analyses assessed changes in astrocytic morphology, F-/G-actin, and localizations of EAAT1/2. RESULTS: Fasudil and Y27632 increased [(3)H]-D-aspartate (D-Asp) uptake into astrocytes, and the action of Fasudil was time-dependent and concentration-related. The rapid stellation of astrocytes (glial fibrillary acidic protein immunocytochemistry) induced by Fasudil was accompanied by reduced phalloidin staining of F-actin and increased V(max) for [(3)H]-D-Asp uptake. Immunoblotting after biotinylation demonstrated that Fasudil increased the expression of EAAT1 and EAAT2 on the cell surface. Immunocytochemistry indicated that Fasudil induced prominent labelling of astrocytic processes by EAAT1/2. CONCLUSION AND IMPLICATIONS: These data show for the first time that ROCK plays a major role in determining the cell surface expression of EAAT1/2, providing new evidence for an association between transporter function and astrocytic phenotype. ROCK inhibitors, via the actin cytoskeleton, effect a consequent elevation of glutamate transporter function - this activity profile may contribute to their beneficial actions in neuropathologies.

Differential insult-dependent recruitment of the intrinsic mitochondrial pathway during neuronal programmed cell death.

Programmed cell death contributes to neurological diseases and may involve mitochondrial dysfunction with redistribution of apoptogenic proteins. We examined neuronal death to elucidate whether the intrinsic mitochondrial pathway and the crosstalk between caspase-dependent/-independent injury was differentially recruited by stressors implicated in neurodegeneration. After exposure of cultured cerebellar granule cells to various insults, the progression of injury was correlated with mitochondrial involvement, including the redistribution of intermembrane space (IMS) proteins, and patterns of protease activation. Injury occurred across a continuum from Bax- and caspase-dependent (trophic- factor withdrawal) to Bax-independent, calpain-dependent (excitotoxicity) injury. Trophic-factor withdrawal produced classical recruitment of the intrinsic pathway with activation of caspase-3 and redistribution of cytochrome c, whereas excitotoxicity induced early redistribution of AIF and HtrA2/Omi, elevation of intracellular calcium and mitochondrial depolarization. Patterns of engagement of neuronal programmed cell death and the redistribution of mitochondrial IMS proteins were canonical, reflecting differential insult-dependencies.

Transmembrane protein 50b (C21orf4), a candidate for Down syndrome neurophenotypes, encodes an intracellular membrane protein expressed in the rodent brain.

Transmembrane protein 50b, Tmem50b, previously referred to as C21orf4, encodes a predicted transmembrane protein and is one of few genes significantly over-expressed during cerebellar development in a Down syndrome mouse model, Ts1Cje. In order to assess potential mechanisms by which Tmem50b could contribute to Down syndrome-related phenotypes, we determined the expression patterns of Tmem50b mRNA, as well as Tmem50b protein distribution, expression and subcellular localization. In situ hybridization in mice at embryonic day 14.5 showed cortical plate and spinal cord mRNA expression. By postnatal day 7, strong mRNA expression was seen in the cerebellum, hippocampus and olfactory bulb, with diffuse cortical expression. Quantitative PCR of adult mouse tissue showed Tmem50b mRNA expression in the brain, heart and testis. A rabbit polyclonal antibody was generated against Tmem50b and rat and mouse tissue screening by Western blot, and immunohistochemistry showed that protein expression concurred with mRNA expression. Double immunofluorescence revealed that Tmem50b is highly expressed in rat and mouse glial fibrillary acidic protein-positive cells in vivo and in vitro, but less so in neuronal MAP2- or beta-tubulin II-positive cells in vitro. Tmem50b is invariably expressed in cultured mouse neural precursor cells. In adult mouse cerebellum sections, Tmem50b immunoreactivity was found in Purkinje and Golgi cell somata and in Bergmann glial processes. Electron microscopy confirmed that Tmem50b was present on endoplasmic reticulum (ER) and Golgi apparatus membranes. Results indicate that Tmem50b is a developmentally-regulated intracellular ER and Golgi apparatus membrane protein that may prove important for correct brain development through functions associated with precursor cells and glia.

Neuropharmacology of addiction--setting the scene.

Addiction is a complex disorder, affecting not only the individual addict, but also their family and the community at large. While therapeutic strategies are available for the treatment of some forms of substance abuse/dependence, these are not without problems and are not universally efficacious. Moreover, in some instances (for example, cocaine addiction), there are still no medications specifically registered as treatment options. In this themed issue of the British Journal of Pharmacology, we highlight a number of addictions from a pharmacological perspective, with an emphasis on both mechanism and potential therapeutic approaches that are either under development or reflect preclinical work. As such, the authors endeavour to describe the latest thinking on the neural theory of addiction and corresponding novel pharmacotherapeutic targets, and in this way to set the stage for future advances in research and drug development. In addition, we have also attempted to draw attention to the clinicians' perspective in terms of the interface between basic science and care provision.

Comparison of [(3)H]-(2S,4R)-4-methylglutamate and [(3)H]D-aspartate as ligands for binding and autoradiographic analyses of glutamate transporters.

While studies with [(3)H]D-aspartate ([(3)H]d-Asp) illustrate specific interactions with excitatory amino acid transporters (EAATs), new insights into the pharmacological characteristics and localization of specific EAAT subtypes depend upon the availability of novel ligands. One such ligand is [(3)H]-(2S,4R)-4-methylglutamate ([(3)H]4MG) which labels astrocytic EAATs in homogenate binding studies. This study examined the utility of [(3)H]4MG for binding and autoradiography in coronal sections of rat brain. Binding of [(3)H]4MG was optimal in 5mM HEPES buffer containing 96 mM NaCl, pH 7.5. Specific binding of [(3)H]4MG exhibited two components, but was to a single site when glutamate receptor (GluR) sites were masked with kainate (KA; 1 microM): t(1/2) approximately 5 min, K(d) 250 nM and B(max) 5.4 pmol/mg protein. Pharmacological studies revealed that [(3)H]4MG, unlike [(3)H]d-Asp, labeled both EAAT and ionotropic GluR sites. Further studies employed 6-cyano-7-nitroquinoxaline (30 microM) to block GluR sites, but selective EAAT ligands displayed lower potency than expected for binding to transporters relative to drugs possessing mixed transporter/receptor activities. Autoradiography in conjunction with densitometry with [(3)H]4MG and [(3)H]d-Asp revealed wide, but discrete distributions in forebrain; significant differences in binding levels were found in hippocampus, nucleus accumbens and cortical sub-areas. Although EAAT1 and EAAT2 components were detectable using 3-methylglutamate and serine-O-sulphate, respectively, the majority of [(3)H]4MG binding was to KA-related sites. Overall, in tissue sections [(3)H]4MG proved unsuitable for studying the autoradiographic localization of EAATs apparently due to its inability to selectively discriminate Na(+)-dependent binding to Glu transporters.

Transporters for L-glutamate: an update on their molecular pharmacology and pathological involvement.

L-Glutamate (Glu) is the major excitatory neurotransmitter in the mammalian CNS and five types of high-affinity Glu transporters (EAAT1-5) have been identified. The transporters EAAT1 and EAAT2 in glial cells are responsible for the majority of Glu uptake while neuronal EAATs appear to have specialized roles at particular types of synapses. Dysfunction of EAATs is specifically implicated in the pathology of neurodegenerative conditions such as amyotrophic lateral sclerosis, epilepsy, Huntington's disease, Alzheimer's disease and ischemic stroke injury, and thus treatments that can modulate EAAT function may prove beneficial in these conditions. Recent advances have been made in our understanding of the regulation of EAATs, including their trafficking, splicing and post-translational modification. This article summarises some recent developments that improve our understanding of the roles and regulation of EAATs.

Lactacystin-induced apoptosis of cultured mouse cortical neurons is associated with accumulation of PTEN in the detergent-resistant membrane fraction.

The tumor suppressor function of PTEN is attributed to its phospholipid phosphatase activity that dephosphorylates the plasma membrane phosphatidylinositol-(3,4,5)-triphosphate [PtdIns(3,4,5)P3]. Implicit in this notion is that PTEN needs to be targeted to the plasma membrane to dephosphorylate PtdIns(3,4,5)P3. However, the recruitment of PTEN to the plasma membrane is not fully understood. Here, we demonstrate PTEN accumulation in the detergent-insoluble fraction of neuronal cells in response to treatment by the proteasome inhibitor lactacystin. First, lactacystin induces apoptosis and the activation of caspase-3 in cultured cortical neurons. Second, PTEN undergoes proteolysis to form a truncated 50-kDa form that lacks parts of its C-terminal tail. Third, the truncated PTEN is stably associated with the detergent-insoluble fraction in which the plasma membrane marker protein flotillin-1 resides. Taken together, our results suggest that truncation and accumulation of PTEN to the detergent-insoluble membrane fraction are two events associated with the apoptotic signals of the proteasome inhibitor in cortical neurons.

Sodium channel blocking activity of AM-36 and sipatrigine (BW619C89): in vitro and in vivo evidence.

Sodium channel blockers are neuroprotective against cerebral ischemia in animal models. A novel neuroprotective compound AM-36, when screened for activity at the most common receptor and ion channel binding sites, revealed activity at site 2 Na+ channels. Studies then investigated this Na+ channel blocking activity in vitro and in vivo relative to other Na+ channel blockers, including the neuroprotective agent sipatrigine (BW619C89). AM-36 inhibited batrachotoxinin (BTX)-sensitive Na+ channel binding in rat brain homogenates with an IC50 of 0.28 microM. Veratridine (100 microM)-induced neurotoxicity in murine cerebellar granule cells was completely inhibited by AM-36 (1.7 microM) compared to only partial inhibition by sipatrigine (26 microM). Veratridine-stimulated glutamate release, as measured through a microdialysis probe in the cortex of anesthetised rats, was inhibited by 90% by superfusion of AM-36 (1000 microM). In the endothelin-1 (ET-1) model of middle cerebral artery occlusion (MCAo) in conscious rats, both AM-36 (6 mg/kg i.p.) and sipatrigine (10 mg/kg i.p.) 30 min post-MCAo significantly reduced cortical, but not striatal infarct volume. As the refractiveness of the striatum is likely to be dependent on the route and time of drug administration, AM-36 (1 mg/kg i.v.) was administered 3 or 5 h after MCAo and significantly reduced both cortical and striatal infarct volumes. The present studies demonstrate Na+ channel blocking activity of AM-36 both in vitro and in vivo, together with significant neuroprotection when administration is delayed up to 5 h following experimental stroke.

Excitotoxic profiles of novel, low-affinity kainate receptor agonists in primary cultures of murine cerebellar granule cells.

The involvement of low-affinity kainate (KA) receptors in neuronal injury was investigated by employing a variety of agonists active at GluR5-7. Their excitotoxic profiles were determined in primary cultures of cerebellar granule cells, which abundantly expressed low-affinity KA receptors, and in the absence of any AMPA receptor-mediated neurotoxicity. Neurotoxicity induced by these compounds was analysed by phase contrast microscopy, a cell viability assay, the TUNEL technique (apoptosis), and by employing propidium iodide (PI; necrosis). All agonists induced concentration-dependent neurotoxicity, with rank order (EC(50) values; microM): (S)-iodowillardiine (IW) 0.2>(2S,4R)-4-methylglutamate (4-MG) 36>(2S,4R,6E)-2-amino-4-carboxy-7-(2-naphthyl)hept-6-enoic acid (LY339434) 46>KA 74>(RS)-2-amino-3-(hydroxy-5-tert-butylisoxazol-4yl)propanoic acid (ATPA) 88. IW exposure resulted in apoptosis at lower concentrations (<30 microM) and necrosis at higher concentrations, both of which were attenuated by CNQX (50 microM), but not MK-801 (10 microM). ATPA-mediated neurotoxicity was purely apoptotic and was attenuated by the non-NMDA receptor antagonists. Both IW and ATPA induced injury with the morphological characteristics of apoptosis shown by the presence of TUNEL-positive neurones. LY339434-mediated neuronal injury was only attenuated by MK-801 and was necrotic in nature. Similarly, 4-MG (>30 microM) exposure caused necrosis that was partially attenuated by MK-801 (10 microM) and CNQX (50 microM). The patterns of neurotoxicity possessed a complex pharmacological profile, demonstrated an apoptotic-necrotic continuum and were inconsistent with past findings, further outlining the importance of characterizing novel compounds at native receptors. ATPA and to a lesser extent IW appear to be suitable drugs for low-affinity KA receptors. Since toxicity-mediated by low-affinity KA receptors seem likely to contribute to neurodegenerative conditions, our study importantly examines the excitotoxic profile of these novel agonists.

Anti-epileptic activity of group II metabotropic glutamate receptor agonists (--)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268) and (--)-2-thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY389795).

The selective group II metabotropic glutamate receptor (mGlu(2/3)) agonists (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268) and (-)-2-thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY389795) have been evaluated as anti-epileptic drugs in dilute brown agouti (DBA/2) mice, lethargic (lh/lh) mice, genetically epilepsy-prone-9 (GEP) rats and amygdala-kindled rats. Sound-induced clonic seizures in DBA/2 mice were transiently inhibited by both agonists intracerebroventricularly (i.c.v.), LY379268 ED(50)=0.08 [0.02-0.33]nmol and LY389795 ED(50)=0.82 [0.27-3.24]nmol or intraperitoneally (i.p.), LY379268 ED(50)=2.9 [0.9-9.6]mg/kg and LY389795 ED(50)=3.4 [1.0-11.7]mg/kg. Both mGlu(2/3) agonists inhibited seizures induced by the group I mGlu receptor agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG), where LY379268, i.c.v. ED(50)=0.3 [0.02-5.0]pmol and LY389795, i.c.v. ED(50)=0.03 [0.05-0.19]nmol. The spike and wave discharge (SWD) duration of absence seizures in lh/lh mice was significantly reduced by both agonists at 1 and 10nmol (i.c.v.) up to 90min following infusion. The electrically induced seizure score and afterdischarge duration of amygdala-kindled rats was partially inhibited by the agonists 30min after i.p. injection of 10mg/kg. The agonists did not inhibit sound-induced seizures in GEP rats (0.1-1mg/kg, 30min 1h, i.p.), but were proconvulsant following sound stimulus (> or =0.1mg/kg). These findings identify a potential role for mGlu(2/3) agonists in the amelioration of generalised and partial epileptic seizures.

Group II mGlu receptor agonists fail to protect against various neurotoxic insults induced in murine cortical, striatal and cerebellar granular pure neuronal cultures.

Since group II metabotropic glutamate (mGlu) receptors are a potential target for the amelioration of neuronal injury, we evaluated the ability of group II mGlu receptor agonists to attenuate toxicity induced by various insults in cortical, striatal and cerebellar granular (CGCs) pure neuronal cultures. The three cultures, when maintained under serum-free, anti-oxidant rich conditions for up to 13 days in vitro (div) were shown by immunocytochemistry to contain a maximum of 2-7% glia. At 6, 9 and 13 div a graded pattern of injury to cortical and striatal cultures was achieved with either hydrogen peroxide (60-110 microM), staurosporine (1 microM), N-methyl-D-aspartate (NMDA, 70 microM), alpha-amino-3-hydroxy-methylisoxazole-4-propionate (AMPA, 100 microM) or kainate (100 microM) over either 4, 24 or 48 h. CGCs were similarly exposed to low K(+) (5.4 mM KCl). Cell viability was examined via phase-contrast microscopy and assessed by a 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide assay. Treatment with group II mGlu receptor agonists (1-300 microM), 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate ((2R,4R)-APDC), (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I), (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) and N-acetylaspartylglutamate (NAAG) failed to attenuate the toxicity. Pretreatment of cultures with the agonists and treatment following acute insult also failed to attenuate toxicity. Further investigations demonstrated the presence of second messenger activation whereby (2R,4R)-APDC reduced forskolin-stimulated production of cAMP in each culture. Thus, despite receptor coupling to intracellular signaling cascades, and regardless of culture development, agonist concentration, extent and mode of injury, group II mGlu receptor agonists were unable to protect against injury induced in cortical, striatal and cerebellar granular pure neuronal cultures. This result is in contrast to mixed cultures of neurones and glia and implies an important role for glia in the neuroprotective effects of group II mGlu receptor agonists.

[(3)H](2S,4R)-4-Methylglutamate: a novel ligand for the characterization of glutamate transporters.

[(3)H](2S,4R)-4-Methylglutamate ([(3)H]4MG), used previously as a ligand for low-affinity kainate receptors, was employed to establish a binding assay for glutamate transporters (GluTs), as 4MG has also been shown to have affinity for the glial GluTs, GLT1 and GLAST. In rat brain membrane homogenates in the presence of Na(+) ions at 4 degrees C, specific binding of [(3)H]4MG was rapid and saturable (t(1/2) approximately 15 min), representing > 90% of total binding. Dissociation of [(3)H]4MG occurred in a biphasic manner, however, saturation studies and Scatchard analysis indicated a single site of binding (n(H) = 0.85) and a K(d) of 6.2 +/- 0.8 microM with a B(max) of 111.8 +/- 23.8 pmol/mg protein. Specific binding of [(3)H]4MG was Na(+)-dependent and inhibited by K(+) and HCO(3-). Pharmacological inhibition with compounds acting at GluTs revealed that Glu, D- and L-aspartate, L-serine-O-sulfate and Ltrans-pyrrolidine-2,4-dicarboxylate fully displaced specific binding. Drugs having preferential affinity for GLT1, kainate, dihydrokainate and Lthreo-3-methylglutamate, all inhibited approximately 40% of specific binding. The inhibition pattern of L-serine-O-sulfate in the presence of a saturating concentration of dihydrokainate was suggestive of [(3)H]4MG also labelling GLAST. 6-Cyano-7-nitroquinoxaline, a kainate receptor antagonist, and a range of Glu receptor agonists and antagonists failed to significantly inhibit [(3)H]4MG binding. The pharmacological profile of binding of [(3)H]4MG resembled that found for [(3)H]D-aspartate, a ligand specific for GluTs, reinforcing the hypothesis that [(3)H]4MG was labelling GluTs in this assay. Together, these data illustrate the development of an efficient, economic binding assay that is suitable for the characterization of different subtypes of GLuTs.

Anticonvulsant activity of 3,4-dicarboxyphenylglycines in DBA/2 mice.

The 3,4-dicarboxyphenylglycines (3,4-DCPG) inhibit sound-induced seizures in DBA/2 mice with the racemate being notably more potent than either isomer (ED(50) (nmol, i.c.v.)): (RS)-3,4-DCPG (0.004; 86 mg/kg, i.p.)>>the mGlu(8) agonist (S)-3,4-DCPG (0.11)>the AMPA antagonist (R)-3,4-DCPG (0.38). A potentiation of anticonvulsant activity between AMPA and mGlu(8) receptors was confirmed by combining (R)-3,4-DCPG with the mGlu(8) agonist (RS)-4-phosphonophenylglycine. This potentiating mechanism provides a novel strategy for the treatment of epileptic seizures.