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Biomedical subjects

G L Collingridge

Publications and source records attributed to G L Collingridge.

At least 19 recordsLinked to original sources
PubMed1999

Rapid internalization and surface expression of a functional, fluorescently tagged G-protein-coupled glutamate receptor.

l-Glutamate is the principal excitatory neurotransmitter in the vertebrate central nervous system, where it mediates many of its actions via G-protein-coupled metabotropic glutamate (mGlu) receptors. Since little is known about the dynamics of mGlu receptors at the plasma membrane, we have constructed a fusion protein comprising the mGlu receptor subtype 1alpha (mGlu1alpha) and green fluorescent protein (GFP). Using imaging of Ca2+ release from intracellular stores as a functional assay, the agonist pharmacology of this fluorescently tagged receptor was found to be similar to that of the wild-type receptor when expressed in HEK-293 cells. Receptor movement and function were measured simultaneously by combined imaging of Ca2+, using fura-red, and GFP fluorescence in single cells. Exposure to agonist induced a rapid loss of up to 30% of membrane-associated fluorescence, with a corresponding decrease in the functional response. Following removal of the agonist there was recovery of both the membrane fluorescence and the functional response. These data suggest that the surface expression of G-protein-coupled glutamate receptors might be rapidly regulated in response to agonist activation.

Biological Transport↗
PubMed1999

Expression of early hippocampal CA1 LTP does not lead to changes in AMPA-EPSC kinetics or sensitivity to cyclothiazide.

We have analysed whether the expression of long-term potentiation (LTP) in rat hippocampal CA1 neurons involves a change in the kinetics of (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (EPSCs) (AMPA-EPSCs) or their susceptibility to the AMPA receptor modulator cyclothiazide. AMPA-EPSCs in the CA1 region were evoked by alternate stimulation of two independent Schaffer collateral-commissural inputs of slices of adult rat hippocampus. In the current-clamp mode a strong tetanus (100 Hz, 1 s) applied to one input (input I) induced stable LTP of AMPA-EPSCs in this input, while the control input (input II) remained unaffected. For neither input were EPSC rise time and decay kinetics significantly changed. The application of cyclothiazide prolonged the rise time and the decay time constants of the AMPA-EPSCs in both control and potentiated inputs to the same extent (Input I-rise time: 198+/-8%, decay: 148+/-12%; input II-rise time: 212+/-14%, decay: 144+/-19%; n=8). Furthermore, when present during tetanization cyclothiazide did not occlude LTP, suggesting that cyclothiazide and tetanic stimulation enhance AMPA-EPSCs via independent mechanisms. Our findings argue against changes in (de-)activation or desensitization of AMPA receptors as the molecular basis for the expression of LTP.

Animals↗
PubMed1999

Mechanisms contributing to the deficits in hippocampal synaptic plasticity in mice lacking amyloid precursor protein.

Abnormal processing of amyloid precursor protein (APP), in particular the generation of beta-amyloid (Abeta) peptides, has been implicated in the pathogenesis of Alzheimer's disease. This study examined the consequences of deleting the APP gene on hippocampal synaptic plasticity, and upon the biophysical properties of morphologically identified neurones in APP-null mice. The hippocampus of APP-null mice had a characteristic increase in gliosis throughout the CA1 region and a disruption of staining for the dendritic marker MAP2 and the presynaptic marker synaptophysin. The disruption of MAP2 staining was associated with a significant reduction in overall dendritic length and projection depth of biocytin labeled CA1 neurones. In two groups of APP-null mice that were examined at 8-12 months, and 20-24 months of age, there was an impairment in the formation of long-term potentiation (LTP) in the CA1 region compared to isogenic age matched controls. This LTP deficit was not associated with an alteration in the amplitude of EPSPs at low stimulus frequencies (0.033 Hz) or facilitation during a 100 Hz stimulus train, but was associated with a reduction in post-tetanic potentiation. Paired-pulse depression of GABA-mediated inhibitory post-synaptic currents was also attenuated in APP-null mice. These data demonstrate that the impaired synaptic plasticity in APP deficient mice is associated with abnormal neuronal morphology and synaptic function within the hippocampus.

Aging↗
PubMed1999

A CaMKII inhibitor, KN-62, facilitates DHPG-induced LTD in the CA1 region of the hippocampus.

We have shown previously that activation of mGlu receptors using a group I specific mGlu receptor agonist, (R,S)-3,5-dihydroxyphenylglycine (DHPG), can induce long-term depression (LTD) in the CA1 region of the hippocampus (Palmer et al., 1997). We now report that DHPG-induced LTD is facilitated by treatment with KN-62, an inhibitor of certain Ca2+/calmodulin-dependent protein kinases (CaMKs), including CaMKII.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1999

Synaptic depression induced by pharmacological activation of metabotropic glutamate receptors in the perirhinal cortex in vitro.

The perirhinal cortex is crucially involved in various forms of learning and memory. Decrements in neuronal responsiveness occur in the perirhinal cortex with stimulus repetition during visual recognition performance. However, very little is known concerning the underlying mechanisms of synaptic transmission and plasticity in this cortical region. In this study, we provide evidence demonstrating the presence of functional group I, II and III metabotropic glutamate receptors in the rat perirhinal cortex in vitro. Furthermore, the results demonstrate long-lasting synaptic depression in the perirhinal cortex. Extracellular synaptic responses were recorded from superficial layers of the perirhinal cortex directly below the rhinal sulcus, in response to electrical stimuli delivered in the superficial or intermediate layers to the entorhinal or temporal cortex sides of the rhinal sulcus. Evoked synaptic potentials were depressed during bath perfusion of each of the following: the broad-spectrum metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid, the selective group I agonist (R,S)-3,5-dihydroxyphenylglycine, the group II agonist (2S,1'R,2'R,3'R)-(2',3'-dicarboxycyclopropyl)glycine and the group III agonist (S)-2-amino-4-phosphonobutanoate. Furthermore, there was a long-lasting depression of synaptic transmission following washout of (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid, (R,S)-3,5-dihydroxyphenylglycine or (2S,1'R,2'R,3'R)-(2',3'-dicarboxy-cyclopropyl)glycine. Activation of group III metabotropic glutamate receptors by (S)-2-amino-4-phosphonobutanoate did not result in long-lasting changes in synaptic transmission. Thus, the pharmacological activation of metabotropic glutamate receptors can produce short- or long-term changes in synaptic transmission in the perirhinal cortex. It is possible therefore, that metabotropic glutamate receptors are involved in the decrement in neuronal responsiveness associated with visual recognition in the perirhinal cortex.

Animals↗
PubMed1999

Surface expression of AMPA receptors in hippocampal neurons is regulated by an NSF-dependent mechanism.

Here, we show that disruption of N-ethylmaleimide-sensitive fusion protein- (NSF-) GluR2 interaction by infusion into cultured hippocampal neurons of a blocking peptide (pep2m) caused a rapid decrease in the frequency but no change in the amplitude of AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs). N-methyl-D-aspartate (NMDA) receptor-mediated mEPSCs were not changed. Viral expression of pep2m reduced the surface expression of alpha-amino-3-hydroxy-5-methyl-isoxazolepropionate (AMPA) receptors, whereas NMDA receptor surface expression in the same living cells was unchanged. In permeabilized neurons, the total amount of GluR2 immunoreactivity was unchanged, and a punctate distribution of GluR2 was observed throughout the dendritic tree. These data suggest that the NSF-GluR2 interaction is required for the surface expression of GluR2-containing AMPA receptors and that disruption of the interaction leads to the functional elimination of AMPA receptors at synapses.

Adenoviridae↗
PubMed1999

Roles of metabotropic glutamate receptors in LTP and LTD in the hippocampus.

Metabotropic L-glutamate receptors are involved in various forms of synaptic plasticity in the hippocampus. The use of a new antagonist (LY341495) that blocks all known metabotropic L-glutamate receptors in the brain, together with subtype-selective antagonists, has identified multiple roles both for cloned and novel metabotropic L-glutamate receptors in hippocampal long-term potentiation and long-term depression.

Animals↗
PubMed1999

Antagonist activity of alpha-substituted 4-carboxyphenylglycine analogues at group I metabotropic glutamate receptors expressed in CHO cells.

1. We have investigated the antagonist properties of 6 alpha-substituted phenylglycine analogues based on the structure of 4-carboxyphenylglycine (4-CPG) for group I metabotropic glutamate receptors (mGlu1alpha and mGlu5a) permanently expressed in CHO cells. 2. (S)-4-CPG and (S)-MCPG were the most selective mGlu1alpha receptor antagonists. Longer chain alpha-carbon substitutions resulted in a progressive loss of antagonist affinity at mGlu1alpha receptors but not at mGlu5a receptors. Thus mGlu1alpha receptor antagonists require small aliphatic groups at the alpha-position. Alpha-cyclopropyl-4-CPG showed a tendency towards mGlu5a selectivity, suggesting that bulky groups at this position may favour mGlu5a receptor antagonism. 3. We demonstrate that the mGlu5a receptor displays agonist-dependent antagonism. L-glutamate-induced Ca2+ release in mGlu5a receptor expressing cells was more susceptible to antagonism by cyclic alpha-carbon derivatives than (S)-3,5-dihydroxyphenylglycine (DHPG)-induced Ca2+ release in the same cell line. 4. The data presented suggests that mGlu1alpha and mGlu5a receptors have different steric and/or conformational requirements for the binding of antagonists and different amino acids which could interact with agonists. 5. These phenylglycine analogues could provide leads for the development of subtype selective antagonists.

Animals↗
PubMed1998

A characterization of muscarinic receptor-mediated intracellular Ca2+ mobilization in cultured rat hippocampal neurones.

1. The properties of muscarinic receptor-mediated Ca2+ mobilization were investigated in hippocampal cultures using fluorescent imaging techniques. 2. Somatic responses to carbachol (1-10 microM) were observed in 21 % of neurones under control conditions (5.4 mM K+, 1. 8 mM Ca2+, 0.5-1 microM tetrodotoxin). Smaller responses were observed in Ca2+-free medium. 3. In cells where responses to carbachol were absent under control conditions, responses were often observed following depolarization with high extracellular K+ (16. 2-25 mM). These responses decreased in magnitude with time after the depolarizing episode. Mobilization of Ca2+ from stores using caffeine (50 mM) exhibited similar properties. 4. Carbachol responses were greatly facilitated in the presence of moderate elevations in extracellular K+ or Ca2+ levels (2- or 3-fold, respectively). These conditions were usually, but not always, associated with a small increase in cytosolic Ca2+ levels (< 50 nM). 5. Muscarinic responses in 10.8 mM K+ were inhibited by 80-95 % in the presence of the L-type voltage-gated Ca2+ channel antagonists nitrendipine (2-5 microM) or nifedipine (10 microM). Depletion of intracellular Ca2+ stores with thapsigargin (2-10 microM) blocked responses. 6. Oscillatory Ca2+ mobilizing responses were observed in some cells. Their expression was facilitated by moderate cytosolic Ca2+ elevations and by increasing the duration of carbachol exposure. 7. Ca2+ mobilizing responses were also observed in dendritic regions. These were smaller than somatic responses, but had faster decay kinetics. 8. In conclusion, muscarinic receptor-mediated Ca2+ mobilization in cultured hippocampal neurones shows a strong Ca2+ dependence. Moderate intracellular Ca2+ rises greatly facilitate muscarinic responses and uncover, in some cells, oscillatory Ca2+ mobilization. These effects appear to reflect the loading state of intracellular Ca2+ stores.

Animals↗
PubMed1998

Modulation of AMPA receptor unitary conductance by synaptic activity.

Activity-dependent alteration in synaptic strength is a fundamental property of the vertebrate central nervous system and is thought to underlie learning and memory. The most extensively studied model of activity-dependent synaptic plasticity is long-term potentiation (LTP) of glutamate-responsive (glutamatergic) synapses, a widespread phenomenon involving multiple mechanisms. The best characterized form of LTP occurs in the CA1 region of the hippocampus, in which LTP is initiated by transient activation of NMDA (N-methyl-D-aspartate) receptors and is expressed as a persistent increase in synaptic transmission through AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors. This increase is due, at least in part, to a postsynaptic modification of AMPA-receptor function; this modification could be caused by an increase in the number of receptors, their open probability, their kinetics or their single-channel conductance. Here we show that the induction of LTP in the CA1 region of the hippocampus is often associated with an increase in single-channel conductance of AMPA receptors. This shows that elementary channel properties can be rapidly modified by synaptic activity and provides an insight into one molecular mechanism by which glutamatergic synapses can alter their strength.

Animals↗
PubMed1998

The potent mGlu receptor antagonist LY341495 identifies roles for both cloned and novel mGlu receptors in hippocampal synaptic plasticity.

Understanding the roles of metabotropic glutamate (mGlu) receptors has been severely hampered by the lack of potent antagonists. LY341495 (2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-y l)propanoic acid) has been shown to block group II mGlu receptors in low nanomolar concentrations (Kingston, A.E., Ornstein, P.L., Wright, R.A., Johnson, B.G., Mayne, N.G., Burnett, J.P., Belagaje, R., Wu, S., Schoepp, D.D., 1998. LY341495 is a nanomolar potent and selective antagonist at group II metabotropic glutamate receptors. Neuropharmacology 37, 1-12) but can be used in higher concentrations to block all hippocampal mGlu receptors, identified so far by molecular cloning (mGlu1-5,7,8). Here we have further characterised the mGlu receptor antagonist activity of LY341495 and have used this compound to investigate roles of mGlu receptors in hippocampal long-term potentiation (LTP) and long-term depression (LTD). LY341495 competitively antagonised DHPG-stimulated PI hydrolysis in AV12-664 cells expressing either human mGlu1 or mGlu5 receptors with Ki-values of 7.0 and 7.6 microM, respectively. When tested against 10 microM L-glutamate-stimulated Ca2+ mobilisation in rat mGlu5 expressing CHO cells, it produced substantial or complete block at a concentration of 100 microM. In rat hippocampal slices, LY341495 eliminated 30 microM DHPG-stimulated PI hydrolysis and 100 microM (1S,3R)-ACPD-inhibition of forskolin-stimulated cAMP formation at concentrations of 100 and 0.03 microM, respectively. In area CA1, it antagonised DHPG-mediated potentiation of NMDA-induced depolarisations and DHPG-induced long-lasting depression of AMPA receptor-mediated synaptic transmission. LY341495 also blocked NMDA receptor-independent depotentiation and setting of a molecular switch involved in the induction of LTP; effects which have previously been shown to be blocked by the mGlu receptor antagonist (S)-MCPG. These effects may therefore be due to activation of cloned mGlu receptors. In contrast, LY341495 did not affect NMDA receptor-dependent homosynaptic LTD; an effect which may therefore be independent of cloned mGlu receptors. Finally, LY341495 failed to antagonise NMDA receptor-dependent LTP and, in area CA3, NMDA receptor-independent, mossy fibre LTP. Since in the same inputs these forms of LTP were blocked by (S)-MCPG, a novel type of mGlu receptor may be involved in their induction.

Aging↗
PubMed1998

NSF binding to GluR2 regulates synaptic transmission.

Here, we show that N-ethylmaleimide-sensitive fusion protein (NSF) interacts directly and selectively with the intracellular C-terminal domain of the GluR2 subunit of AMPA receptors. The interaction requires all three domains of NSF but occurs between residues Lys-844 and Gln-853 of rat GluR2, with Asn-851 playing a critical role. Loading of decapeptides corresponding to the NSF-binding domain of GluR2 into rat hippocampal CA1 pyramidal neurons results in a marked, progressive decrement of AMPA receptor-mediated synaptic transmission. This reduction in synaptic transmission was also observed when an anti-NSF monoclonal antibody (mAb) was loaded into CA1 neurons. These results demonstrate a previously unsuspected direct interaction in the postsynaptic neuron between two major proteins involved in synaptic transmission and suggest a rapid NSF-dependent modulation of AMPA receptor function.

Amino Acid Sequence↗
PubMed1998

A new intrathalamic pathway linking modality-related nuclei in the dorsal thalamus.

Transmission of sensory information through the dorsal thalamus involves two types of modality-related nuclei, first order and higher order, between which there are thought to be no intrathalamic interactions. We now show that within the somatosensory thalamus, cells in one nucleus, the ventrobasal complex, can influence activity in another nucleus, the medial division of the posterior complex. Stimulation of ventrobasal complex cells evoked inhibitory postsynaptic currents in cells of the medial division of the posterior complex. These currents exhibited the reversal potential and pharmacology of a GABAA receptor-mediated chloride conductance, indicating that they result from the activation of a disynaptic pathway involving the GABAergic cells of the thalamic reticular nucleus. These findings provide the first direct evidence for intrathalamic interactions between dorsal thalamic nuclei.

Animals↗
PubMed1997

A hippocampal GluR5 kainate receptor regulating inhibitory synaptic transmission.

The principal excitatory neurotransmitter in the vertebrate central nervous system, L-glutamate, acts on three classes of ionotripic glutamate receptors, named after the agonists AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxalole-4-propionic acid), NMDA (N-methyl-D-aspartate) and kainate. The development of selective pharmacological agents has led to a detailed understanding of the physiological and pathological roles of AMPA and NMDA receptors. In contrast, the lack of selective kainate receptor ligands has greatly hindered progress in understanding the roles of kainate receptors. Here we describe the effects of a potent and selective agonist, ATPA ((RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid) and a selective antagonist, LY294486 ((3SR, 4aRS, 6SR, 8aRS)-6-((((1H-tetrazol-5-yl) methyl)oxy)methyl)-1, 2, 3, 4, 4a, 5, 6, 7, 8, 8a-decahydroisoquinoline-3-carboxylic acid), of the GluR5 subtype of kainate receptor. We have used these agents to show that kainate receptors, comprised of or containing GluR5 subunits, regulate synaptic inhibition in the hippocampus, an action that could contribute to the epileptogenic effects of kainate.

Animals↗
PubMed1997

The synaptic activation of kainate receptors.

L-Glutamate, the principal excitatory neurotransmitter in the vertebrate central nervous system, acts on three classes of ionotropic glutamate receptors, named after the agonists AMPA, NMDA and kainate. AMPA receptors are known to mediate fast synaptic responses and NMDA receptors to mediate slow synaptic responses at most excitatory synapses in the brain. Kainate receptors are formed from a separate set of genes (GluR5-7, KA-1 and KA-2) and are widely distributed throughout the brain. They are implicated in epileptogenesis and cell death. However, the physiological functions of kainate receptors are not known. The development of 2,3-benzodiazepine antagonists that are selective for AMPA receptors enables kainate receptors to be specifically activated by exogenous ligands, such as kainate. Here we demonstrate that high-frequency stimulation of mossy fibres in rat hippocampal slices, in the presence of the highly selective AMPA receptor antagonist GYKI 53655 plus NMDA- and GABA-receptor antagonists, activates an inward current in CA3 neurons that has a pharmacology typical of kainate receptors. The finding that kainate receptors can be activated synaptically adds to the diversity of information transfer at glutamatergic synapses.

2-Amino-5-phosphonovalerate↗
PubMed1997

(RS)-2-chloro-5-hydroxyphenylglycine (CHPG) activates mGlu5, but no mGlu1, receptors expressed in CHO cells and potentiates NMDA responses in the hippocampus.

A new phenylglycine derivative, (RS)-2-chloro-5-hydroxyphenylglycine (CHPG), has been synthesized and shown to selectively activate mGlu5a receptors, compared to mGlu1 alpha receptors, when expressed in CHO cells. This selective mGlu5 receptor agonist also potentiates NMDA-induced depolarizations in rat hippocampal slices. CHPG may be a useful tool for studying the role of mGlu5 receptors in the central nervous system.

Animals↗