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G L Collingridge

Publications and source records attributed to G L Collingridge.

At least 91 records · Page 5Linked to original sources
PubMed1994

In vitro translation and membrane topology of rat recombinant mGluR1 alpha.

The structure and post-translational processing of the metabotropic glutamate receptor 1 alpha (mGluR1 alpha) was analysed by in vitro cell-free translation, protease protection and deglycosylation. We show that mGluR1 alpha can be synthesized in the rabbit-reticulocyte translation system to yield a predominant polypeptide product with an apparent molecular weight of 142 kDa. In the presence of dog-pancreatic microsomes this polypeptide was processed to an apparent molecular weight of 147 kDa. Treatment with the enzyme peptide-N-glycosidase F (PNGF) demonstrated that the increase in the apparent molecular weight of the processed translation product was due to N-linked glycosylation. Addition of the non-selective protease, proteinase K; resulted in the loss of this 147 kDa band and the appearance of a protected fragment of approx 92 kDa. A carboxy-terminal deletion mutant of mGluR1 alpha was almost completely protected from protease action. These data show that the amino terminal of mGluR1 alpha is translocated into the lumen of the endoplasmic reticulum and will consequently be located extracellularly when targeted to the plasma membrane. The data presented here on mGluR1 alpha indicates the potential of in vitro translation and protease protection in the study of the molecular structure and processing of glutamate receptors.

Amidohydrolases↗
PubMed1993

Carbachol can potentiate N-methyl-D-aspartate responses in the rat hippocampus by a staurosporine and thapsigargin-insensitive mechanism.

Experiments were performed to investigate the mechanism underlying the potentiation of N-methyl-D-aspartate (NMDA) responses by carbachol (CCh) in the CA1 region of rat hippocampal slices. CCh (300 nM) potentiated responses to NMDA, but not to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), in a readily reversible manner. Potentiation occurred in slices treated with 200 nM tetrodotoxin and perfused with Mg(2+)-free medium. It also occurred in slices treated with either staurosporine (1 microM), which is a potent inhibitor of a variety of protein kinases including protein kinase C (PKC), or thapsigargin (10 microM), which depletes intracellular Ca2+ stores by preventing their refilling. However, CCh-induced potentiation was abolished in slices perfused with Ca(2+)-free medium. These data suggest that low concentrations of CCh can acutely potentiate NMDA responses in the hippocampus by a Ca(2+)-sensitive process that is probably independent of both the activation of PKC and the release of Ca2+ from intracellular stores. This mechanism is similar to that underlying the potentiation of NMDA responses by the metabotropic glutamate receptor (mGluR) agonist, aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD).

Alkaloids↗
PubMed1993

N-Methyl-D-aspartate receptors are clustered and immobilized on dendrites of living cortical neurons.

The response of nerve cells to synaptic inputs and the propagation of this activation is critically dependent on the cell-surface distribution of ion channels. In the hippocampus, Ca2+ influx through N-methyl-D-aspartate receptors (NMDAR) and/or voltage-dependent calcium channels on dendrites is thought to be critically involved in long-term potentiation, neurite outgrowth, epileptogenesis, synaptogenesis, and cell death. We report that conantokin-G (CntxG), a peptide from Conus geographus venom, competitively blocked with high affinity and specificity NMDAR-mediated currents in hippocampal neurons and is a reliable probe for exploring NMDAR distribution. Fluorescent derivatives of CntxG were prepared and used to directly determine NMDAR distribution on living hippocampal neurons by digital imaging and confocal fluorescence microscopy. In hippocampal slices, the CA1 dendritic subfield was strongly labeled by CntxG, whereas the CA3 mossy fiber region was not. On CA1 hippocampal neurons in culture, dendritic CntkG-sensitive NMDAR were clustered at sites of synaptic contacts, whereas somatic NMDAR were distributed diffusely and in patches. NMDAR distribution differed from the distribution of voltage-dependent calcium channels. A significant fraction of labeled NMDAR on somata and dendrites was found to be highly mobile: rates were consistent with the possible rapid recruitment of NMDAR to specific synaptic locations. The localization of NMDAR and modulation of this distribution demonstrated here may have important implications for the events that underlie neuronal processing and synaptic remodeling during associative synaptic modification.

2-Amino-5-phosphonovalerate↗
PubMed1993

Induction of LTP in the hippocampus needs synaptic activation of glutamate metabotropic receptors.

Understanding the mechanisms of long-term potentiation (LTP) should provide insights into the molecular basis of learning and memory in vertebrates. Ionotropic glutamate receptors play a central role in LTP; AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors and NMDA (N-methyl-D-aspartate) receptors mediate synaptic responses that are enhanced in LTP and, in addition, NMDA receptors are necessary for the induction of LTP in most pathways. There is also circumstantial evidence that metabotropic glutamate receptors (mGluRs) may be involved in LTP because the specific mGluR agonist aminocyclopentane dicarboxylate can augment tetanus-induced LTP2 and, under certain circumstances, can itself induce a slow-onset potentiation. But the absence of any effective mGluR antagonist has prevented the determination of whether mGluRs are involved in the induction of tetanus-induced LTP. We report here that (RS)-alpha-methyl-4-carboxyphenylglycine is a specific mGluR antagonist in the hippocampus and have used this compound to examine the nature of the involvement of mGluRs in LTP. We show that synaptic activation of mGluRs is necessary for the induction of both NMDA receptor-dependent and NMDA receptor-independent forms of LTP in the hippocampus.

Action Potentials↗
PubMed1993

A synaptic model of memory: long-term potentiation in the hippocampus.

Long-term potentiation of synaptic transmission in the hippocampus is the primary experimental model for investigating the synaptic basis of learning and memory in vertebrates. The best understood form of long-term potentiation is induced by the activation of the N-methyl-D-aspartate receptor complex. This subtype of glutamate receptor endows long-term potentiation with Hebbian characteristics, and allows electrical events at the postsynaptic membrane to be transduced into chemical signals which, in turn, are thought to activate both pre- and postsynaptic mechanisms to generate a persistent increase in synaptic strength.

Animals↗
PubMed1993

Metabotropic glutamate receptors and calcium signalling in dendrites of hippocampal CA1 neurones.

We have combined patch-clamp recording with confocal microscopy to investigate how the synaptic activation of metabotropic glutamate receptors (mGluRs) may participate in the modulation of intracellular free calcium (Ca2+) in the dendrites of single CA1 pyramidal neurones, within hippocampal slices. Tetanic stimulation (100 Hz, 1 sec) of the Schaffer collateral-commissural pathway led to a transient rise in Ca2+ in the dendrites of neurones voltage- clamped at -35 mV, as determined using the fluorescent indicator fluo-3. The specific mGluR antagonist (+)-alpha-methyl-4-carboxyphenylglycine (MCPG), applied at a concentration of 250 or 500 microM, reduced the size of the Ca2+ transient whilst either producing a small reduction or, more commonly, having no effect on the synaptic current evoked by the tetanus. These data suggest that the synaptic activation of mGluRs can contribute to Ca2+ signalling in hippocampal neurones.

2-Amino-5-phosphonovalerate↗
PubMed1993

Antagonism of baclofen-induced depression of whole-cell synaptic currents in spinal dorsal horn neurones by the potent GABAB antagonist CGP55845.

The potencies of two GABAB receptor antagonists P-[3-aminopropyl]- P-diethoxymethyl-phosphinic acid (CGP35348) and the novel compound 3-N[1-(S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)-hydroxypropyl-P- benzyl-phosphinic acid (CGP55845) have been compared in an in vitro spinal cord preparation. They have been tested as antagonists of baclofen-induced depression of EPSCs of patch-clamped dorsal horn neurons following electrical stimulation of dorsal roots. Mean EC50 values for the depressant action of baclofen were increased by 50- and 140-fold respectively in the presence of CGP35348 (200 microM) (n = 5) and CGP55845 (100 nM) (n = 4). This potency of CGP55845 is > 1000-fold higher than that reported previously for other GABAB receptor antagonists.

Action Potentials↗
PubMed1993

CGP 55845A: a potent antagonist of GABAB receptors in the CA1 region of rat hippocampus.

The new GABAB receptor antagonist CGP 55845A was tested on pre- and post-synaptic GABAB receptors in the hippocampus. CGP 55845A (1 microM) blocked (-)-baclofen (5-10 microM)-induced postsynaptic hyperpolarization and depression of evoked IPSPs and EPSPs. It also blocked three physiological consequences of GABAB receptor activation: the late IPSP, paired-pulse depression of IPSCs, and heterosynaptic depression of EPSPs. Therefore, CGP 55845A is an antagonist at pre- and post-synaptic GABAB receptors in the hippocampus and is approximately three orders of magnitude more potent than previously described GABAB receptor antagonists.

Animals↗
PubMed1993

Characterisation of LTP induced by the activation of glutamate metabotropic receptors in area CA1 of the hippocampus.

The transient activation of the N-methyl-D-aspartate (NMDA) receptor system by high frequency (tetanic) stimulation results in a rapidly developing and long-lasting potentiation of synaptic transmission in the CA1 region of the hippocampus. This potentiation can be divided into an early decremental component, known as short-term potentiation (STP), and a more slowly developing persistent phase, termed long-term potentiation (LTP). Here we describe how activation of metabotropic glutamate receptors (mGluRs), by aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD), can induce the same stable form of LTP, but without the STP component. 1S,3R-ACPD-induced LTP does not require electrical stimulation during its induction, but is dependent on an intact connection between the CA3 and CA1 regions of the hippocampus. 1S,3R-ACPD-induced LTP circumvents the need for the activation of NMDA receptors and is likely to involve both the stimulation of protein kinase C (PKC) and the release of Ca2+ from intracellular stores.

Alkaloids↗
PubMed1993

Signal transduction pathways involved in the acute potentiation of NMDA responses by 1S,3R-ACPD in rat hippocampal slices.

1. A grease-gap recording technique has been used to investigate the mechanisms underlying the acute potentiation of N-methyl-D-aspartate (NMDA) responses by aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD) in area CA1 of rat hippocampal slices. 2. 1S,3R-ACPD (10 microM), but not 1R,3S- ACPD (10 microM), potentiated submaximal responses to NMDA (dose-ratio of 0.81 +/- 0.02 (mean +/- s.e.mean); n = 55), but not to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), in a readily reversible manner. Potentiation also occurred in slices treated with 0.2 microM tetrodotoxin, and in slices perfused with Mg(2+)-free medium. 3. 1S,3R-ACPD-induced potentiation was unaffected by the protein kinase inhibitors K-252b (0.1 microM) and staurosporine (1 microM) and the intracellular Ca2+ store depletor, thapsigargin (10 microM). Coapplication of staurosporine and thapsigargin was also without effect. 4. 1S,3R-ACPD-induced potentiation was unaffected by inhibitors of arachidonic acid formation, bromophenacyl bromide (50 microM) and RG80267 (100 microM). Arachidonic acid (10-50 microM) depressed reversibly NMDA-induced responses. The potentiation was unaffected by 8-bromo cyclic AMP (500 microM) or the PKA inhibitor Rp-adenosine 3,5-cyclic monophosphothioate triethylamine (Rp-cAMPS; 50 microM). 5. 1S,3R-ACPD-induced potentiation was abolished in slices perfused with Ca(2+)-free medium. The potentiation was also blocked by phorbol-12,13-diacetate (1 microM), in a staurosporine-sensitive manner. 6. It is concluded that the potentiation of NMDA responses by 1S,3R-ACPD is not mediated by protein kinase A or C, by release of Ca2+ from intracellular stores or by arachidonic acid. It involves a Ca2+-sensitive process and is negatively regulated by protein kinase C.

Animals↗
PubMed1993

Characterization of Ca2+ signals induced in hippocampal CA1 neurones by the synaptic activation of NMDA receptors.

1. A combination of confocal microscopy, whole-cell patch-clamp recording, intracellular dialysis and pharmacological techniques have been employed to study Ca2+ signalling in CA1 pyramidal neurones, within rat hippocampal slices. 2. In the soma of CA1 neurones, depolarizing steps applied through the patch-pipette resulted in transient increases in the fluorescence emitted by the Ca2+ indicator fluo-3. The intensity of the fluorescence transients was proportional to the magnitude of the Ca2+ currents recorded through the pipette. Both the somatic fluorescence transients and the voltage-activated Ca2+ currents ran down in parallel over a period of between approximately 15-45 min. The fluorescence transients were considered, therefore, to be caused by increases in cytosolic free Ca2+. 3. Under current-clamp conditions, high-frequency (tetanic) stimulation (100 Hz, 1 s) of the Schaffer collateral-commissural pathway led to compound excitatory postsynaptic potentials (EPSPs) and somatic Ca2+ transients. The somatic Ca2+ transients were sensitive to the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonopentanoate (AP5; 100 microM). These transients, but not the EPSPs, disappeared with a time course similar to that of the run-down of voltage-gated Ca2+ currents. Tetanus-induced somatic Ca2+ transients could not be elicited under voltage-clamp conditions. 4. Fluorescence images were obtained from the dendrites of CA1 pyramidal neurones starting at least 30 min after obtaining whole-cell access to the neurone. Measurements were obtained only after voltage-gated Ca2+ channel activity had run down completely. 5. Tetanic stimulation of the Schaffer collateral-commissural pathway resulted in compound EPSPs and excitatory postsynaptic currents (EPSCs), under current- and voltage-clamp, respectively. In both cases, these were invariably associated with dendritic Ca2+ transients. In cells voltage-clamped at -35 mV, the fluorescent signal increased on average 2-fold during the tetanus and decayed to baseline values with a half-time (t1/2) of approximately 5 s. 6. The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM) partially reduced the tetanus-induced EPSC without affecting the Ca2+ transients. In contrast, AP5, which also depressed the EPSC, substantially reduced or eliminated the Ca2+ transients. 7. In normal (i.e. 1 mM Mg(2+)-containing) medium, NMDA receptor-mediated synaptic currents displayed the typical region of negative slope conductance in the peak I-V relationship (between -90 and -35 mV). The dendritic tetanus-induced Ca2+ transients also displayed a similar anomalous voltage dependence, decreasing in size from -35 to -90 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

The physiological regulation of synaptic inhibition by GABAB autoreceptors in rat hippocampus.

1. Intracellular recording techniques were used to study the effects of repetitive stimulation on monosynaptically activated inhibitory postsynaptic currents (IPSCs) in rat hippocampal slices. This was achieved by stimulation in stratum radiatum close to a recorded CA1 pyramidal neurone after pharmacological blockade of excitatory synaptic responses, using a combination of the N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonists D-2-amino-5-phosphonopentanoate (AP5; 0.04-0.1 mM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 0.02-0.04 mM), respectively. 2. Fixed-intensity stimulation at frequencies of less than 0.1 Hz evoked biphasic IPSCs of constant amplitude and waveform. In contrast, when two shocks (paired pulse) or longer trains of ten or more stimuli (i.e. tetani) were delivered at frequencies of between 0.2 and 20 Hz there was marked depression of both phases of every IPSC (by 60-100%) relative to the first or 'priming' IPSC evoked. 3. The gamma-aminobutyric acid (GABA)B receptor antagonists phaclofen (0.4-2 mM), 2-hydroxy-saclofen (0.02-0.4 mM) and 3-aminopropyl(diethoxymethyl)phosphinic acid (CGP 35348; 0.01-1 mM) reduced or abolished, in a concentration-dependent and reversible manner, both the late phase of the IPSC (IPSCB) and paired-pulse depression of the early phase of the IPSC (IPSCA). Expressed in terms of IC50 values, all three antagonists were 5-10 times more potent at blocking IPSCB than paired-pulse depression. 4. Paired-pulse depression, at 5 and 10 Hz, has been shown to be mediated by GABA acting on presynaptic GABAB receptors (i.e. GABAB autoreceptors). We now show that GABAB receptor antagonists reverse paired-pulse depression over the entire range of frequencies (0.1-50 Hz) that it occurs. 5. GABAB receptor antagonists reversed substantially the depression of IPSCs during tetani delivered at 5 or 10 Hz. However at 20 Hz, GABAB receptor antagonists appeared to be less effective. At 100 Hz they appeared to be ineffective at reversing the depression of IPSCA; since the antagonists block IPSCB the net effect was to reduce the level of outward current. 6. At frequencies of 20 Hz or more, there was also the appearance of a slow inward current which increased in size in proportion to the frequency and number of shocks in the tetanus. This current (termed here IPSCI) was more pronounced at hyperpolarized membrane potentials and was blocked by picrotoxin (0.1 mM) or bicuculline (0.05 mM). 7. 'Priming' is considered to represent a more physiological pattern of activity than a tetanus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Thapsigargin blocks the induction of long-term potentiation in rat hippocampal slices.

Experiments were performed to investigate whether intact intracellular Ca2+ pools are necessary for long-term potentiation (LTP) in the CA1 region of rat hippocampal slices. Thapsigargin (1 microM), which depletes most intracellular Ca2+ pools by blocking ATP-dependent Ca2+ uptake into intracellular compartments, blocked the induction but not the expression of LTP. Thapsigargin had no effect on synaptic transmission or on responses mediated by N-methyl-D-aspartate (NMDA) receptor activation. These data suggest that Ca2+ release from intracellular stores is required for the induction of LTP.

Animals↗
PubMed1992

Activation of glutamate metabotropic receptors induces long-term potentiation.

The specific glutamate metabotropic receptor agonist 1S,3R-aminocyclopentane dicarboxylate (ACPD), but not its inactive enantiomer 1R,3S-ACPD, induced a slowly developing potentiation of synaptic transmission in rat hippocampal slices. This effect was independent of its ability to potentiate responses mediated by the activation of N-methyl-D-aspartate receptors. Perfusion with 1S,3R-ACPD provides, therefore, a means of chemically inducing a form of long-term potentiation.

Animals↗
PubMed1992

The synaptic activation of NMDA receptors and Ca2+ signalling in neurons.

Long-term potentiation (LTP) in the hippocampus is a model system for understanding the synaptic basis of learning and memory. We have studied the mechanism of induction of LTP using voltage-clamp techniques and confocal imaging of Ca2+ in rat hippocampal slices. In the Schaffer collateral-commissural pathway the neurotransmitter L-glutamate activates two classes of ionotropic receptor, named after the selective ligands AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate) and NMDA (N-methyl-D-aspartate). During low frequency transmission the excitatory postsynaptic potential (EPSP) is mediated predominantly by AMPA receptors. NMDA receptors play a minor role because their ion channels are substantially blocked by Mg2+, and this block is intensified by GABA-mediated synaptic inhibition. During high frequency transmission the GABA-mediated inhibition is depressed, by mechanisms initiated by GABAB autoreceptors. This allows a greater contribution from the NMDA receptors, through which Ca2+ enters the dendrites of the postsynaptic neurons to initiate a cascade of biochemical processes which ultimately result in enhanced synaptic efficiency.

Animals↗