1. Focal electrographic seizures arose in the CA1 region of rat hippocampal slices bathed in elev... more 1. Focal electrographic seizures arose in the CA1 region of rat hippocampal slices bathed in elevated (8.5 mM) external potassium [( K+]o). High [K+]o also induced spontaneous interictal bursts that originated in area CA3 and propagated to CA1. To examine the contribution to electrographic seizure initiation of excitatory mechanisms that are influenced by extracellular volume, we studied the effect of hyperosmotic expansion of interstitial volume on seizure occurrence, interictal bursts, and excitatory synaptic transmission. The tissue electrical resistance was also measured leading up to and during seizures. 2. Media made 5-30 mosmol/kg hyperosmotic by addition of agents restricted to the extracellular space (mannitol, sucrose, raffinose, L-glucose, dextran) rapidly and reversibly abolished [K+]o-induced spontaneous CA1 seizures in 86% of slices tested. However, similar increases in osmolality effected by agents that access the intracellular compartment (D-glucose, glycerol) did no...
The inhibitory and excitatory amino acid neurotransmitter receptors in the mammalian central nerv... more The inhibitory and excitatory amino acid neurotransmitter receptors in the mammalian central nervous system mediate functionally opposite synaptic responses yet appear to share certain structural features. Recent conceptual advances in this field have relied heavily on information obtained by single channel analyses, by the expression of receptors in oocytes, and by autoradiographic studies of receptor distribution among brain receptors. This article reviews the pharmacology, cellular physiology, and regional distribution of these receptors and discusses their role in several well-characterized neurological disease states. Also reviewed are the recent advances made in purifying (in some instances cloning) the receptors and uptake sites involved in synaptic transmission in the brain. Throughout, the emphasis is on synthesis and concept rather than on methodological detail.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1991
The whole-cell patch-clamp technique was used to record Ba2+ currents through voltage-activated c... more The whole-cell patch-clamp technique was used to record Ba2+ currents through voltage-activated calcium channels in the clonal dorsal root ganglion cell line F11-B9. The pain-producing peptide bradykinin (BK; 100 nM) reduced the sustained Ba2+ current in F11-B9 cells by 30%. In cultures prelabeled with 3H-arachidonic acid and tested under ionic conditions similar to those used for recording Ba2+ currents, BK also induced a concentration-dependent, transient, 2.7-fold accumulation of 3H-diacylglycerol. Both the elevation of 3H-diacylglycerol and the inhibition of Ba2+ current began within 5 sec following BK exposure, and the effective concentration range of BK was similar for the 2 responses. In whole-cell recordings, extracellularly applied 1-oleoyl-2-acetylglycerol (OAG; 0.5-5 microM) mimicked the degree of block and occluded the block of sustained current by BK. Another protein kinase C (PKC) activator, 1,2-dioctanoylglycerol (diC8), blocked 70-100% of sustained current when appli...
... in CI" conductance that are associated with the actions of GABA (Dreifuss et al., 1969) ... more ... in CI" conductance that are associated with the actions of GABA (Dreifuss et al., 1969) and glycine (Ten Bruggencate and Engberg, 1971). ... In Reticular Formation of the Brain, HH Jasper, LD Proctor, RS Knighton, WC Noshay and RT Costello (Eds.), Little Brown, Boston, pp. ...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2001
Impaired GABAergic inhibition may contribute to the development of hyperexcitability in epilepsy.... more Impaired GABAergic inhibition may contribute to the development of hyperexcitability in epilepsy. We used the pilocarpine model of epilepsy to demonstrate that regulation of excitatory synaptic drive onto GABAergic interneurons is impaired during epileptogenesis. Synaptic input from granule cells (GCs), perforant path, and CA3 inputs onto hilar border interneurons of the dentate gyrus were examined in rat hippocampal slices during the latent period (1-8 d) after induction of status epilepticus (SE). Short-term depression (STD) of GC inputs to interneurons induced by brief (500-800 msec), repetitive (5-20 Hz) stimulation, as well as paired-pulse depression at both GC and CA3 inputs to interneurons, were significantly (p < 0.05) enhanced in SE-experienced rats. In contrast, we found no significant differences between SE-experienced and age-matched control rats in the properties of minimal EPSCs evoked at low frequency (0.3 Hz). Consistent with reduced GABAergic inhibition onto gran...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 1997
The GluR2 subunit controls three key features of ion flux through the AMPA subtype of glutamate r... more The GluR2 subunit controls three key features of ion flux through the AMPA subtype of glutamate receptors-calcium permeability, inward rectification, and channel block by external polyamines, but whether each of these features is equally sensitive to GluR2 abundance is unknown. The relations among these properties were compared in native AMPA receptors expressed by acutely isolated hippocampal interneurons and in recombinant receptors expressed by Xenopus oocytes. The shape of current-voltage (I-V) relations between -100 and +50 mV for either recombinant or native AMPA receptors was well described by a Woodhull block model in which the affinity for internal polyamine varied over a 1000-fold range in different cells. In oocytes injected with mixtures of GluR2:non-GluR2 mRNA, the relative abundance of GluR2 required to reduce the log of internal blocker affinity by 50% was two- to fourfold higher than that needed to half-maximally reduce divalent permeability or channel block by exter...
The Journal of pharmacology and experimental therapeutics, 1996
A variety of polyamine spider and wasp toxins are known to block N-methyl-D-aspartate receptor ch... more A variety of polyamine spider and wasp toxins are known to block N-methyl-D-aspartate receptor channels and recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors that lack the edited glutamate receptor (GluR)2 subunit. Recently, inward rectification of GluR2-lacking AMPA receptors was shown to be caused by voltage-dependent block by intracellular spermine. Here we demonstrate that, when applied extracellularly, the endogenous polyamines spermine and spermidine, as well as monoacylated spermine analogs and the polyamine toxins ageltoxin-489 and philanthotoxin-433, exerted a use-dependent and weakly voltage-dependent block of AMPA receptors that lack the edited GluR2 subunit, when the recombinant receptors were expressed in Xenopus oocytes. External spermine and polyamine toxins were also effective blockers of AMPA receptor mutants that did not not show inwardly rectifying kainate responses but had high calcium permeability. The polyamines and polyamine...
1. Whole-cell recordings were made from interneurons located within CA3 stratum radiatum of neona... more 1. Whole-cell recordings were made from interneurons located within CA3 stratum radiatum of neonate rat hippocampal slices. All experiments were performed in the continued presence of tetrodotoxin (1 microM) and bicuculline (5 microM) to permit the isolation of spontaneous miniature excitatory synaptic currents (mEPSCs). 2. Two distinct populations of interneurones were identified based on current-voltage relations of kainate and the kinetic properties of spontaneous mEPSCs. These cell types were classified as type I and type II interneurones. 3. The I-V relation of kainate in type I cells was linear or modestly outwardly rectifying. Currents reversed polarity close to 0 mV. The kainate I-V relationship in type II interneurones was strongly inwardly rectifying with little or no outward current passed at potentials up to +50 mV. 4. Spontaneous mEPSCs were observed at a low frequency. At -70 mV mEPSCs received by type I interneurones had fast rise times (approximately 1 ms) and decay ...
1. Extra- and intracellular recordings were made from CA1 cells in hippocampal slices in vitro. T... more 1. Extra- and intracellular recordings were made from CA1 cells in hippocampal slices in vitro. The effects of ionophoretically applied GABA on somatic and dendritic regions were studied. 2. Ionophoresis of GABA at dendritic sites gave a reciprocal effect by inhibiting the effect of excitatory synapses close to the dendritic application, while facilitating those lying further away. For example, GABA delivered to the mid-radiatum dendritic region reduced the population spike generated by a radiatum volley, while facilitating the population spike evoked by oriens fibre stimulation. Similarly, when single cells were recorded from, mid-apical dendritic delivery of GABA abolished the synaptically driven discharges evoked by fibres terminating at this part of the dendritic tree, but facilitated the responses to input from fibres terminating on the basal dendrites of the same cell. 3. With intracellular recording two effects were observed. Applied near the soma, GABA induced a hyperpolariz...
In rat hippocampal slices, opioids potentiate the synaptic activation of pyramidal neurons as rev... more In rat hippocampal slices, opioids potentiate the synaptic activation of pyramidal neurons as revealed by the shift to the left in the input-output curve constructed by plotting the population spike as a function of the field EPSP. The peak effect was obtained within 12-25 min with D-Ala2,D-Leu5-enkephalin (DADLE), morphiceptin and morphine. However, the effect of both peptides declined during constant superfusion. About 60% peak effect was lost after 1 hr superfusion with morphiceptin or after 4 hr with DADLE. In contrast, the effect of morphine gradually increased over a 4 hr incubation. Following superfusion of the slices for 4 hr in DADLE or morphine, or 1.5 hr in morphiceptin, the membrane particulate fractions were prepared from the homogenate of slices. Opiate receptor binding activities were measured with 125I-DADLE (delta-receptors) and 125I-FK 33824 (mu-receptors). A significant reduction in delta- but not mu-receptor binding was detected in slices treated with DADLE. This...
&#39;Population&#39; afferent spike and &#39;population&#39; EPSP were recorded w... more &#39;Population&#39; afferent spike and &#39;population&#39; EPSP were recorded with extracellular microelectrodes in slices of hippocampal tissue maintained in vitro. Calcium concentration was changed in the bathing solution, and calcium activity ([Ca2+]0) was measured in interstitial fluid of the slice with ion-selective microelectrodes. Synaptic transfer was a non-linear continuous function of [Ca2+]0. Deviation of [Ca2+]0 by 0.1 mM from the 1.2 mM control level caused a change of approximately 15% in the slope of the input-output function.
The depolarizing actions of N-methyl-DL-aspartate (NMA) and L-glutamate on pyramidal neurones wer... more The depolarizing actions of N-methyl-DL-aspartate (NMA) and L-glutamate on pyramidal neurones were compared in a hippocampal slice preparation. Tetrodotoxin (1 microM) was added to the perfusion solution to suppress regenerative Na conductances. Depolarization evoked by ionophoretic application of NMA triggered slow, high-threshold regenerative spikes. These are considered to be Ca spikes since the amplitude and rate of rise could be reduced by verapamil, D-600, Co2+ and Mn2+, and increased by Ba2+. Multiple Ca-spike thresholds could be demonstrated in the same cell. In contrast, depolarizations evoked by L-glutamate only rarely triggered Ca-spikes. The minimum latency to the onset of depolarization evoked by NMA was less than 20 ms. The latency and amplitude of NMA-evoked responses were highly dependent on the position of the ionophoretic pipette; movements of the pipette by as little as 10-50 micron could markedly change the size of the response. Spatially separate hot spots for N...
The Journal of pharmacology and experimental therapeutics, 1984
The effects of the opioid peptides morphiceptin and [N-MePhe3-D-Pro4]morphiceptin (PL017), both m... more The effects of the opioid peptides morphiceptin and [N-MePhe3-D-Pro4]morphiceptin (PL017), both mu receptor agonists, were examined by electrophysiological techniques in the rat hippocampal slice and ligand binding techniques in hippocampal membrane preparations. The electrophysiological actions of the mu agonists were similar to those of the previously studied delta receptor agonist [D-Ala2, D-Leu5]enkephalin. Thus, for a given size field excitatory postsynaptic potential the amplitude of both population spike and intracellular excitatory postsynaptic potential was increased by morphiceptin. These effects were concentration dependent and reversed by naloxone. The EC50 for morphiceptin was 1.6 microM, which is consistent with the mu-selective binding properties of this peptide. Similar results were obtained with the more potent analog PL017. Morphiceptin and morphine had similar displacement profiles in competition experiments performed with hippocampal membranes and a variety of ra...
The effects of the N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonovaleric ... more The effects of the N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonovaleric acid (D-APV), and other excitatory amino acid antagonists, were studied on CA1 pyramidal neurones treated with picrotoxin or bicuculline to reduce synaptic inhibition mediated by gamma-aminobutyric acid (GABA). Under these conditions epileptiform burst firing is readily produced by orthodromic stimulation of the pyramidal cell population. D-APV reduced the plateau amplitude and duration of the depolarization underlying evoked and spontaneous bursts without affecting membrane potential, input resistance or the ability of the cell to fire a Ca2+ spike or a short train of Na+ spikes. A late component of the subthreshold excitatory post-synaptic potential (e.p.s.p.) was voltage dependent, being reduced in amplitude on membrane hyperpolarization. D-APV selectively removed this component of the e.p.s.p. in disinhibited slices. In contrast, in the absence of GABA antagonists, D-APV had no notic...
Xenopus oocytes injected with rat brain mRNA were used to identify and characterize the effects o... more Xenopus oocytes injected with rat brain mRNA were used to identify and characterize the effects of compounds that are antagonists at both the glycine site on N-methyl-D-aspartate (NMDA) receptors and the quisqualate/kainate receptor. Oocytes were voltage-clamped at -60 mV and inward currents were measured at equilibrium following perfusion with agonists and antagonists. Application of 7-chlorokynurenic acid (7-Cl-Kyn) or 6,7-dichloro-3-hydroxy-2-quinoxaline carboxylic acid (6,7-diCl-HQC), each at 15 microM, produced a parallel shift to the right of the glycine concentration-response curve. Schild analysis indicated a KB of 300 nM for 6,7-diCl-HQC and 350 nM for 7-Cl-Kyn. The slopes of the Schild plots were 1.01-1.02 in each case, suggesting that both compounds are competitive glycine antagonists. Both compounds also blocked the receptor mediating kainate-induced inward current. Schild analysis of 6,7-diCl-HQC (KB = 3.0 microM, slope = 0.98) indicated competitive antagonism of kainat...
1. Spontaneous discharges that resemble interictal spikes arise in area CA3 b/c of rat hippocampa... more 1. Spontaneous discharges that resemble interictal spikes arise in area CA3 b/c of rat hippocampal slices bathed in 8.5 mM [K+]o. Excitatory postsynaptic potentials (EPSPs) also appear at irregular intervals in these cells. The role of local synaptic excitation in burst initiation was examined with intracellular and extracellular recordings from CA3 pyramidal neurons. 2. Most (70%) EPSPs were small (less than 2 mV in amplitude), suggesting that they were the product of quantal release or were evoked by a single presynaptic action potential in another cell. It is unlikely that most EPSPs were evoked by a presynaptic burst of action potentials. Indeed, intrinsic burst firing was not prominent in CA3 b/c pyramidal cells perfused in 8.5 mM [K+]o. 3. The likelihood of occurrence and the amplitude of EPSPs were higher in the 50-ms interval just before the onset of each burst than during a similar interval 250 ms before the burst. This likely reflects increased firing probability of CA3 ne...
1. Focal electrographic seizures arose in the CA1 region of rat hippocampal slices bathed in elev... more 1. Focal electrographic seizures arose in the CA1 region of rat hippocampal slices bathed in elevated (8.5 mM) external potassium [( K+]o). High [K+]o also induced spontaneous interictal bursts that originated in area CA3 and propagated to CA1. To examine the contribution to electrographic seizure initiation of excitatory mechanisms that are influenced by extracellular volume, we studied the effect of hyperosmotic expansion of interstitial volume on seizure occurrence, interictal bursts, and excitatory synaptic transmission. The tissue electrical resistance was also measured leading up to and during seizures. 2. Media made 5-30 mosmol/kg hyperosmotic by addition of agents restricted to the extracellular space (mannitol, sucrose, raffinose, L-glucose, dextran) rapidly and reversibly abolished [K+]o-induced spontaneous CA1 seizures in 86% of slices tested. However, similar increases in osmolality effected by agents that access the intracellular compartment (D-glucose, glycerol) did no...
The inhibitory and excitatory amino acid neurotransmitter receptors in the mammalian central nerv... more The inhibitory and excitatory amino acid neurotransmitter receptors in the mammalian central nervous system mediate functionally opposite synaptic responses yet appear to share certain structural features. Recent conceptual advances in this field have relied heavily on information obtained by single channel analyses, by the expression of receptors in oocytes, and by autoradiographic studies of receptor distribution among brain receptors. This article reviews the pharmacology, cellular physiology, and regional distribution of these receptors and discusses their role in several well-characterized neurological disease states. Also reviewed are the recent advances made in purifying (in some instances cloning) the receptors and uptake sites involved in synaptic transmission in the brain. Throughout, the emphasis is on synthesis and concept rather than on methodological detail.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1991
The whole-cell patch-clamp technique was used to record Ba2+ currents through voltage-activated c... more The whole-cell patch-clamp technique was used to record Ba2+ currents through voltage-activated calcium channels in the clonal dorsal root ganglion cell line F11-B9. The pain-producing peptide bradykinin (BK; 100 nM) reduced the sustained Ba2+ current in F11-B9 cells by 30%. In cultures prelabeled with 3H-arachidonic acid and tested under ionic conditions similar to those used for recording Ba2+ currents, BK also induced a concentration-dependent, transient, 2.7-fold accumulation of 3H-diacylglycerol. Both the elevation of 3H-diacylglycerol and the inhibition of Ba2+ current began within 5 sec following BK exposure, and the effective concentration range of BK was similar for the 2 responses. In whole-cell recordings, extracellularly applied 1-oleoyl-2-acetylglycerol (OAG; 0.5-5 microM) mimicked the degree of block and occluded the block of sustained current by BK. Another protein kinase C (PKC) activator, 1,2-dioctanoylglycerol (diC8), blocked 70-100% of sustained current when appli...
... in CI" conductance that are associated with the actions of GABA (Dreifuss et al., 1969) ... more ... in CI" conductance that are associated with the actions of GABA (Dreifuss et al., 1969) and glycine (Ten Bruggencate and Engberg, 1971). ... In Reticular Formation of the Brain, HH Jasper, LD Proctor, RS Knighton, WC Noshay and RT Costello (Eds.), Little Brown, Boston, pp. ...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2001
Impaired GABAergic inhibition may contribute to the development of hyperexcitability in epilepsy.... more Impaired GABAergic inhibition may contribute to the development of hyperexcitability in epilepsy. We used the pilocarpine model of epilepsy to demonstrate that regulation of excitatory synaptic drive onto GABAergic interneurons is impaired during epileptogenesis. Synaptic input from granule cells (GCs), perforant path, and CA3 inputs onto hilar border interneurons of the dentate gyrus were examined in rat hippocampal slices during the latent period (1-8 d) after induction of status epilepticus (SE). Short-term depression (STD) of GC inputs to interneurons induced by brief (500-800 msec), repetitive (5-20 Hz) stimulation, as well as paired-pulse depression at both GC and CA3 inputs to interneurons, were significantly (p < 0.05) enhanced in SE-experienced rats. In contrast, we found no significant differences between SE-experienced and age-matched control rats in the properties of minimal EPSCs evoked at low frequency (0.3 Hz). Consistent with reduced GABAergic inhibition onto gran...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 1997
The GluR2 subunit controls three key features of ion flux through the AMPA subtype of glutamate r... more The GluR2 subunit controls three key features of ion flux through the AMPA subtype of glutamate receptors-calcium permeability, inward rectification, and channel block by external polyamines, but whether each of these features is equally sensitive to GluR2 abundance is unknown. The relations among these properties were compared in native AMPA receptors expressed by acutely isolated hippocampal interneurons and in recombinant receptors expressed by Xenopus oocytes. The shape of current-voltage (I-V) relations between -100 and +50 mV for either recombinant or native AMPA receptors was well described by a Woodhull block model in which the affinity for internal polyamine varied over a 1000-fold range in different cells. In oocytes injected with mixtures of GluR2:non-GluR2 mRNA, the relative abundance of GluR2 required to reduce the log of internal blocker affinity by 50% was two- to fourfold higher than that needed to half-maximally reduce divalent permeability or channel block by exter...
The Journal of pharmacology and experimental therapeutics, 1996
A variety of polyamine spider and wasp toxins are known to block N-methyl-D-aspartate receptor ch... more A variety of polyamine spider and wasp toxins are known to block N-methyl-D-aspartate receptor channels and recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors that lack the edited glutamate receptor (GluR)2 subunit. Recently, inward rectification of GluR2-lacking AMPA receptors was shown to be caused by voltage-dependent block by intracellular spermine. Here we demonstrate that, when applied extracellularly, the endogenous polyamines spermine and spermidine, as well as monoacylated spermine analogs and the polyamine toxins ageltoxin-489 and philanthotoxin-433, exerted a use-dependent and weakly voltage-dependent block of AMPA receptors that lack the edited GluR2 subunit, when the recombinant receptors were expressed in Xenopus oocytes. External spermine and polyamine toxins were also effective blockers of AMPA receptor mutants that did not not show inwardly rectifying kainate responses but had high calcium permeability. The polyamines and polyamine...
1. Whole-cell recordings were made from interneurons located within CA3 stratum radiatum of neona... more 1. Whole-cell recordings were made from interneurons located within CA3 stratum radiatum of neonate rat hippocampal slices. All experiments were performed in the continued presence of tetrodotoxin (1 microM) and bicuculline (5 microM) to permit the isolation of spontaneous miniature excitatory synaptic currents (mEPSCs). 2. Two distinct populations of interneurones were identified based on current-voltage relations of kainate and the kinetic properties of spontaneous mEPSCs. These cell types were classified as type I and type II interneurones. 3. The I-V relation of kainate in type I cells was linear or modestly outwardly rectifying. Currents reversed polarity close to 0 mV. The kainate I-V relationship in type II interneurones was strongly inwardly rectifying with little or no outward current passed at potentials up to +50 mV. 4. Spontaneous mEPSCs were observed at a low frequency. At -70 mV mEPSCs received by type I interneurones had fast rise times (approximately 1 ms) and decay ...
1. Extra- and intracellular recordings were made from CA1 cells in hippocampal slices in vitro. T... more 1. Extra- and intracellular recordings were made from CA1 cells in hippocampal slices in vitro. The effects of ionophoretically applied GABA on somatic and dendritic regions were studied. 2. Ionophoresis of GABA at dendritic sites gave a reciprocal effect by inhibiting the effect of excitatory synapses close to the dendritic application, while facilitating those lying further away. For example, GABA delivered to the mid-radiatum dendritic region reduced the population spike generated by a radiatum volley, while facilitating the population spike evoked by oriens fibre stimulation. Similarly, when single cells were recorded from, mid-apical dendritic delivery of GABA abolished the synaptically driven discharges evoked by fibres terminating at this part of the dendritic tree, but facilitated the responses to input from fibres terminating on the basal dendrites of the same cell. 3. With intracellular recording two effects were observed. Applied near the soma, GABA induced a hyperpolariz...
In rat hippocampal slices, opioids potentiate the synaptic activation of pyramidal neurons as rev... more In rat hippocampal slices, opioids potentiate the synaptic activation of pyramidal neurons as revealed by the shift to the left in the input-output curve constructed by plotting the population spike as a function of the field EPSP. The peak effect was obtained within 12-25 min with D-Ala2,D-Leu5-enkephalin (DADLE), morphiceptin and morphine. However, the effect of both peptides declined during constant superfusion. About 60% peak effect was lost after 1 hr superfusion with morphiceptin or after 4 hr with DADLE. In contrast, the effect of morphine gradually increased over a 4 hr incubation. Following superfusion of the slices for 4 hr in DADLE or morphine, or 1.5 hr in morphiceptin, the membrane particulate fractions were prepared from the homogenate of slices. Opiate receptor binding activities were measured with 125I-DADLE (delta-receptors) and 125I-FK 33824 (mu-receptors). A significant reduction in delta- but not mu-receptor binding was detected in slices treated with DADLE. This...
&#39;Population&#39; afferent spike and &#39;population&#39; EPSP were recorded w... more &#39;Population&#39; afferent spike and &#39;population&#39; EPSP were recorded with extracellular microelectrodes in slices of hippocampal tissue maintained in vitro. Calcium concentration was changed in the bathing solution, and calcium activity ([Ca2+]0) was measured in interstitial fluid of the slice with ion-selective microelectrodes. Synaptic transfer was a non-linear continuous function of [Ca2+]0. Deviation of [Ca2+]0 by 0.1 mM from the 1.2 mM control level caused a change of approximately 15% in the slope of the input-output function.
The depolarizing actions of N-methyl-DL-aspartate (NMA) and L-glutamate on pyramidal neurones wer... more The depolarizing actions of N-methyl-DL-aspartate (NMA) and L-glutamate on pyramidal neurones were compared in a hippocampal slice preparation. Tetrodotoxin (1 microM) was added to the perfusion solution to suppress regenerative Na conductances. Depolarization evoked by ionophoretic application of NMA triggered slow, high-threshold regenerative spikes. These are considered to be Ca spikes since the amplitude and rate of rise could be reduced by verapamil, D-600, Co2+ and Mn2+, and increased by Ba2+. Multiple Ca-spike thresholds could be demonstrated in the same cell. In contrast, depolarizations evoked by L-glutamate only rarely triggered Ca-spikes. The minimum latency to the onset of depolarization evoked by NMA was less than 20 ms. The latency and amplitude of NMA-evoked responses were highly dependent on the position of the ionophoretic pipette; movements of the pipette by as little as 10-50 micron could markedly change the size of the response. Spatially separate hot spots for N...
The Journal of pharmacology and experimental therapeutics, 1984
The effects of the opioid peptides morphiceptin and [N-MePhe3-D-Pro4]morphiceptin (PL017), both m... more The effects of the opioid peptides morphiceptin and [N-MePhe3-D-Pro4]morphiceptin (PL017), both mu receptor agonists, were examined by electrophysiological techniques in the rat hippocampal slice and ligand binding techniques in hippocampal membrane preparations. The electrophysiological actions of the mu agonists were similar to those of the previously studied delta receptor agonist [D-Ala2, D-Leu5]enkephalin. Thus, for a given size field excitatory postsynaptic potential the amplitude of both population spike and intracellular excitatory postsynaptic potential was increased by morphiceptin. These effects were concentration dependent and reversed by naloxone. The EC50 for morphiceptin was 1.6 microM, which is consistent with the mu-selective binding properties of this peptide. Similar results were obtained with the more potent analog PL017. Morphiceptin and morphine had similar displacement profiles in competition experiments performed with hippocampal membranes and a variety of ra...
The effects of the N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonovaleric ... more The effects of the N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonovaleric acid (D-APV), and other excitatory amino acid antagonists, were studied on CA1 pyramidal neurones treated with picrotoxin or bicuculline to reduce synaptic inhibition mediated by gamma-aminobutyric acid (GABA). Under these conditions epileptiform burst firing is readily produced by orthodromic stimulation of the pyramidal cell population. D-APV reduced the plateau amplitude and duration of the depolarization underlying evoked and spontaneous bursts without affecting membrane potential, input resistance or the ability of the cell to fire a Ca2+ spike or a short train of Na+ spikes. A late component of the subthreshold excitatory post-synaptic potential (e.p.s.p.) was voltage dependent, being reduced in amplitude on membrane hyperpolarization. D-APV selectively removed this component of the e.p.s.p. in disinhibited slices. In contrast, in the absence of GABA antagonists, D-APV had no notic...
Xenopus oocytes injected with rat brain mRNA were used to identify and characterize the effects o... more Xenopus oocytes injected with rat brain mRNA were used to identify and characterize the effects of compounds that are antagonists at both the glycine site on N-methyl-D-aspartate (NMDA) receptors and the quisqualate/kainate receptor. Oocytes were voltage-clamped at -60 mV and inward currents were measured at equilibrium following perfusion with agonists and antagonists. Application of 7-chlorokynurenic acid (7-Cl-Kyn) or 6,7-dichloro-3-hydroxy-2-quinoxaline carboxylic acid (6,7-diCl-HQC), each at 15 microM, produced a parallel shift to the right of the glycine concentration-response curve. Schild analysis indicated a KB of 300 nM for 6,7-diCl-HQC and 350 nM for 7-Cl-Kyn. The slopes of the Schild plots were 1.01-1.02 in each case, suggesting that both compounds are competitive glycine antagonists. Both compounds also blocked the receptor mediating kainate-induced inward current. Schild analysis of 6,7-diCl-HQC (KB = 3.0 microM, slope = 0.98) indicated competitive antagonism of kainat...
1. Spontaneous discharges that resemble interictal spikes arise in area CA3 b/c of rat hippocampa... more 1. Spontaneous discharges that resemble interictal spikes arise in area CA3 b/c of rat hippocampal slices bathed in 8.5 mM [K+]o. Excitatory postsynaptic potentials (EPSPs) also appear at irregular intervals in these cells. The role of local synaptic excitation in burst initiation was examined with intracellular and extracellular recordings from CA3 pyramidal neurons. 2. Most (70%) EPSPs were small (less than 2 mV in amplitude), suggesting that they were the product of quantal release or were evoked by a single presynaptic action potential in another cell. It is unlikely that most EPSPs were evoked by a presynaptic burst of action potentials. Indeed, intrinsic burst firing was not prominent in CA3 b/c pyramidal cells perfused in 8.5 mM [K+]o. 3. The likelihood of occurrence and the amplitude of EPSPs were higher in the 50-ms interval just before the onset of each burst than during a similar interval 250 ms before the burst. This likely reflects increased firing probability of CA3 ne...
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Papers by R. Dingledine