Biomedical subjects

S F Traynelis

Publications and source records attributed to S F Traynelis.

At least 37 records · Page 2Linked to original sources

PubMed1997

Control of rat GluR6 glutamate receptor open probability by protein kinase A and calcineurin.

1. We have used non-stationary variance analysis to examine the single channel conductance and the probability of channel opening at the peak of the homomeric GluR6 response (Po,peak) to 100-200 ms application (10-90% exchange time, 0.3 ms) of glutamate onto excised membrane patches from transiently transfected human embryonic kidney cells (HEK 293). 2. Our determinations of both Po,peak and single channel conductance of simulated current responses are insensitive to system filtering, response rise time, desensitization rate and measured variation in our drug perfusion speed. Isolation of stochastic current fluctuations using the local mean response waveform minimizes problems associated with modest rundown of response amplitude during the experiment. 3. The slope conductance calculated from the weighted mean unitary currents for the channels activated in response to glutamate application is 16 pS. Chord conductance between-40 and -80 mV is independent of agonist concentration. Conversion of the codon for glutamine621 to arginine (Q621R) by RNA editing reduces conductance by more than 35-fold to less than 0.4 pS without changing response time course, desensitization, or Po,peak. 4. Po,peak is high at saturating glutamate concentrations (0.65 +/- 0.23; mean +/- S.D.) and varies with agonist concentrations. The half-maximally effective glutamate concentration (EC50) determined for Po,peak (0.2 mM; Hill slope = 0.6) is similar to that determined for the macroscopic peak current amplitude (0.5 mM; Hill slope = 1.0) in response to rapid agonist application. 5. Inclusion of the purified catalytic subunit of cAMP-dependent protein kinase A (PKA) in the patch pipette increases Po,peak to 0.85 +/- 0.12 and co-transfection of cells with a cDNA encoding the catalytic subunit of PKA (C alpha-PKA) increases Po,peak to 0.94 +/- 0.09. 6. Inclusion of purified calcineurin plus its coactivators 200 nM Ca2+ and calmodulin in the patch pipette decreases Po,peak to 0.48 +/- 0.10. The calcineurin-stimulated decrease of Po,peak in cells co-transfected with C alpha-PKA is blocked by 800 nM deltamethrin, a calcineurin inhibitor. Calmodulin, 200 nM Ca2+ and deltamethrin have no effect on Po,peak in the absence of calcineurin. As predicted from its effects on Po,peak, inclusion of calcineurin in the patch pipette accelerates the run-down of whole cell GluR6 responses in cells co-transfected with C alpha-PKA. 7. The effects of both calcineurin and PKA on Po,peak for GluR6 receptors in excised patches occur without any detectable changes to response time course, desensitization, or chord conductance. 8. We conclude that the binding of glutamate to homomeric GluR6 receptors is associated with a high probability of channel opening, which is under the control of two signalling systems that are known to be co-localized at the neuronal membrane: PKA (Po,peak near 1.0) and calcineurin (Po,peak near 0.5).

Animals↗

PubMed1997

4-Methylhomoibotenic acid activates a novel metabotropic glutamate receptor coupled to phosphoinositide hydrolysis.

Metabotropic glutamate receptors (mGluRs) are a family of glutamate receptors that are coupled to a variety of second messenger systems through GTP-binding proteins. Of the eight subtypes cloned to date, mGluR1 and mGluR5 are coupled to phosphoinositide hydrolysis in expression systems, and both are activated by the glutamate analogue 1-aminocyclopentane-1S,3R-dicarboxylic acid. Previously, we provided evidence that in rat cortical slices, 4-bromohomoibotenic acid (BrHI) and 4-methylhomoibotenic acid (MHI) activate a 1-aminocyclopentane-1S,3R-dicarboxylic acid-insensitive phosphoinositide hydrolysis-coupled mGluR. We further examine these compounds in expression systems. In a stable cell line expressing mGluR1a, BrHI is a weak partial agonist whereas MHI has no agonist activity. In Xenopus oocytes expressing mGluR1a or mGluR5a, BrHI is a weak agonist at mGluR5a whereas MHI is without effect on either receptor. Both BrHI and MHI have weak agonist activity at mGluRs 4a and 7a expressed in stable BHK cell lines whereas neither compound had any activity on BHK cells expressing mGluR2. Finally, we found that the novel mGluR antagonist LY341495 completely blocked the activation of mGluR1 and mGluR5 and blocked the phosphoinositide hydrolysis response to DHPG in rat cortical slices. In contrast, LY341495 did not block the phosphoinositide hydrolysis response to MHI in rat cortical slices. This provides further evidence that the phosphoinositide hydrolysis response to MHI in rat cortical slices is due to activation of a novel receptor that is distinct from the previously cloned mGluRs.

Animals↗

PubMed1995

Control of proton sensitivity of the NMDA receptor by RNA splicing and polyamines.

The function of the N-methyl-D-aspartate (NMDA)-preferring glutamate receptor can be regulated by extracellular pH, a process that may be important during ischemia in the brain or during seizures. Protons inhibit NMDA receptor function by 50 percent at pH 7.3 through interactions with the NR1 subunit, and both polyamines and NR1 exon 5 potentiate receptor function through relief of the tonic proton inhibition present at physiological pH. A single amino acid (lysine 211) was identified that mediates the effects of exon 5 in the rat brain. Electroneutral substitutions at this position restored pH sensitivity and, consequently, polyamine relief of tonic inhibition. This effect, together with the structural similarities between polyamines and the surface loop encoded by exon 5, suggest that exon 5 may act as a tethered pH-sensitive constitutive modulator of NMDA receptor function.

Alternative Splicing↗

PubMed1994

Identification of two cysteine residues that are required for redox modulation of the NMDA subtype of glutamate receptor.

Modulation of NMDA-mediated responses by oxidizing and reducing reagents has been described in a variety of neuronal preparations. Here, we report that NMDA-gated currents of oocytes expressing heteromeric NMDA receptors are also modulated by sulfhydryl redox reagents. Each cysteine residue in the NMDAR1 (NR1) subunit and each conserved NMDAR2 (NR2) cysteine residue in a prototypical subunit (NR2B) was tested for its role in redox modulation. We have identified 2 cysteines in the NR1 subunit that are required for redox modulation of NMDA-gated currents in oocytes expressing NR1-NR2B, NR1-NR2C, or NR1-NR2D receptors. Mutation of these same 2 cysteines also eliminated potentiation by spermine and shifted the IC50 for H+ inhibition and the EC50 for NMDA. Redox modulation of heteromeric NR1-NR2A receptors appeared to be different from that of the other heteromeric receptors, indicating the presence of one or more unique redox modulatory sites on NR1-NR2A receptors.

Animals↗

PubMed1994

Selective RNA editing and subunit assembly of native glutamate receptors.

RNA editing and subunit assembly of ionotropic glutamate receptors (GluRs) were examined in an oligodendrocyte progenitor cell line, CG4, which expresses GluR2-GluR4, GluR6, GluR7, KA1, and KA2. AMPA-evoked currents rapidly desensitize, whereas kainate-evoked currents contain a steady-state component with a nearly linear current-voltage relation and a fast desensitizing component that is inwardly rectifying. The Q/R site is edited > 95% to the arginine codon in GluR2(Q607) mRNA, and < 5% in GluR6(Q621) mRNA. Immunoprecipitation experiments demonstrate that GluR6 and/or GluR7 subunits assemble with KA2, but not with GluR2-GluR4. These results indicate that oligodendrocyte progenitor cells selectively edit and assemble glutamate receptors into at least two functionally and structurally distinct heteromeric channels.

Animals↗

PubMed1993

Estimated conductance of glutamate receptor channels activated during EPSCs at the cerebellar mossy fiber-granule cell synapse.

We have analyzed the variance associated with the decay of the non-NMDA receptor component of synaptic currents, recorded from mossy fiber-granule cell synapses in cerebellar slices, to obtain a conductance estimate for the synaptic channel. Current fluctuations arising from the random channel gating properties were separated from those arising from the fluctuations in the population of channels by subtracting the mean excitatory postsynaptic current (EPSC) waveform scaled to the EPSC peak amplitude. A weighted mean single-channel conductance of approximately 20 pS was determined from the relationship between the mean current and the variance around the mean during the decay of evoked and spontaneous synaptic currents. This result suggests that high conductance non-NMDA channels, such as the 10-30 pS glutamate receptor channel previously characterized in granule cells, carry the majority of the fast component of the EPSC at this synapse. In addition, our data are consistent with the activation of surprisingly few (approximately 10) non-NMDA channels by a single packet of transmitter.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1993

Evidence for more than one type of non-NMDA receptor in outside-out patches from cerebellar granule cells of the rat.

1. Application of non-NMDA (non-N-methyl-D-aspartate) receptor agonists onto outside-out patches of cerebellar granule cells gave two characteristic types of response (in different patches) which we have referred to as 'high conductance' and 'low conductance' responses. At a qualitative level these patches could be readily distinguished by the size of the noise increase accompanying their membrane currents. 2. In high conductance patches both AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) and kainate gave discrete single-channel conductances (10-30 pS), while in low conductance patches, AMPA produced small discrete events (6-10 pS), and kainate opened channels with conductances too small to be directly resolved. All patches examined contained NMDA receptor channels with characteristic 50 and 40 pS conductance levels. 3. Despite the marked differences in single-channel conductances, kainate dose-response curves constructed for high and low conductance patches had similar EC50 values of approximately 150 microM. 4. Spectral analysis of low conductance kainate responses gave an estimated channel conductance of approximately 1.5 pS. In these same low conductance patches AMPA produced discrete openings with two conductance levels; their mean conductances (and relative proportions) were 6 (87%) and 10 pS (13%). 5. In high conductance patches, glutamate (10-30 microM), AMPA (3-10 microM), and kainate (10-30 microM), each activated non-NMDA channels with three multiple conductance levels. The amplitudes of these conductance levels (approximately 10, 20 and 30 pS) were similar for each of the agonists, and their relative proportions (i.e. areas in the amplitude histograms) were constant for all three agonists. In addition, the relative proportion of levels was constant between patches, and all three levels were invariably present. These observations are all consistent with the idea that the three multiple conductances originate from a single receptor channel, activated by AMPA, kainate and glutamate. 6. Non-NMDA single-channel current-voltage (I-V) plots showed outward rectification in high conductance patches. For all three multiple conductance levels the ratio of outward to inward single-channel slope conductance was 1.8 +/- 0.1 and this rectification remained present in symmetrical Na+ solutions. 7. In high conductance patches, the events produced by a rapid application of 20-50 microM glutamate were compared with those activated during steady-state application.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Potentiation of NMDA receptor currents by arachidonic acid.

Arachidonic acid is released by phospholipase A2 when activation of N-methyl-D-aspartate (NMDA) receptors by neurotransmitter glutamate raises the calcium concentration in neurons, for example during the initiation of long-term potentiation and during brain anoxia. Here we investigate the effect of arachidonic acid on glutamate-gated ion channels by whole-cell clamping isolated cerebellar granule cells. Arachidonic acid potentiates, and makes more transient, the current through NMDA receptor channels, and slightly reduces the current through non-NMDA receptor channels. Potentiation of the NMDA receptor current results from an increase in channel open probability, with no change in open channel current. We observe potentiation even with saturating levels of agonist at the glutamate- and glycine-binding sites on these channels; it does not result from conversion of arachidonic acid to lipoxygenase or cyclooxygenase derivatives, or from activation of protein kinase C. Arachidonic acid may act by binding to a site on the NMDA receptor, or by modifying the receptor's lipid environment. Our results suggest that arachidonic acid released by activation of NMDA (or other) receptors will potentiate NMDA receptor currents, and thus amplify increases in intracellular calcium concentration caused by glutamate. This may explain why inhibition of phospholipase A2 blocks the induction of long-term potentiation.

Animals↗

PubMed1992

Rapid-time-course miniature and evoked excitatory currents at cerebellar synapses in situ.

Neurotransmission from mossy fibre terminals onto cerebellar granule cells is almost certainly mediated by L-glutamate. By taking advantage of the small soma size, limited number of processes and short dendrite length of granule cells, we have obtained high-resolution recordings of spontaneous miniature excitatory postsynaptic currents (m.e.p.s.cs) and evoked currents in thin cerebellar slices. Miniature currents have a similar time-course and pharmacology to evoked currents and consist of an exceptionally fast non-NMDA (N-methyl-D-aspartate) component (measured rise-time, 200 microseconds; estimated pre-filtered rise-time less than 100 microseconds; decay time constant, tau = 1.0 ms), followed by 50 pS NMDA channel openings that are directly resolvable. We could find no evidence for the recent proposal that miniature currents in granule cells are mediated solely by NMDA channels with a novel time course. The non-NMDA receptor component of m.e.p.s.cs has a skewed amplitude distribution, which suggests potential complications for quantal analysis. The difference in time course between the m.e.p.s.cs reported here and other synaptic currents in the brain could reflect differences in synaptic function or electrotonic filtering; the relative contribution of these possibilities has yet to be established.

Animals↗

PubMed1991

Pharmacological properties and H+ sensitivity of excitatory amino acid receptor channels in rat cerebellar granule neurones.

1. N-Methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and kainate receptor channels have been examined in rat cerebellar granule neurones with whole-cell and single-channel patch-clamp methods. The whole-cell peak and steady-state aspartate and NMDA currents were reversibly inhibited by extracellular protons; the IC50 (concentration producing half-maximal inhibition) for the full H+ inhibition curve for NMDA receptors corresponded to pH 7.3, near to physiological pH. (S)-AMPA and kainate whole-cell currents were inhibited by protons with IC50 values that corresponded to pH 6.3 and 5.7, respectively; these receptors were, however, insensitive to H+ concentrations that inhibited NMDA receptor responses. 2. Proton inhibition of the NMDA, AMPA and kainate receptor-mediated responses was voltage insensitive, and did not involve a shift in reversal potential. 3. The EC50 (concentration producing half-maximal effect) for aspartate calculated from the whole-cell dose-response curve was similar at pH 6.8 and 7.6 (mean 11.2 microM). Although the EC50 for glycine potentiation of the aspartate response was marginally increased from 273 nM at pH 7.6 to 373 nM at pH 6.8, H+ inhibition was not overcome by up to 1 mM-external glycine. Inhibiting concentrations of H+ appropriate for AMPA and kainate receptors did not markedly alter the EC50 values determined for (S)-AMPA (3.4 microM) and kainate (114 microM) at pH 7.2. 4. Treatment of neurones with N-ethylmaleimide, iodoacetic acid, dithiothretiol or diethyl pyrocarbonate did not influence proton inhibition of NMDA receptor responses. However, treatment with diethyl pyrocarbonate, which potentiated aspartate responses, appeared to reduce the effectiveness of Zn2+ inhibition of NMDA receptors. 5. Desensitization of whole-cell NMDA and (S)-AMPA currents was studied with ionophoretic application of agonist to the cell soma. Whole-cell aspartate currents desensitized rapidly, irrespective of the glycine concentration. Increased H+ concentrations did not detectably alter the ratio of peak/steady-state current, or the time constants describing the onset of, or recovery from, desensitization. The time constant describing desensitization of (S)-AMPA-induced whole-cell currents also appeared unchanged by inhibiting pH (6.2). 6. The amplitudes of aspartate- or NMDA-activated single-channel multiple conductance levels were unchanged by decreasing the pH to 6.8.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Regional variation of extracellular space in the hippocampus.

The factors responsible for the unusual susceptibility of the hippocampus to seizures and ischemic cell damage are not well understood. The CA1 pyramidal subfield of the hippocampus is particularly vulnerable to seizure activity and damage after ischemia. The possibility was examined that regional differences exist in extracellular volume, which might influence neuronal excitability and response to injury in the hippocampus. CA1 stratum pyramidale exhibited an exceptionally low extracellular volume fraction (EVF) of 0.12, whereas the EVFs of CA3 and dentate were considerably higher--0.18 and 0.15, respectively. The EVF of CA1 stratum pyramidale was reversibly reduced by 30 percent when the extracellular potassium concentration was raised from 3.5 to 8.5 mM, a procedure that induced spontaneous electrographic seizures in CA1. Thus there are regional variations in the properties of the extracellular space in the hippocampus that might underlie the propensity of the CA1 region to develop seizures and to suffer damage after ischemia.

Animals↗

PubMed1990

Proton inhibition of N-methyl-D-aspartate receptors in cerebellar neurons.

Mammalian neurons contain at least three types of excitatory amino-acid receptors, selectively activated by N-methyl-D-aspartate (NMDA) or aspartate, (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionate ((S)-AMPA) and kainate. An important aspect of NMDA receptors is their regulation by a variety of factors such as glycine, Mg2+ and Zn2+ that are present in vivo. We show here that NMDA receptor responses are selectively inhibited by protons, with a 50% inhibitory concentration (IC50) that is close to physiological pH, implying that NMDA receptors are not fully active under normal conditions. (S)-AMPA and kainate responses remain unchanged at similar pH levels. Proton inhibition is voltage-insensitive and does not result either from fast channel block, a change in channel conductance, or an increase in the 50% excitatory concentration (EC50) of aspartate/NMDA or glycine. Instead, protons seem to decrease markedly the opening frequency of 30-50 pS NMDA channels, and reduce the relative proportion of longer bursts. This feature of NMDA receptors could be relevant to neurotoxic activation of NMDA receptors during ischaemia, as well as to seizure generation, as extracellular proton changes occur during both of these pathological situations. Furthermore, these results may have implications for normal NMDA receptor function as transient changes in extracellular protons occur during synaptic transmission.

Animals↗

PubMed1990

Different responses of CA1 and CA3 regions to hypoxia in rat hippocampal slice.

1. To study the effects of brief periods of hypoxia on cellular functions in the rat hippocampal slice, extracellular and intracellular recordings were made from pyramidal neurons, and interstitial potassium activity ([K+]o) was measured in the pyramidal cell layers. Slices were perfused in an interface chamber at 36-37 degrees C with medium containing 8.5 mM [K+]o. Hypoxia was induced by switching the overflow gas from O2-CO2 to N2-CO2. 2. Brief periods of hypoxia (5-60 s) produced electrographic seizures with typical tonic and clonic components in 53% of 293 slices that generated spontaneous interictal bursts. Hypoxia-induced seizures were usually initiated in and restricted to the Ca1 region; only 2.5% of these slices generated seizures in CA3. In contrast to the CA1 region, the CA3 region could undergo spreading depression during hypoxia. The probability of seizure generation in CA1 was increased with increasing duration of hypoxia and was greatly reduced by lowering the bath temperature a few degrees. 3. [K+]o gradually increased in the CA1 and CA3 cell layers during the 20 s leading up to an hypoxia-induced seizure. [K+]o rose to approximately 9.8 mM (from a base line of 8.5 mM) in CA1 just before a seizure and to 11.4 mM during the seizure. After hypoxia, [K+]o reached a higher level in CA1 than in CA3, regardless of whether 1 microM tetrodotoxin was present to eliminate differences in cell firing in the two regions. CA1 pyramidal cells and glia gradually depolarized by several millivolts during and after hypoxia; no initial hyperpolarizing phase was detected. 4. Burst input from CA3 was necessary for hypoxia-induced seizures. The frequency and intensity of spontaneous burst-firing in CA3 remained steady in the period leading up to a CA1 seizure episode. In contrast, the intensity of synaptically driven bursts in CA1 grew markedly just before seizure onset. N-methyl-D-aspartate (NMDA) receptors participated in the crescendo of increasingly synchronous activity in CA1, because the competitive NMDA receptor antagonist, D-2-amino-5-phosphonovaleric acid (D-APV, 30 microM), stereoselectively reduced seizure intensity. 5. Hypoxia-induced seizures were followed by a depressant phase, which was manifested most prominently by a prolonged (up to several minutes) reduction in the frequency and intensity of burst-firing in the CA3 region, hyperpolarization of CA1 neurons, and undershoot of [K+]o. In normal (3.5 mM) [K+]o, synaptically driven population spikes in CA1 were only reduced in amplitude by hypoxia; hypoxia did not induce seizures in 3.5 mM [K+]o.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1989

Effect of kindling on potassium-induced electrographic seizures in vitro.

The properties of high [K+]o-induced spontaneous bursting and electrographic seizures in hippocampal slices prepared from rats subjected to kindling from either the lateral entorhinal cortex or the angular bundle were compared to those in control slices. Kindling enhanced the frequency of K+-induced burst-firing in the CA3 region and the duration of triggered bursts in the dentate gyrus, as previously reported. However, kindling had no influence on the characteristics or occurrence of electrographic seizures in the CA1 region of slices bathed in elevated [K+]o. In addition, the development of electrographic seizures in slices from control animals did not require a preconditioning period of burst input from the CA3 region.

Alkaloids↗

PubMed1989

Modification of potassium-induced interictal bursts and electrographic seizures by divalent cations.

Reduction of external calcium and magnesium from 1.5 to 1.2 mM intensified potassium-induced interictal bursts, increased the likelihood of electrographic seizure occurrence in CA1, and rendered seizure initiation independent of N-methyl-D-aspartate (NMDA) receptor activation. In contrast to slices bathed in 1.5 mM divalent cations, in 1.2 mM divalents spontaneous CA1 seizures still occurred in CA1 minislices that contained at least 1500 neurons after removal of the CA3 burst generator, suggesting that divalent cations critically modulate the dependence of CA1 seizure initiation on interictal input. Since this slight reduction in external divalent cations enhanced tissue excitability, similar changes might promote epileptogenesis in situ.

2-Amino-5-phosphonovalerate↗

PubMed1989

Role of extracellular space in hyperosmotic suppression of potassium-induced electrographic seizures.

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 not influence electrographic seizure occurrence. Hyperosmotic changes with plasma membrane impermeable compounds, but not permeable compounds, produced significant concentration-dependent decreases (1-10%) in the electrical resistance of CA1 stratum pyramidale. Because tissue resistance is proportional to extracellular volume, these results suggest that hyperosmotic suppression of electrographic seizures is associated with expansion of the extracellular space in hippocampal slices. 3. Measurement of electrical resistance of the CA1 stratum pyramidale during spreading depression and electrographic seizure revealed an increase in tissue resistance to 122% and 108% of control, respectively. Furthermore, a slight (approximately 2%) but significant increase in electrical resistance gradually occurred over the 20 s immediately preceding seizure generation. The observed increase in tissue resistance suggests extracellular space is decreased during these events. 4. Hyperosmolality did not alter CA3 interictal burst frequency. However, burst intensity, estimated from the total length of the burst waveform, was significantly reduced in both the CA3 (83% control) and CA1 region (67% control) when osmotic changes were imposed by plasma membrane impermeant compounds. Additionally, media made hypoosmotic by removal of 7.5 mM NaCl reversibly increased burst intensity. 5. High [K+]o potentiated excitatory synaptic transmission and excitatory postsynaptic potential (EPSP) spike coupling.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Potassium-induced spontaneous electrographic seizures in the rat hippocampal slice.

1. The CA1 region of rat hippocampal slices bathed in 8.5 mM interstitial K+ ([K+]o) exhibited spontaneous 20- to 90-s electrographic seizures at regular intervals of 1-8 min. In these same slices CA3 neurons generated spontaneous interictal bursts that propagated throughout the pyramidal cell subfields. CA1 electrographic seizures contained components reminiscent of discharges recorded in vivo during tonic-clonic motor seizures. The tonic phase lasted 1-10 s, consisted of a sustained depolarization and firing of CA1 pyramidal cells, and was associated with a negative extracellular potential in the cell layer. The clonic phase lasted tens of seconds and was composed of paroxysmal bursts with afterdischarges in pyramidal cells. 2. Electrographic seizures in CA1 were focal in nature in that they did not invade the CA3 region. Moreover, in approximately 85% of all slices the frequency and amplitude of interictal bursts in CA3 did not change during a CA1 seizure. 3. Both the tonic phase and each clonic discharge of an electrographic seizure were triggered synaptically by a CA3 interictal burst. Microlesions of the Schaffer collateral input abolished CA1 seizures in high [K+]o, and electrical stimulation of these afferents, in a pattern designed to mimic interictal input, restored seizures. Likewise, similarly patterned electrical stimulation of these fibers in slices bathed in high [K+]o with the CA3 region removed reliably evoked electrographic seizures with period and duration similar to spontaneous seizures in whole slices. 4. Electrographic seizures but not CA3 interictal bursts could be reversibly abolished by lowering the temperature from 35-37 to 28-30 degrees C or by the competitive N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovaleric acid (5-10 microM). The inactive isomer, L-2-amino-5-phosphonovaleric acid (25 microM) did not eliminate seizures. 5. Neither the frequency nor intensity of interictal bursts recorded in the CA3 region changed in the minute preceding seizure initiation. Thus, although the presence of interictal input from the CA3 region is required for CA1 seizure generation, it appears that electrographic seizures do not result from a change in the quality or quantity of interictal input to the CA1 region. 6. During the 30- to 60-s period leading to a seizure the excitability of CA1 pyramidal cells appeared to increase gradually. Over the interseizure interval both CA1 pyramidal cells and glia gradually depolarized, the intensity of interictal bursts recorded in the CA1 region increased, and the extracellular DC potential recorded in the CA1 cell layer drifted negative.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Amino acid receptors and uptake systems in the mammalian central nervous system.

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.

Animals↗