Modulation of extracellular pH by glutamate and GABA in rat hippocampal slices

1992 ◽  
Vol 67 (1) ◽  
pp. 29-36 ◽  
Author(s):  
J. C. Chen ◽  
M. Chesler
Keyword(s):  
Hippocampal Slices ◽  
Extracellular Ph ◽  
Gamma Aminobutyric Acid ◽  
Local Pressure ◽  
Schaffer Collateral ◽  
Ca1 Region ◽  
Stratum Oriens ◽  
Alkaline Shift ◽  
Similar Appearance ◽  
Stimulation Of

1. Alkaline extracellular pH transients evoked by afferent stimulation, and local pressure ejection of glutamate and gamma-aminobutyric acid (GABA), were studied in the CA1 region of rat hippocampal slices. Amino acid-evoked responses were obtained by use of a dual micromanipulator, with the tip of a double-barreled pH-sensitive microelectrode positioned 50 microns from a pressure ejection pipette. 2. At 31 degrees C, in Ringer solutions buffered with 26 mM HCO3- and 5% CO2, mean extracellular pH in submerged 300-microns slices was 7.15 +/- 0.12 (n = 27 slices), at a tissue depth of approximately 150 microns. In Ringer buffered with 35 mM HCO3- and 5% CO2, extracellular pH was 7.29 +/- 0.10 (n = 19 slices). 3. Repetitive stimulation of the Schaffer collaterals caused an extracellular alkaline shift in stratum oriens, pyramidale, and radiatum, averaging 0.05 +/- 0.03 pH units among all regions (n = 138), with a maximum response of 0.16 pH units. Alkaline transients of similar appearance were obtained by local ejection of glutamate (0.01-0.12 pH units, n = 110) and GABA (0.01-0.18 pH units, n = 137). Control ejection of these amino acids into dilute agar caused only small acid shifts. 4. Superfusion of 100 microM picrotoxin abolished the GABA-evoked alkaline shift but failed to inhibit the Schaffer collateral- and glutamate-evoked alkalinizations. 5. Superfusion of 10(-5)-10(-3) M acetazolamide acidified the baseline by 0.05-0.10 pH units and amplified the Schaffer collateral- and glutamate-evoked alkaline shifts.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of voltage-gated calcium channels in the generation of activity-induced extracellular pH transients in the rat hippocampal slice

1996 ◽  
Vol 75 (6) ◽  
pp. 2354-2360 ◽  
Author(s):  
P. Paalasmaa ◽  
K. Kaila
Keyword(s):  
Calcium Channels ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Extracellular Ph ◽  
Stratum Radiatum ◽  
Gamma Aminobutyric Acid ◽  
Voltage Gated ◽  
Voltage Gated Calcium Channels ◽  
Alkaline Shift

1. The role of voltage-gated calcium channels in the generation of activity-induced alkaline shifts in extracellular pH (pHo) was studied in rat hippocampal slices (area CAI) by means of Ca(2+)-and H(+)-selective microlectrodes inserted into the stratum pyramidale and/or stratum radiatum. 2. After complete pharmacological blockade of ionotropic glutamate receptors and gamma-aminobutyric acid-A (GABAA) receptors, trains (5-10 Hz, 5-10s) of antidromic spikes in pyramidal neurons were associated with a fast alkaline transient of up to 0.17 pH units and a fall in the extracellular Ca2+ concentration ([Ca2+]o). The alkaline shift was strongly enhanced upon inhibition of extracellular carbonic anhydrase. 3. Application of 100 microM Ni2+ plus 100 microM Cd2+ inhibited both the fall in [Ca2+]o and the alkaline transient triggered by antidromic spikes. The alkaline shift was abolished in the absence of extracellular Ca2+. 4. In the absence of postsynaptic receptor antagonists, alkaline transients linked to a given level of synaptic excitation in s. radiatum were strongly suppressed after blockade of somatic (and, consequently, of dendritic “backpropagating”) spikes by microdrop application of tetrodotoxin to the cell-body layer. 5. We have previously shown that activity-induced alkaline transients in the CAI region are due to an influx of Ca2+ into neurons, which triggers an influx of H+ ions probably caused by activation of a plasmalemmal Ca2+/H+ ATPase. The present results indicate that much (in s. pyramidale perhaps all) of the pH-changing influx of Ca2+ is mediated by voltage-gated Ca2+ channels.

Agent-selective Effects of Volatile Anesthetics on GABAAReceptor–mediated Synaptic Inhibition in Hippocampal Interneurons

2001 ◽  
Vol 94 (2) ◽  
pp. 340-347 ◽  
Author(s):  
Koichi Nishikawa ◽  
M. Bruce MacIver
Keyword(s):  
Gabaa Receptor ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Volatile Anesthetics ◽  
Stratum Radiatum ◽  
Synaptic Inhibition ◽  
Gamma Aminobutyric Acid ◽  
Ca1 Region ◽  
Whole Cell Patch Clamp ◽  
Cortical Regions

Background A relatively small number of inhibitory interneurons can control the excitability and synchronization of large numbers of pyramidal cells in hippocampus and other cortical regions. Thus, anesthetic modulation of interneurons could play an important role for the maintenance of anesthesia. The aim of this study was to compare effects produced by volatile anesthetics on inhibitory postsynaptic currents (IPSCs) of rat hippocampal interneurons. Methods Pharmacologically isolated gamma-aminobutyric acid type A (GABAA) receptor-mediated IPSCs were recorded with whole cell patch-clamp techniques in visually identified interneurons of rat hippocampal slices. Neurons located in the stratum radiatum-lacunosum moleculare of the CA1 region were studied. The effects of clinically relevant concentrations (1.0 rat minimum alveolar concentration) of halothane, enflurane, isoflurane, and sevoflurane were compared on kinetics of both stimulus-evoked and spontaneous GABAA receptor-mediated IPSCs in interneurons. Results Halothane (1.2 vol% approximately 0.35 mm), enflurane (2.2 vol% approximately 0.60 mm), isoflurane (1.4 vol% approximately 0.50 mm), and sevoflurane (2.7 vol% approximately 0.40 mm) preferentially depressed evoked IPSC amplitudes to 79.8 +/- 9.3% of control (n = 5), 38.2 +/- 8.6% (n = 6), 52.4 +/- 8.4% (n = 5), and 46.1 +/- 16.0% (n = 8), respectively. In addition, all anesthetics differentially prolonged the decay time constant of evoked IPSCs to 290.1 +/- 33.2% of control, 423.6 +/- 47.1, 277.0 +/- 32.2, and 529 +/- 48.5%, respectively. The frequencies of spontaneous IPSCs were increased by all anesthetics (twofold to threefold). Thus, the total negative charge transfer mediated by GABAA receptors between synaptically connected interneurons was enhanced by all anesthetics. Conclusions Volatile anesthetics differentially enhanced GABAA receptor-mediated synaptic inhibition in rat hippocampal interneurons, suggesting that hippocampal interneuron circuits are depressed by these anesthetics in an agent-specific manner.

Role of Na-K pump potassium regulation and IPSPs in seizures and spreading depression in immature rabbit hippocampal slices

1990 ◽  
Vol 63 (2) ◽  
pp. 225-239 ◽  
Author(s):  
M. M. Haglund ◽  
P. A. Schwartzkroin
Keyword(s):  
Membrane Potential ◽  
Spreading Depression ◽  
Hippocampal Slices ◽  
Response Threshold ◽  
Resting Membrane Potential ◽  
Extracellular Potassium ◽  
Local Pressure ◽  
Ca1 Region ◽  
Potassium Regulation ◽  
Ca3 Region

1. Using the immature (8-12 days postnatal) rabbit hippocampal slice preparation, we investigated regional extracellular potassium concentration [( K+]o) changes that occur during spontaneous and evoked spreading depression (SD) episodes. We report here a difference between the CA1 and CA3 cell populations in the immature hippocampus with regard to 1) resting [K+]o, 2) magnitude of the [K+]o change during seizurelike events and SDs, and 3) susceptibility to SD episodes. Experiments were also performed to elucidate the roles that the Na-K pump and synaptic inhibition play in controlling SD onset, duration, and recovery. We demonstrated a major role for potassium regulation by the Na-K pump and a lesser modulatory role for inhibitory postsynaptic potentials (IPSPs) in preventing SD in the CA3 region. 2. Simultaneous intra- and extracellular recordings were made in the CA1 and CA3 regions of the immature rabbit hippocampus during spontaneous or evoked SD, while potassium ion-sensitive microelectrodes (K-ISMs) monitored changes in [K+]o. The CA1 region had 1) a higher frequency of spontaneous SD episodes than CA3, 2) a lower threshold to potassium-triggered SD, 3) a longer duration SD episode, and 4) smaller post-SD membrane potential and [K+]o undershoots (below the original resting membrane potential and resting [K+]o). 3. During the onset of a SD episode in the CA1 region, the local [K+]o rose either before or at the same time as the membrane potential depolarization. 4. In the CA3 region, spontaneous ictallike events consisting of tonic cell depolarization with repetitive activity followed by clonic afterdischarges were more likely to occur than SD episodes. During these ictallike episodes, [K+]o rose above the 10- to 12-mM ceiling level reported for adult CNS tissue during seizures. Increases in [K+]o evoked by repetitive stimulation were regulated at a lower level in CA3 (average [K+]o rise to 11.4 mM) than in CA1 (average [K+]o rise to 18.3 mM). 5. In CA3, bath application of 10 microM bicuculline or 3.4 mM penicillin did not change the frequency of spontaneously occurring SDs or the SD response threshold to local pressure ejection of 2 M KCl. However, blockade of IPSPs did lead to lower thresholds for SD or seizurelike episodes elicited by stimulation of the mossy fibers. 6. A single application of ouabain (10 microM) to CA3 by local pressure ejection caused a slow rise in local [K+]o measured with K-ISMs. The ouabain treatment also increased the frequency of spontaneous postsynaptic potential activity and decreased the amplitude and duration of CA3 pyramidal cell afterhyperpolarizations (AHPs).(ABSTRACT TRUNCATED AT 400 WORDS)

The uptake inhibitor L-trans-PDC enhances responses to glutamate but fails to alter the kinetics of excitatory synaptic currents in the hippocampus

1993 ◽  
Vol 70 (5) ◽  
pp. 2187-2191 ◽  
Author(s):  
J. S. Isaacson ◽  
R. A. Nicoll
Keyword(s):  
Time Course ◽  
Glutamate Uptake ◽  
Hippocampal Slices ◽  
Synaptic Cleft ◽  
Gamma Aminobutyric Acid ◽  
Patch Clamp Recording ◽  
Glutamatergic Synapses ◽  
Synaptic Currents ◽  
Ca1 Region ◽  
Transmitter Uptake

1. We have used patch-clamp recording techniques to study the physiological properties of a recently described glutamate uptake blocker, L-trans-pyrrolidine-2,4-dicarboxylic acid (L-trans-PDC), in the CA1 region of the guinea pig hippocampus. 2. L-trans-PDC markedly potentiated the action of exogenously applied glutamate and raised the ambient extracellular levels of glutamate in hippocampal slices. Despite these actions, L-trans-PDC did not affect the time course of either the N-methyl-D-aspartate (NMDA) or non-NMDA receptor-mediated synaptic currents evoked by the stimulation of a large number of neighboring synapses. 3. These findings are consistent with models of fast synaptic transmission in which transmitter is rapidly cleared from the synaptic cleft by diffusion. However, in marked contrast to fast gamma-aminobutyric acid A (GABAA) synapses in the hippocampus, uptake does not appear to play a role in regulating the "spill-over" of transmitter from neighboring, co-activated glutamatergic synapses. Therefore, either diffusion alone can effectively limit the temporal and spatial domain of synaptically released glutamate, or alternatively, L-trans-PDC like other currently available blockers is not sufficiently potent to reveal a role for transmitter uptake at glutamatergic synapses.

Differences between presynaptic and postsynaptic GABAB mechanisms in rat hippocampal pyramidal cells

1994 ◽  
Vol 72 (5) ◽  
pp. 2317-2327 ◽  
Author(s):  
T. A. Pitler ◽  
B. E. Alger
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Pertussis Toxin ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Gamma Aminobutyric Acid ◽  
Ca1 Region ◽  
Kinase C ◽  
First Response

1. Whole cell voltage-clamp techniques were used in the CA1 region of rat hippocampal slices to study presynaptic and postsynaptic gamma-aminobutyric acid B (GABAB) response mechanisms. The effects of the protein kinase C activator phorbol 12,13-diacetate (PDA), barium (Ba2+), and pertussis toxin were compared on the presynaptic and postsynaptic GABAB actions of bath-applied baclofen and paired-pulse depression (PPD) of the monosynaptic GABAA inhibitory postsynaptic current (IPSC). The magnitude of PPD was dependent on the amplitude of the first response. PPD was predominantly a GABAB-mediated effect, as it was very much reduced by the GABAB antagonist CGP 35348. 2. PDA enhanced monosynaptic GABAA IPSCs through an apparently presynaptic mechanism. Iontophoretic GABAA responses were unaffected, and there was no change in EIPSC. PDA increased the frequency of spontaneous, tetrodotoxin-insensitive IPSCs without significantly affecting their amplitudes. The inactive phorbol ester, 4 alpha-PDA did not alter IPSCs. After PDA application, stimulus intensity was adjusted to produce responses of comparable amplitude to control responses. PDA had a marked and reversible depressant effect on the postsynaptic GABAB response and caused a lesser, but still significant, reduction in the baclofen-induced reduction of monosynaptic IPSCs. PDA had no effect on PPD. 3. Ba2+ dramatically reduced postsynaptic GABAB responses; it had no effect on PPD. Ba2+ tended to decrease the presynaptic baclofen reduction of IPSCs, although this was not statistically significant. 4. Pertussis toxin, injected 2–3 days earlier into the intact hippocampus, blocked all three GABAB responses equally (approximately 70% decrease). 5. We conclude that presynaptic and postsynaptic GABAB mechanisms are mediated by G proteins that couple to different mechanisms. Discrepancies with previous work are evidently due to the use of different tissue preparations and different target responses. Even though protein kinase C activation caused a partial reduction in the presynaptic effect of baclofen, its lack of effect on PPD makes a significant role for protein kinase C in modulation of PPD unlikely.

Relative contributions of excitatory and inhibitory neuronal activity to alkaline transients evoked by stimulation of Schaffer collaterals in the rat hippocampal slice

1995 ◽  
Vol 74 (2) ◽  
pp. 643-649 ◽  
Author(s):  
T. Taira ◽  
P. Paalasmaa ◽  
J. Voipio ◽  
K. Kaila
Keyword(s):  
Hippocampal Slices ◽  
Low Frequency ◽  
Gamma Aminobutyric Acid ◽  
Schaffer Collaterals ◽  
Stratum Pyramidale ◽  
Low Frequency Stimulation ◽  
S 100 ◽  
Drug Inhibition ◽  
Frequency Stimulation ◽  
Stimulation Of

1. The neuronal basis of alkaline shifts in extracellular pH (pHo) evoked by stimulation of Schaffer collaterals was studied by means of double-barreled H(+)-selective microelectrodes in the area CA1 of rat hippocampal slices. 2. Alkaline transients in stratum pyramidale evoked by stimulation at a low frequency (5–10 Hz) were enhanced by pentobarbital sodium (100 microM). In the absence of the drug, inhibition of extracellular carbonic anhydrase (CAo) by benzolamide or by prontosildextran 5000 (PD 5000) resulted in an increase in the alkaline shifts. In contrast to this, alkaloses evoked by low-frequency stimulation in the presence of pentobarbital were attenuated by a subsequent inhibition of CAo. 3. Blockade of gamma-aminobutyric acid-A (GABAA) receptors with picrotoxin (PiTX; 100 microM) resulted in an enhancement of alkaline transients in s. pyramidale evoked by low-frequency stimulation (10 Hz) but suppressed alkaline shifts evoked by brief high-frequency (1 s, 100 Hz) trains of stimuli. 4. Application of trains of stimuli consisting of a constant number of pulses (50 or 100) revealed a striking dependence of the effect of benzolamide on stimulation frequency (10-200 Hz) in s. pyramidale: the enhancement of the alkaloses seen upon inhibition of CAo became progressively smaller with an increase in frequency, and at 100-200 Hz benzolamide produced a suppression or a complete block of the alkaline transients. However, alkaline transients evoked with the use of a constant train duration (5 s) were enhanced by benzolamide at all stimulation frequencies examined (5–200 Hz).(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular alkaline shifts in rat hippocampal slice are mediated by NMDA and non-NMDA receptors

1992 ◽  
Vol 68 (1) ◽  
pp. 342-344 ◽  
Author(s):  
J. C. Chen ◽  
M. Chesler
Keyword(s):  
Hippocampal Slice ◽  
Hippocampal Slices ◽  
Ca1 Region ◽  
Hippocampal Ca1 Region ◽  
Alkaline Shift ◽  
Hippocampal Ca1 ◽  
Antidromic Stimulation ◽  
Nmda Glutamate Receptors ◽  
Cell Firing ◽  
Ca1 Area

1. The pharmacology of synaptically evoked extracellular alkaline shifts was studied in the CA1 area of rat hippocampal slices. 2. Stimulus-evoked alkalinizations were unaffected by 2-amino-5-phosphonovalerate (APV) (20 microM). 3. 6-Cyano-7-nitro-nitroquinoxaline-2,3-dione (CNQX) (10 microM) inhibited the alkalinizations. In the continued presence of CNQX, an APV-sensitive, picrotoxin-insensitive, alkaline shift was elicited in low Mg2+ media. 4. Antidromic stimulation produced small alkaline shifts in comparison with orthodromic activation. 5. Our results demonstrate that in the hippocampal CA1 region, synaptically evoked alkalinizations can arise through both N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors. These responses cannot be explained by cell firing per se.

Alkaline extracellular pH shifts generated by two transmitter-dependent mechanisms

1992 ◽  
Vol 70 (S1) ◽  
pp. S286-S292 ◽  
Author(s):  
M. Chesler ◽  
J. C. T. Chen
Keyword(s):  
Repetitive Stimulation ◽  
Extracellular Ph ◽  
Aminobutyric Acid ◽  
Anion Channels ◽  
Gaba A ◽  
Bicarbonate Ions ◽  
Alkaline Shift ◽  
Independent Process ◽  
Free Media ◽  
Stimulation Of

Recent studies of the effect of γ-aminobutyric acid (GABA) on brain extracellular pH are reviewed. Experiments were performed on isolated turtle cerebellum, using double-barrelled pH-sensitive microelectrodes. Superfusion of GABA (1 mM) caused a rapid extracellular alkaline shift accompanied by a rise in extracellular K+. Washout of GABA was often associated with an acid rebound, concomitant with an undershoot of extracellular K+. The GABA-evoked alkaline shift was blocked by picrotoxin and mimicked by the GABA-A agonists isoguvacine and muscimol. The response persisted in the nominal absence of extracellular calcium, but it was reversibly abolished in nominally bicarbonate free media. In contrast, extracellular alkaline shifts evoked by repetitive stimulation of the parallel fibers were amplified in bicarbonate-free media and were insensitive to picrotoxin. These results indicate the existence of separate, transmitter-dependent mechanisms of extracellular alkalinization: (i) a GABA-A receptor mediated process, most likely associated with efflux of bicarbonate ions across GABA-A anion channels and (ii) a bicarbonate-independent process associated with excitatory synaptic transmission.Key words: GABA, bicarbonate, extracellular pH, alkaline shift.

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