Variant firing patterns in rat hippocampal pyramidal cells modulated by extracellular potassium

1994 ◽  
Vol 71 (3) ◽  
pp. 831-839 ◽  
Author(s):  
M. S. Jensen ◽  
R. Azouz ◽  
Y. Yaari
Keyword(s):  
Action Potentials ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Resting Membrane Potential ◽  
Extracellular Potassium ◽  
Differential Distribution ◽  
Ca1 Pyramidal Cells ◽  
Current Pulses ◽  
High K ◽  
Single Spike

1. The distribution of distinctive firing modes within the population of CA1 pyramidal cells and their modulation by the extracellular concentration of potassium ([K+]o) were investigated with intracellular recordings in rat hippocampal slices. 2. Pyramidal cells were injected with long (> 250 ms) and brief (3-5 ms) positive current pulses of increasing intensity. In normal [K+]o (3.5 mM), most cells (38 of 46 cells; 83%) were regular spiking neurons (generating accommodating trains of independent action potentials during long depolarizations and a single spike in response to brief stimuli). The remaining pyramidal cells (8 of 46; 17%) displayed differential tendencies to generate stereotyped clusters of action potentials, or bursts, according to which they were grouped into three subsets of endogenous bursters: grade I, bursting only when stimulated with long depolarizing current pulses (6 of 46; 13%); grade II, bursting also in response to brief stimulation (1 of 46; 2%); grade III, bursting also spontaneously even in absence of synaptic transmission (1 of 46; 2%). 3. Raising [K+]o from 3.5 to 7.5 mM (high [K+]o) significantly reduced resting membrane potential and input impedance but did not change the threshold potential for eliciting an action potential. 4. Raising [K+]o to 7.5 mM reversibly converted many regular spiking cells to bursters. Likewise, the burst tendency of normally bursting pyramidal cells increased to a higher grade in high [K+]o. Consequently, the fraction of bursters in high [K+]o (17 of 41 cells; 42%) was approximately 2.5-fold higher than in normal [K+]o and their differential distribution was shifted toward higher grades of bursting.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Chloride-Cotransport Blockade Desynchronizes Neuronal Discharge in the “Epileptic” Hippocampal Slice

2000 ◽  
Vol 83 (1) ◽  
pp. 406-417 ◽  
Author(s):  
Daryl W. Hochman ◽  
Philip A. Schwartzkroin
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Hippocampal Slices ◽  
Field Potential ◽  
Pyramidal Cells ◽  
Extracellular Potassium ◽  
Intracellular Recordings ◽  
Population Activity ◽  
Ca1 Pyramidal Cells ◽  
Epileptiform Discharges

Antagonism of the chloride-cotransport system in hippocampal slices has been shown to block spontaneous epileptiform (i.e., hypersynchronized) discharges without diminishing excitatory synaptic transmission. Here we test the hypotheses that chloride-cotransport blockade, with furosemide or low-chloride (low-[Cl−]o) medium, desynchronizes the firing activity of neuronal populations and that this desynchronization is mediated through nonsynaptic mechanisms. Spontaneous epileptiform discharges were recorded from the CA1 and CA3 cell body layers of hippocampal slices. Treatment with low-[Cl−]o medium led to cessation of spontaneous synchronized bursting in CA1 ≥5–10 min before its disappearance from CA3. During the time that CA3 continued to burst spontaneously but CA1 was silent, electrical stimulation of the Schaffer collaterals showed that hyperexcited CA1 synaptic responses were maintained. Paired intracellular recordings from CA1 pyramidal cells showed that during low-[Cl−]otreatment, the timing of action potential discharges became desynchronized; desynchronization was identified with phase lags in firing times of action potentials between pairs of neurons as well as a with a broadening and diminution of the CA1 field amplitude. Continued exposure to low-[Cl−]o medium increased the degree of the firing-time phase shifts between pairs of CA1 pyramidal cells until the epileptiform CA1 field potential was abolished completely. Intracellular recordings during 4-aminopyridine (4-AP) treatment showed that prolonged low-[Cl−]oexposure did not diminish the frequency or amplitude of spontaneous postsynaptic potentials. CA3 antidromic responses to Schaffer collateral stimulation were not significantly affected by prolonged low-[Cl−]o exposure. In contrast to CA1, paired intracellular recordings from CA3 pyramidal cells showed that chloride-cotransport blockade did not cause a significant desynchronization of action potential firing times in the CA3 subregion at the time that CA1 synchronous discharge was blocked but did reduce the number of action potentials associated with CA3 burst discharges. These data support our hypothesis that the anti-epileptic effects of chloride-cotransport antagonism in CA1 are mediated through the desynchronization of population activity. We hypothesize that interference with Na+,K+,2Cl−cotransport results in an increase in extracellular potassium ([K+]o) that reduces the number of action potentials that are able to invade axonal arborizations and varicosities in all hippocampal subregions. This reduced efficacy of presynaptic action potential propagation ultimately leads to a reduction of synaptic drive and a desynchronization of the firing of CA1 pyramidal cells.

Network Interactions Mediated by New Excitatory Connections Between CA1 Pyramidal Cells in Rats With Kainate-Induced Epilepsy

2002 ◽  
Vol 87 (3) ◽  
pp. 1655-1658 ◽  
Author(s):  
Bret N. Smith ◽  
F. Edward Dudek
Keyword(s):  
Status Epilepticus ◽  
Action Potentials ◽  
Cell Layer ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Ca1 Pyramidal Cells ◽  
Axon Sprouting ◽  
Synaptic Interactions ◽  
Network Bursts ◽  
Ca1 Area

Axon sprouting and synaptic reorganization in the hippocampus are associated with the development of seizures in temporal lobe epilepsy. Synaptic interactions among CA1 pyramidal cells were examined in fragments of hippocampal slices containing only the CA1 area from saline- and kainate-treated rats. Glutamate microapplication to the pyramidal cell layer increased excitatory postsynaptic current (EPSC) frequency, but only in rats with kainate-induced epilepsy. In bicuculline, action potentials evoked in single pyramidal cells increased the frequency of network bursts only in slices from rats with kainate-induced epilepsy. These data further support the hypothesis that excitatory connections between CA1 pyramidal cells increase after kainate-induced status epilepticus.

Differential Fall in ATP Accounts for Effects of Temperature on Hypoxic Damage in Rat Hippocampal Slices

2000 ◽  
Vol 83 (6) ◽  
pp. 3462-3472 ◽  
Author(s):  
J. Wang ◽  
G. Chambers ◽  
J. E. Cottrell ◽  
I. S. Kass
Keyword(s):  
Glucose Concentration ◽  
Action Potentials ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Cytosolic Calcium ◽  
Ca1 Neurons ◽  
Ca1 Pyramidal Cells ◽  
Artificial Cerebrospinal Fluid ◽  
Intracellular Ca ◽  
Effects Of Temperature

Intracellular recordings, ATP and cytosolic calcium measurements from CA1 pyramidal cells in rat hippocampal slices were used to examine the mechanisms by which temperature alters hypoxic damage. Hypothermia (34°C) preserved ATP (1.7 vs. 0.8 nM/mg) and improved electrophysiologic recovery of the CA1 neurons after hypoxia; 58% of the neurons subjected to 10 min of hypoxia (34°C) recovered their resting and action potentials, while none of the neurons at 37°C recovered. Increasing the glucose concentration from 4 to 6 mM during normothermic hypoxia improved ATP (1.3 vs. 0.8 nM/mg) and mimicked the effects of hypothermia; 67% of the neurons recovered their resting and action potentials. Hypothermia attenuated the membrane potential changes and the increase in intracellular Ca2+(212 vs. 384 nM) induced by hypoxia. Changing the glucose concentration in the artificial cerebrospinal fluid primarily affects ATP levels during hypoxia. Decreasing the glucose concentration from 4 to 2 mM during hypothermic hypoxia worsened ATP, cytosolic Ca2+, and electrophysiologic recovery. Ten percent of the neurons subjected to 4 min of hypoxia at 40°C recovered their resting and action potentials; this compared with 60% of the neurons subjected to 4 min of normothermic hypoxia. None of the neurons subjected to 10 min of hypoxia at 40°C recovered their resting and action potentials. Hyperthermia (40°C) worsens the electrophysiologic changes and induced a greater increase in intracellular Ca2+(538 vs. 384 nM) during hypoxia. Increasing the glucose concentration from 4 to 8 mM during 10 min of hyperthermic hypoxia improved ATP (1.4 vs. 0.6 nM/mg), Ca2+(267 vs. 538 nM), and electrophysiologic recovery (90 vs. 0%). Our results indicate that the changes in electrophysiologic recovery with temperature are primarily due to changes in ATP and that the changes in depolarization and Ca2+are secondary to these ATP changes. Both primary and secondary changes are important for explaining the improved electrophysiologic recovery with hypothermia.

Extracellular Chloride and the Maintenance of Spontaneous Epileptiform Activity in Rat Hippocampal Slices

1999 ◽  
Vol 81 (1) ◽  
pp. 49-59 ◽  
Author(s):  
Daryl W. Hochman ◽  
Raimondo D'Ambrosio ◽  
Damir Janigro ◽  
Philip A. Schwartzkroin
Keyword(s):  
Prolonged Exposure ◽  
Epileptiform Activity ◽  
Hippocampal Slices ◽  
Field Potential ◽  
Pyramidal Cells ◽  
Spontaneous Discharge ◽  
Extracellular Potassium ◽  
Ca1 Pyramidal Cells ◽  
Ca1 Region ◽  
Negative Field

Hochman, Daryl W., Raimondo D'Ambrosio, Damir Janigro, and Philip A. Schwartzkroin. Extracellular chloride and the maintenance of spontaneous epileptiform activity in rat hippocampal slices. J. Neurophysiol. 81: 49–59, 1999. Previous studies showed that furosemide blocks spontaneous epileptiform activity without diminishing synaptic transmission or reducing hyperexcited field responses to electrical stimuli. We now test the hypothesis that the antiepileptic effects of furosemide are mediated through its blockade of the Na+,K+,2Cl− cotransporter and thus should be mimicked by a reduction of extracellular chloride ([Cl−]o). In the first set of experiments, field recordings from the CA1 cell body layer of hippocampal slices showed that spontaneous bursting developed within 10–20 min in slices perfused with low-[Cl−]o (7 mM) medium but that this spontaneous epileptiform activity ceased after a further 10–20 min. Intracellular recordings from CA1 pyramidal cells showed that normal action potential discharge could be elicited by membrane depolarization, even after the tissue was perfused with low-[Cl−]o medium for >2 h. In a second set of experiments, spontaneous bursting activity was induced in slices by perfusion with high-[K+]o (10 mM), bicuculline (100 μM), or 4-aminopyridine (100 μM). In each case, recordings from the CA1 region showed that reduction of [Cl−]o to 21 mM reversibly blocked the bursting within 1 h. Similar to previous observations with furosemide treatment, low-[Cl−]o medium blocked spontaneous hypersynchronous discharges without reducing synaptic hyperexcitability (i.e., hyperexcitable field responses evoked by electrical stimulation). In a third set of experiments, prolonged exposure (>1 h after spontaneous bursting ceased) of slices to systematically varied [Cl−]o and [K+]o resulted in one of three types of events: 1) spontaneous, long-lasting, and repetitive negative field potential shifts (7 mM [Cl−]o; 3 mM [K+]o); 2) oscillations consisting of 5- to 10-mV negative shifts in the field potential, with a period of ∼1 cycle/40 s (16 mM [Cl−]o; 12 mM [K+]o); and 3) shorter, infrequently occurring negative field shifts lasting 20–40 s (21 mM [Cl−]o; 3 mM [K+]o). Our observations indicate that the effects of low [Cl−]o on neuronal synchronization and spontaneous discharge are time dependent. Similar effects were seen with furosemide and low [Cl−]o, consistent with the hypothesis that the antiepileptic effect of furosemide is mediated by the drug's effect on chloride transporters. Finally, the results of altering extracellular potassium along with chloride suggest that blockade of the Na+, K+,2Cl− cotransporter, which normally transports chloride from the extracellular space into glial cells, is key to these antiepileptic effects.

Enhanced NMDAR-dependent epileptiform activity is controlled by oxidizing agents in a chronic model of temporal lobe epilepsy

1996 ◽  
Vol 76 (6) ◽  
pp. 4185-4189 ◽  
Author(s):  
J. C. Hirsch ◽  
O. Quesada ◽  
M. Esclapez ◽  
H. Gozlan ◽  
Y. Ben-Ari ◽  
...  
Keyword(s):  
Synaptic Transmission ◽  
Ex Vivo ◽  
Epileptiform Activity ◽  
Hippocampal Slices ◽  
Nmda Antagonist ◽  
Pyramidal Cells ◽  
Resting Membrane Potential ◽  
Postsynaptic Potentials ◽  
Epileptiform Discharges ◽  
Late Part

1. Graded N-methyl-D-aspartate receptor (NMDAR)-dependent epileptiform discharges were recorded from ex vivo hippocampal slices obtained from rats injected a week earlier with an intracerebroventricular dose of kainic acid. Intracellular recordings from pyramidal cells of the CA1 area showed that glutamate NMDAR actively participated in synaptic transmission, even at resting membrane potential. When NMDAR were pharmacologically isolated, graded burst discharges could still be evoked. 2. The oxidizing reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB, 200 microM, 15 min) suppressed the late part of the epileptiform burst that did not recover after wash but could be reinstated by the reducing agent tris (2-carboxyethyl) phosphine (TCEP, 200 microM, 15 min) and again abolished with the NMDA antagonist D-2-amino-5-phosphonovaleric acid (D-APV). 3. Pharmacologically isolated NMDAR-mediated responses were decreased by DTNB (56 +/- 10%, mean +/- SD, n = 6), an effect reversed by TCEP. 4. When only the fast glutamateric synaptic component was blocked, NMDA-dependent excitatory postsynaptic potentials (EPSPs) could be evoked despite the presence of underlying fast and slow inhibitory postsynaptic potentials (IPSPs). DTNB decreased EPSPs to 48 +/- 12% (n = 5) of control. 5. Since a decrease of the NMDAR-mediated response by +/- 50% is sufficient to suppress the late part of the burst, we suggest that epileptiform activity can be controlled by manipulation of the redox sites of NMDAR. Our observations raise the possibility of developing new anticonvulsant drugs that would spare alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-R (AMPAR)-mediated synaptic responses and decrease NMDAR-mediated synaptic transmission without blocking it completely.

Characterization of an early afterhyperpolarization after a brief train of action potentials in rat hippocampal neurons in vitro

1990 ◽  
Vol 63 (1) ◽  
pp. 72-81 ◽  
Author(s):  
A. Williamson ◽  
B. E. Alger
Keyword(s):  
Action Potentials ◽  
Hippocampal Neurons ◽  
Pyramidal Cells ◽  
Chloride Ions ◽  
Membrane Potentials ◽  
Resting Potential ◽  
K Channel ◽  
Delayed Rectifier ◽  
Extracellular Potassium

1. In rat hippocampal pyramidal cells in vitro, a brief train of action potentials elicited by direct depolarizing current pulses injected through an intracellular recording electrode is followed by a medium-duration afterhyperpolarization (mAHP) and a longer, slow AHP. We studied the mAHP with the use of current-clamp techniques in the presence of dibutyryl cyclic adenosine 3',5'-monophosphate (cAMP) to block the slow AHP and isolate the mAHP. 2. The mAHP evoked at hyperpolarized membrane potentials was complicated by a potential generated by the anomalous rectifier current, IQ. The mAHP is insensitive to chloride ions (Cl-), whereas it is sensitive to the extracellular potassium concentration ([K+]o). 3. At slightly depolarized levels, the mAHP is partially Ca2+ dependent, being enhanced by increased [Ca2+]o and BAY K 8644 and depressed by decreased [Ca2+]o, nifedipine, and Cd2+. The Ca2(+)-dependent component of the mAHP was also reduced by 100 microM tetraethylammonium (TEA) and charybdotoxin (CTX), suggesting it is mediated by the voltage- and Ca2(+)-dependent K+ current, IC. 4. Most of the Ca2(+)-independent mAHP was blocked by carbachol, implying that IM plays a major role. In a few cells, a small Ca2(+)- and carbachol-insensitive mAHP component was detectable, and this component was blocked by 10 mM TEA, suggesting it was mediated by the delayed rectifier current, IK. The K+ channel antagonist 4-aminopyridine (4-AP, 500 microM) did not reduce the mAHP. 5. We infer that the mAHP is a complex potential due either to IQ or to the combined effects of IM and IC. The contributions of each current depend on the recording conditions, with IC playing a role when the cells are activated from depolarized potentials and IM dominating at the usual resting potential. IQ is principally responsible for the mAHP recorded at hyperpolarized membrane potentials.

Evidence from simultaneous intracellular recordings in rat hippocampal slices that area CA3 pyramidal cells innervate dentate hilar mossy cells

1994 ◽  
Vol 72 (5) ◽  
pp. 2167-2180 ◽  
Author(s):  
H. E. Scharfman
Keyword(s):  
Pyramidal Cell ◽  
Action Potentials ◽  
Granule Cells ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Probability Of Failure ◽  
Mossy Cells ◽  
Mossy Cell ◽  
Ca3 Pyramidal Cells ◽  
Area Ca3

1. Simultaneous intracellular recordings of area CA3 pyramidal cells and dentate hilar “mossy” cells were made in rat hippocampal slices to test the hypothesis that area CA3 pyramidal cells excite mossy cells monosynaptically. Mossy cells and pyramidal cells were differentiated by location and electrophysiological characteristics. When cells were impaled near the border of area CA3 and the hilus, their identity was confirmed morphologically after injection of the marker Neurobiotin. 2. Evidence for monosynaptic excitation of a mossy cell by a pyramidal cell was obtained in 7 of 481 (1.4%) paired recordings. In these cases, a pyramidal cell action potential was followed immediately by a 0.40 to 6.75 (mean, 2.26) mV depolarization in the simultaneously recorded mossy cell (mossy cell membrane potentials, -60 to -70 mV). Given that pyramidal cells used an excitatory amino acid as a neurotransmitter (Cotman and Nadler 1987; Ottersen and Storm-Mathisen 1987) and recordings were made in the presence of the GABAA receptor antagonist bicuculline (25 microM), it is likely that the depolarizations were unitary excitatory postsynaptic potentials (EPSPs). 3. Unitary EPSPs of mossy cells were prone to apparent “failure.” The probability of failure was extremely high (up to 0.72; mean = 0.48) if the effects of all presynaptic action potentials were examined, including action potentials triggered inadvertently during other spontaneous EPSPs of the mossy cell. Probability of failure was relatively low (as low as 0; mean = 0.24) if action potentials that occurred during spontaneous activity of the mossy cell were excluded. These data suggest that unitary EPSPs produced by pyramidal cells are strongly affected by concurrent synaptic inputs to the mossy cell. 4. Unitary EPSPs were not clearly affected by manipulation of the mossy cell's membrane potential. This is consistent with the recent report that area CA3 pyramidal cells innervate distal dendrites of mossy cells (Kunkel et al. 1993). Such a distal location also may contribute to the high incidence of apparent failures. 5. Characteristics of unitary EPSPs generated by pyramidal cells were compared with the properties of the unitary EPSPs produced by granule cells. In two slices, pyramidal cell and granule cell inputs to the same mossy cell were compared. In other slices, inputs to different mossy cells were compared. In all experiments, unitary EPSPs produced by granule cells were larger in amplitude but similar in time course to unitary EPSPs produced by pyramidal cells. Probability of failure was lower and paired-pulse facilitation more common among EPSPs triggered by granule cells.(ABSTRACT TRUNCATED AT 400 WORDS)

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