Isoflurane Modulates Hippocampal Cornu Ammonis Pyramidal Neuron Excitability by Inhibition of Both Transient and Persistent Sodium Currents in Mice

Abstract Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Volatile anesthetics inhibit presynaptic voltage-gated sodium channels to reduce neurotransmitter release, but their effects on excitatory neuron excitability by sodium current inhibition are unclear. The authors hypothesized that inhibition of transient and persistent neuronal sodium currents by the volatile anesthetic isoflurane contributes to reduced hippocampal pyramidal neuron excitability. Methods Whole-cell patch-clamp recordings of sodium currents of hippocampal cornu ammonis pyramidal neurons were performed in acute mouse brain slices. The actions of isoflurane on both transient and persistent sodium currents were analyzed at clinically relevant concentrations of isoflurane. Results The median inhibitory concentration of isoflurane for inhibition of transient sodium currents was 1.0 ± 0.3 mM (~3.7 minimum alveolar concentration [MAC]) from a physiologic holding potential of −70 mV. Currents from a hyperpolarized holding potential of −120 mV were minimally inhibited (median inhibitory concentration = 3.6 ± 0.7 mM, ~13.3 MAC). Isoflurane (0.55 mM; ~2 MAC) shifted the voltage-dependence of steady-state inactivation by −6.5 ± 1.0 mV (n = 11, P < 0.0001), but did not affect the voltage-dependence of activation. Isoflurane increased the time constant for sodium channel recovery from 7.5 ± 0.6 to 12.7 ± 1.3 ms (n = 13, P < 0.001). Isoflurane also reduced persistent sodium current density (median inhibitory concentration = 0.4 ± 0.1 mM, ~1.5 MAC) and resurgent currents. Isoflurane (0.55 mM; ~2 MAC) reduced action potential amplitude, and hyperpolarized resting membrane potential from −54.6 ± 2.3 to −58.7 ± 2.1 mV (n = 16, P = 0.001). Conclusions Isoflurane at clinically relevant concentrations inhibits both transient and persistent sodium currents in hippocampal cornu ammonis pyramidal neurons. These mechanisms may contribute to reductions in both hippocampal neuron excitability and synaptic neurotransmission.

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Methods for intracellular recording from hippocampal brain slices under high helium pressure

Journal of Applied Physiology ◽

10.1152/jappl.1991.71.1.365 ◽

1991 ◽

Vol 71 (1) ◽

pp. 365-371 ◽

Cited By ~ 5

Author(s):

A. P. Southan ◽

K. T. Wann

Keyword(s):

Intracellular Recording ◽

Pyramidal Neurons ◽

Brain Slices ◽

Pressure Chamber ◽

Resting Membrane Potential ◽

Helium Pressure ◽

Remote Manipulation ◽

Current Voltage ◽

Chamber Temperature ◽

Current Voltage Relationship

A method for intracellular recording from rat hippocampal brain slices under helium pressure is described. The preparation is mounted on a horizontal mobile platform that is rolled into the pressure chamber and can be viewed at pressure. Remote manipulation of the glass microelectrodes is achieved by a high-resolution electrically driven commercially available system. The slice is superfused continuously from a closed system within the chamber. Temperature is maintained at 37 degrees C and PO2 at 0.5 atm within the pressure chamber. A pressure of 200 ATA can be obtained, although thus far recordings have been made up to only 130 ATA. The experiments demand that a number of sample recordings be made from the same slice at both ambient and high pressure, and tests have proved that, although difficult, this can be achieved. The resting membrane potential, the current-voltage relationship, and the action potential responses to short (8 ms), medium (80 ms), and long (800 ms) depolarizing current pulses have all been measured in CA1 pyramidal neurons.

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Divergent behavioral consequences of manipulations enhancing pyramidal neuron excitability in the prelimbic cortex

10.1101/2020.06.04.134486 ◽

2020 ◽

Author(s):

Timothy R. Rose ◽

Ezequiel Marron Fernandez de Velasco ◽

Baovi N. Vo ◽

Megan E. Tipps ◽

Kevin Wickman

Keyword(s):

Pyramidal Neuron ◽

Pyramidal Neurons ◽

Fear Learning ◽

Channel Activity ◽

Cocaine Exposure ◽

Gaba Neurons ◽

Neuron Excitability ◽

Girk Channel ◽

Drug Naïve ◽

The Impact

ABSTRACTBackgroundDrug-induced neuroadaptations in the prefrontal cortex are thought to underlie impaired executive functions that reinforce addictive behaviors. Repeated cocaine exposure increased layer 5/6 pyramidal neuron excitability in the mouse prelimbic cortex (PL), an adaptation attributable to a suppression of G protein-gated inwardly rectifying K+ (GIRK/Kir3) channel activity. GIRK channel suppression in the PL of drug-naïve mice enhanced the motor-stimulatory effect of cocaine. The impact of cocaine on PL GABA neurons, key pyramidal neuron regulators, and the behavioral relevance of increased PL pyramidal neuron excitability, remain unclear.MethodsThe effect of repeated cocaine on mouse layer 5/6 PL GABA neurons was assessed using slice electrophysiology. Adaptations enhancing PL pyramidal neuron excitability were modeled in drug-naïve mice using persistent viral Cre ablation and acute chemogenetic approaches. The impact of these manipulations on PL-dependent behavior was assessed in motor activity and trace fear conditioning tests.ResultsRepeated cocaine treatment did not impact GIRK channel activity in, or excitability of, layer 5/6 PL GABA neurons. GIRK channel ablation in PL pyramidal neurons enhanced the motor-stimulatory effect of cocaine but did not impact baseline activity or fear learning. In contrast, direct or indirect chemogenetic activation of PL pyramidal neurons increased baseline and cocaine-induced motor activity and disrupted fear learning. These effects were mirrored by chemogenetic activation of PL pyramidal neurons projecting to the ventral tegmental area.ConclusionsManipulations enhancing the excitability of PL pyramidal neurons, including those projecting to the VTA, recapitulate behavioral hallmarks of repeated cocaine exposure.

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Functional Roles of Kv1 Channels in Neocortical Pyramidal Neurons

Journal of Neurophysiology ◽

10.1152/jn.00933.2006 ◽

2007 ◽

Vol 97 (3) ◽

pp. 1931-1940 ◽

Cited By ~ 41

Author(s):

D. Guan ◽

J. C. F. Lee ◽

M. H. Higgs ◽

W. J. Spain ◽

R. C. Foehring

Keyword(s):

Voltage Clamp ◽

Pyramidal Neurons ◽

Brain Slices ◽

Outward Current ◽

Input Resistance ◽

Repetitive Firing ◽

Resting Membrane Potential ◽

Voltage Threshold ◽

Functional Roles ◽

Ramp Voltage

Pyramidal neurons from layers II/III of somatosensory and motor cortex express multiple Kv1 α-subunits and a current sensitive to block by α-dendrotoxin (α-DTX). We examined functional roles of native Kv1 channels in these cells using current-clamp recordings in brain slices and current- and voltage-clamp recordings in dissociated cells. α-DTX caused a significant negative shift in voltage threshold for action potentials (APs) and reduced rheobase. Correspondingly, a ramp-voltage protocol revealed that the α-DTX–sensitive current activated at subthreshold voltages. AP width at threshold increased with successive APs during repetitive firing. The steady-state threshold width for a given firing rate was similar in control and α-DTX, despite an initially broader AP in α-DTX. AP voltage threshold increased similarly during a train of spikes under control conditions and in the presence of α-DTX. α-DTX had no effect on input resistance or resting membrane potential and modest effects on the amplitude or width of a single AP. Accordingly, experiments using AP waveforms (APWs) as voltage protocols revealed that α-DTX–sensitive current peaked late during the AP repolarization phase. Application of α-DTX increased the rate of firing to intracellular current injection and increased gain (multiplicative effects), but did not alter spike-frequency adaptation. Consistent with these findings, voltage-clamp experiments revealed that the proportion of outward current sensitive to α-DTX was highest during the interval between two APWs, reflecting slow deactivation kinetics at −50 mV. Finally, α-DTX did not alter the selectivity of pyramidal neurons for DC versus time-varying stimuli.

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Neurotoxicity of NMDA antagonists: a glutamatergic theory of schizophrenia based on selective impairment of local inhibitory feedback circuits

Dialogues in Clinical Neuroscience ◽

10.31887/dcns.2000.2.3/hgrunze ◽

2000 ◽

Vol 2 (3) ◽

pp. 287-298

Keyword(s):

Pyramidal Neurons ◽

Brain Slices ◽

Nmda Antagonist ◽

Long Term Potentiation ◽

Normal Function ◽

Recurrent Inhibition ◽

Resting Membrane Potential ◽

Nmda Antagonists ◽

Inhibitory Feedback

Modulation of recurrent inhibition is critical not only for the normal function of highly excitable regions of the brain, especially the limbic system, but may also be a primary determining factor for the viability of neurons in these regions. Standard extracellular and intracellular recordings from in vitro brain slices of rat hippocampi were employed to show that recurrent inhibition onto CA1 neurons can be modulated by N-methyl-D-aspartate (NMDA) antagonists. Besides reducing the amplitude of inhibitory postsynaptic potentials (IPSPs) at resting membrane potential conditions, different NMDA antagonists, including the endogenous substance N-acetyl-L-aspartyl-L-glutamic acid (NAAG), are able to block long-term potentiation (LIP) of recurrent inhibition completely at concentrations that are not sufficient to block LTP of the excitatory drive onto pyramidal neurons. This LTP of recurrent inhibition may play a significant role in stimulus discrimination and learning, as simulated in a biophysical computer model of a basic neuronal circuit. Both the amplitude of the IPSP and LTP of the recurrent inhibitory circuit also undergo developmental changes showing their highest expression and vulnerability to chronic NMDA antagonist injections in juvenile rats. Finally, blocking NMDA receptor-dependent transmission in the recurrent inhibition loop may lead to an overall increased excitability of the neuronal network. This may resemble the positive schizophrenic symptoms observed in man, presumably caused by elevated levels of the endogenous NMDA antagonist NAAG.

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Intra-individual Physiomic Landscape of Pyramidal Neurons in the Human Neocortex

10.1101/2021.11.08.467668 ◽

2021 ◽

Author(s):

Henrike Planert ◽

Franz Xaver Mittermaier ◽

Sabine Grosser ◽

Pawel Fidzinski ◽

Ulf Christoph Schneider ◽

...

Keyword(s):

Pyramidal Neuron ◽

Pyramidal Neurons ◽

Phenotypic Variability ◽

Temporal Cortex ◽

Brain Slices ◽

Individual Variability ◽

Dimensional Parameter ◽

Electrophysiological Properties ◽

Synaptic Interactions ◽

Organizational Principle

Computation within cortical microcircuits is determined by functional properties of the neurons and their synaptic interactions. While heterogeneity of inhibitory interneurons is well established, the anatomical, physiological, and molecular differentiation of excitatory pyramidal neurons is not fully resolved. To identify functional subtypes within the pyramidal neuron population, we focused on human layer 2-3 cortex which greatly expanded during evolution. We performed multi-neuron patch-clamp recordings in brain slices from the temporal cortex of 22 epilepsy patients. We characterized the electrophysiological properties of up to 80 pyramidal neurons per patient, enabling us to assess inter- and intra-individual functional variability. Hierarchical clustering of the high-dimensional parameter space yielded functionally distinct clusters of pyramidal neurons which were present across individuals. This may represent a generic organizational principle converging with previously described transcriptomic heterogeneity. We further observed substantial heterogeneity in physiological parameters with intra-individual variability being severalfold larger than inter-individual variability. The phenotypic variability within and across pyramidal neuron subtypes has important implications for the computational capacity of the cortical microcircuit.

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TRPM4 Expression During Postnatal Developmental of Mouse CA1 Pyramidal Neurons

Frontiers in Neuroanatomy ◽

10.3389/fnana.2021.643287 ◽

2021 ◽

Vol 15 ◽

Author(s):

Denise Riquelme ◽

Oscar Cerda ◽

Elias Leiva-Salcedo

Keyword(s):

Membrane Potential ◽

Patch Clamp ◽

Postnatal Development ◽

Pyramidal Neurons ◽

Brain Slices ◽

Long Term Potentiation ◽

Neuronal Firing ◽

Resting Membrane Potential ◽

Ca1 Pyramidal Neurons ◽

Apical Dendrites

TRPM4 is a non-selective cation channel activated by intracellular calcium and permeable to monovalent cations. This channel participates in the control of neuronal firing, neuronal plasticity, and neuronal death. TRPM4 depolarizes dendritic spines and is critical for the induction of NMDA receptor-dependent long-term potentiation in CA1 pyramidal neurons. Despite its functional importance, no subcellular localization or expression during postnatal development has been described in this area. To examine the localization and expression of TRPM4, we performed duplex immunofluorescence and patch-clamp in brain slices at different postnatal ages in C57BL/6J mice. At P0 we found TRPM4 is expressed with a somatic pattern. At P7, P14, and P35, TRPM4 expression extended from the soma to the apical dendrites but was excluded from the axon initial segment. Patch-clamp recordings showed a TRPM4-like current active at the resting membrane potential from P0, which increased throughout the postnatal development. This current was dependent on intracellular Ca2+ (ICAN) and sensitive to 9-phenanthrol (9-Ph). Inhibiting TRPM4 with 9-Ph hyperpolarized the membrane potential at P14 and P35, with no effect in earlier stages. Together, these results show that TRPM4 is expressed in CA1 pyramidal neurons in the soma and apical dendrites and associated with a TRPM4-like current, which depolarizes the neurons. The expression, localization, and function of TRPM4 throughout postnatal development in the CA1 hippocampal may underlie an important mechanism of control of membrane potential and action potential firing during critical periods of neuronal development, particularly during the establishment of circuits.

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Excitatory GABA in Rodent Developing Neocortex In Vitro

Journal of Neurophysiology ◽

10.1152/jn.90402.2008 ◽

2008 ◽

Vol 100 (2) ◽

pp. 609-619 ◽

Cited By ~ 80

Author(s):

Sylvain Rheims ◽

Marat Minlebaev ◽

Anton Ivanov ◽

Alfonso Represa ◽

Rustem Khazipov ◽

...

Keyword(s):

Cortical Neurons ◽

Pyramidal Neurons ◽

Brain Slices ◽

Reversal Potential ◽

Pyramidal Cells ◽

Oscillatory Activity ◽

Resting Membrane Potential ◽

Network Oscillations ◽

Excitatory Gaba

GABA depolarizes immature cortical neurons. However, whether GABA excites immature neocortical neurons and drives network oscillations as in other brain structures remains controversial. Excitatory actions of GABA depend on three fundamental parameters: the resting membrane potential ( Em), reversal potential of GABA ( EGABA), and threshold of action potential generation ( Vthr). We have shown recently that conventional invasive recording techniques provide an erroneous estimation of these parameters in immature neurons. In this study, we used noninvasive single N-methyl-d-aspartate and GABA channel recordings in rodent brain slices to measure both Em and EGABA in the same neuron. We show that GABA strongly depolarizes pyramidal neurons and interneurons in both deep and superficial layers of the immature neocortex (P2–P10). However, GABA generates action potentials in layer 5/6 (L5/6) but not L2/3 pyramidal cells, since L5/6 pyramidal cells have more depolarized resting potentials and more hyperpolarized Vthr. The excitatory GABA transiently drives oscillations generated by L5/6 pyramidal cells and interneurons during development (P5–P12). The NKCC1 co-transporter antagonist bumetanide strongly reduces [Cl−]i, GABA-induced depolarization, and network oscillations, confirming the importance of GABA signaling. Thus a strong GABA excitatory drive coupled with high intrinsic excitability of L5/6 pyramidal neurons and interneurons provide a powerful mechanism of synapse-driven oscillatory activity in the rodent neocortex in vitro. In the companion paper, we show that the excitatory GABA drives layer-specific seizures in the immature neocortex.

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A Ba2+-Sensitive K+ Current Contributes to the Resting Membrane Potential of Neurons in Rat Suprachiasmatic Nucleus

Journal of Neurophysiology ◽

10.1152/jn.2002.88.2.869 ◽

2002 ◽

Vol 88 (2) ◽

pp. 869-878 ◽

Cited By ~ 14

Author(s):

Marcel de Jeu ◽

Alwin Geurtsen ◽

Cyriel Pennartz

Keyword(s):

Membrane Potential ◽

Suprachiasmatic Nucleus ◽

Voltage Dependence ◽

Brain Slices ◽

Resting Potential ◽

Resting Membrane Potential ◽

Delayed Rectifier ◽

Patch Clamp Technique ◽

M Current ◽

Whole Cell Patch Clamp

A Ba2+-sensitive K+ current was studied in neurons of the suprachiasmatic nucleus (SCN) using the whole cell patch-clamp technique in acutely prepared brain slices. This Ba2+-sensitive K+ current was found in approximately 90% of the SCN neurons and was uniformly distributed across the SCN. Current-clamp studies revealed that Ba2+ (500 μM) reversibly depolarized the membrane potential by 6.7 ± 1.3 mV ( n = 22) and concomitantly Ba2+ induced an increase in the spontaneous firing rate of 0.8 ± 0.2 Hz ( n = 12). The Ba2+-evoked depolarizations did not depend on firing activity or spike dependent synaptic transmission. No significant day/night difference in the hyperpolarizing contribution to the resting membrane potential of the present Ba2+-sensitive current was observed. Voltage-clamp experiments showed that Ba2+ (500 μM) reduced a fast-activating, voltage-dependent K+ current. This current was activated at levels below firing threshold and exhibited outward rectification. The Ba2+-sensitive K+ current was strongly reduced by tetraethylammonium (TEA; 20 and 60 mM) but was insensitive to 4-aminopyridine (4-AP; 5 mM) and quinine (100 μM). A component of Ba2+-sensitive K+ current remaining in the presence of TEA exhibited no clear voltage dependence and is less likely to contribute to the resting membrane potential. The voltage dependence, kinetics and pharmacological properties of the Ba2+- and TEA-sensitive K+ current make it unlikely that this current is a delayed rectifier, Ca2+-activated K+ current, ATP-sensitive K+ current, M-current or K+ inward rectifier. Our data are consistent with the Ba2+- and TEA-sensitive K+ current in SCN neurons being an outward rectifying K+ current of a novel identity or belonging to a known family of K+ channels with related properties. Regardless of its precise molecular identity, the current appears to exert a significant hyperpolarizing effect on the resting potential of SCN neurons.

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M1 and M4 Receptors Modulate Hippocampal Pyramidal Neurons

Journal of Neurophysiology ◽

10.1152/jn.00686.2010 ◽

2011 ◽

Vol 105 (2) ◽

pp. 779-792 ◽

Cited By ~ 75

Author(s):

Sameera Dasari ◽

Allan T. Gulledge

Keyword(s):

Pyramidal Neuron ◽

Pyramidal Neurons ◽

Glutamate Release ◽

Stratum Radiatum ◽

Cholinergic Modulation ◽

Schaffer Collateral ◽

Hippocampal Pyramidal Neurons ◽

Ca1 Neurons ◽

Neuron Excitability ◽

M1 Receptors

Acetylcholine (ACh), acting at muscarinic ACh receptors (mAChRs), modulates the excitability and synaptic connectivity of hippocampal pyramidal neurons. CA1 pyramidal neurons respond to transient (“phasic”) mAChR activation with biphasic responses in which inhibition is followed by excitation, whereas prolonged (“tonic”) mAChR activation increases CA1 neuron excitability. Both phasic and tonic mAChR activation excites pyramidal neurons in the CA3 region, yet ACh suppresses glutamate release at the CA3-to-CA1 synapse (the Schaffer–collateral pathway). Using mice genetically lacking specific mAChRs (mAChR knockout mice), we identified the mAChR subtypes responsible for cholinergic modulation of hippocampal pyramidal neuron excitability and synaptic transmission. Knockout of M1 receptors significantly reduced, or eliminated, most phasic and tonic cholinergic responses in CA1 and CA3 pyramidal neurons. On the other hand, in the absence of other Gq-linked mAChRs (M3 and M5), M1 receptors proved sufficient for all postsynaptic cholinergic effects on CA1 and CA3 pyramidal neuron excitability. M3 receptors were able to participate in tonic depolarization of CA1 neurons, but otherwise contributed little to cholinergic responses. At the Schaffer–collateral synapse, bath application of the cholinergic agonist carbachol suppressed stratum radiatum–evoked excitatory postsynaptic potentials (EPSPs) in wild-type CA1 neurons and in CA1 neurons from mice lacking M1 or M2 receptors. However, Schaffer–collateral EPSPs were not significantly suppressed by carbachol in neurons lacking M4 receptors. We therefore conclude that M1 and M4 receptors are the major mAChR subtypes responsible for direct cholinergic modulation of the excitatory hippocampal circuit.

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α5GABAA Receptors Regulate the Intrinsic Excitability of Mouse Hippocampal Pyramidal Neurons

Journal of Neurophysiology ◽

10.1152/jn.00482.2007 ◽

2007 ◽

Vol 98 (4) ◽

pp. 2244-2254 ◽

Cited By ~ 73

Author(s):

Robert P. Bonin ◽

Loren J. Martin ◽

John F. MacDonald ◽

Beverley A. Orser

Keyword(s):

Action Potential ◽

Pyramidal Neurons ◽

Brain Slices ◽

Physiological Role ◽

Network Activity ◽

Equilibrium Potential ◽

Resting Membrane Potential ◽

Action Potential Firing ◽

Membrane Hyperpolarization ◽

Hippocampal Pyramidal Neurons

GABAA receptors generate both phasic and tonic forms of inhibition. In hippocampal pyramidal neurons, GABAA receptors that contain the α5 subunit generate a tonic inhibitory conductance. The physiological role of this tonic inhibition is uncertain, although α5GABAA receptors are known to influence hippocampal-dependent learning and memory processes. Here we provide evidence that α5GABAA receptors regulate the strength of the depolarizing stimulus that is required to generate an action potential in pyramidal neurons. Neurons from α5 knock-out (α5−/−) and wild-type (WT) mice were studied in brain slices and cell cultures using whole cell and perforated-patch-clamp techniques. Membrane resistance was 1.6-fold greater in α5−/− than in WT neurons, but the resting membrane potential and chloride equilibrium potential were similar. Membrane hyperpolarization evoked by an application of exogenous GABA was greater in WT neurons. Inhibiting the function of α5GABAA receptor with nonselective (picrotoxin) or α5 subunit-selective (L-655,708) compounds depolarized WT neurons by ∼3 mV, whereas no change was detected in α5−/− neurons. The depolarizing current required to generate an action potential was twofold greater in WT than in α5−/− neurons, whereas the slope of the input-output relationship for action potential firing was similar. We conclude that shunting inhibition mediated by α5GABAA receptors regulates the firing of action potentials and may synchronize network activity that underlies hippocampal-dependent behavior.

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