scholarly journals Interneuron dysfunction in a new knock-in mouse model of SCN1A GEFS+

2019 ◽  
Author(s):  
Antara Das ◽  
Bingyao Zhu ◽  
Yunyao Xie ◽  
Lisha Zeng ◽  
An T. Pham ◽  
...  
Keyword(s):  
Action Potential ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Inhibitory Interneurons ◽  
Wild Type ◽  
Action Potential Firing ◽  
Potential Firing ◽  
Acute Hippocampal Slices ◽  
Firing Properties ◽  
Genetic Epilepsies

AbstractAdvances in genome sequencing have identified over 1300 mutations in the SCN1A sodium channel gene that result in genetic epilepsies. However, how individual mutations within SCN1A produce seizures remains elusive for most mutations. Previous work from our lab has shown that the K1270T (KT) mutation, which is linked to GEFS+ (Genetic Epilepsy with Febrile Seizure plus) in humans, causes reduced firing of GABAergic neurons in a Drosophila knock-in model. To examine the effect of this mutation in mammals, we introduced the equivalent KT mutation into the mouse Scn1a (Scn1aKT) gene using CRISPR/Cas9. Mouse lines carrying this mutation were examined in two widely used genetic backgrounds, C57BL/6NJ and 129×1/SvJ. In both backgrounds, homozygous mutants had spontaneous seizures and died by postnatal day 23. There was no difference in the lifespan of mice heterozygous for the mutation in either background when compared to wild-type littermates up to 6 months. Heterozygous mutants had heat-induced seizures at ~42 deg. Celsius, a temperature that did not induce seizures in wild-type littermates. In acute hippocampal slices, current-clamp recordings revealed a significant depolarized shift in action potential threshold and reduced action potential amplitude in parvalbumin-expressing inhibitory interneurons in Scn1aKT/+ mice. There was no change in the firing properties of excitatory CA1 pyramidal neurons. Our results indicate that Scn1aKT/+ mice develop seizures, and impaired action potential firing of inhibitory interneurons in Scn1aKT/+ mice may produce hyperexcitability in the hippocampus.

scholarly journals Zinc Enhances the Inhibitory Effects of Strychnine-Sensitive Glycine Receptors in Mouse Hippocampal Neurons

2007 ◽  
Vol 98 (6) ◽  
pp. 3666-3676 ◽  
Author(s):  
Hai Xia Zhang ◽  
Liu Lin Thio
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Hippocampal Slices ◽  
Glycine Receptors ◽  
Inhibitory Effects ◽  
Action Potential Firing ◽  
Embryonic Mouse ◽  
Potential Firing

Although extracellular Zn2+ is an endogenous biphasic modulator of strychnine-sensitive glycine receptors (GlyRs), the physiological significance of this modulation remains poorly understood. Zn2+ modulation of GlyR may be especially important in the hippocampus where presynaptic Zn2+ is abundant. Using cultured embryonic mouse hippocampal neurons, we examined whether 1 μM Zn2+, a potentiating concentration, enhances the inhibitory effects of GlyRs activated by sustained glycine applications. Sustained 20 μM glycine (EC25) applications alone did not decrease the number of action potentials evoked by depolarizing steps, but they did in 1 μM Zn2+. At least part of this effect resulted from Zn2+ enhancing the GlyR-induced decrease in input resistance. Sustained 20 μM glycine applications alone did not alter neuronal bursting, a form of hyperexcitability induced by omitting extracellular Mg2+. However, sustained 20 μM glycine applications depressed neuronal bursting in 1 μM Zn2+. Zn2+ did not enhance the inhibitory effects of sustained 60 μM glycine (EC70) applications in these paradigms. These results suggest that tonic GlyR activation could decrease neuronal excitability. To test this possibility, we examined the effect of the GlyR antagonist strychnine and the Zn2+ chelator tricine on action potential firing by CA1 pyramidal neurons in mouse hippocampal slices. Co-applying strychnine and tricine slightly but significantly increased the number of action potentials fired during a depolarizing current step and decreased the rheobase for action potential firing. Thus Zn2+ may modulate neuronal excitability normally and in pathological conditions such as seizures by potentiating GlyRs tonically activated by low agonist concentrations.

scholarly journals pigkMutation underliesmachobehavior and affects Rohon-Beard cell excitability

2015 ◽  
Vol 114 (2) ◽  
pp. 1146-1157 ◽  
Author(s):  
V. Carmean ◽  
M. A. Yonkers ◽  
M. B. Tellez ◽  
J. R. Willer ◽  
G. B. Willer ◽  
...  
Keyword(s):  
Action Potential ◽  
Sensory Neurons ◽  
Sodium Current ◽  
Genetic Defect ◽  
Sensory Cells ◽  
Loss Of Function ◽  
Wild Type ◽  
Action Potential Firing ◽  
Potential Firing ◽  
Touch Response

The study of touch-evoked behavior allows investigation of both the cells and circuits that generate a response to tactile stimulation. We investigate a touch-insensitive zebrafish mutant, macho (maco), previously shown to have reduced sodium current amplitude and lack of action potential firing in sensory neurons. In the genomes of mutant but not wild-type embryos, we identify a mutation in the pigk gene. The encoded protein, PigK, functions in attachment of glycophosphatidylinositol anchors to precursor proteins. In wild-type embryos, pigk mRNA is present at times when mutant embryos display behavioral phenotypes. Consistent with the predicted loss of function induced by the mutation, knock-down of PigK phenocopies maco touch insensitivity and leads to reduced sodium current (INa) amplitudes in sensory neurons. We further test whether the genetic defect in pigk underlies the maco phenotype by overexpressing wild-type pigk in mutant embryos. We find that ubiquitous expression of wild-type pigk rescues the touch response in maco mutants. In addition, for maco mutants, expression of wild-type pigk restricted to sensory neurons rescues sodium current amplitudes and action potential firing in sensory neurons. However, expression of wild-type pigk limited to sensory cells of mutant embryos does not allow rescue of the behavioral touch response. Our results demonstrate an essential role for pigk in generation of the touch response beyond that required for maintenance of proper INa density and action potential firing in sensory neurons.

scholarly journals β3-Adrenergic receptor-dependent modulation of the medium afterhyperpolarization in rat hippocampal CA1 pyramidal neurons

2019 ◽  
Vol 121 (3) ◽  
pp. 773-784 ◽  
Author(s):  
Timothy W. Church ◽  
Jon T. Brown ◽  
Neil V. Marrion
Keyword(s):  
Action Potential ◽  
Adrenergic Receptors ◽  
Adrenergic Receptor ◽  
Neuronal Excitability ◽  
Pyramidal Neurons ◽  
Intracellular Camp ◽  
Action Potential Firing ◽  
Hippocampal Pyramidal Neurons ◽  
Potential Firing ◽  
H Channels

Action potential firing in hippocampal pyramidal neurons is regulated by generation of an afterhyperpolarization (AHP). Three phases of AHP are recognized, with the fast AHP regulating action potential firing at the onset of a burst and the medium and slow AHPs supressing action potential firing over hundreds of milliseconds and seconds, respectively. Activation of β-adrenergic receptors suppresses the slow AHP by a protein kinase A-dependent pathway. However, little is known regarding modulation of the medium AHP. Application of the selective β-adrenergic receptor agonist isoproterenol suppressed both the medium and slow AHPs evoked in rat CA1 hippocampal pyramidal neurons recorded from slices maintained in organotypic culture. Suppression of the slow AHP was mimicked by intracellular application of cAMP, with the suppression of the medium AHP by isoproterenol still being evident in cAMP-dialyzed cells. Suppression of both the medium and slow AHPs was antagonized by the β-adrenergic receptor antagonist propranolol. The effect of isoproterenol to suppress the medium AHP was mimicked by two β3-adrenergic receptor agonists, BRL37344 and SR58611A. The medium AHP was mediated by activation of small-conductance calcium-activated K+ channels and deactivation of H channels at the resting membrane potential. Suppression of the medium AHP by isoproterenol was reduced by pretreating cells with the H-channel blocker ZD7288. These data suggest that activation of β3-adrenergic receptors inhibits H channels, which suppresses the medium AHP in CA1 hippocampal neurons by utilizing a pathway that is independent of a rise in intracellular cAMP. This finding highlights a potential new target in modulating H-channel activity and thereby neuronal excitability. NEW & NOTEWORTHY The noradrenergic input into the hippocampus is involved in modulating long-term synaptic plasticity and is implicated in learning and memory. We demonstrate that activation of functional β3-adrenergic receptors suppresses the medium afterhyperpolarization in hippocampal pyramidal neurons. This finding provides an additional mechanism to increase action potential firing frequency, where neuronal excitability is likely to be crucial in cognition and memory.

scholarly journals Action potential counting at giant mossy fiber terminals gates information transfer in the hippocampus

2018 ◽  
Vol 115 (28) ◽  
pp. 7434-7439 ◽  
Author(s):  
Simon Chamberland ◽  
Yulia Timofeeva ◽  
Alesya Evstratova ◽  
Kirill Volynski ◽  
Katalin Tóth
Keyword(s):  
Action Potential ◽  
Granule Cell ◽  
Pyramidal Neurons ◽  
Mossy Fiber ◽  
Glutamate Release ◽  
Mossy Fibers ◽  
Action Potential Firing ◽  
Potential Firing ◽  
Ca3 Pyramidal Neurons ◽  
Calbindin D

Neuronal communication relies on action potential discharge, with the frequency and the temporal precision of action potentials encoding information. Hippocampal mossy fibers have long been recognized as conditional detonators owing to prominent short-term facilitation of glutamate release displayed during granule cell burst firing. However, the spiking patterns required to trigger action potential firing in CA3 pyramidal neurons remain poorly understood. Here, we show that glutamate release from mossy fiber terminals triggers action potential firing of the target CA3 pyramidal neurons independently of the average granule cell burst frequency, a phenomenon we term action potential counting. We find that action potential counting in mossy fibers gates glutamate release over a broad physiological range of frequencies and action potential numbers. Using rapid Ca2+ imaging we also show that the magnitude of evoked Ca2+ influx stays constant during action potential trains and that accumulated residual Ca2+ is gradually extruded on a time scale of several hundred milliseconds. Using experimentally constrained 3D model of presynaptic Ca2+ influx, buffering, and diffusion, and a Monte Carlo model of Ca2+-activated vesicle fusion, we argue that action potential counting at mossy fiber boutons can be explained by a unique interplay between Ca2+ dynamics and buffering at release sites. This is largely determined by the differential contribution of major endogenous Ca2+ buffers calbindin-D28K and calmodulin and by the loose coupling between presynaptic voltage-gated Ca2+ channels and release sensors and the relatively slow Ca2+ extrusion rate. Taken together, our results identify a previously unexplored information-coding mechanism in the brain.

scholarly journals The GluN2A subunit of the NMDA receptor modulates the rate of functional maturation in parvalbumin-positive interneurons

2021 ◽  
Author(s):  
Chad R Camp ◽  
Lindsey Shapiro ◽  
Anna Vlachos ◽  
Riley E Perszyk ◽  
Nima Shariatzadeh ◽  
...  
Keyword(s):  
Action Potential ◽  
Expression Pattern ◽  
Knockout Mice ◽  
Time Course ◽  
Neuronal Development ◽  
Critical Role ◽  
Gabaergic Interneuron ◽  
Wild Type ◽  
Action Potential Firing ◽  
Potential Firing

N-methyl-D-aspartate receptors (NMDARs) are excitatory glutamate-gated ion channels that are expressed throughout the central nervous system. NMDARs mediate calcium entry into cells, and are involved in a host of neurological functions, including neuronal development and maturation. The GluN2A subunit, encoded by the GRIN2A gene, has a slightly delayed expression pattern, with low transcript levels during embryonic development that peak in the early neonatal period. Given its unique expression pattern and ability to speed up the synaptic time course after incorporation into the postsynaptic density compared to other GluN2 subunits, the GluN2A subunit is well positioned to participate in synaptic maturation and circuit refinement. By using Grin2a knockout mice, we show that the loss of GluN2A signaling impacts parvalbumin-positive GABAergic interneuron development in the hippocampal CA1 subfield. Specifically, Grin2a knockout mice have 33% more parvalbumin-positive cells in CA1 compared to wild type controls, with no impact on cholecystokinin-positive cell density. By using immunohistochemical colocalization staining and electrophysiological recordings, we demonstrate that these excess parvalbumin cells do eventually incorporate into the hippocampal network and participate in phasic inhibition, although their presynaptic release probability may be dampened. Moreover, we show that although the morphology of Grin2a knockout parvalbumin-positive cells is unaffected, key measures of intrinsic excitability and action-potential firing properties show age-dependent alterations. Preadolescent (P20-25) parvalbumin-positive cells have an increased input resistance, longer membrane time constant, longer action-potential half-width, a lower current threshold for depolarization-induced block of action-potential firing, and a decrease in peak action-potential firing rate. Each of these electrophysiological measures becomes corrected in adulthood, reaching wild type levels, suggesting a delay of electrophysiological maturation. The circuit and behavioral implications of delayed parvalbumin-positive interneuron maturation are not known; however, we find that neonatal Grin2a knockout mice are more susceptible to lipopolysaccharide and febrile-induced seizures, consistent with a critical role for early GluN2A signaling in neuronal development and maintenance of excitatory-inhibitory balance. These results could provide insights into how loss-of-function GRIN2A human variants can generate an epileptic phenotype.

scholarly journals The organization of the sino-atrial node microvasculature varies regionally to match local myocyte excitability

Function ◽  
2021 ◽  
Author(s):  
Nathan Grainger ◽  
Laura Guarina ◽  
Robert H Cudmore ◽  
L Fernando Santana
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Vascular Density ◽  
Metabolic Demand ◽  
Action Potential Firing ◽  
Voltage Fluctuations ◽  
Potential Firing ◽  
Subthreshold Voltage ◽  
Firing Properties ◽  
The Relationship

Abstract The cardiac cycle starts when an action potential is produced by pacemaking cells in the sino-atrial node. This cycle is repeated approximately 100,000 times in humans and 1 million times in mice per day, imposing a monumental metabolic demand on the heart, requiring efficient blood supply via the coronary vasculature to maintain cardiac function. Although the ventricular coronary circulation has been extensively studied, the relationship between vascularization and cellular pacemaking modalities in the sino-atrial node is poorly understood. Here, we tested the hypothesis that the organization of the sino-atrial node micro-vasculature varies regionally, reflecting local myocyte firing properties. We show that vessel densities are higher in the superior versus inferior sino-atrial node. Accordingly, sino-atrial node myocytes are closer to vessels in the superior versus inferior regions. Superior and inferior sino-atrial node myocytes produce stochastic subthreshold voltage fluctuations and action potentials. However, the intrinsic action potential firing rate of sino-atrial node myocytes is higher in the superior versus inferior node. Our data support a model in which the micro-vascular densities vary regionally within the sino-atrial node to match the electrical and Ca2+ dynamics of nearby myocytes, effectively determining the dominant pacemaking site within the node. In this model, the high vascular density in the superior sino-atrial node places myocytes with metabolically demanding, high frequency action potentials near vessels. The lower vascularization and electrical activity of inferior sino-atrial node myocytes could limit these cells to function to support sino-atrial node periodicity with sporadic voltage fluctuations via a stochastic resonance mechanism.

scholarly journals Spike-frequency dependent inhibition and excitation of neural activity by high-frequency ultrasound

2020 ◽  
Author(s):  
Martin Loynaz Prieto ◽  
Kamyar Firouzi ◽  
Butrus T. Khuri-Yakub ◽  
Daniel V. Madison ◽  
Merritt Maduke
Keyword(s):  
Action Potential ◽  
Sodium Channels ◽  
High Frequency ◽  
Pyramidal Neurons ◽  
Potassium Conductance ◽  
Firing Frequency ◽  
Resting Membrane Potential ◽  
Action Potential Firing ◽  
Voltage Dependent ◽  
Potential Firing

ABSTRACTUltrasound can modulate action-potential firing in vivo and in vitro, but the mechanistic basis of this phenomenon is not well understood. To address this problem, we used patch-clamp recording to quantify the effects of focused, high-frequency (43 MHz) ultrasound on evoked action potential firing in CA1 pyramidal neurons in acute rodent hippocampal brain slices. We find that ultrasound can either inhibit or potentiate firing in a spike-frequency-dependent manner: at low (near-threshold) input currents and low firing frequencies, ultrasound inhibits firing, while at higher input currents and higher firing frequencies, ultrasound potentiates firing. The net result of these two competing effects is that ultrasound increases the threshold current for action potential firing, the slope of frequency-input curves, and the maximum firing frequency. In addition, ultrasound slightly hyperpolarizes the resting membrane potential, decreases action potential width, and increases the depth of the afterhyperpolarization. All of these results can be explained by the hypothesis that ultrasound activates a sustained potassium conductance. According to this hypothesis, increased outward potassium currents hyperpolarize the resting membrane potential and inhibit firing at near-threshold input currents, but potentiate firing in response to higher input currents by limiting inactivation of voltage-dependent sodium channels during the action potential. This latter effect is a consequence of faster action-potential repolarization, which limits inactivation of voltage-dependent sodium channels, and deeper (more negative) afterhyperpolarization, which increases the rate of recovery from inactivation. Based on these results we propose that ultrasound activates thermosensitive and mechanosensitive two-pore-domain potassium (K2P) channels, through heating or mechanical effects of acoustic radiation force. Finite-element modelling of the effects of ultrasound on brain tissue suggests that the effects of ultrasound on firing frequency are caused by a small (less than 2°C) increase in temperature, with possible additional contributions from mechanical effectsSUMMARYPrieto et al. describe how ultrasound can either inhibit or potentiate action potential firing in hippocampal pyramidal neurons and demonstrate that these effects can be explained by increased potassium conductance.

scholarly journals The role of parvalbumin interneuron GIRK signaling in regulation of affect and cognition in male and female mice

2020 ◽  
Author(s):  
EM Anderson ◽  
S Demis ◽  
H D’Acquisto ◽  
A Engelhardt ◽  
M Hearing
Keyword(s):  
Action Potential ◽  
Pyramidal Neurons ◽  
Forced Swim Test ◽  
Membrane Excitability ◽  
Cellular Mechanisms ◽  
Action Potential Firing ◽  
Male And Female ◽  
Female Mice ◽  
Potential Firing ◽  
Affect And Cognition

ABSTRACTPathological impairments in the regulation of affect (i.e. emotion) and flexible decision-making are commonly observed across numerous neuropsychiatric disorders and are thought to reflect dysfunction of cortical and subcortical circuits that arise in part from imbalances in excitation and inhibition within these structures. Disruptions in GABA transmission, in particular that from parvalbumin-expressing interneurons (PVI), has been highlighted as a likely mechanism by which this imbalance arises, as they regulate excitation and synchronization of principle output neurons. G protein-gated inwardly rectifying potassium ion (GIRK/Kir3) channels are known to modulate excitability and output of pyramidal neurons in areas like the medial prefrontal cortex and hippocampus, however the role GIRK plays in PVI excitability and behavior is unknown. Male and female mice lacking GIRK1 in PVI (Girk1flox/flox:PVcre) and expressing td-tomato in PVI (Girk1flox/flox:PVCre:PVtdtom) exhibited increased open arm time in the elevated plus maze, while males showed an increase in immobile episodes during the forced swim test. Loss of GIRK1 did not alter motivated behavior for an appetitive reward or impair overall performance in an operant-based attention set-shifting model of cognitive flexibility, however it did alter types of errors committed during the visual cue test. Unexpectedly, baseline sex differences were also identified in these tasks, with females exhibiting overall poorer performance compared to males and distinct types of errors, highlighting potential differences in task-related problem solving. Interestingly, reductions in PVI GIRK signaling did not correspond to changes in membrane excitability but did increase action potential firing at higher current injections in PVI of males, but not females. This is the first investigation on the role that PVI GIRK-signaling has on membrane excitability, action potential firing, and their role on affect and cognition together increasing understanding of PVI cellular mechanisms and function.

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