scholarly journals Gain of Function in FHM-1 Cav2.1 Knock-In Mice Is Related to the Shape of the Action Potential

2010 ◽  
Vol 104 (1) ◽  
pp. 291-299 ◽  
Author(s):  
Carlota González Inchauspe ◽  
Francisco J. Urbano ◽  
Mariano N. Di Guilmi ◽  
Ian D. Forsythe ◽  
Michel D. Ferrari ◽  
...  
Keyword(s):  
Pyramidal Cells ◽  
Familial Hemiplegic Migraine ◽  
Cortical Layer ◽  
Calcium Currents ◽  
Inhibitory Neurons ◽  
Missense Mutations ◽  
Calyx Of Held ◽  
Gain Of Function ◽  
Layer 2 ◽  
Presynaptic Calcium

Familial hemiplegic migraine type-1 FHM-1 is caused by missense mutations in the CACNA1A gene that encodes the α1A pore-forming subunit of CaV2.1 Ca2+ channels. We used knock-in (KI) transgenic mice harboring the pathogenic FHM-1 mutation R192Q to study neurotransmission at the calyx of Held synapse and cortical layer 2/3 pyramidal cells (PCs). Using whole cell patch-clamp recordings in brain stem slices, we confirmed that KI CaV2.1 Ca2+ channels activated at more hyperpolarizing potentials. However, calyceal presynaptic calcium currents ( IpCa) evoked by presynaptic action potentials (APs) were similar in amplitude, kinetic parameters, and neurotransmitter release. CaV2.1 Ca2+ channels in cortical layer 2/3 PCs from KI mice also showed a negative shift in their activation voltage. PCs had APs with longer durations and smaller amplitudes than the calyx of Held. AP-evoked Ca2+ currents ( ICa) from PCs were larger in KI compared with wild-type (WT) mice. In contrast, when ICawas evoked in PCs by calyx of Held AP waveforms, we observed no amplitude differences between WT and KI mice. In the same way, Ca2+ currents evoked at the presynaptic terminals ( IpCa)of the calyx of Held by the AP waveforms of the PCs had larger amplitudes in R192Q KI mice that in WT. These results suggest that longer time courses of pyramidal APs were a key factor for the expression of a synaptic gain of function in the KI mice. In addition, our results indicate that consequences of FHM-1 mutations might vary according to the shape of APs in charge of triggering synaptic transmission (neurons in the calyx of Held vs. excitatory/inhibitory neurons in the cortex), adding to the complexity of the pathophysiology of migraine.

scholarly journals Gain-of-function mutations in the UNC-2/CaV2α channel lead to hyperactivity and excitation-dominant synaptic transmission in Caenorhabditis elegans

2019 ◽  
Author(s):  
Yung-Chi Huang ◽  
Jennifer K. Pirri ◽  
Diego Rayes ◽  
Shangbang Gao ◽  
Ben Mulcahy ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Familial Hemiplegic Migraine ◽  
Calcium Currents ◽  
Dependent Manner ◽  
Cellular Mechanisms ◽  
Gain Of Function ◽  
Motor Behaviors ◽  
Insight Into ◽  
Α1 Subunit

AbstractMutations in pre-synaptic voltage gated calcium channels can lead to familial hemiplegic migraine type 1 (FHM1). While mammalian studies indicate that the migraine brain is hyperexcitable due to enhanced excitation or reduced inhibition, the molecular and cellular mechanisms underlying this excitatory/inhibitory (E/I) imbalance are poorly understood. We identified a gain-of-function (gf) mutation in the Caenorhabditis elegans CaV2 channel α1 subunit, UNC-2, which leads to increased calcium currents. unc-2(gf) mutants exhibit hyperactivity and seizure-like motor behaviors. Expression of the unc-2 gene with FHM1 substitutions R192Q and S218L leads to hyperactivity similar to that of unc-2(gf) mutants unc-2(gf) mutants display increased cholinergic- and decreased GABAergic-transmission. Moreover, we reveal that and increased cholinergic transmission in unc-2(gf) mutants leads to reduction of GABA synapses in a TAX-6/calcineurin dependent manner. Our studies provide mechanistic insight into how CaV2 gain-of-function mutations disrupt excitation-inhibition balance in the nervous system.

An Increase in Calcium Influx Contributes to Post-Tetanic Potentiation at the Rat Calyx of Held Synapse

2006 ◽  
Vol 96 (6) ◽  
pp. 2868-2876 ◽  
Author(s):  
Ron L. P. Habets ◽  
J. Gerard G. Borst
Keyword(s):  
Action Potential ◽  
Calcium Influx ◽  
Calcium Currents ◽  
Calyx Of Held ◽  
Calcium Buffer ◽  
Whole Cell Patch Clamp ◽  
Auditory Brain Stem ◽  
Post Tetanic Potentiation ◽  
Presynaptic Calcium ◽  
Fluorescence Transients

We studied the contribution of a change in presynaptic calcium influx to posttetanic potentiation (PTP) in the calyx of Held synapse, an axosomatic synapse in the auditory brain stem. We made whole cell patch-clamp recordings of a principal cell after loading of the presynaptic terminal with a calcium dye. After induction of PTP by a high-frequency train of afferent stimuli, the Fluo-4 fluorescence transients evoked by an action potential became on average 15 ± 4% larger ( n = 7). Model predictions did not match the fluorescence transients evoked by trains of brief calcium currents unless the endogenous calcium buffer had low affinity for calcium, making a contribution of saturation of the endogenous buffer to the synaptic potentiation we observed in the present experiments less likely. Our data therefore suggest that the increase of release probability during PTP at the calyx of Held synapse is largely explained by an increase in the calcium influx per action potential.

scholarly journals Ipsi- and contralateral corticocortical projection-dependent subcircuits in layer 2 of the rat frontal cortex

2019 ◽  
Vol 122 (4) ◽  
pp. 1461-1472 ◽  
Author(s):  
Yoshifumi Ueta ◽  
Jaerin Sohn ◽  
Fransiscus Adrian Agahari ◽  
Sanghun Im ◽  
Yasuharu Hirai ◽  
...  
Keyword(s):  
Motor Cortex ◽  
Frontal Cortex ◽  
Pyramidal Cell ◽  
Pyramidal Tract ◽  
Pyramidal Cells ◽  
Cortical Layer ◽  
Electrophysiological Properties ◽  
Monosynaptic Connection ◽  
Layer 2 ◽  
Rat Frontal Cortex

In the neocortex, both layer 2/3 and layer 5 contain corticocortical pyramidal cells projecting to other cortices. We previously found that among L5 pyramidal cells of the secondary motor cortex (M2), not only intratelencephalic projection cells but also pyramidal tract cells innervate ipsilateral cortices and that the two subtypes are different in corticocortical projection diversity and axonal laminar distributions. Layer 2/3 houses intratelencephalically projecting pyramidal cells that also innervate multiple ipsilateral and contralateral cortices. However, it remained unclear whether layer 2/3 pyramidal cells can be divided into projection subtypes each with distinct innervation to specific targets. In the present study we show that layer 2 pyramidal cells are organized into subcircuits on the basis of corticocortical projection targets. Layer 2 corticocortical cells of the same projection subtype were monosynaptically connected. Between the contralaterally and ipsilaterally projecting corticocortical cells, the monosynaptic connection was more common from the former to the latter. We also found that ipsilaterally and contralaterally projecting corticocortical cell subtypes differed in their morphological and physiological characteristics. Our results suggest that layer 2 transfers separate outputs from M2 to individual cortices and that its subcircuits are hierarchically organized to form the discrete corticocortical outputs. NEW & NOTEWORTHY Pyramidal cell subtypes and their dependent subcircuits are well characterized in cortical layer 5, but much less is understood for layer 2/3. We demonstrate that in layer 2 of the rat secondary motor cortex, ipsilaterally and contralaterally projecting corticocortical cells are largely segregated. These layer 2 cell subtypes differ in dendrite morphological and intrinsic electrophysiological properties, and form subtype-dependent connections. Our results suggest that layer 2 pyramidal cells form distinct subcircuits to provide discrete corticocortical outputs.

scholarly journals Presynaptic CaV2.1 calcium channels carrying familial hemiplegic migraine mutation R192Q allow faster recovery from synaptic depression in mouse calyx of Held

2012 ◽  
Vol 108 (11) ◽  
pp. 2967-2976 ◽  
Author(s):  
Carlota González Inchauspe ◽  
Francisco J. Urbano ◽  
Mariano N. Di Guilmi ◽  
Michel D. Ferrari ◽  
Arn M. J. M. van den Maagdenberg ◽  
...  
Keyword(s):  
Synaptic Transmission ◽  
Close Association ◽  
Low Frequency ◽  
Familial Hemiplegic Migraine ◽  
Missense Mutations ◽  
Calyx Of Held ◽  
Hemiplegic Migraine ◽  
Calcium Sensors ◽  
Medial Nucleus ◽  
Key Factor

CaV2.1 Ca2+ channels have a dominant and specific role in initiating fast synaptic transmission at central excitatory synapses, through a close association between release sites and calcium sensors. Familial hemiplegic migraine type 1 (FHM-1) is an autosomal-dominant subtype of migraine with aura, caused by missense mutations in the CACNA1A gene that encodes the α1A pore-forming subunit of CaV2.1 channel. We used knock-in (KI) transgenic mice harboring the FHM-1 mutation R192Q to study the consequences of this mutation in neurotransmission at the giant synapse of the auditory system formed by the presynaptic calyx of Held terminal and the postsynaptic neurons of the medial nucleus of the trapezoid body (MNTB). Although synaptic transmission seems unaffected by low-frequency stimulation in physiological Ca2+ concentration, we observed that with low Ca2+ concentrations (<1 mM) excitatory postsynaptic currents (EPSCs) showed increased amplitudes in R192Q KI mice compared with wild type (WT), meaning significant differences in the nonlinear calcium dependence of nerve-evoked transmitter release. In addition, when EPSCs were evoked by broadened presynaptic action potentials (achieved by inhibition of K+ channels) via Cav2.1-triggered exocytosis, R192Q KI mice exhibited further enhancement of EPSC amplitude and charge compared with WT mice. Repetitive stimulation of afferent axons to the MNTB at different frequencies caused short-term depression of EPSCs that recovered significantly faster in R192Q KI mice than in WT mice. Faster recovery in R192Q KI mice was prevented by the calcium chelator EGTA-AM, pointing to enlarged residual calcium as a key factor in accelerating the replenishment of synaptic vesicles.

scholarly journals Using ephaptic coupling to estimate the synaptic cleft resistivity of the calyx of Held synapse.

2021 ◽  
Author(s):  
Martijn C Sierksma ◽  
J. Gerard G. Borst
Keyword(s):  
Action Potential ◽  
Time Derivative ◽  
Synaptic Cleft ◽  
Calcium Currents ◽  
Fourth Power ◽  
Calyx Of Held ◽  
Presynaptic Action ◽  
Postsynaptic Cell ◽  
Presynaptic Calcium ◽  
Ephaptic Coupling

At synapses, the pre- and postsynaptic cell get so close that currents entering the cleft do not flow exclusively along its conductance, gcl. A prominent example is found in the calyx of Held synapse in the medial nucleus of the trapezoid body, where the presynaptic action potential can be recorded in the postsynaptic cell in the form of a prespike. Here, we developed a theoretical framework for ephaptic coupling via the synaptic cleft. We found that the capacitive component of the prespike recorded in voltage clamp is closely approximated by the second time derivative of the presynaptic action potential. Its size scales with the fourth power of the radius of the synapse, explaining why intracellularly recorded prespikes are uncommon in the CNS. We show that presynaptic calcium currents can contribute to the prespike and that their contribution is closely approximated by the scaled first derivative of these currents. We confirmed these predictions in juvenile rat brainstem slices, and used the presynaptic calcium currents to obtain an estimate for gcl of ~1 μS. We demonstrate that for a typical synapse geometry, gcl is scale-invariant and only defined by extracellular resistivity, which was ~75 Ωcm, and by cleft height. During development the calyx of Held develops fenestrations. These fenestrations effectively minimize the cleft potentials generated by the adult action potential, which would otherwise interfere with calcium channel opening. We thus provide a quantitative account of the dissipation of currents by the synaptic cleft, which can be readily extrapolated to conventional, bouton-like synapses.

scholarly journals Gain-of-function mutations in the UNC-2/CaV2α channel lead to excitation-dominant synaptic transmission in Caenorhabditis elegans

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Yung-Chi Huang ◽  
Jennifer K Pirri ◽  
Diego Rayes ◽  
Shangbang Gao ◽  
Ben Mulcahy ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Familial Hemiplegic Migraine ◽  
Calcium Currents ◽  
Cellular Mechanisms ◽  
Gain Of Function ◽  
Motor Behaviors ◽  
Voltage Gated Calcium Channels ◽  
Cholinergic Synapses ◽  
Α1 Subunit

Mutations in pre-synaptic voltage-gated calcium channels can lead to familial hemiplegic migraine type 1 (FHM1). While mammalian studies indicate that the migraine brain is hyperexcitable due to enhanced excitation or reduced inhibition, the molecular and cellular mechanisms underlying this excitatory/inhibitory (E/I) imbalance are poorly understood. We identified a gain-of-function (gf) mutation in the Caenorhabditis elegans CaV2 channel α1 subunit, UNC-2, which leads to increased calcium currents. unc-2(zf35gf) mutants exhibit hyperactivity and seizure-like motor behaviors. Expression of the unc-2 gene with FHM1 substitutions R192Q and S218L leads to hyperactivity similar to that of unc-2(zf35gf) mutants. unc-2(zf35gf) mutants display increased cholinergic and decreased GABAergic transmission. Moreover, increased cholinergic transmission in unc-2(zf35gf) mutants leads to an increase of cholinergic synapses and a TAX-6/calcineurin-dependent reduction of GABA synapses. Our studies reveal mechanisms through which CaV2 gain-of-function mutations disrupt excitation-inhibition balance in the nervous system.

scholarly journals Using ephaptic coupling to estimate the synaptic cleft resistivity of the calyx of Held synapse

2021 ◽  
Vol 17 (10) ◽  
pp. e1009527
Author(s):  
Martijn C. Sierksma ◽  
J. Gerard G. Borst
Keyword(s):  
Action Potential ◽  
Synaptic Cleft ◽  
Calcium Currents ◽  
Fourth Power ◽  
Scale Invariant ◽  
Calyx Of Held ◽  
Presynaptic Action ◽  
Medial Nucleus ◽  
Presynaptic Calcium ◽  
Ephaptic Coupling

At synapses, the pre- and postsynaptic cells get so close that currents entering the cleft do not flow exclusively along its conductance, gcl. A prominent example is found in the calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB), where the presynaptic action potential can be recorded in the postsynaptic cell in the form of a prespike. Here, we developed a theoretical framework for ephaptic coupling via the synaptic cleft, and we tested its predictions using the MNTB prespike recorded in voltage-clamp. The shape of the prespike is predicted to resemble either the first or the second derivative of the inverted presynaptic action potential if cleft currents dissipate either mostly capacitively or resistively, respectively. We found that the resistive dissipation scenario provided a better description of the prespike shape. Its size is predicted to scale with the fourth power of the radius of the synapse, explaining why intracellularly recorded prespikes are uncommon in the central nervous system. We show that presynaptic calcium currents also contribute to the prespike shape. This calcium prespike resembled the first derivative of the inverted calcium current, again as predicted by the resistive dissipation scenario. Using this calcium prespike, we obtained an estimate for gcl of ~1 μS. We demonstrate that, for a circular synapse geometry, such as in conventional boutons or the immature calyx of Held, gcl is scale-invariant and only defined by extracellular resistivity, which was ~75 Ωcm, and by cleft height. During development the calyx of Held develops fenestrations. We show that these fenestrations effectively minimize the cleft potentials generated by the adult action potential, which might otherwise interfere with calcium channel opening. We thus provide a quantitative account of the dissipation of currents by the synaptic cleft, which can be readily extrapolated to conventional, bouton-like synapses.

scholarly journals Dendritic branch structure compartmentalizes voltage-dependent calcium influx in cortical layer 2/3 pyramidal cells

2022 ◽  
Author(s):  
Andrew Tyler Landau ◽  
Pojeong Park ◽  
David Wong-Campos ◽  
Tian He ◽  
Adam Ezra Cohen ◽  
...  
Keyword(s):  
Calcium Influx ◽  
Dendritic Tree ◽  
Pyramidal Cells ◽  
Cortical Layer ◽  
Calcium Signals ◽  
Local Reduction ◽  
Layer 2 ◽  
Voltage Dependent ◽  
Dendritic Branches ◽  
Kinetics Of

Back-propagating action potentials (bAPs) regulate synaptic plasticity by evoking voltage-dependent calcium influx throughout dendrites. Attenuation of bAP amplitude in distal dendritic compartments alters plasticity in a location-specific manner by reducing bAP-dependent calcium influx. However, it is not known if neurons exhibit branch-specific variability in bAP-dependent calcium signals, independent of distance-dependent attenuation. Here, we reveal that bAPs fail to evoke calcium influx through voltage-gated calcium channels (VGCCs) in a specific population of dendritic branches in cortical layer 2/3 pyramidal cells, despite evoking substantial VGCC-mediated calcium influx in sister branches. These branches contain VGCCs and successfully propagate bAPs in the absence of synaptic input; nevertheless, they fail to exhibit bAP-evoked calcium influx due to a branch-specific reduction in bAP amplitude. We demonstrate that these branches have more elaborate branch structure compared to sister branches, which causes a local reduction in electrotonic impedance and bAP amplitude. Finally, we show that bAPs still amplify synaptically-mediated calcium influx in these branches because of differences in the voltage-dependence and kinetics of VGCCs and NMDA-type glutamate receptors. Branch-specific compartmentalization of bAP-dependent calcium signals may provide a mechanism for neurons to diversify synaptic tuning across the dendritic tree.

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