Abnormal cortical synaptic transmission in CaV2.1 knockin mice with the S218L missense mutation which causes a severe familial hemiplegic migraine syndrome in humans.

Dania Vecchia,Daniela Pietrobon,Angelita Tottene,Arn M.J.M Van Den Maagdenberg

doi:10.3389/fncel.2015.00008

Dania Vecchia, Daniela Pietrobon + Show 2 more

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https://doi.org/10.3389/fncel.2015.00008

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Abstract

Familial hemiplegic migraine type 1 (FHM1) is caused by gain-of-function mutations in CaV2.1 (P/Q-type) Ca2+ channels. Knockin (KI) mice carrying the FHM1 R192Q missense mutation show enhanced cortical excitatory synaptic transmission at pyramidal cell synapses but unaltered cortical inhibitory neurotransmission at fast-spiking interneuron synapses. Enhanced cortical glutamate release was shown to cause the facilitation of cortical spreading depression (CSD) in R192Q KI mice. It, however, remains unknown how other FHM1 mutations affect cortical synaptic transmission. Here, we studied neurotransmission in cortical neurons in microculture from KI mice carrying the S218L mutation, which causes a severe FHM syndrome in humans and an allele-dosage dependent facilitation of experimental CSD in KI mice, which is larger than that caused by the R192Q mutation. We show gain-of-function of excitatory neurotransmission, due to increased action-potential evoked Ca2+ influx and increased probability of glutamate release at pyramidal cell synapses, but unaltered inhibitory neurotransmission at multipolar interneuron synapses in S218L KI mice. In contrast with the larger gain-of-function of neuronal CaV2.1 current in homozygous than heterozygous S218L KI mice, the gain-of-function of evoked glutamate release, the paired-pulse ratio and the Ca2+ dependence of the excitatory postsynaptic current were similar in homozygous and heterozygous S218L KI mice, suggesting compensatory changes in the homozygous mice. Furthermore, we reveal a unique feature of S218L KI cortical synapses which is the presence of a fraction of mutant CaV2.1 channels being open at resting potential. Our data suggest that, while the gain-of-function of evoked glutamate release may explain the facilitation of CSD in heterozygous S218L KI mice, the further facilitation of CSD in homozygous S218L KI mice is due to other CaV2.1-dependent mechanisms, that likely include Ca2+ influx at voltages sub-threshold for action potential generation.

Highlights

CaV2.1 (P/Q-type) Ca2+ channels play a prominent role in initiating action potential (AP)-evoked neurotransmitter release at brain excitatory and inhibitory synapses (Pietrobon, 2005, 2010)
To assess whether the Familial hemiplegic migraine type 1 (FHM1) S218L mutation leads to increased AP-evoked Ca2+ influx and increased glutamate release at cortical pyramidal cell synapses, we studied excitatory neurotransmission in cortical neurons from neonatal SL/WT KI and WT mice grown in microculture
Our analysis of excitatory and inhibitory synaptic transmission in microcultures of cortical neurons from S218L KI and WT mice revealed that the severer FHM1 S218L mutation, like previously found for the milder FHM1 R192Q mutation (Tottene et al, 2009; Vecchia et al, 2014), enhances excitatory neurotransmission at cortical pyramidal cell synapses without affecting inhibitory neurotransmission at multipolar interneuron synapses, despite www.frontiersin.org the large contribution of P/Q-type Ca2+ channels in controlling GABA release at these synapses

Summary

Introduction

CaV2.1 (P/Q-type) Ca2+ channels play a prominent role in initiating action potential (AP)-evoked neurotransmitter release at brain excitatory and inhibitory synapses (Pietrobon, 2005, 2010). Several neurological disorders including familial hemiplegic migraine type 1 (FHM1), a rare monogenic form of migraine with aura, are caused by mutations in the CACNA1A gene, which encodes for the α1A pore-forming subunit of CaV2.1 channels (Ophoff et al, 1996; de Vries et al, 2009; Pietrobon, 2010). The mechanisms of primary brain dysfunction that lead to the onset of a migraine attack and to increased susceptibility to CSD, remain a major open issue. Insights into these mechanisms can be obtained from the functional analysis of transgenic knockin (KI) mice carrying FHM1 missense mutations that were introduced into the orthologous Cacna1a gene. FHM1 KI mice were shown to exhibit a lower threshold for induction of experimental CSD and a higher velocity of CSD propagation compared with wild-type (WT) mice (van den Maagdenberg et al, 2004, 2010)

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