A Systems Neuroscience Approach to Migraine

Migraine is an extremely common but poorly understood nervous system disorder. We conceptualize migraine as a disorder of sensory network gain and plasticity, and we propose that this framing makes it amenable to the tools of current systems neuroscience

Modal Gating of Human CaV2.1 (P/Q-type) Calcium Channels: II. The b Mode and Reversible Uncoupling of Inactivation

The single channel gating properties of human CaV2.1 (P/Q-type) calcium channels were investigated with cell-attached patch-clamp recordings on HEK293 cells stably expressing these calcium channels. Human CaV2.1 channels showed a complex modal gating, which is described in this and the preceding paper (Luvisetto, S., T. Fellin, M. Spagnolo, B. Hivert, P.F. Brust, M.M. Harpold, K.A. Stauderman, M.E. Williams, and D. Pietrobon. 2004. J. Gen. Physiol. 124:445–461). Here, we report the characterization of the so-called b gating mode. A CaV2.1 channel in the b gating mode shows a bell-shaped voltage dependence of the open probability, and a characteristic low open probability at high positive voltages, that decreases with increasing voltage, as a consequence of both shorter mean open time and longer mean closed time. Reversible transitions of single human CaV2.1 channels between the b gating mode and the mode of gating in which the channel shows the usual voltage dependence of the open probability (nb gating mode) were much more frequent (time scale of seconds) than those between the slow and fast gating modes (time scale of minutes; Luvisetto et al., 2004), and occurred independently of whether the channel was in the fast or slow mode. We show that the b gating mode produces reversible uncoupling of inactivation in human CaV2.1 channels. In fact, a CaV2.1 channel in the b gating mode does not inactivate during long pulses at high positive voltages, where the same channel in both fast-nb and slow-nb gating modes inactivates relatively rapidly. Moreover, a CaV2.1 channel in the b gating mode shows a larger availability to open than in the nb gating modes. Regulation of the complex modal gating of human CaV2.1 channels could be a potent and versatile mechanism for the modulation of synaptic strength and plasticity as well as of neuronal excitability and other postsynaptic Ca2+-dependent processes

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

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 EPSC were all 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

Increased Susceptibility to Cortical Spreading Depression in the Mouse Model of Familial Hemiplegic Migraine Type 2

Familial hemiplegic migraine type 2 (FHM2) is an autosomal dominant form of migraine with aura that is caused by mutations of the α2-subunit of the Na,K-ATPase, an isoform almost exclusively expressed in astrocytes in the adult brain. We generated the first FHM2 knock-in mouse model carrying the human W887R mutation in the Atp1a2 orthologous gene. Homozygous Atp1a2R887/R887 mutants died just after birth, while heterozygous Atp1a2+/R887 mice showed no apparent clinical phenotype. The mutant α2 Na,K-ATPase protein was barely detectable in the brain of homozygous mutants and strongly reduced in the brain of heterozygous mutants, likely as a consequence of endoplasmic reticulum retention and subsequent proteasomal degradation, as we demonstrate in transfected cells. In vivo analysis of cortical spreading depression (CSD), the phenomenon underlying migraine aura, revealed a decreased induction threshold and an increased velocity of propagation in the heterozygous FHM2 mouse. Since several lines of evidence involve a specific role of the glial α2 Na,K pump in active reuptake of glutamate from the synaptic cleft, we hypothesize that CSD facilitation in the FHM2 mouse model is sustained by inefficient glutamate clearance by astrocytes and consequent increased cortical excitatory neurotransmission. The demonstration that FHM2 and FHM1 mutations share the ability to facilitate induction and propagation of CSD in mouse models further support the role of CSD as a key migraine trigger

Specific Kinetic Alterations of Human CaV2.1 Calcium Channels Produced by Mutation S218L Causing Familial Hemiplegic Migraine and Delayed Cerebral Edema and Coma after Minor Head Trauma

Mutation S218L in the Ca(V)2.1 alpha(1) subunit of P/Q-type Ca(2+) channels produces a severe clinical phenotype in which typical attacks of familial hemiplegic migraine (FHM) triggered by minor head trauma are followed, after a lucid interval, by deep (even fatal) coma and long lasting severe cerebral edema. We investigated the functional consequences of this mutation on human Ca(V)2.1 channels expressed in human embryonic kidney 293 cells and in neurons from Ca(V)2.1 alpha(1)(-/-) mice by combining single channel and whole cell patch clamp recordings. Mutation S218L produced a shift to lower voltages of the single channel activation curve and a consequent increase of both single channel and whole cell Ba(2+) influx in both neurons and human embryonic kidney 293 cells. Compared with the other FHM-1 mutants, the S218L shows one of the largest gains of function, especially for small depolarizations, which are insufficient to open the wild-type channel. S218L channels open at voltages close to the resting potential of many neurons. Moreover, the S218L mutation has unique effects on the kinetics of inactivation of the channel because it introduces a large component of current that inactivates very slowly, and it increases the rate of recovery from inactivation. During long depolarizations at voltages that are attained during cortical spreading depression, the extent of inactivation of the S218L channel is considerably smaller than that of the wild-type channel. We discuss how the unique combination of a particularly slow inactivation during cortical spreading depression and a particularly low threshold of channel activation might lead to delayed severe cerebral edema and coma after minor head trauma

Diagnostic and therapeutic aspects of hemiplegic migraine

Hemiplegic migraine (HM) is a clinically and genetically heterogeneous condition with attacks of headache and motor weakness which may be associated with impaired consciousness, cerebellar ataxia and intellectual disability. Motor symptoms usually last <72 hours and are associated with visual or sensory manifestations, speech impairment or brainstem aura. HM can occur as a sporadic HM or familiar HM with an autosomal dominant mode of inheritance. Mutations in CACNA1A, ATP1A2 and SCN1A encoding proteins involved in ion transport are implicated. The pathophysiology of HM is close to the process of typical migraine with aura, but appearing with a lower threshold and more severity. We reviewed epidemiology, clinical presentation, diagnostic assessment, differential diagnosis and treatment of HM to offer the best evidence of this rare condition. The differential diagnosis of HM is broad, including other types of migraine and any condition that can cause transitory neurological signs and symptoms. Neuroimaging, cerebrospinal fluid analysis and electroencephalography are useful, but the diagnosis is clinical with a genetic confirmation. The management relies on the control of triggering factors and even hospitalisation in case of long-lasting auras. As HM is a rare condition, there are no randomised controlled trials, but the evidence for the treatment comes from small studies

Modal Gating of Human CaV2.1 (P/Q-type) Calcium Channels: I. The Slow and the Fast Gating Modes and their Modulation by β Subunits

The single channel gating properties of human CaV2.1 (P/Q-type) calcium channels and their modulation by the auxiliary β1b, β2e, β3a, and β4a subunits were investigated with cell-attached patch-clamp recordings on HEK293 cells stably expressing human CaV2.1 channels. These calcium channels showed a complex modal gating, which is described in this and the following paper (Fellin, T., S. Luvisetto, M. Spagnolo, and D. Pietrobon. 2004. J. Gen. Physiol. 124:463–474). Here, we report the characterization of two modes of gating of human CaV2.1 channels, the slow mode and the fast mode. A channel in the two gating modes differs in mean closed times and latency to first opening (both longer in the slow mode), in voltage dependence of the open probability (larger depolarizations are necessary to open the channel in the slow mode), in kinetics of inactivation (slower in the slow mode), and voltage dependence of steady-state inactivation (occurring at less negative voltages in the slow mode). CaV2.1 channels containing any of the four β subtypes can gate in either the slow or the fast mode, with only minor differences in the rate constants of the transitions between closed and open states within each mode. In both modes, CaV2.1 channels display different rates of inactivation and different steady-state inactivation depending on the β subtype. The type of β subunit also modulates the relative occurrence of the slow and the fast gating mode of CaV2.1 channels; β3a promotes the fast mode, whereas β4a promotes the slow mode. The prevailing mode of gating of CaV2.1 channels lacking a β subunit is a gating mode in which the channel shows shorter mean open times, longer mean closed times, longer first latency, a much larger fraction of nulls, and activates at more positive voltages than in either the fast or slow mode

Complete Loss of P/Q Calcium Channel Activity Caused by a CACNA1A Missense Mutation Carried by Patients with Episodic Ataxia Type 2

Familial hemiplegic migraine, episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 are allelic disorders of the CACNA1A gene (coding for the α1A subunit of P/Q calcium channels), usually associated with different types of mutations (missense, protein truncating, and expansion, respectively). However, the finding of expansion and missense mutations in patients with EA2 has blurred this genotype-phenotype correlation. We report the first functional analysis of a new missense mutation, associated with an EA2 phenotype—that is, T→C transition of nt 4747 in exon 28, predicted to change a highly conserved phenylalanine residue to a serine at codon 1491, located in the putative transmembrane segment S6 of domain III. Patch-clamp recording in HEK 293 cells, coexpressing the mutagenized human α1A-2 subunit, together with human β4 and α2δ subunits, showed that channel activity was completely abolished, although the mutated protein is expressed in the cell. These results indicate that a complete loss of P/Q channel function is the mechanism underlying EA2, whether due to truncating or to missense mutations