Pregabalin Modulation of Neurotransmitter Release Is Mediated by Change in Intrinsic Activation/Inactivation Properties of Cav2.1 Calcium ChannelsS⃞

In this work, we studied the effects of the anticonvulsant and analgesic drug pregabalin (PGB) on excitatory postsynaptic currents (EPSCs) at principal neurons of the mouse medial nucleus of the trapezoid body and on presynaptic calcium currents at the calyx of Held. We found that the acute application of PGB reduced the amplitude of EPSCs in a dose-dependent manner with a maximal blocking effect of approximately 30%. A clinical high-concentration dose of PGB (e.g., 500 μM) blocked Cav2.1 channel-mediated currents and decreased their facilitation during a 100-Hz train, without changing their voltage-dependent activation. Furthermore, PGB also removed the inactivation of Cav2.1 channels at a clinically relevant low concentration of 100 μM. These results suggest novel modulatory mechanisms mediated by the acute administration of PGB on fast excitatory synaptic transmission and might contribute to better understanding PGB anticonvulsant/analgesic clinical effects

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

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

Presynaptic Ca[subscript v]2.1 calcium channels carrying familial hemiplegic migraine mutation R192Q allow faster recovery from synaptic depression in mouse calyx of Held

Ca[subscript V]2.1 Ca[superscript 2+] 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 α[subscript 1A] pore-forming subunit of Ca[subscript V]2.1 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 Ca[superscript 2+] concentration, we observed that with low Ca[superscript 2+] 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[superscript +] channels) via Ca[subscript v]2.1-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

Synaptic gain-of-function effects of mutant Ca[subscript v]2.1 channels in a mouse model of familial hemiplegic migraine are due to increased basal [Ca[superscript 2+]]i

Specific missense mutations in the CACNA1A gene, which encodes a subunit of voltage-gated Ca[subscript V]2.1 channels, are associated with familial hemiplegic migraine type 1 (FHM1), a rare monogenic subtype of common migraine with aura. We used transgenic knock-in (KI) mice harboring the human pathogenic FHM1 mutation S218L to study presynaptic Ca[superscript 2+]) currents, EPSCs, and in vivo activity at the calyx of Held synapse. Whole-cell patch-clamp recordings of presynaptic terminals from S218L KI mice showed a strong shift of the calcium current I-V curve to more negative potentials, leading to an increase in basal [Ca[superscript 2+]]i, increased levels of spontaneous transmitter release, faster recovery from synaptic depression, and enhanced synaptic strength despite smaller action-potential-elicited Ca[superscript 2+] currents. The gain-of-function of transmitter release of the S218L mutant was reproduced in vivo, including evidence for an increased release probability, demonstrating its relevance for glutamatergic transmission. This synaptic phenotype may explain the misbalance between excitation and inhibition in neuronal circuits resulting in a persistent hyperexcitability state and other migraine-relevant mechanisms such as an increased susceptibility to cortical spreading depression