Dopamine-Dependent Ketamine Modulation of Glutamatergic Synaptic Plasticity in the Prelimbic Cortex of Adult Rats Exposed to Acute Stress.

Traumatic stress is the main environmental risk factor for the development of psychiatric disorders. We have previously shown that acute footshock (FS) stress in male rats induces rapid and long-lasting functional and structural changes in the prefrontal cortex (PFC), which are partly reversed by acute subanesthetic ketamine. Here, we asked if acute FS may also induce any changes in glutamatergic synaptic plasticity in the PFC 24 h after stress exposure and whether ketamine administration 6 h after stress may have any effect. We found that the induction of long-term potentiation (LTP) in PFC slices of both control and FS animals is dependent on dopamine and that dopamine-dependent LTP is reduced by ketamine. We also found selective changes in ionotropic glutamate receptor subunit expression, phosphorylation, and localization at synaptic membranes induced by both acute stress and ketamine. Although more studies are needed to understand the effects of acute stress and ketamine on PFC glutamatergic plasticity, this first report suggests a restoring effect of acute ketamine, supporting the potential benefit of ketamine in limiting the impact of acute traumatic stress.

Neuropsin cleaves EphB2 in the amygdala to control anxiety.

A minority of individuals experiencing traumatic events develop anxiety disorders. The reason for the lack of correspondence between the prevalence of exposure to psychological trauma and the development of anxiety is unknown. Extracellular proteolysis contributes to fear-associated responses by facilitating neuronal plasticity at the neuron-matrix interface. Here we show in mice that the serine protease neuropsin is critical for stress-related plasticity in the amygdala by regulating the dynamics of the EphB2-NMDA-receptor interaction, the expression of Fkbp5 and anxiety-like behaviour. Stress results in neuropsin-dependent cleavage of EphB2 in the amygdala causing dissociation of EphB2 from the NR1 subunit of the NMDA receptor and promoting membrane turnover of EphB2 receptors. Dynamic EphB2-NR1 interaction enhances NMDA receptor current, induces Fkbp5 gene expression and enhances behavioural signatures of anxiety. On stress, neuropsin-deficient mice do not show EphB2 cleavage and its dissociation from NR1 resulting in a static EphB2-NR1 interaction, attenuated induction of the Fkbp5 gene and low anxiety. The behavioural response to stress can be restored by intra-amygdala injection of neuropsin into neuropsin-deficient mice and disrupted by the injection of either anti-EphB2 antibodies or silencing the Fkbp5 gene in the amygdala of wild-type mice. Our findings establish a novel neuronal pathway linking stress-induced proteolysis of EphB2 in the amygdala to anxiety.

Nonfunctional NaV1.1 familial hemiplegic migraine mutant transformed into gain of function by partial rescue of folding defects.

Familial hemiplegic migraine (FHM) is a rare subtype of migraine with aura. Mutations causing FHM type 3 have been identified in SCN1A, the gene encoding the Nav1.1 Na(+) channel, which is also a major target of epileptogenic mutations and is particularly important for the excitability of GABAergic neurons. However, functional studies of NaV1.1 FHM mutations have generated controversial results. In particular, it has been shown that the NaV1.1-L1649Q mutant is nonfunctional when expressed in a human cell line because of impaired plasma membrane expression, similarly to NaV1.1 mutants that cause severe epilepsy, but we have observed gain-of-function effects for other NaV1.1 FHM mutants. Here we show that NaV1.1-L1649Q is nonfunctional because of folding defects that are rescuable by incubation at lower temperatures or coexpression of interacting proteins, and that a partial rescue is sufficient for inducing an overall gain of function because of the modifications in gating properties. Strikingly, when expressed in neurons, the mutant was partially rescued and was a constitutive gain of function. A computational model showed that 35% rescue can be sufficient for inducing gain of function. Interestingly, previously described folding-defective epileptogenic NaV1.1 mutants show loss of function also when rescued. Our results are consistent with gain of function as the functional effect of NaV1.1 FHM mutations and hyperexcitability of GABAergic neurons as the pathomechanism of FHM type 3.

Sound localization ability and glycinergic innervation of the superior olivary complex persist after genetic deletion of the medial nucleus of the trapezoid body.

The medial nucleus of the trapezoid body (MNTB) in the superior olivary complex (SOC) is an inhibitory hub considered critical for binaural sound localization. We show that genetic ablation of MNTB neurons in mice only subtly affects this ability by prolonging the minimum time required to detect shifts in sound location. Furthermore, glycinergic innervation of the SOC is maintained without an MNTB, consistent with the existence of parallel inhibitory inputs. These findings redefine the role of MNTB in sound localization and suggest that the inhibitory network is more complex than previously thought.

Lipocalin-2 controls neuronal excitability and anxiety by regulating dendritic spine formation and maturation.

Psychological stress causes adaptive changes in the nervous system directed toward maintaining homoeostasis. These biochemical and structural mechanisms regulate animal behavior, and their malfunction may result in various forms of affective disorders. Here we found that the lipocalin-2 (Lcn2) gene, encoding a secreted protein of unknown neuronal function, was up-regulated in mouse hippocampus following psychological stress. Addition of lipocalin-2 to cultured hippocampal neurons reduced dendritic spine actin's mobility, caused retraction of mushroom spines, and inhibited spine maturation. These effects were further enhanced by inactivating iron-binding residues of Lcn-2, suggesting that they were facilitated by the iron-free form of Lcn-2. Concurrently, disruption of the Lcn2 gene in mice promoted stress-induced increase in spine density and caused an increase in the proportion of mushroom spines. The above changes correlated with higher excitability of CA1 principal neurons and with elevated stress-induced anxiety in Lcn-2(-/-) mice. Our study demonstrates that lipocalin-2 promotes stress-induced changes in spine morphology and function to regulate neuronal excitability and anxiety.

Pure haploinsufficiency for Dravet syndrome Na(V)1.1 (SCN1A) sodium channel truncating mutations.

PURPOSE: Dravet syndrome (DS), a devastating epileptic encephalopathy, is mostly caused by mutations of the SCN1A gene, coding for the voltage-gated Na(+) channel Na(V)1.1 α subunit. About 50% of SCN1A DS mutations truncate Na(V)1.1, possibly causing complete loss of its function. However, it has not been investigated yet if Na(V)1.1 truncated mutants are dominant negative, if they impair expression or function of wild-type channels, as it has been shown for truncated mutants of other proteins (e.g., Ca(V) channels). We studied the effect of two DS truncated Na(V)1.1 mutants, R222* and R1234*, on coexpressed wild-type Na(+) channels. METHODS: We engineered R222* or R1234* in the human cDNA of Na(V)1.1 (hNa(V)1.1) and studied their effect on coexpressed wild-type hNa(V)1.1, hNa(V)1.2 or hNa(V)1.3 cotransfecting tsA-201 cells, and on hNa(V)1.6 transfecting an human embryonic kidney (HEK) cell line stably expressing this channel. We also studied hippocampal neurons dissociated from Na(V)1.1 knockout (KO) mice, an animal model of DS expressing a truncated Na(V)1.1 channel. KEY FINDINGS: We found no modifications of current amplitude coexpressing the truncated mutants with hNa(V)1.1, hNa(V)1.2, or hNa(V)1.3, but a 30% reduction coexpressing them with hNa(V)1.6. However, we showed that also coexpression of functional full-length hNa(V)1.1 caused a similar reduction. Therefore, this effect should not be involved in the pathomechanism of DS. Some gating properties of hNa(V)1.1, hNa(V)1.3, and hNa(V)1.6 were modified, but recordings of hippocampal neurons dissociated from Na(V)1.1 KO mice did not show any significant modifications of these properties. Therefore, Na(V)1.1 truncated mutants are not dominant negative, consistent with haploinsufficiency as the cause of DS. SIGNIFICANCE: We have better clarified the pathomechanism of DS, pointed out an important difference between pathogenic truncated Ca(V)2.1 mutants and hNa(V)1.1 ones, and shown that hNa(V)1.6 expression can be reduced in physiologic conditions by coexpression of hNa(V)1.1. Moreover, our data may provide useful information for the development of therapeutic approaches.

Acute Ketamine Facilitates Fear Memory Extinction in a Rat Model of PTSD Along With Restoring Glutamatergic Alterations and Dendritic Atrophy in the Prefrontal Cortex.

Stress represents a major risk factor for psychiatric disorders, including post-traumatic stress disorder (PTSD). Recently, we dissected the destabilizing effects of acute stress on the excitatory glutamate system in the prefrontal cortex (PFC). Here, we assessed the effects of single subanesthetic administration of ketamine (10 mg/kg) on glutamate transmission and dendritic arborization in the PFC of footshock (FS)-stressed rats, along with changes in depressive, anxious, and fear extinction behaviors. We found that ketamine, while inducing a mild increase of glutamate release in the PFC of naïve rats, blocked the acute stress-induced enhancement of glutamate release when administered 24 or 72 h before or 6 h after FS. Accordingly, the treatment with ketamine 6 h after FS also reduced the stress-dependent increase of spontaneous excitatory postsynaptic current (sEPSC) amplitude in prelimbic (PL)-PFC. At the same time, ketamine injection 6 h after FS was found to rescue apical dendritic retraction of pyramidal neurons induced by acute stress in PL-PFC and facilitated contextual fear extinction. These results show rapid effects of ketamine in animals subjected to acute FS, in line with previous studies suggesting a therapeutic action of the drug in PTSD models. Our data are consistent with a mechanism of ketamine involving re-establishment of synaptic homeostasis, through restoration of glutamate release, and structural remodeling of dendrites.

Target promiscuity and heterogeneous effects of tarantula venom peptides affecting Na+ and K+ ion channels.

Venom-derived peptide modulators of ion channel gating are regarded as essential tools for understanding the molecular motions that occur during the opening and closing of ion channels. In this study, we present the characterization of five spider toxins on 12 human voltage-gated ion channels, following observations about the target promiscuity of some spider toxins and the ongoing revision of their "canonical" gating-modifying mode of action. The peptides were purified de novo from the venom of Grammostola rosea tarantulas, and their sequences were confirmed by Edman degradation and mass spectrometry analysis. Their effects on seven tetrodotoxin-sensitive Na(+) channels, the three human ether-à-go-go (hERG)-related K(+) channels, and two human Shaker-related K(+) channels were extensively characterized by electrophysiological techniques. All the peptides inhibited ion conduction through all the Na(+) channels tested, although with distinctive patterns. The peptides also affected the three pharmaceutically relevant hERG isoforms differently. At higher concentrations, all peptides also modified the gating of the Na(+) channels by shifting the activation to more positive potentials, whereas more complex effects were recorded on hERG channels. No effects were evident on the two Shaker-related K(+) channels at concentrations well above the IC(50) value for the affected channels. Given the sequence diversity of the tested peptides, we propose that tarantula toxins should be considered both as multimode and target-promiscuous ion channel modulators; both features should not be ignored when extracting mechanistic interpretations about ion channel gating. Our observations could also aid in future structure-function studies and might help the development of novel ion channel-specific drugs.

Four disulfide-bridged scorpion beta neurotoxin CssII: heterologous expression and proper folding in vitro.

The gene of the four disulfide-bridged Centruroides suffusus suffusus toxin II was cloned into the expression vector pQE30 containing a 6His-tag and a FXa proteolytic cleavage region. This recombinant vector was transfected into Escherichia coli BL21 cells and expressed under induction with isopropyl thiogalactoside (IPTG). The level of expression was 24.6 mg/l of culture medium, and the His tagged recombinant toxin (HisrCssII) was found exclusively in inclusion bodies. After solubilization the HisrCssII peptide was purified by affinity and hydrophobic interaction chromatography. The reverse-phase HPLC profile of the HisrCssII product obtained from the affinity chromatography step showed several peptide fractions having the same molecular mass of 9392.6 Da, indicating that HisrCssII was oxidized forming several distinct disulfide bridge arrangements. The multiple forms of HisrCssII after reduction eluted from the column as a single protein component of 9400.6 Da. Similarly, an in vitro folding of the reduced HisrCssII generated a single oxidized component of HisrCssII, which was cleaved by the proteolytic enzyme FXa to the recombinant CssII (rCssII). The molecular mass of rCssII was 7538.6 Da as expected. Since native CssII (nCssII) is amidated at the C-terminal residue whereas the rCssII is heterologously expressed in the format of free carboxyl end, there is a difference of 1 Da, when comparing both peptides (native versus heterologously expressed). Nevertheless, they show similar toxicity when injected intracranially into mice, and both nCssII and rCssII show the typical electrophysiological properties of beta-toxins in Na(v)1.6 channels, which is for the first time demonstrated here. Binding and displacement experiments conducted with radiolabelled CssII confirms the electrophysiological results. Several problems associated with the heterologously expressed toxins containing four disulfide bridges are discussed.

Revisiting cangitoxin, a sea anemone peptide: purification and characterization of cangitoxins II and III from the venom of Bunodosoma cangicum.

Sodium channel toxins from sea anemones are employed as tools for dissecting the biophysical properties of inactivation in voltage-gated sodium channels. Cangitoxin (CGTX) is a peptide containing 48 amino acid residues and was formerly purified from Bunodosoma cangicum. Nevertheless, previous works reporting the isolation procedures for such peptide from B. cangicum secretions are controversial and may lead to incorrect information. In this paper, we report a simple and rapid procedure, consisting of two chromatographic steps, in order to obtain a CGTX analog directly from sea anemone venom. We also report a substitution of N16D in this peptide sample and the co-elution of an inseparable minor isoform presenting the R14H substitution. Peptides are named as CGTX-II and CGTX-III, and their effects over Nav1.1 channels in patch clamp experiments are demonstrated.

Neuroinflammation and ER-stress are key mechanisms of acute bilirubin toxicity and hearing loss in a mouse model.

Hyperbilirubinemia (jaundice) is caused by raised levels of unconjugated bilirubin in the blood. When severe, susceptible brain regions including the cerebellum and auditory brainstem are damaged causing neurological sequelae such as ataxia, hearing loss and kernicterus. The mechanism(s) by which bilirubin exerts its toxic effect have not been completely understood to date. In this study we investigated the acute mechanisms by which bilirubin causes the neurotoxicity that contributes to hearing loss. We developed a novel mouse model that exhibits the neurological features seen in human Bilirubin-Induced Neurological Dysfunction (BIND) syndrome that we assessed with a behavioural score and auditory brainstem responses (ABR). Guided by initial experiments applying bilirubin to cultured cells in vitro, we performed whole genome gene expression measurements on mouse brain tissue (cerebellum and auditory brainstem) following bilirubin exposure to gain mechanistic insights into biochemical processes affected, and investigated further using immunoblotting. We then compared the gene changes induced by bilirubin to bacterial lipopolysaccharide (LPS), a well characterized inducer of neuroinflammation, to assess the degree of similarity between them. Finally, we examined the extent to which genetic perturbation of inflammation and both known and novel anti-inflammatory drugs could protect hearing from bilirubin-induced toxicity. The in vitro results indicated that bilirubin induces changes in gene expression consistent with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). These gene changes were similar to the gene expression signature of thapsigargin-a known ER stress inducer. It also induced gene expression changes associated with inflammation and NF-κB activation. The in vivo model showed behavioural impairment and a raised auditory threshold. Whole genome gene expression analysis confirmed inflammation as a key mechanism of bilirubin neurotoxicity in the auditory pathway and shared gene expression hallmarks induced by exposure to bacterial lipopolysaccharide (LPS) a well-characterized inducer of neuroinflammation. Interestingly, bilirubin caused more severe damage to the auditory system than LPS in this model, but consistent with our hypothesis of neuroinflammation being a primary part of bilirubin toxicity, the hearing loss was protected by perturbing the inflammatory response. This was carried out genetically using lipocalin-2 (LCN2)-null mice, which is an inflammatory cytokine highly upregulated in response to bilirubin. Finally, we tested known and novel anti-inflammatory compounds (interfering with NF-κB and TNFα signalling), and also demonstrated protection of the auditory system from bilirubin toxicity. We have developed a novel, reversible, model for jaundice that shows movement impairment and auditory loss consistent with human symptoms. We used this model to establish ER-stress and inflammation as major contributors to bilirubin toxicity. Because of the rapid and reversible onset of toxicity in this novel model it represents a system to screen therapeutic compounds. We have demonstrated this by targeting inflammation genetically and with anti-inflammatory small molecules that offered protection against bilirubin toxicity. This also suggests that anti-inflammatory drugs could be of therapeutic use in hyperbilirubinemia.

Novel alpha-conotoxins from Conus spurius and the alpha-conotoxin EI share high-affinity potentiation and low-affinity inhibition of nicotinic acetylcholine receptors.

alpha-Conotoxins from marine snails are known to be selective and potent competitive antagonists of nicotinic acetylcholine receptors. Here we describe the purification, structural features and activity of two novel toxins, SrIA and SrIB, isolated from Conus spurius collected in the Yucatan Channel, Mexico. As determined by direct amino acid and cDNA nucleotide sequencing, the toxins are peptides containing 18 amino acid residues with the typical 4/7-type framework but with completely novel sequences. Therefore, their actions (and that of a synthetic analog, [gamma15E]SrIB) were compared to those exerted by the alpha4/7-conotoxin EI from Conus ermineus, used as a control. Their target specificity was evaluated by the patch-clamp technique in mammalian cells expressing alpha(1)beta(1)gammadelta, alpha(4)beta(2) and alpha(3)beta(4) nicotinic acetylcholine receptors. At high concentrations (10 microm), the peptides SrIA, SrIB and [gamma15E]SrIB showed weak blocking effects only on alpha(4)beta(2) and alpha(1)beta(1)gammadelta subtypes, but EI also strongly blocked alpha(3)beta(4) receptors. In contrast to this blocking effect, the new peptides and EI showed a remarkable potentiation of alpha(1)beta(1)gammadelta and alpha(4)beta(2) nicotinic acetylcholine receptors if briefly (2-15 s) applied at concentrations several orders of magnitude lower (EC(50), 1.78 and 0.37 nm, respectively). These results suggest not only that the novel alpha-conotoxins and EI can operate as nicotinic acetylcholine receptor inhibitors, but also that they bind both alpha(1)beta(1)gammadelta and alpha(4)beta(2) nicotinic acetylcholine receptors with very high affinity and increase their intrinsic cholinergic response. Their unique properties make them excellent tools for studying the toxin-receptor interaction, as well as models with which to design highly specific therapeutic drugs.

Crotamine inhibits preferentially fast-twitching muscles but is inactive on sodium channels.

Crotamine is a peptide toxin from the venom of the rattlesnake Crotalus durissus terrificus that induces a typical hind-limb paralysis of unknown nature. Hind limbs have a predominance of fast-twitching muscles that bear a higher density of sodium channels believed until now to be the primary target of crotamine. Hypothetically, this makes these muscles more sensitive to crotamine and would explain such hind-limb paralysis. To challenge this hypothesis, we performed concentration vs. response curves on fast (extensor digitorum longus (EDL)) and slow (soleus) muscles of adult male rats. Crotamine was tested on various human Na+ channel isoforms (Na(v)1.1-Na(v)1.6 alpha-subunits) expressed in HEK293 cells in patch-clamp experiments, as well as in acutely dissociated dorsal root ganglion (DRG) neurons. Also, the behavioral effects of crotamine intoxication were compared with those of a muscle-selective sodium channel antagonist mu-CgTx-GIIIA, and other sodium-acting toxins such as tetrodotoxin alpha- and beta-pompilidotoxins, sea anemone toxin BcIII, spider toxin Tx2-6. Results pointed out that EDL was more susceptible to crotamine than soleus under direct electrical stimulation. Surprisingly, electrophysiological experiments in human Na(v)1.1 to Na(v)1.6 Na+ channels failed to show any significant change in channel characteristics, in a clear contrast with former studies. DRG neurons did not respond to crotamine. The behavioral effects of the toxins were described in detail and showed remarkable differences. We conclude that, although differences in the physiology of fast and slow muscles may cause the typical crotamine syndrome, sodium channels are not the primary target of crotamine and therefore, the real mechanism of action of this toxin is still unknown.

Stress-induced lipocalin-2 controls dendritic spine formation and neuronal activity in the amygdala.

Behavioural adaptation to psychological stress is dependent on neuronal plasticity and dysfunction at this cellular level may underlie the pathogenesis of affective disorders such as depression and post-traumatic stress disorder. Taking advantage of genome-wide microarray assay, we performed detailed studies of stress-affected transcripts in the amygdala - an area which forms part of the innate fear circuit in mammals. Having previously demonstrated the role of lipocalin-2 (Lcn-2) in promoting stress-induced changes in dendritic spine morphology/function and neuronal excitability in the mouse hippocampus, we show here that the Lcn-2 gene is one of the most highly upregulated transcripts detected by microarray analysis in the amygdala after acute restraint-induced psychological stress. This is associated with increased Lcn-2 protein synthesis, which is found on immunohistochemistry to be predominantly localised to neurons. Stress-naïve Lcn-2(-/-) mice show a higher spine density in the basolateral amygdala and a 2-fold higher rate of neuronal firing rate compared to wild-type mice. Unlike their wild-type counterparts, Lcn-2(-/-) mice did not show an increase in dendritic spine density in response to stress but did show a distinct pattern of spine morphology. Thus, amygdala-specific neuronal responses to Lcn-2 may represent a mechanism for behavioural adaptation to psychological stress.

Negative-shift activation, current reduction and resurgent currents induced by ß-toxins from Centruroides scorpions in sodium channels.

The ß-toxins purified from the New World scorpion venoms of the Centruroides species affect several voltage-gated sodium channels (VGSCs) and thus are essential tools not only for the discrimination of different channel sub-types but also for studying the structure-function relationship between channels and toxins. This communication reports the results obtained with four different peptides purified from three species of Centruroides scorpions and assayed on seven distinct isoforms of VGSC (Na(v)1.1-Na(v)1.7) by specific functional analysis conducted through single cell electrophysiology. The toxins studied were CssII from Centruroides suffusus suffusus, Cll1 and Cll2 from Centruroides limpidus limpidus and a novel toxin from Centruroides noxius, which was characterized for the first time here. It has 67 amino acid residues and four disulfide bridges with a molecular mass of 7626 Da. Three different functional features were identified: current reduction of macroscopic conductance, left shift of the voltage-dependent activation and induction of resurgent currents at negative voltages following brief, strong depolarizations. The isoforms which revealed to be more affected resulted to be Na(v)1.6 > 1.1 > 1.2 and, for the first time, a ß-toxin is here shown to induce resurgent current also in isoforms different from Na(v)1.6. Additionally, these results were analyzed with molecular modelling. In conclusion, although the four toxins have a high degree of identity, they display tri-modal function, each of which shows selectivity among the different sub-types of Na+ -channels. Thus, they are invaluable as tools for structure-function studies of ß-toxins and offer a basis for the design of novel ion channel-specific drugs.

Characterization of selectivity and pharmacophores of type 1 sea anemone toxins by screening seven Na(v) sodium channel isoforms.

During their evolution, animals have developed a set of cysteine-rich peptides capable of binding various extracellular sites of voltage-gated sodium channels (VGSC). Sea anemone toxins that target VGSCs delay their inactivation process, but little is known about their selectivities. Here we report the investigation of three native type 1 toxins (CGTX-II, δ-AITX-Bcg1a and δ-AITX-Bcg1b) purified from the venom of Bunodosoma cangicum. Both δ-AITX-Bcg1a and δ-AITX-Bcg1b toxins were fully sequenced. The three peptides were evaluated by patch-clamp technique among Nav1.1-1.7 isoforms expressed in mammalian cell lines, and their preferential targets are Na(v)1.5>1.6>1.1. We also evaluated the role of some supposedly critical residues in the toxins which would interact with the channels, and observed that some substitutions are not critical as expected. In addition, CGTX-II and δ-AITX-Bcg1a evoke different shifts in activation/inactivation Boltzmann curves in Nav1.1 and 1.6. Moreover, our results suggest that the interaction region between toxins and VGSCs is not restricted to the supposed site 3 (S3-S4 linker of domain IV), and this may be a consequence of distinct surface of contact of each peptide vs. targeted channel. Our data suggest that the contact surfaces of each peptide may be related to their surface charges, as CGTX-II is more positive than δ-AITX-Bcg1a and δ-AITX-Bcg1b.

Voltage-gated sodium channel isoform-specific effects of pompilidotoxins.

Pompilidotoxins (PMTXs, alpha and beta) are small peptides consisting of 13 amino acids purified from the venom of the solitary wasps Anoplius samariensis (alpha-PMTX) and Batozonellus maculifrons (beta-PMTX). They are known to facilitate synaptic transmission in the lobster neuromuscular junction, and to slow sodium channel inactivation. By using beta-PMTX, alpha-PMTX and four synthetic analogs with amino acid changes, we conducted a thorough study of the effects of PMTXs on sodium current inactivation in seven mammalian voltage-gated sodium channel (VGSC) isoforms and one insect VGSC (DmNa(v)1). By evaluating three components of which the inactivating current is composed (fast, slow and steady-state components), we could distinguish three distinct groups of PMTX effects. The first group concerned the insect and Na(v)1.6 channels, which showed a large increase in the steady-state current component without any increase in the slow component. Moreover, the dose-dependent increase in this steady-state component was correlated with the dose-dependent decrease in the fast component. A second group of effects concerned the Na(v)1.1, Na(v)1.2, Na(v)1.3 and Na(v)1.7 isoforms, which responded with a large increase in the slow component, and showed only a small steady-state component. As with the first group of effects, the slow component was dose-dependent and correlated with the decrease in the fast component. Finally, a third group of effects concerned Na(v)1.4 and Na(v)1.5, which did not show any change in the slow or steady-state component. These data shed light on the complex and intriguing behavior of VGSCs in response to PMTXs, helping us to better understand the molecular determinants explaining isoform-specific effects.

Actions of sea anemone type 1 neurotoxins on voltage-gated sodium channel isoforms.

As voltage-gated Na(+) channels are responsible for the conduction of electrical impulses in most excitable tissues in the majority of animals (except nematodes), they have become important targets for the toxins of venomous animals, from sea anemones to molluscs, scorpions, spiders and even fishes. During their evolution, different animals have developed a set of cysteine-rich peptides capable of binding different extracellular sites of this channel protein. A fundamental question concerning the mechanism of action of these toxins is whether they act at a common receptor site in Na(+) channels when exerting their different pharmacological effects, or at distinct receptor sites in different Na(v) channels subtypes whose particular properties lead to these pharmacological differences. The alpha-subunits of voltage-gated Na(+) channels (Na(v)1.x) have been divided into at least nine subtypes on the basis of amino acid sequences. Sea anemones have been extensively studied from the toxinological point of view for more than 40 years. There are about 40 sea anemone type 1 peptides known to be active on Na(v)1.x channels and all are 46-49 amino acid residues long, with three disulfide bonds and their molecular weights range between 3000 and 5000 Da. About 12 years ago a general model of Na(v)1.2-toxin interaction, developed for the alpha-scorpion toxins, was shown to fit also to action of sea anemone toxin such as ATX-II. According to this model these peptides are specifically acting on the type 3 site known to be between segments 3 and 4 in domain IV of the Na(+) channel protein. This region is indeed responsible for the normal Na(+) currents fast inactivation that is potently slowed by these toxins. This fundamental "gain-of-function" mechanism is responsible for the strong increase in the action potential duration. They constitute a class of tools by means of which physiologists and pharmacologists can study the structure/function relationships of channel proteins. As most of the structural and electrophysiological studies were performed on type 1 sea anemone sodium channel toxins, we will present a comprehensive and updated review on the current understanding of the physiological actions of these Na channel modifiers.

Electroclinical features of a family with simple febrile seizures and temporal lobe epilepsy associated with SCN1A loss-of-function mutation.

PURPOSE: To report in detail the electroclinical features of a large family in which we recently identified a missense mutation (M145T) of a well-conserved amino acid in the first transmembrane segment of domain I of the human SCN1A. We showed that the mutation is associated with a loss of SCN1A function. METHODS: The family originates from southern Italy and contains 35 members spread over four generations. Of the 14 affected individuals, the 13 still living members (7 males, mean age 36.6 +/- 20.4) underwent a complete electroclinical evaluation. RESULTS: All 13 affected family members had febrile seizures (FS) up to the age of 6 years. Age at onset of FS ranged from 5 to 45 months with a mean age of 12.8 +/- 12.9 months. One of the 13 was affected by post-traumatic epilepsy. Three of the 13 later developed temporal lobe epilepsy (TLE) with both simple focal seizures, and also very rare focal complex or nocturnal secondary generalized tonic-clonic seizures. In two of the three patients who later developed TLE, the MRI studies revealed mesial temporal sclerosis. CONCLUSIONS: Our findings illustrate that SCN1A mutations can cause simple FS associated with TLE, which differ from the characteristic clinical spectrum of GEFS+. It is open to conjecture if this unusual phenotype might at least in part be related to the fact that M145T is the first missense mutation found in DIS1 of SCN1A.

Resurgent current and voltage sensor trapping enhanced activation by a beta-scorpion toxin solely in Nav1.6 channel. Significance in mice Purkinje neurons.

Resurgent currents are functionally crucial in sustaining the high frequency firing of cerebellar Purkinje neurons expressing Na(v)1.6 channels. Beta-scorpion toxins, such as CssIV, induce a left shift in the voltage-dependent activation of Na(v)1.2 channels by "trapping" the IIS4 voltage sensor segment. We found that the dangerous Cn2 beta-scorpion peptide induces both the left shift voltage-dependent activation and a transient resurgent current only in human Na(v)1.6 channels (among 1.1-1.7), whereas CssIV did not induce the resurgent current. Cn2 also produced both actions in mouse Purkinje cells. These findings suggest that only distinct beta-toxins produce resurgent currents. We suggest that the novel and unique selectivity of Cn2 could make it a model drug to replace deep brain stimulation of the subthalamic nucleus in patients with Parkinson disease.