Rapid‐acting antidepressant ketamine,its metabolites and other candidates: A historical overview and future perspective

Major depressive disorder (MDD) is one of the most disabling psychiatric disorders. Approximately one‐third of the patients with MDD are treatment resistant to the current antidepressants. There is also a significant therapeutic time lag of weeks to months. Furthermore, depression in patients with bipolar disorder (BD) is typically poorly responsive to antidepressants. Therefore, there exists an unmet medical need for rapidly acting antidepressants with beneficial effects in treatment‐resistant patients with MDD or BD. Accumulating evidence suggests that the N‐methyl‐D‐aspartate receptor (NMDAR) antagonist ketamine produces rapid and sustained antidepressant effects in treatment‐resistant patients with MDD or BD. Ketamine is a racemic mixture comprising equal parts of (R)‐ketamine (or arketamine) and (S)‐ketamine (or esketamine). Because (S)‐ketamine has higher affinity for NMDAR than (R)‐ketamine, esketamine was developed as an antidepressant. On 5 March 2019, esketamine nasal spray was approved by the US Food and Drug Administration. However, preclinical data suggest that (R)‐ketamine exerts greater potency and longer‐lasting antidepressant effects than (S)‐ketamine in animal models of depression and that (R)‐ketamine has less detrimental side‐effects than (R,S)‐ketamine or (S)‐ketamine. In this article, the author reviews the historical overview of the antidepressant actions of enantiomers of ketamine and its major metabolites norketamine and hydroxynorketamine. Furthermore, the author discusses the other potential rapid‐acting antidepressant candidates (i.e., NMDAR antagonists and modulators, low‐voltage‐sensitive T‐type calcium channel inhibitor, potassium channel Kir4.1 inhibitor, negative modulators of γ‐aminobutyric acid, and type A [GABA_A] receptors) to compare them with ketamine. Moreover, the molecular and cellular mechanisms of ketamine’s antidepressant effects are discussed.     

Painful neuropathies: the emerging role of sodium channelopathies

Pain is a frequent debilitating feature reported in peripheral neuropathies with involvement of small nerve (Aδ and C) fibers. Voltage‐gated sodium channels are responsible for the generation and conduction of action potentials in the peripheral nociceptive neuronal pathway where Na_V1.7, Na_V1.8, and Na_V1.9 sodium channels (encoded by SCN9A, SCN10A, and SCN11A) are preferentially expressed. The human genetic pain conditions inherited erythromelalgia and paroxysmal extreme pain disorder were the first to be linked to gain‐of‐function SCN9A mutations. Recent studies have expanded this spectrum with gain‐of‐function SCN9A mutations in patients with small fiber neuropathy and in a new syndrome of pain, dysautonomia, and small hands and small feet (acromesomelia). In addition, painful neuropathies have been recently linked to SCN10A mutations. Patch‐clamp studies have shown that the effect of SCN9A mutations is dependent upon the cell‐type background. The functional effects of a mutation in dorsal root ganglion (DRG) neurons and sympathetic neuron cells may differ per mutation, reflecting the pattern of expression of autonomic symptoms in patients with painful neuropathies who carry the mutation in question. Peripheral neuropathies may not always be length‐dependent, as demonstrated in patients with initial facial and scalp pain symptoms with SCN9A mutations showing hyperexcitability in both trigeminal ganglion and DRG neurons. There is some evidence suggesting that gain‐of‐function SCN9A mutations can lead to degeneration of peripheral axons. This review will focus on the emerging role of sodium channelopathies in painful peripheral neuropathies, which could serve as a basis for novel therapeutic strategies.     

Development of novel PET probe [11C](R,R)HAPT and its stereoisomer [11C](S,S)HAPT for vesicular acetylcholine transporter imaging: A PET study in conscious monkey

Carbon‐11‐labeled (R,R)trans‐8‐methyl‐2‐hydroxy‐3‐[4‐[2‐aminophenyl]piperizinyl]‐tetralin ([¹¹C](R,R)HAPT) and its stereoisomer [¹¹C](S,S)HAPT were developed for imaging vesicular acetylcholine transporters (VAChTs), exclusively located in presynaptic cholinergic neurons. Both positron emission tomography (PET) probes were evaluated in the brain of conscious monkey (Macaca mulatta) using high‐resolution PET. Time‐activity curves (TACs) of [¹¹C](R,R)HAPT peaked within 5 min after the injection in all regions except the caudate and putamen, both of which showed peaks around 20 min postinjection. The regional distribution patterns of [¹¹C](R,R)HAPT determined as total distribution volume (V_t) were highest in the putamen, high in the caudate, intermediate in the amygdala, hippocampus, and thalamus, lower in the cingulate gyrus and frontal, temporal, and occipital cortices, and lowest in the cerebellum. In contrast, the distribution and TACs of [¹¹C](S,S)HAPT were homogeneous in all regions. The uptake of [¹¹C](R,R)HAPT was reduced by 1 mg/kg (?)‐vesamicol, a specific VAChT antagonist, in all regions except the cerebellum, but not by 0.1 mg/kg SA4503, a specific sigma‐1 receptor agonist. These results well reflect the in vitro affinity assessments using rat cerebral membranes. They also demonstrate that [¹¹C](R,R)HAPT is a potential PET probe for noninvasive and quantitative imaging of VAChT in the living brain. Synapse 68:283–292, 2014 . © 2014 Wiley Periodicals, Inc.     

Metabotropic glutamate receptor agonists reduce glutamate release from cultured astrocytes

Astrocytes are thought to control extracellular glutamate concentrations ([Glu]_o) in the brain, thereby protecting neurons from excitotoxic injury. We investigated the effects of metabotropic glutamate receptor (mGluR) agonists on glutamate transport and [Glu]_o in primary hippocampal astrocytic cultures. Acute or chronic exposure of astrocytes to the mGluR agonist trans‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (trans‐ACPD) or its active isomer 1S,3R‐ACPD reduced [Glu]_o in a time‐ and dose‐dependent manner (44.5 ± 3.6% reductions of [Glu]_o in astrocytes from P0–P10 rats and 65.9 ± 4.1 % from rats P20 by 100 μM 1S,3R‐ACPD, EC₅₀ ∼ 5 μM). 1S,3R‐ACPD effects developed slowly (median effective at ∼60 min) and persisted for several hours after agonist removal. ACPD‐pretreated astrocytes established lower steady‐state [Glu]_o levels. ACPD effects persisted in the presence of the glutamate uptake inhibitors D ,L ‐threo‐β‐hydroxyaspartate (THA) and L ‐trans‐pyrrolidine‐2,4‐dicarboxylate (PDC) but were impaired by disruption of the transmembrane Na⁺, K⁺, or H⁺ gradients. In addition, 1S,3R‐ACPD had no effects on intracellular glutamate content and did not directly block glutamate transport. Furthermore, ACPD effects could be mimicked by glutamate per se and several other compounds presumed to be mGluR agonists, although (S)‐3,5‐dihydroxyphenylglycine (DHPG), (2S,2R,3R)‐2‐(2,3‐dicarboxycyclopropyl)glycine (DCG‐IV), and L ‐(+)‐2‐amino‐4‐phosphonobutyric acid (L ‐AP4) were without effect. These data suggest that glutamate and certain mGluR agonists may regulate [Glu]_o by modulating the transmembrane equilibrium of glutamate transport, especially by attenuating glutamate release. GLIA 25:270–281, 1999. © 1999 Wiley‐Liss, Inc.     

Adenosine drives recycled vesicles to a slow‐release pool at the mouse neuromuscular junction

The effects of adenosine on neurotransmission have been widely studied by monitoring transmitter release. However, the effects of adenosine on vesicle recycling are still unknown. We used fluorescence microscopy of FM2‐10‐labeled synaptic vesicles in combination with intracellular recordings to examine whether adenosine regulates vesicle recycling during high‐frequency stimulation at mouse neuromuscular junctions. The A₁ adenosine receptor antagonist (8‐cyclopentyl‐1,3‐dipropylxanthine) increased the quantal content released during the first endplate potential, suggesting that vesicle exocytosis can be restricted by endogenous adenosine, which accordingly decreases the size of the recycling vesicle pool. Staining protocols designed to label specific vesicle pools that differ in their kinetics of release showed that all vesicles retrieved in the presence of 8‐cyclopentyl‐1,3‐dipropylxanthine were recycled towards the fast‐release pool, favoring its loading with FM2‐10 and suggesting that endogenous adenosine promotes vesicle recycling towards the slow‐release pool. In accordance with this effect, exogenous applied adenosine prevented the replenishment of the fast‐release vesicle pool and, thus, hindered its loading with the dye. We had found that, during high‐frequency stimulation, Ca²⁺ influx through L‐type channels directs newly formed vesicles to a fast‐release pool (Perissinotti et al., 2008). We demonstrated that adenosine did not prevent the effect of the L‐type blocker on transmitter release. Therefore, activation of the A₁ receptor promotes vesicle recycling towards the slow‐release pool without a direct effect on the L‐type channel. Further studies are necessary to elucidate the molecular mechanisms involved in the regulation of vesicle recycling by adenosine.     

The role of semantic knowledge in relearning spellings: Evidence from deep dysgraphia

Background: Remediation techniques for dysgraphia have focused on targeting different components of the theoretical models for spelling. Studies have revealed that targeting lexically oriented strategies can prove beneficial for patients with deep dysgraphia. Studies on short‐term memory have also demonstrated a role of semantic knowledge in short‐term retention

Aims: Two variants of lexically oriented strategies were applied to remediate a deep dysgraphic patient, PH, and the role of imagery in supporting the learning was examined.

Methods & Procedures: Retraining was explored using a visual‐kinaesthetic learning technique, contrasting performance with high‐ and low‐imagery words.

Outcomes & Results: Positive effects of learning were demonstrated. There was effective initial learning of blocks of both high‐imagery and low‐imagery target words, but high‐imagery words had a clear advantage in terms of longer‐term maintenance.

Conclusions: The data demonstrate that semantic knowledge may play a role in strengthening graphemic representations of words, helping in the maintenance of the orthography of target words over time.     

Intraseptal administration of (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid induces immediate early gene expression in lateral septal neurons

Prior work has shown that activation of metabotropic glutamate receptors can induce burst firing and a form of NMDA receptor independent long term potentiation in lateral septal slice preparations. To study this phenomenon in vivo we used the expression of immediate early gene products as markers for increased neuronal activity following intraseptal injection of the metabotropic agonist 1S,3R-ACPD. Intraseptal injection of 1S, 3R ACPD induced the expression of Fos-like, Jun 13-like and Krox24-like immunoreactivity in lateral septal neurons in a dose-dependent fashion. Immediate early gene product expression peaked at 4 to 6 h post-injection and then declined to baseline. Immediate early gene expression was diminished by co-injection of -AP3 and was not elicited by intraseptal injection of -AP4, cysteine sulfinic acid or DHPG. Immediate early gene expression was not diminished by chronic lithium treatment but was diminished by chronic treatment with the phospholipase A₂ inhibitor quinacrine. Co-injection of the phospholipase AZ inhibitor NDGA partially suppressed the induction of immediate early gene expression. Metabotropic glutamate receptors regulate lateral septal neuron excitability in vivo and some of their effects may be mediated by activation of phospholipase A₂. Alternatively, arachidonic acid may play a permissive role it the effects of metabotropic glutamate receptors on lateral septal neurons.     

Cardiac arrhythmias in hypokalemic periodic paralysis: Hypokalemia as only cause?

It is unknown how often cardiac arrhythmias occur in hypokalemic periodic paralysis (HypoPP) and if they are caused by hypokalemia alone or other factors. This systematic review shows that cardiac arrhythmias were reported in 27 HypoPP patients. Cases were confirmed genetically (13 with an R528H mutation in CACNA1S, 1 an R669H mutation in SCN4A) or had a convincing clinical diagnosis of HypoPP (13 genetically undetermined) if reported prior to the availability of genetic testing. Arrhythmias occurred during severe hypokalemia (11 patients), between attacks at normokalemia (4 patients), were treatment‐dependent (2 patients), or unspecified (10 patients). Nine patients died from arrhythmia. Convincing evidence for a pro‐arrhythmogenic factor other than hypokalemia is still lacking. The role of cardiac expression of defective skeletal muscle channels in the heart of HypoPP patients remains unclear. Clinicians should be aware of and prevent treatment‐induced cardiac arrhythmia in HypoPP. Muscle Nerve 50 : 327–332, 2014     

RAB2A Polymorphism impacts prefrontal morphology,functional connectivity,and working memory

Calbindin‐containing γ‐aminobutyric acid (GABA)ergic interneurons in the prefrontal cortex (PFC) have been found to play an important role in working memory (WM) and their malfunctions have been linked to psychiatric disorders. A recent genome‐wide association and expression‐SNP study indicated that the RAB2A gene was associated with the density of prefrontal calbindin‐positive neurons, suggesting this gene may have a broader influence on prefrontal structure and function. Using multimodal MRI and behavioral tasks, the current study investigated the effect of RAB2A on prefrontal morphology, resting‐state functional connectivity, and WM performance in a large sample of healthy Han Chinese subjects. Results showed that the RAB2A AGCAAA haplotype was associated with improved WM accuracy, increased cortical thickness in the left inferior frontal gyrus, and decreased functional connectivity between the left inferior frontal gyrus and the left dorsolateral PFC. Our findings provide consistent evidence supporting the effect of RAB2A on the structure and function of the PFC and related cognitive functions. These results should provide new insights into the neural mechanisms underlying the GABAergic genes' role in WM as well as its dysfunction. Hum Brain Mapp 36:4372–4382, 2015. © 2015 Wiley Periodicals, Inc.     

An SCN2A mutation in a family with infantile seizures from Madagascar reveals an increased subthreshold Na+ current

Missense mutations in SCN2A, encoding the brain sodium channel Na_V1.2, have been described in benign familial neonatal‐infantile seizures (BFNIS), a self‐limiting disorder, whereas several SCN2A de novo nonsense mutations have been found in patients with more severe phenotypes including epileptic encephalopathy. We report a family with BFNIS originating from Madagascar. Onset extended from 3 to 9 months of age. Interictal EEGs were normal. In two patients, ictal electroencephalography (EEG) studies showed partial seizure patterns with secondary generalization in one. Seizures remitted before 18 months of age, with or without medication. Intellectual development was normal. A novel missense mutation of SCN2A, c.4766A>G/p.Tyr1589Cys, was found in a highly conserved region of Na_V1.2 (D4/S2‐S3). Functional studies using heterologous expression in tsA201 cells and whole‐cell patch clamping revealed a depolarizing shift of steady‐state inactivation, increased persistent Na⁺ current, a slowing of fast inactivation and an acceleration of its recovery, thus a gain‐of‐function. Using an action potential waveform in a voltage‐clamp experiment we indicated an increased inward Na⁺ current at subthreshold voltages, which can explain a neuronal hyperexcitability. Our results suggest that this mutation induces neuronal hyperexcitability, resulting in infantile epilepsy with favorable outcome.     

Identification of a novel “almost neutral” μ‐opioid receptor antagonist in CHO cells expressing the cloned human μ‐opioid receptor

The basal (constitutive) activity of G protein‐coupled receptors allows for the measurement of inverse agonist activity. Some competitive antagonists turn into inverse agonists under conditions where receptors are constitutively active. In contrast, neutral antagonists have no inverse agonist activity, and they block both agonist and inverse agonist activity. The μ‐opioid receptor (MOR) demonstrates detectable constitutive activity only after a state of dependence is produced by chronic treatment with a MOR agonist. We therefore sought to identify novel MOR inverse agonists and novel neutral MOR antagonists in both untreated and agonist‐treated MOR cells. CHO cells expressing the cloned human mu receptor (hMOR‐CHO cells) were incubated for 20 h with medium (control) or 10 μM (2S,4aR,6aR,7R,9S,10aS,10bR)‐9‐(benzoyloxy)‐2‐(3‐furanyl)dodecahydro‐6a,10b‐dimethyl‐4,10‐dioxo‐2H‐naphtho‐[2,1‐c]pyran‐7‐carboxylic acid methyl ester (herkinorin, HERK). HERK treatment generates a high degree of basal signaling and enhances the ability to detect inverse agonists. [³⁵S]‐GTP‐γ‐S assays were conducted using established methods. We screened 21 MOR “antagonists” using membranes prepared from HERK‐treated hMOR‐CHO cells. All antagonists, including CTAP and 6β‐naltrexol, were inverse agonists. However, LTC‐274 ((?)‐3‐cyclopropylmethyl‐2,3,4,4α,5,6,7,7α‐octahydro‐1H‐benzofuro[3,2‐e]isoquinolin‐9‐ol)) showed the lowest efficacy as an inverse agonist, and, at concentrations less than 5 nM, had minimal effects on basal [³⁵S]‐GTP‐γ‐S binding. Other efforts in this study identified KC‐2‐009 ((+)‐3‐((1R,5S)‐2‐((Z)‐3‐phenylallyl)‐2‐azabicyclo[3.3.1]nonan‐5‐yl)phenol hydrochloride) as an inverse agonist at untreated MOR cells. In HERK‐treated cells, KC‐2‐009 had the highest efficacy as an inverse agonist. In summary, we identified a novel and selective MOR inverse agonist (KC‐2‐009) and a novel MOR antagonist (LTC‐274) that shows the least inverse agonist activity among 21 MOR antagonists. LTC‐274 is a promising lead compound for developing a true MOR neutral antagonist. Synapse 64:280–288, 2010. © 2009 Wiley‐Liss, Inc.     

Confirming an expanded spectrum of SCN2A mutations: a case series

Mutations in sodium channel genes are highly associated with epilepsy. Mutation of SCN1A, the gene encoding the voltage gated sodium channel (VGSC) alpha subunit type 1 (Nav1.1), causes Dravet syndrome spectrum disorders. Mutations in SCN2A have been identified in patients with benign familial neonatal‐infantile epilepsy (BFNIE), generalised epilepsy with febrile seizures plus (GEFS+), and a small number of reported cases of other infantile‐onset severe intractable epilepsy. Here, we report three patients with infantile‐onset severe intractable epilepsy found to have de novo mutations in SCN2A. While a causal role for these mutations cannot be directly established, these findings contribute to growing evidence that mutation of SCN2A is associated with a range of epilepsy phenotypes including severe infantile‐onset epilepsy.     

GABAA‐benzodiazepine receptor availability in smokers and nonsmokers: Relationship to subsyndromal anxiety and depression

Many smokers experience subsyndromal anxiety symptoms while smoking and during acute abstinence, which may contribute to relapse. We hypothesized that cortical gamma aminobutyric acid_A‐benzodiazepine receptor (GABA_A‐BZR) availability in smokers and nonsmokers might be related to the expression of subsyndromal anxiety, depressive, and pain symptoms. Cortical GABA_A‐BZRs were imaged in 15 smokers (8 men and 7 women), and 15 healthy age and sex‐matched nonsmokers, and 4 abstinent tobacco smokers (3 men; 1 woman) using [¹²³I]iomazenil and single photon emission computed tomography (SPECT). Anxiety and depressive symptoms were measured using the Spielberger's State‐Trait Anxiety Index (STAI) and the Center for Epidemiology Scale for Depressive Symptoms (CES‐D). The cold pressor task was administered to assess pain tolerance and sensitivity. The relationship between cortical GABA_A‐BZR availability, smoking status, and subsyndromal depression and anxiety symptoms, as well as pain tolerance and sensitivity, were evaluated. Surprisingly, there were no statistically significant differences in overall GABA_A‐BZR availability between smokers and nonsmokers or between active and abstinent smokers; however, cortical GABA_A‐BZR availability negatively correlated with subsyndromal state anxiety symptoms in nonsmokers but not in smokers. In nonsmokers, the correlation was seen across many brain areas with state anxiety [parietal (r = ?0.47, P = 0.03), frontal (r = ?0.46, P = 0.03), anterior cingulate (r = ?0.47, P = 0.04), temporal (r = ?0.47, P = 0.03), occipital (r = ?0.43, P = 0.05) cortices, and cerebellum (r = ?0.46, P = 0.04)], trait anxiety [parietal (r = ?0.72, P = 0.02), frontal (r = ?0.72, P = 0.02), and occipital (r = ?0.65, P = 0.04) cortices] and depressive symptoms [parietal (r = ?0.68; P = 0.02), frontal (r = ?0.65; P = 0.03), anterior cingulate (r = ?0.61; P = 0.04), and temporal (r = ?0.66; P = 0.02) cortices]. The finding that a similar relationship between GABA_A‐BZR availability and anxiety symptoms was not observed in smokers suggests that there is a difference in GABA_A‐BZR function, but not number, in smokers. Thus, while subsyndromal anxiety and depressive symptoms in nonsmokers may be determined in part by GABA_A‐BZR availability, smoking disrupts this relationship. Aberrant regulation of GABA_A‐BZR function in vulnerable smokers may explain why some smokers experience subsyndromal anxiety and depression. Synapse 63:1089–1099, 2009. © 2009 Wiley‐Liss, Inc.     

Systemic inflammation regulates microglial responses to tissue damage in vivo

Microglia, the resident immune cells of the central nervous system, exist in either a “resting” state associated with physiological tissue surveillance or an “activated” state in neuroinflammation. We recently showed that ATP is the primary chemoattractor to tissue damage in vivo and elicits opposite effects on the motility of activated microglia in vitro through activation of adenosine A_2A receptors. However, whether systemic inflammation affects microglial responses to tissue damage in vivo remains largely unknown. Using in vivo two‐photon imaging of mice, we show that injection of lipopolysaccharide (LPS) at levels that can produce both clear neuroinflammation and some features of sepsis significantly reduced the rate of microglial response to laser‐induced ablation injury in vivo. Under proinflammatory conditions, microglial processes initially retracted from the ablation site, but subsequently moved toward and engulfed the damaged area. Analyzing the process dynamics in 3D cultures of primary microglia indicated that only A_2A, but not A₁ or A₃ receptors, mediate process retraction in LPS‐activated microglia. The A_2A receptor antagonists caffeine and preladenant reduced adenosine‐mediated process retraction in activated microglia in vitro. Finally, administration of preladenant before induction of laser ablation in vivo accelerated the microglial response to injury following systemic inflammation. The regulation of rapid microglial responses to sites of injury by A_2A receptors could have implications for their ability to respond to the neuronal death occurring under conditions of neuroinflammation in neurodegenerative disorders. GLIA 2014;62:1345–1360     

Novel Dystonia Genes: Clues on Disease Mechanisms and the Complexities of High‐Throughput Sequencing

Dystonia is a genetically heterogenous disease and a prototype disorder where next‐generation sequencing has facilitated the identification of new pathogenic genes. This includes the first two genes linked to recessively inherited isolated dystonia, that is, HPCA (hippocalcin) and COL6A3 (collagen VI alpha 3). These genes are proposed to underlie cases of the so‐called DYT2‐like dystonia, while also reiterating two distinct pathways in dystonia pathogenesis. First, deficiency in HPCA function is thought to alter calcium homeostasis, a mechanism that has previously been forwarded for CACNA1A and ANO3. The novel myoclonus‐dystonia genes KCTD17 and CACNA1B also implicate abnormal calcium signaling in dystonia. Second, the phenotype in COL6A3‐loss‐of‐function zebrafish models argues for a neurodevelopmental defect, which has previously been suggested as a possible biological mechanism for THAP1, TOR1A, and TAF1 based on expression data. The newly reported myoclonus‐dystonia gene, RELN, plays also a role in the formation of brain structures. Defects in neurodevelopment likewise seem to be a recurrent scheme underpinning mainly complex dystonias, for example those attributable to biallelic mutations in GCH1, TH, SPR, or to heterozygous TUBB4A mutations. To date, it remains unclear whether dystonia is a common phenotypic outcome of diverse underlying disease mechanisms, or whether the different genetic causes converge in a single pathway. Importantly, the relevance of pathways highlighted by novel dystonia genes identified by high‐throughput sequencing depends on the confirmation of mutation pathogenicity in subsequent genetic and functional studies. However, independent, careful validation of genetic findings lags behind publications of newly identified genes. We conclude with a discussion on the characteristics of true‐positive reports. © 2016 International Parkinson and Movement Disorder Society     

Febrile infection‐related epilepsy syndrome (FIRES) is not caused by SCN1A,POLG, PCDH19 mutations or rare copy number variations

Aim Febrile infection‐related epilepsy syndrome (FIRES) is an enigmatic seizure disorder in childhood with an innocuous febrile infection triggering severe and intractable multifocal epilepsy, mostly with status epilepticus. FIRES shares several phenotypic features with epilepsies seen in patients with protocadherin 19 (PCDH19), sodium channel protein type 1 subunit alpha (SCN1A), and DNA polymerase subunit gamma‐1 (POLG) mutations. The aim of the study was the mutation analysis of these prime candidate genes in a cohort of patients with FIRES. Additionally, given that rare copy number variations (CNVs) have recently been established as important risk factors for epilepsies, we performed a genome‐wide CNV analysis. Method We analysed the protein coding region, including splice sites of the three candidate genes in 15 patients (eight males, seven females) with FIRES (age at onset 3–15y, median 6) using Sanger sequencing. Inclusion criteria were a status epilepticus without identifiable cause and a preceding febrile infection in previously healthy children. In addition, we performed genome‐wide human single‐nucleotide polymorphism 6.0 arrays in a subset of 10 patients to identify pathological CNVs. Results We could not identify the most likely pathogenic mutations or CNVs in FIRES. Interpretation Mutations in PCDH19, SCN1A, POLG, or CNVs are not responsible for FIRES.     

EZH2 expression in gliomas: Correlation with CDKN2A gene deletion/ p16 loss and MIB‐1 proliferation index

Enhancer of zeste homolog 2 (EZH2) mediated down‐regulation of CDKN2A/p16 has been observed in cell lines as well as in a few carcinomas. However, there is no study correlating EZH2 expression with CDKN2A/p16 status in gliomas. Hence, the present study was conducted to evaluate EZH2 expression in astrocytic and oligodendroglial tumors and correlate with CDKN2A/p16 status as well as MIB‐1 labeling index (LI). Gliomas of all grades (n = 118) were studied using immunohistochemistry to assess EZH2, p16 and MIB‐1 LI and fluorescence in situ hybrization to evaluate CDKN2A gene status. EZH2 expression and CDKN2A homozygous deletion (HD) were both significantly more frequent in high‐grade gliomas (HGG). Further, strong EZH2 expression (LI ≥ 25%) was significantly more common in HGGs without CDKN2A HD (48.7%; 19/39) as compared to cases with deletion (15.8%; 3/19). Loss of p16 expression was noted in 100% and 51.3% of CDKN2A deleted and non‐deleted tumors, respectively. Notably, 80% (16/20) of the CDKN2A non‐deleted HGGs with p16 loss had strong EZH2 expression, in contrast to only 15.8% (3/19) in the deleted group. Loss of p16 expression significantly correlated with MIB‐1 LI, irrespective of EZH2 status. Thus, this study shows that EZH2 expression correlates with tumor grade in both astrocytic and oligodendroglial tumors and hence can be used as a diagnostic marker to differentiate between low and HGGs. Further, this is the first report demonstrating an inverse correlation of strong EZH2 expression with CDKN2A HD in HGGs. Loss of p16 protein expression is mostly attributable to CDKN2A HD and correlates significantly with MIB‐1 LI. Notably, our study for the first time suggests a possible epigenetic mechanism of p16 loss in CDKN2A non‐deleted HGGs mediated by strong EZH2 expression. A hypothetical model for control of proliferative activity in low versus HGGs is therefore proposed.     

Metabotropic glutamate receptor 1 activity generates persistent, N-methyl-d-aspartate receptor-dependent depression of hippocampal pyramidal cell excitability

Metabotropic glutamate receptors (mGluRs) are involved in many forms of neuronal plasticity. In the hippocampus, they have well‐defined roles in long‐lasting forms of both synaptic and intrinsic plasticity. Here, we describe a novel form of long‐lasting intrinsic plasticity that we call (S)‐3,5‐dihydroxyphenylglycine (DHPG)‐mediated long‐term depression of excitability (DHPG‐LDE), and which is generated following transient pharmacological activation of group I mGluRs. In extracellular recordings from hippocampal slices, DHPG‐LDE was expressed as a long‐lasting depression of antidromic compound action potentials (cAPs) in CA1 or CA3 cells following a 4‐min exposure to the group I mGluR agonist (S)‐DHPG. A similar phenomenon was also seen for orthodromic fibre volleys evoked in CA3 axons. In single‐cell recordings from CA1 pyramids, DHPG‐LDE was manifest as persistent failures in antidromic action potential generation. DHPG‐LDE was blocked by (S)‐(+)‐a‐amino‐4‐carboxy‐2‐methylbenzeneacetic acid (LY367385), an antagonist of mGluR1, but not 2‐methyl‐6‐(phenylethynyl)pyridine hydrochloride (MPEP), an mGluR5 inhibitor. Although insensitive to antagonists of α‐amino‐3‐hydroxyl‐5‐methyl‐4‐isoxazole‐propionate/kainate and γ‐aminobutyric acid_A receptors, DHPG‐LDE was blocked by antagonists of N‐methyl‐d ‐aspartate (NMDA) receptors. Similarly, in single‐cell recordings, DHPG‐mediated antidromic spike failures were eliminated by NMDA receptor antagonism. Long after (S)‐DHPG washout, DHPG‐LDE was reversed by mGluR1 antagonism. A 4‐min application of (S)‐DHPG also produced an NMDA receptor‐dependent persistent depolarization of CA1 pyramidal cells. This depolarization was not solely responsible for DHPG‐LDE, because a similar level of depolarization elicited by raising extracellular K⁺ increased the amplitude of the cAP. DHPG‐LDE did not involve HCN channels or protein synthesis, but was eliminated by blockers of protein kinase C or tyrosine phosphatases.     

Trait Openness and serotonin 2A receptors in healthy volunteers: A positron emission tomography study

Recent research found lasting increases in personality trait Openness in healthy individuals and patients after administration of the serotonin 2A receptor (5‐HT_2AR) agonist psilocybin. However, no studies have investigated whether 5‐HT_2AR availability as imaged using positron emission tomography (PET) is associated with this trait. In 159 healthy individuals (53 females), the association between 5‐HT_2AR binding in neocortex imaged with [¹⁸F]altanserin or [¹¹C]Cimbi‐36 PET and personality trait Openness was investigated using linear regression models. In these models the influence of sex on the association was also investigated. Trait Openness was assessed with the NEO Personality Inventory‐Revised. No significant associations between neocortical 5‐HT_2AR binding and trait Openness were found for [¹⁸F]altanserin (p = 0.5) or [¹¹C]Cimbi‐36 (p = 0.8). Pooling the data in a combined model did not substantially change our results (p = 0.4). No significant interactions with sex were found (p > 0.35). Our results indicate that differences in 5‐HT_2AR availability are not related to variations in trait Openness in healthy individuals. Although stimulation of the 5‐HT_2AR with compounds such as psilocybin may contribute to long‐term changes in trait Openness, there is no evidence in favor of an association between 5‐HT_2AR and trait Openness.