HCN channels and absence seizures

ZD7288 ameliorates long-term cerebral ischemia reperfusion-induced deterioration of spatial memory by regulating the expressions of NMDA receptor subunits in rats

To study the effect of inhibition of hyperpolarization-activated cyclic nucleotide-gated cation channel (HCN) on spatial memory with cerebral ischemia-reperfusion (IR) in rats, the middle cerebral artery occlusion was performed to induce the IR injury. ZD7288 (5 µg/µl) and MK-801 (100 µg/µl) were administrated by lateral ventricular injection. Except for the sham group, all other groups were subjected to ischemia for 2 h followed by reperfusion for 4 weeks. The neurological impairment was evaluated using the neurological deficit score, and the Morris water maze detected changes in spatial memory. The cerebral infarction volume was determined by TTC staining, and the morphology and number of hippocampal neurons on the ischemic side were observed through HE staining. Immunoblotting and qPCR were used to detect the expressions of HCN1, HCN2, and N-methyl-D-aspartic acid receptor (NMDAR) subunits in the hippocampus. The expression changes of NMDAR subunits were applied by immunohistochemistry in different hippocampus regions. Our study found that ZD7288 could improve the spatial memory deficits induced by IR and exert neuroprotective effects. The possible mechanism is related to the fact that ZD7288 regulates the expression of various subunits of NMDAR by inhibiting HCN, including its effect on their phosphorylation states.

Recent Advances in Ionic Mechanisms in Pituitary Cells: Implications for Electrophysiological and Electropharmacological Research

Pituitary cells are specialized cells located within the pituitary gland, a small, pea-sized gland situated at the base of the brain. Through the use of cellular electrophysiological techniques, the electrical properties of these cells have been revealed. This review paper aims to introduce the ion currents that are known to be functionally expressed in pituitary cells. These currents include a voltage-gated Na+ current (INa), erg-mediated K+ current (IK(erg)), M-type K+ current (IK(M)), hyperpolarization-activated cation current (Ih), and large-conductance Ca2+-activated K+ (BKCa) channel. The biophysical characteristics of the respective ion current were described. Additionally, we also provide explanations for the effect of various drugs or compounds on each of these currents. GH3-cell exposure to GV-58 can increase the magnitude of INa with a concurrent rise in the inactivation time constant of the current. The presence of esaxerenone, an antagonist of the aldosterone receptor, directly suppresses the magnitude of peak and late INa. Risperidone, an atypical antipsychotic agent, is effective at suppressing the IK(erg) amplitude directly, and di(2-ethylhexyl)-phthalate suppressed IK(erg). Solifenacin and kynurenic acid can interact with the KM channel to stimulate IK(M), while carisbamate and cannabidiol inhibit the Ih amplitude activated by sustained hyperpolarization. Moreover, the presence of either rufinamide or QO-40 can enhance the activity of single BKCa channels. To summarize, alterations in ion currents within native pituitary cells or pituitary tumor cells can influence their functional activity, particularly in processes like stimulus-secretion coupling. The effects of small-molecule modulators, as demonstrated here, bear significance in clinical, therapeutic, and toxicological contexts.

Ontogeny of the Epileptic System in the Krushinsky-Molodkina Rat Strain with Genetically Determined Audiogenic Epilepsy

Susceptibility to audiogenic epilepsy (AE) seizures and phenotypic manifestations of epileptic activity in rats of the Krushinsky-Molodkina (KM) strain were shown to develop in parallel with the appearance of seizure EEG patterns from 2 to 7 months of age. The seizure latency decreased with age, while the intensity of convulsive seizures increased. Two types of epileptiform discharges (EDs) were identified in background EEGs (no exposure to sound) of KM rats. One type had a form of high-amplitude generalized packs of waves with the animal shuddering. The other type had a form of generalized non-seizure absence-like spike-and-wave discharges with the animal freezing. The total and mean durations of single absence-like discharges increased with age. Parallel age-related increases in the severity of AE seizures and the number of generalized absence-like discharges in the forebrain EEG suggests the development of the epileptic system in KM rats.

The Role of Acetylcholinesterase Enzyme Inhibitor Rivastigmine on Spike-Wave Discharges, Learning-Memory, Anxiety, and TRPV1 Channel Expression in Genetic Absence Epileptic WAG/Rij Rats

In the present study, the effects of the acetylcholinesterase (AChE) enzyme inhibitor rivastigmine (RIVA) on spike-wave discharges (SWDs), memory impairment, anxiety-like behavior, and the transient receptor potential vanilloid 1 (TRPV1) gene expression were investigated in genetic absence epileptic Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. After tripolar electrodes were implanted on the WAG/Rij rats' skulls, single doses of 0.125, 0.25, 0.5, 1, and 2 mg/kg RIVA were intraperitoneally (i.p.) administered, and electrocorticogram (ECoG) recordings of SWDs were recorded for three hours before and after injections. Additionally, once significant doses were determined in acute studies, WAG/Rij rats were administered low-dose (0.5 mg/kg) and high-dose (2 mg/kg) of RIVA for 21 consecutive days and SWDs were recorded. Learning-memory abilities (Y-maze test), anxiety-like behavior (elevated plus maze test), and TRPV1 gene expression were determined and compared in 8-month-old WAG/Rij and age-matched Wistar rats. Acute RIVA administration dose-dependently reduced the total number of SWDs and was even entirely inhibited at 1 and 2 mg/kg RIVA doses. On the other hand, long-term high-dose RIVA administration increased the total number of SWDs. Long-term high-dose RIVA treatment reduced learning-memory and anxiety-like behavior in WAG/Rij rats, while only anxiety-like behavior decreased in Wistar rats. TRPV1 gene expression increased in WAG/Rij rats and decreased in Wistar rats with long-term RIVA administration. These data indicate that the sudden increase of acetylcholine (ACh) causes a significant decrease in absence seizures. In contrast, prolonged maintenance of ACh elevation causes an increase in absence seizures, probably by altering the expression of channels such as TRPV1.

The enigmatic HCN channels: A cellular neurophysiology perspective

What physiological role does a slow hyperpolarization-activated ion channel with mixed cation selectivity play in the fast world of neuronal action potentials that are driven by depolarization? That puzzling question has piqued the curiosity of physiology enthusiasts about the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which are widely expressed across the body and especially in neurons. In this review, we emphasize the need to assess HCN channels from the perspective of how they respond to time-varying signals, while also accounting for their interactions with other co-expressing channels and receptors. First, we illustrate how the unique structural and functional characteristics of HCN channels allow them to mediate a slow negative feedback loop in the neurons that they express in. We present the several physiological implications of this negative feedback loop to neuronal response characteristics including neuronal gain, voltage sag and rebound, temporal summation, membrane potential resonance, inductive phase lead, spike triggered average, and coincidence detection. Next, we argue that the overall impact of HCN channels on neuronal physiology critically relies on their interactions with other co-expressing channels and receptors. Interactions with other channels allow HCN channels to mediate intrinsic oscillations, earning them the "pacemaker channel" moniker, and to regulate spike frequency adaptation, plateau potentials, neurotransmitter release from presynaptic terminals, and spike initiation at the axonal initial segment. We also explore the impact of spatially non-homogeneous subcellular distributions of HCN channels in different neuronal subtypes and their interactions with other channels and receptors. Finally, we discuss how plasticity in HCN channels is widely prevalent and can mediate different encoding, homeostatic, and neuroprotective functions in a neuron. In summary, we argue that HCN channels form an important class of channels that mediate a diversity of neuronal functions owing to their unique gating kinetics that made them a puzzle in the first place.

Analysis of epilepsy-associated variants in HCN3 - Functional implications and clinical observations

OBJECTIVE

This case study investigates the role of hyperpolarization-activated, cyclic nucleotide-gated (HCN) ion channels, which are integral membrane proteins crucial for regulating neuronal excitability. HCN channels are composed of four subunits (HCN1-4), with HCN1, HCN2, and HCN4 previously linked to epilepsy. However, the role of the HCN3 in epileptogenesis remains underexplored.

METHODS

We recruited a cohort of 298 epilepsy patients to screen for genetic variants in the HCN3 (NM_020897.3) using Sanger sequencing. We identified rare variants and conducted functional assays to evaluate their pathogenicity.

RESULTS

We identified three rare heterozygous variants in HCN3: c.1370G > A (R457H), c.1982G > A (R661Q), and c.1982G > A(P630L). In vitro functional analyses demonstrated that these variants affected the expression level of HCN3 protein without altering its membrane localization. Whole-cell voltage-clamp experiments showed that two variants (R457H and R661Q) significantly reduced current density in cells, while P630L has no effect on ion channel current.

SIGNIFICANCE

Our findings suggest that the identified HCN3 genetic variants disrupt HCN ion channel function, highlighting HCN3 as a novel candidate gene involved in epileptic disorders. This expands the genetic landscape of epilepsy and provides new insights into its molecular underpinnings.

PLAIN LANGUAGE SUMMARY

Epilepsy is a brain disease that can be caused by mutations in specific genes. We found three rare variants in HCN3 gene in 298 patients with epilepsy, and two of the three mutations could be pathogenic and cause epilepsy and another one is single-nucleotide polymorphism, which could have no effect and no contribution to the development of epilepsy.

Spinal Nerve Axotomy: Effects on Ih In Vivo and HCNs in DRG Neurons

In vitro experiments performed on dissociated dorsal root ganglion (DRG) neurons suggest the involvement of the hyperpolarization-activated cation current (Ih) in enhancing neuronal excitability, potentially contributing to neuropathic pain. However, the more confirmative in vivo information about how nerve injury interacts with Ih is lacking. In this study, Ih was recorded in vivo using the dynamic single-electrode voltage clamp (dSEVC) technique on L5 DRG neurons of normal rats and those seven days after spinal nerve axotomy (SNA). Compared to normal rats, SNA unexpectedly inhibited the activity of Ih channels on A-fiber DRG neurons: (a) the Ih current magnitude, density, and conductance were consistently diminished; and (b) the Ih activation velocity was slowed and the voltage for Ih activation was hyperpolarized. The half-activation voltage (V0.5) exhibited a negative shift, and the time constant for Ih activation was prolonged across all test potentials, indicating the reduced availability of Ih after SNA. To further investigate the mechanisms of SNA on Ih, the underlying HCN channels and the correlated mRNA were quantified and compared. The mRNA expression level of HCN1-4 was uniformly enhanced after SNA, which might have contributed to the increased cytoplasmic HCN1 intensity observed in both medium- and large-sized DRG neurons. This finding contradicted the functional reduction of Ih after SNA. Surprisingly, the HCN labeling pattern was altered after SNA: the labeling area of HCN1 and HCN2 at the membranous ring region of the axotomized large neurons became significantly thinner or absent. We concluded that the diminished ring immunoreactivity for HCN1 and HCN2 correlated with a reduced availability of Ih channels, elucidating the observed decrease in Ih in axotomized A-fiber neurons.

A sexually dimorphic signature of activity-dependent BDNF signaling on the intrinsic excitability of pyramidal neurons in the prefrontal cortex

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders with strong genetic heterogeneity and more prevalent in males than females. We and others hypothesize that diminished activity-dependent neural signaling is a common molecular pathway dysregulated in ASD caused by diverse genetic mutations. Brain-derived neurotrophic factor (BDNF) is a key growth factor mediating activity-dependent neural signaling in the brain. A common single nucleotide polymorphism (SNP) in the pro-domain of the human BDNF gene that leads to a methionine (Met) substitution for valine (Val) at codon 66 (Val66Met) significantly decreases activity-dependent BDNF release without affecting basal BDNF secretion. By using mice with genetic knock-in of this human BDNF methionine (Met) allele, our previous studies have shown differential severity of autism-like social deficits in male and female BDNF+/Met mice. Pyramidal neurons are the principal neurons in the prefrontal cortex (PFC), a key brain region for social behaviors. Here, we investigated the impact of diminished activity-dependent BDNF signaling on the intrinsic excitability of pyramidal neurons in the PFC. Surprisingly, diminished activity-dependent BDNF signaling significantly increased the intrinsic excitability of pyramidal neurons in male mice, but not in female mice. Notably, significantly decreased thresholds of action potentials were observed in male BDNF+/Met mice, but not in female BDNF+/Met mice. Voltage-clamp recordings revealed that the sodium current densities were significantly increased in the pyramidal neurons of male BDNF+/Met mice, which were mediated by increased transcriptional level of Scn2a encoding sodium channel NaV 1.2. Medium after hyperpolarization (mAHP), another important parameter to determine intrinsic neuronal excitability, is strongly associated with neuronal firing frequency. Further, the amplitudes of mAHP were significantly decreased in male BDNF+/Met mice only, which were mediated by the downregulation of Kcnn2 encoding small conductance calcium-activated potassium channel 2 (SK2). This study reveals a sexually dimorphic signature of diminished activity-dependent BDNF signaling on the intrinsic neuronal excitability of pyramidal neurons in the PFC, which provides possible cellular and molecular mechanisms underpinning the sex differences in idiopathic ASD patients and human autism victims who carry BDNF Val66Met SNP.

Voltage-gated ion channels in epilepsies: circuit dysfunctions and treatments

Epileptic encephalopathies are generally considered to be functional disruptions in the balance between neural excitation and inhibition. Excitatory and inhibitory voltage-gated ion channels are key targets of antiepileptic drugs, playing a critical role in regulating neuronal excitation and synaptic transmission. Recent research has highlighted the significance of ion channels in various aspects of epilepsy, including presynaptic neurotransmitter release, intrinsic neuronal excitability, and neural synchrony. Genetic alterations in excitatory and inhibitory ion channels within principal neurons and in inhibitory interneurons have also been identified as key contributors to the development of epilepsies. We review these recent studies and shed light on the bidirectional relationship between epilepsy and neuronal excitability and the latest advancements in pharmacological therapeutics targeting ion channels for epilepsy treatment.

Structural mechanism of human HCN1 hyperpolarization-activated channel inhibition by ivabradine

The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels play a crucial role in regulating neuronal excitability. Despite growing evidence supporting the therapeutic potential of HCN1 inhibition in treating neurological disorders, the structural basis of channel inhibition by inhibitor has remained elusive. Here, we present the cryo-electron microscopy structure of human HCN1 channel in complex with inhibitor ivabradine, the drug on the market that acts on HCN channels. Combining electrophysiology, mutagenesis, and molecular dynamics simulations, our findings reveal that ivabradine binds to a previously unidentified pocket formed between the S4, S1, and HCN domain. Furthermore, through structure-based virtual screening, we identify two Food and Drug Administration-approved drugs that can inhibit the HCN1 channel by interacting with the ivabradine-binding site. Our results not only provide insights into the structural intricacies of ivabradine-mediated inhibition, but also offer a potential pharmacological framework for developing novel drugs targeting the HCN1 channel. The elucidation of these molecular interactions serves as a foundational step in advancing therapeutic strategies for modulating HCN1 activity, contributing to the broader landscape of drug discovery and development in this area.

Channelopathies in epilepsy: an overview of clinical presentations, pathogenic mechanisms, and therapeutic insights

Pathogenic variants in genes encoding ion channels are causal for various pediatric and adult neurological conditions. In particular, several epilepsy syndromes have been identified to be caused by specific channelopathies. These encompass a spectrum from self-limited epilepsies to developmental and epileptic encephalopathies spanning genetic and acquired causes. Several of these channelopathies have exquisite responses to specific antiseizure medications (ASMs), while others ASMs may prove ineffective or even worsen seizures. Some channelopathies demonstrate phenotypic pleiotropy and can cause other neurological conditions outside of epilepsy. This review aims to provide a comprehensive exploration of the pathophysiology of seizure generation, ion channels implicated in epilepsy, and several genetic epilepsies due to ion channel dysfunction. We outline the clinical presentation, pathogenesis, and the current state of basic science and clinical research for these channelopathies. In addition, we briefly look at potential precision therapy approaches emerging for these disorders.

The Neurovascular Unit Dysfunction in the Molecular Mechanisms of Epileptogenesis and Targeted Therapy

Epilepsy is a multifaceted neurological syndrome characterized by recurrent, spontaneous, and synchronous seizures. The pathogenesis of epilepsy, known as epileptogenesis, involves intricate changes in neurons, neuroglia, and endothelium, leading to structural and functional disorders within neurovascular units and culminating in the development of spontaneous epilepsy. Although current research on epilepsy treatments primarily centers around anti-seizure drugs, it is imperative to seek effective interventions capable of disrupting epileptogenesis. To this end, a comprehensive exploration of the changes and the molecular mechanisms underlying epileptogenesis holds the promise of identifying vital biomarkers for accurate diagnosis and potential therapeutic targets. Emphasizing early diagnosis and timely intervention is paramount, as it stands to significantly improve patient prognosis and alleviate the socioeconomic burden. In this review, we highlight the changes and molecular mechanisms of the neurovascular unit in epileptogenesis and provide a theoretical basis for identifying biomarkers and drug targets.

Alterations in HCN1 expression and distribution during epileptogenesis in rats

BACKGROUND

The hyperpolarization-activated cyclic nucleotide-gated cation channel (HCN1) is predominantly located in key regions associated with epilepsy, such as the neocortex and hippocampus. Under normal physiological conditions, HCN1 plays a crucial role in the excitatory and inhibitory regulation of neuronal networks. In temporal lobe epilepsy, the expression of HCN1 is decreased in the hippocampi of both animal models and patients. However, whether HCN1 expression changes during epileptogenesis preceding spontaneous seizures remains unclear.

OBJECTIVE

The aim of this study was to determine whether the expression of HCN1 is altered during the epileptic prodromal phase, thereby providing evidence for its role in epileptogenesis.

METHODS

We utilized a cobalt wire-induced rat epilepsy model to observe changes in HCN1 during epileptogenesis and epilepsy. Additionally, we also compared HCN1 alterations in epileptogenic tissues between cobalt wire- and pilocarpine-induced epilepsy rat models. Long-term video EEG recordings were used to confirm seizures development. Transcriptional changes, translation, and distribution of HCN1 were assessed using high-throughput transcriptome sequencing, total protein extraction, membrane and cytoplasmic protein fractionation, western blotting, immunohistochemistry, and immunofluorescence techniques.

RESULTS

In the cobalt wire-induced rat epilepsy model during the epileptogenesis phase, total HCN1 mRNA and protein levels were downregulated. Specifically, the membrane expression of HCN1 was decreased, whereas cytoplasmic HCN1 expression showed no significant change. The distribution of HCN1 in the distal dendrites of neurons decreased. During the epilepsy period, similar HCN1 alterations were observed in the neocortex of rats with cobalt wire-induced epilepsy and hippocampus of rats with lithium pilocarpine-induced epilepsy, including downregulation of mRNA levels, decreased total protein expression, decreased membrane expression, and decreased distal dendrite expression.

CONCLUSIONS

Alterations in HCN1 expression and distribution are involved in epileptogenesis beyond their association with seizure occurrence. Similarities in HCN1 alterations observed in epileptogenesis-related tissues from different models suggest a shared pathophysiological pathway in epileptogenesis involving HCN1 dysregulation. Therefore, the upregulation of HCN1 expression in neurons, maintenance of the HCN1 membrane, and distal dendrite distribution in neurons may represent promising disease-modifying strategies in epilepsy.

The role of HCN channels on the effects of T-type calcium channels and GABAA receptors in the absence epilepsy model of WAG/Rij rats

In this study we used ivabradine (IVA), a hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blocker, to identify its effect on spike-wave discharges (SWDs); and aimed to determine the role of IVA on the effects of T-type calcium channel blocker NNC 55-0396, GABAA receptor agonist muscimol and antagonist bicuculline in male WAG/Rij rats. After tripolar electrodes for electrocorticogram (ECoG) recordings were placed on the WAG/Rij rats' skulls, 5, 10, and 20 mg/kg IVA were intraperitoneally administered for 7 consecutive days and ECoG recordings were obtained on days 0th, 3rd, 6th, and 7th for three hours before and after injections. While acute injection of 5, 10, and 20 mg/kg IVA did not affect the total number and the mean duration of SWDs, subacute administration (7 days) of IVA decreased the SWDs parameters 24 hours after the 7th injection. Interestingly, when IVA was administered again 24 hours after the 6th IVA injection, it increased the SWDs parameters. Western-blot analyses showed that HCN1 and HCN2 expressions decreased and HCN4 increased in the 5-month-old WAG/Rij rats compared to the 1-month-old WAG/Rij and 5-month-old native Wistar rats, while subacute IVA administration increased the levels of HCN1 and HCN2 channels, except HCN4. Subacute administration of IVA reduced the antiepileptic activity of NNC, while the proepileptic activity of muscimol and the antiepileptic activity of bicuculline were abolished. It might be suggested that subacute IVA administration reduces absence seizures by changing the HCN channel expressions in WAG/Rij rats, and this affects the T-type calcium channels and GABAA receptors.

Contribution of membrane-associated oscillators to biological timing at different timescales

Environmental rhythms such as the daily light-dark cycle selected for endogenous clocks. These clocks predict regular environmental changes and provide the basis for well-timed adaptive homeostasis in physiology and behavior of organisms. Endogenous clocks are oscillators that are based on positive feedforward and negative feedback loops. They generate stable rhythms even under constant conditions. Since even weak interactions between oscillators allow for autonomous synchronization, coupling/synchronization of oscillators provides the basis of self-organized physiological timing. Amongst the most thoroughly researched clocks are the endogenous circadian clock neurons in mammals and insects. They comprise nuclear clockworks of transcriptional/translational feedback loops (TTFL) that generate ∼24 h rhythms in clock gene expression entrained to the environmental day-night cycle. It is generally assumed that this TTFL clockwork drives all circadian oscillations within and between clock cells, being the basis of any circadian rhythm in physiology and behavior of organisms. Instead of the current gene-based hierarchical clock model we provide here a systems view of timing. We suggest that a coupled system of autonomous TTFL and posttranslational feedback loop (PTFL) oscillators/clocks that run at multiple timescales governs adaptive, dynamic homeostasis of physiology and behavior. We focus on mammalian and insect neurons as endogenous oscillators at multiple timescales. We suggest that neuronal plasma membrane-associated signalosomes constitute specific autonomous PTFL clocks that generate localized but interlinked oscillations of membrane potential and intracellular messengers with specific endogenous frequencies. In each clock neuron multiscale interactions of TTFL and PTFL oscillators/clocks form a temporally structured oscillatory network with a common complex frequency-band comprising superimposed multiscale oscillations. Coupling between oscillator/clock neurons provides the next level of complexity of an oscillatory network. This systemic dynamic network of molecular and cellular oscillators/clocks is suggested to form the basis of any physiological homeostasis that cycles through dynamic homeostatic setpoints with a characteristic frequency-band as hallmark. We propose that mechanisms of homeostatic plasticity maintain the stability of these dynamic setpoints, whereas Hebbian plasticity enables switching between setpoints via coupling factors, like biogenic amines and/or neuropeptides. They reprogram the network to a new common frequency, a new dynamic setpoint. Our novel hypothesis is up for experimental challenge.

Cognitive comorbidities of experimental absence seizures are independent of anxiety

Typical absence seizures (ASs) are brief periods of lack of consciousness, associated with 2.5-4 Hz spike-wave discharges (SWDs) in the EEG, which are highly prevalent in children and teenagers. The majority of probands in these young epileptic cohorts show neuropsychological comorbidities, including cognitive, memory and mood impairments, even after the seizures are pharmacologically controlled. Similar cognition and memory deficits have been reported in different, but not all, genetic animal models of ASs. However, since these impairments are subtle and highly task-specific their presence may be confounded by an anxiety-like phenotype and no study has tested anxiety and memory in the same animals. Moreover, the majority of studies used non-epileptic inbred animals as the only control strain and this may have contributed to a misinterpretation of these behavioural results. To overcome these issues, here we used a battery of behavioural tests to compare anxiety and memory in the same animals from the well-established inbred model of Genetic Absence Epilepsy Rats from Strasbourg (GAERS), their inbred strain of Non-Epileptic Control (NEC) strain (that lack ASs) and normal outbred Wistar rats. We found that GAERS do not exhibit increased anxiety-like behavior and neophobia compared to both NEC and Wistar rats. In contrast, GAERS show decreased spontaneous alternation, spatial working memory and cross-modal object recognition compared to both NEC and Wistar rats. Furthermore, GAERS preferentially used egocentric strategies to perform spatial memory tasks. In summary, these results provide solid evidence of memory deficits in GAERS rats that do not depend on an anxiety or neophobic phenotype. Moreover, the presence of differences between NEC and Wistar rats stresses the need of using both outbred and inbred control rats in behavioural studies involving genetic models of ASs.