Selective targeting of M-type potassium Kv 7.4 channels demonstrates their key role in the regulation of dopaminergic neuronal excitability and depression-like behaviour

Potassium and calcium channels in different nerve cells act as therapeutic targets in neurological disorders

The central nervous system, information integration center of the body, is mainly composed of neurons and glial cells. The neuron is one of the most basic and important structural and functional units of the central nervous system, with sensory stimulation and excitation conduction functions. Astrocytes and microglia belong to the glial cell family, which is the main source of cytokines and represents the main defense system of the central nervous system. Nerve cells undergo neurotransmission or gliotransmission, which regulates neuronal activity via the ion channels, receptors, or transporters expressed on nerve cell membranes. Ion channels, composed of large transmembrane proteins, play crucial roles in maintaining nerve cell homeostasis. These channels are also important for control of the membrane potential and in the secretion of neurotransmitters. A variety of cellular functions and life activities, including functional regulation of the central nervous system, the generation and conduction of nerve excitation, the occurrence of receptor potential, heart pulsation, smooth muscle peristalsis, skeletal muscle contraction, and hormone secretion, are closely related to ion channels associated with passive transmembrane transport. Two types of ion channels in the central nervous system, potassium channels and calcium channels, are closely related to various neurological disorders, including Alzheimer's disease, Parkinson's disease, and epilepsy. Accordingly, various drugs that can affect these ion channels have been explored deeply to provide new directions for the treatment of these neurological disorders. In this review, we focus on the functions of potassium and calcium ion channels in different nerve cells and their involvement in neurological disorders such as Parkinson's disease, Alzheimer's disease, depression, epilepsy, autism, and rare disorders. We also describe several clinical drugs that target potassium or calcium channels in nerve cells and could be used to treat these disorders. We concluded that there are few clinical drugs that can improve the pathology these diseases by acting on potassium or calcium ions. Although a few novel ion-channel-specific modulators have been discovered, meaningful therapies have largely not yet been realized. The lack of target-specific drugs, their requirement to cross the blood-brain barrier, and their exact underlying mechanisms all need further attention. This review aims to explain the urgent problems that need research progress and provide comprehensive information aiming to arouse the research community's interest in the development of ion channel-targeting drugs and the identification of new therapeutic targets for that can increase the cure rate of nervous system diseases and reduce the occurrence of adverse reactions in other systems.

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response. Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region-specific, particularly involving the corticolimbic system, including the ventral tegmental area, nucleus accumbens, prefrontal cortex, amygdala, and hippocampus. Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology. In this review, we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression. We focused on associated molecular pathways and neural circuits, with special attention to the brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling pathway and the ventral tegmental area-nucleus accumbens dopamine circuit. We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature, severity, and duration of stress, especially in the above-mentioned brain regions of the corticolimbic system. Therefore, BDNF might be a biological indicator regulating stress-related processes in various brain regions.

The involvement of K+ channels in depression and pharmacological effects of antidepressants on these channels

Depression is a common and complex psychiatric illness with multiple clinical symptoms, even leading to the disability and suicide. Owing to the partial understanding of the pathogenesis of depressive-like disorders, available pharmacotherapeutic strategies are developed mainly based on the "monoamine hypothesis", resulting in a limited effectiveness and a number of adverse effects in the clinical practice. The concept of multiple pathogenic factors be helpful for clarifying the etiology of depression and developing the antidepressants. It is well documented that K+ channels serve crucial roles in modulating the neuronal excitability and neurotransmitter release in the brain, and abnormality of these channels participated in the pathogenic process of diverse central nervous system (CNS) pathologies, such as seizure and Alzheimer's disease (AD). The clinical and preclinical evidence also delineates that the involvement of several types of K+ channels in depressive-like behaviors appear to be evident, suggesting these channels being one of the multiple factors in the etiology of this debilitating disorder. Emerging data manifest that diverse antidepressants impact distinct K+ channels, such as Kv, Kir and K2P, meaning the functioning of these drug via a "multi-target" manner. On the other hand, the scenario of antidepressants impinging K+ channels could render an alternative interpretation for the pharmacological effectiveness and numerous side effects in clinical trials. Furthermore, these channels serve to be considered as a "druggable target" to develop novel therapeutic compound to antagonize this psychiatry.

The role of KCNQ channel activators in management of major depressive disorder

Depression, a complex disorder with significant treatment challenges, necessitates innovative therapeutic approaches to address its multifaceted nature and enhance treatment outcomes. The modulation of KCNQ potassium (K+) channels, pivotal regulators of neuronal excitability and neurotransmitter release, is a promising innovative therapeutic target in psychiatry. Widely expressed across various tissues, including the nervous and cardiovascular systems, KCNQ channels play a crucial role in modulating membrane potential and regulating neuronal activity. Recent preclinical evidence suggests that KCNQ channels, particularly KCNQ3, contribute to the regulation of neuronal excitability within the reward circuitry, offering a potential target for alleviating depressive symptoms, notably anhedonia. Studies using animal models demonstrate that interventions targeting KCNQ channels can restore dopaminergic firing balance and mitigate depressive symptoms. Human studies investigating the effects of KCNQ channel activators, such as ezogabine, have shown promising results in alleviating depressive symptoms and anhedonia. The aforementioned observations underscore the therapeutic potential of KCNQ channel modulation in depression management and highlight the need and justification for phase 2 and phase 3 dose-finding studies as well as studies prespecifying symptomatic targets in depression including anhedonia.

Kv7 channel opener retigabine reduces self-administration of cocaine but not sucrose in rats

The increasing rates of drug misuse highlight the urgency of identifying improved therapeutics for treatment. Most drug-seeking behaviours that can be modelled in rodents utilize the repeated intravenous self-administration (SA) of drugs. Recent studies examining the mesolimbic pathway suggest that Kv7/KCNQ channels may contribute to the transition from recreational to chronic drug use. However, to date, all such studies used noncontingent, experimenter-delivered drug model systems, and the extent to which this effect generalizes to rats trained to self-administer drugs is not known. Here, we tested the ability of retigabine (ezogabine), a Kv7 channel opener, to regulate instrumental behaviour in male Sprague Dawley rats. We first validated the ability of retigabine to target experimenter-delivered cocaine in a conditioned place preference (CPP) assay and found that retigabine reduced the acquisition of place preference. Next, we trained rats for cocaine-SA under a fixed-ratio or progressive-ratio reinforcement schedule and found that retigabine pretreatment attenuated the SA of low to moderate doses of cocaine. This was not observed in parallel experiments, with rats self-administering sucrose, a natural reward. Compared with sucrose-SA, cocaine-SA was associated with reductions in the expression of the Kv7.5 subunit in the nucleus accumbens, without alterations in Kv7.2 and Kv7.3. Therefore, these studies reveal a reward-specific reduction in SA behaviour and support the notion that Kv7 is a potential therapeutic target for human psychiatric diseases with dysfunctional reward circuitry.

The Formation and Function of the VTA Dopamine System

The midbrain dopamine system is a sophisticated hub that integrates diverse inputs to control multiple physiological functions, including locomotion, motivation, cognition, reward, as well as maternal and reproductive behaviors. Dopamine is a neurotransmitter that binds to G-protein-coupled receptors. Dopamine also works together with other neurotransmitters and various neuropeptides to maintain the balance of synaptic functions. The dysfunction of the dopamine system leads to several conditions, including Parkinson's disease, Huntington's disease, major depression, schizophrenia, and drug addiction. The ventral tegmental area (VTA) has been identified as an important relay nucleus that modulates homeostatic plasticity in the midbrain dopamine system. Due to the complexity of synaptic transmissions and input-output connections in the VTA, the structure and function of this crucial brain region are still not fully understood. In this review article, we mainly focus on the cell types, neurotransmitters, neuropeptides, ion channels, receptors, and neural circuits of the VTA dopamine system, with the hope of obtaining new insight into the formation and function of this vital brain region.

PI4KIIIβ-Mediated Phosphoinositides Metabolism Regulates Function of the VTA Dopaminergic Neurons and Depression-Like Behavior

Phosphoinositides, including phosphatidylinositol-4,5-bisphosphate (PIP2), play a crucial role in controlling key cellular functions such as membrane and vesicle trafficking, ion channel, and transporter activity. Phosphatidylinositol 4-kinases (PI4K) are essential enzymes in regulating the turnover of phosphoinositides. However, the functional role of PI4Ks and mediated phosphoinositide metabolism in the central nervous system has not been fully revealed. In this study, we demonstrated that PI4KIIIβ, one of the four members of PI4Ks, is an important regulator of VTA dopaminergic neuronal activity and related depression-like behavior of mice by controlling phosphoinositide turnover. Our findings provide new insights into possible mechanisms and potential drug targets for neuropsychiatric diseases, including depression. Both sexes were studied in basic behavior tests, but only male mice could be used in the social defeat depression model.

A novel dual serotonin transporter and M-channel inhibitor D01 for antidepression and cognitive improvement

Cognitive dysfunction is a core symptom common in psychiatric disorders including depression that is primarily managed by antidepressants lacking efficacy in improving cognition. In this study, we report a novel dual serotonin transporter and voltage-gated potassium Kv7/KCNQ/M-channel inhibitor D01 (a 2-methyl-3-aryloxy-3-heteroarylpropylamines derivative) that exhibits both anti-depression effects and improvements in cognition. D01 inhibits serotonin transporters (Ki = 30.1 ± 6.9 nmol/L) and M channels (IC50 = 10.1 ± 2.4 μmol/L). D01 also reduces the immobility duration in the mouse FST and TST assays in a dose-dependent manner without a stimulatory effect on locomotion. Intragastric administrations of D01 (20 and 40 mg/kg) can significantly shorten the immobility time in a mouse model of chronic restraint stress (CRS)-induced depression-like behavior. Additionally, D01 dose-dependently improves the cognitive deficit induced by CRS in Morris water maze test and increases the exploration time with novel objects in normal or scopolamine-induced cognitive deficits in mice, but not fluoxetine. Furthermore, D01 reverses the long-term potentiation (LTP) inhibition induced by scopolamine. Taken together, our findings demonstrate that D01, a dual-target serotonin reuptake and M channel inhibitor, is highly effective in the treatment-resistant depression and cognitive deficits, thus holding potential for development as therapy of depression with cognitive deficits.

Activation of Kv7 channels normalizes hyperactivity of the VTA-NAcLat circuit and attenuates methamphetamine-induced conditioned place preference and sensitization in mice

The brain circuit projecting from the ventral tegmental area (VTA) to the nucleus accumbens lateral shell (NAcLat) has a key role in methamphetamine (MA) addiction. As different dopamine (DA) neuron subpopulations in the VTA participate in different neuronal circuits, it is a challenge to isolate these DA neuron subtypes. Using retrograde tracing and Patch-seq, we isolated DA neurons in the VTA-NAcLat circuit in MA-treated mice and performed gene expression profiling. Among the differentially expressed genes, KCNQ genes were dramatically downregulated. KCNQ genes encode Kv7 channel proteins, which modulate neuronal excitability. Injection of both the Kv7.2/3 agonist ICA069673 and the Kv7.4 agonist fasudil into the VTA attenuated MA-induced conditioned place preference and locomotor sensitization and decreased neuronal excitability. Increasing Kv7.2/3 activity decreased neural oscillations, synaptic plasticity and DA release in the VTA-NacLat circuit in MA-treated mice. Furthermore, overexpression of only Kv7.3 channels in the VTA-NacLat circuit was sufficient to attenuate MA-induced reward behavior and decrease VTA neuron excitability. Activation of Kv7 channels in the VTA may become a novel treatment strategy for MA abuse.

K v 7 Channel Opener Retigabine Reduces Self-Administration of Cocaine but Not Sucrose in Rats

The increasing rates of drug misuse highlight the urgency of identifying improved therapeutics for treatment. Most drug-seeking behaviors that can be modeled in rodents utilize the repeated intravenous self-administration (SA) of drugs. Recent studies examining the mesolimbic pathway suggest that K v 7/KCNQ channels may contribute in the transition from recreational to chronic drug use. However, to date, all such studies used noncontingent, experimenter-delivered drug model systems, and the extent to which this effect generalizes to rats trained to self-administer drug is not known. Here, we tested the ability of retigabine (ezogabine), a K v 7 channel opener, to regulate instrumental behavior in male Sprague Dawley rats. We first validated the ability of retigabine to target experimenter-delivered cocaine in a CPP assay and found that retigabine reduced the acquisition of place preference. Next, we trained rats for cocaine-SA under a fixed-ratio or progressive-ratio reinforcement schedule and found that retigabine-pretreatment attenuated the self-administration of low to moderate doses of cocaine. This was not observed in parallel experiments, with rats self-administering sucrose, a natural reward. Compared to sucrose-SA, cocaine-SA was associated with reductions in the expression of the K v 7.5 subunit in the nucleus accumbens, without alterations in K v 7.2 and K v 7.3. Therefore, these studies reveal a reward specific reduction in SA behavior considered relevant for the study of long-term compulsive-like behavior and supports the notion that K v 7 is a potential therapeutic target for human psychiatric diseases with dysfunctional reward circuitry.

The Role of Beta-Adrenergic Receptors in Depression and Resilience

Norepinephrine is a catecholamine neurotransmitter that has been extensively implicated in the neurobiology of major depressive disorder (MDD). An accumulating body of evidence indicates that investigations into the action of norepinephrine at the synaptic/receptor level hold high potential for a better understanding of MDD neuropathology and introduce possibilities for developing novel treatments for depression. In this review article, we discuss recent advances in depression neuropathology and the effects of antidepressant medications based on preclinical and clinical studies related to beta-adrenergic receptor subtypes. We also highlight a beta-3 adrenergic receptor-involved mechanism that promotes stress resilience, through which antidepressant efficacy is achieved in both rodent models for depression and patients with major depression-an alternative therapeutic strategy that is conceptually different from the typical therapeutic approach in which treatment efficacy is achieved by reversing pathological alterations rather than by enhancing a good mechanism such as natural resilience. Altogether, in this review, we systematically describe the role of beta-adrenergic receptors in depression and stress resilience and provide a new avenue for developing a conceptually innovative treatment for depression.

Repressor element 1-silencing transcription factor deficiency yields profound hearing loss through Kv7.4 channel upsurge in auditory neurons and hair cells

Repressor element 1-silencing transcription factor (REST) is a transcriptional repressor that recognizes neuron-restrictive silencer elements in the mammalian genomes in a tissue- and cell-specific manner. The identity of REST target genes and molecular details of how REST regulates them are emerging. We performed conditional null deletion of Rest (cKO), mainly restricted to murine hair cells (HCs) and auditory neurons (aka spiral ganglion neurons [SGNs]). Null inactivation of full-length REST did not affect the development of normal HCs and SGNs but manifested as progressive hearing loss in adult mice. We found that the inactivation of REST resulted in an increased abundance of K_v7.4 channels at the transcript, protein, and functional levels. Specifically, we found that SGNs and HCs from Rest cKO mice displayed increased K_v7.4 expression and augmented K_v7 currents; SGN’s excitability was also significantly reduced. Administration of a compound with K_v7.4 channel activator activity, fasudil, recapitulated progressive hearing loss in mice. In contrast, inhibition of the K_v7 channels by XE991 rescued the auditory phenotype of Rest cKO mice. Previous studies identified some loss-of-function mutations within the K_v7.4-coding gene, Kcnq4, as a causative factor for progressive hearing loss in mice and humans. Thus, the findings reveal that a critical homeostatic K_v7.4 channel level is required for proper auditory functions.

The Potential of KCNQ Potassium Channel Openers as Novel Antidepressants

Major depressive disorder (MDD) is a leading cause of disability worldwide and less than one-third of patients with MDD achieve stable remission of symptoms, despite currently available treatments. Although MDD represents a serious health problem, a complete understanding of the neurobiological mechanisms underlying this condition continues to be elusive. Accumulating evidence from preclinical and animal studies provides support for the antidepressant potential of modulators of KCNQ voltage-gated potassium (K⁺) channels. KCNQ K⁺ channels, through regulation of neuronal excitability and activity, contribute to neurophysiological mechanisms underlying stress resilience, and represent potential targets of drug discovery for depression. The present article focuses on the pharmacology and efficacy of KCNQ2/3 K⁺ channel openers as novel therapeutic agents for depressive disorders from initial studies conducted on animal models showing depressive-like behaviors to recent work in humans that examines the potential for KCNQ2/3 channel modulators as novel antidepressants. Data from preclinical work suggest that KCNQ-type K⁺ channels are an active mediator of stress resilience and KCNQ2/3 K⁺ channel openers show antidepressant efficacy. Similarly, evidence from clinical trials conducted in patients with MDD using the KCNQ2/3 channel opener ezogabine (retigabine) showed significant improvements in depressive symptoms and anhedonia. Overall, KCNQ channel openers appear a promising target for the development of novel therapeutics for the treatment of psychiatric disorders and specifically for MDD.

Ion Channel Dysfunction and Neuroinflammation in Migraine and Depression

Migraine and major depression are debilitating disorders with high lifetime prevalence rates. Interestingly these disorders are highly comorbid and show significant heritability, suggesting shared pathophysiological mechanisms. Non-homeostatic function of ion channels and neuroinflammation may be common mechanisms underlying both disorders: The excitation-inhibition balance of microcircuits and their modulation by monoaminergic systems, which depend on the expression and function of membrane located K⁺, Na⁺, and Ca⁺² channels, have been reported to be disturbed in both depression and migraine. Ion channels and energy supply to synapses not only change excitability of neurons but can also mediate the induction and maintenance of inflammatory signaling implicated in the pathophysiology of both disorders. In this respect, Pannexin-1 and P2X7 large-pore ion channel receptors can induce inflammasome formation that triggers release of pro-inflammatory mediators from the cell. Here, the role of ion channels involved in the regulation of excitation-inhibition balance, synaptic energy homeostasis as well as inflammatory signaling in migraine and depression will be reviewed.

Autism-associated mutations in KV7 channels induce gating pore current

Autism spectrum disorder (ASD) adversely impacts >1% of children in the United States, causing social interaction deficits, repetitive behaviors, and communication disorders. Genetic analysis of ASD has advanced dramatically through genome sequencing, which has identified >500 genes with mutations in ASD. Mutations that alter arginine gating charges in the voltage sensor of the voltage-gated potassium (K_V) channel K_V7 (KCNQ) are among those frequently associated with ASD. We hypothesized that these gating charge mutations would induce gating pore current (also termed ω-current) by causing an ionic leak through the mutant voltage sensor. Unexpectedly, we found that wild-type K_V7 conducts outward gating pore current through its native voltage sensor at positive membrane potentials, owing to a glutamine in the third gating charge position. In bacterial and human K_V7 channels, gating charge mutations at the R1 and R2 positions cause inward gating pore current through the resting voltage sensor at negative membrane potentials, whereas mutation at R4 causes outward gating pore current through the activated voltage sensor at positive potentials. Remarkably, expression of the K_V7.3/R2C ASD-associated mutation in vivo in midbrain dopamine neurons of mice disrupts action potential generation and repetitive firing. Overall, our results reveal native and mutant gating pore current in K_V7 channels and implicate altered control of action potential generation by gating pore current through mutant K_V7 channels as a potential pathogenic mechanism in autism.

Activation of parabrachial nucleus - ventral tegmental area pathway underlies the comorbid depression in chronic neuropathic pain in mice

Depression symptoms are often found in patients suffering from chronic pain, a phenomenon that is yet to be understood mechanistically. Here, we systematically investigate the cellular mechanisms and circuits underlying the chronic-pain-induced depression behavior. We show that the development of chronic pain is accompanied by depressive-like behaviors in a mouse model of trigeminal neuralgia. In parallel, we observe increased activity of the dopaminergic (DA) neuron in the midbrain ventral tegmental area (VTA), and inhibition of this elevated VTA DA neuron activity reverses the behavioral manifestations of depression. Further studies establish a pathway of glutamatergic projections from the spinal trigeminal subnucleus caudalis (Sp5C) to the lateral parabrachial nucleus (LPBN) and then to the VTA. These glutamatergic projections form a direct circuit that controls the development of the depression-like behavior under the state of the chronic neuropathic pain.

Physiology and Therapeutic Potential of SK, H, and M Medium AfterHyperPolarization Ion Channels

SK, HCN, and M channels are medium afterhyperpolarization (mAHP)-mediating ion channels. The three channels co-express in various brain regions, and their collective action strongly influences cellular excitability. However, significant diversity exists in the expression of channel isoforms in distinct brain regions and various subcellular compartments, which contributes to an equally diverse set of specific neuronal functions. The current review emphasizes the collective behavior of the three classes of mAHP channels and discusses how these channels function together although they play specialized roles. We discuss the biophysical properties of these channels, signaling pathways that influence the activity of the three mAHP channels, various chemical modulators that alter channel activity and their therapeutic potential in treating various neurological anomalies. Additionally, we discuss the role of mAHP channels in the pathophysiology of various neurological diseases and how their modulation can alleviate some of the symptoms.

Impact of the KCNQ2/3 Channel Opener Ezogabine on Reward Circuit Activity and Clinical Symptoms in Depression: Results From a Randomized Controlled Trial

OBJECTIVE

Preclinical studies point to the KCNQ2/3 potassium channel as a novel target for the treatment of depression and anhedonia, a reduced ability to experience pleasure. The authors conducted the first randomized placebo-controlled trial testing the effect of the KCNQ2/3 positive modulator ezogabine on reward circuit activity and clinical outcomes in patients with depression.

METHODS

Depressed individuals (N=45) with elevated levels of anhedonia were assigned to a 5-week treatment period with ezogabine (900 mg/day; N=21) or placebo (N=24). Participants underwent functional MRI during a reward flanker task at baseline and following treatment. Clinical measures of depression and anhedonia were collected at weekly visits. The primary endpoint was the change from baseline to week 5 in ventral striatum activation during reward anticipation. Secondary endpoints included depression and anhedonia severity as measured using the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Snaith-Hamilton Pleasure Scale (SHAPS), respectively.

RESULTS

The study did not meet its primary neuroimaging endpoint. Participants in the ezogabine group showed a numerical increase in ventral striatum response to reward anticipation following treatment compared with participants in the placebo group from baseline to week 5. Compared with placebo, ezogabine was associated with a significantly larger improvement in MADRS and SHAPS scores and other clinical endpoints. Ezogabine was well tolerated, and no serious adverse events occurred.

CONCLUSIONS

The study did not meet its primary neuroimaging endpoint, although the effect of treatment was significant on several secondary clinical endpoints. In aggregate, the findings may suggest that future studies of the KCNQ2/3 channel as a novel treatment target for depression and anhedonia are warranted.

Brain circuit dysfunction in specific symptoms of depression

Since the depressive disorder manifests complex and diverse symptoms clinically, its pathological mechanism and therapeutic options are difficult to determine. In recent years, the advent of optogenetics, chemogenetics and viral tracing techniques, along with the well-established rodent model of depression, has led to a shift in the focus of depression research from single molecules to neural circuits. In virtue of the powerful tools above, psychiatric disorder such as depression could be well related to the disfunction of brain's connection. Moreover, compelling studies also support that the diversity of depressive behaviour could be involved with the discrete changes in a distinct circuit of the brain. Therefore, summarising the differential changes of the neural circuits in mice with depression-like behaviour may provide a better understanding of the causal relationships between neural circuit and depressive behaviour. Here, we focus on the changes in the neural circuitry underlying various depression-like phenotypes, including motivation, despair, social avoidance and comorbid sequelae, which may provide an explanation to circuit-specific discrepancy in depression-like behaviour.

Absorption, tissue disposition, and excretion of fasudil hydrochloride, a RHO kinase inhibitor, in rats and dogs

Fasudil hydrochloride as an intracellular calcium ion antagonist that dilates blood vessels has exhibited a very potent pharmacological effect in the treatment of angina pectoris. The purpose of this study was to determine the absorption, distribution, and excretion profiles of fasudil in rats and beagle dogs, respectively, to clarify its pharmacokinetic pattern. A sensitive and reliable LC-MS/MS method has been developed and established and successfully applied to pharmacokinetic study, including absorption, tissue distribution, and excretion. The results revealed that in the range of 2-6 mg/kg, the pharmacokinetic behavior for instance, AUC and C_max , in rats was observed in a dose dependent manner. However, the plasma concentrations were indicative of a significant gender difference in the pharmacokinetics of fasudil in rats, in terms of absolute bioavailability and excretion. Interestingly, the resulting data obtained from beagle dogs showed that there was no gender difference in the absolute bioavailability of fasudil hydrochloride after single or repeated administrations. In conclusion, this study characterized the pharmacokinetic pattern fasudil both in rats and beagle dogs through absorption, tissue distribution and excretion study. The findings may be valuable and provide a rationale for further study and its safe use in clinical practice.

Kv7 Channels and Excitability Disorders

Kv7.1-Kv7.5 (KCNQ1-5) K⁺ channels are voltage-gated K⁺ channels with major roles in neurons, muscle cells and epithelia where they underlie physiologically important K⁺ currents, such as neuronal M current and cardiac I_Ks. Specific biophysical properties of Kv7 channels make them particularly well placed to control the activity of excitable cells. Indeed, these channels often work as 'excitability breaks' and are targeted by various hormones and modulators to regulate cellular activity outputs. Genetic deficiencies in all five KCNQ genes result in human excitability disorders, including epilepsy, arrhythmias, deafness and some others. Not surprisingly, this channel family attracts considerable attention as potential drug targets. Here we will review biophysical properties and tissue expression profile of Kv7 channels, discuss recent advances in the understanding of their structure as well as their role in various neurological, cardiovascular and other diseases and pathologies. We will also consider a scope for therapeutic targeting of Kv7 channels for treatment of the above health conditions.

In vitro and in vivo characterization of Lu AA41178: A novel, brain penetrant, pan-selective Kv7 potassium channel opener with efficacy in preclinical models of epileptic seizures and psychiatric disorders

Activation of the voltage-gated Kv7 channels holds therapeutic promise in several neurological and psychiatric disorders, including epilepsy, schizophrenia, and depression. Here, we present a pharmacological characterization of Lu AA41178, a novel, pan-selective Kv7.2-7.5 opener, using both in vitro assays and a broad range of in vivo assays with relevance to epilepsy, schizophrenia, and depression. Electrophysiological characterization in Xenopus oocytes expressing human Kv7.2-Kv7.5 confirmed Lu AA41178 as a pan-selective opener of Kv7 channels by significantly left-shifting the activation threshold. Additionally, Lu AA41178 was tested in vitro for off-target effects, demonstrating a clean Kv7-selective profile, with no impact on common cardiac ion channels, and no potentiating activity on GABAA channels. Lu AA41178 was evaluated across preclinical in vivo assays with relevance to neurological and psychiatric disorders. In the maximum electroshock seizure threshold test and PTZ seizure threshold test, Lu AA41178 significantly increased the seizure thresholds in mice, demonstrating anticonvulsant efficacy. Lu AA41178 demonstrated antipsychotic-like activity by reducing amphetamine-induced hyperlocomotion in mice as well as lowering conditioned avoidance responses in rats. In the mouse forced swim test, a model with antidepressant predictivity, Lu AA41178 significantly reduced immobility. Additionally, behavioral effects typically observed with Kv7 openers was also characterized. In vivo assays were accompanied by plasma and brain exposures, revealing minimum effective plasma levels <1000 ng/ml. Lu AA41178, a potent opener of neuronal Kv7 channels demonstrate efficacy in assays of epilepsy, schizophrenia and depression and might serve as a valuable tool for exploring the role of Kv7 channels in both neurological and psychiatric disorders.

Pharmacological Manipulation of K v 7 Channels as a New Therapeutic Tool for Multiple Brain Disorders

K _v 7 ("M-type," KCNQ) K⁺ currents, play dominant roles in controlling neuronal excitability. They act as a "brake" against hyperexcitable states in the central and peripheral nervous systems. Pharmacological augmentation of M current has been developed for controlling epileptic seizures, although current pharmacological tools are uneven in practical usefulness. Lately, however, M-current "opener" compounds have been suggested to be efficacious in preventing brain damage after multiple types of insults/diseases, such as stroke, traumatic brain injury, drug addiction and mood disorders. In this review, we will discuss what is known to date on these efforts and identify gaps in our knowledge regarding the link between M current and therapeutic potential for these disorders. We will outline the preclinical experiments that are yet to be performed to demonstrate the likelihood of success of this approach in human trials. Finally, we also address multiple pharmacological tools available to manipulate different K _v 7 subunits and the relevant evidence for translational application in the clinical use for disorders of the central nervous system and multiple types of brain insults. We feel there to be great potential for manipulation of K _v 7 channels as a novel therapeutic mode of intervention in the clinic, and that the paucity of existing therapies obligates us to perform further research, so that patients can soon benefit from such therapeutic approaches.

Kv7.4 Channel Contribute to Projection-Specific Auto-Inhibition of Dopamine Neurons in the Ventral Tegmental Area

Dopaminergic neurons in the ventral tegmental area (VTA) encode behavioral patterns important in reward and drug addiction as well as in emotional disorders. These functions of dopamine neurons are directly related to the release of dopamine in the targeted regions of the brain which are, thus, controlled by the excitability of dopamine neurons. One mechanism for modulation of dopamine neuronal excitability is mediated by the auto dopamine type 2 (D2) receptors, through activation of a Kir3/GIRK K⁺ channel which inhibits the firing of dopamine neurons. In this study, we provide evidence that Kv7.4, in addition to Kir3.2 channels, contributes to dopamine (DA)-mediated auto-inhibition of DA activity projecting to NAc and to basolateral amygdale (BLA). Furthermore, we demonstrate that D2 receptors enhance Kv7.4 currents through G_i/o protein and redox-dependent cellular pathway. Finally, we show this D2 mediated auto-inhibition is blunted in a social defeat mice model of depression, a phenomenon that may contribute to the altered excitability of VTA DA neurons in depressed animals. These results provide a new perspective for understanding the molecular mechanism of the excitability of VTA DA neurons and for potential new strategies against mental disorders involving altered excitability of DA neurons, such as major depression and drug addictions.

The molecular and cellular mechanisms of depression: a focus on reward circuitry

Depression is a complex disorder that takes an enormous toll on individual health. As affected individuals display a wide variation in their clinical symptoms, the precise neural mechanisms underlying the development of depression remain elusive. Although it is impossible to phenocopy every symptom of human depression in rodents, the preclinical field has had great success in modeling some of the core affective and neurovegetative depressive symptoms, including social withdrawal, anhedonia, and weight loss. Adaptations in select cell populations may underlie these individual depressive symptoms and new tools have expanded our ability to monitor and manipulate specific cell types. This review outlines some of the most recent preclinical discoveries on the molecular and neurophysiological mechanisms in reward circuitry that underlie the expression of behavioral constructs relevant to depressive symptoms.

How to replace the lost keys? Strategies toward safer KV7 channel openers

The highly structurally similar drugs flupirtine and retigabine have been regarded as safe and effective for many years but lately they turned out to exert intolerable side effects. While the twin molecules share the mode of action, both stabilize the open state of voltage-gated potassium channels, the form and severity of adverse effects is different. The analgesic flupirtine caused drug-induced liver injury in rare but fatal cases, whereas prolonged use of the antiepileptic retigabine led to blue tissue discoloration. Because the adverse effects seem unrelated to the mode of action, it is likely, that both drugs that occupied important therapeutic niches, could be replaced. Reasons for the clinically relevant toxicity will be clarified and future substitutes for these drugs presented in this review.

Selective Modulation of K+ Channel Kv7.4 Significantly Affects the Excitability of DRN 5-HT Neurons

The serotonin (5-HT) system originating in the dorsal raphe nucleus (DRN) is implicated in various mood- and emotion-related disorders, such as anxiety, fear and stress. Abnormal activity of DRN 5-HT neurons is the key factor in the development of these disorders. Here, we describe a crucial role for the Kv7.4 potassium channel in modulating DRN 5-HT neuronal excitability. We demonstrate that Kv7.4 is selectively expressed in 5-HT neurons of the DRN. Using selective Kv7.4 opener fasudil and Kv7.4 knock-out mice, we demonstrate that Kv7.4 is a potent modulator of DRN 5-HT neuronal excitability. Furthermore, we demonstrate that the cellular redox signaling mechanism is involved in this 5-HT activation of Kv7.4. The current study suggests a new strategy for treating psychiatric disorders related to altered activity of DRN 5-HT neurons using K⁺ channel modulators.

Selective targeting of M-type potassium Kv 7.4 channels demonstrates their key role in the regulation of dopaminergic neuronal excitability and depression-like behaviour

BACKGROUND AND PURPOSE

The mesolimbic dopamine system originating in the ventral tegmental area (VTA) is involved in the development of depression, and firing patterns of VTA dopaminergic neurons are key determinants in this process. Here, we describe a crucial role for the M-type K_v 7.4 channels in modulating excitability of VTA dopaminergic neurons and in the development of depressive behaviour in mice.

EXPERIMENTAL APPROACH

We used K_v 7.4 channel knockout mice and a social defeat model of depression in combination with electrophysiological techniques (patch clamp recording and in vivo single-unit recordings), immunohistochemistry, single-cell PCR and behavioural analyses (social interaction time and glucose preference tests) to investigate VTA circuits involved in the development of depression-like behaviour.

KEY RESULTS

Among the K_v 7 channels, K_v 7.4 channels are selectively expressed in dopaminergic neurons of the VTA. Using a newly identified selective K_v 7.4 channel activator, fasudil, and K_v 7.4 channel knockout mice, we demonstrate that these channels are a dominant modulator of excitability of VTA dopaminergic neurons, in vitro and in vivo. Down-regulation of K_v 7.4 channels could be a causal factor of the altered excitability of VTA dopaminergic neurons and depression-like behaviour. The selective K_v 7.4 channel activator, fasudil, strongly alleviated depression-like behaviour in the social defeat mouse model of depression.

CONCLUSION AND IMPLICATIONS

Because expression of K_v 7.4 channels in the CNS is limited, selectively targeting this M channel subunit is likely to produce less on-target side effects than non-selective M channel modulators. Thus, K_v 7.4 channels may offer alternative targets in treatment of depression.