5-HT2A receptor activation normalizes stress-induced dysregulation of GABAergic signaling in the ventral tegmental area

Midbrain KCC2 downregulation: Implications for stress-related and substance use behaviors

Stress-related and substance use disorders are both characterized by disruptions in reward-related behaviors, and these disorders are often comorbid with one another. Recent investigations have identified a novel mechanism of inhibitory plasticity induced by both stress and substance use within the ventral tegmental area (VTA), a key region in reward processing. This mechanism involves the neuron-specific potassium chloride cotransporter isoform 2 (KCC2), which is essential in modulating inhibitory signaling through the regulation of intracellular chloride (Cl-) in VTA GABA neurons. Experiences, such as exposure to stress or substance use, diminish KCC2 expression in VTA GABA neurons, leading to abnormal reward-related behaviors. Here, we review literature suggesting that KCC2 downregulation contributes to irregular dopamine (DA) transmission, impacting multiple reward circuits and promoting maladaptive behaviors. Activating KCC2 restores canonical GABA functioning and reduces behavioral deficits in preclinical models, leading us to advocate for KCC2 as a target for therapies aimed at alleviating and mitigating various stress-related and substance use disorders.

Alcohol exacerbates psychosocial stress-induced neuropsychiatric symptoms: Attenuation by geraniol

Adaptation to psychosocial stress is psychologically distressing, initiating/promoting comorbidity with alcohol use disorders. Emerging evidence moreover showed that ethanol (EtOH) exacerbates social-defeat stress (SDS)-induced behavioral impairments, neurobiological sequelae, and poor therapeutic outcomes. Hence, this study investigated the effects of geraniol, an isoprenoid monoterpenoid alcohol with neuroprotective functions on EtOH escalated SDS-induced behavioral impairments, and neurobiological sequelae in mice. Male mice chronically exposed to SDS for 14 days were repeatedly fed with EtOH (2 g/kg, p. o.) from days 8-14. From days 1-14, SDS-EtOH co-exposed mice were concurrently treated with geraniol (25 and 50 mg/kg) or fluoxetine (10 mg/kg) orally. After SDS-EtOH translational interactions, arrays of behavioral tasks were examined, followed by investigations of oxido-inflammatory, neurochemicals levels, monoamine oxidase-B and acetylcholinesterase activities in the striatum, prefrontal-cortex, and hippocampus. The glial fibrillary acid protein (GFAP) expression was also quantified in the prefrontal-cortex immunohistochemically. Adrenal weights, serum glucose and corticosterone concentrations were measured. EtOH exacerbated SDS-induced low-stress resilience, social impairment characterized by anxiety, depression, and memory deficits were attenuated by geraniol (50 and 100 mg/kg) and fluoxetine. In line with this, geraniol increased the levels of dopamine, serotonin, and glutamic-acid decarboxylase enzyme, accompanied by reduced monoamine oxidase-B and acetylcholinesterase activities in the prefrontal-cortex, hippocampus, and striatum. Geraniol inhibited SDS-EtOH-induced adrenal hypertrophy, corticosterone, TNF-α, IL-6 release, malondialdehyde and nitrite levels, with increased antioxidant activities. Immunohistochemical analyses revealed that geraniol enhanced GFAP immunoreactivity in the prefrontal-cortex relative to SDS-EtOH group. We concluded that geraniol ameliorates SDS-EtOH interaction-induced behavioral changes via normalization of neuroimmune-endocrine and neurochemical dysregulations in mice brains.

Early establishment of chloride homeostasis in CRH neurons is altered by prenatal stress leading to fetal HPA axis dysregulation

Corticotropin-releasing hormone (CRH) neurons play an important role in the regulation of neuroendocrine responses to stress. The excitability of CRH neurons is regulated by inhibitory GABAergic inputs. However, it is unclear when GABAergic regulation of CRH neurons is established during fetal brain development. Furthermore, the exact progression of the developmental shift of GABA action from depolarization to hyperpolarization remains unelucidated. Considering the importance of CRH neuron function in subsequent hypothalamic-pituitary-adrenal (HPA) axis regulation during this critical phase of development, we investigated the ontogeny of GABAergic inputs to CRH neurons and consequent development of chloride homeostasis. Both CRH neuron soma in the paraventricular nucleus (PVN) and axons projecting to the median eminence could be identified at embryonic day 15 (E15). Using acute slices containing the PVN of CRF-VenusΔNeo mice, gramicidin perforated-patch clamp-recordings of CRH neurons at E15, postnatal day 0 (P0), and P7 were performed to evaluate the developmental shift of GABA action. The equilibrium potential of GABA (EGABA) was similar between E15 and P0 and showed a further hyperpolarizing shift between P0 and P7 that was comparable to EGABA values in adult CRH neurons. GABA primarily acted as an inhibitory signal at E15 and KCC2 expression was detected in CRH neurons at this age. Activation of the HPA axis has been proposed as the primary mechanism through which prenatal maternal stress shapes fetal development and subsequent long-term disease risk. We therefore examined the impact of maternal food restriction stress on the development of chloride homeostasis in CRH neurons. We observed a depolarization shift of EGABA in CRH neurons of pups exposed to maternal food restriction stress. These results suggest that Cl- homeostasis in early developmental CRH neurons attains mature intracellular Cl- levels, GABA acts primarily as inhibitory, and CRH neurons mature and function early compared with neurons in other brain regions, such as the cortex and hippocampus. Maternal food restriction stress alters chloride homeostasis in CRH neurons of pups, reducing their inhibitory control by GABA. This may contribute to increased CRH neuron activity and cause activation of the HPA axis in pups.

A paradoxical switch: the implications of excitatory GABAergic signaling in neurological disorders

Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. In the mature brain, inhibitory GABAergic signaling is critical in maintaining neuronal homeostasis and vital human behaviors such as cognition, emotion, and motivation. While classically known to inhibit neuronal function under physiological conditions, previous research indicates a paradoxical switch from inhibitory to excitatory GABAergic signaling that is implicated in several neurological disorders. Various mechanisms have been proposed to contribute to the excitatory switch such as chloride ion dyshomeostasis, alterations in inhibitory receptor expression, and modifications in GABAergic synaptic plasticity. Of note, the hypothesized mechanisms underlying excitatory GABAergic signaling are highlighted in a number of neurodevelopmental, substance use, stress, and neurodegenerative disorders. Herein, we present an updated review discussing the presence of excitatory GABAergic signaling in various neurological disorders, and their potential contributions towards disease pathology.

Geraniol attenuates behavioral and neurochemical impairments by inhibitions of HPA-axis and oxido-inflammatory perturbations in mice exposed to post-traumatic stress disorder

Geraniol is an acyclic isoprenoid monoterpenoid analogue that has been shown to elicit neuroprotective functions, primarily through its ability to stimulate antioxidant and anti-inflammatory systems. An increase in inflammatory cytokines and oxidative stress exacerbate activation hypothalamic-pituitary-adrenal axis (HPA), leading to neurochemical dysfunction, which has important roles in the pathogenesis of post-traumatic disorder (PTSD), a mental health disorder characterized of post-trauma-induced intense fear. The aim of this study was to evaluate the anti-PTSD-like effects and underlying mechanisms of geraniol against single-prolonged-stress (SPS)-induced PTSD in mice. Following concomitant exposure to SPS (triple-paradigm traumatic events) and isolation for 7 days, mice (n = 9) were treated with geraniol (50 and 100 mg/kg, p.o.) or fluoxetine (10 mg/kg, p.o.) from days 8-21. Mice were assessed for behavioral changes. Neurochemical changes, inflammatory, oxido-nitrergic markers, adrenal weight, serum glucose and corticosterone concentrations were assayed. Geraniol inhibits SPS-induced anxiety- and depressive-like features as well as behavioral despair in the depression paradigms. SPS-induced locomotor and memory impairments were also abated by geraniol treatment similarly to fluoxetine. SPS-induced adrenal hypertrophy and increased blood glucose and corticosterone concentrations, were attenuated by the geraniol treatment. Elevated levels of TNF-α and IL-6, and malondialdehyde, nitrite, acetylcholinesterase enzyme were reduced by geraniol. Geraniol also increased glutathione, superoxide-dismutase, and catalase levels as well as dopamine, serotonin concentrations and GABAergic glutamic acid decarboxylase enzyme activity in the striatum, prefrontal cortex and hippocampus in the PTSD-mice relative to SPS control. In conclusion, geraniol attenuates behavioral impairments and neurochemical dysregulations by inhibitions of HPA-axis and oxido-inflammatory perturbations in mice exposed to PTSD.

Exploring the Role of Drug Repurposing in Bridging the Hypoxia-Depression Connection

High levels of oxidative stress are implicated in hypoxia, a physiological response to low levels of oxygen. Evidence supports a connection between this response and depression. Previous studies indicate that tryptophan hydroxylase can be negatively affected in hypoxia, impairing serotonin synthesis and downstream pathways. Some studies also hypothesize that increasing hypoxia-inducible factor-1 (HIF-1) levels may be a new therapeutic modality for depression. Hence, this study delved into the influence of hypoxia on the cellular response to drugs designed to act in depression. By the induction of hypoxia in SH-SY5Y cells through a hypoxia incubator chamber or Cobalt Chloride treatment, the effect of Mirtazapine, an antidepressant, and other drugs that interact with serotonin receptors (TCB-2, Dextromethorphan, Ketamine, Quetiapine, Scopolamine, Celecoxib, and Lamotrigine) on SH-SY5Y cellular viability and morphology was explored. The selection of drugs was initially conducted by literature search, focusing on compounds with established potential for employment in depression therapy. Subsequently, we employed in silico approaches to forecast their ability to traverse the blood-brain barrier (BBB). This step was particularly pertinent as we aimed to assess their viability for inducing potential antidepressant effects. The effect of these drugs in hypoxia under the inhibition of HIF-1 by Echinomycin was also tested. Our results revealed that all the potential repurposed drugs promoted cell viability, especially when hypoxia was chemically induced. When combined with Echinomycin, all drugs decreased cellular viability, possibly by the inability to interact with HIF-1.

Sex differences in VTA GABA transmission and plasticity during opioid withdrawal

The effectiveness of current treatments for opioid use disorder (OUD) varies by sex. Our understanding of the neurobiological mechanisms mediating negative states during withdrawal is lacking, particularly with regard to sex differences. Based on preclinical research in male subjects, opioid withdrawal is accompanied by increased gamma-aminobutyric acid (GABA) release probability at synapses onto dopamine neurons in the ventral tegmental area (VTA). It is unclear, however, if the physiological consequences of morphine that were originally elucidated in male rodents extend to females. The effects of morphine on the induction of future synaptic plasticity are also unknown. Here, we show that inhibitory synaptic long-term potentiation (LTP_GABA) is occluded in the VTA in male mice after repeated morphine injections and 1 day of withdrawal, while morphine-treated female mice maintain the ability to evoke LTP_GABA and have basal GABA activity similar to controls. Our observation of this physiological difference between male and female mice connects previous reports of sex differences in areas upstream and downstream of the GABA-dopamine synapse in the VTA during opioid withdrawal. The sex differences highlight the mechanistic distinctions between males and females that can be targeted when designing and implementing treatments for OUD.

Ketamine and serotonergic psychedelics: An update on the mechanisms and biosignatures underlying rapid-acting antidepressant treatment

The discovery of ketamine as a rapid-acting antidepressant spurred significant research to understand its underlying mechanisms of action and to identify other novel compounds that may act similarly. Serotonergic psychedelics (SPs) have shown initial promise in treating depression, though the challenge of conducting randomized controlled trials with SPs and the necessity of long-term clinical observation are important limitations. This review summarizes the similarities and differences between the psychoactive effects associated with both ketamine and SPs and the mechanisms of action of these compounds, with a focus on the monoaminergic, glutamatergic, gamma-aminobutyric acid (GABA)-ergic, opioid, and inflammatory systems. Both molecular and neuroimaging aspects are considered. While their main mechanisms of action differ-SPs increase serotonergic signaling while ketamine is a glutamatergic modulator-evidence suggests that the downstream mechanisms of action of both ketamine and SPs include mechanistic target of rapamycin complex 1 (mTORC1) signaling and downstream GABAA receptor activity. The similarities in downstream mechanisms may explain why ketamine, and potentially SPs, exert rapid-acting antidepressant effects. However, research on SPs is still in its infancy compared to the ongoing research that has been conducted with ketamine. For both therapeutics, issues with regulation and proper controls should be addressed before more widespread implementation. This article is part of the Special Issue on "Ketamine and its Metabolites".

Role of KCC2 in the Regulation of Brain-Derived Neurotrophic Factor on Ethanol Consumption in Rats

Alcohol use disorder (AUD) is a common and complex disorder resulting from repetitive alcohol drinking. The mesocorticolimbic dopamine (DA) system, originating from the ventral tegmental area (VTA) in the midbrain, is involved in the rewarding effect of ethanol. The γ-aminobutyric acid (GABA) neurons in VTA appear to be key substrates of acute and chronic ethanol, which regulates DA neurotransmission indirectly in the mesocorticolimbic system. Despite significant research on the relationship between brain-derived neurotrophic factor (BDNF) and reduced alcohol consumption in male rats involving tropomyosin-related kinase B (TrkB), the mechanisms of BDNF-TrkB regulating alcohol behavior remain scarce. K⁺-Cl^- cotransporter 2 (KCC2) plays a crucial role in synaptic function in GABAergic neurons by modulating intracellular chlorine homeostasis. Here, we found that 4-week intermittent alcohol exposure impaired the function of KCC2 in VTA, evidenced by a lower expression level of phosphorylated KCC2 and decreased ratio of phosphorylated KCC2 to total KCC2, especially 72 h after withdrawal from 4-week ethanol exposure in male rats. CLP290 (a KCC2 activator) reduced excessive alcohol consumption after alcohol withdrawal, whereas VU0240551 (a specific KCC2 inhibitor) further enhanced alcohol intake. Importantly, VU0240551 reversed the attenuating effects of BDNF and 7,8-dihydroxyflavone (7,8-DHF) on alcohol consumption after withdrawal. Moreover, intraperitoneal injection of 7,8-DHF upregulated KCC2 expression and phosphorylated KCC2 in VTA 72 h after withdrawal from ethanol exposure in male rats. Collectively, our data indicate that KCC2 may be critical in the regulating action of BDNF-TrkB on ethanol consumption in AUD.

Habenula as a Possible Target for Treatment-Resistant Depression Phenotype in Wistar Kyoto Rats

The mechanisms of treatment-resistant depression (TRD) are not clear and are difficult to study. An animal model resembling human TRD is the Wistar Kyoto rat strain. In the present study, we focused on selecting miRNAs that differentiate rats of the WKY strain from Wistar Han (WIS) rats in two divisions of the habenula, the lateral and medial (LHb and MHb, respectively). Based on our preliminary study and literature survey, we identified 32 miRNAs that could be potentially regulated in the habenula. Six miRNAs significantly differentiated WKY rats from WIS rats within the MHb, and three significantly differentiated WKY from WIS rats within the LHb. Then, we selected relevant transcripts regulated by those miRNAs, and their expression in the habenular nuclei was investigated. For mRNAs that differentiated WKY rats from WIS rats in the MHb (Cdkn1c, Htr7, Kcnj9, and Slc12a5), their lower expression correlated with a higher level of relevant miRNAs. In the LHb, eight mRNAs significantly differentiated WKY from WIS rats (upregulated Htr4, Drd2, Kcnj5, and Sstr4 and downregulated Htr2a, Htr7, Elk4, and Slc12a5). These data indicate that several important miRNAs are expressed in the habenula, which differentiates WKY rats from WIS rats and in turn correlates with alterations in the expression of target transcripts. Of particular note are two genes whose expression is altered in WKY rats in both LHb and MHb: Slc12a5 and Htr7. Regulation of KCC2 via the 5-HT7 receptor may be a potential target for the treatment of TRD.

Classic psychedelics and alcohol use disorders: A systematic review of human and animal studies

Classic psychedelics refer to substances such as lysergic acid diethylamide (LSD), psilocybin, ayahuasca, and mescaline, which induce altered states of consciousness by acting mainly on 5-HT2A receptors. Recently, the interest of psychedelics as pharmacological treatment for psychiatric disorders has increased significantly, including their use on problematic use of alcohol. This systematic review is aimed to analyse the last two decades of studies examining the relationship between classic psychedelics and alcohol consumption. We searched PubMed and PsycInfo for human and preclinical studies published between January 2000 to December 2021. The search identified 639 publications. After selection, 27 studies were included. Human studies (n = 20) generally show promising data and seem to indicate that classic psychedelics could help reduce alcohol consumption. Nevertheless, some of these studies present methodological concerns such as low number of participants, lack of control group or difficulty in determining the effect of classic psychedelics in isolation. On the other hand, preclinical studies (n = 7) investigating the effect of these compounds on voluntary alcohol consumption are scarce and show some conflicting data. Among these compounds, psilocybin seems to show the most consistent data indicating that this compound could be a potential candidate to treat alcohol use disorders. In the absence of understanding the biological and/or psychological mechanisms, more studies including methodological quality parameters are needed to finally determine the effects of classic psychedelics on alcohol consumption.

Stressed and wired: The effects of stress on the VTA circuits underlying motivated behavior

Stress affects many brain regions, including the ventral tegmental area (VTA), which is critically involved in reward processing. Excessive stress can reduce reward-seeking behaviors but also exacerbate substance use disorders, two seemingly contradictory outcomes. Recent research has revealed that the VTA is a heterogenous structure with diverse populations of efferents and afferents serving different functions. Stress has correspondingly diverse effects on VTA neuron activity, tending to decrease lateral VTA dopamine (DA) neuron activity, while increasing medial VTA DA and GABA neuron activity. Here we review the differential effects of stress on the activity of these distinct VTA neuron populations and how they contribute to decreases in reward-seeking behavior or increases in drug self-administration.

Role of 5-HT2A receptor in modulating glutamatergic activity in the ventrolateral orbital cortex: implication in trigeminal neuralgia

5-HT_2A receptors (5-HT_2ARs) are widely expressed in the central nervous system, including in the ventrolateral orbital cortex (VLO). The VLO is an important cortical component for pain processing. Brain 5-HT_2ARs are implicated in both pro- and anti- nociceptive functions. However, the roles of 5-HT_2ARs in the VLO in trigeminal neuralgia and neuronal synaptic function remain to be understood. We used chronic constriction injury of infraorbital nerve (IoN-CCI) model and shRNA mediated gene knockdown in mice to investigate the role of 5-HT_2ARs in the VLO in trigeminal neuralgia. We found that knockdown of 5-HT_2ARs in the VLO aggravated spontaneous pain and mechanical allodynia in mice after IoN-CCI. At the synaptic level, decreasing 5-HT_2AR expression by shRNA or inhibition of 5-HT_2AR activity by its antagonist ketanserin decreased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) of the neurons in the VLO, whereas 5-HT_2AR partial agonist 2,5-Dimethoxy-4-iodoamphetamine (DOI) enhanced sEPSCs of the neurons in the VLO. In summary, 5-HT_2ARs in the VLO modulate the trigeminal pain by regulating neuronal glutamatergic activity.

Molecular Mechanisms of Epilepsy: The Role of the Chloride Transporter KCC2

Epilepsy is a neurological disease characterized by abnormal or synchronous brain activity causing seizures, which may produce convulsions, minor physical signs, or a combination of symptoms. These disorders affect approximately 65 million people worldwide, from all ages and genders. Seizures apart, epileptic patients present a high risk to develop neuropsychological comorbidities such as cognitive deficits, emotional disturbance, and psychiatric disorders, which severely impair quality of life. Currently, the treatment for epilepsy includes the administration of drugs or surgery, but about 30% of the patients treated with antiepileptic drugs develop time-dependent pharmacoresistence. Therefore, further investigation about epilepsy and its causes is needed to find new pharmacological targets and innovative therapeutic strategies. Pharmacoresistance is associated to changes in neuronal plasticity and alterations of GABA_A receptor-mediated neurotransmission. The downregulation of GABA inhibitory activity may arise from a positive shift in GABA_A receptor reversal potential, due to an alteration in chloride homeostasis. In this paper, we review the contribution of K⁺-Cl^--cotransporter (KCC2) to the alterations in the Cl^- gradient observed in epileptic condition, and how these alterations are coupled to the increase in the excitability.

The serotonin 2A receptor agonist TCB-2 attenuates heavy alcohol drinking and alcohol-induced midbrain inhibitory plasticity

Disruption of neuronal chloride ion (Cl^- ) homeostasis has been linked to several pathological conditions, including substance use disorder, yet targeted pharmacotherapies are lacking. In this study, we explored the potential of serotonin 2A receptor (5-HT_2A R) agonism to reduce alcohol consumption in male wild-type C57Bl/6J mice and to ameliorate alcohol-induced inhibitory plasticity in the midbrain. We found that administration of the putative 5-HT_2A R agonist TCB-2 attenuated alcohol consumption and preference but did not alter water or saccharin consumption. We hypothesized that the selective behavioural effects of TCB-2 on alcohol drinking were due, at least in part, to effects of the agonist on ventral tegmental area (VTA) neurocircuitry. Alcohol consumption impairs Cl^- transport in VTA GABA neurons, which acts as a molecular adaptation leading to increased alcohol self-administration. Using ex vivo electrophysiological recordings, we found that exposure to either intermittent volitional alcohol drinking or an acute alcohol injection diminished homeostatic Cl^- transport in VTA GABA neurons. Critically, in vivo TCB-2 administration normalized Cl^- transport in the VTA after alcohol exposure. Thus, we show a potent effect of alcohol consumption on VTA inhibitory circuitry, in the form of dysregulated Cl^- homeostasis that is reversible with agonism of 5-HT_2A Rs. Our results provide insight into the potential therapeutic action of 5-HT_2A R agonists for alcohol abuse.

Role of Descending Serotonergic Fibers in the Development of Pathophysiology after Spinal Cord Injury (SCI): Contribution to Chronic Pain, Spasticity, and Autonomic Dysreflexia

As the nervous system develops, nerve fibers from the brain form descending tracts that regulate the execution of motor behavior within the spinal cord, incoming sensory signals, and capacity to change (plasticity). How these fibers affect function depends upon the transmitter released, the receptor system engaged, and the pattern of neural innervation. The current review focuses upon the neurotransmitter serotonin (5-HT) and its capacity to dampen (inhibit) neural excitation. A brief review of key anatomical details, receptor types, and pharmacology is provided. The paper then considers how damage to descending serotonergic fibers contributes to pathophysiology after spinal cord injury (SCI). The loss of serotonergic fibers removes an inhibitory brake that enables plasticity and neural excitation. In this state, noxious stimulation can induce a form of over-excitation that sensitizes pain (nociceptive) circuits, a modification that can contribute to the development of chronic pain. Over time, the loss of serotonergic fibers allows prolonged motor drive (spasticity) to develop and removes a regulatory brake on autonomic function, which enables bouts of unregulated sympathetic activity (autonomic dysreflexia). Recent research has shown that the loss of descending serotonergic activity is accompanied by a shift in how the neurotransmitter GABA affects neural activity, reducing its inhibitory effect. Treatments that target the loss of inhibition could have therapeutic benefit.

The Multifaceted Roles of KCC2 in Cortical Development

KCC2, best known as the neuron-specific chloride-extruder that sets the strength and polarity of GABAergic currents during neuronal maturation, is a multifunctional molecule that can regulate cytoskeletal dynamics via its C-terminal domain (CTD). We describe the molecular and cellular mechanisms involved in the multiple functions of KCC2 and its splice variants, ranging from developmental apoptosis and the control of early network events to the formation and plasticity of cortical dendritic spines. The versatility of KCC2 actions at the cellular and subcellular levels is also evident in mature neurons during plasticity, disease, and aging. Thus, KCC2 has emerged as one of the most important molecules that shape the overall neuronal phenotype.

Preclinical insights into therapeutic targeting of KCC2 for disorders of neuronal hyperexcitability

INTRODUCTION

Epilepsy is a common neurological disorder of neuronal hyperexcitability that begets recurrent and unprovoked seizures. The lack of a truly satisfactory pharmacotherapy for epilepsy highlights the clinical urgency for the discovery of new drug targets. To that end, targeting the electroneutral K⁺/Cl^- cotransporter KCC2 has emerged as a novel therapeutic strategy for the treatment of epilepsy.

AREAS COVERED

We summarize the roles of KCC2 in the maintenance of synaptic inhibition and the evidence linking KCC2 dysfunction to epileptogenesis. We also discuss preclinical proof-of-principle studies that demonstrate that augmentation of KCC2 function can reduce seizure activity. Moreover, potential strategies to modulate KCC2 activity for therapeutic benefit are highlighted.

EXPERT OPINION

Although KCC2 is a promising drug target, questions remain before clinical translation. It is unclear whether increasing KCC2 activity can reverse epileptogenesis, the ultimate curative goal for epilepsy therapy that extends beyond seizure reduction. Furthermore, the potential adverse effects associated with increased KCC2 function have not been studied. Continued investigations into the neurobiology of KCC2 will help to translate promising preclinical insights into viable therapeutic avenues that leverage fundamental properties of KCC2 to treat medically intractable epilepsy and other disorders of failed synaptic inhibition with attendant neuronal hyperexcitability.