Repeated stress-induced expression pattern alterations of the hippocampal chloride transporters KCC2 and NKCC1 associated with behavioral abnormalities in female mice

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.

Effects of New Psychoactive Substance Esketamine on Behaviors and Transcription of Genes in Dopamine and GABA Pathways in Zebrafish Larvae

Esketamine (ESK) is the S-enantiomer of ketamine racemate (a new psychoactive substance) that can result in illusions, and alter hearing, vision, and proprioception in human and mouse. Up to now, the neurotoxicity caused by ESK at environmental level in fish is still unclear. This work studied the effects of ESK on behaviors and transcriptions of genes in dopamine and GABA pathways in zebrafish larvae at ranging from 12.4 ng L- 1 to 11141.1 ng L- 1 for 7 days post fertilization (dpf). The results showed that ESK at 12.4 ng L- 1 significantly reduced the touch response of the larvae at 48 hpf. ESK at 12.4 ng L- 1 also reduced the time and distance of larvae swimming at the outer zone during light period, which implied that ESK might potentially decrease the anxiety level of larvae. In addition, ESK increased the transcription of th, ddc, drd1a, drd3 and drd4a in dopamine pathway. Similarly, ESK raised the transcription of slc6a1b, slc6a13 and slc12a2 in GABA pathway. This study suggested that ESK could affect the heart rate and behaviors accompanying with transcriptional alterations of genes in DA and GABA pathways at early-staged zebrafish, which resulted in neurotoxicity in zebrafish larvae.

Neuroinflammation and Post-Stroke Depression: Focus on the Microglia and Astrocytes

Post-stroke depression (PSD), a frequent and disabling complication of stroke, has a strong impact on almost thirty percent of stroke survivors. The pathogenesis of PSD is not completely clear so far. Neuroinflammation following stroke is one of underlying mechanisms that involves in the pathophysiology of PSD and plays an important function in the development of depression and is regarded as a sign of depression. During the neuroinflammation after ischemic stroke onset, both astrocytes and microglia undergo a series of morphological and functional changes and play pro-inflammatory or anti-inflammatory effect in the pathological process of stroke. Importantly, astrocytes and microglia exert dual roles in the pathological process of PSD due to the phenotypic transformation. We summarize the latest evidence of neuroinflammation involving in PSD in this review, focus on the phenotypic transformation of microglia and astrocytes following ischemic stroke and reveal the dual roles of both microglia and astrocytes in the PSD via modulating the neuroinflammation.

Therapeutic potential for KCC2-targeted neurological diseases

Patients with neurological diseases, such as schizophrenia, tend to show low K+-Cl- co-transporter 2 (KCC2) levels in the brain. The cause of these diseases has been associated with stress and neuroinflammation. However, since the pathogenesis of these diseases is not yet fully investigated, drug therapy is still limited to symptomatic therapy. Targeting KCC2, which is mainly expressed in the brain, seems to be an appropriate approach in the treatment of these diseases. In this review, we aimed to discuss about stress and inflammation, KCC2 and Gamma-aminobutyric acid (GABA) function, diseases which decrease the KCC2 levels in the brain, factors that regulate KCC2 activity, and the possibility to overcome neuronal dysfunction targeting KCC2. We also aimed to discuss the relationships between neurological diseases and LPS caused by Porphyromonas gingivalis (P. g), which is a type of oral bacterium. Clinical trials on oxytocin, sirtuin 1 (SIRT1) activator, and transient receptor potential cation channel subfamily V Member 1 activator have been conducted to develop effective treatment methods. We believe that KCC2 modulators that regulate mitochondria, such as oxytocin, glycogen synthase kinase 3β (GSK3β), and SIRT1, can be potential targets for neurological diseases.

Delaying the GABA Shift Indirectly Affects Membrane Properties in the Developing Hippocampus

During the first two postnatal weeks, intraneuronal chloride concentrations in rodents gradually decrease, causing a shift from depolarizing to hyperpolarizing GABA responses. The postnatal GABA shift is delayed in rodent models for neurodevelopmental disorders and in human patients, but the impact of a delayed GABA shift on the developing brain remains obscure. Here we examine the direct and indirect consequences of a delayed postnatal GABA shift on network development in organotypic hippocampal cultures made from 6- to 7-d-old mice by treating the cultures for 1 week with VU0463271, a specific inhibitor of the chloride exporter KCC2. We verified that VU treatment delayed the GABA shift and kept GABA signaling depolarizing until DIV9. We found that the structural and functional development of excitatory and inhibitory synapses at DIV9 was not affected after VU treatment. In line with previous studies, we observed that GABA signaling was already inhibitory in control and VU-treated postnatal slices. Surprisingly, 14 d after the VU treatment had ended (DIV21), we observed an increased frequency of spontaneous inhibitory postsynaptic currents in CA1 pyramidal cells, while excitatory currents were not changed. Synapse numbers and release probability were unaffected. We found that dendrite-targeting interneurons in the stratum radiatum had an elevated resting membrane potential, while pyramidal cells were less excitable compared with control slices. Our results show that depolarizing GABA signaling does not promote synapse formation after P7, and suggest that postnatal intracellular chloride levels indirectly affect membrane properties in a cell-specific manner.SIGNIFICANCE STATEMENT During brain development, the action of neurotransmitter GABA shifts from depolarizing to hyperpolarizing. This shift is a thought to play a critical role in synapse formation. A delayed shift is common in rodent models for neurodevelopmental disorders and in human patients, but its consequences for synaptic development remain obscure. Here, we delayed the GABA shift by 1 week in organotypic hippocampal cultures and carefully examined the consequences for circuit development. We find that delaying the shift has no direct effects on synaptic development, but instead leads to indirect, cell type-specific changes in membrane properties. Our data call for careful assessment of alterations in cellular excitability in neurodevelopmental disorders.

Intergenerational Perioperative Neurocognitive Disorder

Accelerated neurocognitive decline after general anesthesia/surgery, also known as perioperative neurocognitive disorder (PND), is a widely recognized public health problem that may affect millions of patients each year. Advanced age, with its increasing prevalence of heightened stress, inflammation, and neurodegenerative alterations, is a consistent contributing factor to the development of PND. Although a strong homeostatic reserve in young adults makes them more resilient to PND, animal data suggest that young adults with pathophysiological conditions characterized by excessive stress and inflammation may be vulnerable to PND, and this altered phenotype may be passed to future offspring (intergenerational PND). The purpose of this narrative review of data in the literature and the authors' own experimental findings in rodents is to draw attention to the possibility of intergenerational PND, a new phenomenon which, if confirmed in humans, may unravel a big new population that may be affected by parental PND. In particular, we discuss the roles of stress, inflammation, and epigenetic alterations in the development of PND. We also discuss experimental findings that demonstrate the effects of surgery, traumatic brain injury, and the general anesthetic sevoflurane that interact to induce persistent dysregulation of the stress response system, inflammation markers, and behavior in young adult male rats and in their future offspring who have neither trauma nor anesthetic exposure (i.e., an animal model of intergenerational PND).

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.

Effect of Epigallocatechin-3-gallate on Stress-Induced Depression in a Mouse Model: Role of Interleukin-1β and Brain-Derived Neurotrophic Factor

Epigallocatechin 3-gallate (EGCG) is a natural polyphenolic antioxidant in green tea leaves with well-known health-promoting properties. However, the influence of EGCG on a chronic animal model of depression remains to be fully investigated, and the details of the molecular and cellular changes are still unclear. Therefore, the present study aimed to investigate the antidepressant effect of EGCG in mice subjected to chronic unpredictable mild stress (CUMS). After eight consecutive weeks of CUMS, the mice were treated with EGCG (200 mg/kg b.w.) by oral gavage for two weeks. A forced swimming test (FST) was used to assess depressive symptoms. EGCG administration significantly alleviated CUMS-induced depression-like behavior in mice. EGCG also effectively decreased serum interleukin-1β (IL-1β) and increased the mRNA expression levels of brain-derived neurotrophic factor (BDNF) in the hippocampal CA3 region of CUMS mice. Furthermore, electron microscopic examination of CA3 neurons in CUMS mice showed morphological features of apoptosis, loss or disruption of the myelin sheath, and degenerating synapses. These neuronal injuries were diminished with the administration of EGCG. The treatment effect of EGCG in CUMS-induced behavioral alterations was comparable with that of clomipramine hydrochloride (Anafranil), a tricyclic antidepressant drug. In conclusion, our study demonstrates that the antidepressive action of EGCG involves downregulation of serum IL-1β, upregulation of BDNF mRNA in the hippocampus, and reduction of CA3 neuronal lesions.

GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks

Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.

Environmental regulation of the chloride transporter KCC2: switching inflammation off to switch the GABA on?

Chloride homeostasis, the main determinant factor for the dynamic tuning of GABAergic inhibition during development, has emerged as a key element altered in a wide variety of brain disorders. Accordingly, developmental disorders such as schizophrenia, Autism Spectrum Disorder, Down syndrome, epilepsy, and tuberous sclerosis complex (TSC) have been associated with alterations in the expression of genes codifying for either of the two cotransporters involved in the excitatory-to-inhibitory GABA switch, KCC2 and NKCC1. These alterations can result from environmental insults, including prenatal stress and maternal separation which share, as common molecular denominator, the elevation of pro-inflammatory cytokines. In this review we report and systemize recent research articles indicating that different perinatal environmental perturbations affect the expression of chloride transporters, delaying the developmental switch of GABA signaling, and that inflammatory cytokines, in particular interleukin 1β, may represent a key causal factor for this phenomenon. Based on literature data, we provide therefore a unifying conceptual framework, linking environmental hits with the excitatory-to-inhibitory GABA switch in the context of brain developmental disorders.

Ketogenic Diet Provided During Three Months Increases KCC2 Expression but Not NKCC1 in the Rat Dentate Gyrus

Ketogenic diet, a high fat and low carbohydrate diet, has been used as a non-pharmacological treatment in refractory epilepsy since 1920. In recent years, it has demonstrated to be effective in the treatment of numerous neurological and non-neurological diseases. Some neurological and neuropsychiatric disorders are known to be caused by gamma-aminobutyric acid (GABA)-mediated neurotransmission dysfunction. The strength and polarity of GABA-mediated neurotransmission are determined by the intracellular chloride concentration, which in turn is regulated by cation-chloride cotransporters NKCC1 and KCC2. Currently, it is unknown if the effect of ketogenic diet is due to the modulation of these cotransporters. Thus, we analyzed the effect of a ketogenic diet on the cation-chloride cotransporters expression in the dentate gyrus. We estimated the total number of NKCC1 immunoreactive (NKCC1-IR) neuronal and glial cells by stereology and determined KCC2 labeling intensity by densitometry in the molecular and granule layers as well as in the hilus of dentate gyrus of rats fed with normal or ketogenic diet for 3 months. The results indicated that ketogenic diet provided during 3 months increased KCC2 expression, but not NKCC1 in the dentate gyrus of the rat. The significant increase of KCC2 expression could explain, at least in part, the beneficial effect of ketogenic diet in the diseases where the GABAergic system is altered by increasing its inhibitory efficiency.

Interleukin-18 from neurons and microglia mediates depressive behaviors in mice with post-stroke depression

Post-stroke depression (PSD) is a common and serious complication that is affecting one thirds of stroke patients which leaves them with a poor quality of life, high mortality rate, high recurrent rate, and slow recovery. Recent studies showed that serum interleukin-18 (IL-18) level is a biomarker for patients with PSD. However, the role of IL-18 in the pathology of PSD is still unclear. In this study, we demonstrated that the IL-18 level in the ischemic brain significantly increased in mice with depression-like behaviors that were caused by the combined use of chronic spatial restraint stress and middle cerebral artery occlusion. Interestingly, IL-18 expression was mainly found in neurons at early phase and in microglia at a later phase. Injection of the exogenous IL-18 into the amygdala, but not the hippocampus or the striatum caused severe depression-like behaviors. On the contrary, the blockage of endogenous IL-18 by IL-18 binding protein, a specific antagonist of IL-18, repressed depressive phenotypes in SIR mice. IL-18 KO mice exhibited the resistance to spatial restraint stress and cerebral ischemia injury. Finally, we found that IL-18 mediated depressive behaviors by the interaction of IL-18 receptor and NKCC1, a sodium-potassium chloride co-transporter that is related to GABAergic inhibition. Administration of NKCC1 antagonist bumetanide exerted a therapeutic effect on the in IL-18-induced depressive mice. In conclusion, we demonstrated that increased IL-18 in the brain causes depression-like behaviors by promoting the IL-18 receptor/NKCC1 signaling pathway. Targeting IL-18 and its downstream pathway is a promising strategy for the prevention and treatment of PSD.

Temporal Lobe Epilepsy, Stroke, and Traumatic Brain Injury: Mechanisms of Hyperpolarized, Depolarized, and Flow-Through Ion Channels Utilized as Tri-Coordinate Biomarkers of Electrophysiologic Dysfunction

The brain is an integrated network of multiple variables that when compromised create a diseased state. The neuropathology of temporal lobe epilepsy (TLE), stroke, and traumatic brain injury (TBI) demonstrate both similarity and complexity that reflects this integrated variability; TLE with its live human tissue resection provides opportunity for translational science to demonstrate scale equivalent experimentation between the macroscopic world of clinical disease and the microscopic world of basic science. The extended value of this research is that the neuroinflammatory abnormalities that occur throughout astrocytes with hippocampal sclerosis and damaged or even reversed signaling pathways (inhibition to excitation such as with gaba-aminobutyric acid) are similar to those seen in post-stroke and TBI models. In evaluation of the epilepsy population this interconnectedness of pathology warrants further evaluation with collaborative efforts. This review summarizes patterns that could shift experimentation closer to the macro level of humanity, but still represent the micro world of genetics, epigenetics, and neuro-injury across etiologies of physiologic dysfunction such as TLE, stroke, and TBI with evaluation of cell function using electrophysiology. In conclusion we demonstrate the plausibility of electrophysiologic voltage and current measurement of brain tissue by patch clamp analysis to specify actual electrophysiologic function for comparison to electroencephalography in order to aid neurologic evaluation. Finally, we discuss the opportunity with multiscale modeling to display integration of the hyperpolarization cyclic-nucleotide gated channel, the depolarized calcium channels, and sodium-potassium-chloride-one/potassium-chloride-two co-transporter channels as potential mechanisms utilized as tri-coordinate biomarkers with these three forms of neurologic disease at a molecular scale of electrophysiologic pathology.

Neonatal maternal separation delays the GABA excitatory-to-inhibitory functional switch by inhibiting KCC2 expression

The excitatory-to-inhibitory functional switch of γ-aminobutyric acid (GABA; GABA switch), which normally occurs in the first to the second postnatal week in the hippocampus, is necessary for the development of appropriate central nervous system function. A deficit in GABAergic inhibitory function could cause excitatory/inhibitory (E/I) neuron imbalance that is found in many neurodegenerative disorders. In the present study, we examined whether neonatal stress can affect the timing of the GABA functional switch and cause disorders during adolescence. Neonatal stress was induced in C57BL/6J male mouse pups by maternal separation (MS) on postnatal days (PND) 1-21. Histological quantification of K+-Cl- co-transporter (KCC2) and Ca2+ imaging were performed to examine the timing of the GABA switch during the MS period. To evaluate the influence of neonatal MS on adolescent hippocampal function, we quantified KCC2 expression and evaluated hippocampal-related behavioral tasks at PND35-38. We showed that MS delayed the timing of the GABA switch in the hippocampus and inhibited the increase in membrane KCC2 expression, with KCC2 expression inhibition persisting until adolescence. Behavioral tests showed impaired cognition, declined attention, hyperlocomotion, and aggressive character in maternally separated mice. Taken together, our results show that neonatal stress delayed the timing of the GABA switch, which could change the E/I balance and cause neurodegenerative disorders in later life.

Retracing your footsteps: developmental insights to spinal network plasticity following injury

During development of the spinal cord, a precise interaction occurs between descending projections and sensory afferents, with spinal networks that lead to expression of coordinated motor output. In the rodent, during the last embryonic week, motor output first occurs as regular bursts of spontaneous activity, progressing to stochastic patterns of episodes that express bouts of coordinated rhythmic activity perinatally. Locomotor activity becomes functionally mature in the 2nd postnatal wk and is heralded by the onset of weight-bearing locomotion on the 8th and 9th postnatal day. Concomitantly, there is a maturation of intrinsic properties and key conductances mediating plateau potentials. In this review, we discuss spinal neuronal excitability, descending modulation, and afferent modulation in the developing rodent spinal cord. In the adult, plastic mechanisms are much more constrained but become more permissive following neurotrauma, such as spinal cord injury. We discuss parallel mechanisms that contribute to maturation of network function during development to mechanisms of pathological plasticity that contribute to aberrant motor patterns, such as spasticity and clonus, which emerge following central injury.

Genome-wide transcriptome analysis of hippocampus in rats indicated that TLR/NLR signaling pathway was involved in the pathogenisis of depressive disorder induced by chronic restraint stress

Data from clinical investigations and laboratory fundings have provided preliminary evidence for the effectiveness and safety of acupuncture therapy in depression. However, the mechanisms underlying the antidepressant response of acupuncture are not fully elucidated. To elucidate the potential effects of acupuncture for depression on the hippocampal genome-wide transcriptome at the molecular level, we evaluated the transcriptomic profile of depression rats under treatment of acupuncture, and fluoxetine. We identified a very significant effect of acupucture intervention, with 107 genes differentially expressed in acupuncture vs. model group; while 41 genes between fluoxetine vs. model group. Notably, the 54 differentially expressed genes between acupuncture and fluoxetine showed the significantly different effect between acupuncture and fluoxetine. Through GO (gene ontology) functional term and KEGG (kyoto encyclopedia of genes and genomes) pathway analysis, we identified that the upregulation of gene sets were related to inflammatory response, innate immunity and immune response. We found that toll-like receptor signalling pathway and NOD like receptor signalling pathway were associated with the function of inflammatory response, innate immunity and immune response. Importantly, acupuncture reversed the upregulation of gene sets that were related to inflammatory response, innate immunity and immune response (including toll-like receptor signalling pathway and NOD like receptor signalling pathway), which might be critical for the pathogenesis of depression and provide evidence for the antidepressive effects of acupuncture by regulating inflammatory response, innate immunity and immune response via toll-like receptor signalling pathway and NOD like receptor signalling pathway.

Compromising KCC2 transporter activity enhances the development of continuous seizure activity

Impaired neuronal inhibition has long been associated with the increased probability of seizure occurrence and heightened seizure severity. Fast synaptic inhibition in the brain is primarily mediated by the type A γ-aminobutyric acid receptors (GABAARs), ligand-gated ion channels that can mediate Cl(-) influx resulting in membrane hyperpolarization and the restriction of neuronal firing. In most adult brain neurons, the K(+)/Cl(-) co-transporter-2 (KCC2) establishes hyperpolarizing GABAergic inhibition by maintaining low [Cl(-)]i. In this study, we sought to understand how decreased KCC2 transport function affects seizure event severity. We impaired KCC2 transport in the 0-Mg(2+) ACSF and 4-aminopyridine in vitro models of epileptiform activity in acute mouse brain slices. Experiments with the selective KCC2 inhibitor VU0463271 demonstrated that reduced KCC2 transport increased the duration of SLEs, resulting in non-terminating discharges of clonic-like activity. We also investigated slices obtained from the KCC2-Ser940Ala (S940A) point-mutant mouse, which has a mutation at a known functional phosphorylation site causing behavioral and cellular deficits under hyperexcitable conditions. We recorded from the entorhinal cortex of S940A mouse brain slices in both 0-Mg(2+) ACSF and 4-aminopyridine, and demonstrated that loss of the S940 residue increased the susceptibility of continuous clonic-like discharges, an in vitro form of status epilepticus. Our experiments revealed KCC2 transport activity is a critical factor in seizure event duration and mechanisms of termination. Our results highlight the need for therapeutic strategies that potentiate KCC2 transport function in order to decrease seizure event severity and prevent the development of status epilepticus.

Reduced tonic inhibition in the dentate gyrus contributes to chronic stress-induced impairments in learning and memory

It is well established that stress impacts the underlying processes of learning and memory. The effects of stress on memory are thought to involve, at least in part, effects on the hippocampus, which is particularly vulnerable to stress. Chronic stress induces hippocampal alterations, including but not limited to dendritic atrophy and decreased neurogenesis, which are thought to contribute to chronic stress-induced hippocampal dysfunction and deficits in learning and memory. Changes in synaptic transmission, including changes in GABAergic inhibition, have been documented following chronic stress. Recently, our laboratory demonstrated shifts in EGABA in CA1 pyramidal neurons following chronic stress, compromising GABAergic transmission and increasing excitability of these neurons. Interestingly, here we demonstrate that these alterations are unique to CA1 pyramidal neurons, since we do not observe shifts in EGABA following chronic stress in dentate gyrus granule cells. Following chronic stress, there is a decrease in the expression of the GABAA receptor (GABAA R) δ subunit and tonic GABAergic inhibition in dentate gyrus granule cells, whereas there is an increase in the phasic component of GABAergic inhibition, evident by an increase in the peak amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs). Given the numerous changes observed in the hippocampus following stress, it is difficult to pinpoint the pertinent contributing pathophysiological factors. Here we directly assess the impact of a reduction in tonic GABAergic inhibition of dentate gyrus granule cells on learning and memory using a mouse model with a decrease in GABAA R δ subunit expression specifically in dentate gyrus granule cells (Gabrd/Pomc mice). Reduced GABAA R δ subunit expression and function in dentate gyrus granule cells is sufficient to induce deficits in learning and memory. Collectively, these findings suggest that the reduction in GABAA R δ subunit-mediated tonic inhibition in dentate gyrus granule cells contributes, at least in part, to deficits in learning and memory associated with chronic stress. These findings have significant implications regarding the pathophysiological mechanisms underlying impairments in learning and memory associated with stress and suggest a role for GABAA R δ subunit containing receptors in dentate gyrus granule cells. © 2016 Wiley Periodicals, Inc.

The effect of repeated stress on KCC2 and NKCC1 immunoreactivity in the hippocampus of female mice

K⁺–Cl⁻ co-transporter (KCC2) and Na⁺–K⁺–2Cl⁻ co-transporter (NKCC1) are the main regulators of neuronal intracellular chloride concentration; altered expression patterns of KCC2 and NKCC1 have been reported in several neurodegenerative diseases. In this paper, we show the effect of repeated stress on KCC2, NKCC1, and serine 940 phosphorylated KCC2 (pKCC2^ser940) immunoreactivity.

The data were obtained from the hippocampus of female mice using single-plane confocal microscopy images. The mean fluorescence intensity of the perisomatic area of neurons, defined as raw fluorescence intensity (RFI) was calculated. Repeated stress (RS) resulted in a decrease in perisomatic area of immunoreactive (IR)-KCC2 and an increase of the IR-NKCC1. In addition, RS decreased perisomatic IR-pKCC2^ser940, corresponding to that of KCC2. The data in this article support the results of a previous study [1] and provide the details of immunohistological methods. Interpretation of the data in this article can be found in “Repeated stress-induced expression pattern alterations of the hippocampal chloride transporters KCC2 and NKCC1 associated with behavioral abnormalities in female mice” by Tsukahara et al. [1].