Crosstalk between GABAA receptors in astrocytes and neurons triggered by general anesthetic drugs

General anesthetic drugs cause cognitive deficits that persist after the drugs have been eliminated. Astrocytes may contribute to such cognition-impairing effects through the release of one or more paracrine factors that increase a tonic inhibitory conductance generated by extrasynaptic γ-aminobutyric acid type A (GABAA) receptors in hippocampal neurons. The mechanisms underlying this astrocyte-to-neuron crosstalk remain unknown. Interestingly, astrocytes express anesthetic-sensitive GABAA receptors. Here, we tested the hypothesis that anesthetic drugs activate astrocytic GABAA receptors to initiate crosstalk leading to a persistent increase in extrasynaptic GABAA receptor function in neurons. We also investigated the signaling pathways in neurons and aimed to identify the paracrine factors released from astrocytes. Astrocytes and neurons from mice were grown in primary cell cultures and studied using in vitro electrophysiological and biochemical assays. We discovered that the commonly used anesthetics etomidate (injectable) and sevoflurane (inhaled) stimulated astrocytic GABAA receptors, which in turn promoted the release paracrine factors, that increased the tonic current in neurons via a p38 MAPK-dependent signaling pathway. The increase in tonic current was mimicked by exogenous IL-1β and abolished by blocking IL-1 receptors; however, unexpectedly, IL-1β and other cytokines were not detected in astrocyte-conditioned media. In summary, we have identified a novel form of crosstalk between GABAA receptors in astrocytes and neurons that engages a p38 MAPK-dependent pathway. Brief commentary BACKGROUND: Many older patients experience cognitive deficits after surgery. Anesthetic drugs may be a contributing factor as they cause a sustained increase in the function of "memory blocking" extrasynaptic GABAA receptors in neurons. Interestingly, astrocytes are required for this increase; however, the mechanisms underlying the astrocyte-to-neuron crosstalk remain unknown. TRANSLATIONAL SIGNIFICANCE: We discovered that commonly used general anesthetic drugs stimulate GABAA receptors in astrocytes, which in turn release paracrine factors that trigger a persistent increase in extrasynaptic GABAA receptor function in neurons via p38 MAPK. This novel form of crosstalk may contribute to persistent cognitive deficits after general anesthesia and surgery.

Tabernanthalog and ibogainalog inhibit the α7 and α9α10 nicotinic acetylcholine receptors via different mechanisms and with higher potency than the GABAA receptor and CaV2.2 channel

In this study, we have investigated the pharmacological activity and structural interaction of two novel psychoplastogens, tabernanthalog (TBG) and ibogainalog (IBG) at heterologously-expressed rat (r) and human (h) nicotinic acetylcholine receptors (nAChRs), the rα1β2γ2L γ-aminobutyric acid type A receptor (GABAAR), and the human voltage-gated N-type calcium channel (CaV2.2 channel). Both compounds inhibited the nAChRs with the following receptor selectivity: α9α10 > α7 > α3β2 ≅ α3β4, indicating that β2/β4 subunits are relatively less important for their activity. The potencies of TBG and IBG were comparable at hα7 and hα9α10 subtypes, and comparable to their rat counterparts. TBG- and IBG-induced inhibition of rα7 was ACh concentration-independent and voltage-dependent, whereas rα9α10 inhibition was ACh concentration-dependent and voltage-independent, suggesting that they interact with the α7 ion channel pore and α9α10 orthosteric ligand binding site, respectively. These results were supported by molecular docking studies showing that at the α7 model TBG forms stable interactions with luminal rings at 9', 13', and 16', whereas IBG mostly interacts with the extracellular-transmembrane junction. In the α9α10 model, however, these compounds interacted with several residues from the principal (+) and complementary (-) sides in the transmitter binding site. Ibogaminalog (DM506) also interacted with a non-luminal site at α7, and one α9α10 orthosteric site. TBG and IBG inhibited the GABAAR and CaV2.2 channels with 10 to 30-fold lower potencies. In sum, we show that TBG and IBG inhibit the α7 and α9α10 nAChRs by noncompetitive and competitive mechanisms, respectively, and with higher potency than the GABAAR and CaV2.2 channel.

Sustained antidepressant effects of ketamine metabolite involve GABAergic inhibition-mediated molecular dynamics in aPVT glutamatergic neurons

Despite the rapid and sustained antidepressant effects of ketamine and its metabolites, their underlying cellular and molecular mechanisms are not fully understood. Here, we demonstrate that the sustained antidepressant-like behavioral effects of (2S,6S)-hydroxynorketamine (HNK) in repeatedly stressed animal models involve neurobiological changes in the anterior paraventricular nucleus of the thalamus (aPVT). Mechanistically, (2S,6S)-HNK induces mRNA expression of extrasynaptic GABAA receptors and subsequently enhances GABAA-receptor-mediated tonic currents, leading to the nuclear export of histone demethylase KDM6 and its replacement by histone methyltransferase EZH2. This process increases H3K27me3 levels, which in turn suppresses the transcription of genes associated with G-protein-coupled receptor signaling. Thus, our findings shed light on the comprehensive cellular and molecular mechanisms in aPVT underlying the sustained antidepressant behavioral effects of ketamine metabolites. This study may support the development of potentially effective next-generation pharmacotherapies to promote sustained remission of stress-related psychiatric disorders.

Alpha1- and Beta-norepinephrinergic receptors of dorsomedial and ventromedial hypothalamic nuclei modulate panic attack-like defensive behaviour elicited by diencephalic GABAergic neurotransmission disinhibition

Gamma-aminobutyric acid (GABA) disinhibition in medial hypothalamus (MH) nuclei of rats elicits some defensive reactions that are considered panic attack-like behaviours. Recent evidence showed that the norepinephrine-mediated system modulates fear-related defensive behaviours organised by MH neurons at least in part via noradrenergic receptors recruitment on midbrain tegmentum. However, it is unknown whether noradrenergic receptors of the MH also modulate the panic attack-like reactions. The aim of this work was to investigate the distribution of noradrenergic receptors in MH, and the effects of either α1-, α2- or β-noradrenergic receptors blockade in the MH on defensive behaviours elaborated by hypothalamic nuclei. Defensive behaviours were evaluated after the microinjection of the selective GABAA receptor antagonist bicuculline into the MH that was preceded by microinjection of either WB4101, RX821002, propranolol (α1-, α2- and β-noradrenergic receptor selective antagonists, respectively), or physiological saline into the MH of male Wistar rats. The α1-, α2- and β-noradrenergic receptors were found in neuronal perikarya of all MH nuclei, and the α2-noradrenergic receptor were also found on glial cells mainly situated in the ventrolateral division of the ventromedial hypothalamic nucleus. The α1- and β-noradrenergic receptors blockade in the MH decreased defensive attention and escape reactions elicited by the intra-MH microinjections of bicuculline. These findings suggest that, despite the profuse distributions of α1-, α2- and β-noradrenergic receptors in the MH, both α1- and β-noradrenergic receptor- rather than α2-noradrenergic receptor-signalling in MH are critical for the neuromodulation of panic-like behaviour.

Reduced SV2A and GABAA receptor levels in the brains of type 2 diabetic rats revealed by [18F]SDM-8 and [18F]flumazenil PET

PURPOSE

Type 2 diabetes mellitus (T2DM) is associated with a greater risk of Alzheimer's disease. Synaptic impairment and protein aggregates have been reported in the brains of T2DM models. Here, we assessed whether neurodegenerative changes in synaptic vesicle 2 A (SV2A), γ-aminobutyric acid type A (GABAA) receptor, amyloid-β, tau and receptor for advanced glycosylation end product (RAGE) can be detected in vivo in T2DM rats.

METHODS

Positron emission tomography (PET) using [18F]SDM-8 (SV2A), [18F]flumazenil (GABAA receptor), [18F]florbetapir (amyloid-β), [18F]PM-PBB3 (tau), and [18F]FPS-ZM1 (RAGE) was carried out in 12-month-old diabetic Zucker diabetic fatty (ZDF) and SpragueDawley (SD) rats. Immunofluorescence staining, Thioflavin S staining, proteomic profiling and pathway analysis were performed on the brain tissues of ZDF and SD rats.

RESULTS

Reduced cortical [18F]SDM-8 uptake and cortical and hippocampal [18F]flumazenil uptake were observed in 12-month-old ZDF rats compared to SD rats. The regional uptake of [18F]florbetapir and [18F]PM-PBB3 was comparable in the brains of 12-month-old ZDF and SD rats. Immunofluorescence staining revealed Thioflavin S-negative, phospho-tau-positive inclusions in the cortex and hypothalamus in the brains of ZDF rats and the absence of amyloid-beta deposits. The level of GABAA receptors was lower in the cortex of ZDF rats than SD rats. Proteomic analysis further demonstrated that, compared with SD rats, synaptic-related proteins and pathways were downregulated in the hippocampus of ZDF rats.

CONCLUSION

These findings provide in vivo evidence for regional reductions in SV2A and GABAA receptor levels in the brains of aged T2DM ZDF rats.

Integrated workflow for the identification of new GABAA R positive allosteric modulators based on the in silico screening with further in vitro validation. Case study using Enamine's stock chemical space

Numerous studies reported an association between GABAA R subunit genes and epilepsy, eating disorders, autism spectrum disorders, neurodevelopmental disorders, and bipolar disorders. This study was aimed to find some potential positive allosteric modulators and was performed by combining the in silico approach with further in vitro evaluation of its real activity. We started from the GABAA R-diazepam complexes and assembled a lipid embedded protein ensemble to refine it via molecular dynamics (MD) simulation. Then we focused on the interaction of α1β2γ2 with some Z-drugs (non-benzodiazepine compounds) using an Induced Fit Docking (IFD) into the relaxed binding site to generate a pharmacophore model. The pharmacophore model was validated with a reference set and applied to decrease the pre-filtered Enamine database before the main docking procedure. Finally, we succeeded in identifying a set of compounds, which met all features of the docking model. The aqueous solubility and stability of these compounds in mouse plasma were assessed. Then they were tested for the biological activity using the rat Purkinje neurons and CHO cells with heterologously expressed human α1β2γ2 GABAA receptors. Whole-cell patch clamp recordings were used to reveal the GABA induced currents. Our study represents a convenient and tunable model for the discovery of novel positive allosteric modulators of GABAA receptors. A High-throughput virtual screening of the largest available database of chemical compounds resulted in the selection of 23 compounds. Further electrophysiological tests allowed us to determine a set of 3 the most outstanding active compounds. Considering the structural features of leader compounds, the study can develop into the MedChem project soon.

Application of ensemble learning for predicting GABAA receptor agonists

BACKGROUND

Over the past few decades, agonists binding to the benzodiazepine site of the GABAA receptor have been successfully developed as clinical drugs. Different modulators (agonist, antagonist, and reverse agonist) bound to benzodiazepine sites exhibit different or even opposite pharmacological effects, however, their structures are so similar that it is difficult to distinguish them based solely on molecular skeleton. This study aims to develop classification models for predicting the agonists.

METHODS

306 agonists or non-agonists were collected from literature. Six machine learning algorithms including RF, XGBoost, AdaBoost, GBoost, SVM, and ANN algorithms were employed for model development. Using six descriptors including 1D/2D Descriptors, ECFP4, 2D-Pharmacophore, MACCS, PubChem, and Estate fingerprint to characterize chemical structures. The model interpretability was explored by SHAP method.

RESULTS

The best model demonstrated an AUC value of 0.905 and an MCC value of 0.808 for the test set. The PubMac-based model (PubMac-GB) achieved best AUC values of 0.935 for test set. The SHAP analysis results emphasized that MaccsFP62, ECFP_624, ECFP_724, and PubchemFP213 were the crucial molecular features. Applicability domain analysis was also performed to determine reliable prediction boundaries for the model. The PubMac-GB model was applied to virtual screening for potential GABAA agonists and the top 100 compounds were given.

CONCLUSION

Overall, our ensemble learning-based model (PubMac-GB) achieved comparable performance and would be helpful in effectively identifying agonists of GABAA receptors.

Long-term α5 GABA A receptor negative allosteric modulator treatment reduces NMDAR-mediated neuronal excitation and maintains basal neuronal inhibition

α5 subunit-containing GABA type-A receptors (α5 GABAARs) are enriched in the hippocampus and play critical roles in neurodevelopment, synaptic plasticity, and cognition. α5 GABAAR preferring negative allosteric modulators (α5 NAMs) show promise mitigating cognitive impairment in preclinical studies of conditions characterized by excess GABAergic inhibition, including Down syndrome and memory deficits post-anesthesia. However, previous studies have primarily focused on acute application or single-dose α5 NAM treatment. Here, we measured the effects of chronic (7-day) in vitro treatment with L-655,708 (L6), a highly selective α5 NAM, on glutamatergic and GABAergic synapses in rat hippocampal neurons. We previously showed that 2-day in vitro treatment with L6 enhanced synaptic levels of the glutamate NMDA receptor (NMDAR) GluN2A subunit without modifying surface α5 GABAAR expression, inhibitory synapse function, or L6 sensitivity. We hypothesized that chronic L6 treatment would further increase synaptic GluN2A subunit levels while maintaining GABAergic inhibition and L6 efficacy, thus increasing neuronal excitation and glutamate-evoked intracellular calcium responses. Immunofluorescence experiments revealed that 7-day L6 treatment slightly increased the synaptic levels of gephyrin and surface α5 GABAARs. Functional studies showed that chronic α5 NAM treatment did not alter inhibition or α5 NAM sensitivity. Surprisingly, chronic L6 exposure decreased surface levels of GluN2A and GluN2B subunits, concurrent with reduced NMDAR-mediated neuronal excitation as seen by faster synaptic decay rates and reduced glutamate-evoked calcium responses. Together, these results show that chronic in vitro treatment with an α5 NAM leads to subtle homeostatic changes in inhibitory and excitatory synapses that suggest an overall dampening of excitability.

Tenuigenin promotes non-rapid eye movement sleep via the GABAA receptor and exerts somnogenic effect in a MPTP mouse model of Parkinson's disease

Sleep disturbances are commonly non-motor symptoms in Parkinson's diseases (PD). However, standard dopamine replacement therapies for the treatment of motor symptoms often prove inadequate in combating sleep disturbances. Previous studies conducted by our research group have reported the neuroprotective effects of tenuigenin, a natural extract from Polygala tenuifolia root, which has been traditionally employed in treating insomnia. The objective of this study was to investigate the potential of tenuigenin in modulating sleep-wake behaviors and elucidate the underlying mechanisms. We employed EEG/EMG recordings to evaluate the impact of tenuigenin on sleep-wake profiles. Furthermore, we utilized c-Fos immunostaining, whole-cell patch clamping and local field potentials (LFP) recording to explore the mechanisms involved in sleep-promoting effects of tenuigenin. Additionally, we examined the effects of tenuigenin on sleep-promoting in MPTP PD mice. Here, we found tenuigenin demonstrated a significant increase in NREM sleep and a reduction in sleep latency in mice, without altering the EEG power density. Moreover, tenuigenin increased c-Fos expression in the ventrolateral preoptic area (VLPO) and stimulated sleep-promoting neurons in VLPO. The sleep-promoting effects of tenuigenin were abolished when mice were pretreated with flumazenil, an antagonist at the benzodiazepine site of the GABAA receptor. Furthermore, tenuigenin was found to ameliorate sleep disturbances in MPTP-induced mice. The results suggesting that tenuigenin facilitated a type of NREM sleep comparable to physiological NREM sleep through interaction with the GABAA receptor. Additionally, tenuigenin demonstrated improvements in sleep disturbances in MPTP-induced PD mice, suggesting its potential as a sleep-promoting substance, particularly for PD patients experiencing sleep disturbances.

GABAA receptors as targets for treating affective and cognitive symptoms of depression

In the past 20 years, our understanding of the pathophysiology of depression has evolved from a focus on an imbalance of monoaminergic neurotransmitters to a multifactorial picture including an improved understanding of the role of glutamatergic excitatory and GABAergic inhibitory neurotransmission. FDA-approved treatments targeting the glutamatergic [esketamine for major depressive disorder (MDD)] and GABAergic (brexanolone for peripartum depression) systems have become available. This review focuses on the GABAA receptor (GABAAR) system as a target for novel antidepressants and discusses the mechanisms by which modulation of δ-containing GABAARs with neuroactive steroids (NASs) or of α5-containing GABAARs results in antidepressant or antidepressant-like actions and discusses clinical data on NASs. Moreover, a potential mechanism by which α5-GABAAR-positive allosteric modulators (PAMs) may improve cognitive deficits in depression is presented.

The hepatic GABAergic system promotes liver macrophage M2 polarization and mediates HBV replication in mice

Macrophages display functional phenotypic plasticity. Hepatitis B virus (HBV) infection induces polarizations of liver macrophages either to M1-like pro-inflammatory phenotype or to M2-like anti-inflammatory phenotype. Gamma-aminobutyric acid (GABA) signaling exists in various non-neuronal cells including hepatocytes and some immune cells. Here we report that macrophages express functional GABAergic signaling components and activation of type A GABA receptors (GABAARs) promotes M2-polarization thus advancing HBV replication. Notably, intraperitoneal injection of GABA or the GABAAR agonist muscimol increased HBV replication in HBV-carrier mice that were generated by hydrodynamical injection of adeno-associated virus/HBV1.2 plasmids (pAAV/HBV1.2). The GABA-augmented HBV replication in HBV-carrier mice was significantly reduced by the GABAAR inhibitor picrotoxin although picrotoxin had no significant effect on serum HBsAg levels in control HBV-carrier mice. Depletion of liver macrophages by liposomal clodronate treatment also significantly reduced the GABA-augmented HBV replication. Yet adoptive transfer of liver macrophages isolated from GABA-treated donor HBV-carrier mice into the liposomal clodronate-pretreated recipient HBV-carrier mice restored HBV replication. Moreover, GABA or muscimol treatment increased the expression of "M2" cytokines in macrophages, but had no direct effect on HBV replication in the HepG2.2.15 cells, HBV1.3-transfected Huh7, HepG2, or HepaRG cells, or HBV-infected Huh7-NTCP cells. Taken together, these results suggest that increasing GABA signaling in the liver promotes HBV replication in HBV-carrier mice by suppressing the immunity of liver macrophages, but not by increasing the susceptibility of hepatocytes to HBV infection. Our study shows that a previously unknown GABAergic system in liver macrophage has an essential role in HBV replication.

Inhibitory and excitatory synaptic neuroadaptations in the diazepam tolerant brain

Benzodiazepine (BZ) drugs treat seizures, anxiety, insomnia, and alcohol withdrawal by potentiating γ2 subunit containing GABA type A receptors (GABAARs). BZ clinical use is hampered by tolerance and withdrawal symptoms including heightened seizure susceptibility, panic, and sleep disturbances. Here, we investigated inhibitory GABAergic and excitatory glutamatergic plasticity in mice tolerant to benzodiazepine sedation. Repeated diazepam (DZP) treatment diminished sedative effects and decreased DZP potentiation of GABAAR synaptic currents without impacting overall synaptic inhibition. While DZP did not alter γ2-GABAAR subunit composition, there was a redistribution of extrasynaptic GABAARs to synapses, resulting in higher levels of synaptic BZ-insensitive α4-containing GABAARs and a concomitant reduction in tonic inhibition. Conversely, excitatory glutamatergic synaptic transmission was increased, and NMDAR subunits were upregulated at synaptic and total protein levels. Quantitative proteomics further revealed cortex neuroadaptations of key pro-excitatory mediators and synaptic plasticity pathways highlighted by Ca2+/calmodulin-dependent protein kinase II (CAMKII), MAPK, and PKC signaling. Thus, reduced inhibitory GABAergic tone and elevated glutamatergic neurotransmission contribute to disrupted excitation/inhibition balance and reduced BZ therapeutic power with benzodiazepine tolerance.

Adamtsl3 mediates DCC signaling to selectively promote GABAergic synapse function

The molecular code that controls synapse formation and maintenance in vivo has remained quite sparse. Here, we identify that the secreted protein Adamtsl3 functions as critical hippocampal synapse organizer acting through the transmembrane receptor DCC (deleted in colorectal cancer). Traditionally, DCC function has been associated with glutamatergic synaptogenesis and plasticity in response to Netrin-1 signaling. We demonstrate that early post-natal deletion of Adamtsl3 in neurons impairs DCC protein expression, causing reduced density of both glutamatergic and GABAergic synapses. Adult deletion of Adamtsl3 in either GABAergic or glutamatergic neurons does not interfere with DCC-Netrin-1 function at glutamatergic synapses but controls DCC signaling at GABAergic synapses. The Adamtsl3-DCC signaling unit is further essential for activity-dependent adaptations at GABAergic synapses, involving DCC phosphorylation and Src kinase activation. These findings might be particularly relevant for schizophrenia because genetic variants in Adamtsl3 and DCC have been independently linked with schizophrenia in patients.

Insulin potentiates inhibitory synaptic currents between fast-spiking and pyramidal neurons in the rat insular cortex

Insulin plays roles in brain functions such as neural development and plasticity and is reported to be involved in dementia and depression. However, little information is available on the insulin-mediated modulation of electrophysiological activities, especially in the cerebral cortex. This study examined how insulin modulates the neural activities of inhibitory neurons and inhibitory postsynaptic currents (IPSCs) in rat insular cortex (IC; either sex) by multiple whole-cell patch-clamp recordings. We demonstrated that insulin increased the repetitive spike firing rate with a decrease in the threshold potential without changing the resting membrane potentials and input resistance of fast-spiking GABAergic neurons (FSNs). Next, we found a dose-dependent enhancement of unitary IPSCs (uIPSCs) by insulin in the connections from FSNs to pyramidal neurons (PNs). The insulin-induced enhancement of uIPSCs accompanied decreases in the paired-pulse ratio, suggesting that insulin increases GABA release from presynaptic terminals. The finding of miniature IPSC recordings of the increased frequency without changing the amplitude supports this hypothesis. Insulin had little effect on uIPSCs under the coapplication of S961, an insulin receptor antagonist, or lavendustin A, an inhibitor of tyrosine kinase. The PI3-K inhibitor wortmannin or the PKB/Akt inhibitors, deguelin and Akt inhibitor VIII, blocked the insulin-induced enhancement of uIPSCs. Intracellular application of Akt inhibitor VIII to presynaptic FSNs also blocked insulin-induced enhancement of uIPSCs. In contrast, uIPSCs were enhanced by insulin in combination with the MAPK inhibitor PD98059. These results suggest that insulin facilitates the inhibition of PNs by increases in FSN firing frequency and IPSCs from FSNs to PNs. (250 words).

The α1 and γ2 subunit-containing GABAA receptor-mediated inhibitory transmission in the anteroventral bed nucleus of stria terminalis is involved in the regulation of anxiety in rats with substantia nigra lesions

The anteroventral bed nucleus of the stria terminalis (avBNST) is widely acknowledged as a key brain structure that regulates negative emotional states, such as anxiety. At present, it is still unclear whether GABA_A receptor-mediated inhibitory transmission in the avBNST is involved in Parkinson's disease (PD)-related anxiety. In this study, unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (SNc) in rats induced anxiety-like behaviors, increased GABA synthesis and release, and upregulated expression of GABA_A receptor subunits in the avBNST, as well as decreased level of dopamine (DA) in the basolateral amygdala (BLA). In both sham and 6-OHDA rats, intra-avBNST injection of GABA_A receptor agonist muscimol induced the following changes: (i) anxiolytic-like responses, (ii) inhibition of the firing activity of GABAergic neurons in the avBNST, (iii) excitation of dopaminergic neurons in the ventral tegmental area (VTA) and serotonergic neurons in the dorsal raphe nucleus (DRN), and (iv) increase of DA and 5-HT release in the BLA, whereas antagonist bicuculline induced the opposite effects. Collectively, these findings suggest that degeneration of the nigrostriatal pathway enhances GABA_A receptor-mediated inhibitory transmission in the avBNST, which is involved in PD-related anxiety. Further, activation and blockade of avBNST GABA_A receptors affect the firing activity of VTA dopaminergic and DRN serotonergic neurons, and then change release of BLA DA and 5-HT, thereby regulating anxiety-like behaviors.

A neolignan from Connarus tuberosus as an allosteric GABAA receptor modulator at the neurosteroid binding site

In a screening of a small library of extracts from plants of the Amazonian and Cerrado biomes, a hexane extract of Connarus tuberosus roots was found to significantly potentiate the GABA induced fluorescence in a fluorescence (FLIPR) assay in CHO cells stably expressing the α₁β₂γ₂ subtype of human GABA_A receptors. With the aid of HPLC-based activity profiling the activity was linked to the neolignan connarin. In CHO cells the activity of connarin was not abolished by increasing concentrations of flumazenil, while the effect of diazepam was increased by increasing concentrations of connarin. The effect of connarin was abolished by pregnenolone sulfate (PREGS) in a concentration-dependent manner, and the effect of allopregnanolone was further increased by increasing concentrations of connarin. In a two-microelectrode voltage clamp assay with Xenopus laevis oocytes transiently expressing GABA_A receptors composed of human α₁β₂γ₂S and α1β2 subunits connarin potentiated the GABA-induced currents, with EC₅₀ values of 1.2 ± 0.3 μM (α₁β₂γ₂S) and 1.3 ± 0.4 μM (α₁β₂), and with a maximum enhancement of currents E_max of 1959 ± 70% (α₁β₂γ₂S) and 185 ± 48% (α₁β₂). The activation induced by connarin was abolished by increasing concentrations of PREGS.

Prolactin-Releasing Peptide Contributes to Stress-Related Mood Disorders and Inhibits Sleep/Mood Regulatory Melanin-Concentrating Hormone Neurons in Rats

Stress disorders impair sleep and quality of life; however, their pathomechanisms are unknown. Prolactin-releasing peptide (PrRP) is a stress mediator; we therefore hypothesized that PrRP may be involved in the development of stress disorders. PrRP is produced by the medullary A1/A2 noradrenaline (NA) cells, which transmit stress signals to forebrain centers, and by non-NA cells in the hypothalamic dorsomedial nucleus. We found in male rats that both PrRP and PrRP-NA cells innervate melanin-concentrating hormone (MCH) producing neurons in the dorsolateral hypothalamus (DLH). These cells serve as a key hub for regulating sleep and affective states. Ex vivo, PrRP hyperpolarized MCH neurons and further increased the hyperpolarization caused by NA. Following sleep deprivation, intracerebroventricular PrRP injection reduced the number of REM sleep-active MCH cells. PrRP expression in the dorsomedial nucleus was upregulated by sleep deprivation, while downregulated by REM sleep rebound. Both in learned helplessness paradigm and after peripheral inflammation, impaired coping with sustained stress was associated with (1) overactivation of PrRP cells, (2) PrRP protein and receptor depletion in the DLH, and (3) dysregulation of MCH expression. Exposure to stress in the PrRP-insensitive period led to increased passive coping with stress. Normal PrRP signaling, therefore, seems to protect animals against stress-related disorders. PrRP signaling in the DLH is an important component of the PrRP's action, which may be mediated by MCH neurons. Moreover, PrRP receptors were downregulated in the DLH of human suicidal victims. As stress-related mental disorders are the leading cause of suicide, our findings may have particular translational relevance.SIGNIFICANCE STATEMENT Treatment resistance to monoaminergic antidepressants is a major problem. Neuropeptides that modulate the central monoaminergic signaling are promising targets for developing alternative therapeutic strategies. We found that stress-responsive prolactin-releasing peptide (PrRP) cells innervated melanin-concentrating hormone (MCH) neurons that are crucial in the regulation of sleep and mood. PrRP inhibited MCH cell activity and enhanced the inhibitory effect evoked by noradrenaline, a classic monoamine, on MCH neurons. We observed that impaired PrRP signaling led to failure in coping with chronic/repeated stress and was associated with altered MCH expression. We found alterations of the PrRP system also in suicidal human subjects. PrRP dysfunction may underlie stress disorders, and fine-tuning MCH activity by PrRP may be an important part of the mechanism.

Novel variants in GABA(A) receptor subunits: A possible association with benzodiazepine resistance in patients with drug-resistant epilepsy

Benzodiazepines (BDZ) such as diazepam and lorazepam are popular as first-line treatment for acute seizures due to their rapid action and high efficacy. However, long-term usage of BDZ leads to benzodiazepine resistance, a phenomenon whose underlying mechanisms are still being investigated. One of the hypothesised mechanisms contributing to BDZ resistance is the presence of mutations in benzodiazepine-sensitive receptors. While a few genetic variants have been reported previously, knowledge of relevant pathogenic variants is still scarce. We used Sanger Sequencing to detect variants in the ligand-binding domain of BDZ-sensitive GABA_A receptor subunits α1-3 and 5 expressed in resected brain tissues of drug-resistant epilepsy (DRE) patients with a history of BDZ resistance and found two previously unreported predicted pathogenic frameshifting variants - NM_000807.4(GABRA2):c.367_368insG and NM_000810.4(GABRA5):c.410del - significantly enriched in these patients. The findings were further explored in resected DRE brain tissues through cellular electrophysiological experiments.

Anti-seizure mechanisms of midazolam and valproate at the β2(L51M) variant of the GABAA receptor

Genetic sequencing is identifying an expanding number of variants of GABAA receptors associated with human epilepsies. We identified a new de novo variant of the β2 subunit (β2L51M) of the inhibitory GABAA receptor associated with seizures. Our analysis determined the pathogenicity of the variant and the effects of anti-seizure medications. Our data demonstrates that the variant reduced cell surface trafficking and peak GABA-gated currents. Synaptic currents mediated by variant-containing receptors decayed faster than wild-type and single receptor currents showed that the variant shortened the duration of receptor activity by decreasing receptor open times. We tested the effects of the anti-seizure medications, midazolam, carbamazepine and valproate and found that all three enhance variant receptor surface expression. Additionally, midazolam restored receptor function by increasing single receptor active periods and synaptic current decay times towards wild-type levels. By contrast, valproate increased synaptic peak currents, event frequency and promoted synaptic bursting. Our study identifies a new disease-causing variant to the GABAA receptor, profiles its pathogenic effects and demonstrates how anti-seizure drugs correct its functional deficits.

Quantitative interactome proteomics identifies a proteostasis network for GABAA receptors

Gamma-aminobutyric acid type A (GABAA) receptors are the primary inhibitory neurotransmitter-gated ion channels in the mammalian central nervous system. Maintenance of GABAA receptor protein homeostasis (proteostasis) in cells utilizing its interacting proteins is essential for the function of GABAA receptors. However, how the proteostasis network orchestrates GABAA receptor biogenesis in the endoplasmic reticulum is not well understood. Here, we employed a proteomics-based approach to systematically identify the interactomes of GABAA receptors. We carried out a quantitative immunoprecipitation-tandem mass spectrometry analysis utilizing stable isotope labeling by amino acids in cell culture. Furthermore, we performed comparative proteomics by using both WT α1 subunit and a misfolding-prone α1 subunit carrying the A322D variant as the bait proteins. We identified 125 interactors for WT α1-containing receptors, 105 proteins for α1(A322D)-containing receptors, and 54 overlapping proteins within these two interactomes. Our bioinformatics analysis identified potential GABAA receptor proteostasis network components, including chaperones, folding enzymes, trafficking factors, and degradation factors, and we assembled a model of their potential involvement in the cellular folding, degradation, and trafficking pathways for GABAA receptors. In addition, we verified endogenous interactions between α1 subunits and selected interactors by using coimmunoprecipitation in mouse brain homogenates. Moreover, we showed that TRIM21 (tripartite motif containing-21), an E3 ubiquitin ligase, positively regulated the degradation of misfolding-prone α1(A322D) subunits selectively. This study paves the way for understanding the molecular mechanisms as well as fine-tuning of GABAA receptor proteostasis to ameliorate related neurological diseases such as epilepsy.

Gamma-Aminobutyric Acid A Receptor Subunit Expression and Cellular Localization in the Human Parkinsonian Globus Pallidus

BACKGROUND

The gamma-aminobutyric acid A (GABA_A) receptor is an important mediator of cellular signaling in the globus pallidus and might be implicated in the pathophysiology of Parkinson disease (PD). The goal of the present study was to characterize GABA_A receptor subunit expression in the normal and parkinsonian human globus pallidus.

METHODS

Postmortem brain specimens were obtained from 8 patients with pathological evidence of PD at autopsy and from 4 control patients without such evidence. These tissues were exposed to primary antibodies directed against the α1 and α3 subunits of the GABA_A receptor and were visualized and quantified using fluorescence microscopy.

RESULTS

No differences were found in the pallidal neuronal density in the control versus PD tissues. Projection neurons strongly expressed the α1, α3, and β2 GABA_A receptor subunits. After normalizing the immunofluorescence intensities in the globus pallidus to those in the adjacent structures, no significant differences were found in GABA_A receptor subunit expression in the globus pallidus between the PD specimens and the control specimens.

CONCLUSIONS

Compensatory changes in GABA_A receptor α1 and α3 subunit expression in response to PD-related signaling abnormalities in the globus pallidus did not occur in our PD cohort.

Structural mechanisms of GABAA receptor autoimmune encephalitis

Autoantibodies targeting neuronal membrane proteins can cause encephalitis, seizures, and severe behavioral abnormalities. While antibodies for several neuronal targets have been identified, structural details on how they regulate function are unknown. Here we determined cryo-electron microscopy structures of antibodies derived from an encephalitis patient bound to the γ-aminobutyric acid type A (GABA_A) receptor. These antibodies induced severe encephalitis by directly inhibiting GABA_A function, resulting in nervous-system hyperexcitability. The structures reveal mechanisms of GABA_A inhibition and pathology. One antibody directly competes with a neurotransmitter and locks the receptor in a resting-like state. The second antibody targets the subunit interface involved in binding benzodiazepines and antagonizes diazepam potentiation. We identify key residues in these antibodies involved in specificity and affinity and confirm structure-based hypotheses for functional effects using electrophysiology. Together these studies define mechanisms of direct functional antagonism of neurotransmission underlying autoimmune encephalitis in a human patient.

Anti-neuropathic effect of 7,3'-dihydroxyflavone in paclitaxel induced peripheral neuropathy in mice involving GABAA, KATP channel and adenosine receptors

Peripheral neuropathy induced by chemotherapeutic agents is the most common dose-limiting adverse effect observed in patients during and after treatment of malignancies. Many flavones have been reported to ameliorate neuropathy of different origin in experimental animals and their possible mode of action explored. The present study aims to investigate 7,3'-dihydroxyflavone for its anti-neuropathic effect against paclitaxel induced peripheral neuropathy in mice by employing behavioural tests such as mechanical allodynia, cold allodynia and thermal hyperalgesia. The possible involvement of GABA_A, K_ATP channels and adenosine receptors in the anti-neuropathic effect of 7,3'-dihydroxyflavone was also studied by employing suitable interacting drugs. Treatment with 7,3'-dihydroxyflavone (50, 100 or 200 mg/kg, s.c) significantly and dose-dependently reduced the paw withdrawal response score in both mechanical and cold allodynia and also increased the tail flick response time in thermal hyperalgesia due to paclitaxel-induced neuropathy. Pre-treatment with glibenclamide (10 mg/kg, i.p), caffeine (50 mg/kg, i.p) or bicuculline (2 mg/kg, i.p) significantly reversed the anti-neuropathic effect of 7,3'-dihydroxyflavone in behavioral tests. In conclusion, the present investigation identified 7,3'-dihydroxyflavone as a potential candidate with anti-neuropathic effect against paclitaxel induced peripheral neuropathy involving K_ATP channels, adenosine and GABA_A receptors.

Axial chirality and affinity at the GABAA receptor of triazolobenzodiazepines

Triazolobenzodiazepines substituted with a methyl group at the C1- and C10-positions and chloro group at C2' of pendant-phenyl were prepared and their physicochemical properties were investigated. The atropisomers of 1,10-disubstituted triazolobenzodiazepines, 1d and 1f, were isolated as (a¹R, a²S) and (a¹S, a²R) isomers. Their absolute configurations were determined on the basis of CD spectra in comparison with those of stereochemically defined 9-methyl-1,4-benzodiazepin-2-ones. Examination of the affinity at the human GABA_A receptors revealed that each (a¹R, a²S) isomer of 1d and 1f possessed higher activity than its antipode (a¹S, a²R) isomer. It was also found that 1a, which behaves achirally due to the rapid conformational change, had the highest GABA_A affinity, equal to that of triazolam. Considering that each eutomer of 1d and 1f is (a¹R, a²S), the conformation of 1a at the binding site of the GABA_A receptor is expected to be (a¹R, a²S).

Deficiency of Glycosylated α-Dystroglycan in Ventral Hippocampus Bridges the Destabilization of Gamma-Aminobutyric Acid Type A Receptors With the Depressive-like Behaviors of Male Mice

BACKGROUND

Depression is a common psychiatric disorder associated with defects in GABAergic (gamma-aminobutyric acidergic) neurotransmission. α-Dystroglycan (α-DG), a cell adhesion molecule known to be essential for skeletal muscle integrity, is also present at inhibitory synapses in the central nervous system and forms a structural element in certain synapses. However, the role of α-DG in the regulation of depressive-like behaviors remains largely unknown.

METHODS

Depressive-like behaviors were induced by chronic social defeat stress in adult male mice. Surface protein was extracted by a biotin kit, and the expression of protein was detected by Western blotting. Intrahippocampal microinjection of the lentivirus or adeno-associated virus or agrin intervention was carried out using a stereotaxic instrument and followed by behavioral tests. Miniature inhibitory postsynaptic currents were recorded by whole-cell patch-clamp techniques.

RESULTS

The expression of α-DG and glycosylated α-DG in the ventral hippocampus was significantly lower in chronic social defeat stress-susceptible male mice than in control mice, accompanied by a decreased surface expression of GABA_A receptor γ2 subunit and reduced GABAergic neurotransmission. RNA interference-mediated knockdown of Dag1 increased the susceptibility of mice to subthreshold stress. Both in vivo administration of agrin and overexpression of like-acetylglucosaminyltransferase ameliorated depressive-like behaviors and restored the decrease in surface expression of GABA_A receptor γ2 subunit and the amplitude of miniature inhibitory postsynaptic currents in chronic social defeat stress-exposed mice.

CONCLUSIONS

Our findings demonstrate that glycosylated α-DG plays a role in the pathophysiological process of depressive-like behaviors by regulating the surface expression of GABA_A receptor γ2 subunit and GABAergic neurotransmission in the ventral hippocampus.

Midazolam exhibits antitumour and anti-inflammatory effects in a mouse model of pancreatic ductal adenocarcinoma

BACKGROUND

Anaesthesia and perioperative management contribute to long-term outcomes of patients with cancer, including pancreatic ductal adenocarcinoma. We assessed the antitumour, anti-inflammatory, and analgesic effects of midazolam on LSL-Kras^G12D/+;Trp53^flox/flox;Pdx-1^cre/+ transgenic mice with pancreatic ductal adenocarcinoma.

METHODS

Six-week-old transgenic mice were administered midazolam 30 mg kg^-1 day^-1 p.o. (n=13); midazolam 30 mg kg^-1 day^-1 with 1-(2-chlorophenyl)-N-methyl-N(1-methylpropyl)-3-isoquinoline carboxamide (PK11195) 3 mg kg^-1 day^-1 i.p., a peripheral benzodiazepine receptor antagonist (n=10); or vehicle (water; n=14) until the humane endpoint. Cancer-associated pain was evaluated using hunching score and mouse grimace scale. Tumour stage and immuno-inflammatory status were determined histopathologically. Anti-proliferative and apoptotic potentials of midazolam were investigated using mouse pancreatic ductal adenocarcinoma cell lines.

RESULTS

Midazolam significantly inhibited tumour size and proliferative index of Ki-67 and cyclins in pancreatic ductal adenocarcinoma, which was blocked by administration of PK11195. Local myeloperoxidase⁺ tumour-associated neutrophils, arginase-1⁺ M2-like tumour-associated macrophages, and CD11b⁺Ly-6G⁺ polymorphonuclear myeloid-derived suppressor cells were reduced by midazolam, which was antagonised by administration of PK11195. Hunching and mouse grimace scale were improved by midazolam, whereas the scores increased with midazolam+PK11195 treatment. Plasma pro-inflammatory cytokines, such as interleukin-6 and CC chemokine ligand (CCL)2, CCL3, and CCL5, were reduced by midazolam, whereas these cytokines increased with PK11195. Midazolam inhibited pancreatic ductal adenocarcinoma proliferation through downregulation of cyclins and cyclin-dependent kinases and induced apoptosis in vitro.

CONCLUSIONS

These results suggest that midazolam inhibits pancreatic ductal adenocarcinoma proliferation and local infiltration of tumour-associated neutrophils, tumour-associated macrophages, and polymorphonuclear myeloid-derived suppressor cells, thereby inhibiting pancreatic ductal adenocarcinoma progression.

Why are Drosophila larvae more sensitive to avermectin than adults?

The insects have different physiological and morphological characteristics in various developmental stages. The difference in the characteristics may be related to the different sensitivity of insects to insecticides. In avermectin resistant strain screening assay, we found that the Drosophila larvae displayed a higher sensitivity to the insecticidal effect of avermectin, compared with adults. In this study, we found that the Drosophila larvae have relatively thicker chitin layer, faster avermectin metabolism and lower P-glycoprotein (P-gp) level, when compared with the adults. Besides, the expression levels of the molecular targets of avermectin, glutamate-gated chloride channel and γ-aminobutyric acid (GABA)-gated chloride channel, are lower in the larval stage than the adult. These results suggested that lower P-gp level in the body especially in brain may be the major reason for the higher sensitivity of Drosophila larvae to the insecticide. In summary, these results shed new light on the concept that different developmental stages of insects display different sensitivity to the same insecticide, which also provided a physiological explanation of the relevant mechanism of the difference of sensitivity of insect at its larval and adult stages to insecticide.

From benzodiazepines to fatty acids and beyond: revisiting the role of ACBP/DBI

Four decades ago Costa and colleagues identified a small, secreted polypeptide in the brain that can displace the benzodiazepine diazepam from the GABA_A receptor, and was thus termed diazepam binding inhibitor (DBI). Shortly after, an identical polypeptide was identified in liver by its ability to induce termination of fatty acid synthesis, and was named acyl-CoA binding protein (ACBP). Since then, ACBP/DBI has been studied in parallel without a clear and integrated understanding of its dual roles. The first genetic loss-of-function models have revived the field, allowing targeted approaches to better understand the physiological roles of ACBP/DBI in vivo. We discuss the roles of ACBP/DBI in central and tissue-specific functions in mammals, with an emphasis on metabolism and mechanisms of action.

GABAA receptor agonist muscimol rescues inhibitory microcircuit defects in the olfactory bulb and improves olfactory function in APP/PS1 transgenic mice

Olfactory damage develops at the early stages of Alzheimer's disease (AD). While amyloid-β (Aβ) oligomers are shown to impair inhibitory circuits in the olfactory bulb (OB), its underlying mechanisms remain unclear. Here, we investigated the olfactory dysfunction due to impaired inhibitory transmission to mitral cells (MCs) of the OB in APP/PS1 mice. Using electrophysiological studies, we found that MCs exhibited increased spontaneous firing rates as early as 3 months, much before development of Aβ deposits in the brain. Furthermore, the frequencies but not amplitudes of MC inhibitory postsynaptic currents decreased markedly, suggesting that presynaptic GABA release is impaired while postsynaptic GABA_A receptor responses remain intact. Notably, muscimol, a GABA_A receptor agonist, improved odor identification and discrimination behaviors in APP/PS1 mice, reduced MC basal firing activity, and rescued inhibitory circuits along with reducing the Aβ burden in the OB. Our study links the presynaptic deficits of GABAergic transmission to olfactory dysfunction and subsequent AD development and implicates the therapeutic potential of maintaining local inhibitory microcircuits against early AD progression.

Sustained treatment with an α5 GABA A receptor negative allosteric modulator delays excitatory circuit development while maintaining GABAergic neurotransmission

α5 subunit GABA type A receptor (GABA_AR) preferring negative allosteric modulators (NAMs) are cognitive enhancers with antidepressant-like effects. α5-NAM success in treating mouse models of neurodevelopmental disorders with excessive inhibition have led to Phase 2 clinical trials for Down syndrome. Despite in vivo efficacy, no study has examined the effects of continued α5-NAM treatment on inhibitory and excitatory synapse plasticity to identify mechanisms of action. Here we used L-655,708, an imidazobenzodiazepine that acts as a highly selective but weak α5-NAM, to investigate the impact of sustained treatment on hippocampal neuron synapse and dendrite development. We show that 2-day pharmacological reduction of α5-GABA_AR signaling from DIV12-14, when GABA_ARs contribute to depolarization, delays dendritic spine maturation and the NMDA receptor (NMDAR) GluN2B/GluN2A developmental shift. In contrast, α5-NAM treatment from DIV19-21, when hyperpolarizing GABA_AR signaling predominates, enhances surface synaptic GluN2A while decreasing GluN2B. Despite changes in NMDAR subtype surface levels and localization, total levels of key excitatory synapse proteins were largely unchanged, and mEPSCs were unaltered. Importantly, 2-day α5-NAM treatment does not alter the total surface levels or distribution of α5-GABA_ARs, reduce the gephyrin inhibitory synaptic scaffold, or impair phasic or tonic inhibition. Furthermore, α5-NAM inhibition of the GABA_AR tonic current in mature neurons is maintained after 2-day α5-NAM treatment, suggesting reduced tolerance liability, in contrast to other clinically relevant GABA_AR-targeting drugs such as benzodiazepines. Together, these results show that α5-GABA_ARs contribute to dendritic spine maturation and excitatory synapse development via a NMDAR dependent mechanism without perturbing overall neuronal excitability.

Delta-containing GABAA receptors in pain management: Promising targets for novel analgesics

Communication between nerve cells depends on the balance between excitatory and inhibitory circuits. GABA, the major inhibitory neurotransmitter, regulates this balance and insufficient GABAergic activity is associated with numerous neuropathological disorders including pain. Of the various GABA_A receptor subtypes, the δ-containing receptors are particularly interesting drug targets in management of chronic pain. These receptors are pentameric ligand-gated ion channels composed of α, β and δ subunits and can be activated by ambient levels of GABA to generate tonic conductance. However, only a few ligands preferentially targeting δ-containing GABA_A receptors have so far been identified, limiting both pharmacological understanding and drug-discovery efforts, and more importantly, understanding of how they affect pain pathways. Here, we systemically review and discuss the known drugs and ligands with analgesic potential targeting δ-containing GABA_A receptors and further integrate the biochemical nature of the receptors with clinical perspectives in pain that might generate interest among researchers and clinical physicians to encourage analgesic discovery efforts leading to more efficient therapies.

GABAA receptor-mediated inhibition of Dahlgren cells electrical activity in the olive flounder, Paralichthys olivaceus

γ-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system. We investigated its potential role as a neurotransmitter in the neuroendocrine Dahlgren cell population of the caudal neurosecretory system (CNSS) of the flounder Paralichthys olivaceus. The application of GABA in vitro resulted in a decrease in electrical activity of Dahlgren cells, followed by an increase of the number of silent cells, together with a decreased firing frequency of all three activity patterns (tonic, phasic, bursting). GABA_A receptor agonist etomidate decreased Dahlgren cell firing activity, in a similar way to GABA. The response to GABA was blocked by the GABA_A receptor antagonist bicuculline. GABA_A receptor gamma2 subunit (Gabrg2) and chloride channel (Clcn2) mRNA expression were significantly upregulated in the CNSS after GABA superfusion. These data suggest that GABA may modulate CNSS activity in vivo mediated by GABA_A receptors.

Gastrodin alleviates seizure severity and neuronal excitotoxicities in the rat lithium-pilocarpine model of temporal lobe epilepsy via enhancing GABAergic transmission

ETHNOPHARMACOLOGICAL RELEVANCE

Temporal lobe epilepsy remains one of the most drug-resistant focal epilepsy, leading to enormous healthcare burden. Among traditional herb medicine, some ingredients have the potential to treat seizure and alleviate the neuronal excitoxicity. The dried rhizome of Gastrodia elata Blume has been used to treat convulsive disorder, dizziness, dementia and migraine in eastern Asia.

AIM OF THE STUDY

To determine whether gastrodin, an active ingredient of Gastrodia elata Blume, can reduce lithium-pilocarpine induced seizure severity and neuronal excitotoxicity and explore the underlying mechanism.

MATERIALS AND METHODS

We divided the Sprague-Dawley rats into an experimental group (gastrodin group) and a control group (Dimethyl sulfoxide, vehicle group) and performed the behavioral analysis and electroencephalography to determine the effect of gastrodin on the seizure severity induced by lithium-pilocarpine injection. Nissl-stained histopathology elucidated the degree of rat hippocampal neuronal damage as markers of acute and subacute neuronal excitotoxicity. Besides, the Western blotting of dissected hippocampus was carried out to demonstrate the protein expression involving GABAergic transmission and metabolic pathway.

RESULTS

Gastrodin reduced the acute seizure severity in lithium-pilocarpine-induced seizure model. In electroencephalography recording, gastrodin exerted inhibitory action on epileptiform discharge. Compared with control group, gastrodin exhibited neuroprotective effect against seizure related hippocampal neuronal damage at acute and subacute stages. The Western blotting showed that gastrodin reversed the degradation of GABAA receptor after pilocarpine-induced seizures.

CONCLUSIONS

In the experimental seizure model, gastrodin showed anti-seizure and neuroprotective abilities. Enhancing the expression of GABAA receptor plays an important role in its antiepileptic mechanism. The results offer a new insight of developing new antiepileptic drugs from traditional Chinese medicine.

Activity- and sleep-dependent regulation of tonic inhibition by Shisa7

Tonic inhibition mediated by extrasynaptic γ-aminobutyric acid type A receptors (GABAARs) critically regulates neuronal excitability and brain function. However, the mechanisms regulating tonic inhibition remain poorly understood. Here, we report that Shisa7 is critical for tonic inhibition regulation in hippocampal neurons. In juvenile Shisa7 knockout (KO) mice, α5-GABAAR-mediated tonic currents are significantly reduced. Mechanistically, Shisa7 is crucial for α5-GABAAR exocytosis. Additionally, Shisa7 regulation of tonic inhibition requires protein kinase A (PKA) that phosphorylates Shisa7 serine 405 (S405). Importantly, tonic inhibition undergoes activity-dependent regulation, and Shisa7 is required for homeostatic potentiation of tonic inhibition. Interestingly, in young adult Shisa7 KOs, basal tonic inhibition in hippocampal neurons is unaltered, largely due to the diminished α5-GABAAR component of tonic inhibition. However, at this stage, tonic inhibition oscillates during the daily sleep/wake cycle, a process requiring Shisa7. Together, these data demonstrate that intricate signaling mechanisms regulate tonic inhibition at different developmental stages and reveal a molecular link between sleep and tonic inhibition.

Nelumbo nucifera promotes non-rapid eye movement sleep by regulating GABAergic receptors in rat model

ETHNOPHARMACOLOGICAL RELEVANCE

Nelumbo nucifera are used in folk medicine for anti-depressant, anti-convulsant, neuroprotective, and many other purposes.

AIM OF THE STUDY

The present work evaluated the sleep potentiating effects of water extract from lotus seed in rat, and the neuropharmacological mechanisms underlying these effects.

MATERIALS AND METHODS

Pentobarbital-induced sleep test and electroencephalogram (EEG) analysis were applied to investigate sleep latency, duration, total sleeping time and sleep quality of Lotus extract. In addition, real-time PCR and HPLC analysis were applied to analyze the signaling pathway.

RESULTS

We found that the amounts of the possible active compounds GABA (2.33 mg/g) and L-tryptophan (2.00 mg/g) were higher than quinidine (0.55 mg/g) and neferine (0.16 mg/g) in lotus seed extract. High dose (160 mg/kg) administration of lotus extract led to a tendency towards decreased sleep latency time and an increase in sleep duration time compared to the control group in a pentobarbital-induced sleep model (p < 0.05). After high dose administration, total sleep and NREM were significantly increased compared to control, while wake time and REM were significantly decreased. Lotus extract-treated rats showed significantly reduced wake time and increased sleep time in a caffeine-induced model of arousal. The transcription level of GABAA receptor, GABAB receptor, and serotonin receptor tended to increase with dose, and lotus extract showed a strong dose-dependent binding capacity to the GABAA receptor.

CONCLUSION

The above results strongly suggest that GABA contained in lotus seed extract acts as a sleep potentiating compound, and that sleep-potentiating activity involves GABAA receptor binding.

Flavonoid compounds isolated from Tibetan herbs, binding to GABAA receptor with anxiolytic property

ETHNOPHARMACOLOGICAL RELEVANCE

Previously, the phytochemical constituents of Biebersteinia heterostemon Maxim (BHM) and Arenaria kansuensis Maxim (AKM) were studied and the evaluation of anxiolytic effect based on their extracts was also investigated. The two traditional Tibetan herbs, BHM and AKM, have been widely used in Qinghai-Tibet Plateau for cardiopulmonary disorders and neuropsychiatric diseases. The anxiolytic activities of a number of agents mediated by α2/3-containing GABAA receptors (GABAARs) have been demonstrated through the genetic and pharmacological studies. Flavonoids, such as flavones and flavanols, are a class of ligands that act at GABAARs and exhibit anxiolytic effects in vivo. Here, the flavonoids are the predominant constituents isolated from BHM and AKM. And our purpose is to investigate structure-activity relationships of the flavonoid compounds with binding to BZ-S of GABAAR complexes, and to search for anxiolytic constituents that lack undesirable-effects such as sedation and myorelaxation.

MATERIALS AND METHODS

The flavonoid constituents were separated and purified through the repeatedly silica gel or/and C18 column chromatography. The affinities of the compounds for BZ-S of GABAARs were detected by the radioreceptor binding assay with bovine cerebellum membranes, in which the different recombinant subunits-containing GABAARs were expressed in HEK 293T cells. The behavior tests, including elevated plus maze, locomotor activity, holeboard, rotarod and horizontal wire, were used to determine and evaluate the anxiolytic, sedative, and myorelaxant effects of these flavonoids.

RESULTS

Eleven total flavonoid compounds were obtained from the Tibetan herbs (BHM and AKM). The flavones with 6-and/or 8-OMe possessed the most potent binding affinity to GABAARs, which were based on the result of structure-activity relationships analysis. Demethoxysudachitin (DMS, Ki = 0.59 μM), a flavone that binds to recombinant α1-3/5 subunit-containing GABAARs, was isolated from BHM, and exhibited high anxiolytic activity, without inducing sedation and myorelaxation. Moreover, the anxiolytic effect of DMS was antagonized by flumazenil, suggesting that a mode of action was mediated via the BZ-S of GABAARs.

CONCLUSIONS

This present study indicated that the flavones, especially DMS, are novel GABAAR ligands and therapeutic potential candidates for anxiety.

GABA in the medial prefrontal cortex regulates anxiety-like behavior during the postpartum period

The postpartum period is commonly accompanied by emotional changes, which for many new mothers includes a reduction in anxiety. Previous research in rodents has shown that the postpartum attenuation in anxiety is dependent on offspring contact and has further implicated enhanced GABAergic neurotransmission as an underlying mechanism. However, the specific brain regions where GABA acts to regulate the offspring-induced reduction in postpartum anxiety requires further investigation. Here, we test the hypothesis that offspring interactions suppress anxiety-like behavior in postpartum female rats via GABA signaling in the medial prefrontal cortex (mPFC). Our results show a postpartum reduction in anxiety-like behavior, an effect which was abolished by localized infusion of the GABAA receptor antagonist bicuculline in the mPFC. We also show that activation of GABAA receptors in the mPFC by the agonist muscimol was effective in restoring anxiolyisis in mothers separated from their pups. Lastly, we show that heightened anxiety-like behavior in pup-separated mothers was accompanied by a lower number and percentage of activated GABAergic neurons within the mPFC. Together, these results suggest that mother-offspring interactions reduce anxiety-like behavior in postpartum females via GABAA neurotransmission in the mPFC and in doing so provide insight into mechanisms that may become dysfunctional in mothers who experience high postpartum anxiety.

Dissociation of endocrine responses to the Trier Social Stress Test in Virtual Reality (VR-TSST) by the benzodiazepine alprazolam and the translocator protein 18 kDa (TSPO) ligand etifoxine

BACKGROUND

Activity of the two major stress systems, the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-adrenal-medullary (SAM) axis, has already been shown to be modulated by different compounds that bind to the central benzodiazepine receptor. Less is known about ligands that modulate the peripheral benzodiazepine receptor - meanwhile known as the translocator protein 18 kDa (TSPO) - which constitute promising candidates in the search of novel anxiolytics. To close this gap, the present study compared the effects of the benzodiazepine alprazolam and the TSPO ligand etifoxine on responses of the HPA and SAM axes to the Trier Social Stress Test, a standardized paradigm to induce acute psychosocial stress in humans, performed in Virtual Reality (VR-TSST).

METHODS

Sixty healthy males, aged between 18 and 55 years, were randomly assigned to receive either a daily dose of 1.5 mg alprazolam, 150 mg etifoxine, or placebo over five days. On the last day of intake, they were exposed to the VR-TSST. We assessed changes of salivary cortisol, allopregnanolone, (nor-) epinephrine in serum, TSPO expression in platelets as well as heart rate (HR), skin conductance level (SCL) and self-reports in response to the stress task. Repeated measures ANOVAs were conducted to examine treatment effects on these stress response variables during the course of VR-TSST.

RESULTS

The response of salivary cortisol to the VR-TSST was significantly blunted in participants pre-treated with alprazolam but was not affected by etifoxine. While levels of allopregnanolone, epinephrine and norepinephrine increased in response to stress, TSPO expression decreased. None of those endocrine stress markers was affected by the active treatments, whereas TSPO expression increased after etifoxine administration over all study days. There were no effects of the two anxiolytics on HR, SCL or any self-report measurement.

CONCLUSION

The current study confirmed the attenuating effects of benzodiazepines on stress-induced HPA axis activity but did not reveal a comparable effect of the TSPO ligand etifoxine. The long-term consequences of a pharmacologically blunted response of the HPA axis to an acute stressor should be further elucidated. Due to the missing effects of etifoxine on stress-related parameters in our sample of healthy subjects, it might be concluded that the therapeutic effects of this TSPO ligand are restricted to stronger or pathological stress responses, respectively.

Regulation of GABAARs by Transmembrane Accessory Proteins

The vast majority of fast inhibitory transmission in the brain is mediated by GABA acting on GABAA receptors (GABAARs), which provides inhibitory balance to excitatory drive and controls neuronal output. GABAARs are also effectively targeted by clinically important drugs for treatment in a number of neurological disorders. It has long been hypothesized that function and pharmacology of GABAARs are determined by the channel pore-forming subunits. However, recent studies have provided new dimensions in studying GABAARs due to several transmembrane proteins that interact with GABAARs and modulate their trafficking and function. In this review, we summarize recent findings on these novel GABAAR transmembrane regulators and highlight a potential avenue to develop new GABAAR psychopharmacology by targeting these receptor-associated membrane proteins.

Scaling of Network Excitability and Inhibition may Contribute to the Septotemporal Differentiation of Sharp Waves-Ripples in Rat Hippocampus In Vitro

The functional organization of the hippocampus along its longitudinal (septotemporal or dorsoventral) axis is conspicuously heterogeneous. This functional diversification includes the activity of sharp wave and ripples (SPW-Rs), a complex intrinsic network pattern involved in memory consolidation. In this study, using transverse slices from the ventral and the dorsal rat hippocampus and recordings of CA1 field potentials we studied the development of SPW-Rs and possible changes in local network excitability and inhibition, during in vitro maintenance of the hippocampal tissue. We found that SPW-Rs develop gradually in terms of magnitude and rate of occurrence in the ventral hippocampus. On the contrary, neither the magnitude nor the rate of occurrence significantly changed in dorsal hippocampal slices during their in vitro maintenance. The development of SPW-Rs was accompanied by an increase in local network excitability more in the ventral than in the dorsal hippocampus, and an increase in local network inhibition in the ventral hippocampus only. Furthermore, the amplitude of SPWs positively correlated with the level of maximum excitation of the local neuronal network in both segments of the hippocampus, and the local network excitability and inhibition in the ventral but not the dorsal hippocampus. Blockade of α5 subunit-containing GABA_A receptor by L-655,708 significantly reduced the rate of occurrence of SPWs and enhanced the probability of their generation in the form of clusters in the ventral hippocampus without affecting activity in the dorsal hippocampus. The present evidence suggests that a dynamic upregulation of excitation and inhibition in the local neuronal network may significantly contribute to the generation of SPW-Rs, particularly in the ventral hippocampus.

The botanical eurycomanone is a potent growth regulator of the diamondback moth

Eurycomanone is a quassinoid compound that is derived from Eurycoma longifolia, and it is often used as an indicator to evaluate the active ingredients of Eurycoma longifolia. However, Eurycomanone has rarely been reported to have biological activity toward pests. In this study, we evaluated the antifeedant activity of eurycomanone against the diamondback moth(Plutella xylostella), with a non-selective AFC₅₀(the concentration that corresponds to 50% antifeedant action) value and selective AFC₅₀ of 17.5 mg/L and 14.2 mg/L, respectively, which were 2.1-fold (36.9 mg/L) and 2-fold (28.5 mg/L) lower than that of azadirachtin, respectively. In addition, eurycomanone was used to treat the roots of Brassica chinensis L. at a concentration of 100 µg/g for 72 h. The antifeedant index was found to reach 93% by tracking the leaves. After feeding with 20 µg/g eurycomanone, no pupae or eclosion were observed. To explore this mechanism, we used scanning electron microscopy to discover that eurycomanone could prevent the development of taste receptors on the maxillary palp of diamondback moth larvae. Additional electrophysiological measurements showed that eurycomanone exhibited excitatory action to the central taste neurons of diamondback moth and significantly inhibited the GABA_A receptor current. Eurycomanone exhibited significant activity as an antifeedant, inhibited growth and excelled at systemic absorption.

Resveratrol noncompetitively inhibits glycine receptor-mediated currents in neurons of rat central auditory neurons

Resveratrol, a naturally occurring stilbene found in red wine, is known to modulate the activity of several types of ion channels and membrane receptors, including Ca²⁺, K⁺, and Na⁺ ion channels. However, little is known about the effects of resveratrol on some important receptors, such as glycine receptors and GABA_A receptors, in the central nervous system (CNS). In the present study, the effects of resveratrol on glycine receptor or GABA_A receptor-mediated currents in cultured rat inferior colliculus (IC) and auditory cortex (AC) neurons were studied using whole-cell voltage-clamp recordings. Resveratrol itself did not evoke any currents in IC neurons but it reversibly decreased the amplitude of glycine-induced current (I_Gly) in a concentration-dependent manner. Resveratrol did not change the reversal potential of I_Gly but it shifted the concentration-response relationship to the right without changing the Hill coefficient and with decreasing the maximum response of I_Gly. Interestingly, resveratrol inhibited the amplitude of I_Gly but not that of GABA-induced current (I_GABA) in AC neurons. More importantly, resveratrol inhibited GlyR-mediated but not GABA_AR-mediated inhibitory postsynaptic currents in IC neurons using brain slice recordings. Together, these results demonstrate that resveratrol noncompetitively inhibits I_Gly in auditory neurons by decreasing the affinity of glycine to its receptor. These findings suggest that the native glycine receptors but not GABA_A receptors in central neurons are targets of resveratrol during clinical administrations.

Extrasynaptic δ-subunit containing GABAA receptors

γ-Aminobutyric acid type A receptors (GABA_ARs) are GABA gated heteropentameric chloride channels responsible for the adult brain's primary inhibition. In specific brain cells, such as in the hippocampus, one of the subtypes of GABA_ARs, the δ subunit containing GABA_ARs (δ-GABA_ARs), is predominantly expressed and located in extrasynaptic or perisynaptic positions. δ-GABA_ARs mediate a slow constant inhibitory current called tonic inhibition. While δ-GABA_ARs and tonic inhibition is critical for the excitability of single neurons, accumulating data suggest that the function of δ-GABA_ARs are broader and includes an integrative role in the network oscillations. While these open new horizons on the neurobiology of δ-GABA_ARs, the complexity continues to challenge the analysis of GABA_ARs and their subtypes. This review will summarize the current knowledge of molecular, cellular and physiological characteristics of δ-GABA_ARs during health and disease.

Inhibitory role of taurine in the caudal neurosecretory Dahlgren cells of the olive flounder, Paralichthys olivaceus

Taurine plays role in neural development and physiological functions such as endocrine regulation in the central nervous system (CNS), and it is one of the most abundant free amino acid there. We investigated its potential effect as a neurotransmitter in the group of neuroendocrine Dahlgren cells at flounder Paralichthys olivaceus caudal neurosecretory system (CNSS). The application of taurine in vitro led to a reduction in electrical activity of Dahlgren cells, followed by a rise in the number of silent cells, at the same time the frequency of all three activity patterns (tonic, phasic, bursting) in Dahlgren cells was reduced. Both strychnine (a glycine receptor antagonist) and bicuculline (a GABA_A receptor antagonist) can block the response to taurine separately. Transcriptome sequencing analysis showed the existence of glycine receptor (GlyR) and GABA_A receptor (GABA_AR) in the flounder CNSS, and the GlyR, GABA_AR, and Cl^- channel mRNA expression were significantly raised after taurine superfusion according to quantitative RT-PCR results. These data indicate that taurine may mediate Dahlgren cell population of CNSS activity in vivo through GlyR and GABA_AR, thereby, regulating stress-response.

Coordinated downregulation of KCC2 and GABAA receptor contributes to inhibitory dysfunction during seizure induction

The GABAA receptor (GABAAR) is the main inhibitory receptor in the adult mammalian brain. GABAAR function is dependent on its expression, distribution, and the chloride (Cl-) transmembrane gradient, which is determined by the potassium-chloride cotransporter 2 (KCC2) in the adult brain. KCC2 and GABAAR are downregulated in an activity-dependent manner during seizure induction. Functionally, KCC2 and GABAAR are closely related membrane proteins which modulate GABAergic inhibition. However, it remains unclear how their downregulation during seizure induction is coordinated. This study aimed to assess this interaction. Our results revealed that KCC2 and GABAAR were simultaneously downregulated in both in vivo and in vitro seizure models induced by the convulsant cyclothazide (CTZ), which was at least partly due to structural coupling in hippocampal neuronal membranes. Immunohistochemistry revealed colocalization of gephyrin with KCC2 and co-immunoprecipitation exhibited a direct coupling between GABAAR α1-subunit and KCC2 protein in hippocampal cell membranes. KCC2 specific short hairpin RNA (KCC2-shRNA) was employed to specifically reduce the expression of KCC2 in cultured hippocampal neurons. This resulted in a significant reduction in KCC2-independent GABAergic miniature inhibitory post-synaptic current (mIPSC) amplitude in shKCC2-transfected neurons. Further, pre-treatment with furosemide, a KCC2 inhibitor, during CTZ stimulation followed by washout significantly prevented convulsant stimulation-induced membrane KCC2 downregulation and significantly attenuated GABAAR downregulation concomitant with recovery of suppressed KCC2-independent GABAergic mIPSC amplitude. Our results suggest that the coordinated downregulation of KCC2 and GABAAR during seizure induction exerts a strong functional impact on GABAAR, highlighting an important regulatory mechanism in epilepsy.

A novel fluorescence probe based on specific recognition of GABAA receptor for imaging cell membrane

Long and real time imaging of cell membrane is very important for better understanding of cell performances in physiological and pathological processes. Nowadays, fluorescence probe analysis has become an indispensable tool for monitoring cell membrane. Herein, a novel fluorescent probe based on specific recognition of GABA_A receptor was developed for imaging cell membrane. The probe synthesized in this work has been successfully applied to image different kinds of cell membrane with some advantages over the reported probes. Moreover, the probe also showed good superiority in the preliminary screening GABA_A drugs.

Anxiolytic properties of Cymbopogon citratus (DC.) stapf extract, essential oil and its constituents in zebrafish (Danio rerio)

ETHNOPHARMACOLOGICAL RELEVANCE

Cymbopogon citratus (DC.) Stapf (Poaceae) leaves is often consumed as infusion in folk medicine due to its therapeutic properties. This plant is also rich in essential oil, which has several beneficial effects to the human health. It is known that medications commonly used to treat anxiety disorders cause undesirable side effects. Thus, it is important to evaluate the anxiolytic effects of natural products from plants, such as C. citratus, as an alternative therapy to treat these disorders.

OBJECTIVE

The aim of this study was to investigate the anxiolytic properties of C. citratus essential oil (EO), hydroalcoholic extract (E1), citral (CIT), geraniol (GER) and the mixture of these terpenoids, as well as its possible mechanism of action by using zebrafish as an anxiety model.

METHODS

Adult zebrafish were treated (by immersion) with C. citratus EO, E1, CIT and/or GER. The anxiolytic effects were analyzed by using the light-dark test. The mechanism involved in the anxiolytic effects was further investigated by the coadministration of flumazenil (FMZ), an antagonist of GABA_A receptors. The total polyphenols (phenolic and flavonoid compounds) content of E1 was determined by using spectrophotometric assays.

RESULTS

All analyzed samples showed a remarkable anxiolytic effect on zebrafish in the highest concentrations, as the animals showed a preference for the light side of the tank. Furthermore, the observed effect of EO, E1, CIT and GER was reversed by pre-treatment with FMZ, suggesting that GABAergic receptors were involved in the anxiolytic effect displayed by these samples. The association between CIT and GER in the lowest studied concentrations showed an interesting synergistic behavior on anxiolytic effect observed in light-dark test. Besides, it was demonstrated that E1 was constituted by phenolic and flavonoid compounds, which could be involved in the observed effect.

CONCLUSION

This work has proved that the low-cost zebrafish can be an adequate alternative as an animal model to evaluate the anxiolytic effect of C. citratus and its related compounds. Moreover, the involvement of GABA_A receptors could be responsible for the effect showed by the samples. These obtained results can potentially validate the ethnopharmacological use of C. citratus as a medicinal plant for the treatment of anxiety disorders in folk medicine.

Chrysin reduces anxiety-like behavior through actions on GABAA receptors during metestrus-diestrus in the rat

Low concentrations of ovarian hormones, among other factors, are associated with greater vulnerability to negative effects of environmental stressors and may trigger anxiety symptoms in females. The flavonoid chrysin (5,7-dihydroxyflavone) exerts anxiolytic-like effects in male and ovariectomized female rats, but it is unknown if chrysin could reduce anxiety-like behavior that naturally occurs through the ovarian cycle phases. The present study evaluated the effect of chrysin on anxiety-like behavior associated with the ovarian cycle phases in rats and the participation of γ-aminobutyric acid-A (GABA_A) receptors in these actions. The acute effects of chrysin (2 mg/kg) were investigated in female cycling Wistar rats in the elevated plus maze, locomotor activity test, and light/dark test. Diazepam (2 mg/kg) was used as reference anxiolytic drug. The participation of GABA_A receptor in the anxiolytic actions of chrysin was explored by pretreating the rats with the noncompetitive GABA_A chloride ion channel antagonist picrotoxin (1 mg/kg). Chrysin and diazepam prevented anxiety-like behavior that was associated with the metestrus-diestrus phase in both the elevated plus maze and light/dark test, and these effects were reversed by picrotoxin, with no significant changes in spontaneous locomotor activity. No significant motor effects of chrysin were detected in either behavioral test during proestrus-estrus or metestrus-diestrus phases, whereas diazepam produced motor hypoactivity in the locomotor activity test during proestrus-estrus phase. These results indicate that the flavonoid chrysin prevents anxiety-like behavior that naturally occurs during metestrus-diestrus in two unconditioned models that are used to evaluate anxiety-like behavior, and these effects were mediated by actions on GABA_A receptors.