Positive Allosteric Modulators Of GABAA Receptors Research Articles

Antinociceptive effects of α2/α3-subtype selective GABAA receptor positive allosteric modulators KRM-II-81 and NS16085 in rats: behavioral specificity.

Recent studies suggest that amongst the GABAA receptor subtype heterogeneity, α2/α3 subunits of GABAA receptors mediate pain processing. Therefore, α2/α3-subtype selective GABAA receptor positive allosteric modulators (PAMs) may be candidate analgesics. Antinociceptive effects of α2/α3-subtype selective GABAA receptor PAMs have been reported, but the behavioral effects of these compounds have not been systematically evaluated. This study examined the behavioral effects of two α2/α3 subtype-selective GABAA receptor PAMs, KRM-II-81 and NS16085, in male rats. The antinociceptive effects of KRM-II-81 and NS16085 were examined using rat models of inflammatory (complete Freund's adjuvant) and neuropathic pain (chronic constriction injury). The effect of KRM-II-81 on affective pain was measured using the place escape/avoidance paradigm (PEAP). Rate-response of food-maintained operant responding, horizontal wire test, and the spontaneous alternation T-maze, were assessed to study the side-effect profiles of KRM-II-81 and NS16085. The benzodiazepine midazolam was used as a comparator in these studies. KRM-II-81 and NS16085 attenuated mechanical allodynia but not thermal hyperalgesia in both pain states, and their effects were attenuated by the benzodiazepine receptor antagonist flumazenil. KRM-II-81 attenuated affective pain-related behavior in the PEAP test. In the operant responding procedure and horizontal wire test, only midazolam produced significant effects at the dose that produced maximal antinociception. In the T-maze assay, only midazolam significantly decreased the percentage of alternation at an antinociceptive dose. Thus, KRM-II-81 and NS16085 but not midazolam selectively produced antinociceptive effects. Collectively, these data suggest that α2/α3-subtype selective GABAA PAMs could be a novel class of analgesics and warrant further investigation. Significance Statement This study demonstrates that α2/α3-subtype selective GABAA PAMs KRM-II-81 and NS16085 produce selective antinociceptive effects devoid of sedation, myorelaxation, cognitive impairment in two rat models of persistent pain. Unlikely classical benzodiazepines, this study supports the development of α2/α3-subtype selective GABAA PAMs as safe and novel analgesics for pain management.

Periodic and aperiodic changes to cortical EEG in response to pharmacological manipulation.

Cortical electroencephalograms (EEGs) may help understanding of neuropsychiatric illness and new treatment mechanisms. The aperiodic component (1/f) of EEG power spectra is often treated as noise, but recent studies suggest that changes to the aperiodic exponent of power spectra may reflect changes in excitation/inhibition balance, a concept linked to antidepressant effects, epilepsy, autism, and other clinical conditions. One confound of previous studies is behavioral state, because factors associated with behavioral state other than excitation/inhibition ratio may alter EEG parameters. Thus, to test the robustness of the aperiodic exponent as a predictor of excitation/inhibition ratio, we analyzed video-EEG during active exploration in mice of both sexes during various pharmacological manipulations with the fitting oscillations and one over f (FOOOF) algorithm. We found that GABAA receptor (GABAAR)-positive allosteric modulators increased the aperiodic exponent, consistent with the hypothesis that an increased exponent signals enhanced cortical inhibition, but other drugs (ketamine and GABAAR antagonists at subconvulsive doses) did not follow the prediction. To tilt excitation/inhibition ratio more selectively toward excitation, we suppressed the activity of parvalbumin-positive interneurons with Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). Contrary to our expectations, circuit disinhibition with the DREADD increased the aperiodic exponent. We conclude that the aperiodic exponent of EEG power spectra does not yield a universally reliable marker of cortical excitation/inhibition ratio.NEW & NOTEWORTHY Neuropsychiatric illness may be associated with altered excitation/inhibition balance. A single electroencephalogram (EEG) parameter, the aperiodic exponent of power spectra, may predict the ratio between excitation and inhibition. Here, we use cortical EEGs in mice to evaluate this hypothesis, using pharmacological manipulations of known mechanism. We show that the aperiodic exponent of EEG power spectra is not a reliable marker of excitation/inhibition ratio. Thus, alternative markers of this ratio must be sought.

Schisandrin B, a dual positive allosteric modulator of GABAA and glycine receptors, alleviates seizures in multiple mouse models.

Epilepsy is a prevalent and severe neurological disorder and approximately 30% of patients are resistant to existing medications. It is of utmost importance to develop alternative therapies to treat epilepsy. Schisandrin B (SchB) isa major bioactive constituent of Schisandra chinensis (Turcz.) Bailland has multiple neuroprotective effects, sedative and hypnotic activities.In this study, we investigated the antiseizure effect of SchB in various mouse models of seizure and explored the underlying mechanisms. Pentylenetetrazole (PTZ), strychnine (STR), and pilocarpine-induced mouse seizure models were established.We showed that injection ofSchB (10, 30, 60 mg/kg, i.p.) dose-dependentlydelayed the onset of generalized tonic-clonic seizures (GTCS), reduced the incidence of GTCS and mortality in PTZ and STR models. Meanwhile, injection ofSchB (30 mg/kg, i.p.) exhibited therapeutic potential in pilocarpine-induced status epilepticus model, which was considered as a drug-resistant model. In whole-cell recording from CHO/HEK-239 cells stably expressing recombinant human GABAA receptors (GABAARs) and glycine receptors (GlyRs) and cultured hippocampal neurons, co-application of SchB dose-dependently enhanced GABA or glycine-induced current with EC50 values at around 5 μM, and application of SchB (10 μM) alone did not activate the channels in the absence of GABA or glycine.Furthermore, SchB (10 μM) eliminated both PTZ-induced inhibition on GABA-induced current (IGABA) and strychnine (STR)-induced inhibition on glycine-induced current (Iglycine).Moreover, SchB(10 μM) efficiently rescued the impaired GABAARs associated with genetic epilepsies. In addition,the homologous mutants in both GlyRs-α1(S267Q) and GABAARs-α1(S297Q)β2(N289S)γ2L receptors by site-directed mutagenesis testsabolishedSchB-induced potentiation of IGABA and Iglycine. In conclusion, we have identified SchB as a natural positive allosteric modulator of GABAARs and GlyRs, supporting its potential as alternative therapies for epilepsy.

Structural insights into opposing actions of neurosteroids on GABAA receptors

γ-Aminobutyric acid type A (GABAA) receptors mediate fast inhibitory signaling in the brain and are targets of numerous drugs and endogenous neurosteroids. A subset of neurosteroids are GABAA receptor positive allosteric modulators; one of these, allopregnanolone, is the only drug approved specifically for treating postpartum depression. There is a consensus emerging from structural, physiological and photolabeling studies as to where positive modulators bind, but how they potentiate GABA activation remains unclear. Other neurosteroids are negative modulators of GABAA receptors, but their binding sites remain debated. Here we present structures of a synaptic GABAA receptor bound to allopregnanolone and two inhibitory sulfated neurosteroids. Allopregnanolone binds at the receptor-bilayer interface, in the consensus potentiator site. In contrast, inhibitory neurosteroids bind in the pore. MD simulations and electrophysiology support a mechanism by which allopregnanolone potentiates channel activity and suggest the dominant mechanism for sulfated neurosteroid inhibition is through pore block.

Sex-specific hypnotic effects of the neuroactive steroid (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile are mediated by peripheral metabolism into an active hypnotic steroid

BackgroundThe novel synthetic neuroactive steroid (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile (3β-OH) blocks T-type calcium channels but does not directly modulate neuronal γ-aminobutyric acid type A (GABAA) currents like other anaesthetic neurosteroids. As 3β-OH has sex-specific hypnotic effects in adult rats, we studied the mechanism contributing to sex differences in its effects. MethodsWe used a combination of behavioural loss of righting reflex, neuroendocrine, pharmacokinetic, in vitro patch-clamp electrophysiology, and in vivo electrophysiological approaches in wild-type mice and in genetic knockouts of the CaV3.1 T-type calcium channel isoform to study the mechanisms by which 3β-OH and its metabolite produces sex-specific hypnotic effects. ResultsAdult male mice were less sensitive to the hypnotic effects of 3β-OH compared with female mice, and these differences appeared during development. Adult males had higher 3β-OH brain concentrations despite being less sensitive to its hypnotic effects. Females metabolised 3β-OH into the active GABAA receptor positive allosteric modulator (3α,5β,17β)-3-hydroxyandrostane-17-carbonitrile (3α-OH) to a greater extent than males. The 3α-OH metabolite has T-channel blocking properties with sex-specific hypnotic and pharmacokinetic effects. Sex-dependent suppression of the cortical electroencephalogram is more pronounced with 3α-OH compared with 3β-OH. ConclusionsThe sex-specific differences in the hypnotic effect of 3β-OH in mice are attributable to differences in its peripheral metabolism into the more potent hypnotic metabolite 3α-OH.

The flavonoid kaempferol protects the fruit fly Drosophila melanogaster against the motor impairment produced by exposure to the insecticide fipronil.

Exposure to pesticides across species has been associated with cognitive and motor impairments. As the problem impacts ecosystem stability, food production and public health, it is urgent to develop multifactorial solutions, from regulatory legislation to pharmacological alternatives that ameliorate the impairments. Fipronil, a commonly used insecticide, acts as a GABAA receptor (GABAAR) antagonist and induces motor impairments in vertebrates and invertebrates. Here, we hypothesized that kaempferol, a secondary metabolite derived from plants, acting as an allosteric modulator of GABAARs, would protect against the negative effects induced by the administration of fipronil in adults of the fruit fly Drosophila melanogaster. We further evaluated our hypothesis via co-administration of flumazenil, a competitive antagonist on the GABAAR, and through in silico analyses. We administered kaempferol prophylactically at three concentrations (10, 30 and 50 µmol l-1) and evaluated its protective effects against motor impairments induced by fipronil. We then used a single dose of kaempferol (50 µmol l-1) to evaluate its protective effect while administering flumazenil. We found that oral administration of fipronil impaired motor control and walking ability. In contrast, kaempferol was innocuous and protected flies from developing the motor-impaired phenotype, whereas the co-administration of flumazenil counteracted these protective effects. These results are supported by the binding of the ligands with the receptor. Together, our results suggest that kaempferol exerts a protective effect against fipronil via positive allosteric modulation of GABAARs, probably within brain areas such as the central complex and the mushroom bodies. These findings further support current attempts to use metabolites derived from plants as protectors against impairments produced by pesticides.

Diffuse noxious inhibitory controls and conditioned pain modulation: a shared neurobiology within the descending pain inhibitory system?

Diffuse noxious inhibitory controls and conditioned pain modulation: a shared neurobiology within the descending pain inhibitory system?

Synthesis and evaluation of avermectin–imidazo[1,2-a]pyridine hybrids as potent GABAA receptor modulators

The γ-aminobutyric acid type A (GABAA) receptors are pentameric transmembrane protein complexes. They have attracted extensive attention from the scientific community due to their significant pharmacological potential. Here we report the first synthesis of avermectin–imidazo[1,2-a]pyridine hybrids promising as GABAA receptor positive allosteric modulators (PAMs). An efficient multi-step protocol was elaborated for the installation of the 6-methyl-2-(p-tolyl)imidazo[1,2-a]pyridine pendant to the Avermectin B1a and Ivermectin skeletons through a linker. A variety of linkers were used in order to study the effect of disturbances in the hybrid structure on the GABAA receptor affinity. In vitro experiments showed that the lead compounds exhibited high potency (IC50 = 207 and 359 nM) for binding at the benzodiazepine site of GABAA receptors. In silico studies suggest that the hybrids are able to bind at the Ivermectin binding site of the GABAA receptor. The functional properties of the highest-affinity hybrid (compound 15e) as GABAAR PAM were evaluated by patch-clamp electrophysiological recordings of GABA-mediated currents in rat cerebellar Purkinje neurons. The results obtained suggest that the potentiating effect of hybrid compound 15e is due to its interaction both with benzodiazepine- and Ivermectin-binding sites of GABAARs. Drug-induced behavioral responses in adult zebrafish for hybrids correlate with an alternative mode of action of avermectin and imidazo[1,2-a]pyridine pharmacophores. The investigation of avermectin–imidazo[1,2-a]pyridine hybrid molecules with activity as GABAA receptor modulators is important for the discovery of safe and effective drugs for the treatment of neurological disorders and pest control agents.

Clinical Efficacy of a 2-Week Treatment Course of Zuranolone for the Treatment of Major Depressive Disorder and Postpartum Depression: Outcomes From the Clinical Development Program

IntroductionAntidepressants that offer a rapid onset of action without requiring chronic use are greatly needed in both major depressive disorder (MDD) and postpartum depression (PPD). Zuranolone is an investigational, oral, neuroactive steroid and GABAA receptor positive allosteric modulator in clinical development as a 2-week treatment course for MDD and PPD.ObjectivesTo present the efficacy and safety of zuranolone vs placebo in Phase 2 and 3 trials.MethodsIn the studies presented (Table 1), improvements in depressive symptoms were assessed by least-squares mean (LSM) using a mixed-effects model for repeated measures on the change from baseline (CFB) at Day 15 in the 17-item Hamilton Rating Scale for Depression total score (HAMD-17; primary endpoint for all trials) and the Montgomery–Åsberg Depression Rating Scale (MADRS; secondary endpoint) following a 14-day treatment course of once-daily zuranolone.ResultsCompared with placebo, zuranolone treatment led to rapid improvements in depressive symptoms across clinical trials, with significant improvements (LSM treatment difference [SE] in CFB) in HAMD-17 and MADRS scores at Day 15 in 3 of the 4 trials (Table 2). Common treatment-emergent adverse events (≥5% in zuranolone treatment arms) were headache, somnolence, dizziness, nausea, sedation, diarrhea, upper respiratory tract infection, and fatigue (Table 3). No incidences of loss of consciousness or excessive sedation were observed.ConclusionsAcross the completed studies in the zuranolone clinical trial program, patients receiving zuranolone consistently experienced improvement in depressive symptoms following a 2-week treatment course. Treatment with zuranolone was generally well tolerated with a consistent safety and tolerability profile.DisclosureThe MDD-201B, MOUNTAIN, and ROBIN studies were sponsored by Sage Therapeutics, Inc; the WATERFALL study was sponsored by Sage Therapeutics, Inc, and Biogen. Medical writing and editorial support were provided by MediTech Media, Ltd, and funded by Biogen.

Antinociceptive effects of α2/α3‐selective GABAA receptor positive allosteric modulators on opioid‐induced hyperalgesia

Opioids have been increasingly prescribed to treat chronic pain since the 1980s, despite evidence that long‐term use of opioids may lead to tolerance and pain sensitization called opioid‐induced hyperalgesia (OIH). OIH has been demonstrated in both preclinical models and healthy human volunteers, but is understudied and there is need for novel analgesics capable of mitigating OIH. α2/α3‐selective GABAA receptor positive allosteric modulators (PAMs) act specifically at subunits of the GABAA receptor found to mediate analgesia, and have demonstrated antinociceptive effects in models of chronic inflammatory and neuropathic pain. However, the efficacy of these compounds at relieving opioid‐induced pain hypersensitivity have not yet been investigated. This study systematically examined the antinociceptive effects of α2/α3‐selective GABAA receptor PAMs alone and in combination with acetaminophen in an OIH rat model wherein repeated treatment with the opioid fentanyl induces mechanical hyperalgesia. The von Frey test was used to measure mechanical nociception. Duration of actions of α2/α3‐selective GABAA receptor PAMs (KRM‐II‐81, NS16085, HZ‐166) alone were studied, and combinations of KRM‐II‐81 and acetaminophen were also studied at fixed ratios (1:1, 1:3, 3:1). Dose‐addition analysis was used to assess the antinociceptive interactions between KRM‐II‐81 and acetaminophen. α2/α3‐selective GABAA receptor PAMs were able to fully reverse mechanical sensitivity caused by OIH. Furthermore, KRM‐II‐81/acetaminophen combinations produced additive to supra‐additive interactions depending on the drug mixture ratios. These findings support the idea that α2/α3‐selective GABAA receptor PAMs could serve as novel analgesics for treating OIH, and may interact favorably with other non‐opioid analgesics.

P387. PRAX-114, An Extrasynaptic-Preferring GABAA Receptor Positive Allosteric Modulator: A Phase 2 Trial Evaluating Multiple Dose Safety, Tolerability, and Preliminary Efficacy in Major Depressive Disorder

PRAX-114 is an extrasynaptic-preferring GABAA receptor positive allosteric modulator in development for treatment of major depressive disorder (MDD). Extrasynaptic preference was hypothesized to explain preclinical findings demonstrating >20-fold separation between antidepressant- and sedative-like doses in rodents, and the lack of dose-limiting sedation in a Phase 1 trial assessing PRAX-114 safety and tolerability in healthy participants. Here we report results from an open-label Phase 2 trial assessing safety, tolerability and preliminary efficacy in MDD.

Differential sleep/wake response and sex differences following acute suvorexant, MK-1064 and zolpidem administration in the rTg4510 mouse model of tauopathy.

Background and PurposeTransgenic mouse models of tauopathy display prominent sleep/wake disturbances which manifest primarily as a hyperarousal phenotype during the active phase, suggesting that tau pathology contributes to sleep/wake changes. However, no study has yet investigated the effect of sleep‐promoting compounds in these models. Such information has implications for the use of hypnotics as potential therapeutic tools in tauopathy‐related disorders.Experimental ApproachThis study examined polysomnographic recordings in 6‐6.5‐month‐old male and female rTg4510 mice following acute administration of suvorexant (50 mg·kg−1), MK‐1064 (30 mg·kg−1) or zolpidem (10 mg·kg−1), administered at the commencement of the active phase.Key ResultsSuvorexant, a dual OX receptor antagonist, promoted REM sleep in rTg4510 mice, without affecting wake or NREM sleep. MK‐1064, a selective OX2 receptor antagonist, reduced wake and increased NREM and total sleep time. MK‐1064 normalised the hyperarousal phenotype of male rTg4510 mice, whereas female rTg4510 mice exhibited a more transient response. Zolpidem, a GABAA receptor positive allosteric modulator, decreased wake and increased NREM sleep in both male and female rTg4510 mice. Of the three compounds, the OX2 receptor antagonist MK‐1064 promoted and normalised physiologically normal sleep, especially in male rTg4510 mice.Conclusions and ImplicationsOur findings indicate that hyperphosphorylated tau accumulation and associated hyperarousal does not significantly alter the responses of tauopathy mouse models to hypnotics. However, the sex differences observed in the sleep/wake response of rTg4510 mice to MK‐1064, but not suvorexant or zolpidem, raise questions about therapeutic implications for the use of OX2 receptor antagonists in human neurodegenerative disorders.

Evaluation of Insomnia Symptoms in a Double-Blind, Randomized, Placebo-Controlled Phase 3 Trial of Zuranolone in Postpartum Depression

Zuranolone is an investigational, oral neuroactive steroid GABAA receptor positive allosteric modulator with improvements in depressive and anxiety symptoms versus placebo from a Phase 3 (NCT02978326; ROBIN) trial in postpartum depression (PPD). This ROBIN trial post-hoc analysis evaluated insomnia symptoms, a common comorbidity in PPD.

PRAX-114 Produces Robust Increases in EEG Beta Frequency Power, a Translational Biomarker of GABA-A Receptor Modulation, Without Dose-Limiting Sedation

PRAX-114 is a GABA-A receptor positive allosteric modulator (GABAA-R-PAM) neuroactive steroid which achieves preferential potentiation of extrasynaptic GABAAR compared to synaptic GABAAR. GABAAR-PAMs cause increases in EEG β-frequency band power. The effects of PRAX-114 on quantitative EEG (qEEG) were measured in rodents and healthy human volunteers.

GABA-A Receptor Positive Allosteric Modulators as a Novel Approach to Treating Depression: A Review of Available Data

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P.305 The GABAA receptor positive allosteric modulator zuranolone in major depressive disorder: a double-blind, randomized, placebo-controlled phase 3 trial

In this study, an exergoeconomic analysis is performed on an integrated four-step thermochemical copper-chlorine cycle developed at the Ontario Tech. University through exergy, cost, energy, and mass (EXCEM) method. A thermodynamic model is first constructed in Aspen-plus (a process simulation software) to simulate and investigate the integrated cycle through exergy and energy analyses. The capital costs, thermodynamic loss rates, and the ratio of the thermodynamic loss rate to the capital cost of various system's components are also determined. Moreover, the average unit cost of hydrogen is evaluated and the influence of several system's parameters on the unit cost of hydrogen is analyzed. The results show that the cost of hydrogen is strongly dependent on the production capacity of the plant. Based on the analysis, our system generates hydrogen at an average unit cost of 5.54 $/kg with a plant capacity of 1619.3 kg/h considering both internal (operating and maintenance costs, etc.) and external (costs of various inputs, etc.) parameters.

Preclinical characterization of zuranolone (SAGE-217), a selective neuroactive steroid GABAA receptor positive allosteric modulator

Zuranolone (SAGE-217) is a novel, synthetic, clinical stage neuroactive steroid GABAA receptor positive allosteric modulator designed with the pharmacokinetic properties to support oral daily dosing. In vitro, zuranolone enhanced GABAA receptor current at nine unique human recombinant receptor subtypes, including representative receptors for both synaptic (γ subunit-containing) and extrasynaptic (δ subunit-containing) configurations. At a representative synaptic subunit configuration, α1β2γ2, zuranolone potentiated GABA currents synergistically with the benzodiazepine diazepam, consistent with the non-competitive activity and distinct binding sites of the two classes of compounds at synaptic receptors. In a brain slice preparation, zuranolone produced a sustained increase in GABA currents consistent with metabotropic trafficking of GABAA receptors to the cell surface. In vivo, zuranolone exhibited potent activity, indicating its ability to modulate GABAA receptors in the central nervous system after oral dosing by protecting against chemo-convulsant seizures in a mouse model and enhancing electroencephalogram β-frequency power in rats. Together, these data establish zuranolone as a potent and efficacious neuroactive steroid GABAA receptor positive allosteric modulator with drug-like properties and CNS exposure in preclinical models. Recent clinical data support the therapeutic promise of neuroactive steroid GABAA receptor positive modulators for treating mood disorders; brexanolone is the first therapeutic approved specifically for the treatment of postpartum depression. Zuranolone is currently under clinical investigation for the treatment of major depressive episodes in major depressive disorder, postpartum depression, and bipolar depression.

0535 Evaluation of Insomnia Symptoms in a Double-Blind, Randomized, Placebo-Controlled Phase 3 Trial of Sage-217 in Postpartum Depression

Abstract Introduction Postpartum depression (PPD) is a specifier of major depressive disorder (MDD) with peripartum onset. SAGE-217, an investigational, oral neuroactive steroid GABAA receptor positive allosteric modulator, demonstrated improvements in depressive and anxiety symptoms versus placebo in a Phase 3 trial in PPD (NCT02978326; ROBIN) and a pivotal trial in MDD (NCT03000530). In PPD and MDD, insomnia symptoms are key diagnostic features, comorbid sleep disorders are frequent, and insomnia is a common residual symptom. Here we conducted post-hoc analyses to assess insomnia symptoms in the ROBIN trial. Methods Women (n=151) ages 18-45, ≤6 months postpartum, with PPD (major depressive episode beginning in 3rd trimester or ≤4 weeks postpartum) and a Hamilton Rating Scale for Depression (HAM-D) total score ≥26, were randomized 1:1 to receive outpatient SAGE-217 30mg or placebo for two weeks, with 4 weeks follow-up. Change from baseline (CFB) in HAM-D score at Day 15 was the primary endpoint. Secondary endpoints included CFB in HAM-D at other time points and the Montgomery-Åsberg Depression Rating Scale (MADRS). Post-hoc analyses assessed HAM-D insomnia subscale (HAM-D-Ins) and MADRS individual insomnia item (MADRS-Ins) scores. HAM-D and MADRS measures were evaluated using a mixed-effects model for repeated measures. Safety and tolerability were assessed by adverse event (AE) reporting. Results SAGE-217 demonstrated statistically significant Day 15 CFB versus placebo in HAM-D (primary endpoint: -17.8 vs. -13.6, p=0.0028), MADRS (-22.1 vs. -17.6, p=0.0180), and associated insomnia sub-scales/items (difference SAGE-217 vs. placebo; HAM-D-Ins: -1.003, p=0.0038; MADRS-Ins: -0.773, p=0.0116). Significant CFB in insomnia sub-scales/items favoring SAGE-217 were observed by Day 3 (HAM-D-Ins: -0.841, p=0.0142; MADRS-Ins: -0.710, p=0.017) and at Day 45 (HAM-D-Ins: -0.730, p=0.0207; MADRS-Ins: -0.636, p=0.0221). Most common (≥5%) AEs were somnolence, headache, dizziness, upper respiratory tract infection, diarrhea, and sedation. Conclusion SAGE-217 demonstrated improvements in depression symptoms, including insomnia symptoms, and was generally well tolerated. Support This study was sponsored by Sage Therapeutics, Inc.

GABAA Receptor Subtypes and the Reinforcing Effects of Benzodiazepines in Remifentanil-Experienced Rhesus Monkeys

BackgroundOpioid-use disorder is associated with a high degree of co-abuse with benzodiazepines. While the mechanisms underlying the co-abuse of opioids and benzodiazepines remain unknown, α1 subunit-containing GABAA receptors may play a critical role in the reinforcing effects of benzodiazepine-type compounds, depending on whether the monkeys have a history of benzodiazepine or stimulant self-administration. The present study extended our prior research by comparing the reinforcing effects of a compound lacking activity at α1 subunit-containing GABAA receptors with the reinforcing effects of non-selective GABAA receptor positive allosteric modulators in monkeys with a history of opioid self-administration. MethodsThe reinforcing effects of L-838,417 (partial intrinsic efficacy at α2, α3, and α5 subunit-containing GABAA receptors, but no efficacy at α1 subunit-containing GABAA receptors, i.e., “α1-sparing compound”) were compared with those of the non-selective GABAA receptor partial modulator MRK-696, and non-selective GABAA receptor full modulators, triazolam and lorazepam, in rhesus monkeys (n = 3) experienced in remifentanil self-administration under a progressive-ratio schedule of intravenous drug injection. ResultsNeither the partial modulator nor the α1-sparing compound were self-administered above vehicle levels. The full modulators triazolam and lorazepam were self-administered significantly above vehicle levels, albeit at lower levels than remifentanil. ConclusionsOur findings suggest that relatively high efficacy at one or more GABAA receptor subtypes is required for a compound to have reinforcing effects in monkeys with a history of remifentanil self-administration, in contrast to monkeys with benzodiazepine or stimulant self-administration histories.

The involvement of GABAergic system in the antidepressant-like effect of agmatine.

Considering the involvement of GABAergic system in the action of the fast-acting antidepressant ketamine, and that agmatine may exert an antidepressant-like effect through mechanisms similar to ketamine, the purpose of the present study was to evaluate the involvement of GABAA and GABAB receptors in the antidepressant-like effect of agmatine. The administration of muscimol (0.1 mg/kg, i.p., GABAA receptor agonist) or diazepam (0.05 mg/kg, p.o., GABAA receptor positive allosteric modulator) at doses that caused no effect in the tail suspension test (TST) combined with a subeffective dose of agmatine (0.0001 mg/kg, p.o.) produced a synergistic antidepressant-like effect in the TST. In another set of experiments, the administration of baclofen (1 mg/kg, i.p., GABAB receptor agonist) abolished the reduction of immobility time in the TST elicited by agmatine (0.1 mg/kg, p.o., active dose). In another cohort of animals, treatment with NMDA (0.1 pmol/site, i.c.v.) prevented the antidepressant-like effect of the combined administration of agmatine and muscimol as well as ketamine and muscimol in the TST. Results suggest that the effect of agmatine in the TST may involve an activation of GABAA receptors dependent on NMDA receptor inhibition, similar to ketamine, as well as modulation of GABAB receptors.