Long-term reductions in disease impact in patients with chronic migraine following preventive treatment with eptinezumab.

BACKGROUND: Eptinezumab is an anti-calcitonin gene-related peptide humanized monoclonal antibody approved for the preventive treatment of migraine in adults. The PREVAIL study demonstrated a favorable safety profile with sustained reductions in overall migraine-related burden in patients with chronic migraine (CM). This post hoc analysis aimed to examine item-level changes in the Migraine Disability Assessment (MIDAS) questionnaire over 2 years in participants with CM on eptinezumab treatment. METHODS: PREVAIL was an open-label, phase 3 trial that included 96 weeks of treatment where 128 adults received intravenous eptinezumab administered over 30 min every 12 weeks (wks) for up to 8 doses of 300 mg. MIDAS was administered at baseline, Wk12, and every 12wks thereafter. Two supplementary MIDAS items not included in the total score calculation assessed number of headache days in the past 3 months (MIDAS headache) and average headache pain severity (from 0 [none] to 10 [worst]). MIDAS total scores were summed from 5 items, each quantifying the number of days in the past 3 months with migraine-related disability. Items 1, 3, and 5 assessed absenteeism, namely how many days the patient missed work/school (Q1), household work (Q3), or family/social/leisure activities (Q5). Items 2 and 4 were measures of presenteeism, namely how many days the patient had reduced productivity in work/school (Q2) or household work (Q4). RESULTS: Mean MIDAS headache days decreased from 47.4 (baseline) to 17.1 (Wk12) and 16.3 (Wk104). The average headache pain severity score (0‒10) decreased from a mean of 7.3 (baseline) to 5.5 (Wk12) to 4.5 (Wk104). Mean MIDAS scores measuring absenteeism (Q1, 3, 5) changed from 9.7 days at baseline to 3.2 days (Wk12) and to 3.9 days (Wk104). Mean MIDAS scores measuring presenteeism (Q2, 4) at Wk12 decreased from 14.2 days at baseline to 5.2 days (Wk12, 104). Patients categorized with very severe MIDAS disability had a mean total MIDAS score of 84.8, with an average reduction of 56.7 days (Wk12), which was maintained at 32 days at Wk104. CONCLUSIONS: Long-term treatment with eptinezumab in patients with CM suggested sustained reductions in MIDAS-quantified disability, consistent with the sustained reductions in headache frequency and pain severity. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02985398 .

An ethnographic study of the effects of cognitive symptoms in patients with major depressive disorder: the IMPACT study.

BACKGROUND: The manifestation of major depressive disorder (MDD) may include cognitive symptoms that can precede the onset of MDD and persist beyond the resolution of acute depressive episodes. However, little is known about how cognitive symptoms are experienced by MDD patients and the people around them. METHODS: In this international (Brazil, Canada, China, France, and Germany) ethnographic study, we conducted semi-structured interviews and observations of remitted as well as symptomatic MDD patients (all patients self-reported being diagnosed by an HCP and self-reported being on an antidepressant) aged 18-60 years with self-reported cognitive symptoms (N = 34). In addition, participating depressed patients' close family or friends (N = 31) were interviewed. Separately recruited from depressed participants, work colleagues (N = 21) and healthcare providers (HCPs; N = 13) of depressed individuals were interviewed. RESULTS: Key insights were that: (1) patients were generally unaware that their cognitive symptoms were linked to their depression and, instead, attributed these symptoms to negative aspects of their person (e.g., age, separate disease, laziness, exhaustion); (2) cognitive symptoms in MDD appeared to negatively impact patients' social relationships and patients' ability to handle daily tasks at work and at home; (3) patients' cognitive symptoms also impacted relationships with family members and coworkers; (4) patients' cognitive symptoms increased stress and feelings of failure, which in turn seemed to worsen the cognitive symptoms, thereby creating a destructive cycle; and (5) although HCPs recommended that patients re-engage in everyday activities to help overcome their depression, cognitive symptoms seemed to impede such functional recovery. CONCLUSIONS: Taken together, these findings highlight a negative impact of patients' cognitive symptoms on their social functioning, work performance, and quality of life on the people close to them, and consequently on the degree of functional recovery after depression.

GABA site agonist gaboxadol induces addiction-predicting persistent changes in ventral tegmental area dopamine neurons but is not rewarding in mice or baboons.

Dopamine neurons of the ventral tegmental area (VTA) are involved at early phases of drug addiction. Even the first in vivo dose of various abused drugs induces glutamate receptor plasticity at the excitatory synapses of these neurons. Benzodiazepines that suppress the inhibitory GABAergic interneurons in the VTA via facilitation of synaptic GABA(A) receptors have induced neuroplasticity in dopamine neurons due to this disinhibitory mechanism. Here, we have tested a non-benzodiazepine direct GABA site agonist 4,5,6,7-tetrahydroisoxazolol[4,5-c]pyridine-3-ol (THIP) (also known as gaboxadol) that acts preferentially via high-affinity extrasynaptic GABA(A) receptors. A single sedative dose of THIP (6 mg/kg) to mice induced glutamate receptor plasticity for at least 6 d after administration. Increased AMPA/NMDA receptor current ratio and increased frequency, amplitude, and rectification of AMPA receptor responses suggested persistent targeting of GluA2-lacking AMPA receptors in excitatory synapses of VTA dopamine neurons ex vivo after THIP administration. This effect was abolished in GABA(A) receptor δ(-/-) mice, which have a loss of extrasynaptic GABA(A) receptors. In behavioral experiments, we found neither acute reinforcement in intravenous self-administration sessions with THIP at relevant doses using a yoked control paradigm in mice nor in baboons using a standard paradigm for assessing drug abuse liability; nor was any place preference found after conditioning sessions with various doses of THIP but rather a persistent aversion in 6 mg/kg THIP-conditioned mice. In summary, we found that activation of extrasynaptic δ-subunit-containing GABA(A) receptors leads to glutamate receptor plasticity of VTA dopamine neurons, but is not rewarding, and, instead, induces aversion.

The rapid recovery of 5-HT cell firing induced by the antidepressant vortioxetine involves 5-HT(3) receptor antagonism.

The therapeutic effect of current antidepressant drugs appears after several weeks of treatment and a significant number of patients do not respond to treatment. Here, we report the effects of the multi-modal antidepressant vortioxetine (Lu AA21004), a 5-HT(3) and 5-HT(7) receptor antagonist, 5-HT(1B) receptor partial agonist, 5-HT(1A) receptor agonist and 5-HT transporter (SERT) inhibitor, on rat 5-HT neurotransmission. Using in vivo electrophysiological recordings in the dorsal raphe nucleus of anaesthetized rats, we assessed the acute and subchronic effects of vortioxetine and/or the selective 5-HT(3) receptor agonist, SR57227 or the selective 5-HT(1A) receptor agonist flesinoxan, on 5-HT neuronal firing activity. Using ex-vivo autoradiography, we correlated SERT occupancy and presumed 5-HT firing activity. The selective serotonin reuptake inhibitor, fluoxetine, was used as comparator. Importantly, the recovery of 5-HT neuronal firing was achieved after 1 d with vortioxetine and 14 d with fluoxetine. SR57227 delayed this recovery. In contrast, vortioxetine failed to alter the reducing action of 3 d treatment of flesinoxan. Acute dosing of vortioxetine inhibited neuronal firing activity more potently than fluoxetine. SR57227 prevented the suppressant effect of vortioxetine, but not of fluoxetine. In contrast, flesinoxan failed to modify the suppressant effect of vortioxetine acutely administered. Differently to fluoxetine, vortioxetine suppressed neuronal firing without saturating occupancy at the SERT. Vortioxetine produced a markedly faster recovery of 5-HT neuronal firing than fluoxetine. This is at least partly due to 5-HT(3) receptor antagonism of vortioxetine in association with its reduced SERT occupancy.

Multi-omics data integration methods and their applications in psychiatric disorders.

To study mental illness and health, in the past researchers have often broken down their complexity into individual subsystems (e.g., genomics, transcriptomics, proteomics, clinical data) and explored the components independently. Technological advancements and decreasing costs of high throughput sequencing has led to an unprecedented increase in data generation. Furthermore, over the years it has become increasingly clear that these subsystems do not act in isolation but instead interact with each other to drive mental illness and health. Consequently, individual subsystems are now analysed jointly to promote a holistic understanding of the underlying biological complexity of health and disease. Complementing the increasing data availability, current research is geared towards developing novel methods that can efficiently combine the information rich multi-omics data to discover biologically meaningful biomarkers for diagnosis, treatment, and prognosis. However, clinical translation of the research is still challenging. In this review, we summarise conventional and state-of-the-art statistical and machine learning approaches for discovery of biomarker, diagnosis, as well as outcome and treatment response prediction through integrating multi-omics and clinical data. In addition, we describe the role of biological model systems and in silico multi-omics model designs in clinical translation of psychiatric research from bench to bedside. Finally, we discuss the current challenges and explore the application of multi-omics integration in future psychiatric research. The review provides a structured overview and latest updates in the field of multi-omics in psychiatry.

Combining escitalopram with gaboxadol provides no additional benefit in the treatment of patients with severe major depressive disorder.

The aim of this proof-of-concept study was to compare the efficacy of escitalopram (20 mg/d) in combination with fixed doses of gaboxadol to escitalopram (20 mg) in the treatment of patients with severe major depressive disorder (MDD). Adult patients were randomized to 8 wk of double-blind treatment with fixed doses of placebo (n=71), escitalopram (20 mg, n=140), escitalopram (20 mg)+gaboxadol (5 mg) (n=139), or escitalopram (20 mg)+gaboxadol (10 mg) (n=140). The pre-defined primary analysis of efficacy was an analysis of covariance (ANCOVA) of change from baseline to endpoint (week 8) in Montgomery-Åsberg Depression Rating Scale (MADRS) total score using last observation carried forward (LOCF). There was no statistically significant difference in the mean change from baseline in MADRS total score between the 20 mg escitalopram+10 mg gaboxadol group and the 20 mg escitalopram group [difference=-0.45 MADRS points (95% CI -2.5 to 1.6, p=0.6619, full analysis set (FAS), LOCF, ANCOVA)] at week 8. The mean treatment differences to placebo at week 8 were -5.6 (95% CI -8.0 to -3.1, p<0.0001) (20 mg escitalopram), -5.1 (95% CI -7.5 to -2.7, p<0.0001) (20 mg escitalopram+5 mg gaboxadol), and -6.0 (95% CI -8.4 to -3.6, p<0.0001) (20 mg escitalopram+10 mg gaboxadol). The most common adverse events reported in the active treatment groups for which the incidence was higher than that in the placebo group, comprised nausea, anxiety and insomnia. There were no clinically relevant efficacy differences between a combination of escitalopram and gaboxadol compared to escitalopram alone in the treatment of severe MDD. All active treatment groups were superior in efficacy to placebo and were well tolerated.

Selective GABA transporter inhibitors tiagabine and EF1502 exhibit mechanistic differences in their ability to modulate the ataxia and anticonvulsant action of the extrasynaptic GABA(A) receptor agonist gaboxadol.

Modulation of the extracellular levels of GABA via inhibition of the synaptic GABA transporter GAT1 by the clinically effective and selective GAT1 inhibitor tiagabine [(R)-N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]nipecotic acid; Gabitril] has proven to be an effective treatment strategy for focal seizures. Even though less is known about the therapeutic potential of other GABA transport inhibitors, previous investigations have demonstrated that N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]-3-hydroxy-4-(methylamino)-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol (EF1502), which, like tiagabine, is inactive on GABA(A) receptors, inhibits both GAT1 and the extrasynaptic GABA and betaine transporter BGT1, and exerts a synergistic anticonvulsant effect when tested in combination with tiagabine. In the present study, the anticonvulsant activity and motor impairment associated with systemic administration of gaboxadol (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol), which, at the doses used in this study (i.e., 1-5 mg/kg) selectively activates extrasynaptic α4-containing GABA(A) receptors, was determined alone and in combination with either tiagabine or EF1502 using Frings audiogenic seizure-susceptible and CF1 mice. EF1502, when administered in combination with gaboxadol, resulted in reduced anticonvulsant efficacy and Rotarod impairment associated with gaboxadol. In contrast, tiagabine, when administered in combination with gaboxadol, did not modify the anticonvulsant action of gaboxadol or reverse its Rotarod impairment. Taken together, these results highlight the mechanistic differences between tiagabine and EF1502 and support a functional role for BGT1 and extrasynaptic GABA(A) receptors.

Patient Expectations and Experiences of Antidepressant Therapy for Major Depressive Disorder: A Qualitative Study.

PURPOSE: This qualitative study explored patient perceptions of the most burdensome symptoms of major depressive disorder (MDD), the impact of symptoms on patients' daily lives, and patient expectations and experiences regarding the timing of onset of antidepressant pharmacotherapy. PATIENTS AND METHODS: Data were collected through facilitated, patient focus-group sessions in the USA between May and June 2019. Participants were adults with confirmed MDD who reported a major depressive episode within the past 2 years, for which they had received pharmacologic treatment for ≥6 weeks. The semi-structured discussion focused on the key topics of bothersome symptoms of MDD, the impact of symptoms on quality of life, and the effects of antidepressant treatment. Interviews were audio-recorded; findings were summarized using a content-analysis approach. RESULTS: Five focus-group sessions were undertaken, involving a total of 29 patients (each attended one session; mean age, 43.4 years; 72.4% female). Mean time since confirmed diagnosis of MDD was 13.1 years. The most commonly prescribed antidepressants received were bupropion (41.4% of participants), escitalopram (34.5%), and sertraline (34.5%). The most frequently reported bothersome MDD symptoms were fatigue (mentioned by 58.6% of participants), lack of motivation/loss of interest (51.7%), anxiety/panic (44.8%), sadness (41.4%), and lack of concentration/brain fog (41.4%). Socialization, family life, and work were the areas in which quality of life was most impacted. Participants expressed dissatisfaction with their antidepressant treatment. Fast symptom resolution was mentioned as a priority (defined as <1 week by 38.5% of participants and ≤1 month by 65.4%). Most participants had not experienced fast relief from their symptoms with current or previous antidepressant medications. CONCLUSION: Results of this qualitative study suggest that fatigue, anhedonia, cognitive symptoms, and anxiety are some of the most bothersome symptoms for patients with MDD and highlight the importance of obtaining rapid relief from these symptoms in order to improve outcomes and patient satisfaction with antidepressant medication.

Distinct activities of GABA agonists at synaptic- and extrasynaptic-type GABAA receptors.

The activation characteristics of synaptic and extrasynaptic GABA(A) receptors are important for shaping the profile of phasic and tonic inhibition in the central nervous system, which will critically impact on the activity of neuronal networks. Here, we study in isolation the activity of three agonists, GABA, muscimol and 4,5,6,7-tetrahydoisoxazolo[5,4-c]pyridin-3(2H)-one (THIP), to further understand the activation profiles of alpha 1 beta 3 gamma 2, alpha 4 beta 3 gamma 2 and alpha 4 beta 3 delta receptors that typify synaptic- and extrasynaptic-type receptors expressed in the hippocampus and thalamus. The agonists display an order of potency that is invariant between the three receptors, which is reliant mostly on the agonist dissociation constant. At delta subunit-containing extrasynaptic-type GABA(A) receptors, both THIP and muscimol additionally exhibited, to different degrees, superagonist behaviour. By comparing whole-cell and single channel currents induced by the agonists, we provide a molecular explanation for their different activation profiles. For THIP at high concentrations, the unusual superagonist behaviour on alpha 4 beta 3 delta receptors is a consequence of its ability to increase the duration of longer channel openings and their frequency, resulting in longer burst durations. By contrast, for muscimol, moderate superagonist behaviour was caused by reduced desensitisation of the extrasynaptic-type receptors. The ability to specifically increase the efficacy of receptor activation, by selected exogenous agonists over that obtained with the natural transmitter, may prove to be of therapeutic benefit under circumstances when synaptic inhibition is compromised or dysfunctional.

Triton X-100 inhibits agonist-induced currents and suppresses benzodiazepine modulation of GABA(A) receptors in Xenopus oocytes.

Changes in lipid bilayer elastic properties have been proposed to underlie the modulation of voltage-gated Na(+) and L-type Ca(2+) channels and GABA(A) receptors by amphiphiles. The amphiphile Triton X-100 increases the elasticity of lipid bilayers at micromolar concentrations, assessed from its effects on gramicidin channel A appearance rate and lifetime in artificial lipid bilayers. In the present study, the pharmacological action of Triton-X 100 on GABA(A) receptors expressed in Xenopus laevis oocytes was examined. Triton-X 100 inhibited GABA(A) alpha(1)beta(3)gamma(2S) receptor currents in a noncompetitive, time- and voltage-dependent manner and increased the apparent rate and extent of desensitization at 10 muM, which is 30 fold below the critical micelle concentration. In addition, Triton X-100 induced picrotoxin-sensitive GABA(A) receptor currents and suppressed allosteric modulation by flunitrazepam at alpha(1)beta(3)gamma(2S) receptors. All effects were independent of the presence of a gamma(2S) subunit in the GABA(A) receptor complex. The present study suggests that Triton X-100 may stabilize open and desensitized states of the GABA(A) receptor through changes in lipid bilayer elasticity.

Alterations in cyclic alternating pattern associated with phase advanced sleep are differentially modulated by gaboxadol and zolpidem.

OBJECTIVE: to evaluate cyclic alternating pattern (CAP) in a phase advance model of transient insomnia and the effects of gaboxadol and zolpidem. DESIGN: a randomized, double-blind, cross-over study in which habitual sleep time was advanced by 4 h. SETTING: 6 sleep research laboratories in US PARTICIPANTS: 55 healthy subjects (18-57 y) INTERVENTIONS: Gaboxadol 15 mg (GBX), zolpidem 10 mg (ZOL), and placebo (PBO). MEASUREMENTS: routine polysomnographic (PSG) measures, CAP, spectral power density, and self-reported sleep measures RESULTS: The phase advance model of transient insomnia produced significant changes in CAP parameters. Both GBX and ZOL significantly and differentially modified CAP parameters in the direction of more stable sleep. GBX brought the CAP rate in stage 1 sleep and slow wave sleep (SWS) closer to baseline levels but did not significantly change the CAP rate in stage 2. ZOL reduced the CAP rate in stage 2 to near baseline levels, whereas the CAP rate in stage 1 and SWS was reduced substantially below baseline levels. The CAP parameter A1 index (associated with SWS and sleep continuity) showed the highest correlation with self-reported sleep quality, higher than any traditional PSG, spectral, or other self-reported measures. CONCLUSION: disruptions in CAP produced by phase advanced sleep were significantly and differentially modulated by gaboxadol and zolpidem. The relative independence of CAP parameters from other electrophysiological measures of sleep, their high sensitivity to sleep disruption, and their strong association with subjective sleep quality suggest that CAP variables may serve as valuable endpoints in future insomnia research.

Gaboxadol -- a different hypnotic profile with no tolerance to sleep EEG and sedative effects after repeated daily dosing.

Gaboxadol, a selective extra synaptic GABA(A) receptor agonist, has been in clinical development for the treatment of insomnia. Development of tolerance to therapeutic effects (e.g. hypnotic and anticonvulsant and sedative) and withdrawal symptoms (e.g. REM sleep rebound and reduced seizure threshold) upon treatment discontinuation is reported for GABA(A) receptor allosteric modulators acting via the benzodiazepine binding site, e.g. zolpidem and indiplon. We conducted a head to head comparison in rats of the hypnotic (sleep EEG after 21 daily doses and 24 and 48 h after the last dose) and seizure threshold modifying (bicuculline assay 24 h after 28 daily doses) effects of gaboxadol and benzodiazepine ligands. Furthermore, we investigated in further details a previously reported apparent rapid development of tolerance to gaboxadol's effects in a rat rotarod motor coordination assay and related this effect to CNS exposure levels and in vitro potency at extra synaptic GABA(A) receptors. Sleep EEG studies demonstrated lack of tolerance and withdrawal effects after 28 daily doses with gaboxadol, whereas zolpidem produced both tolerance and withdrawal effects under a similar dosing regimen. Daily dosing with gaboxadol, zolpidem or indiplon for 28 days and acute discontinuation of treatment left the threshold to bicuculline-induced seizures unchanged. The rapidly attenuated effect of repeated gaboxadol dosing was confirmed in the rotarod model. However, re-challenge of gaboxadol insensitive animals with gaboxadol produced a maximum response, ruling out that receptor desensitisation accounts for these effects. By comparing CNS exposure at rotarod responses and concentration response relation at cloned GABA(A) receptors expressed in Xenopus oocytes it appears that the decline in response in the rotarod model coincides with the steep part of the concentration response curve for gaboxadol at extra synaptic GABA(A) receptors. In conclusion, rat sleep EEG repeated dose studies of gaboxadol confirm a hypnotic-like profile and no withdrawal effects, whereas tolerance and withdrawal effects were shown with zolpidem. Withdrawal from gaboxadol, zolpidem and indiplon did not affect the seizure threshold to bicuculline. Gaboxadol's apparent rapid development of tolerance in the rotarod assay appears to be kinetically determined.

The multimodal antidepressant vortioxetine may facilitate pyramidal cell firing by inhibition of 5-HT3 receptor expressing interneurons: An in vitro study in rat hippocampus slices.

The multimodal antidepressant vortioxetine is thought to mediate its pharmacological effects via 5-HT1A receptor agonism, 5-HT1B receptor partial agonism, 5-HT1D, 5-HT3, 5-HT7 receptor antagonism and 5-HT transporter inhibition. Here we studied vortioxetine's functional effects across species (canine, mouse, rat, guinea pig and human) in cellular assays with heterologous expression of 5-HT3A receptors (in Xenopus oocytes and HEK-293 cells) and in mouse neuroblastoma N1E-115 cells with endogenous expression of 5-HT3A receptors. Furthermore, we studied the effects of vortioxetine on activity of CA1 Stratum Radiatum interneurons in rat hippocampus slices using current- and voltage-clamping methods. The patched neurons were subsequently filled with biocytin for confirmation of 5-HT3 receptor mRNA expression by in situ hybridization. Whereas, both vortioxetine and the 5-HT3 receptor antagonist ondansetron potently antagonized 5-HT-induced currents in the cellular assays, vortioxetine had a slower off-rate than ondansetron in oocytes expressing 5-HT3A receptors. Furthermore, vortioxetine's but not ondansetron's 5-HT3 receptor antagonistic potency varied considerably across species. Vortioxetine had the highest potency at rat and the lowest potency at guinea pig 5-HT3A receptors. Finally, in 5-HT3 receptor-expressing GABAergic interneurons from the CA1 stratum radiatum, vortioxetine and ondansetron blocked depolarizations induced by superfusion of either 5-HT or the 5-HT3 receptor agonist mCPBG. Taken together, these data add to a growing literature supporting the idea that vortioxetine may inhibit GABAergic neurotransmission in some brain regions via a 5-HT3 receptor antagonism-dependent mechanism and thereby disinhibit pyramidal neurons and enhance glutamatergic signaling.

Treating insomnia: Current and investigational pharmacological approaches.

Chronic insomnia affects a significant proportion of young adult and elderly populations. Treatment strategies should alleviate nighttime symptoms, the feeling of nonrestorative sleep, and impaired daytime function. Current pharmacological approaches focus primarily on GABA, the major inhibitory neurotransmitter in the central nervous system. Benzodiazepine receptor agonists (BzRA) have been a mainstay of pharmacotherapy; the classical benzodiazepines and non-benzodiazepines share a similar mode of action and allosterically enhance inhibitory chloride currents through the GABA(A) receptor, a ligand-gated protein comprising 5 subunits pseudosymmetrically arranged around a core anion channel. Variations in GABA(A) receptor subunit composition confer unique pharmacological, biophysical, and electrophysiological properties on each receptor subtype. Classical benzodiazepines bind non-selectively to GABA(A) receptors containing a gamma2 subunit, whereas non-benzodiazepine hypnotics bind with higher relative affinity to alpha1-containing receptors. The non-benzodiazepine compounds generally represent an improvement over benzodiazepines as a result of improved binding selectivity and pharmacokinetic profiles. However, the enduring potential for amnestic effects, next day residual sedation, and abuse and physical dependence, particularly at higher doses, underscores the need for new treatment strategies. Novel pharmacotherapies in development act on systems believed to be specifically involved in the regulation of the sleep-wake cycle. The recently approved melatonin receptor agonist, ramelteon, targets circadian mechanisms. Gaboxadol, an investigational treatment and a selective extrasynaptic GABA(A) receptor agonist (SEGA), targets GABA(A) receptors containing a delta subunit, which are located outside the synaptic junctions of thalamic and cortical neurons thought to play an important regulatory role in the onset, maintenance, and depth of the sleep process.

4-aryl-5-(4-piperidyl)-3-isoxazolol GABAA antagonists: synthesis, pharmacology, and structure-activity relationships.

A series of 4-aryl-5-(4-piperidyl)-3-isoxazolol GABAA antagonists have been synthesized and pharmacologically characterized. The meta-phenyl-substituted compounds 9k and 9m and the para-phenoxy-substituted compound 9l all display high affinities (Ki=10-70 nM) and antagonist potencies in the low nanomolar range (Ki=9-10 nM). These potencies are significantly higher than those of previously reported 4-PIOL antagonists and considerably higher than that of the standard GABAA antagonist SR 95531.

5-Substituted imidazole-4-acetic acid analogues: synthesis, modeling, and pharmacological characterization of a series of novel gamma-aminobutyric acid(C) receptor agonists.

A series of ring-substituted analogues of imidazole-4-acetic acid (IAA, 4), a partial agonist at both GABAA and GABAC receptors (GABA = gamma-aminobutyric acid), have been synthesized. The synthesized compounds 8a-l have been evaluated as ligands for the alpha1beta2gamma2S GABAA receptors and the rho1 GABAC receptors using the FLIPR membrane potential (FMP) assay and by electrophysiology techniques. None of the tested compounds displayed activity at the GABAA receptors at concentrations up to 1000 microM. However, the 5-Me, 5-Ph, 5-p-Me-Ph, and 5-p-F-Ph IAA analogues, 8a,c,f,g, displayed full agonist activities at the rho1 receptors in the FMP assay (EC50 in the range 22-420 microM). Ligand-protein docking identified the Thr129 in the alpha1 subunit and the corresponding Ser168 residue in rho1 as determinants of the selectivity displayed by the 5-substituted IAA analogues. The fact that GABA, 4, and 8a displayed decreased agonist potencies at a rho1Ser168Thr mutant compared to the WT rho1 receptor strongly supported this hypothesis. However, in contrast to GABA and 4, which exhibited increased agonist potencies at a alpha1(Thr129Ser)beta2gamma2 mutant compared to WT GABAA receptor, the data obtained for 8a at the WT and mutant receptors were nonconclusive.

A tetrazolyl-substituted subtype-selective AMPA receptor agonist.

Replacement of the methyl group of the AMPA receptor agonist 2-amino-3-[3-hydroxy-5-(2-methyl-2H-5-tetrazolyl)-4-isoxazolyl]propionic acid (2-Me-Tet-AMPA) with a benzyl group provided the first AMPA receptor agonist, compound 7, capable of discriminating GluR2-4 from GluR1 by its more than 10-fold preference for the former receptor subtypes. An X-ray crystallographic analysis of this new analogue in complex with the GluR2-S1S2J construct shows that accommodation of the benzyl group creates a previously unobserved pocket in the receptor, which may explain the remarkable pharmacological profile of compound 7.

Lack of generalisation between the GABAA receptor agonist, gaboxadol, and allosteric modulators of the benzodiazepine binding site in the rat drug discrimination procedure.

INTRODUCTION: The binding sites for gamma-aminobutyric acid (GABA) and GABA(A) receptor agonists are located differently from the binding sites for benzodiazepine receptor agonists. Furthermore, the major pharmacological effects of benzodiazepine receptor agonists and the GABA(A) receptor agonist gaboxadol (4,5,6,7-tetrahydrroisoxazolo(5,4-c)pyridin-3-ol, THIP) are mediated by different GABA(A) receptor subunit compositions; that is, gaboxadol may interact primarily with extra-synaptically located alpha(4)beta(2/3)delta-containing receptors and benzodiazepines with the synaptically located alpha(1)beta(2/3)gamma(2)-containing receptors. OBJECTIVES: The aim of the present study was to address if this different receptor subtype selectivity was reflected in vivo. MATERIALS AND METHODS: A two-lever liquid reinforced operant discrimination procedure was conducted. Three groups of rats were trained to discriminate gaboxadol, diazepam and zolpidem 5.5, 1.5 and 0.7 mg/kg i.p., respectively, from vehicle. RESULTS: Substitution tests showed that gaboxadol-trained animals failed to recognize diazepam (0.75-1.5 mg/kg), zolpidem (0.4-0.7 mg/kg), zopiclone (2.5 mg/kg), zaleplon (1.0-1.5 mg/kg) or indiplon (0.31 mg/kg). In contrast, all benzodiazepine receptor agonists, but not gaboxadol (4.5-5.5 mg/kg), generalised to the discriminative stimulus in diazepam- and zolpidem-trained animals. DISCUSSION: In agreement with these data, the competitive benzodiazepine receptor antagonist flumazenil (10 mg/kg s.c.) antagonised the discriminative stimulus of zolpidem but not of gaboxadol. Interaction tests showed no synergistic interaction of concomitant administration of gaboxadol and zolpidem or diazepam. CONCLUSION: Previous studies have shown that gaboxadol and benzodiazepines interact with different receptor populations, and the present study confirms that in vivo functional consequences of this receptor selectivity exist in the form of differential behavioural responses in rats.

Plasma and CNS concentrations of Gaboxadol in rats following subcutaneous administration.

Gaboxadol has been suggested to be a selective extrasynaptic GABA(A) receptor agonist. However, there is little information on Gaboxadol concentrations in the central nervous system (CNS) at therapeutically relevant doses. In order to investigate this, rats were injected subcutaneously with Gaboxadol and plasma and CNS concentrations were determined using the dynamic-no-net-flux and ultraslow microdialysis methods. Results using the 2 methods were similar and showed that Gaboxadol rapidly entered the brain and that peak CNS concentrations after 2.5, 5 and 10 mg/kg were in the range of 0.7 to 3 microM. Furthermore, a very short half-life (28 min) in both plasma and CNS was observed. It is concluded that concentrations of Gaboxadol in the CNS are in a range, which are likely to activate only extrasynaptic (nongamma subunit containing) GABA(A) receptors.

Gaboxadol--a new awakening in sleep.

Drugs that enhance synaptic gamma-aminobutyric acid (GABA)ergic neurotransmission are widely utilized in the clinical setting. Barbiturates and benzodiazepine receptor agonists, for example, both potentiate an inhibitory chloride conductance through GABA-gated channels, and thereby achieve their sedative-hypnotic effects. The primary locus of action of these agents, and indeed most neuroactive drugs, is the postsynaptic junction. By contrast, gaboxadol, a selective extrasynaptic GABA receptor agonist and late-stage investigational treatment for insomnia, acts on a unique delta-containing GABAA receptor subtype found exclusively outside of the synapse. Although the mechanistic details of extrasynaptic neurotransmission remain to be fully established, it is now clear that these receptors demonstrate unique pharmacological, biophysical and electrophysiological properties. Importantly, the delta-containing GABAA receptor subtype activated by gaboxadol is highly expressed in the thalamus, where it might behave as a 'gain control' (independently controlling the strength of signals) in the corticothalamic pathways that govern sleep-relevant neuronal oscillations. This unique mechanism has contributed to our increased understanding of sleep mechanisms, and targeting of this system offers potential advantages over existing insomnia treatments.