extrasynaptic gaba-a receptor: nootropics and compounds | sci-wiki

3α-Androstanediol

3α-Androstanediol (5α-androstane-3α,17β-diol) is an endogenous neurosteroid formed as the terminal 3α-reduced metabolite of dihydrotestosterone (DHT, the most potent natural androgen). Despite its androgenic origin it binds the androgen receptor only weakly; its defining pharmacology is potent positive allosteric modulation of the GABA-A receptor (the brain's principal inhibitory chloride ion channel), which produces anxiolytic (anxiety-reducing) and anticonvulsant (seizure-suppressing) effects in animal models. It is widely regarded as the androgenic counterpart of allopregnanolone (the analogous progesterone-derived neurosteroid), and is proposed to mediate much of the influence that testosterone exerts on seizure threshold, anxiety, and mood in males. It additionally acts as a ligand of estrogen receptor beta (ERβ), which may underlie some of its cognitive and neuroprotective actions.

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Neurosteroid

Etiocholanolone

Etiocholanolone (3α-hydroxy-5β-androstan-17-one) is an endogenous androstane neurosteroid formed as a major hepatic metabolite of testosterone and androstenedione. It is the 5-beta epimer of androsterone and acts as a positive allosteric modulator (a compound that amplifies a receptor's response to its own natural ligand) of the GABA-A receptor (the brain's principal inhibitory chloride channel), where it enhances inhibitory neurotransmission and produces anticonvulsant effects in animal seizure models. Etiocholanolone is equally notable in classical human physiology as one of the first identified endogenous pyrogens; injection of the unconjugated steroid reliably produces fever by prompting leukocytes to release interleukin-1. It possesses negligible androgenic activity and circulates largely as biologically inactive glucuronide and sulfate conjugates.

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Anticonvulsant

Ganaxolone

Ganaxolone (research code CCD-1042; brand name Ztalmy) is a synthetic neuroactive steroid, specifically the 3-beta-methyl analog of the endogenous neurosteroid allopregnanolone (a metabolite of progesterone). It is a positive allosteric modulator (a molecule that amplifies a receptor's response to its natural activator) of the GABA-A receptor, the brain's principal inhibitory chloride channel, and it enhances both synaptic (phasic) and extrasynaptic (tonic) inhibition, with particularly strong activity at delta-subunit-containing receptors. In March 2022 it became the first medicine approved by the United States Food and Drug Administration for seizures associated with CDKL5 deficiency disorder (a rare genetic developmental and epileptic encephalopathy caused by mutations in the cyclin-dependent kinase-like 5 gene), and the first synthetic neurosteroid approved as an anticonvulsant. The defining 3-beta-methyl group makes ganaxolone orally bioavailable, metabolically stable, and non-hormonal, distinguishing it from its parent neurosteroid, which requires intravenous administration.

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Neurosteroid

SAGE-324

SAGE-324 (also designated BIIB124) is an investigational, orally bioavailable synthetic neuroactive steroid that acts as a positive allosteric modulator (a compound that amplifies a receptor's response to its natural signal) of GABA-A receptors (the brain's principal inhibitory chloride ion channels). Developed on the Sage Therapeutics neuroactive-steroid platform and co-developed with Biogen, it is a next-generation analog engineered for a long duration of action suitable for once-daily oral dosing, distinguishing it from the intravenous and short-acting neurosteroids that preceded it. Its lead clinical indication is essential tremor (a common movement disorder marked by rhythmic shaking of the hands and arms), where the randomized Phase 2 KINETIC trial met its primary endpoint; it has also been explored in the context of epilepsy. As a synthetic congener within the same chemical lineage as brexanolone and zuranolone, SAGE-324 represents an effort to translate the potent inhibitory pharmacology of endogenous neurosteroids into a chronically dosable oral therapeutic.

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Neurosteroid

THDOC

THDOC (3-alpha,5-alpha-tetrahydrodeoxycorticosterone) is an endogenous neurosteroid (a steroid that acts rapidly on neuronal membrane receptors rather than on classical nuclear hormone receptors) and the fully reduced 3-alpha,5-alpha metabolite of the adrenal steroid deoxycorticosterone. It is one of the most potent naturally occurring positive allosteric modulators (compounds that amplify a receptor's response to its own transmitter) of the GABA-A receptor, the brain's principal inhibitory chloride ion channel, where it enhances both fast synaptic and sustained extrasynaptic inhibition. Because its synthesis is driven by adrenocorticotropic hormone and by acute stress, THDOC is regarded as a stress-responsive inhibitory neurosteroid that provides negative feedback on the hypothalamic-pituitary-adrenal axis and transiently raises the seizure threshold. Alongside allopregnanolone, it is a prototypical member of the stress-derived GABAergic neurosteroid family.

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Antidepressant

Zuranolone

Zuranolone (development code SAGE-217; marketed as Zurzuvae) is an orally bioavailable synthetic analog of allopregnanolone (a naturally occurring neurosteroid derived from progesterone) that acts as a positive allosteric modulator (a compound that amplifies a receptor's response to its own transmitter) of the GABA-A receptor (the brain's principal inhibitory chloride channel). It was engineered by Sage Therapeutics from the same neurosteroid scaffold as the intravenous agent brexanolone, but with a modified 3-hydroxy pyrazole substitution that confers metabolic stability suitable for once-daily oral tablets rather than a continuous infusion. In August 2023 the United States Food and Drug Administration approved zuranolone for postpartum depression (a major depressive episode arising in the weeks after childbirth), making it the first oral drug indicated specifically for that condition. It is notable for producing an antidepressant response within days when given as a short, fixed two-week course, in contrast with the weeks-long onset of conventional monoamine antidepressants.

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