allopregnanolone: nootropics and compounds | sci-wiki

Pregnenolone

Pregnenolone (3β-hydroxypregn-5-en-20-one) is an endogenous neurosteroid and the first steroid synthesized from cholesterol, making it the obligatory precursor of every other steroid hormone, including progesterone, dehydroepiandrosterone (DHEA), cortisol, the sex steroids, and the neuroactive metabolites allopregnanolone and pregnenolone sulfate. Once regarded as a metabolically inert intermediate, it is now recognized as a signaling molecule in its own right, most notably as an endogenous negative allosteric modulator of the type-1 cannabinoid receptor (CB1, the principal brain receptor for THC) and as a ligand for microtubule-associated protein 2 (MAP2, a neuronal cytoskeletal scaffolding protein), through which it promotes microtubule assembly and neurite outgrowth. Synthesized de novo in the brain by neurons and glia, it is investigated as an adjunctive treatment for schizophrenia, mood disorders, and cannabis-related conditions, and is sold over the counter as a nootropic and hormonal supplement.

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Nootropic

Etifoxine

Etifoxine (brand name Stresam; also called etafenoxine) is a benzoxazine anxiolytic (an anti-anxiety drug from a chemical family unrelated to the benzodiazepines like Valium). It has been prescribed for the anxious, tense, physical side of stress mainly in France and a handful of other countries since the late 1970s, and it is not approved by the US FDA. What makes it interesting is a dual mechanism: it calms the brain both by directly tuning up GABA-A receptors and by nudging the body to make more of its own calming neurosteroids. In head-to-head trials it eased anxiety comparably to some benzodiazepines while causing less sedation, less memory and psychomotor impairment, and little rebound or dependence when stopped. It has also been explored beyond anxiety for helping injured peripheral nerves heal and for damping neuroinflammation (inflammation inside nervous tissue). The important caveat is safety: rare but serious liver injury and severe skin reactions have been reported.

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Hormone

Progesterone

Progesterone (P4; pregn-4-ene-3,20-dione) is an endogenous pregnane steroid hormone best known for its reproductive roles and is the prototypical neuroactive precursor within the neurosteroid system. Although the parent hormone signals principally through classical nuclear progesterone receptors and through membrane-associated receptors such as PGRMC1 and the mPR/PAQR family, most of its rapid effects on neuronal excitability arise only after sequential metabolism to 5-alpha-dihydroprogesterone and then to allopregnanolone, one of the most potent endogenous positive allosteric modulators of the GABA-A receptor (the brain's principal inhibitory chloride channel). Progesterone and its metabolites are synthesized within the nervous system itself, where they regulate myelination, neuronal survival, neuroinflammation, and inhibitory tone. It has been studied extensively as a neuroprotective agent, with strong preclinical support but negative large-scale human trials in acute traumatic brain injury.

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Neurosteroid

5α-Dihydroprogesterone

5α-Dihydroprogesterone (5α-DHP) is an endogenous neurosteroid and progestogen formed when the enzyme 5α-reductase reduces progesterone at the A-ring of the steroid nucleus, yielding 5α-pregnane-3,20-dione. It occupies the committed first step of the principal neurosteroid pathway, standing between progesterone and allopregnanolone (its 3α-hydroxylated metabolite and one of the most potent naturally occurring positive modulators of the GABA-A receptor, the brain's main inhibitory ion channel). Unlike allopregnanolone, 5α-DHP is itself a high-affinity agonist of the classical (nuclear) progesterone receptor, driving progesterone-responsive gene transcription; in horses it is a fully biopotent progesterone receptor agonist that sustains the second half of pregnancy after circulating progesterone becomes undetectable. It is synthesized in situ within neurons and glia of the central and peripheral nervous systems, where its production rises after nerve injury and falls under chronic stress.

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Nootropic

Emapunil

Emapunil (developmental codes XBD-173 and AC-5216) is an investigational anxiolytic that acts as a selective, high-affinity agonist of the 18-kDa translocator protein (TSPO), a mitochondrial cholesterol-transport protein once known as the peripheral or mitochondrial benzodiazepine receptor. Rather than binding the central benzodiazepine site itself, emapunil stimulates the brain's own synthesis of neurosteroids, most notably allopregnanolone, which then potentiate GABA-A receptors (the brain's main inhibitory chloride channels) to produce anxiolysis. In a landmark 2009 human panic-provocation study it reduced induced anxiety without the sedation, tolerance, or withdrawal that characterise benzodiazepines. It reached Phase 2 clinical evaluation before development was discontinued, and it remains a widely cited proof of concept for neurosteroid-based anxiolysis.

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