Muscimol (also known as agarin or pantherine) is one of the principal psychoactive constituents of Amanita muscaria and related species of mushroom. Muscimol is a potent, selective agonist for the GABAA receptors and displays sedative-hypnotic, depressant and hallucinogenic psychoactivity. This colorless or white solid is classified as an isoxazole.
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||114.104 g·mol−1|
|Melting point||184 to 185 °C (363 to 365 °F; 457 to 458 K)|
|Solubility in ethanol||slightly soluble|
|Solubility in methanol||very soluble|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Muscimol is the psychoactive compound responsible for the effects of Amanita muscaria intoxication. Ibotenic acid, a neurotoxic secondary metabolite of Amanita muscaria, serves as a prodrug to muscimol when the mushroom is ingested or dried, converting to muscimol via decarboxylation.
Muscimol is produced in the mushrooms Amanita muscaria (fly agaric) and Amanita pantherina, along with muscarine, muscazone, and ibotenic acid. A. muscaria and A. pantherina should be eaten with caution and prepared properly to lessen effects of nausea; It is disputed whether any official deaths from poisoning have been recorded from A. muscaria and A. pantherina. In A. muscaria, the layer just below the skin of the cap contains the highest amount of muscimol, and is therefore the most psychoactive portion.
Muscimol is a potent GABAA agonist, activating the receptor for the brain's principal inhibitory neurotransmitter, GABA. Muscimol binds to the same site on the GABAA receptor complex as GABA itself, as opposed to other GABAergic drugs such as barbiturates and benzodiazepines which bind to separate regulatory sites. GABAA receptors are widely distributed in the brain, and so when muscimol is administered, it alters neuronal activity in multiple regions including the cerebral cortex, hippocampus, and cerebellum. While muscimol is normally thought of as a selective GABAA agonist with exceptionally high affinity to GABAA-delta receptors, it is also a partial agonist at the GABAA-rho receptor, and so its range of effects results from a combined action on more than one GABAA receptor subtype.
The psychoactive dose of muscimol is around 10–15 mg for a normal person. A Guide to British Psilocybin Mushrooms by Richard Cooper published in 1977 recommends a smaller dose, 8.5 mg, and suggests that it is possible for this amount to be present in as little as 1 g of dried A. muscaria but this is not consistent with most other reports which suggest 5–10 g is necessary. A correct dose may be difficult to determine because potency varies dramatically from one mushroom to the next.
During a test involving rabbits connected to an EEG, muscimol presented with a distinctly synchronized EEG tracing. This is substantially different from serotonergic psychedelics, with which brainwave patterns generally show a desynchronization. In higher doses (2 mg/kg via IV), the EEG will show characteristic spikes.
The effects of the Amanita mushrooms begin 30–120 minutes after consumption and the effects last for 5–10 hours. Some of the desired effects include euphoria, dream-like (lucid) state of mind, out-of-body experiences and synesthesia. Neutral effects include dizziness, clumsiness, feeling of increased physical strength, loss of equilibrium, and glassy eyed stare. Calming effects may be felt, but completely opposite effects such as extreme energy bursts have been described. Negative effects include mild to moderate nausea, stomach discomfort, increased salivation and muscle twitching or tremors. In large doses strong dissociation or delirium may be felt.
Many of muscimol's effects are consistent with its pharmacology as a GABAA receptor agonist, presenting many depressant or sedative-hypnotic effects. Atypical of the effect profile of sedative drugs generally however, muscimol, like Z-drugs, can cause hallucinogenic changes in perception. The hallucinogenic effect produced by muscimol is most closely comparable to the hallucinogenic side effects produced by some other GABAergic drugs such as zolpidem.
About 90 minutes after ingestion ... I noticed that I was experiencing changes in visual perception. These effects became stronger over the next hour or some, and were characterized by sensing an 'alive quality' in inanimate objects, wavy motion in the visual field like a Van Gogh canvas ... and mild distortion of size, distance and depth perception. Auditory hallucination were also prominent -- especially the effect, called 'anahata sounds' of yoga, of hearing fine high-pitched sounds like bells and violin strings.
It can be produced synthetically from the lithium acetylide derived from propargyl chloride. Treatment with ethyl chloroformate afford ethyl 4-chlorotetrolate, which condenses with hydroxylamine to give the chloromethylisoxazole. Anhydrous ammonia converts this chloride to muscimol. The overall yield achieved in the literature was 18.7%.
The median lethal dose in mice is 3.8 mg/kg s.c, 2.5 mg/kg i.p. The LD50 in rats is 4.5 mg/kg i.v, 45 mg/kg orally.
Muscimol is considered a Schedule 9 prohibited substance in Australia under the Poisons Standard (October 2015). A Schedule 9 substance is a substance "which may be abused or misused, the manufacture, possession, sale or use of which should be prohibited by law except when required for medical or scientific research, or for analytical, teaching or training purposes with approval of Commonwealth and/or State or Territory Health Authorities."
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