Muscimol

Muscimol

Names
IUPAC name 5-(Aminomethyl)-1,2-oxazol-3(2H)-one
Other names Agarin, Pantherine, Agarine, Pantherin
Identifiers
CAS Number	2763-96-4 Y
3D model (JSmol)	Interactive image
Beilstein Reference	774694
ChEBI	CHEBI:7035 Y
ChEMBL	ChEMBL273481 Y
ChemSpider	4116 Y
ECHA InfoCard	100.018.574
EC Number	220-430-4
IUPHAR/BPS	4259
KEGG	C08311 Y
PubChem CID	4266
UNII	D5M179TY2E Y
UN number	2811 3077
CompTox Dashboard (EPA)	DTXSID5041069
InChI InChI=1S/C4H6N2O2/c5-2-3-1-4(7)6-8-3/h1H,2,5H2,(H,6,7) Y Key: ZJQHPWUVQPJPQT-UHFFFAOYSA-N Y InChI=1/C4H6N2O2/c5-2-3-1-4(7)6-8-3/h1H,2,5H2,(H,6,7) Key: ZJQHPWUVQPJPQT-UHFFFAOYAI
SMILES NCc1cc(no1)O
Properties[1]
Chemical formula	C4H6N2O2
Molar mass	114.104 g·mol−1
Melting point	184 to 185 °C (363 to 365 °F; 457 to 458 K)
Solubility in water	very soluble
Solubility in ethanol	slightly soluble
Solubility in methanol	very soluble
Pharmacology
Legal status	AU: S9 (Prohibited substance) in general, uncontrolled
Hazards
GHS labelling:[2]
Hazard statements	H300
Precautionary statements	P264, P270, P301+P316, P321, P330, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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 and selective orthosteric agonist for the GABA_A receptor^[3] and displays sedative-hypnotic, depressant and hallucinogenic psychoactivity. This colorless or white solid is classified as an isoxazole.

Muscimol went under clinical trial phase I for epilepsy, but the trial was discontinued.^[4]

Muscimol, an agonist for the GABA_A receptor, was able to significantly alleviate pain in its peak effect, recent studies from 2023 show. It has since been federally banned in Australia and is pending FDA review in the United States, but scientists believe it may relieve pain as well as some opioids without much of the risk of addiction associated with opioids. ^[5]

The main natural sources of muscimol are fungi of the genus Amanita, such as Amanita muscaria (fly agaric) and Amanita pantherina (panther amanita). It is produced in the mushrooms along with muscarine (which is present in trace amounts and it is not active), muscazone, and ibotenic acid.^[6][7] 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.^[8]

Muscimol is recognized as a potent agonist for ionotropic GABA-A receptors. By mimicking the inhibitory neurotransmitter GABA, muscimol activates these receptors, leading to the opening of chloride channels and subsequent hyperpolarization of neurons. This results in decreased neuronal excitability, which is crucial for maintaining the balance between excitation and inhibition in the central nervous system.^[9]

The biochemical properties of muscimol make it a valuable tool for investigating GABAergic mechanisms. Its high affinity and specificity for GABA-A receptors allow researchers to study synaptic transmission, neural circuit dynamics, and the overall role of GABAergic inhibition in various physiological and pathological states.^[9]

Muscimol is a potent GABA_A agonist, activating the receptor for the brain's principal inhibitory neurotransmitter, GABA. Muscimol binds to the same site on the GABA_A receptor complex as GABA itself, as opposed to other GABAergic drugs such as barbiturates and benzodiazepines which bind to separate regulatory sites.^[10] GABA_A 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 GABA_A agonist with exceptionally high affinity to GABA_A-delta receptors,^[11][12][13] it is also a partial agonist at the GABA_A-rho receptor, and so its range of effects results from a combined action on more than one GABA_A receptor subtype.^[14]

Scientific studies have shown that dosing of the active ingredient muscimol is usually not precise as it has to be extracted from dried amanita mushroom. However, a psychoactive dose of muscimol is reported to be between 8 and 15 mg. As little as a gram of dried Amanita muscaria button may contain this amount of muscimol; however, the potency varies greatly among mushrooms.^[15]

When consumed, a substantial percentage of muscimol goes un-metabolized and thus excreted in urine, a phenomenon exploited by Siberian practitioners of the traditional entheogenic use of Amanita muscaria.^[16]

In patients with Huntington's disease and chronic schizophrenia, oral doses of muscimol have been found to cause a rise of both prolactin and growth hormone.^[17]

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.^[18]

Muscimol primarily functions as a GABA-A receptor agonist, meaning it mimics the action of GABA, the main inhibitory neurotransmitter in the central nervous system. By binding to GABA-A receptors, muscimol increases the inhibitory effects of GABA, leading to hyperpolarization of neurons and decreased neuronal excitability.^{[citation needed]}

Muscimol, as a GABA-A receptor agonist, has shown diverse pharmacological effects, from neuroprotection and pain management to influencing cognitive functions and treating epilepsy^[19]

Ongoing research continues to uncover its potential therapeutic applications, making it a compound of significant interest in neuropharmacology.^[20]

The recent researches on muscimol highlight the next effects:

• Neurotransmission Modulation: By mimicking GABA and binding to GABA-A receptors, muscimol enhances inhibitory neurotransmission. This results in reduced neuronal firing rates, contributing to the overall calming effect on the CNS. This modulation is crucial in maintaining the balance between excitatory and inhibitory signals in the brain.^[21]
• Migraine and Headache: Studies on migraine models demonstrated that extrasynaptic GABA-A receptor agonists like muscimol could prevent migraine-like phenotypes, offering new avenues for migraine treatment.^[22]
• Depressant Effects: By enhancing inhibitory neurotransmission, muscimol acts as a CNS depressant. This can lead to muscle relaxation, reduction in anxiety.^[23]
• Antinociceptive Properties: Muscimol has been found to have antinociceptive effects when used in combination with citalopram, a selective serotonin reuptake inhibitor. This additive effect highlights muscimol's potential in pain management.^[24]
• Decision Making and Cognitive Function: Research on the role of the rat prelimbic cortex indicated that muscimol can influence decision-making processes. By infusing muscimol, researchers observed significant changes in cortical activity, which are crucial for understanding cognitive functions and cognitive disorders.^[25]
• Cerebral Ischemic Injury: Muscimol's role in alleviating cerebral ischemic injury was explored, revealing its ability to suppress oxidative stress, autophagy, and apoptosis pathways. This research underscores muscimol's potential in treating ischemic conditions.^[26]
• Pain Management: Activation of 5-HT5A receptors in the ventrolateral orbital cortex, alongside GABA-A receptor modulation by muscimol, showed significant antinociceptive effects in models of neuropathic pain and inflammatory pain.^[27]
• Epilepsy Models: In studies involving absence epilepsy models, muscimol demonstrated effects on T-type calcium channels and GABA receptors, providing insights into its anticonvulsant properties.^[28]
• Substance Use Disorders: Research into sex differences in GABA receptor regulation highlighted muscimol's potential in addressing cocaine use disorder, emphasizing its role in GABAergic modulation.^{[citation needed]}
• Neurological Pathways: Investigations into neural pathways for internal bias and sensory information interaction in decision-making processes showed the significant impact of muscimol on visual cortex neurons.^{[citation needed]}

Muscimol, a psychoactive compound derived from the ibotenic acid found in certain mushrooms, particularly Amanita muscaria, has garnered significant interest due to its unique effects on the nervous system. Muscimol binds to GABA receptors in the brain, resulting in its sedative and hallucinogenic properties.^{[citation needed]} Muscimol-based products are currently being investigated for their potential therapeutic applications, especially in the treatment of anxiety, insomnia, and other neurological disorders.^[29][30] The psychoactive nature of muscimol necessitates stringent regulation and cautious usage to ensure safety.^[31] However, ongoing research aims to harness its medicinal benefits in a controlled context, highlighting the broader scientific interest in natural compounds as potential sources for novel medical treatments.^{[citation needed]}

Chemical Formula: C_4H_6N_2O_2

Molecular Weight: 114.10 g/mol

Physical and Chemical Properties:

- Water Solubility: Muscimol is highly soluble in water.

- Melting Point: It has a melting point of 175-177 °C.

- Appearance: Typically, muscimol appears as a white crystalline powder.

Muscimol was first isolated from Amanita pantherina by Onda in 1964,^[32] and thought to be an amino acid or peptide. Structure was then elucidated by Takemoto,^[33] Eugster,^[34] and Bowden.^[35] Muscimol is a semi-rigid isoxazole containing both alcohol and aminomethyl substituents.^[36] Muscimol is commonly portrayed as a tautomer, where it adopts an amide-like configuration.^[2] It is also commonly shown as a zwitterion.^[37]

Muscimol can be extracted from the flesh of the Amanita muscaria by treatment with boiling water, followed by rapid cooling, and further treatment with a basic resin. This is washed with water, and eluted with acetic acid using column chromatography. The eluate is freeze dried, dissolved in water, and passed down a column of cellulose phosphate.^[38] A subsequent elution with ammonium hydroxide and recrystallization from alcohol results in pure muscimol.^[39]

In instances where pure muscimol is not required, such as recreational or spiritual use, a crude extract is often prepared by simmering dried Amanita muscaria in water for thirty minutes.^[40]

Muscimol was synthesized in 1965 by Gagneux,^[41] who utilized a bromo-isoxazole starting material in a two step reaction. 3-bromo-5-aminomethyl-isoxazole (1) was refluxed in a mixture of methanol and potassium hydroxide for 30 hours, resulting in 3-methoxy-5-aminomethyl-isoxazole (2) with a yield of 60%.

(2) was then refluxed in concentrated hydrochloric acid to hydrolyze the methoxy group, and the zwitterion crystallized from a solution of methanol and tetrahydrofuran after the addition of triethylamine, resulting in a 50% yield.^[41]

Chemists report having struggled to reproduce these results.^[42][43] More dependable and scalable procedures have been developed, two examples being the syntheses of McCarry^[44] and Varasi.^[37]

McCarry's synthesis is a three step synthesis involving a lithium acetylide produced from propargyl chloride. The acetylide (3), was dissolved in ether, cooled to -40 °C, and treated with excess ethyl chloroformate to afford ethyl 4-chlorotetrolate (4) in a 70% yield. (4) was then added to a solution of water, methanol and hydroxylamine at -35 °C. At a pH of between 8.5 and 9, the isoxazole (5) was recovered in a 41% yield. Muscimol was formed in a 65% yield when (5) was dissolved in a saturated solution of methanol and anhydrous ammonia and heated from 0 °C to 50 °C. The total yield was 18.7%.^[44]

Varasi's synthesis is notable for its inexpensive starting materials and mild conditions. It begins with the combination of 2,3-Dichloro-1-propene (6), potassium bicarbonate, water, and dibromoformaldoxime (7) (which is a well known precursor of bromo nitriloxyde, a reactive dipole for regioselective Diels-Alder cycloadditions, which forms in alkali), all dissolved in ethyl acetate. 5-Chloromethyl-3-bromoisoxazole (8) was extracted with an experimental yield of 81%. 5-Aminomethyl-3-bromoisoxazole (9) was formed in 90% yield by the combination of (8) and ammonium hydroxide in dioxane.^[37]

(9) was then refluxed with potassium hydroxide in methanol to generate 5-Aminomethyl-3-methoxyisoxazole (10) with a 66% yield. Subsequent reflux of (10) with hydrobromic acid and acetic acid generated muscimol with a yield of 62%. The overall synthetic yield was 30%.^[37]

The toxicity and safety profile of Muscimol have been studied in various contexts, both experimental and clinical.

A study on nonhuman primates indicated that muscimol, when administered in escalating doses, caused reversible hyperkinesia and dyskinesias at higher doses (up to 88.8 mM), but no long-term toxicity was observed on histological examination.^[45]

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.^[46]

Muscimol has shown potential as an anticonvulsant, blocking seizures induced by various agents in animal models without causing significant toxicity at therapeutic doses.^[47]

A retrospective review of muscimol poisoning cases from Amanita mushrooms indicated that symptoms included gastrointestinal upset, CNS excitation, but no deaths were reported. Most symptoms resolved within 24 hours.^[48]

Studies on muscimol's distribution in rats showed it enters the brain and is metabolized rapidly, suggesting that its toxicity is low when used in controlled doses.^{[citation needed]}

Muscimol exhibits dose-dependent effects with higher doses leading to significant, but reversible, CNS symptoms.^[49] Its toxicity appears to be low when used in controlled environments, with no long-term damage observed in animal studies and human cases resolving without severe outcomes. However, caution is advised with its use due to its potent effects on the central nervous system.^{[citation needed]}

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."^[50]

Neither Amanita muscaria nor muscimol is considered a controlled substance by the Federal government of the United States. This means that cultivation, possession, and distribution are unregulated by the United States Federal Government.^[51][52] The legality of Amanita muscaria and muscimol as ingredients in food is unclear since neither are approved as food additives by the FDA. However, agriculture regulators in Florida actioned against one seller of Amanita products after the agency had determined such products were considered adulterated under state law.^[53]

Muscimol may be regulated on a state level. Louisiana State Act 159 banned the possession and cultivation of the Amanita muscaria except for ornamental or aesthetic purposes. Except as a constituent of lawfully manufactured food or dietary supplements, the act outlaws preparations of the Amanita muscaria intended for human consumption, including muscimol.^[54]

• Psychoactive Amanitas on Erowid