Names | |
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IUPAC name 5-(Aminomethyl)-1,2-oxazol-3(2H)-one | |
Other names Agarin, Pantherine, Agarine, Pantherin | |
Identifiers | |
3D model (JSmol) | |
774694 | |
ChEBI | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard | 100.018.574 |
EC Number |
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KEGG | |
PubChem CID | |
UNII | |
UN number | 2811 3077 |
CompTox Dashboard (EPA) | |
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Properties [1] | |
C4H6N2O2 | |
Molar mass | 114.104 g·mol−1 |
Melting point | 184 to 185 °C (363 to 365 °F; 457 to 458 K) |
very soluble | |
Solubility in ethanol | slightly soluble |
Solubility in methanol | very soluble |
Pharmacology | |
Legal status |
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Hazards | |
GHS labelling: [2] | |
H300 | |
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). |
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 GABAA 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 GABAA 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 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. [10] 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, [11] [12] [13] 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. [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:
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]
Amanita muscaria, commonly known as the fly agaric or fly amanita, is a basidiomycete of the genus Amanita. It is a large white-gilled, white-spotted, and usually red mushroom.
Muscarine, L-(+)-muscarine, or muscarin is a natural product found in certain mushrooms, particularly in Inocybe and Clitocybe species, such as the deadly C. dealbata. Mushrooms in the genera Entoloma and Mycena have also been found to contain levels of muscarine which can be dangerous if ingested. Muscarine has been found in harmless trace amounts in Boletus, Hygrocybe, Lactarius and Russula. Trace concentrations of muscarine are also found in Amanita muscaria, though the pharmacologically more relevant compound from this mushroom is the Z-drug-like alkaloid muscimol. A. muscaria fruitbodies contain a variable dose of muscarine, usually around 0.0003% fresh weight. This is very low and toxicity symptoms occur very rarely. Inocybe and Clitocybe contain muscarine concentrations up to 1.6%.
The genus Amanita contains about 600 species of agarics, including some of the most toxic known mushrooms found worldwide, as well as some well-regarded edible species. The genus is responsible for approximately 95% of fatalities resulting from mushroom poisoning, with the death cap accounting for about 50% on its own. The most potent toxin present in these mushrooms is α-Amanitin.
Amanita pantherina, also known as the panther cap, false blusher, and the panther amanita due to its similarity to the true blusher, is a species of fungus found in Eurasia with poisonous and psychoactive properties.
The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid (GABA), the chief inhibitory compound in the mature vertebrate central nervous system. There are two classes of GABA receptors: GABAA and GABAB. GABAA receptors are ligand-gated ion channels ; whereas GABAB receptors are G protein-coupled receptors, also called metabotropic receptors.
Ibotenic acid or (S)-2-amino-2-(3-hydroxyisoxazol-5-yl)acetic acid, also referred to as ibotenate, is a chemical compound and psychoactive drug which occurs naturally in Amanita muscaria and related species of mushrooms typically found in the temperate and boreal regions of the northern hemisphere. It is a prodrug of muscimol, broken down by the liver to that much more stable compound. It is a conformationally-restricted analogue of the neurotransmitter glutamate, and due to its structural similarity to this neurotransmitter, acts as a non-selective glutamate receptor agonist. Because of this, ibotenic acid can be a powerful neurotoxin in high doses, and is employed as a "brain-lesioning agent" through cranial injections in scientific research. The neurotoxic effects appear to be dose-related and risks are unclear through consumption of ibotenic-acid containing fungi, although thought to be negligible in small doses.
The GABAA receptor (GABAAR) is an ionotropic receptor and ligand-gated ion channel. Its endogenous ligand is γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system. Accurate regulation of GABAergic transmission through appropriate developmental processes, specificity to neural cell types, and responsiveness to activity is crucial for the proper functioning of nearly all aspects of the central nervous system (CNS). Upon opening, the GABAA receptor on the postsynaptic cell is selectively permeable to chloride ions and, to a lesser extent, bicarbonate ions.
Gaboxadol, also known as 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP), is a conformationally constrained derivative of the alkaloid muscimol that was first synthesized in 1977 by the Danish chemist Poul Krogsgaard-Larsen. In the early 1980s gaboxadol was the subject of a series of pilot studies that tested its efficacy as an analgesic and anxiolytic, as well as a treatment for tardive dyskinesia, Huntington's disease, Alzheimer's disease, and spasticity. It was not until 1996 that researchers attempted to harness gaboxadol's frequently reported sedative "adverse effect" for the treatment of insomnia, resulting in a series of clinical trials sponsored by Lundbeck and Merck. In March, 2007, Merck and Lundbeck cancelled work on the drug, citing safety concerns and the failure of an efficacy trial. It acts on the GABA system, but in a different way from benzodiazepines, Z-Drugs, and barbiturates. Lundbeck states that gaboxadol also increases deep sleep. Unlike benzodiazepines, gaboxadol does not demonstrate reinforcement in mice or baboons despite activation of dopaminergic neurons in the ventral tegmental area.
A GABA receptor agonist is a drug that is an agonist for one or more of the GABA receptors, producing typically sedative effects, and may also cause other effects such as anxiolytic, anticonvulsant, and muscle relaxant effects. There are three receptors of the gamma-aminobutyric acid. The two receptors GABA-α and GABA-ρ are ion channels that are permeable to chloride ions which reduces neuronal excitability. The GABA-β receptor belongs to the class of G-Protein coupled receptors that inhibit adenylyl cyclase, therefore leading to decreased cyclic adenosine monophosphate (cAMP). GABA-α and GABA-ρ receptors produce sedative and hypnotic effects and have anti-convulsion properties. GABA-β receptors also produce sedative effects. Furthermore, they lead to changes in gene transcription.
γ-Amino-β-hydroxybutyric acid (GABOB), also known as β-hydroxy-γ-aminobutyric acid (β-hydroxy-GABA), sold under the brand name Gamibetal among others, is an anticonvulsant which is used for the treatment of epilepsy in Europe, Japan, and Mexico. It is a GABA analogue, or an analogue of the neurotransmitter γ-aminobutyric acid (GABA), and has been found to be an endogenous metabolite of GABA.
Amanita chrysoblema yellow-orange variant, commonly known as the American yellow fly agaric, is a basidiomycete fungus of the genus Amanita. It is one of several varieties of muscaroid fungi, all commonly known as fly agarics or fly amanitas.
A GABA reuptake inhibitor (GRI) is a type of drug which acts as a reuptake inhibitor for the neurotransmitter gamma-Aminobutyric acid (GABA) by blocking the action of the gamma-Aminobutyric acid transporters (GATs). This in turn leads to increased extracellular concentrations of GABA and therefore an increase in GABAergic neurotransmission. Gamma-aminobutyric acid (GABA) is an amino acid that functions as the predominant inhibitory neurotransmitter within the central nervous system, playing a crucial role in modulating neuronal activity in both the brain and spinal cord. While GABA predominantly exerts inhibitory actions in the adult brain, it has an excitatory role during developmental stages. When the neuron receives the action potential, GABA is released from the pre-synaptic cell to the synaptic cleft. After the action potential transmission, GABA is detected on the dendritic side, where specific receptors collectively contribute to the inhibitory outcome by facilitating GABA transmitter uptake. Facilitated by specific enzymes, GABA binds to post-synaptic receptors, with GABAergic neurons playing a key role in system regulation. The inhibitory effects of GABA diminish when presynaptic neurons reabsorb it from the synaptic cleft for recycling by GABA transporters (GATs). The reuptake mechanism is crucial for maintaining neurotransmitter levels and synaptic functioning. Gamma-aminobutyric acid Reuptake Inhibitors (GRIs) hinder the functioning of GATs, preventing GABA reabsorption in the pre-synaptic cell. This results in increased GABA levels in the extracellular environment, leading to elevated GABA-mediated synaptic activity in the brain.
Amanita muscaria var. formosa, known as the yellow orange fly agaric, is a hallucinogenic and poisonous basidiomycete fungus of the genus Amanita. This variety, which can sometimes be distinguished from most other A. muscaria by its yellow cap, is a European taxon, although several North American field guides have referred A. muscaria var. guessowii to this name. American mycologist Harry D. Thiers described a yellow-capped taxon that he called var. formosa from the United States, but it is not the same as the European variety. The Amanita Muscaria is native to temperate or boreal forest regions of the Northern Hemisphere. However, it has also been introduced in New Zealand, Australia, South America, and South Africa.
The rostral ventromedial medulla (RVM), or ventromedial nucleus of the spinal cord, is a group of neurons located close to the midline on the floor of the medulla oblongata. The rostral ventromedial medulla sends descending inhibitory and excitatory fibers to the dorsal horn spinal cord neurons. There are 3 categories of neurons in the RVM: on-cells, off-cells, and neutral cells. They are characterized by their response to nociceptive input. Off-cells show a transitory decrease in firing rate right before a nociceptive reflex, and are theorized to be inhibitory. Activation of off-cells, either by morphine or by any other means, results in antinociception. On-cells show a burst of activity immediately preceding nociceptive input, and are theorized to be contributing to the excitatory drive. Neutral cells show no response to nociceptive input.
Quisqualamine is the α-decarboxylated analogue of quisqualic acid, as well as a relative of the neurotransmitters glutamate and γ-aminobutyric acid (GABA). α-Decarboxylation of excitatory amino acids can produce derivatives with inhibitory effects. Indeed, unlike quisqualic acid, quisqualamine has central depressant and neuroprotective properties and appears to act predominantly as an agonist of the GABAA receptor and also to a lesser extent as an agonist of the glycine receptor, due to the facts that its actions are inhibited in vitro by GABAA antagonists like bicuculline and picrotoxin and by the glycine antagonist strychnine, respectively. Mg2+ and DL-AP5, NMDA receptor blockers, CNQX, an antagonist of both the AMPA and kainate receptors, and 2-hydroxysaclofen, a GABAB receptor antagonist, do not affect quisqualamine's actions in vitro, suggesting that it does not directly affect the ionotropic glutamate receptors or the GABAB receptor in any way. Whether it binds to and acts upon any of the metabotropic glutamate receptors like its analogue quisqualic acid however is unclear.
CI-966 (developmental code name) is a central nervous system depressant acting as a GABA reuptake inhibitor, specifically a highly potent and selective blocker of the GABA transporter 1 (GAT-1) (IC50 = 0.26 μM), and hence indirect and non-selective GABA receptor full agonist. It was investigated as a potential anticonvulsant, anxiolytic, and neuroprotective therapeutic but was discontinued during clinical development due to the incidence of severe adverse effects at higher doses and hence was never marketed.
In pharmacology, GABAA receptor positive allosteric modulators, also known as GABAkines or GABAA receptor potentiators, are positive allosteric modulator (PAM) molecules that increase the activity of the GABAA receptor protein in the vertebrate central nervous system.
A GABA analogue is a compound which is an analogue or derivative of the neurotransmitter gamma-Aminobutyric acid (GABA).
Amanita muscaria var. inzengae, commonly known as Inzenga's fly agaric, is a basidiomycete fungus of the genus Amanita. It is one of several varieties of the Amanita muscaria fungi, all commonly known as fly agarics or fly amanitas.
Famiraprinium is a GABAA receptor antagonist used in scientific research.