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Classics in Chemical Neuroscience: Muscimol
... Nonetheless, it has previously been employed in shamanic ceremonies. Its sedative properties may lead to its investigation as a possible tranquillizer.. (Johnston, 2014;Rivera-Illanes & Recabarren-Gajardo, 2024) Plants including Hyoscyamus niger, Datura stramonium, and Atropa belladonna contain scopolanine. Muscarinic acetylcholine receptors are antagonistic to it. ...
Isoxazoles are a class of five-membered heterocyclic compounds that have gained significant attention in medicinal chemistry due to their diverse biological activities and therapeutic potential. Recent advances in isoxazole chemistry have led to the development of novel synthetic strategies, enabling the creation of a wide array of isoxazole derivatives with enhanced bioactivity and selectivity. This review explores the latest progress in isoxazole synthesis, highlighting key methodologies such as transition metal-catalyzed cycloadditions, green chemistry approaches, and regioselective functionalization techniques. These advances have not only improved the efficiency of isoxazole synthesis but have also facilitated the design of more complex and bioactive derivatives. In addition to their synthetic advances, isoxazoles have demonstrated a broad spectrum of biological activities, including antimicrobial, anticancer, anti-inflammatory, and neuroprotective effects, making them attractive candidates in drug discovery. This review discusses the structural modifications that enhance their pharmacological properties and their potential for developing therapies for diseases such as cancer, neurodegenerative disorders, and infections. Moreover, we examine the emerging trends in isoxazole-based drug discovery, such as the development of multi-targeted therapies and personalized medicine approaches. The evolving role of isoxazoles in drug discovery underscores their continued importance in modern pharmaceutical research and their potential to address unmet medical needs.
Natural product discovery from fungi for drug development and description of novel chemistry has been a tremendous success. This success is expected to accelerate even further, owing to the advent of sophisticated technical advances of technical advances that recently led to the discovery of an unparalleled biodiversity in the fungal kingdom. This review aims to give an overview on i) important secondary metabolite-derived drugs or drug leads, ii) discuss the analytical and strategic framework of how natural product discovery and drug lead identification transformed from earlier days to the present, iii) how knowledge of fungal biology and biodiversity facilitates the discovery of new compounds, and iv) point out endeavors in understanding fungal secondary metabolite chemistry in order to systematically explore fungal genomes by utilizing synthetic biology. An outlook is given, underlining the necessity for a collaborative and cooperative scenario to harness the full potential of the fungal secondary metabolome.
Introduction: The plant-based alkaloid muscimol is a potent agonist of inhibitory GABAA-neurotransmitter receptors. GABAA receptors are a heterogeneous family of pentameric complexes, with 5 out of 19 subunits assembling around the central anion pore. Muscimol is considered to bind to all receptor subtypes at the orthosteric drug binding site at the β+/α− interface. Recently, we observed that the antipsychotic drugs clozapine (CLZ), loxapine (LOX) and chlorpromazine (CPZ) although exerting functional inhibition on multiple GABAA receptor subtypes showed diverging results in displacing 3H-muscimol. While a complete displacement could be observed in hippocampal membranes by bicuculline (BIC), and no displacement with CPZ, the compounds CLZ and LOX competed partially. Non-sigmoidal, complex dose response curves were indicative of multiple sites. In the current study we now aimed to investigate more extensively this heterogeneity of bicuculline sensitive muscimol sites in rat brain.
Methods: We tested membranes from four different brain regions (hippocampus, cerebellum, thalamus and striatum) and selected recombinantly expressed subunit combinations with displacement assays. 3H-muscimol displacement was tested with BIC, LOX, CLZ and CPZ. In silico ligand structural analysis and computational docking was performed.
Results: We observed a unique pharmacology of each tested compound in the studied brain regions. Combining two of the tested ligands suggests that in striatum all CLZ sites are contained in the pool of LOX sites, while the CPZ sites may in part be non-overlapping with LOX sites. Experiments on recombinantly expressed receptors indicate, that BIC can displace 3H-muscimol from all tested receptors, while LOX and CLZ display different and variable competition indicative of multiple sites. Molecular docking produced structural correlates of the observed diversity of muscimol sites on the basis of bicuculline bound experimental structures.
Discussion: These findings indicate that 3H-muscimol binding sites in rat brain are heterogeneous, with different populations of receptors, which are CPZ, LOX or CLZ sensitive or insensitive. These binding sites show a varying distribution in different rat brain regions. Molecular docking suggests that the so-called loop F region of α subunits drives the observed differences.
Pyroptosis is a cell death process that causes inflammation and contributes to numerous diseases. Pyroptosis is mediated by caspase-1 family proteases that cleave the pore-forming protein gasdermin D, causing plasma membrane rupture and release of pathogenic cellular contents. We previously identified muscimol as a small molecule that prevents plasma membrane rupture during pyroptosis via an unidentified mechanism. Here, we show that muscimol has reversible activity to prevent cellular lysis without affecting earlier pyroptotic events. Although muscimol is a well-characterized agonist for neuronal GABAA receptors, muscimol protection is not altered by GABAA receptor antagonists or recapitulated by other GABAA agonists, suggesting that muscimol acts via a novel mechanism. We find that muscimol blocks oligomerization of ninjurin-1, which is required for plasma membrane rupture downstream of gasdermin D pore formation. Our structure-activity relationship studies reveal distinct molecular determinants defining inhibition of pyroptotic lysis compared to GABAA binding. In addition, we demonstrate that muscimol reduces lethality during LPS-induced septic shock. Together, these findings demonstrate that ninjurin-1-mediated plasma membrane rupture can be pharmacologically modulated and pave the way toward identification of therapeutic strategies for pathologic conditions associated with pyroptosis.
Background
Muscimol’s quick onset and GABAergic properties make it a promising candidate for the treatment of pain. This systematic review and meta-analysis of preclinical studies aimed at summarizing the evidence regarding the efficacy of muscimol administration in the amelioration of nerve injury-related neuropathic pain.
Methods
Two independent researchers performed the screening process in Medline, Embase, Scopus and Web of Science extracting data were extracted into a checklist designed according to the PRISMA guideline. A standardized mean difference (SMD [95% confidence interval]) was calculated for each. To assess the heterogeneity between studies, I² and chi-square tests were utilized. In the case of heterogeneity, meta-regression and subgroup analyses were performed to identify the potential source.
Results
Twenty-two articles met the inclusion criteria. Pooled data analysis showed that the administration of muscimol during the peak effect causes a significant reduction in mechanical allodynia (SMD = 1.78 [1.45–2.11]; P < 0.0001; I² = 72.70%), mechanical hyperalgesia (SMD = 1.62 [1.28–1.96]; P < 0.0001; I² = 40.66%), and thermal hyperalgesia (SMD = 2.59 [1.79–3.39]; P < 0.0001; I² = 80.33%). This significant amendment of pain was observed at a declining rate from 15 minutes to at least 180 minutes post-treatment in mechanical allodynia and mechanical hyperalgesia, and up to 30 minutes in thermal hyperalgesia (P < 0 .0001).
Conclusions
Muscimol is effective in the amelioration of mechanical allodynia, mechanical hyperalgesia, and thermal hyperalgesia, exerting its analgesic effects 15 minutes after administration for up to at least 3 hours.
Systemic inflammatory response syndrome plays an important role in the development of sepsis. GABAergic and cholinergic pathways activation are considered important for inflammatory response regulation. Tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-12, IL-10, as well as inducible nitric oxide synthase (iNOS)-derived nitric oxide (NO) are important inflammatory mediators involved in the pathogenesis of sepsis. Muscimol, an active compound from the mushroom Amanita muscaria (L.) Lam., is a potent GABAA agonist, inhibits inflammatory response via activating GABAA receptor and vagus nerve. However, the effect of muscimol on lipopolysaccharide (LPS)-induced systemic inflammatory response is still unclear. Therefore, we studied the effects of muscimol on systemic inflammatory response and survival rate in endotoxemic mice. Mice endotoxemia was induced by LPS. Muscimol was given to mice or RAW264.7 cells 30 min before LPS (10 mg/kg, i.p., or 10 ng/mL, respectively). Mice received GABAergic and cholinergic receptor antagonists 30 min before muscimol and LPS. Muscimol decreased TNF-α, IL-1β, IL-12, iNOS-derived NO, and increased IL-10 levels and survival rate after LPS treatment. Muscimol significantly decreased nuclear factor kappa B (NF-κB) activity, increased IκB expression, and decreased pIKK expression in LPS-treated RAW264.7 cells. GABAergic and cholinergic antagonists failed to reverse muscimol’s protection in LPS-treated mice. In conclusion, muscimol protected against systemic inflammatory response in endotoxemic mice may be partially independent of GABAergic and cholinergic receptors.
Amanita muscaria is the most emblematic mushroom in the popular representation. It is an ectomycorrhizal fungus endemic to the cold ecosystems of the northern hemisphere. The basidiocarp contains isoxazoles compounds that have specific actions on the central nervous system, including hallucinations. For this reason, it is considered an important entheogenic mushroom in different cultures whose remnants are still visible in some modern-day European traditions. In Siberian civilizations, it has been consumed for religious and recreational purposes for millennia, as it was the only inebriant in this region.
Introduction: The modality of γ-aminobutyric acid type a receptors (GABAA) controls dorsal horn neuronal excitability and inhibits sensory information. This study aimed to investigate the expression of the GABAA receptor and the effects of its agonist muscimol on Wide Dynamic Range (WDR) neuronal activity in the Chronic Constriction Injury (CCI) model of neuropathic pain.
Methods: Adult male Wistar rats weighing 200 to 250 g were used to induce CCI neuropathy. Fourteen days after surgery, muscimol (0.5, 1, and 2 mg/kg IP) was injected. Then, the behavioral tests were performed. After that, the animals were killed, and the lumbar segments of the spinal cords were collected for Western blot analysis of the GABAA receptor α1 subunit expression. The electrophysiological properties of WDR neurons were studied by single-unit recordings in separate groups 14 days after CCI.
Results: The outcomes indicated the development of thermal hyperalgesia and mechanical allodynia after neuropathy; nonetheless, the expression of the GABAA receptor α1 subunit did not change significantly. Moreover, the evoked responses of the WDR neurons to electrical, mechanical, and thermal stimuli increased considerably. Fourteen days after CCI, muscimol administration decreased thermal hyperalgesia, mechanical allodynia, and hyper-responsiveness of the WDR neurons in CCI rats.
Conclusion: The modulation of the spinal GABAA receptors after nerve injury can offer further insights to design new therapeutic agents to reduce neuropathic pain symptoms.
Amanita muscaria is considered to be one of the most remarkable and beautiful mushrooms. It has a red or orange cap covered with small white plaques and its distinctive appearance makes accidental and severe intoxication very rare. Its consumption is sometimes used as a means of suicide or it can be consumed for its psychedelic effects, and in some cases, it can be mistaken for edible species. In this paper, we will discuss a patient who fell into a coma after accidental Amanita muscaria poisoning. Rapid identification of the mushroom allowed the regression of symptoms and discharge from the hospital on the fourth day after consumption.
Learning points:
Amanita muscaria is one of the most remarkable mushrooms for its distinctive appearance, but sometimes it can be mistaken for edible species.Amanita muscaria is a highly poisonous mushroom; the primary effects usually involve the central nervous system, and in severe poisoning, symptoms may manifest with coma and in rare cases lead to death.The rapid and correct identification of this mushroom is important for optimal risk assessment and in order to prescribe the best therapy.
Amanita muscaria , commonly known as fly agaric, is a basidiomycete. Its main psychoactive constituents are ibotenic acid and muscimol, both involved in ‘pantherina-muscaria’ poisoning syndrome. The rising pharmacological and toxicological interest based on lots of contradictive opinions concerning the use of Amanita muscaria extracts’ neuroprotective role against some neurodegenerative diseases such as Parkinson’s and Alzheimer’s, its potent role in the treatment of cerebral ischaemia and other socially significant health conditions gave the basis for this review. Facts about Amanita muscaria ’s morphology, chemical content, toxicological and pharmacological characteristics and usage from ancient times to present-day’s opportunities in modern medicine are presented.
Brain GABAΑ receptors are ionotropic receptors belonging to the class of Cys-loop receptors and are important drug targets for the treatment of anxiety and sleep disorders. By screening a compound library (2,112 compounds) at recombinant human α4β1δ GABAΑ receptors heterologously expressed in a HEK cell line, we identified a scaffold of spirocyclic compounds with nanomolar antagonist activity at GABAΑ receptors. The initial screening hit 2027 (IC50 of 1.03 μM) was used for analogue search resulting in 018 (IC50 of 0.088 μM). 018 was most potent at α3,4,5-subunit containing receptors, thus showing preference for forebrain-expressed extrasynaptic receptors. Schild analysis of 018 at recombinant human α4β1δ receptors and displacement of [3H]muscimol binding in rat cortical homogenate independently confirmed a competitive profile. The antagonist profile of 018 was further validated by whole-cell patch-clamp electrophysiology, where kinetic studies revealed a slow dissociation rate and a shallow hill slope was observed. Membrane permeability studies showed that 2027 and 018 do not cross membranes, thus making the compounds less attractive for studying central GABAΑ receptors effects, but conversely more attractive as tool compounds in relation to emerging peripheral GABAΑ receptor-mediated effects of GABA e.g. in the immune system.
The fly agaric, Amanita muscaria, is widely known for its content of the psychoactive metabolites ibotenic acid and muscimol. However, their biosynthetic pathway and the respective enzymes are entirely unknown. 50 years ago, the biosynthesis was hypothesized to start with 3‐hydroxyglutamate. Here, we build on this hypothesis by the identification and recombinant production of a glutamate hydroxylase from A. muscaria. The hydroxylase gene is surrounded by six further biosynthetic genes, which we link to the production of ibotenic acid and muscimol using recent genomic and transcriptomic data. Our results pinpoint the genetic basis for ibotenic acid formation and thus provide new insights into a decades‐old question concerning a centuries‐old drug.
Visual hallucinations (VH) are commonly found in the course of synucleinopathies like Parkinson's disease and dementia with Lewy bodies. The incidence of VH in these conditions is so high that the absence of VH in the course of the disease should raise questions about the diagnosis. VH may take the form of early and simple phenomena or appear with late and complex presentations that include hallucinatory production and delusions. VH are an unmet treatment need. The review analyzes the past and recent hypotheses that are related to the underlying mechanisms of VH and then discusses their pharmacological modulation. Recent models for VH have been centered on the role played by the decoupling of the default mode network (DMN) when is released from the control of the fronto-parietal and salience networks. According to the proposed model, the process results in the perception of priors that are stored in the unconscious memory and the uncontrolled emergence of intrinsic narrative produced by the DMN. This DMN activity is triggered by the altered functioning of the thalamus and involves the dysregulated activity of the brain neurotransmitters. Historically, dopamine has been indicated as a major driver for the production of VH in synucleinopathies. In that context, nigrostriatal dysfunctions have been associated with the VH onset. The efficacy of antipsychotic compounds in VH treatment has further supported the notion of major involvement of dopamine in the production of the hallucinatory phenomena. However, more recent studies and growing evidence are also pointing toward an important role played by serotonergic and cholinergic dysfunctions. In that respect, in vivo and post-mortem studies have now proved that serotonergic impairment is often an early event in synucleinopathies. The prominent cholinergic impairment in DLB is also well established. Finally, glutamatergic and gamma aminobutyric acid (GABA)ergic modulations and changes in the overall balance between excitatory and inhibitory signaling are also contributing factors. The review provides an extensive overview of the pharmacology of VH and offers an up to date analysis of treatment options.
Muscimol, the major psychoactive ingredient in the mushroom Amanita muscaria, has been regarded as a universal non‐selective GABA‐site agonist. Deletion of the GABAA receptor (GABAAR) δ subunit in mice (δKO) leads to a drastic reduction in high‐affinity muscimol binding in brain sections and to a lower behavioral sensitivity to muscimol than their wild type counterparts. Here, we use forebrain and cerebellar brain homogenates from WT and δKO mice to show that deletion of the δ subunit leads to a > 50% loss of high‐affinity 5 nM [³H]muscimol‐binding sites despite the relatively low abundance of δ‐containing GABAARs (δ‐GABAAR) in the brain. By subtracting residual high‐affinity binding in δKO mice and measuring the slow association and dissociation rates we show that native δ‐GABAARs in WT mice exhibit high‐affinity [³H]muscimol‐binding sites (KD ~1.6 nM on α4βδ receptors in the forebrain and ~1 nM on α6βδ receptors in the cerebellum at 22°C). Co‐expression of the δ subunit with α6 and β2 or β3 in recombinant (HEK 293) expression leads to the appearance of a slowly dissociating [³H]muscimol component. In addition, we compared muscimol currents in recombinant α4β3δ and α4β3 receptors and show that δ subunit co‐expression leads to highly muscimol‐sensitive currents with an estimated EC50 of around 1–2 nM and slow deactivation kinetics. These data indicate that δ subunit incorporation leads to a dramatic increase in GABAAR muscimol sensitivity. We conclude that biochemical and behavioral low‐dose muscimol selectivity for δ‐subunit‐containing receptors is a result of low nanomolar‐binding affinity on δ‐GABAARs.
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Background: Amanita muscaria (AM) and A. pantherina (AP) contain ibotenic acid and muscimol and may cause both excitatory and sedating symptoms. Gastrointestinal (GI) symptoms are not classically described but have been reported. There are relatively few reported cases of poisoning with these mushrooms in North America.
Methods: This is a retrospective review of ingestions of ibotenic acid and muscimol containing mushrooms reported to a United States regional poison center from 2002–2016. Cases were included if identification was made by a mycologist or if AM was clearly described.
Results: Thirty-four cases met inclusion criteria. There were 23 cases of AM, 10 AP, and 1 A. aprica. Reason for ingestion included foraging (12), recreational (6), accidental (12), therapeutic (1), self-harm (1), and unknown (2). Of the accidental pediatric ingestions 4 (25%) were symptomatic. None of the children with a symptomatic ingestion of AM required admission. A 3-year-old male who ingested AP had vomiting, agitation, and lethargy and received benzodiazepines. He was intubated and had a 3-day ICU stay. There were 25 symptomatic patients. All but one patient developed symptoms within 6 h. Six patients had symptoms for less than 6 h while 15 had symptoms lasting less than 24 h. Ingestions of AP were more symptomatic than AM with regard to the presence of any GI symptoms (80% vs. 35%), central nervous system (CNS) depression (70% vs. 35%), and CNS excitation (70% vs. 35%) respectively. Five patients were intubated. No patients experienced hypotension, seizures, acute kidney injury, or hepatotoxicity. No deaths were reported.
Discussion: Ingestion of ibotenic acid/muscimol containing mushrooms often produces a syndrome with GI upset, CNS excitation, and CNS depression either alone or in combination. Ingestion of AP was associated with a higher rate of symptoms compared to AM.
This review from the International Consortium on Hallucinations Research intends to question the pertinence of the excitatory-to-inhibitory (E/I) imbalance hypothesis as a model for hallucinations. A large number of studies suggest that subtle impairments of the E/I balance are involved in neurological and psychiatric conditions, such as schizophrenia. Emerging evidence also points to a role of the E/I balance in maintaining stable perceptual representations, suggesting it may be a plausible model for hallucinations. In support, hallucinations have been linked to inhibitory deficits as shown with impairment of gamma-aminobutyric acid transmission, N-methyl-d-aspartate receptor plasticity, reductions in gamma-frequency oscillations, hyperactivity in sensory cortices, and cognitive inhibition deficits. However, the mechanisms by which E/I dysfunctions at the cellular level might relate to clinical symptoms and cognitive deficits remain unclear. Given recent data advances in the field of clinical neuroscience, it is now possible to conduct a synthesis of available data specifically related to hallucinations. These findings are integrated with the latest computational frameworks of hallucinations, and recommendations for future research are provided.
Purpose:
To evaluate efficacy and safety of gaboxadol for treatment of children with Angelman syndrome (AS).
Method:
In this international, double-blind, phase 3 trial, we randomized children 4-12 years old with a molecular diagnosis of AS and a Clinical Global Impression (CGI)-severity score ≥3 to either daily administration of weight-based gaboxadol or matching placebo for 12 weeks. The primary endpoint was the CGI-Improvement-AS (CGI-I-AS) score at week 12. Secondary endpoints included the proportion of participants with CGI-I-AS response of ≤3 (i.e., at least "minimal improvement") and ≤2 (i.e., at least "much improvement") at week 12. Safety and tolerability were monitored throughout the study. Weight based dosing of study drug ranged from 0.125 mg/kg to 0.24 mg/kg depending on weight range.
Results:
Between August 2019 and November 2020, 104 participants were enrolled: participants 4-12 years old were randomly (1:1) assigned to gaboxadol (n = 47) or placebo (n = 50), and 7 other participants 2─3 years old who received gaboxadol and were assessed for safety only. All gaboxadol-treated participants and 48 of 50 placebo-treated participants completed treatment. There was no significant difference in CGI-I-AS between groups: at week 12, mean CGI-I-AS score was 3.3 (SD, 1.00) and 3.2 (SD, 1.05) in the gaboxadol and placebo groups, respectively, yielding a least squares mean difference of zero (p = 0.83). There were no between-group significant differences with respect to CGI-I-AS responses. Gaboxadol was well tolerated in all age groups of this study.
Conclusions:
There was no significant difference in CGI-I-AS between gaboxadol and placebo after 12 weeks of study treatment in pediatric AS participants.
Clinicaltrials:
GOV: NCT04106557.
The presented study focuses on the interaction of the well-known neurotoxin muscimol with water. Two approaches for the water solvent are applied - the explicit and the implicit. The muscimol-water clusters were obtained by the molecular dynamics simulations and the first solvation shell was kept for further studies. Implicit water was mimicked via the polarized continuum model (PCM). All three tautomeric forms of the free muscimol molecule are considered in the calculations. The combined theoretical and experimental vibrational IR and Raman studies determined the stability of the prevailing zwitterion form in water. We proved that water molecules in the first solvation shell are crucial for the correct prediction of structural and spectroscopic parameters of muscimol due to its ability to form strong hydrogen bonds. We believe that our findings will shed some light on the binding preferences of muscimol with the γ-aminobutyric acid (GABA) receptor.
The biologically active alkaloid muscimol is present in fly agaric mushroom (Amanita muscaria) and its structure and action is related to human neurotransmitter ᵞ‐aminobutyric acid (GABA). The current study reports on determination of muscimol form present in water solution using multinuclear 1H and 13C NMR experiments supported by density functional theory (DFT) molecular modeling. Both the structures of three forms of free muscimol molecule in the gas phase and in the presence of water solvent, modeled by polarized continuous model (PCM), and nuclear magnetic isotropic shieldings, the corresponding chemical shifts and indirect spin‐spin coupling constants (SSCC) were calculated. Several J‐couplings observed in proton and carbon NMR spectra, not available before are reported. The obtained experimental spectra, supported by theoretical calculations favor the zwitterion form of muscimol in water. This structure differs from NH isomer, previously determined in DMSO solution. In addition, positions of signals C3 and C5 are reversed in both solvents.
Muscimol is the main compound found in Amanita muscaria. Several studies have proven that muscimol has suppressive effects on essential tremor, without impairing speech and coordination. The effects of muscimol in Parkinson-affected patients is also described in a number of studies. These studies describe the free radical scavenging and antioxidant activity of the mushroom extract. We have evaluated the possible neuroprotective effects of a standardized extract from A. muscaria, containing high amounts of muscimol, on different models of neurotoxicity in rat brain microsomes, mitochondria, synaptosomes as well as on neuroblastoma cell line SH-SY5Y. The possible inhibitory effect on human recombinant monoaminoxidase-B (hMAOB) enzyme was also studied. The extract revealed statistically significant neuroprotective effects on the in vitro neurotoxicity models and no inhibitory activity on hMAOB.
Psilocybin is found in a family of mushrooms commonly known as “magic mushrooms” that have been used throughout history to induce hallucinations. In the late 1950s Albert Hofmann, of Sandoz Laboratories, identified and synthesized the psychoactive compounds psilocybin and psilocin which are found in psilocybe mushrooms. Psilocybin was marketed by Sandoz as Indocybin for basic psychopharmacological and therapeutic clinical research. Psilocybin saw a rapid rise in popularity during the 1960s and was classed as a schedule I drug in 1970. This led to a significant decrease in psilocybin research. Recently, however, preliminary studies with psilocybin have shown promise as potential for the treatment of obsessive compulsive disorder, alcohol addiction, tobacco addiction, major depressive disorder, and the treatment of depression in terminally ill cancer patients. This review describes in detail the synthesis, metabolism, pharmacology, ADRs and importance of psilocybin to neuroscience in the past and present.
The mushroom Amanita muscaria (fly agaric) is widely distributed throughout continental Europe and the UK. Its common name suggests that it had been used to kill flies, until superseded by arsenic. The bioactive compounds occurring in the mushroom remained a mystery for long periods of time, but eventually four hallucinogens were isolated from the fungus: muscarine, muscimol, muscazone and ibotenic acid.
The shamans of Eastern Siberia used the mushroom as an inebriant and a hallucinogen. In 1912, Henry Dale suggested that muscarine (or a closely related substance) was the transmitter at the parasympathetic nerve endings, where it would produce lacrimation, salivation, sweating, bronchoconstriction and increased intestinal motility. He and Otto Loewi eventually isolated the transmitter and showed that it was not muscarine but acetylcholine. The receptor is now known variously as cholinergic or muscarinic. From this basic knowledge, drugs such as pilocarpine (cholinergic) and ipratropium (anticholinergic) have been shown to be of value in glaucoma and diseases of the lungs, respectively.
This volume is the third edition of a monograph series that was first published in 1983. The demand for this work is a testament to the impact of studies on -aminobutyric acid (GABA) receptors on the basic understanding of synaptic transmission and on defining the clinical importance of the neurotransmitter system. Chronicled in The GABA Receptors, Third Edition, are the advances made in understanding the molecular and pharmacological properties of GABA A and GABA receptors since the topic was last reviewed in 1996. Particular B emphasis is placed on describing the assembly, structure, and function of GABA B sites, the first heterodimeric G protein-coupled receptors identified in vivo. In addition, there are reports dealing with the subunit composition, trafficking, and pharmacological selectivity of GABA receptors. Aside from providing A insights into the fundamental properties of ligand-gated ion channels and second messenger systems, the findings detailed in this work point the way for developing novel therapeutics capable of more selectively manipulating these transmitter sites.
Recent studies devoted to neuroprotection have focused on the role of the gamma-aminobutyric acid (GABA) system in regulating neuroinflammatory processes which play a key role in the neurodegenerative processes observed in Alzheimer's disease (AD) by inducing glial cell overactivation and impairing neurotransmission.
Data on the efficacy of classical GABA-A and GABA-B receptor agonists (muscimol and baclofen, respectively) in animal models of AD are not available. Moreover, no published studies have examined the ability of optimal doses of these compounds to prevent neuroinflammation, the alterations in neurotransmission and cognitive deficits. In the present study, we used a non-transgenic rat model of AD obtained by intracerebroventricular streptozocin (STZ) injection and assessed the effects of muscimol and baclofen at very low doses (0.01–0.05 mg/kg) on spatial memory and the expression of cortical and hippocampal proteins related to neuroinflammation, namely proteins involved in astroglial functions (glial fibrillary acidic protein, GFAP), GABA synthesis (GABA synthesizing enzyme, glutamic acid decarboxylase 67, GAD67) and acetylcholine degradation (acetylcholine esterase).
The presented study demonstrated that in a rat model of STZ-induced AD both muscimol and baclofen at the tested doses exerted memory-enhancing and anti-inflammatory effects, as well as normalization of acetylcholine esterase and GABA expression. We suggested that the function of very low doses of GABA receptor agonists differs from typical GABA-related inhibition and may be mediated by the allosteric sites of GABA receptors or other non-specific cell regulatory pathways.
The article presents an integration and analysis of data collected by ethnographers, toxicologists, pharmacologists, travellers, psychiatrists, and chemisists on the psychological effects of Amanita muscaria and its constituent psychoactive substances - iboteic acid and muscimol. The article shows the changes brought about in psyche by Amanita muscaria and its psychoactive components in terms of activation, sleep, motility, perception, memory, speech, attention, thinking, self-consciousness, body sense, orientation in space and time, situation assessment, control over and regulation of behaviour as well as emotional, volitional, and motivation and semantic aspects. The presence or absence of an idea of deliberate Fly Agaric intoxication in a particular culture is discussed as one of possible causes of differing psychological effects of Amanita muscaria identified in different data sets.
Ibotenic acid and its active metabolite muscimol are neurotoxins found in the famous Amanita muscaria mushroom. Cultural folklore vaguely describes historical uses of A. muscaria during rituals but many of these have now been discounted. The clinical effects of A. muscaria ingestion are unpredictable with both neuroexcitatory and neurodepressive symptoms reported. Most ingestions can be managed with supportive care and resolve over a few hours. Amanita muscaria is occasionally ingested intentionally but is a not a highly sought after intoxicant.
Photolysis of 3 hydroxy 5 phenylisoxazole in methanol with a low pressure mercury lamp afforded 5 phenyl 4 oxazolin 2 one, together with small amounts of benzoic acid and benzoylacetamide. Similarly, 3 hydroxy 5 methylisoxazole in distilled water afforded 5 methyl 4 oxazolin 2 one as the major product. Both isoxazoles were stable in sunlight for up to 20 days.
dl-Ibotenic acid (I) was synthesized in a better yield than the known methods, starting from diethyl 3-chloroglutaconate (VII). Reaction of VII with hydroxylamine in the presence of sodium hydroxide followed by esterification afforded ethyl 3-hydroxy-5-isoxazoleacetate (IV), which was, after benzenesulfonylation, brominated with NBS to ethyl α-bromo-3-benzenesulfonyloxy-5-isoxazoleacetate (X). Hydrolysis and treatment with ammonia of X gave I. Synthesis of muscimol (II) from IV was also described.
The preparation of museimol (a potent but toxic GABA neurotransmitter agonist), from dimethyl acetylenedicarboxylate via methyl 3-hydroxyisoxazole-5-carboxylate and the corresponding amide, has been improved and extended to a general synthesis of N-alkyl and N,N-dialkyl derivatives. The efficient route to muscimol itself [muscimol itself costs 60 -170 DM/10 mg] has enabled a study of its chemistry to be undertaken, a first result of which is its incorporation into a peptide, i.e. the preparation of N-glycylmuscimol.
β-Bromocinnamonitrile and hydroxylamine afforded 3-amino-5-phenylisoxazole in the presence of alkali, unexpectedly. So the reaction of acetylenic nitriles and esters with hydroxylamine was examined under alkaline conditions. Phenylpropiolonitrile and propiolonitrile gave 3-amino-5-phenylisoxazole and 3-aminoisoxazole, respectively. Tetrolonitrile afforded a 3 : 1 mixture of 3-amino-5-methyl- and 3-methyl-5-amino-isoxazole in the presence of alkali. Under neutral conditions these nitriles gave the corresponding 5-aminoisoxazoles. Similarly, 3-hydroxy-, 3-hydroxy-5-methyl- and 3-hydroxy-5-phenyl-isoxazole were obtained from the corresponding acetylenic esters. In the case of methyl tetrolate, two isomers of tetrolohydroxamic acid were isolated as the intermediate. On the other hand, free phenylpropiolic acid gave only 3-phenyl-5-isoxazolone under the same alkaline conditions.
A convenient analytical method for ibotenic acid (IBO) and muscimol (MUS) in a toxic mushroom, Amanita muscaria (A. muscaria), was developed. IBO and MUS in the mushroom were extracted with 70% methanol. After filtration, IBO and MUS in the extract were determined by high performance liquid chromatography (HPLC) with a UV detector set at 210nm. The HPLC system adopted was ion-pair chromatography in the reverse-phase mode on an IRICA RP-18 (C18) column (4.0mm×25cm) with sodium dodecyl sulfate as a counter ion. Recoveries of IBO and MUS added to the sample were more than 98%, and the minimum detectable concentration of IBO or MUS was about 1ppm. The concentrations of IBO and MUS in A. muscaria ranged from 258 to 471ppm and from 18 to 27ppm, respectively. Neither of the compounds was detected in commercial edible mushrooms.
It is believed by people in mountainous areas that toxins in A. muscaria are reduced by drying, storing or cooking. The main physiologically active substances, ibotenic acid (IBO) and muscimol (MUS), in A. muscaria were therefore investigated. IBO is readily transformed to into MUS through decarboxylation, and MUS is a hallucinogen. Drying A. muscaria in the sun or with a heater caused an increase of MUS in the mushroom, though a lot of precursor IBO was lost. It was suggested that the toxicity of the mushroom would be intensified by processing. IBO and MUS in the mushroom were stable on storage under dry or salt conditions. MUS increased in concentration while IBO decreased during heat-cooking, and the changes were more marked under acidic than alkaline conditions. However, general cooking (within 10 minutes) hardly reduced the toxic substances. Boiling or soaking A. muscaria in water caused most of the IBO and MUS in the mushroom to be released rapidly into the water.
A. muscaria contains more excitatory ibotenic acid and less depressant muscimol compared to A. pantherina. In this study A. muscaria poisoned patients were more often confused (26/32, p=0.01) and agitated (20/32, p=0.03) compared to those poisoned with A. pantherina (8/17 and 5/17). Patients poisoned with A. pantherina were more commonly comatose (5/17) compared to those poisoned with A. muscaria (2/32) (p=0.03). In conclusion, the so-called ibotenic or pantherina-muscaria syndrome might be divided into two subtypes.
Muscimol, a psychoactive isoxazole from Amanita muscaria and related mushrooms, has proved to be a remarkably selective agonist at ionotropic receptors for the inhibitory neurotransmitter GABA. This historic overview highlights the discovery and development of muscimol and related compounds as a GABA agonist by Danish and Australian neurochemists. Muscimol is widely used as a ligand to probe GABA receptors and was the lead compound in the development of a range of GABAergic agents including nipecotic acid, tiagabine, 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol, (Gaboxadol(®)) and 4-PIOL.
The ionotropic GABAA receptors (GABAARs) are widely distributed in the central nervous system where they play essential roles in numerous physiological and pathological processes. A high degree of structural heterogeneity of the GABAAR has been revealed and extensive effort has been made to develop selective and potent GABAAR agonists. This review investigates the use of heterocyclic carboxylic acid bioisosteres within the GABAAR area. Several heterocycles including 3-hydroxyisoxazole, 3-hydroxyisoxazoline, 3-hydroxyisothiazole, and the 1- and 3-hydroxypyrazole rings have been employed in order to map the orthosteric binding site. The physicochemical properties of the heterocyclic moieties making them suitable for bioisosteric replacement of the carboxylic acid in the molecule of GABA are discussed. A variety of synthetic strategies for synthesis of the heterocyclic scaffolds are available. Likewise, methods for introduction of substituents into specific positions of the heterocyclic scaffolds facilitate the investigation of different regions in the orthosteric binding pocket in close vicinity of the core scaffolds of muscimol/GABA. The development of structural models, from pharmacophore models to receptor homology models, has provided more insight into the molecular basis for binding. Similar binding modes are proposed for the heterocyclic GABA analogues covered in this review by use of ligand-receptor docking into the receptor homology model and the presented structure-activity relationships. A network of interactions between the analogues and the binding pocket is leaving no room for substituents and underline the limited space in the GABAAR orthosteric binding site when in the agonist conformation.
The psychoactive isoxazole muscimol has been synthesized in three steps from propargyl chloride.
A simple and large scale approach to the synthesis of muscimol 7 has been developed starting from the easily available dibromoformaldoxime 1.
It has been reported that little, if any, unchanged muscimol, a GABA receptor agonist, penetrates into mouse brain following systemic administration suggesting that the behavioral effects of this drug may be due to the action of some derivative or to the combined effect of a derivative and muscimol. Further studies have revealed that muscimol degradation can be significantly reduced by the administration of a GABA transaminase inhibitor such as aminooxyacetic acid, ethanolamine-O-sulfate (EOS) or γ-acetylenic GABA. For example, pretreatment of mice with EOS, in doses reported to be effective only on peripheral GABA transaminase, results in a significant increase in the amount of muscimol found in brain. Furthermore, pretreatment of mice with EOS substantially enhances the ability of muscimol to protect against bicuculline-induced seizures. These findings suggest that the anticonvulsant activity of muscimol is intrinsic rather than due to a metabolite and that co-administration of muscimol and a periperal GABA transaminase inhibitor may be a useful method for activating brain GABA receptors in vivo.
: Psychoactive drugs of fungal origin, psilocin, ibotenic acid, and muscimol among them have been proposed for recreational use and popularized since the 1960s, XX century. Despite their well-documented neurotoxicity, they reached reputation of being safe and nonaddictive. Scientific efforts to find any medical application for these hallucinogens in psychiatry, psychotherapy, and even for religious rituals support are highly controversial. Even if they show any healing potential, their usage in psychotherapy is in some cases inadequate and may additionally harm seriously suffering patients. Hallucinogens are thought to reduce cognitive functions. However, in case of indolealkylamines, such as psilocin, some recent findings suggest their ability to improve perception and mental skills, what would motivate the consumption of "magic mushrooms." The present article offers an opportunity to find out what are the main symptoms of intoxication with mushrooms containing psilocybin/psilocin, muscimol, and ibotenic acid. The progress in analytical methods for detection of them in fungal material, food, and body fluids is reviewed. Findings on the mechanisms of their biologic activity are summarized. Additionally, therapeutic potential of these fungal psychoactive compounds and health risk associated with their abuse are discussed.
Abstract The -aminobutyric acid type A (GABAA) receptor agonist muscimol is widely used as a tool for reducing neuronal activities particularly in experiments in vivo. At the synapse formed by the calyx of Held in the rat brainstem slice, the GABAA receptor agonist muscimol (> 10 m) attenuated the amplitude of excitatory post synaptic currents (EPSCs) accompanied by an increase in the coefficient of variation of EPSCs, suggesting its presynaptic inhibitory effect. This muscimol effect was not affected by bicuculline but occluded the presynaptic inhibitory effect of the GABAB receptor agonist baclofen and was abolished by the type B GABA (GABAB) receptor-specific antagonist (+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911; 20 m). We conclude that muscimol activates presynaptic GABAB receptors thereby attenuating synaptic transmission.
The naturally occurring zwitterionic alkaloid muscimol 3 has been of considerable pharmacological interest in recent years, it being the best example of an in vivo active mimetic of the neurotransmitter γ-aminobutyric acid (GABA). A number of syntheses of this compound have been reported over the past fourteen years, culminating in the recent report of Jager and Frey who prepared 1 in three steps and 30% overall yield. These latter authors suggested the shorter two steproute depicted in Equation 1 but were apparently unable to synthesize the requisite hydroxamic acid 2 in adequate yield and purity to complete the synthesis. The original preparation of this hydroxamic acid had been reported by Hines and Stammer in 1977′ from dimethyl acetylenedicarboxylate and hydroxylamine. This procedure also gave a relatively crude and low melting product.
Ibotenic acid and muscimol are considered the principal components responsible of the hallucinogenic properties of Amanita muscaria. In this paper a sensitive ion-interaction HPLC method is presented which permits the simultaneous determination of ibotenic acid and muscimol. A C18 reverse phase is the stationary phase and the mobile phase is an aqueous solution of 5.0 mM octylammonium o-phosphate. A spectrophotometric comparative detection performed at 230 and 254 nm is employed. Detection limits are of 18 μg/L for ibotenic acid and of 30 μg/L for muscimol.
Eine kurze Synthese von Muscimol
Muscimol (1) wurde, ausgehend von Acetylendicarbonsäure‐dimethylester (3) und N ‐Hydroxyharnstoff, in 3 Schritten mit 30proz. Ausbeute synthetisiert.