Compound description
What is Muscimol HCl powder (Agarin)
Why the pure compound rather than the mushroom. 250 mg of pure muscimol is the equivalent of at least 100 g of dried fly agaric caps, and considerably more at concentrations typical for the species. But quantity is not the main point. First, the active content in the mushroom varies several-fold between individual specimens — it depends on soil, altitude and ecosystem, so calculating a dose from the weight of raw material is impossible in principle. Second, drying converts only about 30% of ibotenic acid into muscimol, and dried material retains an excess of it at roughly a 3:2 ratio to muscimol — meaning there is more neurotoxin present than target compound. Third, Amanita muscaria is an efficient bioconcentrator of cadmium, mercury, copper and zinc, with cadmium accumulating specifically in the caps rather than the stems. The pure salt removes all three problems at once: known mass, known purity, no accompanying alkaloids or metals.
Muscimol is an isoxazole alkaloid and the principal active constituent of the fly agaric mushroom Amanita muscaria (Wikipedia). We supply it as the hydrochloride: the salt form is readily water-soluble, whereas the free base dissolves far less well. For preparing aqueous solutions this is a decisive advantage.
The distinguishing feature of the molecule is its geometry. Muscimol positions its binding groups — the amine and the hydroxyl — in a spatial arrangement almost identical to GABA. This is why it is recognised by the highly specific GABAA binding site with a precision most synthetic ligands cannot match (Santa Cruz Biotechnology).
Quantitative binding profile. Muscimol is a full GABAA agonist and a partial GABAC agonist. It binds GABAA at two sites — high- and low-affinity, Kd 10 and 270 nM respectively — and drives chloride efflux with an EC₅₀ of 200 nM. It activates GABAC receptors with an EC₅₀ of 1.3 µM. It has no activity at GABAB receptors, which makes it a clean tool for separating the two branches of GABA signalling (Cayman Chemical).
Muscimol additionally acts as an inhibitor of GABA uptake and as a substrate for GABA transaminase, the GABA-metabolising enzyme (Cayman Chemical). The molecule crosses the blood-brain barrier (Santa Cruz Biotechnology).
Its main use in neuroscience is reversible inactivation. Muscimol has become the standard tool for temporarily silencing a discrete brain region: local injection suppresses neuronal activity in that zone, after which function returns. This makes it possible to establish what a structure actually does without resorting to irreversible lesioning (Majchrzak & Di Scala, Neural Plast 2000). The method appears in hundreds of studies on memory, feeding behaviour, motor control and fear processing.
Other research directions. Muscimol induces a distinct form of long-term depression in the hippocampus involving GABAA but not glutamate receptors (Br J Pharmacol, 1995). Relief of neuropathic pain has been reported in a spinal cord injury model with co-administered intrathecal endomorphin-1 (Brain Behav, 2020).
The compound has a long history: the central actions of muscimol and the related ibotenic acid were described as early as 1968 (Biochem Pharmacol, 1968), and a modern review of its role as an ionotropic GABA agonist summarises half a century of data (Johnston, Neurochem Res 2014). It is one of the few molecules that has remained the reference agonist for its receptor for over fifty years.
Practical note. Muscimol is active at nanomolar concentrations and is a potent central nervous system depressant — the very property that makes it work as an inactivation tool. Calculate weighed amounts using the molecular weight of the salt: 150.56 versus 114.10 for the free base (Wikipedia).
Supplied as a crystalline powder, purity ≥99%, CAS 3579-03-1.
