Ibotenic Acid and Muscimol in Amanita muscaria: Chemistry, Sources of Variability, Analytical Determination, and Toxicological Significance

Amanita muscaria contains two structurally related neuroactive isoxazole metabolites, ibotenic acid (IA) and muscimol (MUS), which differ markedly in pharmacological activity. IA acts as an agonist at NMDA and metabotropic glutamate receptors, whereas MUS is a potent GABAergic agonist. This review critically evaluates their chemistry and biosynthesis, biological variability, post-harvest transformation, analytical determination, and toxicological significance. Direct evidence demonstrates interspecific variation within Amanita section Amanita. Developmental evidence for A. muscaria is limited but direct: an older maturation study identified tissue-dependent changes in IA and MUS, while concentrations calculated for the whole fruiting body remained comparatively stable; observations in A. subglobosa provide additional species-specific evidence. Controlled studies also demonstrate processing-related changes during drying and heating, whereas storage effects remain condition-dependent and less completely characterized. Cross-study comparison is constrained by differences in species identification, tissue selection, developmental stage, hydration, sample handling, normalization, and analytical procedure. Quantitative study-level comparison shows that LC–MS/MS and UHPLC–MS/MS, capillary electrophoresis, GC–MS, NMR, and rapid ambient-MS approaches serve different matrices and analytical purposes. Their reported sensitivity, recovery, precision, and calibration performance cannot be ranked directly across studies, and matrix-specific validation remains essential. Broader fungal research provides mechanistic context for possible environmental regulation, but direct controlled evidence for stress-dependent IA biosynthesis in A. muscaria remains sparse. The IA/MUS ratio is best treated as a secondary chemical descriptor alongside absolute concentrations and a clearly defined normalization basis. Toxicological interpretation additionally requires consideration of total dose, preparation, matrix composition, and individual susceptibility.