Substance biology

The fly agaric in Dr Stone

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As this look back at the first steps of the kingdom of science unfolds, attention turns to an iconic mushroom, bright red and dotted with white flecks, instantly recognizable. The scene underlines its special status in the collective imagination and its extraordinary properties, a far cry from those of an ordinary foraged mushroom.

The subject in depth

The fly agaric, scientific name Amanita muscaria, is arguably the most recognizable mushroom in the world: a scarlet-red cap sprinkled with white flakes, sitting on a pale stem [Wikipedia] . It is the archetypal fairy-tale mushroom, and its image adorns children’s books and video games alike. Its name comes from an old use: crumbled into sweetened milk, it was used to stun and attract flies.

What makes this mushroom singular is not a deadly toxin but a cocktail of psychoactive molecules. The two main ones are ibotenic acid and muscimol [Wikipedia] . In the fresh mushroom, ibotenic acid dominates; as it dries or is heated, part of it is converted by decarboxylation into muscimol, which is markedly more active. Muscimol is an agonist of GABA-A receptors, the brain’s main braking system. By binding in their place, it depresses neuronal activity and causes sedation, disorientation, perceptual distortions and hallucinations, often followed by deep sleep.

Diagram of the red, white-spotted fly agaric with its toxins muscimol and ibotenic acid acting on the brain
Muscimol mimics GABA and presses the brain's brake

This effect is very different from that of the so-called “magic” psilocybin mushrooms, which act on the serotonin system. It also differs radically (and this is essential) from the mode of action of the deadly amanitas. The fly agaric is toxic but rarely lethal in adults: it causes nausea, vomiting, agitation, delirium and sometimes convulsions, with a higher risk in children. Severe poisonings remain possible, especially when species are confused.

That is the real danger. Several amanitas look alike at early stages of development, and some, like the death cap or the destroying angel, are deadly through their amatoxins, which destroy the liver. Mistaking a poisonous amanita for an edible species, or underestimating the toxicity of the fly agaric, can have dramatic consequences.

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