Nerve gases are potentially lethal synthetic chemicals developed during the Second World War. They work by blocking the breakdown of the neurotransmitter acetylcholine. As a result it builds up in the synapse and its actions cannot be stopped. Nerve gases are now banned, but can still fall into the wrong hands: in 1995 Tokyo commuters were poisoned by the nerve gas Sarin. The chemical atropine - itself a poison - is found in the plant Deadly Nightshade. It can be used as an emergency antidote as it blocks the action of acetylcholine.