botulinum toxin

botulinum toxin A toxin produced by the bacterium Clostridium botulinum, which is the most poisonous biological substance known. Botulinum toxin is toxic to nerves. It binds to the nerve ending at the point where the nerve joins a muscle, blocking the release by the nerve of the chemical acetylcholine (the principal neurotransmitter at the neuromuscular junction), preventing the muscle from contracting. The result is weakness and paralysis of the muscle. Purified botulinum toxin A was the first bacterial toxin to be used as a medicine. It is marketed under the trade name Botox. See also botox; botulism.