Botulinum toxin:Atoxinproduced by thebacteriumClostridium botulinumthat is the most poisonous biologicalsubstanceknown.Botulinum toxinacts as aneurotoxin. It binds to thenerveending at the point where the nerve joins amuscle, blocking the release by the nerve of the chemicalacetylcholine(the principalneurotransmitterat theneuromuscularjunction), preventing the muscle from contracting. The result is weakness andparalysisof the muscle. The muscle atrophies. The blockage of acetylcholine release is irreversible. Function can be recovered by the sprouting of nerve terminals and the formation of new synaptic contacts, which usually takes 2 to 3 months.
Very small amounts of botulinum toxin can cause botulisminone of two ways. One way is by ingesting the toxin itself (foodborne botulism), as in canned foods. The other way is byinfectionwith thebacterialspores that produce and release the toxin in the body (infectious botulism). The infection may occur in theintestine(intestinal botulism), as in anewborn(infantbotulism), ordeepwithin a wound (wound botulism).
There is more than one type of botulinum toxin. Different strains of thebacteriaproduce eight distinct neurotoxins. All eight types have a similar molecular weight and structure, consisting of a heavy chain and a light chain joined by a disulfide bond (most publications recognize only seven types; there are eight if the subtypes of C, C1and C2, are counted as separate types. All eight types act in a similar manner. Only types A, B, E and F are known to cause botulism in humans. The toxin is heatlabileand can be destroyed if heated at 80 C (175 F) for 10 minutes or longer although the疾病预防控制中心recommends boiling for 10 minutes or longer.
Purified botulinum toxin A was the first bacterial toxin to be used as a medicine. The USFood and Drug Administration(FDA) approved purified botulinum toxin A (肉毒杆菌) in 1989 for treating twoeye conditions:睑痉挛和斜视。肉毒杆菌has since found other medical and cosmetic uses and was FDA approved in 2002 for treatment of moderate-to-severe frown lines between the eyebrows known as glabellar lines. Botox is often used in other areas of the face for cosmetic purposes. It has been used in the treatment of other medical conditions as well, including migraine headaches,cervicaldystonia ( a muscle disorder of theneckmuscles), andprimaryhyperhidrosis (excessive sweating).
See also:Clostridium botulinum, botulism
