ABSTRACT
The motor system has major importance for the maintenance of life in the animals, including humans. It is composed functionally of the pyramidal and the extrapyramidal tracts, and anatomically of the central nervous system, peripheral nerves, and the muscle. Because disruption to the system can lead directly to death, man has shown much interest in agents acting on the motor system. Thus, a variety of agents have been discovered in nature and synthesized artificially, e.g. curare, -bungarotoxin of snake venom, succinylcholine, anticholinesterase inhibitors known as “nerve gases”, etc. Among them, tetanus and botulinus are the most potent and characteristic agents. They both act on the nerve terminal and inhibit synaptic transmission by blocking the release of neurotransmitter from the presynaptic site. Tetanus and botulinus neurotoxins are produced by the bacteria Clostridium tetani and C. botulinum, respectively which belong to the same genus, Clostridia. These bacteria inhabit the lower gastrointestinal tract of normal domestic and wild animals. They are anaerobic and form spores which are resistant to dryness, irradiation, and chemical disinfectants. Therefore they can regularly be found in soil over the world, and many people are infected and become intoxicated as a result. Mortality rates of these intoxicants, tetanus and botulism, are still high (~50%) in spite of great advances in recent emergency therapeutics. Dominant manifestations of tetanus and botulism arise from disruption of the motor system, although sometimes the autonomic nervous system is affected by severe cases of intoxications. In the cases of tetanus, long-lasting contractions of all the skeletal muscle, easily induced by light or sound stimulations, are observed. On the other hand, weakness or flaccid paralysis of skeletal muscles is observed with botulism. Though the toxic signs and symptoms of tetanus and botulism are quite different, recent studies on the structure of these neurotoxins and on their molecular mode of actions have been revealing great similarities between them. In this chapter, we will focus on comparison of tetanus and botulinum neurotoxin structures, pathophysiology, and molecular modes of action.
