Tetanus toxin as a neurobiological tool to study mechanisms of neuronal cell death in the mammalian brain.

Tetanus toxin is a potent clostridial neurotoxin responsible for causing spastic paralysis in humans, often accompanied by seizures and death. The tetanic syndrome is believed to originate from a disinhibitory action of the toxin in the CNS. To produce its effects, tetanus toxin undergoes retrograde, intra-axonal transport to the CNS, where it blocks preferentially the release of gamma-aminobutyric acid and glycine, two inhibitory neurotransmitters. These effects stem from the cleavage of synaptobrevin, a constitutive small-vesicle protein, by tetanus toxin, whose zinc-dependent metalloprotease characteristics recently have been recognized. Blockade of inhibitory transmission produces a predominance of excitatory amino acid neurotransmission, which is responsible for the neurodegenerative effect caused by tetanus toxin after intrahippocampal injection in rats. In fact, hippocampal damage can effectively be prevented by reduction of glutamate-mediated excitatory transmission, thus suggesting that unopposed excitation may be the underlying mechanism for neuronal cell death.