Chronic focal epilepsy induced by intracerebral tetanus toxin.

A single, minute dose of tetanus toxin injected into mammalian cerebral cortex induces a chronic epileptic syndrome. Seizures lasting up to 3 minutes occur spontaneously and intermittently for several weeks to months. The cellular mechanisms of this model have been studied in detail using brain slices in vitro. Initially the release of the inhibitory neurotransmitter, GABA, is blocked, but after 2-4 weeks, other mechanisms take over. Intrahippocampal tetanus toxin models human complex partial seizures (temporal lobe epilepsy). It results in consistent behavioural changes analogous with those seen clinically, in spite of the limited neuronal loss found in only 10-30% of rats. Treatment with carbamazepine ameliorates both the seizures and their behavioural consequences. Tetanus toxin provides a versatile and long-lasting model of focal epilepsies.