In the course of experiments on
focal epilepsy in rats, we have recognized that there are no adequate models of subacute
focal epilepsy in rodents. We have, therefore, reevaluated a previously described rat model that reliably generates subacute
seizures over 2-3 weeks. After implantation of a short length of
cobalt wire into the left motor cortex, the animals are monitored by standard EEG over the next 3 weeks. They develop three seizure types: 1.
Simple partial seizures with contralateral clonic jerks, lasting 17.9 +/- 46.4 min; these
seizures were characterized by repetitive single spikes; 2. Secondarily
generalized seizures, lasting 34.5 +/- 19.0 s; and 3.
Complex partial seizures with a paroxysmal EEG, lasting 39.6 +/- 55.5 s. Post mortem brains were imaged using standard magnetic resonance techniques, after removal of the ferromagnetic
cobalt wire. There was a localized loss of the MR signal that differed by pulse sequence, indicating spread of the ferromagnetic
cobalt into the brain tissue. The image disruption caused by the
cobalt was quite abrupt, indicating a sharp
cobalt concentration gradient. However, we saw no evidence of widespread cerebral injury. The unilateral
cobalt wire model generates less frequent, but more persistent
seizures than seen in most acute, focal models. The ferromagnetic signal present, even after wire removal, indicates that metallic
cobalt leaches into the cortex and may be responsible for generating the
seizures. This model should be useful for testing new
therapies for neocortical
epilepsy.