Seizures induced by intraventricular microinjection of ionized cobalt in the rat--a new experimental model of epilepsy.

A new animal model for epilepsy was successfully produced by microinjection of cobaltous chloride into the lateral cerebral ventricle of the rat. The median convulsive dose (CD50) and the median lethal dose (LD50) of CoCl2 was 0.45 microM/10 microliters (0.27-0.77 microM/10 microliters) and 1.07 microM/10 microliters (0.73-1.57 microM/10 microliters), respectively. The behavioral changes, electrocorticogram (ECoG), and the action of 5 classical anticonvulsants were studied using this new model. Seizures induced by cobaltous chloride are clinically similar to those produced by systemic administration of kainic acid and amygdala kindling. These are characterized by staring spells, wet dog shakes, mild convulsive movements, and stereotyped convulsions. ECoG findings demonstrated a unique epileptic burst during the wet dog shakes. Generalized epileptiform discharges were seen during typical seizures. The burst of spikes first occurred in the opposite temporal and frontal regions; and then became generalized. Among the 5 anticonvulsants studied, phenobarbital (30 mg/kg) and nitrazepam (3 mg/kg) completely antagonized the seizures; carbamazepine showed a moderate effect; and phenytoin as well as sodium valproate showed little effect. It is postulated that the seizures induced by cobaltous chloride may originate in the limbic system; and that cobalt ions are responsible for the seizure-inducing action. The mechanism remains to be investigated.