Generalized seizures induced by an epileptic focus in the mesencephalic reticular formation: impact on the understanding of the generalizing mechanism.

The mode of seizure propagation was studied using a generalized seizure model induced by microinjection of kainic acid (KA) into a unilateral mesencephalic reticular formation (MRF) in cats and rats. Stereotactic surgery was performed under pentobarbital anesthesia; an injection cannula was placed into a unilateral MRF, and bipolar electrodes were implanted into the MRF and the thalamus. Microinjection of KA induced generalized seizures. Focal electrical seizures were elicited in the injected site of the MRF starting 30 min after the injection. The initial clinical change during each seizure was behavioral arrest. These seizures immediately developed to generalized seizures, which were characterized by generalized tonic convulsions with short-term clonic convulsions. On EEG, each generalized seizure started at the same time in all the sites of the brain recorded. Autoradiographic study using a rat model demonstrated high glucose utilization in the MRF, bilateral thalamus, forebrain and bilateral cerebral cortices. The results demonstrated an active participation of MRF in the mechanism of generalized seizures.