Regional expression of the proto-oncogene c-fos was mapped by in situ hybridization in rat brain sections from animals with kindled seizures from two paradigms. Cocaine-Kindled Seizure: The expression of c-fos mRNA was bilateral in several brain regions and was restricted to those rats exhibiting major motor seizures. The increases were observed in the olfactory bulb, hippocampus and the piriform, occipital, entorhinal and perirhinal cortices. No increases were detected in animals that received cocaine but had no seizures, nor in saline controls. Amygdala-Kindled Seizure: In initial stages of kindling (stages 1 and 2), two patterns of c-fos induction were observed. One involved unilateral expression in cortical regions of the cerebrum with no involvement of the hippocampus. The second pattern involved only the hippocampus with no increases in the cerebral cortex. The hippocampal induction was either unilateral or bilateral. At stage 3, these two initial patterns were combined, showing both cerebral cortical and hippocampal c-fos expression. This expression at stage 3 was not consistently bilateral in the cortical regions. During the latter stages of kindling (stages 4 and 5), the cortical and hippocampal expression of c-fos was bilateral throughout.
