Long-term expression of Fos-related antigen and transient expression of δFosB associated with seizures in the rat hippocampus and striatum

Systemic administration of kainic acid (KA), an analogue of glutamic acid, causes limbic seizures and pathophysiological changes in adult rats that are very similar to human temporal lobe epilepsy. One of the earliest changes in gene expression after treatment with KA is the induction of immediate-early genes. The fos and jun families are frequently studied immediate-early genes that are induced by KA. Several groups, including ours, have recently reported that a 35-kDa Fos-related antigen (FRA) is induced for a protracted time by various stimuli. It has been suggested that this FRA is ΔFosB, which has a molecular mass of ~35 kDa. The present study characterizes the long-term expression of FRA and ΔFosB after systemic treatment with KA. Immunocytochemistry and western blot analysis using an antibody that cross-reacts with all known FRAs showed that a 35-kDa FRA was induced at high levels in both the hippocampus and striatum for up to 1 month by KA. A semiquantitative PCR analysis showed that ΔFosB was induced by KA, but its expression lasted for only 6 h. This result was also verified by northern blot analysis. These results suggested that the 35-kDa FBA with long-term elevated levels seen with western blot analysis and immunocytochemistry is a new species of the FRA and not ΔFosB. The long- term expression of FRA in both the hippocampus and striatum may be associated with the pathophysiological changes after KA administration.