The effect of deep prepyriform cortex (DPC) kindling on the levels of prodynorphin mRNA (DYN mRNA) in rat hippocampus and striatum was examined under two different stimulation paradigms. Electrical stimulations were delivered to rats twice per day (slow kindling) or once every hour (fast kindling) until two consecutive stage 5 kindled seizures occurred. Animals were decapitated 24 h after reaching the second stage 5 seizure, and DYN mRNA levels in the brain were determined by RNA blot analysis. In the slow kindling model, the level of DYN mRNA in the hippocampus was reduced by 57%, whereas the level of striatal DYN mRNA was increased by 34% compared to sham-operated controls. Fast kindling induced a similar decrease in the DYN mRNA level in the hippocampus, but did not alter that in the striatum. These results, together with the previous report that kindling decreased dynorphin A(1-8) level in the hippocampus, suggest that electrical kindling decreases the biosynthesis of dynorphin peptides in the hippocampus and, in the slow DPC kindling model, also increases the gene expression of dynorphin in the striatum.