Region-specific changes in prodynorphin mRNA and ir-dynorphin A levels after kindled seizures.

The opioid peptide dynorphin is thought to be implicated in specific types of seizures. In particular, complex partial seizures have been shown to cause release of dynorphin, activation of prodynorphin gene expression, and new peptide synthesis in the hippocampus. In this study, the kinetics of the seizure-induced changes in prodynorphin mRNA and ir-dynorphin A levels in the hippocampus have been compared with those induced in the temporal and frontal cortex, i.e., in other regions involved in the pathophysiology of complex partial seizures. Experiments have been run using kindling, one of the most valuable models of partial epilepsy. In the hippocampus (1) prodynorphin mRNA levels transiently increase (threefold) 1 h after kindled seizures, and return to baseline by 2 h, and (2) dynorphin A levels are slightly decreased at 1 h, but increase (twofold) at 2 h and return to baseline by 6 h. In the temporal and in the frontal cortex, a late (beginning at 2 h) and prolonged (up to 24 h) decrease in both prodynorphin mRNA and ir-dynorphin A levels have been observed. These data suggest that differential changes in dynorphin metabolism occur in different brain areas after seizures. The mechanisms and functional implications of this observation remain to be investigated.