INDUCTION OF C-FOS MESSENGER-RNA EXPRESSION BY AFTERDISCHARGE IN THE HIPPOCAMPUS OF NAIVE AND KINDLED RATS

Abstract: Periodic induction of focal electrical seizure [afterdischarge (AD)] is an absolute prerequisite for the development of kindling, an animal model of complex partial epilepsy. Once established, it is a permanent condition. The mechanism(s) that translate ADs, which last tens of seconds, into life‐long alterations in the CNS is unclear. Cellular immediate‐early genes have been implicated in the conversion of short‐term stimuli to long‐term alterations in cellular phe‐notypes by regulating target gene expression. We have investigated the contribution of one such early gene, c‐fos, to this process. The relationship between ADs and expression of c‐fos gene in the rat hippocampus, a key structure in kindling development, was studied by analysis of mRNA levels. The low constitutive expression of c‐fos mRNA in the hippocampus was not altered by kindling. There was an “all‐or‐none” relationship between induction of c‐fos and the duration of AD. The threshold for induction was approximately 30 s of AD. Above‐threshold ADs induced c‐fos in both naive and kindled animals to the same extent and with identical temporal profiles. Although the expression of c‐fos is unchanged with kindling, c‐fos may nonetheless contribute to many long‐term changes of kindling, both adaptive and epileptogenic. Copyright © 1990, Wiley Blackwell. All rights reserved