IMMEDIATE-EARLY GENE-EXPRESSION IN EXPERIMENTAL EPILEPSY

Neuronal excitation by experimentally induced seizures elicits the rap id induction of a set of genes called immediate early genes (IEGs). Th e gene products of fos, jun and Krox, multimember gene families that b elong to the class of IEGs, participate in a fundamental biological co ntrol mechanism, the regulation of gene transcription. IEG encoded pro teins act as third messengers in an intracellular signal transduction cascade between neural cell surface receptors, cytoplasmic second mess enger systems and specific target genes in the nucleus, a process for which the term 'stimulus transcription coupling' has been given. Almos t all types of seizures cause dynamic alterations of IEG expression in neurons of the limbic system, but also in non-limbic areas, such as t he cortex, striatum and thalamus. IEG encoded transcription factors ar e thought to up- or down-regulate effector genes with preferential exp ression in the central nervous system, including genes for neurotransm itters, growth factors, receptors, synaptic and axonal proteins. If th e concept holds true that IEGs act as molecular switches converting ep ileptic short-term excitation of neurons into alterations of the molec ular phenotype, future research may help to explain hitherto unexplain ed phenomena in epileptogenesis including changes of synaptic efficacy , kindling and sprouting.