A SINGLE-DOSE OF KAINIC ACID ELEVATES THE LEVELS OF ENKEPHALINS AND ACTIVATOR PROTEIN-1 TRANSCRIPTION FACTORS IN THE HIPPOCAMPUS FOR UP TO 1 YEAR

Neuronal plasticity plays a very important role in brain adaptations t o environmental stimuli, disease, and aging processes. The kainic acid model of temporal lobe epilepsy was used to study the long-term anato mical and biochemical changes in the hippocampus after seizures. Using Northern blot analysis, immunocytochemistry, and Western blot analysi s, we have found a long-term elevation of the proconvulsive opioid pep tide, enkephalin, in the rat hippocampus. We have also demonstrated th at an activator protein-1 transcription factor, the 35-kDa fos-related antigen, can be induced and elevated for at least 1 year after kainat e treatment. This study demonstrated that a single systemic injection of kainate produces almost permanent increases in the enkephalin and a n activator protein-1 transcription factor, the 35-kDa fos-related ant igen, in the rat hippocampus, and it is likely that these two events a re closely associated with the molecular mechanisms of induction of lo ng-lasting enhanced seizure susceptibility in the kainate-induced seiz ure model. The long-term expression of the proenkephalin mRNA and its peptides in the kainate-treated rat hippocampus also suggests an impor tant role in the recurrent seizures of temporal lobe epilepsy.