AIMS: Kainic acid (KA), a rigid analog of the excitatory amino acid glutamate, has been widely used to create an excellent animal model for studying human temporal lobe epilepsy. A single injection of KA to rats induces long-lasting recurrent seizures and perhaps permanent biochemical and morphological changes in the brain which resemble the alterations found in patients with temporal lobe epilepsy. The purpose of this study was to elucidate the molecular mechanisms underlying the regulation of the long-term changes by two classes of opioid peptides, enkephalins and dynorphins, which are important neuromodulators regulating the seizure threshold in the hippocampus. ACCOMPLISHMENTS: Recently, we have demonstrated that a single injection of KA up-regulates proenkephalin (PENK) mRNA in the rat hippocampus for at least one year. However, the molecular mechanisms underlying this long-term increase in PENK mRNA levels have not been clearly defined. To determine the possible involvement of ENKCRE2 and other transcription factors in this regulation, gel mobility-shift assays and Western blot analysis were used after KA treatment. The results showed that there are long-lasting increases in Sp1 and ENKCRE2 DNA-binding activities. However, the increase in Sp1 DNA-binding activity was much more pronounced and more protracted than the ENKCRE2 DNA-binding activity. The Sp1 DNA-binding complexes were only competed by non-radioactive Sp1element but not by ENKCRE2, AP-1 or CRE elements, indicating the specificity of Sp1 DNA-binding. The Sp1 element was located in the intron A of the PENK gene. Since Sp1 transcription factors play a dominant role in this regulation, we hypothesized that for the KA-induced the long-term increase in PENK mRNA, the initiation of transcription starts at intron A. Results from RT-PCR and sequencing analysis have confirmed our hypothesis. These results suggested the presence of a new mechanism in the regulation of PENK transcription after KA treatment. Further studies along this line of research should provide insights into the mechanisms underlying the permanent changes of this opioid peptide and its roles in the regulation of seizure threshold in the hippocampus.
