ONTOGENY OF KAINATE-INDUCED GENE-EXPRESSION IN RAT HIPPOCAMPUS

The ontogeny of kainate induction of AP-I mRNAs, proteins, and DNA bin ding activities was examined in the rat hippocampus. In addition, kain ate induction of preproenkephalin and preprodynorphin mRNAs was examin ed; these genes have been shown to be induced by kainate and have been suggested to be targets of AP-1 regulation in adult rat hippocampus. Despite producing seizures at postnatal day (P) 7, kainate failed to i nduce AP-I or opiate gene expression and did not increase AP-I DNA bin ding activity at this age. Basal levels of AP-I and opiate mRNAs were low in P7 hippocampus. Basal levels of c-jun protein and AP-I DNA bind ing activity were elevated in the P7 hippocampus, to values greater th an induced levels in adult hippocampus. Furthermore, AP-I DNA binding in P7 hippocampal nuclear extract was unaffected by antibodies against fos-related antigens, in contrast to hippocampal extracts from the ol der rats examined. At P14, induction of AP-I and preproenkephalin (but not preprodynorphin) mRNAs was observed with kainate treatment, but t he time course for inductions was delayed relative to kainate inductio ns in the adult hippocampus. At P21, responses to kainate were similar to the adult response. Unlike in adult hippocampus, seizure activity caused by kainate treatment does not increase the transcription factor and opioid peptide gene expression in the hippocampi of P7 rats.