Kainate-evoked secondary gene expression in the rat hippocampus

Kainate treatment provides a model to study elevated expression of genes whose function may be related to neuronal plasticity. In particular, expression of components of AP-1 transcription factor, i.e. Fos and Jun proteins, has been widely investigated in this system. While AP-1 has been repeatedly implicated in various plasticity-related phenomena, very little is known about its downstream gene targets. In the experiments reported here we have analyzed whether genes recently identified as kainate-induced in the rat dentate gyrus and coding for secretogranin II, clathrin heavy chain and heat shock cognate protein 70 can be characterized by a secondary, i.e. possibly inducible transcription factor-dependent mode of activation. Using in situ hybridization and northern studies we have found that expression of all three genes occurs in all hippocampal regions activated following kainate treatment, the time-course of this activation is delayed when compared to mRNA accumulation of AP-1 components, and finally the expression of all three genes is significantly blocked by a cycloheximide-protein synthesis inhibitor. These results suggest that indeed the genes examined are characterized by their secondary mode of activation.