Molecular dissection of corticosteroid action in the rat hippocampus. Application of the differential display techniques.

Both adrenal steroids and glutamate are crucial for hippocampal cell viability. In order to identify adrenal steroid- and glutamate-responsive genes controlling hippocampal cell viability, we have used the PCR-based differential display method. We have described the characteristics of this technique and how it can be automated. Using differential display, we have identified a number of rat hippocampal genes of which the expression is affected by a combination of the glutamate analog kainic acid and adrenalectomy. Administration of kainic acid or removal of the adrenals alone gave a limited number of differentially displayed genes. Therefore, our results indicate that the main mode of corticosteroid receptor-controlled gene expression in the hippocampus is interaction with other transcription factors (e.g., CREB, AP-1) and not by binding to hormone-responsive elements of corticosterone-specific genes. Characterization by multiplex PCR experiments of a differentially displayed fragment of which the expression is increased by the combination of kainic acid and adrenalectomy confirmed our differential display results. Further characterization by DNA sequence analysis of the corresponding full-length cDNA clone revealed a gene product with 91.4% sequence identity with the mouse transcription factor KROX-20, suggesting that we have cloned the rat homolog. This finding suggests a role of KROX-20 in corticosteroid- and kainic acid-controlled hippocampal plasticity.