ENTORHINAL CORTEX LESIONS TRANSIENTLY ALTER GLUCOCORTICOID BUT NOT MINERALOCORTICOID RECEPTOR GENE-EXPRESSION IN THE RAT HIPPOCAMPUS

Entorhinal cortex lesions destroy an important hippocampal input and l ead to axonal sprouting in the dentate gyrus. Glucocorticoids are know n to inhibit this reinnervation process. In the present study, we exam ined changes in hippocampal glucocorticoid receptor (GR) and mineraloc orticoid receptor (MR) mRNA expression using in situ hybridization fol lowing unilateral entorhinal cortex lesioning (ECL) in the rat. As ear ly as 1 day postlesioning, a 33% bilateral decrease in GR mRNA express ion was observed in the dentate gyrus. By contrast, a 36% bilateral in crease in GR mRNA expression was detected in the CA1 cell field. GR mR NA levels in both regions returned to those of control animals 2 days postlesioning, indicating that these effects were transient. Adjacent sections hybridized with probes to MR mRNA revealed no changes in hipp ocampal MR gene expression as a result of ECL. The selective decrease in GR mRNA expression observed in the dentate gyrus following ECL is s pecific to the hippocampal subregion targeted for reactive synaptogene sis and thus may serve to attenuate the inhibitory actions of circulat ing glucocorticoids.