Adult rats were given antidepressant drugs orally. Fluoxetine, but not moclobemide, venlafaxine, tianeptine or desipramine, increased total glucocorticoid receptor (GR) mRNA in the hippocampus after 4 weeks. Further examination revealed that GR mRNA containing the brain-specific exon 1(7) was increased across all hippocampal subregions. In contrast, expression of the major exon 1(10) and another brain-specific exon 1(5)-containing GR mRNAs were unchanged. Tissue-specific first exon usage may contribute to the differential regulation of GR by fluoxetine in brain subregions. (C) 2004 Elsevier B.V. All rights reserved.