Glucocorticoid receptor mRNA ontogeny in the fetal and postnatal rat forebrain

Glucocorticoid receptor (GR) ontogeny and distribution in postnatal rat brain have been demonstrated, but onset and distribution of GR gene expression during fetal life has not been reported. This study focuses on the distribution of GR-mRNA in the fetal and postnatal rat forebrain, with emphasis on hypothalamic and limbic structures. Time pregnant rats were decapitated at 8:30-9:30 AM on Gestational Days 14 (F14), F16, F17, F18, and F19. Postnatally, rats were sacrificed on Days 1, 4, 6, 10, and 16. Cryostat sections were subjected to in situ hybridization, using a cRNA probe directed to the GR-mRNA. GR-mRNA was detectible in the hippocamposeptal formation as early as F14. By F16, GR gene expression was evident in the hypothalamic paraventricular nucleus (PVN) as well. During late gestation (F17-F19), GR-mRNA was localized also in the thalamus, hippocampus, amygdala, and discrete cortical regions. Postnatally, GR-mRNA abundance was high in the PVN, CA1/CA2 hippocampal field, piriform cortex and dorsal endopiriform nucleus, specific amygdaloid nuclei, and the suprachiasmatic nucleus. In PVN, GR-mRNA was present prior to the onset of CRH gene expression (F17), which may suggest a role for GR in neuronal differentiation.