Corticotropin releasing factor mRNA and peptide levels are differentially regulated in the developing ovine brain

Ontogeny and molecular weight of immunoreactive arginine vasopressin and corticotropin-releasing factor in the ovine fetal hypothalamus

In sheep, arginine vasopressin (AVP) and corticotropin-releasing factor (CRF) stimulate adrenocorticotropic hormone (ACTH) secretion. Increased hypothalamic secretion of these peptides at the end of gestation initiates parturition in this species. We hypothesized that CRF and/or AVP content in the fetal hypothalamus increases late in gestation and that this content was comprised of multiple molecular weight forms of these peptides. Hypothalami and pituitaries were collected from fetuses and lambs (74 days' gestation to 4 weeks postnatal). Hypothalamic concentrations of immunoreactive AVP (IR-AVP) and CRF (IR-CRF) significantly increased during late fetal and neonatal development (p < 0.01). Pituitary AVP concentration did not change. Western blot and gel exclusion chromatography revealed both processed and precursor forms of IR-CRF and IR-AVP in the hypothalamus. We conclude that ovine fetal and neonatal hypothalami contain both processed and unprocessed forms of IR-CRF and IR-AVP and that, overall, concentrations of the immunoreactive peptides increase over the course of development.

Cortisol up-regulates corticotropin releasing factor gene expression in the fetal ovine brainstem at 0.70 gestation

Glucocorticoids are important for the development of the central nervous system. In the ovine fetus, increased levels of plasma cortisol at term provide a stimulus to initiate parturition. CRF is central to this event in that it is one of the main modulators of the hypothalamic-pituitary-adrenal (HPA) axis. The purpose of the present study was to determine the effect of physiological increases in fetal plasma cortisol levels on corticotropin-releasing factor (CRF) gene expression in the developing ovine brain. Fetal plasma cortisol levels were chronically elevated at 0.70 gestation (100 days) to physiological levels found at 0.90 gestation (130 days; term 145 +/- 2 days) when glucocorticoid-induced maturational changes are known to occur in the HPA axis. The 3' end of the ovine CRF gene encodes 4 putative polyadenylation (poly(A)) signals that may post-transcriptionally regulate gene expression through stability, translation and localization of the mRNA in a temporal and spatial manner. To determine whether CRF mRNA levels or poly(A) site usage are differentially regulated by cortisol in a region-specific manner, we used an RNase protection assay with an antisense CRF RNA probe from the 3' coding and untranslated regions of the gene to quantify changes in mRNA levels in the hypothalamus (Hypo), hippocampal-amygdala complex (H and A), frontal cerebral cortex (FCC) and brainstem. Our novel finding was a 3.5-fold increase in CRF mRNA levels in the medulla oblongata of fetuses from the cortisol group compared to those from the saline group (P = 0.001). CRF mRNA levels in the Hypo, H and A and FCC did not change significantly in fetuses from the cortisol group.(ABSTRACT TRUNCATED AT 250 WORDS)