Rapid induction of corticotropin-releasing hormone gene transcription in the paraventricular nucleus of the developing rat

Neonates from postnatal days (pnd) 4-14 display a minimal pituitary-adrenal response to mild stress, the so-called stress hyporesponsive period (SHRP) . However, during the SHRP, maternal deprivation (deprived) alters the pitu itary-adrenal. system, enabling neonates to become endocrine responsive to specific stimuli. Although neonates do display stress-induced ACTH, there i s limited evidence for enhanced CRH gene expression early in development. T he present experiment examined whether a mild stimulus (isotonic saline inj ection) administered to deprived and nondeprived neonates would enhance CRH biosynthesis in the paraventricular nucleus. Using in situ hybridization w e measured the time course of CRH heteronuclear RNA (hnRNA) and messenger R NA at 15, 30, and 240 min poststimulus. Pnd 6, 12, and 18 were included to examine the CRH gene response during and outside of the SHRP. Despite the m inimal endocrine response of nondeprived pups during the SHRP, CRH hnRNA an d messenger RNA were elevated at 15 min (all ages). Both transcripts were e nhanced at 15-30 min in deprived (pnd 12 and 18) pups; however, the magnitu de of the response was less than that in nondeprived pups. These data indic ate that during ontogeny there is a rapid stimulus-induced CRH biosynthesis . Thus, during development, the central components of the hypothalamic-pitu itary-adrenal axis may be stress hyperresponsive rather than hyporesponsive .