Developmental expression of corticotropin releasing hormone messenger RNA and peptide in rat hypothalamus

We have examined corticotropin releasing hormone (CRH), arginine vasopressin (AVP) and somatostatin (SOM) mRNA expression and peptide content in the rat hypothalamus from day 20 of fetal life (F20) to the fifteenth day of postnatal life (P15). During this time, hypothalamic CRH mRNA levels did not change significantly, whereas there was a gradual six-fold rise in CRH peptide levels. AVP mRNA levels fell three-fold between F20 and P1 and increased six-fold between P1 and P15. AVP peptide levels increased three-fold, with most of the rise occurring between P1 and P15. From F20 to P15, SOM mRNA and peptide levels rose four- and eight-fold, respectively. The changes in the levels of these three hypothalamic gene products correlate with the previously described alterations in the responsiveness of the HPA axis observed in fetal and early postnatal rats, suggesting a role for these neuropeptides in the modulation of the HPA axis during this developmental period.