STRESS REGULATES DIFFERENTLY THE ARGININE-VASOPRESSIN (AVP)-CONTAINING AND THE AVP-DEFICIENT CORTICOTROPIN-RELEASING FACTOR-SYNTHESIZING CELL-BODIES IN THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS OF THE DEVELOPING RAT

8- or 25-day-old rats were injected with 2.5 IU/kg insulin and sacrifi ced 3 h later. Insulin injection induced a significant decrease of blo od glucose levels and a robust stimulation of ACTH secretion. CRF mRNA levels were measured in the parvocellular portion of the PVN. To iden tify the subpopulation of CRF cells that coexpresses AVP (the so-calle d CRF(+)/AVP(+) subpopulation) we used a double labeling in situ hybri dization technique. In 25-day-old rats, hypoglycemia increased CRF mRN A levels in both the total population of CRF cell bodies and in the CR F(+)/AVP(+) subpopulation. In 8-day-old rats, insulin injection did no t change the concentration of CRF mRNA in the total population of CRF cells and stimulated CRF gene transcription in the CRF(+)/AVP(+) subpo pulation. In both ages, the total number of CRF expressing cells was n ot changed after stress. Concomitantly, the number of CRF(+)/ AVP(+) c ell bodies was significantly increased in 25-day-old rats and was not changed in 8-day-old animals. These data demonstrate that the regulati on in response to stress of the CRF(+)/AVP(+) subpopulation of CRF syn thesizing cells in the PVN is mature as early as 8 day of life, while the regulation of the CRF(+)/AVP(-) subpopulation maturates more slowl y. They suggest that these two subpopulations are regulated by differe nt pathways.