VASOPRESSIN AND OXYTOCIN GENE-EXPRESSION IN INTACT RATS AND UNDER CATECHOLAMINE DEFICIENCY DURING ONTOGENY

The development of the hypothalamic vasopressin (VP) and oxytocin (OT) systems has been studied in rats from the 16th embryonic day (E16) un til the 11th postnatal day (P11). The VP and OT mRNA-producing neurons were identified on cryostat sections by in situ hybridization using o ligonucleotide probes labeled by [S-35], [H-3] Or digoxigenin. Moreove r, VP and OT gene expressions were evaluated either at E21 or at P11 f ollowing chronic depletion of catecholamines(CA). For this purpose, pr egnant rats were daily injected with alpha-methyl-m(p)-tyrosine from g estational day 13 to 20, while neonates were daily injected with alpha -methyl-m(p)-tyrosine and neurotoxin 6-hydroxydopamine from postnatal day 2 to 10. No VP mRNA- or OT mRNA-expressing cells were observed in the hypothalamus of intact fetuses at E16, while 2 days later rather n umerous VP and OT neurons occupied the anterior hypothalamus. One majo r bilateral group of VP and OT neurons was located in the supraoptic n ucleus (SON). Less numerous labeled cells were found in the developing paraventricular nucleus (PVN). Some VP and OT neurons were also sprea d along the ventrolateral surface of the hypothalamus from the level o f the median eminence, caudally, to the level of the optic nerves, ros trally. From E18 until birth, the OT neurons were localized in the dor sal portion of the SON, while its ventral portion was occupied by the VP neurons. The VP mRNA- and OT mRNA-expressing cells seemed to increa se both in size and in number over the perinatal period. Frequent rela tively long neuronal processes contained VP and OT mRNAs in fetuses an d in newborns. When performed during the second half of the fetal life , the chronic depletion of CA did not cause any change in the VP and O T mRNA concentrations in the SON and PVN of fetuses. By contrast, simi lar treatment of neonates resulted in a significant increase of both m RNA levels in the SON. These data suggest that at least in the SON VP and OT gene expressions might be under the inhibitory control of CA du ring the neonatal period.