Alterations in vasopressin and oxytocin messenger RNA in the rat supraoptic nucleus during dehydration-rehydration evaluated by in situ hybridization and Northern blotting

Abstract

Male rats were deprived of water for 5 days, and then given water ad libitum for 3, 7, 10 or 14 days. Plasma osmolarity returned to normal in less than 3 days, while pituitary vasopressin (AVP) and oxytocin (OXT) only returned to control levels after 14 days. Sections of the supraoptic nucleus (SON) were hybridized with 35S-labelled cDNA (OXT) or oligonucleotide (AVP) probes. Relative AVP and OXT mRNA contents were quantitated by counting the number of silver grains on a large standard area of the SON, then extrapolating this value to the volume of the whole SON (deduced from surface areas of all the sections). Dehydration significantly enlarged the volume of the SON (×1.54) and increased the AVP and OXT mRNAcontent (×2). During rehydration, both SON volume and density of silver grains were higher than normal for at least 7–10 days, although levels started to fall by day 3. The distribution of individual cells according to their silver grain densities remained unimodal during the dehydration-rehydration sequence with an extension, then a return to normal of the distribution range. Maximum sizes of AVP and OXT mRNAs on Northern blots of RNAs extracted from 5 pooled SONs were observed on dehydration day 5. The size of these species fell progressively, reaching control values by rehydration day 14. We conclude that during rehydration, at a time when most of the putative inducers of gene transcription are no longer activated, the peptidergic deficit was accompanied by an increased level of AVP and OXT mRNAs. However, both the amount and the size of these mRNAs started to fall as soon as the osmotic stimulus was removed.