REGULATION OF VASOPRESSIN (VP) GENE-EXPRESSION IN THE BED NUCLEUS OF THE STRIA TERMINALIS - GONADAL STEROID-DEPENDENT CHANGES IN VP MESSENGER-RNA ACCUMULATION ARE ASSOCIATED WITH ALTERATIONS IN MESSENGER-RNA POLY-(A) TAIL LENGTH BUT ARE INDEPENDENT OF THE RATE OF VP GENE-TRANSCRIPTION

Forebrain vasopressin (VP) neurons of the bed nucleus of the stria terminalis (BNST) contrast with hypothalamic VP neurons in exhibiting nuclear gonadal steroid receptors which may directly effect steroid-induced changes in VP gene expression observed in BNST cells. A transcription and Northern mRNA analysis has been performed to determine the mechanism through which gonadal steroids regulate VP gene expression in the BNST. In addition to confirming a distinctive, sexually dimorphic pattern of VP mRNA expression in the BNST as compared with the hypothalamic supraoptic nucleus (SON), our results show that the marked decrease in BNST VP mRNA levels observed two weeks after castration is not associated with a change in transcriptional activity of the VP gene. Similarly, VP gene transcription is not increased, relative to castrated animals, in the BNST of castrated rats treated with testosterone which exhibit normal or somewhat elevated levels of VP mRNA in the BNST. A post-transcriptional mechanism therefore appears to underlie the gonadal steroid-regulated changes in VP gene expression in the BNST. Since modulation of mRNA size (due to changes in poly (A) tail length) was also observed following castration and testosterone treatment it is apparent that the post-transcriptional mechanism may involve regulated changes in VP mRNA poly (A) tail length. The present findings contrast with the osmotic up-regulation of VP mRNA levels in the SON which is primarily a transcriptional response, and provide a demonstration of the potential physiological importance of post-transcriptional mechanisms of hormonal gene regulation.