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VASOPRESSIN mRNA IN THE SUPRAOPTIC AND SUPRACHIASMATIC NUCLEI: APPEARANCE AND CIRCADIAN REGULATION DURING DEVELOPMENT

We have studied and quantified the developmental appearance and regulation of hypothalamic vasopressin (prepropressophysin) mRNA using in situ hybridization. Timed pregnant rats were housed under controlled environmental lighting conditions. At various ages, fetuses or pups were decapitated, and the brains immersion-fixed. Coronal (10 μm) sections through the central supraoptic nuclei (SON) and suprachiasmatic nuclei (SCN) were subjected to in situ hybridization using a 40-base S-labeled oligonucleotide probe directed against vasopressin mRNA.Vasopressin mRNA levels in the SON were reliably detected on day 16 of gestation (day 0 = sperm positive), while mRNA levels in the SCN were detectable on day 21. These developmental patterns correlate well with the immunohistochemical appearance of prepropressophysin translation products previously reported in these nuclei. A prominent day-night rhythm of vasopressin mRNA levels was first evident in the SCN on day 21 of gestation; no such rhythm was present in the SON at any developmental stage examined. Thus, vasopressin mRNA levels in the SCN are already under specific circadian control when the nuclei are morphologically immature and virtually devoid of neuropil. The circadian regulation of vasopressin mRNA levels in SCN during fetal life represents one of the earliest and clearest examples of regulated gene expression in the mammalian brain. Supported by PHS grant HD14427 and March of Dimes Grant #1-945.