Regulation of vasopressin expression in cultured diencephalic neurons by glucocorticoids

Glucocorticoids have long been recognized as playing a major role in the regulation of vasopressin synthesis. However, the factors determining cellular specificity and molecular mechanisms of glucocorticoid action on the vasopressin gene are not understood. In the present investigation, we used primary cell cultures derived from 14-day-old fetal rat diencephalon to investigate the regulation of vasopressin expression under controlled conditions. The experimental paradigm used ensured that only magnocellular, but not parvocellular neurons grew in the cultures. The following criteria were used to establish this phenotype. (1) Cultures were derived from fetal brain well before the time parvocellular neurons are generated, and neuronal precursors did not proliferate in vitro. (2) Vasopressinergic neurons measured some 18 x 25 microns, being conspicuously larger than the average neuronal population in vitro, and clearly larger than parvocellular neurons in vivo. (3) Neurons did not express corticotropin releasing factor in vitro. Selective neutralization of glucocorticoids contained in the serum-supplemented culture medium by the drug RU 38 486 resulted in an about 2-fold increase of numbers of vasopressinergic cells and about 4-fold increase in vasopressin mRNA, but did not affect numbers of oxytocinergic neurons or expression of general neuronal marker proteins. The effects of RU 38,486 were not dependent on synaptic communication between cultured cells, as the drug was still effective when cells were synaptically isolated by growth is in 14 mM Mg2+. RU was not mitogenic for vasopressinergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)