Vasopressin Expression in Cultured Neurons is Stimulated by Cyclic AMP

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Abstract
Vasopressin and oxytocin genes are expressed in mutually exclusive sets of magnocellular neurons in the hypothalamus. Cell specificity and regulation are probably controlled by extra- and intracellular signals acting on one or the other gene. In order to identify factors that regulate peptide expression, we have used primary dissociated cultures derived from 14-day old foetal rats. Vasopressin expression was monitored by combined immunocytochemistry and in situ hybridization. Treatment of cultures with forskolin and/or the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), both of which result in elevated intracellular cyclic AMP levels, increased the numbers of vasopressin-expressing cells up to 10-fold. The specific Vasopressin messenger ribonucleic acid accumulation was verified quantitatively by ribonuclease protection assays. Forskolin and IBMX did not change the levels of the general neuronal markers, neuron-specific enolase and synaptophysin, suggesting that the effect of these drugs was specific for vasopressin-expressing cells. The drugs were not mitogenic for magnocellular neurons. Furthermore, their effect was not mediated trans-synaptically, as the drugs were also effective in cultures grown in low Ca(2+)/high Mg(2+) medium, as well as in cultures treated with either tetanus toxin or tetrodotoxin. The presence of putative response elements for the transcription factor AP-2 in the 5'promoter regions of all vasopressin genes sequenced so far may provide the molecular basis of the observed cyclic AMP effect. No such elements are present in the genes for oxytocin, the messenger ribonucleic acid levels of which were not measurably affected by forskolin and IBMX in our cultures.