ESTROGEN INHIBITS HYPOTHALAMIC PROOPIOMELANOCORTIN GENE-EXPRESSION INHYPOTHALAMIC NEURONAL CULTURES

Many in vitro studies show estrogen regulation of the hypothalamic pro -opiomelanocortin (POMC) system, including a decrease in hypothalamic POMC mRNA after estradiol treatment, Because such in vivo experiments do not allow one to determine whether peripheral, interacting systems or extra-hypothalamic brain regions are involved in this regulation, w e sought to establish whether estrogen acts directly in hypothalamus t o decrease POMC mRNA. Using an in vitro approach, we studied effects o f estradiol ((E) over dot(2)) on POMC/cyclophilin mRNA concentrations (RNAse protection assays) in neuronal cultures derived from day 17 fet al rat hypothalamus. Chemically defined medium was deprived of progest erone for 2 days prior to E-2 treatment and for the duration of the st udy. E-2 (10(-13)-10(-9) M) dose-dependently decreased POMC mRNA conce ntrations during a 2-day treatment. Whereas the lowest dose (10(-13) M ) of E-2 resulted in a statistically significant 44% decrease In POMC mRNA concentrations relative to control cultures, this inhibitory effe ct was lost because higher doses (10(-11) and 10(-9) M) did not produc e statistically significant decrements (22 and 16%, respectively) in P OMC mRNA concentrations. Additional time course studies revealed that this decrease in POMC mRNA can be seen as early as 4 h after E-2 (10(- 13) M) treatment. We conclude that E-2 inhibition of POMC mRNA concent rations in hypothalamic neuronal cultures indicates that this inhibiti on can occur directly in hypothalamus. (C) 1997 Elsevier Science B.V.