Involvement of the medial preoptic area in the anorectic action of estrogens

The implication of the medial preoptic area (MPOA) as a site for estrogen in the regulation of energy balance was investigated. Food intake, O2 consumption (VO2), and CO2 production were measured in ovariectomized rats injected with estradiol (E2) in the medial preoptic nucleus (MPN). Moreover, knowing the potential for corticotropin-releasing factor (CRF) in the anorectic effects of estrogens, we identified estrogen receptors (ER) colocalized in CRF-containing cells of the MPOA and how MPN injections of CRF compared with estrogen injections with respect to VO2 and the VO2-to-CO2 production ratio (respiratory quotient RQ). These energy balance measurements after the injections of four different doses of E2 or CRF were carried out in meal-fed rats chronically implanted with a guide cannula targeted to the MPN. The identification of cells colocalizing ER and CRF was determined using a double-immunostaining procedure revealing ER and CRF immunoreactivities with two different couplers. The injection of E2 into the MPN induced a dose-dependent reduction in food intake, whereas it did not affect VO2 or RQ. Conversely, the injection of CRF into the MPN had no effect on food intake but increased VO2 and decreased RQ. The colocalization of ER and CRF immunoreactivities was found in the MPOA and adjacent regions of the bed nucleus of the stria terminalis. In conclusion, the results of this study provide evidence that the MPOA may represent a potential site for the anorectic effects of E2. Furthermore, the presence of ER and CRF in neurons of the MPOA and adjacent areas suggests a direct interaction between estrogens and the CRF system in the MPOA that is consistent with a role for CRF in the anorectic effects of estrogens. Finally, the results of this study indicate that the effects of a CRF injection into the MPOA differ from those of estrogens, suggesting that if CRF neurons are involved in the anorectic effect of estrogens they likely exert their action outside the MPOA.