The role of the estrogen receptor α in the medial preoptic area in sexual incentive motivation, proceptivity and receptivity, anxiety, and wheel running in female rats

Abstract

Ovariectomized females were given an infusion in the medial preoptic area (MPOA) of a viral vector carrying either a shRNA directed against the estrogen receptor α (ERα) or luciferase. The females were subjected to a test for sexual incentive motivation immediately followed by a test for receptivity and proceptive behaviors. Two weeks later they were tested in the light/dark choice procedure, and after another 2 weeks they were subjected to a test in a brightly lit open field. Finally, the females were given free access to a running wheel for 88h. The females were treated with estradiol benzoate (EB), 18 or 1.5μg/kg, in randomized order 52h before each test except the running wheel. In that experiment, they were given EB 48h after introduction into the wheel cage. They were given progesterone, 1mg/rat, about 4h before all tests, except the running wheel. The shRNA reduced the number of ERα with 83%. Females with few ERα in the MPOA showed increased lordosis quotient after the 1.5μg/kg dose of EB. There was no effect on proceptive behaviors or on rejections. When given the 18μg/kg EB dose, there was no difference between females with few preoptic ERα and controls. In the test for sexual incentive motivation, females with few preoptic ERα approached the castrated male incentive more than controls, regardless of EB dose. They also moved a shorter distance. In the light/dark choice test as well as in the open field, females with few ERα in the MPOA showed signs of reduced fear/anxiety, since they spent more time in the light part of the dark/light box and in the center of the open field. Finally, the data from the running wheel showed that females with few preoptic ERα failed to show enhanced activity after treatment with EB. These data show that the preoptic ERα inhibits lordosis in females with an intermediate level of receptivity while it fails to do so in fully receptive females. The ERα in the MPOA seems to be necessary for selective approach to a sexual incentive. Finally, activation of this receptor appears to have anxiogenic effects in the procedures employed here. A hypothesis for how all these actions of the preoptic ERα contributes to efficient reproductive behavior is outlined.