Book Description
Estrogens have been previously identified as regulators of food reward, or motivated behavior towards food, where high levels are correlated with decreased food motivation. However, only ovarian-derived estrogens have been heavily investigated. Estrogen is primarily produced within the ovaries, but it can also be synthesized in the brain, including in the amygdala, by brain aromatase enzymes that convert androgens into estrogens. Here we hypothesized that brain-produced estrogens are important in the control of food intake and food-motivated behavior in female rats, independently of the function of their ovarian counterparts. To further examine the function of amygdala estrogens on food motivation, estrogen levels specifically within the amygdala were manipulated in female and male rats. Estrogen levels were increased through [beta]-estradiol microinjections to the central amygdala of rats or were decreased by viral gene silencing of the aromatase enzyme (knockdown) specifically in the central amygdala. In addition, we also examined whether the estrous cycle, thus ovarian-produced hormones, interacts with the food motivation effect in intra-amygdala estrogen microinjections. Contrary to our hypothesis, estradiol injections did not affect food motivation, but had an acute effect on food seeking and locomotor activity in female rats, and this effect was estrous cycle dependent. Interestingly, we found that aromatase knockdown within the amygdala decreased food motivation, but only in female rats. These results suggest that brain estrogen manipulations might have a greater effect on female rats, and that brain-produced estrogen and ovarian estrogen might play a divergent role in food-motivated behavior, yet the function of brain-produced estrogen interacts with ovarian hormones.