Food intake is reduced by estrogenic hormones, levels of which vary throughout life and fluctuate throughout the ovarian cycle in females. However, estrogens have also been shown to increase reward derived from drugs of abuse, where motivational properties of drugs and progression to addiction are potentiated by estrogens. Whether reward derived from food, and specifically motivational properties of food, are altered by estrogens remains unknown. Here we investigated the effect of the estrous cycle on food reward behavior and show estrous cycle dictated variability in food motivation, measured by progressive ratio operant conditioning, in female rats. Reward behavior was lowest on days associated with high estrogen signaling. We therefore also examined the actions of subcutaneously administered β-estradiol on food reward and found that β-estradiol reduced food reward behavior. The ventral tegmental area (VTA) is a crucial node of the neurocircuitry underlying motivated behavior and estrogen receptors are expressed in this nucleus. Thus, we examined whether the effects of estrogens on reward were exerted directly at the level of the VTA. Intra-VTA microinjection of β-estradiol led to a significant reduction in food-motivated behavior. Interestingly, this effect was not accompanied by a reduction in chow intake or body weight, nor did it alter locomotor activity. Importantly, removal of the ovaries produced a potent and lasting elevation in food reward and food-seeking behavior, suggesting that ovarian sex steroids are critical for maintenance of normal food reward behavior. These data reveal a novel role for estrogens in the control of food reward behavior.
All Science Journal Classification (ASJC) codes
- Endocrinology, Diabetes and Metabolism
- Endocrine and Autonomic Systems
- Psychiatry and Mental health
- Biological Psychiatry