The Effects of the Estrous Cycle on the PCA Index

Lana T. Samuel, Northern Illinois University


Females experience a wide range of hormonal changes throughout their menstrual cycle. These hormonal changes can have significant effects on a female's behavior, food and fluid intake, stress levels, motivation, memory, and social interactions. One effect of hormones is that they can increase sugar cravings, leading to higher sugar intake. Hormonal changes can also cause females to feel unmotivated and depressed, which can impact their daily functioning. To gain a better understanding of these effects, I used the rodent as a model to better understand the impact of hormonal fluctuations on reward processes for a highly palatable sugar reward. The estrous cycle of female rats has similar fluctuations in the gonadal hormones, estrogen, and progesterone, as the menstrual cycle in humans. My capstone project compared a behavior associated with reward, the Pavlovian Conditioned Approach (PCA), across the different hormonal states of the female rat. PCA is a learned behavior that develops when a conditioned stimulus (CS; the lever) precedes a response-independent unconditioned stimulus (US; a food pellet delivered into a pellet magazine) when assessed in an operant chamber. The data evaluated the hypothesis that female rats exhibit a change in motivation for sugar, which will be reflected in their lever-press during behavior, over distinct stages of the estrous cycle was tested. The results showed no difference in the estrous cycle on PCA as most rats showed the greatest propensity to interact with the lever. The research found no significant difference in the impact of hormonal fluctuations on the drive for sugar rewards during the estrous cycle, despite the reported craving for sugar by women.