Influence of Ovarian Hormones on Motivated Behavior in the Female Rat
Logsdon, Molly K.
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The fluctuation of ovarian hormones throughout the menstrual cycle influences behavioral patterns in females. In particular, the influence of gonadal hormones on the modulation of dopamine release has recently come under increasing scrutiny. In this study, we sought to determine the degree of change in motivation in female rats for obtaining food or access to a mate, across varying ovarian hormone levels. We utilized a paradigm in which ovariectomized (OVX) female rats were administered with estradiol benzoate (EB) and Progesterone to mimic the naturally occurring hormone surges of the estrus cycle on a 4-day testing schedule. Female rats were trained in an operant response choice paradigm, designed to ultimately condition them to making multiple nose pokes in order to receive a food reward or access to a mate. Number of successful nose pokes per session serves as a proxy for level of motivation toward the unconditioned stimulus. In the fixed-ratio (FR) 5 phase of testing, we found that administration of progesterone on the final day of the testing schedule was sufficient to reduce nose poking for food when compared to the other testing days, while there was no significant change in nose poking for mate access. The results of the current phase in testing provide further insight into modulatory effects of the ovarian hormone cycle on motivation for rewarding stimuli.