The role of stimulus control in modulating estradiol's influence on behavior in ovariectomized female rats

Stacey Beth Zaremba, Fordham University


While it is well established that estrogen is necessary to maintain respondent behavior (lordosis) exhibited by female rats, much less is known concerning estrogens influence on operant behavior. It has been generally assumed that hormones have no direct influence on operants. Recent findings have indicated that schedule controlled behavior is influenced by estradiol. The focus of this experiment was on estradiols influence on behavior maintained by DRL schedules as the nature of the controlling stimulus was manipulated. Six ovariectomized female rats were exposed to a multiple signalled DRL-40 sec unsignalled DRL 40-sec schedule of reinforcement. Under the signalled condition reinforcement availability was signalled by a change in intensity of a stimulus light. Under the unsignalled condition the availability of reinforcement was not signalled. The addition of a stimulus modified performance considerably, with subjects being much more efficient in timing responses in the signalled component as compared to the unsignalled component. These two conditions were chosen to represent behavior controlled by simple (signalled) and complex (unsignalled) stimulus discriminations. Dose-related increases in efficiency for both responding and time were found in the unsignalled components when estradiol doses of.25,.75, 2.25, 6.75 mg/kg were administered 20 hours prior to the session. Behavior largely controlled by simple discriminations was more resistant to the effects of estradiol than behavior maintained by complex discriminations. This experiment also examined the effects of estradiol on behavior maintained by the signalled component as the discriminability of the controlling stimulus was varied. Discrimination difficulty was varied by manipulating the intensity of the signalling stimulus. The rats were exposed to three levels of discrimination difficulty within the signalled component. It was expected that estradiol would differentially effect behavior maintained by the various levels of discrimination difficulty, with estradiol increasing efficiency more as the discrimination became more difficult. The data did not support this relationship; estradiol did not differentially affect behavior maintained by any of the discrimination difficulty conditions within the signalled component. In fact, all conditions were unaffected by estradiol. The results suggest that the behavioral effects of estradiol depend to a large extent on the complexity of the discrimination under which behavior is maintained. The type of stimulus control is just as important as the estradiol dose itself.

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Recommended Citation

Zaremba, Stacey Beth, "The role of stimulus control in modulating estradiol's influence on behavior in ovariectomized female rats" (1988). ETD Collection for Fordham University. AAI8818485.