ESTRADIOL CONCENTRATION AND THE REGULATION OF LOCOMOTOR-ACTIVITY

We predicted that female prairie voles (Microtus ochrogaster) would no t increase in locomotor activity during ''induced'' proestrus. We deve loped and tested two alternative a priori hypotheses to explain this p redicted lack of activity. The Non-Response Hypothesis in which voles cannot, physiologically, increase activity in response to estradiol an d, the Threshold Effect Hypothesis in which a minimal concentration of estradiol is necessary to achieve estrus, while higher concentrations influence other behavioral parameters. The non-response hypothesis pr edicts that hormone concentration will not affect locomotor activity, while the threshold effects hypothesis predicts that voles achieve est rus at low concentrations, while higher concentrations should trigger increasing locomotor activity. Initial results using running wheels in dicated that females decreased activity during induced proestrus. Radi oimmunoassay revealed that induced proestrus was achieved at relativel y low concentrations of estradiol. Results from a dose response experi ment allowed for rejection of the nonresponse hypothesis and supported the threshold effects hypothesis as females decreased activity at low concentrations of estradiol, showed no relative change at moderate co ncentrations, and increased activity at higher concentrations.