Acquisition Of Novel Exercise During High Estrogen Facilitates Future Exercise Behavior

Exercise variety, learning, maintenance, and benefits differ between men and women. Sex differences in physical activity also exist in rats. For example, female rats allowed access to running wheels run greater distance and faster speeds compared to males; a sex difference mediated by estrogen. In addition to increasing physical activity, estrogen has been reported to facilitate learning and memory. However, it is unknown if beginning a novel exercise under conditions of high estrogen affects future running behavior. PURPOSE: Here we tested the hypothesis that beginning novel VWR during conditions of high estrogen increases future VWR behavior. METHODS: Estrous phase of 20 female rats was monitored daily by vaginal lavage. Rats were randomly assigned to two groups: one which began VWR during the high estradiol phase (proestrus) and the other during the low estradiol phase (metestrus; n = 10 per group). VWR was restricted to the first 3 hours of the active cycle daily, to limit the possibility that estrous phases changed during VWR. Wheel rotations were recorded and used to calculate distance. Running distance over 3 weeks was averaged and compared with two-way ANOVA. RESULTS: Rats that were in proestrus on day one of VWR ran greater average daily distances over the subsequent 3 weeks, relative to rats in metestrus on day one (7284.1 ± 512.77 vs. 4845.14 ± 314.73 m, p < 0.01). This difference was not due to rats beginning in proestrus running more than metestrus rats on day one of VWR (1621.1 ± 157.91 vs. 1500.737 ± 202.65 m, p > 0.05). These results were replicated by analyzing running data from a previous experiment that allowed rats unlimited access to wheels for 4 weeks. Again, rats that began VWR in proestrus on day one ran greater distances than rats beginning in metestrus (n = 13/group, 5223.01 ± 290.72 vs. 4315.81 ± 192.86 m, p < 0.05) and this was not due to proestrus rats running greater distances on the first day (1414.3 ± 174.34 m, p > 0.05). CONCLUSION: Initiating a novel exercise during high estrogen increases later exercise behavior. A proposed mechanism for this effect is estradiol enhancing dopamine signaling in the dorsolateral striatum, an area involved in habit formation. These findings could inform the development of novel sex-specific interventions to increase exercise motivation and maintenance. NIH grant R01MH125898, University of Colorado Office of Undergraduate Research and Creative Activities EURECA Grant