Spontaneous meal patterns in female rats with and without access to running wheels.

Rats display strong behavioral rhythms during the ovarian cycle. During estrus, food intake is minimal due to a decrease in meal size, and locomotor activity is maximal. To investigate how activity influences feeding patterns across the ovarian cycle, we used a computerized system to monitor spontaneous meal patterns in intact, cycling female rats with and without access to running wheels. We found that running wheel access decreased dark meal frequency, increased dark meal size, and increased 24-h water intake during each phase of the ovarian cycle. In contrast, body weight, 24-h food intake, and the ovarian rhythms of reduced food intake, meal size, and body weight during estrus were not affected by running wheel access. In particular, the reduction in food intake during estrus was due to a selective reduction in dark meal size, not dark meal frequency, and this occurred independent of wheel access. These data indicate that estrus-related changes in spontaneous meal patterns and locomotor activity are independently controlled and that the reduction in food intake during estrus involves a selective change in the neurobiological controls of meal size.