Stress-induced responses and open-field behavior in estrous and nonestrous mice

Three experiments were performed to compare the reactions of estrous and nonestrous female CD-1 mice to stressful stimuli. These experiments revealed no effect of estrous state on (a) response latencies to thermal pain in the mouse hot-place test, (b) immediate, active responses to electric foot shock, or (c) open field ambulation under no stress condition or under stress conditions provided by foot shock or bright light. Estrous mice were found to defecate less in a small open field, and to ambulate more in the center of a large open field, than nonestrous mice, but neither of these effects interacted with an effect of stress condition. An incidental finding was a diurnal effect on response latencies in the mouse hot-place test. These experiments, combined with previous experiments with female CD-1 mice, support the conclusion that estrus results in decreased avoidance of potentially dangerous or stressful places, but does not affect the animal's reactivity to unavoidable stressful stimuli.