The effects of avoidance and conflict schedules on the blood pressure and heart rate of rats

Two studies examined the cardiovascular response to aversive conditioning as a function of the degree of control over the stressor. Experiment 1 used 24 normotensive rats assigned to 3 groups: experimental, yoked, and non-shock restraint control. Triplets of rats were exposed to signalled avoidance for 3 weeks. Experimental animals were required to turn a wheel to avoid shocks to themselves and their yoked partners. Direct cardiovascular monitoring via aortic catheters during the final avoidance session revealed that both systolic and diastolic blood pressure (BP) increased significantly in experimental and yoked rats during avoidance but remained elevated throughout avoidance and post-avoidance only in the yoked animals. Experimental rats also exhibited a significant increase in HR during early avoidance. Experiment 2 assessed the cardiovascular response to a reduction in the controllability of the stressor by exposing 24 rats, assigned to groups as above, to 11 weeks of conflict and avoidance conditioning. Indirect systolic BP was significantly higher in experimental and yoked rats as compared to controls when averaged over the 11 weeks of stress. Experimental and yoked rats also had significantly more hypertensive systolic BP readings (SBP≥150 mm Hg), 34% and 38% respectively, than controls (13%). Direct cardiovascular monitoring during a final conflict session showed sustained increases in systolic and diastolic BP during conflict and post-conflict for both experimental and yoked rats, attaining significance, however, only in the yoked group. These studies suggest that the opportunity to cope moderates the systolic BP response to aversive stimulation and the loss or lack of such opportunity leads to a significant increase in the number of hypertensive blood pressure readings.