Open field behavior and cardiovascular responses to stress in normal rats

Experiments were conducted in normal Wistar rats with different patterns of behavior to assess the effects of stress on cardiovascular reactivity. One week after weaning and one month later rats were tested in an open field. Animals that did not cross any square in both open fields were classified as HYPOACTIVE. Those crossing more than 43 squares in the first and any in the second open field were classified as HYPERACTIVE. No difference was found in the basal mean blood pressure (BP) or heart rate (HR) between both groups. After a stress (change of cage, electric shock or immobilization) BP and HR increased. The increase in BP was higher in HYPOACTIVE rats. The HR increase was similar in both groups. Therefore, the ambulatory activity in the open field allowed us to separate groups of rats with different cardiovascular reactivity to stress.