Cardiovascular change in response to prolonged defense area stimulation in freely moving rats

The mean blood pressure and heart rate of freely moving rats were directly recorded over a 1-min period of electrical stimulation of the periaqueductal gray with intensities that induced freezing behavior, intense flight or no behavioral changes. Blood pressure and heart rate increased only when flight was induced and only during the first 15 s of stimulation. These cardiovascular changes suggest that homeostatic mechanisms act during the defense reaction and are markedly inhibited only at the beginning of the stimuli that induce the flight response, this inhibition quickly undergoing attenuation. These data do not suggest that activation of defense area, per se, contributes to the development of primary hypertension.