Cardiorespiratory components of defense reaction elicited from paraventricular nucleus.

The present study was conducted to test the hypothesis that the paraventricular nucleus of the hypothalamus (PVN) is involved in the mediation or modulation of the cardiorespiratory components of the defense reaction (DR) in rabbits. Electrical stimulation of the PVN elicited increases in blood pressure and heart rate, hyperventilation, decreased blood flow to the visceral organs, and an increase in blood flow to the hindlimbs that was mediated by an atropine-sensitive vasodilation system. This response pattern is nearly identical to the one that is elicited by electrical stimulation of the hypothalamic defense area. In addition, the cardiomotor component of the baroreceptor reflex was observed to be suppressed during electrical stimulation of the PVN. Previous studies have shown that electrical stimulation of the hypothalamic defense area also leads to inhibition of the cardiomotor component of the baroreceptor reflex. The results of the present study provide evidence that the PVN is involved in the mediation or modulation of the defense reaction.