Vasodepressor responses elicited by diencephalic stimulation in dogs

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Abstract
Tachycardia and peripheral vasoconstriction are the usual means by which the cardiovascular system, under nervous control, attempts to compensate for a lowering of pressure in the systemic arteries. When such compensatory efforts are absent during sudden, unexpected periods of hypotension, an alteration in central nervous system control should be suspected. The possibility of producing such alterations in the control of the circulation under experimental conditions was studied in five anesthetized dogs. Diencephalic areas were found in which electrical stimulation evoked a lowering of arterial pressure in the absence of tachycardia. Electrodes were chronically implanted in these areas so that stimulation could be performed in the unanesthetized state. The observed effects on the cardiovascular system were not always the same as those induced while the animals were anesthetized. The decrease in arterial pressure was usually less in extent. Occasionally an actual rise in pressure occurred, followed after the period of stimulation by a decrease in arterial pressure and heart rate.