Substance P antagonist inhibits vasomotor responses elicited from ventral medulla in rat

Application of kainic acid to the ventral medulla in rats leads to increases in blood pressure and heart rate. These responses can be attenuated or reversed by infusion of the substance P antagonist--(D-Pro2,D-Trp7,9)-substance P into the spinal subarachnoid space. Kainic acid elicits normal pressor responses from rats that have been treated intracisternally with the serotonin neurotoxin 5,7-dihydroxytryptamine. These results suggest that the substance P-like neurons of the ventral medulla may play a role in maintaining vasomotor tone.