Chemical microstimulation of the septal area lowers arterial pressure in the rat

Abstract

Electrical stimulation of the septal area has been previously reported to result in either an increase or a decrease in arterial pressure (AP) and heart rate (HR) depending on the site of stimulation within the septum or on the anesthetic. These conflicting results could be due to the different proportions of cell bodies and fibers activated by electrical stimulation at different sites and to the different anesthetics acting differently on cell bodies and fibers. To study the cardiovascular responses to activation of cell bodies, DL-homocysteate (20-50 nl) was injected into histologically verified sites in the lateral septum (LS), the medial septum (MS), the nucleus of the vertical limb of the diagonal band of Broca (NDBB), and in the bed nucleus of the stria terminalis (BST) in urethananesthetized, paralyzed, and artificially ventilated rats. Injections in the LS, MS, and NDBB elicited a decrease in AP [-12.6 +/- 0.9 (SE) mmHg, n = 111] accompanied by variable changes in HR. In a group of spontaneously breathing rats anesthetized with urethan, AP responses were not significantly different from those obtained in paralyzed animals. Finally, in a group of animals under alpha-chloralose, AP responses were not significantly different from those observed in animals under urethan. Homocysteate application in the BST resulted in either depressor [-10.8 +/- 0.9 (SE) mmHg, n = 20] or pressor responses [13.7 +/- 1.9 (SE) mmHg, n = 9].(ABSTRACT TRUNCATED AT 250 WORDS)