Cardiovascular responses to glutamate stimulation of diagonal band of Broca.

Experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of L-glutamate stimulation of the diagonal band of Broca (DBB) on arterial pressure (AP) and heart rate (HR). Stimulation of the horizontal limb of the DBB (hDB) elicited decreases in both mean AP (MAP; -32.3 +/- 2.5 mmHg; n = 37) and HR (-32.5 +/- 3.8 beats/min; n = 33) at 84% of the sites stimulated. Stimulation of the vertical limb of the DBB (vDB) elicited significantly smaller decreases in MAP (-9.7 +/- 1.0 mmHg; n = 19) and HR (-13.5 +/- 1.8 beats/min; n = 7) at approximately 13% of the sites stimulated. Intravenous administration of the muscarinic receptor blocker atropine methylbromide had no effect on the magnitude of the MAP and HR responses to stimulation of the hDB. In contrast, administration of the nicotinic receptor blocker hexamethonium bromide abolished both the depressor and the bradycardic responses elicited by stimulation of the hDB. These data indicate that the hDB contains neurons that exert cardiovascular depressor effects and that these circulatory effects are mediated by the inhibition of sympathetic vasoconstrictor fibers to the vasculature, and cardioacceleratory fibers to the heart.