Deficits in conditioned heart rate and taste aversion in area postrema-lesioned rats

Experiments were designed to examine the autonomic mechanisms underlying the decreases in blood pressure and heart rate elicited by electrical stimulation in the rat area postrema (AP). Vagotomy was found to significantly reduce the bradycardia observed in response to AP stimulation (control -123.5 +/- 23.5 beats/min; vagotomized -7 +/- 5.4 beats/min; P less than 0.001) but was without significant effect on blood pressure responses. Hexamethonium significantly reduced both heart rate (control -225.5 +/- 11.9 beats/min; hexamethonium -5.5 +/- 2.8 beats/min; P less than 0.001) and depressor (control -35.4 +/- 4.7 mmHg; hexamethonium -6.4 +/- 0.8 mmHg; P less than 0.001) responses to such stimulation, whereas combined alpha- and beta-adrenergic blockade was without effect. The muscarinic blocking agent atropine also abolished both blood pressure (control -22.0 +/- 4.3 mmHg; atropine 2.8 +/- 4.4 mmHg; P less than 0.01) and heart rate (control -187.0 +/- 41.9 beats/min; atropine 8.8 +/- 2.6 beats/min; P less than 0.01) responses to AP stimulation. These data suggest that AP stimulation influences two separate neural pathways eliciting distinct cardiovascular responses. It would appear that activation of one of these pathways results in activation of vagal efferents to the heart and thus bradycardia. A second parallel pathway influenced by AP stimulation apparently elicits depressor response through actions on cholinergic muscarinic receptors.

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Role of the area postrema in the modulation of the baroreflex control of heart rate by angiotensin II.

Circulation Research ◽

10.1161/01.res.67.6.1462 ◽

1990 ◽

Vol 67 (6) ◽

pp. 1462-1473 ◽

Cited By ~ 67

Author(s):

S Matsukawa ◽

I A Reid

Keyword(s):

Heart Rate ◽

Angiotensin Ii ◽

Area Postrema ◽

Baroreflex Control

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Inhibition of renal sympathetic nervous activity by area postrema stimulation in rabbits

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1987.253.1.h91 ◽

1987 ◽

Vol 253 (1) ◽

pp. H91-H99 ◽

Cited By ~ 2

Author(s):

E. M. Hasser ◽

D. O. Nelson ◽

J. R. Haywood ◽

V. S. Bishop

Keyword(s):

Heart Rate ◽

Electrical Stimulation ◽

Arterial Pressure ◽

Nucleus Tractus Solitarius ◽

Area Postrema ◽

Nervous Activity ◽

Sympathetic Nervous Activity ◽

Consistent Change ◽

Renal Sympathetic ◽

Stimulation Of

This study investigated the effect of chemical and electrical stimulation of the area postrema on renal sympathetic nerve activity (RSNA), arterial pressure, and heart rate in urethan-anesthetized rabbits. Electrical stimulation of the area postrema at 2, 5, 10, 20, 40, and 80 Hz using constant currents of 7.5, 15, and 30 microA (pulse duration = 0.3 ms, train duration = 5 s) produced progressive decreases in RSNA and heart rate, with no consistent change in arterial pressure. To control for electrical activation of fibers of passage in or near the area postrema, L-glutamate was injected into the area postrema using glass micropipettes. Micropressure injection of L-glutamate (10 mM) in volumes of 5-10 nl produced rapid decreases in RSNA averaging 27 +/- 5% (P less than 0.05) accompanied by a small bradycardia. The effects of electrical stimulation of the area postrema, but not the adjacent nucleus tractus solitarius, were totally eliminated by micropressure injection of kainic acid (40 ng in 40 nl) into the area postrema. During continuous electrical stimulation of the area postrema using parameters that produced small decrements in RSNA and heart rate, the slope of the line relating baroreflex inhibition of RSNA to increases in arterial pressure during graded infusions of phenylephrine was significantly enhanced (-6.77 +/- 1.30 vs. -3.81 +/- 0.66% RSNA/mmHg). These data are consistent with the hypothesis that activation of neurons in the area postrema results in an inhibition of RSNA. Furthermore, stimulation of the area postrema augments baroreflex inhibition of RSNA during increases in arterial pressure with phenylephrine.

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