AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 1 1-R8, Copyright © 1991 by American Physiological Society
Autonomic mechanisms underlying area postrema stimulation-induced cardiovascular responses in rats
A. V. Ferguson and P. Smith
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
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.
