AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 6 1025-R1034, Copyright © 1988 by American Physiological Society
Baroreflex unimpaired by operant avoidance or classical aversive conditioning in dogs
R. A. Shammas, A. L. Denison, T. W. Pfennig, D. P. Hemker and R. B. Stephenson
Department of Physiology, Michigan State University, East Lansing 48824.
Previous studies showed that baroreflex control of heart rate is impaired
during operant shock avoidance conditioning and classical aversive
conditioning. However, the effects of such "emotionally stressful"
paradigms on the ability of the baroreflex to control arterial pressure
have not been directly assessed. We prepared the carotid sinus regions of
dogs for reversible isolation from the systemic circulation, and we derived
complete stimulus-response relations for the effects of carotid sinus
pressure on both heart rate and arterial pressure. For any given carotid
sinus pressure, arterial pressure and heart rate were higher during operant
shock-avoidance conditioning and during classical aversive conditioning
than in a neutral environment, which indicates an upward resetting of the
baroreflex. However, threshold and saturation carotid sinus pressures were
unaffected by operant conditioning or classical conditioning, which
indicates that the baroreceptors themselves were not reset. The ranges over
which the carotid baroreflex could vary arterial pressure and heart rate
were significantly increased during both operant conditioning and classical
conditioning. Baroreflex gain was unchanged during operant conditioning and
was significantly increased during classical conditioning. We conclude that
the baroreflex is not impaired during operant shock-avoidance conditioning
or classical aversive conditioning in dogs. However, the baroreflex is
reset and regulates blood pressure at an elevated level.
