A comparison of the autonomic nervous control of the heart during classical aversive vs appetitive conditioning in dog

Abstract

Dogs were trained in either classical (i.e. Pavlovian) appetitive (n = 7) or aversive (n = 7) conditioning by presenting a tone (the conditional stimulus, CS + ) that was followed by either food or shock delivery, respectively. In the first case, dog food was given to the animals during the last 30 s of a 1 min CS + . Aversive conditioning was accomplished by giving a 1 s shock at the end of a 30 s CS+. The control consisted of a different tone (CS - ) which was never followed by food or shock. A chronically implanted transducer was used to record left ventricular pressure from which its first time derivative was calculated; d(LVP)/dt was used as an index of myocardial inotropic state. Heart rate (HR) was also determined. These data were averaged over the 30 s prior to the CS+, the 30 s of the conditional stimulus tone itself, and the 30 s following shock or during food delivery. Well-trained animals evidenced changes in cardiac inotropism and chronotropism during the CS+ and also in response to unconditional shock or food; these are referred to as the conditional and unconditional cardiovascular responses, respectively. No statistically significant HR or d(LVP)/dt changes were observed during the CS-. The conditional response to food was small: relative to the pre-CS+ interval, average HR increased 11 bpm ( P < 0.05) and average d(LVP)/dt increased 309 mm Hg/s ( P < 0.01). During food delivery, HR increased by an additional 23 bpm ( P < 0.01) and d(LVP)/dt increased by another 232 mm Hg/s ( P < 0.01). β-adrenergic blockade virtually eliminated the conditional HR and d(LVP)/dt response to food, indicating that both the chronotropic and inotropic changes during CS+ were due to elevated sympathetic drive. β-blockade did not eliminate the unconditional HR response (+ 17 bpm, P < 0.01), indicating that parasympathetic withdrawal has a mediating role in this persisting tachycardia. The conditional response to shock consisted of a 26 bpm increase in HR ( P < 0.01), while d(LVP)/dt increased 998 mm Hg/s ( P < 0.01). The β-blockade reduced the HR conditional response to +8 bpm (NS) and essentially eliminated the increase in d(LVP)/dt. These data indicate that increases in cardiac sympathetic tone play a primary role in mediating the conditional cardiovascular response for both paradigms. Parasympathetic withdrawal, on the other hand, figures critically in mediating the unconditional response to food.