Alterations in Cardiac Contractility During Classical Aversive Conditioning in Dogs: Methodological and Theoretical Implications

Abstract

An investigation of sympathetic influences on the heart was undertaken in dogs using classical aversive conditioning procedures. For this purpose, heart rate and cardiac contractile changes were measured, the latter using techniques assessing the rate of change or slope at which either the muscles of the left ventricle contract, or blood is accelerated in the ascending aorta, or the pulse pressure wave ascends from diastole to systole. Sympathetic influences were found to be more clearly manifest in contractile rather than heart rate changes as indicated by the greater attenuating influence of beta‐adrenergic blockade on anticipatory and unconditioned responses. Anticipatory sympathetic influences on the heart were commonly acute, becoming minimal upon repeated exposure to the aversive procedures. The rate of change or slope measures appear to detect sensitively extrinsic sympathetic influences on contractility. They are minimally influenced by intrinsic effects on contractility such as heart rate as well as non‐contractile events such as diastolic blood pressure. The slope of the ascending limb of the pulse pressure wave appears to offer a means of assessing contractility in human Ss.

Behavioral determinants of severe cardiac inhibition

“…Nevertheless, a description of the interaction of sympathetic and vagal activity to produce a slowed heart rate has proved difficult to achieve in spite of the volume of work in this field Obrist, Howard, Lawler, Sutterer, Smithson, & Martin, 1972;Obrist, Lawler, Howard, Smithson, Martin, & Manning, 1974;Obrist & Webb, 1967;Obrist et al, 1970;Obrist, Wood, & Perez-Reyes, CUADRAS 1965;Sampson, Schneiderman, Wallach, Gavin, & Francis, 1977, etc.). These works enable a general conclusion: Sympathetic and parasympathetic extrinsic innervation of the heart act synergically, but vagal activity (which can mask sympathetic activity) is of a primary importance in chronotropism of the heart, although sympathetic activity is important in other cardiovascular parameters.…”

Interactions between behavior and the cardiovascular system.

“…However, as training progresses there is an increasing vagal contribution, such that in the well-trained animal either cardiac nerve supply is capable of mediating substantial conditioned tachycardia. Furthermore, there is highly suggestive evidence that a similar situation may obtain in the dog (65,76).…”

“…In contrast, species such as the dog and the pigeon respond to the conditioned, stimulus with increased muscular activity suggestive of escape behavior (8, 75), and it is these species that show conditioned cardioacceleration. This correlation has prompted the suggestion (e.g., 76) that conditioned tachycardia and, probably, increased cardiac output (65,77) occur when the conditioned response ensemble includes movement and that bradycardia accompanies decreased muscular activity and is most prominent when freezing occurs. Supporting this suggestion is Bruner's observation (74) that in a leg flexion conditioning paradigm cats tend to freeze during conditioned stimulus presentations early in the training and that this response is accompanied by cardiodeceleration.…”

“…Moreover, these vagal effects do not appear to be secondary to elevated arterial blood pressure or other responses that can modify vagal activity through the baroreceptor reflexes (78)(79)(80)(81). Conditioned acceleratory responses, on the other hand, are mediated by a combination of increased sympathetic outflow and decreased vagal inhibition (65,76). The most complete data are those of Cohen and Pitts (82).…”

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry

“…These include a series of studies by Obrist et al, who proposed that the velocity representation (i.e., peak slope of the upstroke, d P /d t ) of the carotid pulse could serve as a measure of extrinsic β‐adrenergic influences on the myocardium. The slope measure was observed to increase in such tasks as shock avoidance and nonsignaled reaction time, and the effect was abolished by the administration of the β‐adrenergic blocking agent propranolol (Obrist et al, ). Questions were raised about the quality of the d P /d t measure, with respect to the role of nonneurogenic factors and its purity as a measure of β‐adrenergic effects, as well as methodological issues including the absence of calibration (Heslegrave & Furedy, ; Light & Obrist, ; Obrist & Light, ).…”