Selective autonomic blockades: Effects upon classical conditioning of heart rate and lever-lift suppression in rabbits.

Abstract

Heart rate, blood pressure, and lever lifting were studied during differential classical conditioning. The unconditioned stimulus was electrical stimulation of the septal region or the hypothalamus through chronically implanted electrodes; the conditioned stimuli were 2 tones differing in frequency. Betaadrenergic blockade by propranolol did not affect cardiovascular unconditioned responses (URs, bradycardia and pressor response), conditioned responses (CRs, bradycardia), or lever-lift responses; whereas cholinergic blockade by atropine methylnitrate abolished heart rate responses but not lever-lift responses. This indicates that heart rate responses were mediated by increases in vagal tone. Alpha-adrenergic blockade by phentolamine abolished bradycardia and pressor URs, but not bradycardia CRs. This suggests that separate central mechanisms mediated bradycardia URs and CRs. Removal of the lever diminished without eliminating bradycardia CRs, indicating partial independence between lever lift and cardiac CRs.

Interactions between behavior and the cardiovascular system.

“…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).…”