Effects of cardiac vagotomy on heart rate conditioned responses in cats

Abstract

Normal cats were bilaterally vagotomized at cardiac level and submitted to a classical defensive conditioning using excitatory, inhibitory and differential stimuli. That group was compared with a normal one. Both groups showed an anticipatory bradycardia to the noxious excitatory stimulus and a late deceleration to the inhibitory stimuli. The experimental group presented more variable and labile responses. Basal and intertrial heart rate decreased in normal but not in operated animals. The autonomic regulation of the conditioned bradycardia reflex is discussed according to the hypothesis that both active and passive fear reactions are fundamentally mediated by sympathetic activity.