Abstract
Studied heart rate, blood pressure, and lever lifting during differential classical conditioning in 2 experiments with a total of 8 female Belgian hares. 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. Beta-adrenergic blockade by propranolol did not affect cardiovascular unconditioned responses (bradycardia and pressor UCRs), conditioned responses (bradycardia CRs), or lever-lift responses. Cholinergic blockade by atropine methylnitrate abolished heart-rate responses but not lever-lift responses. Findings suggest that heart-rate responses were mediated by increases in vagal tone. Alpha-adrenergic blockade by phentolamine abolished bradycardia and pressor UCRs, but not bradycardia CRs. It is also suggested that separate central mechanisms mediated bradycardia UCRs and CRs. Removal of the lever diminished without eliminating bradycardia CRs, indicating partial independence between lever-lift and cardiac CRs.
