Selective autonomic blockade of conditioned and unconditioned cardiovascular changes in rhesus monkeys (Macaca...

Changes in heart rate and in systolic and diastolic blood pressures were examined in eight rhesus monkeys during six sessions of differential classical conditioning. The conditioned stimuli consisted of tones differing in frequency and the unconditioned stimuli consisted of tail shock. Both the conditioned responses (CRS) and unconditioned responses (UCRs) consisted of increases in heart rate and in systolic and diastolic pressures, but blood pressure CRs sometimes occurred in the absence of heart rate CRs. Graded doses of the selective blocking agents propranolol, phentolamine, and atropine methylnitrate were systemically administered to four of the monkeys prior to additional conditioning sessions. The results suggested that the CRs and UCRs were mediated by both sympathetic and parasympathetic influences.