Abstract
Examined the effects of alpha-adrenergic (hydergine) and cholinergic (flaxedil, atropine, bilateral vagotomy) blockades upon unconditioned (Exp. I) and conditioned (Exp. II) blood pressure (BP) and heart rate (HR) responses to tones and shocks. Ss were male albino rabbits (N =6 and 54, respectively) in both experiments. The relationship between BP increases and HR decreases, including response diminution to hydergine, suggests that BP increases contributed to HR decreases (CRs and UCRs). Additional observations, however, that HR UCRs were only partially related to BP responses, and that HR CRs occurred in the absence of conditioned BP responses, indicate that other mechanisms also influenced the HR decreases.
