Changes in the heart rate were studied during stimulation of the effector nuclei of the vagus nerves--the dorsal vagal nucleus and the nucleus ambiguus--in anesthetized and unanesthetized cats. If groups of neurons, stimulation of which in anesthetized cats causes slowing of the heart, were stimulated in unanesthetized cats under conditions of free behavior, the heart rate was increased. Pharmacological beta-adrenergic receptor blockade by injection of Obsidan or Inderal (propranolol) demonstrated the parasympathetic nature of these effects. The fact that they are parasympathetic in nature was also confirmed by the character of the response: its short latent period and rapid disappearance of the effect after removal of the stimulation.

No abstract