Interaction of inferior olivary nucleus with reflex bradycardia and tachycardia in the cat.

In chloralose-urethane anesthetized cats, stimulation of the ION, apart from directly producing cardioinhibition, was capable of interacting antagonistically with reflex tachycardia (induced by nitroglycerin) and synergistically with reflex bradycardia (induced by phenylephrine). The degree of the potentiation or antagonism was greater than the sum of the individually elicited responses. It was also directly related to the dose of the drugs and the intensity of the stimulating pulse frequency delivered to the nucleus. The similarity in natures of both cardio-inhibitory mechanisms of the ION and gigantocellular reticular nucleus (GRN) has been discussed. We infer that the ION, GRN, nitroglycerin-induced reflex tachycardia and phenylephrine-induced reflex bradycardia may share a final common neural mechanism which function to suppress heart rate. The neurons in the dorsal motor (DM)/solitary (SN) nuclei may be a good candidate, because bilateral vagotomy or unilateral vagotomy with a contralateral DM/SN destruction substantially abolished the cardio-inhibitory effect of both GRN and ION.