Vagal and sympathetic nerve activities influenced by posterior cerebral circulation in rabbits.

Vagal and sympathetic nervous activities in the rabbit were recorded while vertebral blood flow was partially blocked by the injection of adenosine 5'-diphosphate (ADP; platelet aggregator). When a small dose of ADP (0.2 mg/kg) was administered into a unilateral vertebral artery, sympathetic nerve (SN) activity increased, and its magnitude was inversely correlated with the extent of the decrease in blood pressure (BP). A larger dose (2 mg/kg) of ADP suppressed SN activity on the injected side, whereas the change was small on the non-injected side. Vagal nerve (VN) activity showed a monophasic excitatory response on both sides, although the change was larger on the injected than on the non-injected side. As a result, asymmetry in autonomic nerve activity was more distinct in SN than in VN. The present study demonstrated that asymmetry of autonomic nervous function can result from changes in blood flow in the cerebellum and brainstem.