Convergence of cardiovascular and vestibular inputs on neurons in the medullary paramedian reticular formation.

Extracellular recordings were made from 47 neurons in the caudal medullary paramedian reticular formation of chloralose-urethan anesthetized cats. The firing rate of all of these neurons was affected by stimulation of the contralateral vestibular nerve. The onset latency of the response to vestibular nerve stimulation was accurately determined for 43 of these neurons. The large majority (36 of 43) received short-latency (onset latency less than 5 ms) inputs; 7 were driven within 2 ms and were classified as receiving disynaptic inputs. Twenty of the 47 neurons also received inputs from the ipsilateral carotid sinus nerve. The paramedian reticular formation thus appears to be an important site for the integration of cardiovascular afferent and vestibular signals. However, only a small fraction of the neurons (2 of 13 tested) which received such convergent inputs could be antidromically driven from the upper thoracic spinal cord.