Noxious cardiac input onto neurons in medullary reticular formation.

Responses of reticular formation neurons to electrical stimulation of cardiopulmonary afferents as well as cardiac application of bradykinin were determined. Experiments were performed in chloralose anesthetized, vagotomized and sino-aortic denervated cats paralyzed with pancuronium. The medial reticular formation in the medulla was explored with microelectrodes until single neurons responding to electrical stimulation of the cardiac nerve were isolated. Electrical stimulation evoked an early (latency less than 40 ms) burst only (most common), both an early burst and a late burst, or a late (latency greater than 90 ms) burst only (least common) from medullary neurons. Cells were subsequently tested for responses to epicardial or intracardiac administration of bradykinin. Of the 62 neurons tested, one-third responded to bradykinin. Cells typically exhibited a bursting pattern of spontaneous activity; bradykinin enhanced the duration and intensity of the bursts. Neurons were also tested for somatic, visual and auditory input. Most cells were excited by somatic as well as auditory stimuli, while a fewer number also received visual input. Furthermore, most cells responsive to epicardial bradykinin also received these other inputs. The neurons recorded in this study may mediate cardiac pain, cardiovascular reflexes, alerting responses, and/or arousal responses.