Responses of thoracic spinoreticular and spinothalamic cells to intracardiac bradykinin

The response characteristics of spinoreticular and spinothalamic cells to intracardiac injection of bradykinin were determined in cats anesthetized with chloralose. Extracellular potentials of individual spinoreticular and spinothalamic cells were recorded from the T2-T4 segments of the spinal cord. Only those cells with cardiopulmonary sympathetic afferent input were tested for responses to intracardiac bradykinin (1-6 micrograms/kg). Thirty-seven of the 64 cells studied responded to bradykinin; 36 were excited and one was inhibited. For excited cells, discharge rate increased from 4 +/- 1.0 (SE) spikes/s to a peak of 20 +/- 2.4 spikes/s, a fivefold increase. Latency to onset of cell response was 13 +/- 1.1 s, and latency to peak response was 24 +/- 1.4 s after drug injection. Tachyphylaxis to additional doses of bradykinin was observed in 17 of 32 cells. Occurrence of tachyphylaxis was sometimes altered after bilateral cervical vagotomy. The projection sites in the caudal medulla and thalamus were similar for responsive and nonresponsive cells. Laminar cell locations in the spinal cord had no significant influence on likelihood of cell response to bradykinin. We conclude that spinoreticular and spinothalamic cells have a role in transmitting noxious information from the heart to the brain.