Spinoreticular cell responses to intrarenal injections of bradykinin

Thirty cats were anesthetized with alpha-chloralose, paralyzed, and artificially ventilated. Extracellular unit activity was recorded from 63 spinoreticular tract (SRT) neurons in the T12-L2 segments. All cells were excited by renal nerve stimulation and had somatic receptive fields. Intrarenal injection of bradykinin (4 micrograms/kg) increased activity of 36 cells from 7 +/- 1 to 23 +/- 5 spikes/s. Latency to onset of responses averaged 11 +/- 2 s and latencies to peak were 26 +/- 5 s. Intrarenal injection of isotonic saline vehicle or intravenous injection of the same dose of bradykinin failed to alter activity. Responses increased as dosage increased from 2 to 12 micrograms/kg. Seventeen cells exhibited tachyphylaxis to repeated injections. Cells most likely to respond to bradykinin received both A delta- and C-fiber renal inputs and/or were located in lamina V of the spinal gray matter. Mechanical pressure applied to the renal capsule excited eight of the cells that responded to bradykinin. These results show that activation of renal afferent fibers with bradykinin leads to activation of T12-L2 SRT neurons. These cells may participate in the ascending limb of supraspinal reflexes initiated by renal receptors.