Responses of spinoreticular cells to graded increases in renal venous pressure

Previous work established that occlusion of the renal vein excites spinoreticular tract (SRT) neurons of the cat. The present study was designed to determine the relationship between renal vein pressure level and SRT cell activity. Experiments were performed on 40 cats that were anesthetized with alpha-chloralose. Sixty SRT neurons in the T12-L2 segments were tested for responses to a renal vein pressure (RVP) of 60 mmHg. Twenty-three cells responded with an increase in activity. Stimulus response relationship for these cells were determined over the RVP range of 10-80 mmHg. RVP thresholds averaged 25 +/- 3 mmHg. Above this level greater increases in RVP were associated with greater increases in neuronal activity. At RVP of 80 mmHg cell activity increased from 4 +/- 2 to 21 +/- 5 spikes/s. Cells with both A delta- and C-fiber renal afferent inputs had significantly greater responses and lower thresholds than cells with only A delta input. Renal vein occlusion evoked increases in blood pressure. At a renal vein pressure of 80 mmHg, pressor responses averaged 16 +/- 5 mmHg. No significant changes in heart rate were observed. The results demonstrate that SRT cells are capable of encoding the level of RVP. Such responses may be important for grading of reflexes of renal origin that require supraspinal circuitry.