Renal afferent input to thoracolumbar spinal neurons of the cat

Responses of 65 thoracolumbar spinal neurons to electrical stimulation of the left renal nerves were examined in 19 cats anesthetized with alpha-chloralose. Cells were found primarily in laminae V and VII of the T12-L2 segments on the left side of the spinal cord. Renal nerve stimulation excited 55 and inhibited 10 cells. Excitatory responses were characterized either by short latency or both short and long latency responses (means +/- SE: 13 +/- 1 and 68 +/- 7 ms). Recordings of the compound action potential in the least splanchnic nerve indicated that early responses resulted from A delta-renal afferent input and long latency responses from C-fiber renal input. Maximal responses to A delta-renal input (3.3 +/- 0.5 spikes/stimulus) were significantly greater than maximal responses to C-fiber renal input (1.5 +/- 0.3 spikes/stimulus). Inhibitory responses were best demonstrated by repetitive stimuli; however, responses of five cells to single stimuli showed that these responses had long latencies to onset (36 +/- 6 ms). All cells were excited or inhibited by somatic stimuli. Excitatory somatic receptive fields invariably included the left flank region and lower abdomen, occasionally included the left hindlimb, and in a few cases included the right hindlimb. Thirteen cells had both excitatory and inhibitory somatic receptive fields. The results show that thoracolumbar spinal neurons receive renal A delta- and C-fiber input that converges with input from somatic structures. These cells may participate in renal pain which is referred to somatic structures or reflexes initiated by renal afferent fibers.