Renal and somatic input to spinal neurons antidromically activated from the ventrolateral medulla

1. Studies were done to characterize responses of spinal neurons backfired from the ventrolateral medulla to renal and somatic stimuli. Experiments were performed on 31 cats that were anesthetized with alpha-chloralose. Sixty-six spinal neurons were antidromically activated from the area of the lateral reticular nucleus or the ventrolateral reticular formation just rostral to the lateral reticular nucleus contralateral to the recording site. These cells could not be backfired from the medial reticular formation or from the spinothalamic tract just caudal to the thalamus. 2. Cells were located in laminae I, V, and VII of the T12-L2 segments. Antidromic conduction velocities averaged 35.9 +/- 7.2 m/s. Conduction velocities were unrelated to the projection site or laminar location of the cells. Termination sites of 21 cells were located in antidromic mapping experiments. Terminals were localized to the ventrolateral reticular formation, including the lateral reticular nucleus. 3. Responses to electrical stimulation of the renal nerves were always excitatory. Stimulation of renal A-delta-fibers excited 33 cells. These cells failed to respond to stimulation of renal C-fibers. The other 33 cells responded to both A-delta- and C-fiber stimulation. Latencies to A-delta-fiber stimulation averaged 9 +/- 2 ms, whereas latencies to C-fiber stimulation averaged 57 +/- 10 ms. 4. Renal mechanoreceptors were activated by occlusion of the renal vein or upper portion of the ureter. Renal vein occlusion excited 14 of 32 cells tested. Activity increased from 6 +/- 2 to 14 +/- 4 spike/s. Ureteral occlusion increased activity of 19 of 32 cells from 7 +/- 2 to 16 +/- 5 spikes/s. Cells responding to one of the mechanical stimuli were significantly more likely to receive A-delta-and C-fiber input compared with nonresponding cells. Nonresponders were more likely than responders to receive only A-delta input. 5. All cells received somatic input in addition to renal input. Twelve cells were classified as wide dynamic range, 46 as high threshold, and 8 as Deep. Somatic receptive fields most often included skin and muscle of the left flank and abdomen. Thirty-two cells had bilateral receptive fields, and 22 had inhibitory fields in addition to excitatory fields. 6. These data show that spinal neurons projecting to the ventrolateral medulla receive convergent inputs from the kidney and somatic structures. These cells may participate in a variety of functions including autonomic reflexes of renal origin.