Spinally mediated inhibition of abdominal and lumbar sympathetic activities

Renal, splenic, and lumbar sympathetic nerve activities were recorded in the paralyzed, anesthetized, artificially ventilated, and spinally transected rat. Electrical stimulation of the dorsolateral funiculus caudal to the spinal transection was used to generate stimulus-response curves for changes in sympathetic activity in each of the three sympathetic nerves using five stimulus frequencies. In all rats, spinal stimulation inhibited sympathetic activity in renal and splenogastric nerves by approximately 50%. In grouped data, threshold frequency for inhibition of renal and splenogastric sympathetic nerve activity was 5 Hz, and inhibitions were maximal (50-60%) at 10 Hz. In contrast, activity in the lumbar sympathetic chain was inhibited in only two of five rats, and grouped data did not exhibit any statistically significant inhibitions. We conclude that lumbar sympathetic activity which remains after spinal transection can be inhibited only marginally by spinal stimulation, which substantially reduces renal and splenogastric sympathetic activity.