Differential effects of spinal transection on sympathetic nerve activities in rats.

We measured renal, splenogastric, and lumbar multiunit sympathetic activities in chloralose-anesthetized, paralyzed, and artificially respired Sprague-Dawley rats. Acute spinal transection reduced arterial pressure and lumbar sympathetic activity. However, renal and splenogastric activities were doubled after transection. We conclude that spinal systems exist in the rat that are capable of maintaining renal and splenogastric, but not lumbar, sympathetic activities after spinal transection. Cross-correlation and power spectral analysis of simultaneously recorded sympathetic activities indicated that renal and splenogastric activities often, but not always, shared periodicities near the respiratory rate. These shared periodicities were responsible for high correlations between renal and splenogastric activities. After spinal transection, the shared periodicities usually disappeared, and correlations were reduced. Renal and lumbar activities were rarely strongly correlated, and they rarely shared major periodicities. We conclude that brain stem systems often provide synchronization of abdominal sympathetic activities. However, these activities can be independently generated in both intact and spinally transected rats.