Sympathetic activity in spontaneously hypertensive rats after spinal transection.

To test the hypothesis that sympathetic hyperactivity and hyperexcitability in spontaneously hypertensive rats (SHR) is generated at spinal and/or ganglionic levels, we measured integrated renal nerve activity (before ganglionic blockade) and adrenal nerve activity (after ganglionic blockade) in 12- to 14-wk-old SHR and normotensive Wistar-Kyoto rats (WKY). Rats were anesthetized with alpha-chloralose, artificially respired, and paralyzed. Spinal cords were transected at C1 to eliminate normal supraspinal control of sympathetic activity. The effectiveness of descending sympathoexcitatory and sympathoinhibitory pathways was tested by measuring changes in nerve activity elicited by graded spinal stimulation. Spontaneous renal nerve activity was elevated in SHR, but stimulation of descending excitatory pathways caused similar responses in SHR and WKY. Spontaneous adrenal preganglionic nerve activity was similar in SHR and WKY, but excitatory stimulation elicited larger adrenal nerve responses in SHR. We conclude that spinal and/or ganglionic mechanisms may generate a component of the sympathetic hyperactivity exhibited by SHR. The larger adrenal preganglionic nerve responses to excitatory stimulation in SHR suggest that spinal systems may be partially responsible for adrenomedullary hyperexcitability in spontaneous hypertension.