SYMPATHETIC ACTIVITY AND BLOOD-PRESSURE ARE TIGHTLY COUPLED AT 0.4-HZIN CONSCIOUS RATS

Interactions of sympathetic nerve activity (SNA) with blood pressure ( BP) and heart rate (HR) were assessed in conscious rats while they res ted quietly in a cloth sock (n = 7), roamed freely in their home cage (n = 6), and then after anesthesia with pentobarbital (30 mg/kg; n = 7 ). The power and coherence spectra below 3 Hz were calculated from dat a collected for 9.56 min. In the conscious rat, SNA spectral power pea ked at 0.4 Hz, whereas the majority of spectral power for both BP and HR occurred at frequencies lower than 0.4 Hz. However, there was an in conspicuous peak in the BP power spectra at 0.4 Hz that was not seen i n the HR spectra. Coherence between SNA and BP peaked at a frequency o f similar to 0.4 Hz, the same frequency at which the SNA spectral peak s occurred. In contrast, at frequencies below 0.4 Hz where maximum BP power occurred, the coherence was considerably lower. Anesthesia with pentobarbital lowered spectral power for BP, SNA, and HR but essential ly did not change the coherence between SNA and BP. Interactions betwe en respiration and each of the other variables were weak in the consci ous rat. However, prominent respiratory interactions at similar to 1.2 Hz were evident after anesthesia. These data indicate a close couplin g between SNA and BP at 0.4 Hz, raising the possibility that the BP sp ectral power at 0.4 Hz reliably reflects sympathetic activity.