Dynamic interactions between arterial pressure and sympathetic nerve activity: role of arterial baroreceptors

Abstract

The role of arterial baroreceptors in controlling arterial pressure (AP) variability through changes in sympathetic nerve activity was examined in conscious rats. AP and renal sympathetic nerve activity (RSNA) were measured continuously during 1-h periods in freely behaving rats that had been subjected to sinoaortic baroreceptor denervation (SAD) or a sham operation 2 wk before study (n = 10 in each group). Fast Fourier transform analysis revealed that chronic SAD did not alter high-frequency (0.75-5 Hz) respiratory-related oscillations of mean AP (MAP) and RSNA, decreased by approximately 50% spectral power of both variables in the midfrequency band (MF, 0.27-0.74 Hz) containing the so-called Mayer waves, and induced an eightfold increase in MAP power without altering RSNA power in the low-frequency band (0.005-0.27 Hz). In both groups of rats, coherence between RSNA and MAP was maximal in the MF band and was usually weak at lower frequencies. In SAD rats, the transfer function from RSNA to MAP showed the characteristics of a second-order low-pass filter containing a fixed time delay ( approximately 0.5 s). These results indicate that arterial baroreceptors are not involved in production of respiratory-related oscillations of RSNA but play a major role in the genesis of synchronous oscillations of MAP and RSNA at the frequency of Mayer waves. The weak coupling between slow fluctuations of RSNA and MAP in sham-operated and SAD rats points to the interference of noise sources unrelated to RSNA affecting MAP and of noise sources unrelated to MAP affecting RSNA.

Steady-State and Dynamic Responses of Renal Sympathetic Nerve Activity to Air-Jet Stress in Sinoaortic Denervated Rats

“…Under resting and stressful conditions in SAD rats, the absence of peaks in the MF band of MAP and RSNA spectra does not support the hypothesis that SNA and AP oscillations at Mayer wave's frequency result from the operation of a central oscillator, whatever the level of sympathetic activation. By contrast, the key role played by the arterial baroreceptor reflex in the genesis of Mayer waves in resting rats 29 is confirmed in the present study, and this role is extended to a situation of centrally induced sympathoexcitation. This important contribution of 0.4-Hz oscillations to the MF spectral power of MAP and RSNA has already been reported by Brown et al 32 in rats under conditions of normal (conscious) and low (light pentobarbital anesthesia) sympathetic activation.…”

“…16,17 More recently, the absence of RSNA oscillations at Mayer wave's frequency has been reported in conscious SAD rats. 28,29 However, significant residual power was present in the MF band, considering either MAP or RSNA. 29 The functional significance of this residual RSNA power was demonstrated by the almost complete abolition of MF power of MAP after ganglionic blockade in resting SAD rats.…”

“…28,29 However, significant residual power was present in the MF band, considering either MAP or RSNA. 29 The functional significance of this residual RSNA power was demonstrated by the almost complete abolition of MF power of MAP after ganglionic blockade in resting SAD rats. 16 Interestingly, the presence of slow AP fluctuations in the frequency band containing Mayer waves (0.04 to 0.15 Hz) was reported in patients with multiple system atrophy.…”

“…The major role played by the baroreceptor reflex in the production of coherent AP and SNA oscillations at Mayer wave's frequency has been demonstrated in resting subjects, ie, under conditions of low SNA, 29 and during reflexly induced increases in SNA. 19,20 The present study allows extending this conclusion to a situation of centrally induced sympathetic activation accompanying exposure to a mild environmental stressor, which is particularly relevant to daily life situations.…”

Does acute hyperglycemia alter rat aortic depressor nerve function?

“…The volume of blood needed to cause arterial pressure oscillation around 10 mmHg varied from 0.2 to 0.4 mL. The frequency of 0.3 Hz was chosen to induce rhythmic oscillations because it matches the well-known low frequency oscillation of arterial pressure (Mayer's waves) exhibited by conscious rats (17), which disappears under anesthesia (18). Spontaneous oscillations induced by breathing (~1.5 Hz in anesthetized rats) were also used to assess baroreceptor function in the frequency domain.…”