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1989). We, therefore, suggest that increased low frequency variability of CBF on the denervated side was not a consequence of changes in arterial distensibility. The mechanism of the buffering influence of sympathetic innervation at low frequencies is unclear. It may be that sympathetic activity facilitates myogenic responses at frequencies 0.1 Hz, the main cause of variability in regional blood flows derives learn more from AP Mayer waves (Julien et al. 1995). Mayer waves are generated by rhythmic fluctuations in several regional sympathetic activities (reviewed by Julien, 2006). It is not known, however, whether cerebrovascular sympathetic activity exhibits such rhythm. In the CBF spectra, Mayer waves appeared as a break point rather than a well-defined peak (even on a linear scale; data not shown). This indicates that cerebrovascular resistances showed cyclical changes at this frequency. The disappearance of such oscillations on the denervated side would result in enhanced fluctuations of CBF, which was indeed observed. It is thus likely that cerebrovascular sympathetic activity oscillates to some extent at the frequency of Mayer waves. Direct recordings in conscious animals (Cheng et al. 2004) are needed to provide a definite answer to this question. The second important finding relates to the effect of unilateral sympathectomy on the coherence computed between the two CBFs. As expected, ordinary coherence was quite high in control, intact rats, selleck products especially at heart rate and Mayer waves�� frequency. Coherence was also strong at frequencies (-)-p-Bromotetramisole Oxalate low frequencies and was unaltered after partialization. However, both ordinary and partial coherences in the 0.01�C0.1 Hz frequency band were significantly lowered by denervation. This observation indicates that cerebral sympathetic activity produces a specific pattern of variations, which are responsible for part of the spectral power in this frequency band. After denervation, partial uncoupling occurred between the two internal carotid vascular beds. As it was still observed after partialization with AP, this effect was unrelated to AP fluctuations.