Effect of chronic cervical ganglionectomy on the spontaneous variability of internal carotid blood flow in the conscious rat.

The role of sympathetic innervation in the control of spontaneous fluctuations of cerebral blood flow is still poorly understood. In conscious, unrestrained rats, blood flow velocity (pulsed Doppler) was measured in both internal carotid arteries 1 week after either excision of the right superior cervical ganglion (n = 8) or sham surgery (n = 6). Using Fourier-based techniques, spectral power of each carotid blood flow (CBF) was computed over the whole recording period (246 min), which was segmented into nine consecutive 27.3 min periods. Variability of CBF (spectral power) was ∼40% higher (P < 0.02) on the denervated than on the intact side at frequencies <1 Hz. Coherence between left and right CBFs was similar in the two groups of rats, except in the 0.01-0.1 Hz frequency range where it was lower (P < 0.05) in rats with unilateral sympathectomy (0.54 ± 0.03) than in intact rats (0.74 ± 0.06). In this frequency range, mathematically removing the influence of arterial pressure had little effect on coherence between CBFs in both groups of rats, so that coherence remained significantly lower in rats with unilateral sympathectomy (0.52 ± 0.03) than in intact rats (0.70 ± 0.06). This study indicates that sympathetic innervation has an overall buffering influence on CBF variability. This modulatory role is especially important in a frequency range corresponding to slow fluctuations of CBF (lasting from 10 to 100 s), which are essentially unrelated to fluctuations of arterial pressure.