Spontaneous waves of cerebral blood flow associated with a pattern of electrocortical activity

Abstract

We examined the relationship between spontaneous changes in regional cerebral blood flow and electrocortical (ECoG) activity in spinalized rats anesthetized with 1.5% isoflurane. Regional cerebral blood flow, measured by laser-Doppler flowmetry, and ECoG activity were measured bilaterally in frontal and parietal cortex. Spontaneous cerebrovascular waves (SCWs) were seen in all (n = 80) rats and consisted of sawtoothed waves with an average amplitude of 20.1 +/- 0.78%, a duration of 11.7 +/- 0.6 s, and a frequency of 6.3 +/- 0.2 min-1. SCWs were always preceded by a high-amplitude burst of ECoG activity (averaging 752.0 +/- 41.8 microV at 5.6 +/- 0.2 Hz) and comparable to the well-recognized burst-suppression/barbiturate-spindle patterns of ECoG activity. The latency between bursts and SCWs averaged 1.71 +/- 0.05 s. The frequency of bursts and SCWs was highly correlated within and between cortical areas bilaterally (r > 0.9) and appeared synchronously across brain. Deepening anesthesia (to 1.75% isoflurane) reduced the frequency of bursts and SCWs by > 30% but not their correlation (r > 0.9) and minimally increased burst-SCW latency. SCWs differed from an uncommon sinusoidal oscillation regional cerebral blood flow triggered by changes in arterial pressure and independent of the ECoG. Bursts and SCWs were not affected by inhibition of nitric oxide synthase. The results indicate that a population of local cortical neurons, probably driven from subcortical pacemakers, when excited, elicits local cerebrovascular vasodilation.